## Guide A walkthrough that builds a working todo app in nine steps, introducing one MACH concept at a time. * [1. A Page](#1-a-page) * [2. Show Data](#2-show-data) * [3. Accept Input](#3-accept-input) * [4. Handle Errors](#4-handle-errors) * [5. Nested Data](#5-nested-data) * [6. Tasks](#6-tasks) * [7. Modules & Events](#7-modules--events) * [8. External Assets](#8-external-assets) * [9. External Data](#9-external-data) ### 1. A Page Two resources, each with a GET pipeline. The home page links to the todos page with `{{url:todos}}`, which resolves to the target resource's URL at render time. Change the URL pattern later and every link updates. ```c #include config mach(){ return (config) { .resources = { {"home", "/", .get = { render(.template = "" "

Welcome

" "My Todos" "" ) } }, {"todos", "/todos", .get = { render(.template = "" "

My Todos

" "

Nothing yet.

" "" ) } } } }; } ``` Each resource names itself (`"home"`, `"todos"`) so other pages can reference it by name instead of hard-coded paths. ### 2. Show Data Add a SQLite database with one migration and one seed, then read from it in the GET pipeline. ```diff #include + #include config mach(){ return (config) { .resources = { {"home", "/", .get = { render(.template = "" "

Welcome

" "My Todos" "" ) } }, {"todos", "/todos", .get = { + query({.set_key = "todos", .db = "todos_db", + .query = "select id, title from todos;"}), render(.template = "" "

My Todos

" - "

Nothing yet.

" + "

{{title}}

" "" ) } } - } + }, + + .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: > ```c > 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;"} > ) > ``` > **Sections, not dot paths.** To access fields on a record or table, open a section. Write `{{#todos}}{{title}}{{finished}}{{/todos}}`, not `{{todos.title}}`. The same syntax works for single-row records: `{{#count}}{{n}}{{/count}}`. Dot paths render empty. ### 3. Accept Input Add a POST verb that validates a `title` parameter, inserts it, and redirects back to GET (POST-redirect-GET). ```diff #include #include config mach(){ return (config) { .resources = { {"home", "/", .get = { render(.template = "" "

Welcome

" "My Todos" "" ) } }, {"todos", "/todos", .get = { query({.set_key = "todos", .db = "todos_db", .query = "select id, title from todos;"}), render(.template = "" "

My Todos

" "

{{title}}

" + "" "" ) - } + }, + + .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 the error markup to the form template so the message displays when it's there. ```diff #include #include config mach(){ return (config) { .resources = { {"home", "/", .get = { render(.template = "" "

Welcome

" "My Todos" "" ) } }, {"todos", "/todos", .get = { query({.set_key = "todos", .db = "todos_db", .query = "select id, title from todos;"}), render(.template = "" "

My Todos

" "

{{title}}

" "" "" ) }, .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. If the template later needs to be shared across resources, extracting it into `.context` and referencing it by name from `render()` is straightforward; until then, keeping it inline with the pipeline that uses it is clearer. See [redirect & reroute](#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`. ```diff #include #include config mach(){ return (config) { .resources = { {"home", "/", .get = { render(.template = "" "

Welcome

" "My Todos" "" ) } }, {"todos", "/todos", .get = { query({.set_key = "todos", .db = "todos_db", .query = "select id, title from todos;"}), render(.template = "" "

My Todos

" - "

{{title}}

" + "

{{title}}

" + "

Comments

" + "

{{body}}

" + "{{/todo}}" + "" + ) + } + } }, .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; dot paths like `{{todo.title}}` do not resolve. The same pattern maps onto any parent-children relation: blog + comments, project + tasks, order + line items. See [join](#join) for the full blog + comments version. ### 6. Tasks Tasks are named pipelines that run asynchronously on task reactors. They're 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 that same task from the POST pipeline so the stats stay fresh after every write. ```diff #include #include config mach(){ return (config) { .resources = { {"home", "/", .get = { render(.template = "" "

Welcome

" "My Todos" "" ) } }, {"todos", "/todos", .get = { query({.set_key = "todos", .db = "todos_db", .query = "select id, title from todos;"}), render(.template = "" "

My Todos

" "

{{title}}

" "" "" ) }, .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 = "" "{{#todo}}" "

" "

Comments

" "

{{body}}

" "{{/todo}}" "" ) } } }, + .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 in two ways: `.cron = "0 0 * * *"` runs it at midnight each day, and `task("record_daily_stats")` from the POST pipeline enqueues an on-demand run after every insert. Both invocations land on a task reactor, which runs on separate cores from the request reactors that serve HTTP, so the POST returns immediately rather than waiting for the count query to finish. If the task needs values from the calling context (a `user_id`, a `todo_id`), list them under `.accepts` on the task definition and reference them inside the task with `{{user_id}}` interpolation. Tasks are also durable: if the process crashes mid-task, MACH checkpoints the context after each step and resumes at the step where it left off on the next boot. See [Task Pipelines](#task-pipelines). ### 7. Modules & Events So far everything has lived in one `main.c`. As the app grows, features split into modules, and modules communicate through pub/sub events instead of calling each other directly. A module is a fully self-contained system: it can declare its own resources, databases, migrations, context, error and repair handlers, tasks, and event subscribers. `main.c` just composes them and handles cross-cutting concerns. This step extracts the todos logic into its own module and adds a new `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. ```c #include #include #include "todos/todos.c" #include "activity/activity.c" config mach(){ return (config){ .resources = { {"home", "/", .get = { render(.template = "" "

Welcome

" "My Todos · " "Activity" "" ) } } }, .modules = {todos, activity, sqlite} }; } ``` **`todos/todos.c`** — the todos module, now a publisher. ```c #include #include 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 = "" "

My Todos

" "

{{title}}

" "" "" ) }, .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 = "" "{{#todo}}" "

" "

Comments

" "

{{body}}

" "{{/todo}}" "" ) } } }, .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 module. It has its own database, its own resource to view the log, and its own event subscriber. Nothing in it references the todos module. ```c #include #include 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 = "" "

Activity

" "

{{created_at}}: {{kind}} — {{ref}}

" "" ) } } }, .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 is a self-contained slice of the app. `todos` owns the todos domain: its resources, its database, its publisher contract, its scheduled task. `activity` owns the activity domain: its resource, its database, its event 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 in its own pipeline with `title` available, writing the row to `activity_db`. Because `.publishes` is defined, MACH automatically 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 module is a new file with an `.events` entry — the `todos` module doesn't change. ### 8. External Assets So far templates and SQL have been inline C strings. Once they grow past a few lines, apps extract them into their own files and load them with `(asset){#embed "..."}` in `.context`, then reference them by name from `render()`, `query()`, and `find()`. Each artifact then lives in a file named for what it is, edited with its native tooling (Mustache-aware HTML editors, SQL formatters), and syntax-highlighted on its own terms. Apply this everywhere: 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 (there's no `.c` file in it) — it's a plain directory for root-level templates that `main.c` references. #### Root **`static/home.mustache.html`** ```html

Welcome

My Todos · Activity ``` **`main.c`** — references the home template by name. ```c #include #include #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

My Todos

{{title}}

``` **`todos/get_todos.sql`** — and similarly for each other SQL file. ```sql select id, title from todos; ``` **`todos/create_todo.sql`** ```sql insert into todos(title) values({{title}}); ``` SQL interpolation (`{{title}}`) still works the same as inline — bound as prepared-statement parameters, never spliced. The 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. ```c #include #include 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

Activity

{{created_at}}: {{kind}} — {{ref}}

``` **`activity/insert_activity.sql`** — the event handler's insert, now a named asset. ```sql insert into activities(kind, ref) values('created', {{title}}); ``` **`activity/activity.c`** — same extraction pattern. ```c #include #include 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 across all three files — 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 the entries now read `(asset){#embed "..."}` instead of quoted SQL. Templates are still Mustache (sections, not dot paths); SQL still supports `{{interpolation}}` bound as prepared-statement parameters. ### 9. External Data Pipelines can reach out to external HTTP services the same way they read from databases. `fetch()` makes the request and stores the response in context; JSON is automatically parsed into tables and records, and nested JSON becomes nested context tables. Add a quote of the day to the home page, pulled from a public API. **`static/home.mustache.html`** ```diff

Welcome

+ {{#quote}} +

{{content}} — {{author}}

+ {{/quote}} My Todos · Activity ``` **`main.c`** ```diff #include #include #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 a JSON object like `{"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](#fetch) for the full set of options. 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 self-contained modules, external assets let templates and SQL live alongside the code that uses them, and `fetch()` brings in external HTTP data. See [Modules & Composition](#modules--composition) for more on module boundaries. --- ## Reference The APIs and patterns used to build applications with MACH. Each subsection describes one piece of the framework, then lists every option it accepts with a minimal snippet. * [Notation](#notation) * [Context](#context) * [Databases](#databases) * [Resource Pipelines](#resource-pipelines) * [Template Helpers](#template-helpers) * [Pipeline Steps](#pipeline-steps) * [Conditionals](#conditionals) * [Error and Repair Pipelines](#error-and-repair-pipelines) * [Event Pipelines](#event-pipelines) * [Task Pipelines](#task-pipelines) * [Modules & Composition](#modules--composition) * [Static Files](#static-files) * [External Dependencies](#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({...}, {...})`. > **Fields are only reachable from inside their section.** Templates use Mustache sections, not dot paths. Open the section first, even for single-row queries. A bare `{{title}}` at root looks for a top-level key named `title`; it does not reach into `blog`. Avoiding dots alone is not sufficient. > - ✅ `{{#blog}}{{title}}{{/blog}}` works for single-row or multi-row queries > - ❌ `{{title}}` at root: no top-level `title` exists > - ❌ `{{blog.title}}`: dot paths are not supported ### Context Pipelines read from and write to a shared context: a scoped key-value store that lives for the duration of a request. Every step draws its inputs from context and writes its 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 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. ```c .context = {{"site_name", "MACH App"}} ``` **`(asset){#embed ...}`**: bake a file into the binary as a named asset (templates, SQL, fixtures). Embedded template files must use Mustache sections for nested fields; dot paths like `{{blog.title}}` are not supported. See [Notation](#notation). ```c .context = { {"layout", (asset){#embed "layout.mustache.html"}}, {"get_todos", (asset){#embed "get_todos.sql"}} } ``` Combined: ```c .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"}} } ``` ![Context Scoping](./07-context-scoping.svg) ### 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. ```c .engine = sqlite_db ``` **`.name`**: identifier referenced by `.db` in `query()` and `find()`. ```c .name = "todos_db" ``` **`.connect`**: engine-specific connection string. Supports `{{interpolation}}` for multi-tenancy. ```c .connect = "file:{{user_id}}_todo.db?mode=rwc" ``` **`.migrations`**: array of SQL migration strings or assets, applied once each in order. ```c .migrations = {(asset){#embed "create_todos_table.sql"}} ``` **`.seeds`**: array of idempotent seed statements, safe to re-run on every boot. ```c .seeds = {"INSERT OR IGNORE INTO todos(id, title) VALUES(1, 'Hello');"} ``` Combined: ```c .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 one 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 like `blogs` and `comments` 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` ![Database Multi-Tenancy](./09-database-multi-tenancy.svg) ### Resource Pipelines MACH is resource-based rather than 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()` all take a `name[:arg1:arg2...]` identifier with colon-separated positional args. Args fill the `:params` of the resource's 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.** Arguments after the name are positional, colon-separated, and can be 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()`. ```c {"todos", "/todos", .get = { ... }} ``` **`.url` *(pos)***: URL pattern. Supports `:params`. ```c {"todo", "/todos/:id", .get = { ... }} ``` **`.steps` *(pos)***: shared steps that run before every verb pipeline on the resource. ```c {"todo", "/todos/:id", { validate({"id", .validation = "^\\d+$", .message = "must be a number"}) }, .get = { ... }, .delete = { ... }} ``` **`.mime`**: default response content type for the resource. ```c {"feed", "/feed.json", .mime = mime_json, .get = { ... }} ``` **`.get` `.post` `.put` `.patch` `.delete`**: verb pipelines — ordered arrays of steps that transform a request into a response. ```c {"todos", "/todos", .get = { query({"get_todos", .set_key = "todos", .db = "db"}), render("todos") }, .post = { validate({"title", .validation = validate_not_empty}), redirect("todos") } } ``` **`.sse`**: persistent SSE channel. First positional is the channel name; steps run on connect. ```c {"todos", "/todos", .sse = {"todos/{{user_id}}", query({"get_todos", .set_key = "todos", .db = "db"}), sse(.event = "initial", .data = {"{{todos}}"}) } } ``` **`.errors` / `.repairs`**: resource-scoped error and repair pipelines. See [Error and Repair Pipelines](#error-and-repair-pipelines). ```c {"todos", "/todos", .post = { ... }, .errors = {{http_bad_request, { render("form") }}} } ``` Combined: ```c {"todo", "/todos/:id", { validate({"id", .validation = "^\\d+$", .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 the `{{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. ```c render(.template = "

") ``` **`{{precision:field:N}}`**: format a numeric value with N decimal places. ```c render(.template = "

Total: ${{precision:total:2}}

") ``` **`{{input:field}}`**: raw, unvalidated request parameter from the `input` scope. Typically used to repopulate form fields after a validation error. ```c render(.template = "") ``` **`{{error:field}}`**: truthy when `field` has an error. Used as a Mustache section to conditionally render markup. ```c render(.template = "{{#error:title}}invalid{{/error:title}}") ``` **`{{error_message:field}}`**: the human-readable message for a field error, from `validate()`'s `.message` or from `error_set()`. ```c render(.template = "{{error_message:title}}") ``` **`{{error_code:field}}`**: the HTTP status code associated with a field error (e.g. `400`, `404`). ```c render(.template = "

Code: {{error_code:title}}

") ``` **`{{url:name}}`**: resolve a resource identifier to its URL. Takes positional args to fill `:params` in the target's URL pattern. Args can be literals or context keys. See [Resource Pipelines](#resource-pipelines) for details. ```c render(.template = "All" // /todos "Item 5" // /todos/5 "From context" // /todos/{{id}} ) ``` **`{{asset:filename}}`**: resolve a file in `public/` to a cache-busted URL (content checksum + immutable cache headers). See [Static Files](#static-files). ```c render(.template = "") ``` **`{{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. ```c render(.template = "Log out") ``` **`{{csrf:input}}`**: emit a hidden `` carrying a CSRF token, for use inside a `") ``` Combined: ```c render(.template = "" "

" "{{#post}}" "

" "

Rating: {{precision:score:1}}/5

" "

" "{{/post}}" "" "Log out" "

" ) ``` > **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 step receives the current request context, acts on it, and passes control to the next step. Every step also accepts `.if_context` and `.unless_context` for conditional execution. * [validate](#validate) * [find & query](#find--query) * [join](#join) * [fetch](#fetch) * [exec](#exec) * [emit](#emit) * [task](#task) * [sse](#sse) * [ds_sse](#ds_sse) * [render](#render) * [headers & cookies](#headers--cookies) * [redirect & reroute](#redirect--reroute) * [nest](#nest) ![Request Pipeline Flow](./02-request-pipeline-flow.svg) #### 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](#error-and-repair-pipelines). 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}$"`. **`.param_key` *(pos)***: name of the parameter to validate. ```c validate({"title", .validation = "^\\S+$", .message = "required"}) ``` **`.validation`**: regex pattern, or one of the built-in validator macros. ```c validate({"email", .validation = validate_email, .message = "bad email"}) ``` **`.message`**: human-readable error shown via `{{error_message:name}}`. ```c validate({"age", .validation = "^\\d+$", .message = "must be a number"}) ``` **`.optional`**: flag to skip validation when the parameter is absent. ```c validate({"filter", .optional = true, .validation = "^(active|done)$"}) ``` **`.fallback`**: default value injected when the parameter is absent. ```c validate({"page", .fallback = "1", .validation = "^\\d+$"}) ``` Combined: ```c validate( {"email", .validation = validate_email, .message = "must be a valid email"}, {"title", .validation = validate_not_empty, .message = "cannot be empty"}, {"page", .fallback = "1", .validation = "^\\d+$", .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, in which case it is 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 a `404 Not Found` when zero rows are returned; `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. For concurrency, pass all items to one `query()` call. **`.template_key` *(pos)***: name of a SQL asset stored in `.context`. Mutually exclusive with `.query`. ```c 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. ```c 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. ```c query({.set_key = "active", .db = "db", .query = "select * from todos;"}) ``` **`.db`**: name of the database, matching a `.databases` entry. ```c query({.db = "todos_db", .query = "select 1;"}) ``` **`.if_context` / `.unless_context`** *(per item)*: conditionally include or skip individual queries while running the others concurrently. ```c query( {"get_todos", .set_key = "todos", .db = "db"}, {"get_urgent", .if_context = "show_urgent", .set_key = "u", .db = "db"} ) ``` Combined: ```c 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, similar to a SQL JOIN performed in memory across context tables. 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 (`{{#blog}}...{{/blog}}` alongside `{{#comments}}...{{/comments}}`) treats the `join()` as a no-op. Restructure the render around the outer section when you add a `join()`. **`.target_table_key`**: outer table whose records receive nested children. ```c .target_table_key = "projects" ``` **`.target_field_key`**: field on the outer table to match against. ```c .target_field_key = "id" ``` **`.nested_table_key`**: inner table whose records get nested. ```c .nested_table_key = "todos" ``` **`.nested_field_key`**: field on the inner table that points at the outer. ```c .nested_field_key = "project_id" ``` **`.target_join_field_key`**: new field on outer records holding the matched inner records. ```c .target_join_field_key = "todos" ``` Combined: ```c 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 a parent and its children from separate queries, then render them as one nested structure. Blog + comments, single database: ```c {"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 = "

" "{{#blog}}" "

" "

Comments

" "

{{body}}

" "{{/blog}}" "

" ) } } ``` 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}, ...]}] } // comments nested inside blog ``` `join()` lifts the `comments` table into each `blog` record. Templates reach comments by entering the blog section first. Two common failure modes both produce an empty-looking page even when the `join()` succeeded: (1) assuming the blog's fields are flat at root because `blog` has one row, and (2) iterating `{{#comments}}` at root instead of from within `{{#blog}}`. ```c // ❌ Wrong — fields assumed flat at root, comments iterated at root: render(.template = "

" "

" // empty: title lives inside blog "

" // empty: same reason "

{{body}}

" // empty or unnested: join put comments INSIDE blog "

" ) // ✅ Right — enter {{#blog}} first; reach comments from within: render(.template = "

" "{{#blog}}" "

" "

{{body}}

" "{{/blog}}" "

" ) ``` Dot paths (`{{blog.title}}`, `{{blog.comments.0.body}}`) do not resolve; sections only, see [render](#render). #### 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}}`. ```c fetch("https://api.weather.dev/forecast?city={{city}}", .set_key = "w") ``` **`.set_key`**: context key for the response. ```c fetch("https://api.weather.dev/now", .set_key = "weather") ``` **`.method`**: HTTP method. Defaults to `http_get`. ```c fetch("https://api.dev/charge", .set_key = "r", .method = http_post) ``` **`.headers`**: array of name/value pairs. ```c fetch("https://api.dev/me", .set_key = "r", .headers = {{"Authorization", "Bearer {{token}}"}}) ``` **`.json`**: context key serialized as the JSON request body. ```c fetch("https://api.dev/charge", .set_key = "receipt", .method = http_post, .json = "order") ``` **`.text`**: context key sent as the plain-text request body. ```c fetch("https://api.dev/log", .set_key = "r", .method = http_post, .text = "raw_body") ``` Combined: ```c 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. ```c 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. ```c 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-pipelines). **Event name *(pos)***: name of the event to publish. ```c emit("todo_created") ``` #### task Adds a named job to the task database and continues immediately. Fire-and-forget: the calling pipeline does not wait. Task reactors pick up queued jobs and execute their pipelines. See [Task Pipelines](#task-pipelines). **Task name *(pos)***: name of a task defined in `.tasks`. ```c task("recount_todos") ``` #### sse Pushes a Server-Sent Event. With `.channel`, the event is broadcast to all clients connected on that channel. Without `.channel`, the event is returned directly to the requesting client. See [Resource Pipelines](#resource-pipelines). **`.channel` *(pos)***: channel to broadcast on; supports `{{interpolation}}`. ```c sse(.channel = "todos/{{user_id}}", .event = "new_todo", .data = {"{{todo}}"}) ``` **`.event`**: SSE `event:` line value. ```c sse(.event = "ping") ``` **`.data`**: array of strings, one per SSE `data:` line (multi-line data). ```c sse(.event = "msg", .data = {"line one", "line two"}) ``` **`.comment`**: SSE `:` comment line value, useful for keep-alives. ```c sse(.comment = "keep-alive") ``` Combined: ```c sse( .channel = "todos/{{user_id}}", .event = "todo_updated", .data = {"id: {{todo_id}}", "title: {{title}}"}, .comment = "broadcast at {{timestamp}}" ) ``` #### ds_sse [Datastar](https://data-star.dev) is a hypermedia framework where the server pushes DOM updates and reactive state to the client 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}}`. ```c ds_sse("todos/{{user_id}}", .target = "todos", .elements = {"todo"}) ``` **`.target`**: DOM element id for the update. ```c ds_sse(.target = "todos", .elements = {"todo_row"}) ``` **`.mode`**: fragment insertion mode for the rendered DOM fragment. ```c 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.). ```c ds_sse(.target = "row", .elements = {"todo_row"}) ``` **`.signals`**: JSON string used to update Datastar's reactive client state without touching the DOM. ```c ds_sse(.signals = "{\"count\": {{count}}}") ``` **`.js`**: JavaScript snippet evaluated on the client. ```c ds_sse(.js = "console.log('updated')") ``` Combined: ```c 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` ![SSE / Datastar Flow](./08-sse-datastar-flow.svg) #### render Outputs a Mustache template using the current context. Templates are referenced by name from `.context` or inlined. Templates must use Mustache sections for nested fields; dot paths like `{{blog.title}}` are not supported. See [Notation](#notation). > **Fields are only reachable from inside their section.** Anything stored under a `.set_key` (query/find results, fetch JSON responses, joined data) is a TABLE, even when it has only one row. To read its fields, open the section first. Bare `{{key}}` works only for top-level scalars: `.context` values, validated inputs (after `validate()` promotes them from `input:` to app scope), and framework values like `user_id`. A bare `{{title}}` at root looks for a top-level key named `title`; it does not reach into `blog`. Avoiding dots alone is not sufficient. > - ✅ `{{#blog}}{{title}}{{/blog}}`: fields inside the section, for single-row or multi-row queries > - ✅ `{{#blog}}{{title}}{{#comments}}

{{/comments}}{{/blog}}`: nested sections for joined data > - ✅ `{{#count}}{{n}}{{/count}}`: single-row scalar query (e.g. `select count(*) as n`) > - ✅ `{{site_name}}`: top-level scalar from `.context` > - ✅ `{{title}}` after `validate({"title", ...})`: promoted to app scope > - ❌ `{{title}}` after a query that set `.set_key = "blog"`: title is inside the `blog` table > - ❌ `{{blog.title}}`: dot paths are not supported > - ❌ `{{#comments}}` at root after `join()`: comments is nested inside blog, reach it via `{{#blog}}...{{#comments}}...{{/comments}}...{{/blog}}` > **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 tags 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, used throughout this doc): > ```c > "

" > "{{#blog}}" > "

" > "

{{body}}

" > "{{/blog}}" > "

" > ``` > - ✅ All inline in one string: `"

"` > - ✅ Adjacent strings, section tags sharing lines with content: `"

" "{{#blog}}

{{/blog}}" "

"` > - ❌ Section tags on their own lines **without quotes** — compile error, not a template: > ```c > "

" > {{#blog}} // NOT in quotes > "

" > {{/blog}} // NOT in quotes > "

" > ``` **`.template_key` *(pos)***: asset name in `.context`. The asset is a Mustache template; sections only, no dot paths. ```c render("todos") ``` **`.template`**: inline Mustache template string. Sections only, no dot paths. ```c render(.template = "

") // {{site_name}} is from .context (top-level scalar) ``` **`.status`**: HTTP response status (defaults to `http_ok`). ```c render("not_found", .status = http_not_found) ``` **`.mime`**: override the response content type. ```c render("plain", .mime = mime_txt) ``` **`.engine`**: template engine. Accepts `mustache` / `"mustache"` (the default) or `mdm` / `"mdm"` for Markdown-with-Mustache. The bare identifiers are macros that expand to the string values; either form works. ```c render(.engine = mdm, .template = "# Welcome, {{user_name}}") // {{user_name}} is from validate() or .context ``` **`.json_table_key`**: context table to serialize as the JSON response. Sets `application/json`; nested tables produce nested JSON. ```c 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. ```c 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` in its URL pattern. ```c 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. ```c nest({query({...}), emit("urgent_todo"), render("urgent")}) ``` **`.if_context` / `.unless_context`**: condition applied to the whole group. ```c 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. ```c render("fragment", .if_context = "is_htmx") ``` **`.unless_context`**: context key. Step runs only when the value is absent. ```c render("full_page", .unless_context = "is_htmx") ``` For multi-state branching, set context flags from `exec()`, then key downstream steps off them: ```c 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 matching pipeline sends a response and ends the request. Repairs are resumable: they fix the context and then 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. ```c .errors = { {http_not_found, { render("404") }}, {http_bad_request, { render("form") }} } ``` **`.repairs`**: resumable handlers keyed by error code. ```c .repairs = { {http_not_authorized, { exec(.call = refresh_session_token) }} } ``` Combined: ```c .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 (for the `.error_code` positional):** `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`. ![Error Resolution](./04-error-resolution.svg) ### Event Pipelines Internal pub/sub for cross-module communication. The publisher doesn't know who listens; the subscriber doesn't 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. ```c .publishes = { {"todo_created", .with = {"user_id", "title"}} } ``` **`.events`**: subscriber pipelines keyed by event name. ```c .events = { {"todo_created", { query({"insert_activity", .db = "activity_db"}) }} } ``` Combined: ```c // 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}});"}) }} } }; } ``` ![Event Pub/Sub](./03-event-pub-sub.svg) ### 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 by default. When `.tasks` is defined, MACH creates a `mach_tasks` database and checkpoints the context after each step. If the process crashes mid-task, execution resumes at the step where it left off. A task five steps into an eight-step pipeline restarts at step six, not step one. **`.name` *(pos)***: task identifier, called via `task("name")`. ```c .tasks = { {"recount_todos", { query({.db = "db", .query = "update users set ..."}) }} } ``` **`.accepts`**: context keys to pull from the caller into the task. ```c {"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). ```c {"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. ```c {"name", { query({...}), emit("done"), task("followup") }, .accepts = {...}} ``` Combined: ```c .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. ```c config todos(){ return (config){ .name = "todos", /* resources, databases, ... */ }; } ``` **`.modules`**: other modules to compose into this one (root or nested). ```c .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`: ```c #include #include 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 `#include`ing 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. ```c // main.c #include #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. These are commonly dropped into a resource's shared `.steps` slot as middleware, so every verb on the resource runs through them first: ```c {"dashboard", "/dashboard", {session(), logged_in()}, .get = { render("dashboard") } } ``` ![App Composition Tree](./05-app-composition-tree.svg) ![Middleware Scoping](./06-middleware-scoping.svg) ### Static Files Files placed 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-based checksum and immutable cache headers, so browsers cache indefinitely and refresh when content changes. **`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. ```html ``` ### External Dependencies MACH expects a containerized development environment: you write standard C23 against the MACH APIs, and no local toolchain is 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`. ```dockerfile 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. ```c 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. ```c char *out = third_party_alloc(256); defer_free(out); ```