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- Middleware: no more MixContexts
- zig structs are fine
- more documentation (comments -> autodoc).
- websocket docs
81 lines
2.9 KiB
Markdown
81 lines
2.9 KiB
Markdown
# ZIG-CEPTION!
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In ZAP, we have great zig-ception moment in the [middleware
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example](../examples/middleware/middleware.zig). But first we need to introduce
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one key function of `zap.Middleware`: **combining structs at comptime!**
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## Combining structs at runtime
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Here is how it is used in user-code:
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```zig
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// create a combined context struct
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const Context = struct {
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user: ?UserMiddleWare.User = null,
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session: ?SessionMiddleWare.Session = null,
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};
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```
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Why do we create combined structs? Because all our Middleware handler functions
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need to receive a per-request context. But each wants their own data: the User
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middleware might want to access a User struct, the Session middleware might want
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a Session struct, and so on. So, which struct should we use in the prototype of
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the "on_request" callback function? We could just use an `anyopaque` pointer.
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That would solve the generic function prototype problem. But then everyone
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implementing such a handler would need to cast this pointer back into - what?
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Into the same type that the caller of the handler used. It gets really messy
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when we continue this train of thought.
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So, in ZAP, I opted for one Context type for all request handlers. Since ZAP is
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a library, it cannot know what your preferred Context struct is. What it should
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consist of. Therefore, it lets you combine all the structs your and maybe your
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3rd parties's middleware components require - at comptime! And derive the
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callback function prototype from that. If you look at the [middleware
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example](../examples/middleware/middleware.zig), you'll notice, it's really
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smooth to use.
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**NOTE:** In your contexts, please also use OPTIONALS. They are set null at
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context creation time. And will aid you in not shooting yourself in the foot
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when accessing context fields that haven't been initialized - which may happen
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when the order of your chain of components isn't perfect yet. 😉
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## The zig-ception moment
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Have a look at an excerpt of the example:
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```zig
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// create a combined context struct
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const Context = struct {
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user: ?UserMiddleWare.User = null,
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session: ?SessionMiddleWare.Session = null,
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};
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// we create a Handler type based on our Context
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const Handler = zap.Middleware.Handler(Context);
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//
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// ZIG-CEPTION!!!
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//
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// Note how amazing zig is:
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// - we create the "mixed" context based on the both middleware structs
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// - we create the handler based on this context
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// - we create the middleware structs based on the handler
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// - which needs the context
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// - which needs the middleware structs
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// - ZIG-CEPTION!
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// Example user middleware: puts user info into the context
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const UserMiddleWare = struct {
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handler: Handler,
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// .. the UserMiddleWare depends on the handler
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// which depends on the Context
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// which depends on this UserMiddleWare struct
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// ZIG-CEPTION!!!
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```
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## 🤯
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The comments in the code say it all.
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**Isn't ZIG AMAZING?**
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