mach_examples/README.md

MACH

Why MACH

MACH (Modern Asynchronous C Hypermedia) is a declarative framework for building asynchronous web applications in C23.

• No build configuration. Compilation, hot reload, and dependency wiring are handled by the framework. There are no build scripts, package managers, or ORMs to set up.
• Memory, concurrency, and I/O managed by the framework. Application code does not call malloc/free or manage threads, mutexes, or locks. Database queries run as prepared statements. Pipeline steps emit OpenTelemetry spans, logs, and errors automatically.
• Durable tasks and events. Both are persisted. If the process crashes, incomplete tasks resume at the step where they left off and undelivered events replay on the next boot.
• Bundled modules. SSE plus modules for Datastar, HTMX, Tailwind, SQLite, Postgres, MySQL, Redis/Valkey, DuckDB, and auth. Multi-tenant database support is built in.

---

Table of Contents

• Quick Start
• Philosophy
• Guide
• Reference
• Architecture
• Tooling
• License

---

Quick Start

Everything runs in Docker; no other local dependencies are required.

mkdir myapp && cd myapp
wget https://docker.nightshadecoder.dev/mach/compose.yml

# Dev server on :3000, telemetry on :4000
# Includes file watching, auto compilation, hot code reloading, HMR
docker compose up

Create main.c with the example below. MACH watches for changes and hot-reloads on save. Use your own editor, or attach to the built-in TUI with docker compose attach mach for an integrated environment with editor, AI, LSP, and console.

#include <mach.h>

config mach(){
  return (config) {
    .resources = {
      {"home", "/",
        .get = {
          render(.template = "<h1>Hello, world!</h1>")
        }
      }
    }
  };
}

The mach() function returns a config struct that defines the application. The home resource maps / to a GET pipeline whose only step renders inline HTML. For a step-by-step walkthrough, see the Guide.

---

Philosophy

Applications are data transformations: data enters from sources, flows through business logic, and exits to the client. MACH keeps each piece standard. Data comes from raw SQL, HTTP fetch, and JSON rather than ORMs. Business logic is plain C. Output is HTML, CSS, and JS via Mustache templates. These pieces compose inside pipelines: ordered lists of steps that turn a request into a response.

Tooling is also kept standard — lldb for debugging, Playwright and Criterion for testing, OpenTelemetry for observability — and built in.

Everything is a String

The web is largely text: HTTP, HTML, JSON, SQL. MACH takes this literally. The pipeline context stores and passes data as arena-backed strings; there is no intermediate parsing or serialization layer. Request parameters are not parsed into typed structs and objects are not serialized back to JSON. Data flows through the pipeline as strings, interpolated into SQL, templates, and URLs with {{context_key}}.

When business logic needs a specific C type, convert explicitly inside an exec() step.

CLAD

MACH is organized around four principles.

• (C)omposable: small, independent steps chain into feature pipelines.
• (L)ocality of Behavior: the behavior of a unit of code is apparent from reading it. SQL, templates, and behavior for a feature live together rather than across separate model, view, and controller trees.
• (A)utonomous: modules are self-contained — own schemas, migrations, seeds, routes, UI, and logic. The compiler enforces strict boundaries.
• (D)omain Based: each module owns one slice of the app. A todos module defines everything related to todos and nothing else.

CLAD is influenced by:

• Data Oriented Design
• A Philosophy of Software Design
• CUPID
• Self-Contained Systems
• Locality of Behavior

---

Guide

A walkthrough that builds a working todo app in nine steps, introducing one MACH concept at a time.

MACH doesn't support Mustache dot notation. Don't use it, period. Open the section once around the content and reference fields directly inside — don't repeat section opens for each field.

Don't (dot notation):

<div id="blog">
  <p>{{#blog.title}}</p>
  <p>{{#blog.content}}</p>
</div>

Don't (repeated section opens):

<div id="blog">
  <p>{{#blog}}{{title}}{{/blog}}</p>
  <p>{{#blog}}{{content}}{{/blog}}</p>
</div>

Do (open the section once, nest content inside):

{{#blog}}
<div id="blog">
  <p>{{title}}</p>
  <p>{{content}}</p>
</div>
{{/blog}}

• 1. A Page
• 2. Show Data
• 3. Accept Input
• 4. Handle Errors
• 5. Nested Data
• 6. Tasks
• 7. Modules & Events
• 8. External Assets
• 9. External Data

1. A Page

Two resources, each with a GET pipeline. {{url:todos}} resolves to the target resource's URL at render time, so changing a URL pattern updates every link.

#include <mach.h>

config mach(){
  return (config) {
    .resources = {
      {"home", "/",
        .get = {
          render(.template =
            "<html><body>"
              "<h1>Welcome</h1>"
              "<a href='{{url:todos}}'>My Todos</a>"
            "</body></html>"
          )
        }
      },

      {"todos", "/todos",
        .get = {
          render(.template =
            "<html><body>"
              "<h1>My Todos</h1>"
              "<p>Nothing yet.</p>"
            "</body></html>"
          )
        }
      }
    }
  };
}

Each resource names itself ("home", "todos") so other pages reference it by name, not by hard-coded path.

2. Show Data

Add a SQLite database with one migration and one seed, then read from it in the GET pipeline.

  #include <mach.h>
+ #include <sqlite.h>

  config mach(){
    return (config) {
      .resources = {
        {"home", "/",
          .get = {
            render(.template =
              "<html><body>"
                "<h1>Welcome</h1>"
                "<a href='{{url:todos}}'>My Todos</a>"
              "</body></html>"
            )
          }
        },

        {"todos", "/todos",
          .get = {
+           query({.set_key = "todos", .db = "todos_db",
+             .query = "select id, title from todos;"}),
            render(.template =
              "<html><body>"
                "<h1>My Todos</h1>"
-               "<p>Nothing yet.</p>"
+               "<ul>{{#todos}}<li>{{title}}</li>{{/todos}}</ul>"
              "</body></html>"
            )
          }
        }
-     }
+     },
+
+     .databases = {{
+       .engine     = sqlite_db,
+       .name       = "todos_db",
+       .connect    = "file:todos.db?mode=rwc",
+       .migrations = {
+         "CREATE TABLE todos ("
+           "id INTEGER PRIMARY KEY AUTOINCREMENT,"
+           "title TEXT NOT NULL"
+         ");"
+       },
+       .seeds = {"INSERT INTO todos(title) VALUES('Learn MACH');"}
+     }},
+
+     .modules = {sqlite}
    };
  }

query runs the SELECT and stores the rows under todos in pipeline context. render walks the section with {{#todos}}...{{/todos}}. Migrations run on the first connection.

Concurrent queries. Multiple items in a single query() run concurrently. Two separate query({...}) steps run serially. To fetch the todos and a count together:

query(
  {.set_key = "todos", .db = "todos_db", .query = "select id, title from todos;"},
  {.set_key = "count", .db = "todos_db", .query = "select count(*) as n from todos;"}
)

3. Accept Input

Add a POST verb that validates a title parameter, inserts it, and redirects back to GET (POST-redirect-GET).

  #include <mach.h>
  #include <sqlite.h>

  config mach(){
    return (config) {
      .resources = {
        {"home", "/",
          .get = {
            render(.template =
              "<html><body>"
                "<h1>Welcome</h1>"
                "<a href='{{url:todos}}'>My Todos</a>"
              "</body></html>"
            )
          }
        },

        {"todos", "/todos",
          .get = {
            query({.set_key = "todos", .db = "todos_db",
              .query = "select id, title from todos;"}),
            render(.template =
              "<html><body>"
                "<h1>My Todos</h1>"
                "<ul>{{#todos}}<li>{{title}}</li>{{/todos}}</ul>"
+               "<form method='post' action='{{url:todos}}'>"
+                 "<input name='title' value='{{input:title}}'>"
+                 "<button>Add</button>"
+               "</form>"
              "</body></html>"
            )
-         }
+         },
+
+         .post = {
+           validate({"title",
+             .validation = validate_not_empty,
+             .message    = "title cannot be empty"}),
+           query({.db = "todos_db",
+             .query = "insert into todos(title) values({{title}});"}),
+           redirect("todos")
+         }
        }
      },

      .databases = {{
        .engine     = sqlite_db,
        .name       = "todos_db",
        .connect    = "file:todos.db?mode=rwc",
        .migrations = {
          "CREATE TABLE todos ("
            "id INTEGER PRIMARY KEY AUTOINCREMENT,"
            "title TEXT NOT NULL"
          ");"
        },
        .seeds = {"INSERT INTO todos(title) VALUES('Learn MACH');"}
      }},

      .modules = {sqlite}
    };
  }

The POST pipeline validates first; on success, the title is promoted from input:title to app scope. The interpolated {{title}} in the SQL is bound as a prepared-statement parameter, not spliced. redirect("todos") returns a 302 to /todos.

4. Handle Errors

Validation failure raises http_bad_request. Add a resource-scoped error handler that re-enters the GET pipeline with reroute("todos"), and add error markup to the form template.

  #include <mach.h>
  #include <sqlite.h>

  config mach(){
    return (config) {
      .resources = {
        {"home", "/",
          .get = {
            render(.template =
              "<html><body>"
                "<h1>Welcome</h1>"
                "<a href='{{url:todos}}'>My Todos</a>"
              "</body></html>"
            )
          }
        },

        {"todos", "/todos",
          .get = {
            query({.set_key = "todos", .db = "todos_db",
              .query = "select id, title from todos;"}),
            render(.template =
              "<html><body>"
                "<h1>My Todos</h1>"
                "<ul>{{#todos}}<li>{{title}}</li>{{/todos}}</ul>"
                "<form method='post' action='{{url:todos}}'>"
                  "<input name='title' value='{{input:title}}'>"
+                 "{{#error:title}}<span>{{error_message:title}}</span>{{/error:title}}"
                  "<button>Add</button>"
                "</form>"
              "</body></html>"
            )
          },

          .post = {
            validate({"title",
              .validation = validate_not_empty,
              .message    = "title cannot be empty"}),
            query({.db = "todos_db",
              .query = "insert into todos(title) values({{title}});"}),
            redirect("todos")
-         }
+         },
+
+         .errors = {
+           {http_bad_request, { reroute("todos") }}
+         }
        }
      },

      .databases = {{
        .engine     = sqlite_db,
        .name       = "todos_db",
        .connect    = "file:todos.db?mode=rwc",
        .migrations = {
          "CREATE TABLE todos ("
            "id INTEGER PRIMARY KEY AUTOINCREMENT,"
            "title TEXT NOT NULL"
          ");"
        },
        .seeds = {"INSERT INTO todos(title) VALUES('Learn MACH');"}
      }},

      .modules = {sqlite}
    };
  }

reroute("todos") re-enters the GET pipeline in-process, which already knows how to fetch todos and render the page. The input: and error: scopes persist through the reroute, so {{input:title}} repopulates the field and {{#error:title}} renders the message. See redirect & reroute.

5. Nested Data

Add a /todos/:id page that fetches a todo and its comments concurrently, nests the comments inside the todo record, and renders them together. Comments belong to the same domain as todos, so the new comments table is added as a migration on the existing todos_db.

  #include <mach.h>
  #include <sqlite.h>

  config mach(){
    return (config) {
      .resources = {
        {"home", "/",
          .get = {
            render(.template =
              "<html><body>"
                "<h1>Welcome</h1>"
                "<a href='{{url:todos}}'>My Todos</a>"
              "</body></html>"
            )
          }
        },

        {"todos", "/todos",
          .get = {
            query({.set_key = "todos", .db = "todos_db",
              .query = "select id, title from todos;"}),
            render(.template =
              "<html><body>"
                "<h1>My Todos</h1>"
-               "<ul>{{#todos}}<li>{{title}}</li>{{/todos}}</ul>"
+               "<ul>{{#todos}}<li><a href='{{url:todo:id}}'>{{title}}</a></li>{{/todos}}</ul>"
                "<form method='post' action='{{url:todos}}'>"
                  "<input name='title' value='{{input:title}}'>"
                  "{{#error:title}}<span>{{error_message:title}}</span>{{/error:title}}"
                  "<button>Add</button>"
                "</form>"
              "</body></html>"
            )
          },

          .post = {
            validate({"title",
              .validation = validate_not_empty,
              .message    = "title cannot be empty"}),
            query({.db = "todos_db",
              .query = "insert into todos(title) values({{title}});"}),
            redirect("todos")
          },

          .errors = {
            {http_bad_request, { reroute("todos") }}
          }
-       }
+       },
+
+       {"todo", "/todos/:id",
+         .get = {
+           validate({"id", .validation = validate_integer,
+             .message = "must be an integer"}),
+           query(
+             {.set_key = "todo",     .db = "todos_db",
+              .query = "select id, title from todos where id = {{id}};"},
+             {.set_key = "comments", .db = "todos_db",
+              .query = "select id, todo_id, body from comments where todo_id = {{id}};"}
+           ),
+           join(
+             .target_table_key      = "todo",
+             .target_field_key      = "id",
+             .nested_table_key      = "comments",
+             .nested_field_key      = "todo_id",
+             .target_join_field_key = "comments"
+           ),
+           render(.template =
+             "<html><body>"
+               "{{#todo}}"
+                 "<h1>{{title}}</h1>"
+                 "<h2>Comments</h2>"
+                 "<ul>{{#comments}}<li>{{body}}</li>{{/comments}}</ul>"
+               "{{/todo}}"
+             "</body></html>"
+           )
+         }
+       }
      },

      .databases = {{
        .engine     = sqlite_db,
        .name       = "todos_db",
        .connect    = "file:todos.db?mode=rwc",
        .migrations = {
          "CREATE TABLE todos ("
            "id INTEGER PRIMARY KEY AUTOINCREMENT,"
            "title TEXT NOT NULL"
-         ");"
+         ");",
+         "CREATE TABLE comments ("
+           "id INTEGER PRIMARY KEY AUTOINCREMENT,"
+           "todo_id INTEGER NOT NULL REFERENCES todos(id),"
+           "body TEXT NOT NULL"
+         ");"
        },
        .seeds = {"INSERT INTO todos(title) VALUES('Learn MACH');"}
      }},

      .modules = {sqlite}
    };
  }

The two queries run in parallel under one query() call. join() lifts comments inside each todo record, so the template enters {{#todo}} first and reaches {{#comments}} from within. Iterating {{#comments}} at root would skip the nesting.

The same pattern maps onto any parent-children relation: blog + comments, project + tasks, order + line items. See join for the full blog + comments version.

6. Tasks

Tasks are named pipelines that run asynchronously on task reactors. Triggered on a cron schedule or enqueued from another pipeline with task("name"). Add a nightly task that records the current todo count into a daily_stats table, and re-run the same task from the POST pipeline so stats stay fresh after every write.

  #include <mach.h>
  #include <sqlite.h>

  config mach(){
    return (config) {
      .resources = {
        {"home", "/",
          .get = {
            render(.template =
              "<html><body>"
                "<h1>Welcome</h1>"
                "<a href='{{url:todos}}'>My Todos</a>"
              "</body></html>"
            )
          }
        },

        {"todos", "/todos",
          .get = {
            query({.set_key = "todos", .db = "todos_db",
              .query = "select id, title from todos;"}),
            render(.template =
              "<html><body>"
                "<h1>My Todos</h1>"
                "<ul>{{#todos}}<li><a href='{{url:todo:id}}'>{{title}}</a></li>{{/todos}}</ul>"
                "<form method='post' action='{{url:todos}}'>"
                  "<input name='title' value='{{input:title}}'>"
                  "{{#error:title}}<span>{{error_message:title}}</span>{{/error:title}}"
                  "<button>Add</button>"
                "</form>"
              "</body></html>"
            )
          },

          .post = {
            validate({"title",
              .validation = validate_not_empty,
              .message    = "title cannot be empty"}),
            query({.db = "todos_db",
              .query = "insert into todos(title) values({{title}});"}),
+           task("record_daily_stats"),
            redirect("todos")
          },

          .errors = {
            {http_bad_request, { reroute("todos") }}
          }
        },

        {"todo", "/todos/:id",
          .get = {
            validate({"id", .validation = validate_integer,
              .message = "must be an integer"}),
            query(
              {.set_key = "todo",     .db = "todos_db",
               .query = "select id, title from todos where id = {{id}};"},
              {.set_key = "comments", .db = "todos_db",
               .query = "select id, todo_id, body from comments where todo_id = {{id}};"}
            ),
            join(
              .target_table_key      = "todo",
              .target_field_key      = "id",
              .nested_table_key      = "comments",
              .nested_field_key      = "todo_id",
              .target_join_field_key = "comments"
            ),
            render(.template =
              "<html><body>"
                "{{#todo}}"
                  "<h1>{{title}}</h1>"
                  "<h2>Comments</h2>"
                  "<ul>{{#comments}}<li>{{body}}</li>{{/comments}}</ul>"
                "{{/todo}}"
              "</body></html>"
            )
          }
        }
      },

+     .tasks = {
+       {"record_daily_stats", {
+         query({.db = "todos_db",
+           .query = "insert into daily_stats(todo_count) "
+                    "select count(*) from todos;"})
+       }, .cron = "0 0 * * *"}
+     },

      .databases = {{
        .engine     = sqlite_db,
        .name       = "todos_db",
        .connect    = "file:todos.db?mode=rwc",
        .migrations = {
          "CREATE TABLE todos ("
            "id INTEGER PRIMARY KEY AUTOINCREMENT,"
            "title TEXT NOT NULL"
          ");",
          "CREATE TABLE comments ("
            "id INTEGER PRIMARY KEY AUTOINCREMENT,"
            "todo_id INTEGER NOT NULL REFERENCES todos(id),"
            "body TEXT NOT NULL"
-         ");"
+         ");",
+         "CREATE TABLE daily_stats ("
+           "id INTEGER PRIMARY KEY AUTOINCREMENT,"
+           "recorded_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,"
+           "todo_count INTEGER NOT NULL"
+         ");"
        },
        .seeds = {"INSERT INTO todos(title) VALUES('Learn MACH');"}
      }},

      .modules = {sqlite}
    };
  }

The same task definition is reused two ways: .cron = "0 0 * * *" runs it at midnight, and task("record_daily_stats") from the POST pipeline enqueues an on-demand run after each insert. Both invocations land on a task reactor, on separate cores from the request reactors that serve HTTP, so the POST returns immediately. To pass values from the calling context (a user_id, a todo_id), list them under .accepts on the task definition and reference them with {{user_id}} interpolation.

Tasks are durable: MACH checkpoints the context after each step, so a crash mid-task resumes at the failed step on the next boot. See Task Pipelines.

7. Modules & Events

Features split into modules as the app grows; modules communicate through pub/sub events instead of calling each other directly. A module is a fully self-contained system — its own resources, databases, migrations, context, error and repair handlers, tasks, and event subscribers. main.c composes them and handles cross-cutting concerns.

This step extracts the todos logic into its own module and adds an activity module that logs an entry whenever a todo is created and exposes a page to view the log.

Modules are plain C files. Each defines a function returning config — config todos() { ... }, config activity() { ... } — and main.c pulls them in with #include and registers them under .modules.

Directory layout after this step:

.
├── activity/
│   └── activity.c
├── todos/
│   └── todos.c
└── main.c

main.c — thin root that composes modules and handles cross-cutting concerns.

#include <mach.h>
#include <sqlite.h>
#include "todos/todos.c"
#include "activity/activity.c"

config mach(){
  return (config){
    .resources = {
      {"home", "/",
        .get = {
          render(.template =
            "<html><body>"
              "<h1>Welcome</h1>"
              "<a href='{{url:todos}}'>My Todos</a> · "
              "<a href='{{url:activity}}'>Activity</a>"
            "</body></html>"
          )
        }
      }
    },

    .modules = {todos, activity, sqlite}
  };
}

todos/todos.c — the todos module, now a publisher.

#include <mach.h>
#include <sqlite.h>

config todos(){
  return (config){
    .name = "todos",

    .publishes = {
      {"todo_created", .with = {"title"}}
    },

    .resources = {
      {"todos", "/todos",
        .get = {
          query({.set_key = "todos", .db = "todos_db",
            .query = "select id, title from todos;"}),
          render(.template =
            "<html><body>"
              "<h1>My Todos</h1>"
              "<ul>{{#todos}}<li><a href='{{url:todo:id}}'>{{title}}</a></li>{{/todos}}</ul>"
              "<form method='post' action='{{url:todos}}'>"
                "<input name='title' value='{{input:title}}'>"
                "{{#error:title}}<span>{{error_message:title}}</span>{{/error:title}}"
                "<button>Add</button>"
              "</form>"
            "</body></html>"
          )
        },

        .post = {
          validate({"title",
            .validation = validate_not_empty,
            .message    = "title cannot be empty"}),
          query({.db = "todos_db",
            .query = "insert into todos(title) values({{title}});"}),
          task("record_daily_stats"),
          emit("todo_created"),
          redirect("todos")
        },

        .errors = {
          {http_bad_request, { reroute("todos") }}
        }
      },

      {"todo", "/todos/:id",
        .get = {
          validate({"id", .validation = validate_integer,
            .message = "must be an integer"}),
          query(
            {.set_key = "todo",     .db = "todos_db",
             .query = "select id, title from todos where id = {{id}};"},
            {.set_key = "comments", .db = "todos_db",
             .query = "select id, todo_id, body from comments where todo_id = {{id}};"}
          ),
          join(
            .target_table_key      = "todo",
            .target_field_key      = "id",
            .nested_table_key      = "comments",
            .nested_field_key      = "todo_id",
            .target_join_field_key = "comments"
          ),
          render(.template =
            "<html><body>"
              "{{#todo}}"
                "<h1>{{title}}</h1>"
                "<h2>Comments</h2>"
                "<ul>{{#comments}}<li>{{body}}</li>{{/comments}}</ul>"
              "{{/todo}}"
            "</body></html>"
          )
        }
      }
    },

    .tasks = {
      {"record_daily_stats", {
        query({.db = "todos_db",
          .query = "insert into daily_stats(todo_count) "
                   "select count(*) from todos;"})
      }, .cron = "0 0 * * *"}
    },

    .databases = {{
      .engine     = sqlite_db,
      .name       = "todos_db",
      .connect    = "file:todos.db?mode=rwc",
      .migrations = {
        "CREATE TABLE todos ("
          "id INTEGER PRIMARY KEY AUTOINCREMENT,"
          "title TEXT NOT NULL"
        ");",
        "CREATE TABLE comments ("
          "id INTEGER PRIMARY KEY AUTOINCREMENT,"
          "todo_id INTEGER NOT NULL REFERENCES todos(id),"
          "body TEXT NOT NULL"
        ");",
        "CREATE TABLE daily_stats ("
          "id INTEGER PRIMARY KEY AUTOINCREMENT,"
          "recorded_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,"
          "todo_count INTEGER NOT NULL"
        ");"
      },
      .seeds = {"INSERT INTO todos(title) VALUES('Learn MACH');"}
    }},

    .modules = {sqlite}
  };
}

activity/activity.c — the new subscriber: its own database, its own resource, its own event handler. Nothing references the todos module.

#include <mach.h>
#include <sqlite.h>

config activity(){
  return (config){
    .name = "activity",

    .resources = {
      {"activity", "/activity",
        .get = {
          query({.set_key = "activities", .db = "activity_db",
            .query = "select kind, ref, created_at from activities "
                     "order by created_at desc;"}),
          render(.template =
            "<html><body>"
              "<h1>Activity</h1>"
              "<ul>{{#activities}}"
                "<li>{{created_at}}: {{kind}} — {{ref}}</li>"
              "{{/activities}}</ul>"
            "</body></html>"
          )
        }
      }
    },

    .events = {
      {"todo_created", {
        query({.db = "activity_db",
          .query = "insert into activities(kind, ref) "
                   "values('created', {{title}});"})
      }}
    },

    .databases = {{
      .engine     = sqlite_db,
      .name       = "activity_db",
      .connect    = "file:activity.db?mode=rwc",
      .migrations = {
        "CREATE TABLE activities ("
          "id INTEGER PRIMARY KEY AUTOINCREMENT,"
          "kind TEXT NOT NULL,"
          "ref TEXT NOT NULL,"
          "created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP"
        ");"
      }
    }},

    .modules = {sqlite}
  };
}

Each module owns one slice of the app. todos owns the todos domain (resources, database, publisher contract, scheduled task); activity owns activity (its resource, database, subscriber). Both can also declare their own context, error and repair handlers, and nested modules. Neither references the other — they only agree on the event name and payload.

When the POST pipeline in todos calls emit("todo_created"), MACH propagates title from the current context to every subscriber's pipeline. The activity module's .events entry runs with title available, writing the row to activity_db. Because .publishes is defined, MACH tracks delivery in a mach_events database, so if the process crashes between emit and delivery the event replays on the next boot. Adding a third subscriber is a new file with an .events entry — the todos module doesn't change.

8. External Assets

Once templates and SQL grow past a few lines, extract them into files and load them with (asset){#embed "..."} in .context, then reference them by name from render(), query(), and find(). Each artifact lives in a file named for what it is, edited with native tooling (Mustache-aware HTML editors, SQL formatters), and syntax-highlighted on its own terms. Apply throughout: the root, the todos module, and the activity module.

Directory layout after this step:

.
├── activity/
│   ├── activity.c
│   ├── activity.mustache.html
│   ├── create_activities_table.sql
│   ├── get_activities.sql
│   └── insert_activity.sql
├── static/
│   └── home.mustache.html
├── todos/
│   ├── create_todos_table.sql
│   ├── create_comments_table.sql
│   ├── create_daily_stats_table.sql
│   ├── get_todos.sql
│   ├── create_todo.sql
│   ├── get_todo.sql
│   ├── get_comments.sql
│   ├── record_daily_stats.sql
│   ├── todos.c
│   ├── todos_list.mustache.html
│   └── todo_detail.mustache.html
└── main.c

static/ is not a module (no .c file) — a plain directory for root-level templates that main.c references.

Root

static/home.mustache.html

<html><body>
  <h1>Welcome</h1>
  <a href='{{url:todos}}'>My Todos</a> · <a href='{{url:activity}}'>Activity</a>
</body></html>

main.c — references the home template by name.

#include <mach.h>
#include <sqlite.h>
#include "todos/todos.c"
#include "activity/activity.c"

config mach(){
  return (config){
    .resources = {
      {"home", "/",
        .get = {
          render("home")
        }
      }
    },

    .context = {
      {"home", (asset){#embed "static/home.mustache.html"}}
    },

    .modules = {todos, activity, sqlite}
  };
}

Todos module

todos/todos_list.mustache.html

<html><body>
  <h1>My Todos</h1>
  <ul>{{#todos}}<li><a href='{{url:todo:id}}'>{{title}}</a></li>{{/todos}}</ul>
  <form method='post' action='{{url:todos}}'>
    <input name='title' value='{{input:title}}'>
    {{#error:title}}<span>{{error_message:title}}</span>{{/error:title}}
    <button>Add</button>
  </form>
</body></html>

todos/get_todos.sql — and similarly for each other SQL file.

select id, title from todos;

todos/create_todo.sql

insert into todos(title) values({{title}});

SQL {{interpolation}} works the same as inline — bound as prepared parameters, never spliced. Migration files are plain CREATE TABLE statements, one per file. todos/todo_detail.mustache.html holds the detail-page template from step 5.

todos/todos.c — pipelines now reference assets by name; .context lists every asset the module uses.

#include <mach.h>
#include <sqlite.h>

config todos(){
  return (config){
    .name = "todos",

    .publishes = {
      {"todo_created", .with = {"title"}}
    },

    .resources = {
      {"todos", "/todos",
        .get = {
          query({"get_todos", .set_key = "todos", .db = "todos_db"}),
          render("todos_list")
        },

        .post = {
          validate({"title",
            .validation = validate_not_empty,
            .message    = "title cannot be empty"}),
          query({"create_todo", .db = "todos_db"}),
          task("record_daily_stats"),
          emit("todo_created"),
          redirect("todos")
        },

        .errors = {
          {http_bad_request, { reroute("todos") }}
        }
      },

      {"todo", "/todos/:id",
        .get = {
          validate({"id", .validation = validate_integer,
            .message = "must be an integer"}),
          query(
            {"get_todo",     .set_key = "todo",     .db = "todos_db"},
            {"get_comments", .set_key = "comments", .db = "todos_db"}
          ),
          join(
            .target_table_key      = "todo",
            .target_field_key      = "id",
            .nested_table_key      = "comments",
            .nested_field_key      = "todo_id",
            .target_join_field_key = "comments"
          ),
          render("todo_detail")
        }
      }
    },

    .tasks = {
      {"record_daily_stats", {
        query({"record_daily_stats", .db = "todos_db"})
      }, .cron = "0 0 * * *"}
    },

    .context = {
      {"todos_list",         (asset){#embed "todos_list.mustache.html"}},
      {"todo_detail",        (asset){#embed "todo_detail.mustache.html"}},
      {"get_todos",          (asset){#embed "get_todos.sql"}},
      {"create_todo",        (asset){#embed "create_todo.sql"}},
      {"get_todo",           (asset){#embed "get_todo.sql"}},
      {"get_comments",       (asset){#embed "get_comments.sql"}},
      {"record_daily_stats", (asset){#embed "record_daily_stats.sql"}}
    },

    .databases = {{
      .engine     = sqlite_db,
      .name       = "todos_db",
      .connect    = "file:todos.db?mode=rwc",
      .migrations = {
        (asset){#embed "create_todos_table.sql"},
        (asset){#embed "create_comments_table.sql"},
        (asset){#embed "create_daily_stats_table.sql"}
      },
      .seeds = {"INSERT INTO todos(title) VALUES('Learn MACH');"}
    }},

    .modules = {sqlite}
  };
}

Activity module

activity/activity.mustache.html

<html><body>
  <h1>Activity</h1>
  <ul>{{#activities}}
    <li>{{created_at}}: {{kind}} — {{ref}}</li>
  {{/activities}}</ul>
</body></html>

activity/insert_activity.sql — the event handler's insert, now a named asset.

insert into activities(kind, ref) values('created', {{title}});

activity/activity.c — same extraction pattern.

#include <mach.h>
#include <sqlite.h>

config activity(){
  return (config){
    .name = "activity",

    .resources = {
      {"activity", "/activity",
        .get = {
          query({"get_activities", .set_key = "activities", .db = "activity_db"}),
          render("activity")
        }
      }
    },

    .events = {
      {"todo_created", {
        query({"insert_activity", .db = "activity_db"})
      }}
    },

    .context = {
      {"activity",       (asset){#embed "activity.mustache.html"}},
      {"get_activities", (asset){#embed "get_activities.sql"}},
      {"insert_activity", (asset){#embed "insert_activity.sql"}}
    },

    .databases = {{
      .engine     = sqlite_db,
      .name       = "activity_db",
      .connect    = "file:activity.db?mode=rwc",
      .migrations = {
        (asset){#embed "create_activities_table.sql"}
      }
    }},

    .modules = {sqlite}
  };
}

The pipeline shape is unchanged — only where the strings live has moved. Each render(), query(), and find() step takes an asset name as its positional argument; MACH resolves it against the nearest .context at boot time. .migrations accepts assets directly, which is why entries now read (asset){#embed "..."} instead of quoted SQL. Templates are still Mustache; SQL still supports {{interpolation}} bound as prepared parameters.

9. External Data

Pipelines reach external HTTP services the same way they read from databases. fetch() makes the request and stores the response in context; JSON is parsed into tables and records, with nested JSON becoming nested context tables. Add a quote of the day to the home page, pulled from a public API.

static/home.mustache.html

  <html><body>
    <h1>Welcome</h1>
+   {{#quote}}
+     <blockquote>{{content}} — {{author}}</blockquote>
+   {{/quote}}
    <a href='{{url:todos}}'>My Todos</a> · <a href='{{url:activity}}'>Activity</a>
  </body></html>

main.c

  #include <mach.h>
  #include <sqlite.h>
  #include "todos/todos.c"
  #include "activity/activity.c"

  config mach(){
    return (config){
      .resources = {
        {"home", "/",
          .get = {
+           fetch("https://api.quotable.io/random",
+             .set_key = "quote"),
            render("home")
          }
        }
      },

      .context = {
        {"home", (asset){#embed "static/home.mustache.html"}}
      },

      .modules = {todos, activity, sqlite}
    };
  }

fetch() runs before render("home"). The Quotable API returns {"author": "...", "content": "..."}, which MACH parses into a single-row table under quote. The template opens {{#quote}}...{{/quote}} to read its fields, the same way it does for query results.

Like query(), multiple items in a single fetch() run concurrently. fetch() also supports POST/PUT/PATCH/DELETE, custom headers, JSON or text request bodies, and URLs with {{interpolation}}. See fetch.

That covers the basic shape of a MACH app: resources route requests, pipelines transform them, error handlers recover, joins compose nested views from separate queries, tasks handle background work, events decouple modules, external assets let templates and SQL live alongside the code that uses them, and fetch() brings in external HTTP data. See Modules & Composition for more on module boundaries.

---

Reference

Each subsection describes one piece of the framework and lists every option it accepts with a minimal snippet.

• Notation
• Context
• Databases
• Resource Pipelines
• Template Helpers
• Pipeline Steps
• Conditionals
• Error and Repair Pipelines
• Event Pipelines
• Task Pipelines
• Modules & Composition
• Static Files
• External Dependencies

Notation

MACH uses C designated initializers at different brace depths.

Braces	Meaning	Example
{}	Single value or struct	.get = { ... }
{{}}	Array of structs	.databases = {{ ... }}

For arrays with multiple elements, comma-separate the inner braces: .databases = {{...}, {...}}. Inside steps, each {} initializes one item; steps that accept multiple items (such as query and validate) use comma-separated items: query({...}, {...}).

Context

Pipelines read from and write to a shared, scoped key-value store that lives for the duration of one request. Every step draws inputs from context and writes outputs back to it.

.context seeds that store at the root with variables and assets available on every request. Templates and SQL stored here are referenced by name in render(), query(), and find(). Use (asset){#embed "file"} to bake files into the binary at compile time. Docker secrets exposed to the container are also available in context.

The context uses three scopes: input:xxx for raw request parameters, error:xxx for validation/error data, and unprefixed names for app scope (query results, validated inputs, context variables). validate() bridges input: to app scope.

Inline string value: provide the value directly.

.context = {{"site_name", "MACH App"}}

(asset){#embed ...}: bake a file into the binary as a named asset.

.context = {
  {"layout",    (asset){#embed "layout.mustache.html"}},
  {"get_todos", (asset){#embed "get_todos.sql"}}
}

Combined:

.context = {
  {"site_name", "MACH App"},
  {"version",   "1.2.0"},
  {"layout",    (asset){#embed "static/layout.mustache.html"}},
  {"home",      (asset){#embed "static/home.mustache.html"}},
  {"get_todos", (asset){#embed "todos/get_todos.sql"}},
  {"create_todo", (asset){#embed "todos/create_todo.sql"}}
}

Databases

Each .databases entry defines a data store. Migrations are forward-only and index-based: they run in array order, each applied once, with new migrations appended to the end. Seeds are idempotent and safe to re-run. Both are tracked in a mach_meta table.

Multi-tenant databases use {{interpolation}} in .connect. Connections are pooled with LRU eviction: active tenants stay warm, idle connections are reclaimed.

.engine: database engine constant, provided by a module.

.engine = sqlite_db

.name: identifier referenced by .db in query() and find().

.name = "todos_db"

.connect: engine-specific connection string. Supports {{interpolation}} for multi-tenancy.

.connect = "file:{{user_id}}_todo.db?mode=rwc"

.migrations: array of SQL migration strings or assets, applied once each in order.

.migrations = {(asset){#embed "create_todos_table.sql"}}

.seeds: array of idempotent seed statements, safe to re-run on every boot.

.seeds = {"INSERT OR IGNORE INTO todos(id, title) VALUES(1, 'Hello');"}

Combined:

.databases = {{
  .engine     = sqlite_db,
  .name       = "blog_db",
  .connect    = "file:{{user_id}}_blog.db?mode=rwc",
  .migrations = {
    "CREATE TABLE blogs ("
      "id INTEGER PRIMARY KEY AUTOINCREMENT,"
      "title TEXT NOT NULL,"
      "content TEXT NOT NULL"
    ");",
    "CREATE TABLE comments ("
      "id INTEGER PRIMARY KEY AUTOINCREMENT,"
      "blog_id INTEGER NOT NULL REFERENCES blogs(id),"
      "body TEXT NOT NULL"
    ");"
  },
  .seeds = {
    "INSERT OR IGNORE INTO blogs(id, title, content) VALUES(1, 'Hello', 'First post');"
  }
}}

A single database can contain multiple tables. Declare each as a separate migration; they run in array order, so blogs exists before comments references it.

One database = one domain, many tables. A database maps to a domain (todos_db, blog_db), not to a single entity. Related tables go as additional migrations on the same database. Reach for a second database when the domain is genuinely separate: audit logs, analytics, a third-party cache.

Engines: sqlite_db, postgres_db, mysql_db, redis_db, duckdb_db

Resource Pipelines

MACH is resource-based, not route-based. Each entry in .resources defines a named URL endpoint with HTTP verb pipelines. Resources are identified by name: {{url:name}}, redirect(), and reroute() take a name[:arg1:arg2...] identifier; positional args fill the :params of the URL pattern in order. Path specificity is automatic: exact matches (/todos/active) beat parameterized matches (/todos/:id) regardless of definition order.

{{url:name}} with URL params. Args after the name are positional, colon-separated, literals or context keys:

• ✅ {{url:todo:5}} resolves to /todos/5
• ✅ {{url:todo:id}} reads id from current scope (useful inside {{#todos}}...{{/todos}} where each iteration has its own id)
• ✅ {{url:org_todo:acme:5}} fills multiple :params in URL-pattern order (e.g. /orgs/:org/todos/:id)

Clients select a verb via the request method, or by passing http_method as a query/form parameter. This lets HTML forms (limited to GET/POST) reach any verb, and gives SSE a connection path: /todos?http_method=sse.

.name (pos): resource identifier used by {{url:name}}, redirect(), and reroute().

{"todos", "/todos", .get = { ... }}

.url (pos): URL pattern. Supports :params.

{"todo", "/todos/:id", .get = { ... }}

.steps (pos): shared steps that run before every verb pipeline on the resource.

{"todo", "/todos/:id", {
  validate({"id", .validation = "^\\d+$", .message = "must be a number"})
}, .get = { ... }, .delete = { ... }}

.mime: default response content type for the resource.

{"feed", "/feed.json", .mime = mime_json, .get = { ... }}

.get .post .put .patch .delete: verb pipelines — ordered arrays of steps that transform a request into a response.

{"todos", "/todos",
  .get  = { query({"get_todos", .set_key = "todos", .db = "db"}), render("todos") },
  .post = { validate({"title", .validation = validate_not_empty}), redirect("todos") }
}

.sse: persistent SSE channel. First positional is the channel name; steps run on connect.

{"todos", "/todos",
  .sse = {"todos/{{user_id}}",
    query({"get_todos", .set_key = "todos", .db = "db"}),
    sse(.event = "initial", .data = {"{{todos}}"})
  }
}

.errors / .repairs: resource-scoped error and repair pipelines. See Error and Repair Pipelines.

{"todos", "/todos",
  .post = { ... },
  .errors = {{http_bad_request, { render("form") }}}
}

Combined:

{"todo", "/todos/:id", {
  validate({"id", .validation = "^\\d+$", .message = "must be a number"})
},
  .mime  = mime_html,
  .get   = { find({"get_todo", .set_key = "todo", .db = "todos_db"}),
             render("todo") },
  .patch = { validate({"title", .validation = validate_not_empty, .message = "required"}),
             query({.db = "todos_db",
               .query = "update todos set title = {{title}} where id = {{id}};"}),
             redirect("todo:{{id}}") },
  .delete = { query({.db = "todos_db",
                .query = "delete from todos where id = {{id}};"}),
              redirect("todos") },
  .sse    = {"todo/{{id}}", sse(.event = "ready") },
  .errors = {{http_not_found, { render("404") }}}
}

MIME types (for .mime): mime_html, mime_txt, mime_sse, mime_json, mime_js

Template Helpers

Templates and other interpolated strings support built-in helpers with {{helper:args}} syntax. Arguments are positional and colon-separated; each can be a literal or a context key.

{{raw:field}}: emit a context value without HTML-escaping. render() escapes by default; raw: is the explicit opt-out.

render(.template = "<div>{{raw:article_html}}</div>")

{{precision:field:N}}: format a numeric value with N decimal places.

render(.template = "<p>Total: ${{precision:total:2}}</p>")

{{input:field}}: raw, unvalidated request parameter from the input scope. Typically used to repopulate form fields after a validation error.

render(.template = "<input name='title' value='{{input:title}}'>")

{{error:field}}: truthy when field has an error. Used as a Mustache section to conditionally render markup.

render(.template = "{{#error:title}}<span class='error'>invalid</span>{{/error:title}}")

{{error_message:field}}: human-readable message for a field error, from validate()'s .message or from error_set().

render(.template = "<span>{{error_message:title}}</span>")

{{error_code:field}}: HTTP status code associated with a field error (e.g. 400, 404).

render(.template = "<p>Code: {{error_code:title}}</p>")

{{url:name}}: resolve a resource identifier to its URL. Takes positional args to fill :params. Args can be literals or context keys.

render(.template =
  "<a href='{{url:todos}}'>All</a>"              // /todos
  "<a href='{{url:todo:5}}'>Item 5</a>"          // /todos/5
  "<a href='{{url:todo:id}}'>From context</a>"   // /todos/{{id}}
)

{{asset:filename}}: resolve a file in public/ to a cache-busted URL (content checksum + immutable cache headers). See Static Files.

render(.template = "<link rel='stylesheet' href='{{asset:styles.css}}'>")

{{csrf:token}}: emit a CSRF token, for use in URL query strings. Generates a random hash, sets it on an httponly/secure/samesite cookie, and outputs the same value inline.

render(.template = "<a href='{{url:logout}}?csrf={{csrf:token}}'>Log out</a>")

{{csrf:input}}: emit a hidden <input> carrying a CSRF token, for use inside a <form>. Same cookie-setting behavior as {{csrf:token}}.

render(.template = "<form>{{csrf:input}}<input name='title'><button>Add</button></form>")

Combined:

render(.template =
  "<link rel='stylesheet' href='{{asset:styles.css}}'>"
  "<article>"
    "{{#post}}"
      "<h2>{{title}}</h2>"
      "<p>Rating: {{precision:score:1}}/5</p>"
      "<div>{{raw:body_html}}</div>"
    "{{/post}}"
    "<form method='post' action='{{url:comments}}'>"
      "{{csrf:input}}"
      "<input name='body' value='{{input:body}}'>"
      "{{#error:body}}<span>{{error_message:body}}</span>{{/error:body}}"
      "<button>Comment</button>"
    "</form>"
    "<a href='{{url:logout}}?csrf={{csrf:token}}'>Log out</a>"
  "</article>"
)

CSRF verification is automatic. MACH checks that the incoming token (from the form field or query parameter) matches the value stored in the CSRF cookie and rejects mismatches with a 403. The cookie is httponly, secure, and samesite, so nothing beyond emitting {{csrf:token}} or {{csrf:input}} in the rendered response is required.

Pipeline Steps

Steps are the units of work in a pipeline. Each receives the current context, acts on it, and passes control to the next. All steps accept .if_context and .unless_context for conditional execution.

• validate
• find & query
• join
• fetch
• exec
• emit
• task
• sse
• ds_sse
• render
• headers & cookies
• redirect & reroute
• nest

validate

Checks request parameters (query string, form body, URL params) against regex patterns. On success, each value is promoted from input:name to app scope. On failure, errors land in error:name and a 400 Bad Request triggers the nearest error/repair pipeline. All validations in one call complete before the error fires, so all errors are available together for form re-rendering.

Built-in regex macros are defined in mach.h; define your own the same way: #define validate_zipcode "^\\d{5}$".

.param_key (pos): name of the parameter to validate.

validate({"title", .validation = "^\\S+$", .message = "required"})

.validation: regex pattern, or a built-in validator macro.

validate({"email", .validation = validate_email, .message = "bad email"})

.message: human-readable error shown via {{error_message:name}}.

validate({"age", .validation = "^\\d+$", .message = "must be a number"})

.optional: skip validation when the parameter is absent.

validate({"filter", .optional = true, .validation = "^(active|done)$"})

.fallback: default value injected when the parameter is absent.

validate({"page", .fallback = "1", .validation = "^\\d+$"})

Combined:

validate(
  {"email",  .validation = validate_email,     .message = "must be a valid email"},
  {"title",  .validation = validate_not_empty, .message = "cannot be empty"},
  {"page",   .fallback   = "1",
             .validation = "^\\d+$",            .message = "must be a number"},
  {"filter", .optional   = true,
             .validation = "^(active|done)$",   .message = "must be 'active' or 'done'"}
)

Built-in validators:

• Strings: validate_not_empty, validate_alpha, validate_alphanumeric, validate_slug, validate_no_html
• Numbers: validate_integer, validate_positive, validate_float, validate_percentage
• Identity: validate_email, validate_uuid, validate_username
• Dates & times: validate_date, validate_time, validate_datetime
• Web: validate_url, validate_ipv4, validate_hex_color
• Codes: validate_zipcode_us, validate_phone_e164, validate_cron
• Security: validate_no_sqli, validate_token, validate_base64
• Boolean: validate_boolean, validate_yes_no, validate_on_off

find & query

Both run database queries. .db selects the database; .set_key stores the result in context as a table, even for single-row queries. Templates open the table as a section ({{#blog}}{{title}}{{/blog}}) to reach fields; {{title}} at root does not resolve. SQL is either inlined with .query or referenced by name as the positional (loaded from .context). Multiple items in a single step run concurrently. Queries use prepared statements; interpolated {{values}} are bound, not spliced. For transactions, use BEGIN/COMMIT/ROLLBACK directly in your queries.

The only difference between the two: find() raises 404 Not Found on zero rows; query() does not.

Positional asset name OR .query, not both. Each item picks one:

• ✅ query({"get_todos", .set_key = "todos", .db = "todos_db"}): SQL loaded by asset name from .context
• ✅ query({.set_key = "todos", .db = "todos_db", .query = "select id, title from todos;"}): SQL inlined
• ❌ query({"get_todos", .set_key = "todos", .db = "todos_db", .query = "select ..."}): combining the two is rejected

Concurrency = multiple items in one step, not multiple steps. query({...}, {...}) runs both queries in parallel. Two back-to-back query({...}) steps run serially.

.template_key (pos): name of a SQL asset stored in .context. Mutually exclusive with .query.

query({"get_todos", .set_key = "todos", .db = "todos_db"})

.query: inline SQL string. Supports {{interpolation}}, bound as parameters. Mutually exclusive with the positional asset name.

query({.set_key = "todos", .db = "todos_db",
  .query = "select id, title from todos where user_id = {{user_id}};"})

.set_key: context key for the result table.

query({.set_key = "active", .db = "db", .query = "select * from todos;"})

.db: name of the database, matching a .databases entry.

query({.db = "todos_db", .query = "select 1;"})

.if_context / .unless_context (per item): conditionally include or skip individual queries while running the others concurrently.

query(
  {"get_todos",  .set_key = "todos",  .db = "db"},
  {"get_urgent", .if_context = "show_urgent", .set_key = "u", .db = "db"}
)

Combined:

query(
  {"get_todos", .set_key = "todos", .db = "todos_db"},
  {.set_key = "count", .db = "todos_db",
   .query = "select count(*) as n from todos where user_id = {{user_id}};"},
  {.if_context = "show_urgent", .set_key = "urgent", .db = "todos_db",
   .query = "select id, title from todos where user_id = {{user_id}} and priority = 'high';"}
)

join

Nests records from one context table into each matching record of another, like a SQL JOIN performed in memory. Useful when records come from separate databases or queries and need to be combined for rendering. After the step, each outer record gains a new field holding its matched inner records.

The nesting only has an effect if render() opens the outer table as a section. A template that iterates both tables as siblings at root treats join() as a no-op.

.target_table_key: outer table whose records receive nested children.

.target_table_key = "projects"

.target_field_key: field on the outer table to match against.

.target_field_key = "id"

.nested_table_key: inner table whose records get nested.

.nested_table_key = "todos"

.nested_field_key: field on the inner table that points at the outer.

.nested_field_key = "project_id"

.target_join_field_key: new field on outer records holding the matched inner records.

.target_join_field_key = "todos"

Combined:

join(
  .target_table_key = "projects",
  .target_field_key = "id",
  .nested_table_key = "todos",
  .nested_field_key = "project_id",
  .target_join_field_key = "todos"
)

Full worked example. The common pattern is concurrent query() → join() → render(): fetch parent and children from separate queries, then render them as one nested structure. Blog + comments, single database:

{"blog", "/blogs/:id",
  .get = {
    validate({"id", .validation = validate_integer, .message = "must be an integer"}),

    // Fetch both concurrently — one query() call, two items
    query(
      {.set_key = "blog",     .db = "blog_db",
       .query = "select id, title, content from blogs where id = {{id}};"},
      {.set_key = "comments", .db = "blog_db",
       .query = "select id, blog_id, body from comments where blog_id = {{id}};"}
    ),

    // Nest each comment into its matching blog record
    join(
      .target_table_key      = "blog",
      .target_field_key      = "id",
      .nested_table_key      = "comments",
      .nested_field_key      = "blog_id",
      .target_join_field_key = "comments"
    ),

    // Enter {{#blog}} first — after join(), comments lives INSIDE each blog record
    render(.template =
      "<article>"
        "{{#blog}}"
          "<h1>{{title}}</h1>"
          "<div>{{content}}</div>"
          "<h2>Comments</h2>"
          "<ul>{{#comments}}<li>{{body}}</li>{{/comments}}</ul>"
        "{{/blog}}"
      "</article>"
    )
  }
}

Shape of the context at each step:

after query(): { blog: [{id, title, content}],
                 comments: [{id, blog_id, body}, ...] }       // two sibling tables

after join():  { blog: [{id, title, content,
                         comments: [{id, blog_id, body}, ...]}] }  // nested inside blog

fetch

Makes an HTTP request and stores the response in context. JSON is parsed into tables and records (with nested tables for nested JSON); plain-text responses are stored as a string.

.url (pos): request URL; supports {{interpolation}}.

fetch("https://api.weather.dev/forecast?city={{city}}", .set_key = "w")

.set_key: context key for the response.

fetch("https://api.weather.dev/now", .set_key = "weather")

.method: HTTP method. Defaults to http_get.

fetch("https://api.dev/charge", .set_key = "r", .method = http_post)

.headers: array of name/value pairs.

fetch("https://api.dev/me", .set_key = "r",
  .headers = {{"Authorization", "Bearer {{token}}"}})

.json: context key serialized as the JSON request body.

fetch("https://api.dev/charge", .set_key = "receipt",
  .method = http_post, .json = "order")

.text: context key sent as the plain-text request body.

fetch("https://api.dev/log", .set_key = "r",
  .method = http_post, .text = "raw_body")

Combined:

fetch("https://api.payments.dev/charge",
  .set_key = "receipt",
  .method  = http_post,
  .headers = {
    {"Authorization",   "Bearer {{api_key}}"},
    {"Idempotency-Key", "{{order_id}}"}
  },
  .json    = "order"
)

HTTP methods (for .method): http_get, http_post, http_put, http_patch, http_delete, http_sse_method

exec

Calls a C function or block with access to the context via the Imperative API. Execution is dispatched to the shared thread pool, which releases the reactor; the pipeline resumes on the original reactor when the call returns. Suitable for blocking I/O and CPU-heavy work. To trigger an error/repair pipeline from inside, call error_set().

Block (pos): inline block, convenient for short logic that doesn't need its own function.

exec(^(){
  auto t = get("challengers");
  record_set(table_get(t, 0), "opponent_id",
             record_get(table_get(t, 1), "id"));
})

.call: reference to a named C function.

exec(.call = assign_opponents)

Imperative API (available from exec blocks and functions):

• Context: get(name), set(name, value), has(name), format(fmt)
• Memory: allocate(bytes), defer_free(ptr)
• Errors: error_set(name, err), error_get(name), error_has(name)
• Tables: table_new(), table_count(t), table_get(t, i), table_add(t, r), table_remove(t, r), table_remove_at(t, i)
• Records: record_new(), record_set(r, name, value), record_get(r, name), record_remove(r, name)

emit

Triggers an internal pub/sub event. Subscribers in other modules react in their .events pipelines, with no direct dependency on the emitter. See Event Pipelines.

Event name (pos): name of the event to publish.

emit("todo_created")

task

Adds a named job to the task database; the calling pipeline continues immediately. Task reactors pick up queued jobs and execute their pipelines. See Task Pipelines.

Task name (pos): name of a task defined in .tasks.

task("recount_todos")

sse

Pushes a Server-Sent Event. With .channel, the event is broadcast to all clients on that channel. Without .channel, the event is returned directly to the requesting client. See Resource Pipelines.

.channel (pos): channel to broadcast on; supports {{interpolation}}.

sse(.channel = "todos/{{user_id}}", .event = "new_todo", .data = {"{{todo}}"})

.event: SSE event: line value.

sse(.event = "ping")

.data: array of strings, one per SSE data: line (multi-line data).

sse(.event = "msg", .data = {"line one", "line two"})

.comment: SSE : comment line value, useful for keep-alives.

sse(.comment = "keep-alive")

Combined:

sse(
  .channel = "todos/{{user_id}}",
  .event   = "todo_updated",
  .data    = {"id: {{todo_id}}", "title: {{title}}"},
  .comment = "broadcast at {{timestamp}}"
)

ds_sse

Datastar is a hypermedia framework where the server pushes DOM updates and reactive state over SSE. Provided by the datastar module, ds_sse combines SSE with Datastar-formatted events targeting specific elements. Without a channel the event goes to the requesting client; with one it broadcasts.

.channel (pos): broadcast channel; supports {{interpolation}}.

ds_sse("todos/{{user_id}}", .target = "todos", .elements = {"todo"})

.target: DOM element id for the update.

ds_sse(.target = "todos", .elements = {"todo_row"})

.mode: fragment insertion mode for the rendered DOM fragment.

ds_sse(.target = "todos", .mode = mode_prepend, .elements = {"todo_row"})

.elements: a render_config for the DOM fragment (positional is the asset name, supports .template, .engine, etc.).

ds_sse(.target = "row", .elements = {"todo_row"})

.signals: JSON string used to update Datastar's reactive client state without touching the DOM.

ds_sse(.signals = "{\"count\": {{count}}}")

.js: JavaScript snippet evaluated on the client.

ds_sse(.js = "console.log('updated')")

Combined:

ds_sse("todos/{{user_id}}",
  .target   = "todo-list",
  .mode     = mode_prepend,
  .elements = {"todo_row"},
  .signals  = "{\"count\": {{count}}}",
  .js       = "window.scrollTo(0, 0)"
)

Modes: mode_outer, mode_inner, mode_replace, mode_prepend, mode_append, mode_before, mode_after, mode_remove

render

Outputs a Mustache template using the current context. Templates are referenced by name from .context or inlined.

Mustache tags live inside C string literals. Inline templates are C strings concatenated by adjacent-string-literal rules. Every Mustache tag, including section open/close on their own lines, must be inside quotes. Section tags look like block syntax but they are content.

• ✅ Multi-line with section tags on their own quoted lines (the canonical format):

"<article>"
  "{{#blog}}"
    "<h1>{{title}}</h1>"
    "<ul>{{#comments}}<li>{{body}}</li>{{/comments}}</ul>"
  "{{/blog}}"
"</article>"

• ✅ All inline in one string: "<article>{{#blog}}<h1>{{title}}</h1>{{/blog}}</article>"
• ❌ Section tags on their own lines without quotes — compile error:

"<article>"
  {{#blog}}                               // NOT in quotes
    "<h1>{{title}}</h1>"
  {{/blog}}                               // NOT in quotes
"</article>"

.template_key (pos): asset name in .context. The asset is a Mustache template.

render("todos")

.template: inline Mustache template string.

render(.template = "<h1>{{site_name}}</h1>")        // {{site_name}} from .context

.status: HTTP response status (defaults to http_ok).

render("not_found", .status = http_not_found)

.mime: override the response content type.

render("plain", .mime = mime_txt)

.engine: template engine. Accepts mustache / "mustache" (default) or mdm / "mdm" for Markdown-with-Mustache. The bare identifiers are macros that expand to the string values; either form works.

render(.engine = mdm, .template = "# Welcome, {{user_name}}")

.json_table_key: context table to serialize as the JSON response. Sets application/json; nested tables produce nested JSON.

render(.json_table_key = "todos")

HTTP statuses (for .status): http_ok (200), http_created (201), http_redirect (302), http_bad_request (400), http_not_authorized (401), http_not_found (404), http_error (500)

MIME types (for .mime): mime_html, mime_txt, mime_sse, mime_json, mime_js

headers & cookies

Set HTTP response headers and cookies declaratively. Both accept an array of name/value pairs; values support {{interpolation}}.

Pairs (pos): array of {name, value} entries.

headers({{"X-Request-Id", "{{request_id}}"}, {"Cache-Control", "no-store"}})
cookies({{"session", "{{session_id}}"}})

redirect & reroute

redirect() returns a 302 to the client, causing the browser to navigate. reroute() re-enters the router server-side, executing another resource's pipeline within the same request. Both take a resource identifier in the same name[:arg1:arg2...] format as {{url:name}}: colon-separated positional args that fill the target's :params. Args can be literals or context keys, and support {{interpolation}}.

Resource identifier (pos): target resource name, plus positional args for any :params.

redirect("todos")                // 302 to /todos (bare resource, no args)
redirect("todo:5")               // 302 to /todos/5 (literal id)
redirect("todo:{{id}}")          // 302 to /todos/5 (id from context)
redirect("org_todo:acme:5")      // 302 to /orgs/acme/todos/5 (multi-arg)
reroute("todo:{{id}}")           // run that pipeline in-process

nest

Groups multiple steps into a single composite step. Useful when applying one .if_context/.unless_context to several steps, to avoid repeating the condition on each.

.steps (pos): array of steps that run as a unit.

nest({query({...}), emit("urgent_todo"), render("urgent")})

.if_context / .unless_context: condition applied to the whole group.

nest({query({...}), emit("urgent_todo"), render("urgent")},
  .if_context = "is_urgent")

Conditionals

Every step accepts .if_context and .unless_context, which name a context variable. They work for any context value: validated inputs, query results, framework flags such as is_htmx, or flags set from exec().

.if_context: context key. Step runs only when the value is present.

render("fragment", .if_context = "is_htmx")

.unless_context: context key. Step runs only when the value is absent.

render("full_page", .unless_context = "is_htmx")

For multi-state branching, set context flags from exec(), then key downstream steps off them:

exec(.call = classify_todo),
render("urgent_confirmation",  .if_context     = "is_urgent"),
render("standard_confirmation", .unless_context = "is_urgent")

Error and Repair Pipelines

When a pipeline step fails, execution halts and MACH searches for a handler bottom-up: resource, then module, then root. Errors are terminal: the handler sends a response and ends the request. Repairs are resumable: they fix the context and resume the original pipeline at the step after the failure. If no matching repair is found, resolution falls through to errors. Unhandled errors surface in the TUI console and telemetry.

The error scope is shared across validate() failures and error_set() calls: {{error:name}}, {{error_code:name}}, {{error_message:name}}. The raw input value remains available in input:name for re-rendering forms.

.errors: terminal handlers keyed by error code.

.errors = {
  {http_not_found,    { render("404") }},
  {http_bad_request,  { render("form") }}
}

.repairs: resumable handlers keyed by error code.

.repairs = {
  {http_not_authorized, { exec(.call = refresh_session_token) }}
}

Combined:

.errors = {
  {http_not_found,    { render("404") }},
  {http_bad_request,  { render("form") }},
  {http_error,        { render("500") }}
},
.repairs = {
  {http_not_authorized, { exec(.call = refresh_session_token) }}
}

Built-in error codes: http_ok (200), http_created (201), http_redirect (302), http_bad_request (400), http_not_authorized (401), http_not_found (404), http_error (500). Any integer works; the http_* constants are convenience names. Define your own for domain-specific errors, e.g. #define err_quota_exceeded 723.

Event Pipelines

Internal pub/sub for cross-module communication. The publisher does not know who listens; the subscriber does not know who emits. Adding a subscriber means adding a new module with an .events entry, with no changes to the publisher.

Events are durable by default. When .publishes is defined anywhere in the app, MACH creates a mach_events database to track delivery. If the process crashes, undelivered events are replayed on the next boot.

.publishes: outbound event contracts. .event is the name; .with lists context keys to pass along.

.publishes = {
  {"todo_created", .with = {"user_id", "title"}}
}

.events: subscriber pipelines keyed by event name.

.events = {
  {"todo_created", {
    query({"insert_activity", .db = "activity_db"})
  }}
}

Combined:

// todos/todos.c: publisher
config todos(){
  return (config){
    .name = "todos",
    .publishes = {
      {"todo_created", .with = {"user_id", "title"}},
      {"todo_deleted", .with = {"user_id", "todo_id"}}
    },
    .resources = {
      {"todos", "/todos",
        .post = {
          validate({"title", .validation = validate_not_empty}),
          query({"insert_todo", .db = "todos_db"}),
          emit("todo_created"),
          redirect("todos")
        }
      }
    }
  };
}

// activity/activity.c: subscriber
config activity(){
  return (config){
    .name = "activity",
    .events = {
      {"todo_created", {
        query({.db = "activity_db",
          .query = "insert into activities(kind, user_id, ref) "
                   "values('created', {{user_id}}, {{title}});"})
      }},
      {"todo_deleted", {
        query({.db = "activity_db",
          .query = "insert into activities(kind, user_id, ref) "
                   "values('deleted', {{user_id}}, {{todo_id}});"})
      }}
    }
  };
}

Task Pipelines

Tasks are named pipelines that run asynchronously on task reactors. Fire-and-forget: the calling pipeline continues immediately. Defined at the module or root level. Triggered on demand with task("name") or on a schedule via .cron. Tasks can enqueue more tasks via task().

Tasks are durable: when .tasks is defined, MACH creates a mach_tasks database and checkpoints the context after each step. A crash mid-task resumes at the step where it left off on the next boot.

.name (pos): task identifier, called via task("name").

.tasks = {
  {"recount_todos", { query({.db = "db", .query = "update users set ..."}) }}
}

.accepts: context keys to pull from the caller into the task.

{"recount_todos", {
  query({.db = "db", .query = "update users set todo_count = ... where id = {{user_id}};"})
}, .accepts = {"user_id"}}

.cron: standard cron schedule for recurring tasks (no caller required).

{"daily_digest", {
  query({.db = "db", .query = "insert into digest_reports ..."})
}, .cron = "0 8 * * *"}

Steps (pos): the task's pipeline body, the second positional brace block, before any designated fields.

{"name", { query({...}), emit("done"), task("followup") }, .accepts = {...}}

Combined:

.tasks = {
  // on-demand: enqueued via task("recount_todos")
  {"recount_todos", {
    query({.db = "todos_db",
      .query = "update users set todo_count = "
               "(select count(*) from todos where user_id = users.id) "
               "where id = {{user_id}};"})
  }, .accepts = {"user_id"}},

  // recurring: runs on schedule, no caller
  {"daily_digest", {
    query({.db = "todos_db",
      .query = "insert into digest_reports(generated_at) values(now());"}),
    emit("digest_ready")
  }, .cron = "0 8 * * *"}
}

Modules & Composition

Every MACH app and module returns a config struct. The root main.c must define a function named mach(); modules define their own functions with any name and register them in .modules by bare function reference. A module owns its own resources, databases, migrations, templates, and event contracts.

When the root and a module both define something with the same name (a context variable, a database, an error handler), the root wins. Modules don't call each other directly; they communicate through pub/sub events.

.name: module identifier.

config todos(){ return (config){ .name = "todos", /* resources, databases, ... */ }; }

.modules: other modules to compose into this one (root or nested).

.modules = {todos, activity, sqlite, session_auth}

Complete module file. A module returns a config with the same shape as the root app (.resources, .databases, .events, etc.), plus a .name for identity. Resource fields like .url, .mime, .get are not top-level config fields; they belong inside entries of .resources. A blogs/blogs.c:

#include <mach.h>
#include <sqlite.h>

config blogs(){
  return (config){
    .name = "blogs",
    .resources = {
      {"blog", "/blogs/:id",
        .get = { /* validate → query → join → render; see `join` worked example */ }
      }
    },
    .databases = {{
      .engine     = sqlite_db,
      .name       = "blog_db",
      .connect    = "file:blogs.db?mode=rwc",
      .migrations = {
        "CREATE TABLE blogs ("
          "id INTEGER PRIMARY KEY AUTOINCREMENT,"
          "title TEXT NOT NULL,"
          "content TEXT NOT NULL"
        ");",
        "CREATE TABLE comments ("
          "id INTEGER PRIMARY KEY AUTOINCREMENT,"
          "blog_id INTEGER NOT NULL REFERENCES blogs(id),"
          "body TEXT NOT NULL"
        ");"
      }
    }}
  };
}

Bring the module into scope by #includeing its .c file from main.c, then register it with .modules = {blogs, sqlite}. The module's resources and databases are merged into the app tree at registration.

// main.c
#include <mach.h>
#include "blogs/blogs.c"

config mach(){ return (config){ .modules = {blogs, sqlite} }; }

A typical project layout:

├── todos/                         # todos module
│   ├── todos.c                    # config todos() { ... }
│   ├── todos.mustache.html
│   ├── create_todos_table.sql
│   └── get_todos.sql
├── activity/                      # activity module
│   └── activity.c
├── static/                        # root-level templates (not a module)
│   ├── layout.mustache.html
│   └── home.mustache.html
├── public/                        # static files, served directly
│   └── favicon.png
└── main.c                         # registers modules

Bundled modules (add the initializer to .modules to use): sqlite, postgres, mysql, redis, duckdb, htmx, datastar, tailwind, session_auth

Module-provided steps. Modules can ship step functions that plug into pipelines alongside the built-in steps. The session_auth module provides:

• session() — attaches the current session to context (sets user_id, etc.); no-op when unauthenticated.
• logged_in() — guard that raises http_not_authorized when there's no active session.
• login(), logout(), signup() — use inside POST pipelines to perform the auth action.

Commonly dropped into a resource's shared .steps slot as middleware, so every verb on the resource runs through them first:

{"dashboard", "/dashboard", {session(), logged_in()},
  .get = { render("dashboard") }
}

Static Files

Files in public/ at the project root are served directly. Use it for images, fonts, pre-built CSS/JS, and other assets that don't need to be embedded in the binary. Reference them with {{asset:filename}}, which resolves to a URL with a content checksum and immutable cache headers.

public/ directory: drop in static files; they are served at the root URL space.

public/
├── favicon.png
├── logo.png
└── styles.css

{{asset:filename}}: cache-busting helper for use inside templates.

<link rel="icon" href="{{asset:favicon.png}}">
<link rel="stylesheet" href="{{asset:styles.css}}">
<script src="{{asset:app.js}}"></script>

External Dependencies

MACH expects a containerized development environment: write standard C23 against the MACH APIs, no local toolchain required. Two ways to bring in third-party C libraries, plus two helpers for bridging foreign memory back to the arena.

/vendor directory: drop headers and libraries (.so, .a) here; the auto-compiler discovers, includes, and links them.

/vendor/
├── libsodium.h
└── libsodium.so

Custom Dockerfile: inherit from the MACH base image and apt-get install system dependencies; reference it from compose.yml.

FROM mach:latest
RUN apt-get update && apt-get install -y libsodium-dev

allocate(bytes): provides a buffer from the pipeline arena, reclaimed on request completion.

char *buf = allocate(256);

defer_free(ptr): schedules cleanup for pointers returned by external libraries (e.g. via malloc); runs when the arena is released.

char *out = third_party_alloc(256);
defer_free(out);

---

Architecture

How MACH compiles, executes, and protects an application at runtime.

• Data-Oriented Pipelines
• Multi-Reactor Architecture
• Safe by Default
• String Interpolation

Data-Oriented Pipelines

The mach() function runs once at boot. The returned config is processed into an execution graph with precompiled pipelines, queries, and templates. Each incoming request then executes its matching pipeline as a sequence of pre-warmed steps.

Multi-Reactor Architecture

MACH runs two types of reactors backed by a shared thread pool. The request/task/cpu ratio can be set in compose.yml.

• Request reactors handle HTTP traffic; each gets its own dedicated CPU core and event loop.
• Task reactors handle background work; each gets its own dedicated core, monitors the task database for pending and incomplete tasks, and processes cron schedules.
• Shared thread pool handles CPU-bound and blocking I/O work on the remaining cores.

When any reactor's pipeline executes an exec() step, the work is dispatched to the shared thread pool, which releases the reactor. When the call completes, the pipeline resumes on the original reactor. The task() step adds jobs to the task database, where they are picked up by task reactors. Tasks can call task() themselves to enqueue additional work.

Application code does not manage threads, mutexes, or locks. The architecture isolates request state to the pipeline's context.

Safe by Default

MACH prevents common C and web vulnerabilities at the framework level.

Memory Safety

Each reactor maintains a pool of arena allocators. When a request arrives, the pipeline is assigned an arena, and all allocations draw from it. When the pipeline completes, the arena is cleared and returned to the pool. Application code does not call malloc or free, which avoids leaks, double-frees, and use-after-free.

All framework data structures (tables, records, strings) enforce bounds checking. Out-of-bounds reads and missing context values return nullptr rather than faulting. Pipelines that exceed their memory limit (default 5MB, configurable in compose.yml) abort with a 500, mitigating OOM denial-of-service.

SQL Injection Prevention

Interpolations such as {{user_id}} inside query() or find() are bound as parameters in prepared statements, preventing SQL injection at the framework level.

XSS Prevention

The render() step auto-escapes context values in Mustache templates, so malicious input is rendered as text. Raw HTML requires explicit opt-in via the {{raw:field}} helper.

String Interpolation

Any string (SQL queries, URLs, connection strings, templates) can reference values from the context with {{context_key}}. The same scopes described in Context apply everywhere interpolation is used.

---

Tooling

Development Environment

Built-in TUI editor with HMR, LSP support, integrated source control, and a topology-aware AI assistant. The AI uses the app_info command to inspect the full application topology — routes, pipelines, database schemas, event contracts, and module boundaries — so it reasons about the application's actual execution graph rather than just source text.

Introspection

app_info                    # view topology
app_info resources          # list all resources
app_info pipelines          # inspect pipelines
app_info events             # view pub/sub map
app_info databases          # inspect schemas

Testing

Built-in test runners for unit and end-to-end testing; no external framework setup required.

unit_tests                  # fast, criterion-based tests
e2e_tests                   # playwright-powered browser tests

Debugging

Built-in debugging with pipeline-aware commands. Halt on individual pipeline steps, step through execution, and inspect the full pipeline context including nested tables and records.

app_debug                   # interactive debugger in the TUI

Deployment

MACH deploys as a standard Docker container. It does not terminate TLS; production deployments place MACH behind a reverse proxy or load balancer (Nginx, Caddy, AWS ALB) to handle HTTPS.

app_build                   # outputs slim, optimized production Docker image

Observability

Each pipeline step emits OpenTelemetry spans. Logs, traces, errors, and auto-profiling are visualized on the telemetry server at port 4000. No manual instrumentation required.

Project Management

MACH ships with integrated project infrastructure: issue tracking, wiki, forum, and a project website.

Built With

C23	Language standard
Docker	Development environment, production images, stack orchestration
libmicrohttpd / libuv	HTTP server, event loops, async I/O, file watching, shared thread pool
Mustach	Templating and string interpolation
Jansson	JSON parsing and generation
curl	HTTP client for fetch steps
Fossil	Source control, wiki, forum, issue tracker, project site
Fresh	TUI editor
clangd	Language server
LLDB	Debugger
Criterion	Unit testing
Playwright	End-to-end testing
SigNoz + OpenTelemetry	APM, traces, logs, errors, dashboards
Open Code	AI assistant with custom agent and skill files

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License

MACH is licensed under the LGPL.