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 and has 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 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.

Features
Requirements
Building
Installing the plugin
Quick start
API reference
Status codes
Request and response flow
Limitations
Project layout
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).

# 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:

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!"):

require("dlang.http");

Once loaded, the plugin registers two globals: http and view.

Quick start

app.dl:

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:

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:

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:

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:

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:

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:

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:

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:

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.

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

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

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.

README.md Unescape Escape

dlang.http

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