⚡zap⚡ - blazingly fast backends in zig

Zap is the zig replacement for the REST APIs I used to write in python with Flask and mongodb, etc. It can be considered to be a microframework for web applications.

What I needed as a replacement was a blazingly fast and robust HTTP server that I could use with Zig, and I chose to wrap the superb evented networking C library facil.io. Zap wraps and patches facil.io - the C web application framework.

⚡ZAP⚡ IS FAST, ROBUST, AND STABLE

After having used ZAP in production for years, I can confidently assert that it proved to be:

• ⚡ blazingly fast ⚡
• 💪 extremely robust 💪

FAQ:

• Q: What version of Zig does Zap support?
  • Zap uses the latest stable zig release (0.14.0), so you don't have to keep up with frequent breaking changes. It's an "LTS feature".
• Q: Can Zap build with Zig's master branch?
  • See the zig-master branch. Please note that the zig-master branch is not the official master branch of ZAP. Be aware that I don't provide tagged releases for it. If you know what you are doing, that shouldn't stop you from using it with zig master though.
• Q: Where is the API documentation?
  • Docs are a work in progress. You can check them out here.
  • Run zig build run-docserver to serve them locally.
• Q: Does ZAP work on Windows?
  • No. This is due to the underlying facil.io C library. Future versions of facil.io might support Windows but there is no timeline yet. Your best options on Windows are WSL2 or a docker container.
• Q: Does ZAP support TLS / HTTPS?
  • Yes, ZAP supports using the system's openssl. See the https example and make sure to build with the -Dopenssl flag or the environment variable ZAP_USE_OPENSSL=true:
    • .openssl = true, (in dependent projects' build.zig, b.dependency("zap" .{...}))
    • ZAP_USE_OPENSSL=true zig build https
    • zig build -Dopenssl=true https

Here's what works

I recommend checking out the new App-based or the Endpoint-based examples, as they reflect how I intended Zap to be used.

Most of the examples are super stripped down to only include what's necessary to show a feature.

To see API docs, run zig build run-docserver. To specify a custom port and docs dir: zig build docserver && zig-out/bin/docserver --port=8989 --docs=path/to/docs.

New App-Based Examples

• app_basic: Shows how to use zap.App with a simple Endpoint.
• app_auth: Shows how to use zap.App with an Endpoint using an Authenticator.

See the other examples for specific uses of Zap.

Benefits of using zap.App:

• Provides a global, user-defined "Application Context" to all endpoints.
• Made to work with "Endpoints": an endpoint is a struct that covers a /slug of the requested URL and provides a callback for each supported request method (get, put, delete, options, post, head, patch).
• Each request callback receives:
  • a per-thread arena allocator you can use for throwaway allocations without worrying about freeing them.
  • the global "Application Context" of your app's choice
• Endpoint request callbacks are allowed to return errors:
  • you can use try.
  • the endpoint's ErrorStrategy defines if runtime errors should be reported to the console, to the response (=browser for debugging), or if the error should be returned.

Legacy Endpoint-based examples

• endpoint: a simple JSON REST API example featuring a /users endpoint for performing PUT/DELETE/GET/POST operations and listing users, together with a simple frontend to play with. It also introduces a /stop endpoint that shuts down Zap, so memory leak detection can be performed in main().
  • Check out how main.zig uses ZIG's awesome GeneralPurposeAllocator to report memory leaks when ZAP is shut down. The StopEndpoint just stops ZAP when receiving a request on the /stop route.
• endpoint authentication: a simple authenticated endpoint. Read more about authentication here.

Legacy Middleware-Style examples

• MIDDLEWARE support: chain together request handlers in middleware style. Provide custom context structs, totally type-safe. If you come from GO this might appeal to you.
• MIDDLEWARE with endpoint support: Same as the example above, but this time we use an endpoint at the end of the chain, by wrapping it via zap.Middleware.EndpointHandler. Mixing endpoints in your middleware chain allows for usage of Zap's authenticated endpoints and your custom endpoints. Since Endpoints use a simpler API, you have to use r.setUserContext() and r.getUserContext() with the request if you want to access the middleware context from a wrapped endpoint. Since this mechanism uses an *anyopaque pointer underneath (to not break the Endpoint API), it is less type-safe than zap.Middleware's use of contexts.
• Per Request Contexts : With the introduction of setUserContext() and getUserContext(), you can, of course use those two in projects that don't use zap.Endpoint or zap.Middleware, too, if you really, really, absolutely don't find another way to solve your context problem. We recommend using a zap.Endpoint inside of a struct that can provide all the context you need instead. You get access to your struct in the callbacks via the @fieldParentPtr() trick that is used extensively in Zap's examples, like the endpoint example.

Specific and Very Basic Examples

• hello: welcomes you with some static HTML
• routes: a super easy example dispatching on the HTTP path. NOTE: The dispatch in the example is a super-basic DIY-style dispatch. See endpoint-based examples for more realistic use cases.
• simple_router: See how you can use zap.Router to dispatch to handlers by HTTP path.
• serve: the traditional static web server with optional dynamic request handling
• sendfile: simple example of how to send a file, honoring compression headers, etc.
• bindataformpost: example to receive binary files via form post.
• hello_json: serves you json dependent on HTTP path
• mustache: a simple example using mustache templating.
• http parameters: a simple example sending itself query parameters of all supported types.
• cookies: a simple example sending itself a cookie and responding with a session cookie.
• websockets: a simple websockets chat for the browser.
• Username/Password Session Authentication: A convenience authenticator that redirects un-authenticated requests to a login page and sends cookies containing session tokens based on username/password pairs received via POST request.
• Error Trace Responses: You can now call r.sendError(err, status_code) when you catch an error and a stack trace will be returned to the client / browser.
• HTTPS: Shows how easy it is to use facil.io's openssl support. Must be compiled with -Dopenssl=true or the environment variable ZAP_USE_OPENSSL set to true and requires openssl dev dependencies (headers, lib) to be installed on the system.
  • run it like this: ZAP_USE_OPENSSL=true zig build run-https OR like this: zig build -Dopenssl=true run-https
  • it will tell you how to generate certificates

⚡blazingly fast⚡

Claiming to be blazingly fast is the new black. At least, Zap doesn't slow you down and if your server performs poorly, it's probably not exactly Zap's fault. Zap relies on the facil.io framework and so it can't really claim any performance fame for itself. In this initial implementation of Zap, I didn't care about optimizations at all.

But, how fast is it? Being blazingly fast is relative. When compared with a simple GO HTTP server, a simple Zig Zap HTTP server performed really well on my machine (x86_64-linux):

• Zig Zap was nearly 30% faster than GO
• Zig Zap had over 50% more throughput than GO
• YMMV!!!

So, being somewhere in the ballpark of basic GO performance, zig zap seems to be ... of reasonable performance 😎.

I can rest my case that developing ZAP was a good idea because it's faster than both alternatives: a) staying with Python, and b) creating a GO + Zig hybrid.

On (now missing) Micro-Benchmarks

I used to have some micro-benchmarks in this repo, showing that Zap beat all the other things I tried, and eventually got tired of the meaningless discussions they provoked, the endless issues and PRs that followed, wanting me to add and maintain even more contestants, do more justice to beloved other frameworks, etc.

Case in point, even for me the micro-benchmarks became meaningless. They were just some rough indicator to me confirming that I didn't do anything terribly wrong to facil.io, and that facil.io proved to be a reasonable choice, also from a performance perspective.

However, none of the projects I use Zap for, ever even remotely resembled anything close to a static HTTP response micro-benchmark.

For my more CPU-heavy than IO-heavy use-cases, a thread-based microframework that's super robust is still my preferred choice, to this day.

Having said that, I would still love for other, pure-zig HTTP frameworks to eventually make Zap obsolete. Now, in 2025, the list of candidates is looking really promising.

📣 Shout-Outs

• http.zig : Pure Zig! Close to Zap's model. Performance = good!
• jetzig : Comfortably develop modern web applications quickly, using http.zig under the hood
• zzz : Super promising, super-fast, especially for IO-heavy tasks, io_uring support - need I say more?

💪 Robust

ZAP is very robust. In fact, it is so robust that I was confidently able to only work with in-memory data (RAM) in all my ZAP projects so far: over 5 large online research experiments. No database, no file persistence, until I hit "save" at the end 😊.

So I was able to postpone my cunning data persistence strategy that's similar to a mark-and-sweep garbage collector and would only persist "dirty" data when traffic is low, in favor of getting stuff online more quickly. But even if implemented, such a persistence strategy is risky because when traffic is not low, it means the system is under (heavy) load. Would you confidently NOT save data when load is high and the data changes most frequently -> the potential data loss is maximized?

To answer that question, I just skipped it. I skipped saving any data until receiving a "save" signal via API. And it worked. ZAP just kept on zapping. When traffic calmed down or all experiment participants had finished, I hit "save" and went on analyzing the data.

Handling all errors does pay off after all. No hidden control flow, no hidden errors or exceptions is one of Zig's strengths.

To be honest: There are still pitfalls. E.g. if you request large stack sizes for worker threads, Zig won't like that and panic. So make sure you don't have local variables that require tens of megabytes of stack space.

🛡️ Memory-safe

See the StopEndpoint in the endpoint example. The StopEndpoint just stops ZAP when receiving a request on the /stop route. That example uses ZIG's awesome GeneralPurposeAllocator in main.zig to report memory leaks when ZAP is shut down.

You can use the same strategy in your debug builds and tests to check if your code leaks memory.

Getting started

Make sure you have zig 0.14.0 installed. Fetch it from here.

$ git clone https://github.com/zigzap/zap.git
$ cd zap
$ zig build run-hello
$ # open http://localhost:3000 in your browser

... and open http://localhost:3000 in your browser.

Using ⚡zap⚡ in your own projects

Make sure you have the latest zig release (0.14.0) installed. Fetch it from here.

If you don't have an existing zig project, create one like this:

$ mkdir zaptest && cd zaptest
$ zig init

With an existing Zig project, adding Zap to it is easy:

1. Zig fetch zap
2. Add zap to your build.zig

In your zig project folder (where build.zig is located), run:

zig fetch --save "git+https://github.com/zigzap/zap#v0.10.1"

Then, in your build.zig's build function, add the following before b.installArtifact(exe):

    const zap = b.dependency("zap", .{
        .target = target,
        .optimize = optimize,
        .openssl = false, // set to true to enable TLS support
    });

    exe.root_module.addImport("zap", zap.module("zap"));

From then on, you can use the Zap package in your project via const zap = @import("zap");. Check out the examples to see how to use Zap.

Contribute to ⚡zap⚡ - blazingly fast

At the current time, I can only add to zap what I need for my personal and professional projects. While this happens blazingly fast, some if not all nice-to-have additions will have to wait. You are very welcome to help make the world a blazingly fast place by providing patches or pull requests, add documentation or examples, or interesting issues and bug reports - you'll know what to do when you receive your calling 👼.

We have our own ZAP discord server!!!

Support ⚡zap⚡

Being blazingly fast requires a constant feed of caffeine. I usually manage to provide that to myself for myself. However, to support keeping the juices flowing and putting a smile on my face and that warm and cozy feeling into my heart, you can always buy me a coffee ☕. All donations are welcomed 🙏 blazingly fast! That being said, just saying "hi" also works wonders with the smiles, warmth, and coziness 😊.

Examples

You build and run the examples via:

$ zig build [EXAMPLE]
$ ./zig-out/bin/[EXAMPLE]

... where [EXAMPLE] is one of hello, routes, serve, ... see the list of examples above.

Example: building and running the hello example:

$ zig build hello
$ ./zig-out/bin/hello

To just run an example, like routes, without generating an executable, run:

$ zig build run-[EXAMPLE]

Example: building and running the routes example:

$ zig build run-routes

hello

const std = @import("std");
const zap = @import("zap");

fn on_request(r: zap.Request) void {
    if (r.path) |the_path| {
        std.debug.print("PATH: {s}\n", .{the_path});
    }

    if (r.query) |the_query| {
        std.debug.print("QUERY: {s}\n", .{the_query});
    }
    r.sendBody("<html><body><h1>Hello from ZAP!!!</h1></body></html>") catch return;
}

pub fn main() !void {
    var listener = zap.HttpListener.init(.{
        .port = 3000,
        .on_request = on_request,
        .log = true,
    });
    try listener.listen();

    std.debug.print("Listening on 0.0.0.0:3000\n", .{});

    // start worker threads
    zap.start(.{
        .threads = 2,
        .workers = 2,
    });
}