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# dlang.http
An HTTP/1.1 server plugin for the **dlang** VM. It gives a dlang script a `http` global with
routing, static file serving, custom error pages, a small template engine (`view`) and
file uploads (`multipart/form-data`).
> [!IMPORTANT]
> **This project was generated with AI** (GitHub Copilot) and has not been reviewed by a
> human. Treat the code and this documentation as a starting point: read it, test it, and
> only use it in production once you understand and trust it. See
> [AI-generated code](#ai-generated-code) at the bottom.
> The dlang language and its VM live in their own repository. This repository only contains
> the HTTP plugin; the `dlang/` folder is an unmodified copy of the upstream VM headers and
> sources, kept here so the plugin can be built as a standalone shared library.
---
## Table of contents
- [Features](#features)
- [Requirements](#requirements)
- [Building](#building)
- [Installing the plugin](#installing-the-plugin)
- [Quick start](#quick-start)
- [API reference](#api-reference)
- [`http.server()`](#httpserver)
- [`server.listen(port)`](#serverlistenport)
- [`server.route(path, methods, handler)`](#serverroutepath-methods-handler)
- [Route handler arguments](#route-handler-arguments)
- [`server.static(...)`](#serverstatic)
- [`server.error(code, handler)`](#servererrorcode-handler)
- [`server.maxBody(bytes)`](#servermaxbodybytes)
- [File uploads](#file-uploads)
- [`http.save` / `http.saveTo`](#httpsave--httpsaveto)
- [`view.Render(path, vars)`](#viewrenderpath-vars)
- [Status codes](#status-codes)
- [Request and response flow](#request-and-response-flow)
- [Limitations](#limitations)
- [Project layout](#project-layout)
- [AI-generated code](#ai-generated-code)
---
## Features
| Feature | Summary |
| --- | --- |
| Routing | Exact-path routes with a per-route list of HTTP methods |
| Static files | URL prefix → folder, exact URL → file, MIME type detected by extension |
| Request parsing | Query string, url-encoded bodies, JSON bodies and `multipart/form-data` |
| File uploads | Uploaded files as tables (`filename`, `contentType`, `size`, raw `content`) plus `http.save` / `http.saveTo` helpers to write them to disk |
| Cookies | Parsed `Cookie:` header as a table |
| Error pages | Custom handlers or bodies per status code, with a built-in HTML fallback |
| Templates | `view.Render("page.html", { ... })` with recursive `@include` and `{{ key }}` interpolation |
| Body limit | Configurable request size limit (`server.maxBody`), oversized uploads get `413` |
---
## Requirements
- **Windows** or **Linux** (the plugin refuses to compile on other platforms).
- A **C++20** compiler: MSVC (Windows) or Clang/GCC (Linux).
- **CMake ≥ 3.10** and **Ninja** for the presets in `CMakePresets.json`.
- A **dlang host** (interpreter/runner) that supports plugins, since this repository builds
a plugin, not a program.
---
## Building
The presets use Ninja with `cl.exe`, so run the commands from a *Developer Command Prompt*
(or build the folder from VS Code with the CMake Tools extension, which sets up the
compiler environment automatically).
```bash
# configure
cmake --preset x64-debug # or x64-release, x86-debug, x86-release
# linux-debug on Linux, macos-debug on macOS
# build
cmake --build out/build/x64-debug
```
Available presets: `x64-debug`, `x64-release`, `x86-debug`, `x86-release` (Windows),
`linux-debug` (Linux) and `macos-debug` (macOS).
The build output is a shared library:
| Platform | Output |
| --- | --- |
| Windows | `out/build/<preset>/dlang.http/dlang.http.dll` |
| Linux | `out/build/<preset>/dlang.http/dlang.http.so` |
> The shared library compiles `entry.cpp` together with the VM sources in
> `dlang.http/dlang/src/`, so no external dlang SDK is needed. Windows additionally links
> `ws2_32`; Linux links `dl` and `pthread`.
---
## Installing the plugin
Plugins are looked up in a `plugins/` folder relative to the working directory of the dlang
host. The loader appends the platform extension itself (`.dll` on Windows, `.so` on Linux),
so the file must be named `dlang.http.dll` / `dlang.http.so`:
```text
my-app/
├─ plugins/
│ └─ dlang.http.dll # copied from the build output
└─ app.dl
```
Load it from a script with `require` (the returned string is a status message such as
`"plugin loaded!"`):
```dlang
require("dlang.http");
```
Once loaded, the plugin registers two globals: `http` and `view`.
---
## Quick start
`app.dl`:
```dlang
require("dlang.http");
var server = http.server();
// Serve everything in ./public under /assets (e.g. /assets/css/site.css)
server.static("/assets", "./public");
// A plain text route
server.route("/", ["GET"], func(req, params, cookies, files)
return "Hello world!";
end);
// Query-string parameters arrive in `params`
server.route("/hello", ["GET"], func(req, params, cookies, files)
return "Hello " + params.name + "!";
end);
// Return a table as `body` and the plugin JSON-encodes it for you
server.route("/api/status", ["GET"], func(req, params, cookies, files)
return {
body: {
ok: true,
name: "dlang.http"
}
};
end);
// Uploads: `files` holds the multipart/form-data file fields
server.route("/upload", ["POST"], func(req, params, cookies, files)
if (#files > 0) then
var saved = http.saveTo(files.avatar, "./uploads");
return { body: "Saved to " + saved, contentType: "text/plain" };
end
return { body: "No file uploaded", statusCode: 400 };
end);
// Custom error page
server.error(404, func(req)
return {
body: "<h1>Not found</h1><p>" + req.path + "</p>",
contentType: "text/html"
};
end);
// Blocks and serves requests until the process is stopped
server.listen(8080);
```
> `#files` is the size operator: it returns the number of entries in the table. Because a
> missing table field evaluates to `nil` (and logs a VM warning), checking `#files` first
> keeps handlers free of warnings.
---
## API reference
### `http.server()`
Creates a server table. Every other `server.*` function is called on that table, and the
table itself is not sent to the OS socket until `listen` is called.
### `server.listen(port)`
Binds `0.0.0.0:<port>`, accepts connections in a loop and serves them until the process
ends. Returns `false` when the socket cannot be created, bound or listened on; on success it
never returns.
### `server.route(path, methods, handler)`
Registers a route.
- `path` – the exact request path, e.g. `"/users"` (no wildcards or path parameters; read
`req.path` if you need to match patterns yourself).
- `methods` – a list of method names, e.g. `["GET", "POST"]`. Comparison is
case-sensitive, so use uppercase.
- `handler` – a function (see below).
When a path matches but none of its methods do, the server answers `405 Method Not
Allowed`.
### Route handler arguments
Handlers are called with four arguments:
```dlang
func(req, params, cookies, files)
```
| Argument | Contents |
| --- | --- |
| `req` | Table with `method`, `path`, `query` (only when the URL had one), `params`, `cookies`, `files` and `body` (only when the request body was not empty) |
| `params` | All request parameters merged into one table: query string + body |
| `cookies` | The parsed `Cookie:` header |
| `files` | Uploaded files from a `multipart/form-data` body, keyed by form field name |
`params` is filled from the body depending on the `Content-Type`:
| `Content-Type` | Body handling |
| --- | --- |
| `application/x-www-form-urlencoded` | `a=1&b=2` decoded into strings |
| anything containing `json` | Parsed as a JSON object via the VM's `table.json_decode`, keeping numbers, booleans and nested tables/lists; only the top-level fields are merged |
| `multipart/form-data` | Text fields are merged; file fields go to `files` |
| anything else | Treated as url-encoded form data |
A key that occurs more than once (for example `?tag=a&tag=b`) becomes a list.
The four-argument signature is backward compatible: older three-parameter handlers keep
working, they simply never see `files`.
**Return values.** A handler returns either a string (sent as the body, `text/html` by
default) or a table:
```dlang
return {
body: "text or a table (a table is JSON encoded)",
contentType: "text/plain",
statusCode: 200
};
```
If a handler throws, the server answers `500` using the configured error page.
### `server.static(...)`
Serves files from disk. Four call shapes are supported:
```dlang
server.static("/assets", "./public"); // URL prefix -> folder
server.static("/style.css", "./style.css"); // exact URL -> single file
server.static({ assets: "./public" }); // map of keys -> paths
server.static([["/a.css", "./a.css"]]); // list of [url, file] pairs
```
Details:
- Table keys must be dlang identifiers (dlang tables have no string keys); a leading `/` is
added automatically, so the `{ assets: "./public" }` form serves `/assets/...`.
- Folder mounts answer `/` with `index.html`, pick the longest matching prefix and detect the
MIME type from the file extension.
- Exact URL → file mappings take precedence over folder mounts.
- Static files are only served when no route matches the path.
- Paths are URL-decoded first; anything containing `..` or `\` is rejected, so a request
cannot escape the mounted folder.
### `server.error(code, handler)`
Overrides the page for a status code. The handler may be a body string, a function, or a
table:
```dlang
server.error(404, "<h1>Not found</h1>");
server.error(500, { body: "Something broke", contentType: "text/plain" });
server.error(404, func(req)
// req = { method, path, statusCode }
return { body: "Missing: " + req.path, contentType: "text/html" };
end);
```
Status codes without an override (and handler failures) fall back to a built-in dark-themed
HTML page. A custom body of `""` also falls back to the built-in page.
### `server.maxBody(bytes)`
Changes the maximum request body the server buffers. The default is **16 MiB**. Requests
that announce a larger `Content-Length` are refused with `413 Payload Too Large` before the
body is read:
```dlang
server.maxBody(64 * 1024 * 1024); // allow 64 MiB uploads
```
### File uploads
An upload (`<form enctype="multipart/form-data">`, or `FormData` in `fetch`/XHR) is split
into its parts. Text fields end up in `params` like any other form post, and every file
field becomes an entry in `files`:
```dlang
func(req, params, cookies, files)
var avatar = files.avatar; // one entry per field name
// avatar.field -> "avatar"
// avatar.filename -> "cat.png"
// avatar.contentType -> "image/png"
// avatar.size -> 1234
// avatar.content -> the raw bytes
end
```
If several files are uploaded under the same field name (for example a multi-select), that
entry becomes a list of file tables. `filename*` (RFC 5987), quoted filenames, CRLF and
LF-only framing are all handled; malformed bodies are ignored instead of raising an error.
The same table is available as `req.files`, so a handler can read `req.files.avatar` if it
prefers not to use the fourth parameter. To store an upload, hand it to
[`http.save` / `http.saveTo`](#httpsave--httpsaveto):
```dlang
var saved = http.saveTo(files.avatar, "./uploads");
```
Raw bodies are available too: `req.body` holds the undecoded request body, which is handy
for uploads sent as `application/octet-stream`.
### `http.save` / `http.saveTo`
Write an upload to disk:
```dlang
http.save(upload, "./uploads/cat.png"); // -> true on success, false on failure
http.saveTo(upload, "./uploads"); // -> the written path (e.g. "./uploads/cat.png"), or "" on failure
```
The helpers live on the `http` table rather than a separate global, because a route
handler's fourth parameter is conventionally called `files` and would shadow a global of
the same name.
- `save` takes an explicit path and creates missing parent directories.
- `saveTo` appends the uploaded `filename` to a folder.
- Both accept a plain string as the first argument, so a raw body can be written as well:
`http.save(req.body, "./uploads/blob.bin")`.
- The filename is sanitized before use: any directory part (`C:\Users\me\evil.txt`,
`../../etc/passwd`) is stripped and unsafe characters are replaced, so a client can never
choose the target directory.
### `view.Render(path, vars)`
Renders a small template file and returns the result as a string. `view.render` is an alias.
Template paths are read relative to the process working directory; a missing template raises
an error, which a route handler turns into a `500`.
```dlang
server.route("/", ["GET"], func(req, params, cookies, files)
return view.Render("templates/page.html", {
title: "Home",
user: { name: "Ada" },
items: ["a", "b"]
});
end);
```
Template syntax:
| Syntax | Behaviour |
| --- | --- |
| `@include("partial.html")` | Inlines another template. Recursive, resolved relative to the including file (with a fallback to the working directory); cycles are skipped and nesting is limited to 32 levels |
| `{{ key }}` | Replaced with the matching variable. Strings, numbers and booleans are printed as-is |
| `{{ a.b }}` | Walks into nested tables |
| `{{ list }}` / `{{ table }}` | Serialized to JSON (convenient inside `<script>`) |
Unknown keys are left in the output as literal `{{key}}` text, which makes typos easy to
spot. Missing or cyclic includes are replaced with an HTML comment.
---
## Status codes
Responses use these standard reason phrases — anything else falls back to `OK`, while the
numeric status code is always the one you asked for:
`200 OK`, `201 Created`, `204 No Content`, `301 Moved Permanently`, `302 Found`,
`400 Bad Request`, `401 Unauthorized`, `403 Forbidden`, `404 Not Found`,
`405 Method Not Allowed`, `413 Payload Too Large`, `500 Internal Server Error`,
`501 Not Implemented`.
Responses are always sent with `Content-Length`, `Content-Type` and `Connection: close`.
---
## Request and response flow
```mermaid
flowchart TD
A[Accept connection] --> B[Read headers + Content-Length body]
B --> C{Body within limit?}
C -- no --> D[413]
C -- yes --> E[Parse query, cookies and body<br/>urlencoded / JSON / multipart]
E --> F{Route matches path?}
F -- yes, method allowed --> G[Call handler with req, params, cookies, files]
F -- yes, other method --> H[405]
F -- no --> I{Static mount matches?}
I -- yes --> J[Serve file with detected MIME type]
I -- no --> K[404]
G --> L[Send response: string, or table with body / contentType / statusCode]
G -. handler threw .-> M[500 with error page]
```
---
## Limitations
- **One request at a time.** `listen` accepts and handles connections sequentially in a
blocking loop; there is no thread pool or keep-alive.
- **Exact route paths only.** No `:parameters`, wildcards or regex routes; match on
`req.path` yourself if you need them.
- **`Content-Length` only.** Chunked transfer encoding is not supported, and a request
without `Content-Length` has no body.
- **In-memory bodies.** The whole body (up to `server.maxBody`) is buffered before a handler
runs, and static files are read fully into memory before being sent.
- **HTTP/1.1 only**, no TLS. Put a reverse proxy in front if you need HTTPS.
- **Global server state.** Routes, static mounts, error pages and the socket are
process-wide, so one `listen` call serves one server per process.
---
## Project layout
```text
dlang-http/
├─ CMakeLists.txt # top-level project
├─ CMakePresets.json # Windows / Linux / macOS configure presets
└─ dlang.http/
├─ CMakeLists.txt # builds the `dlang.http` shared library
├─ entry.cpp # the entire plugin: server, routing, static files,
│ # uploads, error pages and the view engine
├─ json.hpp # nlohmann/json (used by the VM's table library)
└─ dlang/ # upstream dlang VM copy — do not edit
├─ vm.hpp, types/, libs/, parser/
└─ src/ # compiler, lexer, parser, VM implementation
```
Everything plugin-specific lives in `dlang.http/entry.cpp`; `dlang.http/dlang/` is a
verbatim copy of the dlang VM so the shared library can be built and link the VM
implementation.
---
## AI-generated code
This repository and this README were produced with the help of an AI assistant
(GitHub Copilot). That means:
- The code was **generated, then verified against its own test harnesses** (request parsing,
multipart uploads, socket-level request handling, `http.save`/`saveTo`), but it has not
been reviewed by a human maintainer.
- Comments and documentation may describe behaviour that has not been audited in every
edge case, and the API is still evolving.
- Treat it as a starting point: review the source in `dlang.http/entry.cpp`, test it with
your own inputs, and add a license before publishing or distributing it.
There is no warranty of any kind. Use it at your own risk.
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