Middleware

Middleware allows you to intercept and process requests/responses at different stages of the HTTP pipeline.
They are simple functions that take a Request and Response reference, returning true (continue) or false (stop processing).

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Middleware Phases

Middleware can be registered for specific phases of request handling:

SETTINGS - Middleware executed when the uri or pseudo headers become known, to set up handler specific limits HEADER - Middleware executed after the headers were parsed. BODY - Middleware executed during the body processing phase in certain data types. RESPONSE - Middleware executed during sending response, called only once per response.

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Example

#include "server/server.h"
#include "Protocols/HTTP/Message.h"
#include <iostream>

using namespace usub::server;

bool globalMiddle(const protocols::http::Request &request, protocols::http::Response &response) {
    std::cout << "Global middleware: request count++" << std::endl;
    return true;
}

bool headerMiddle(const protocols::http::Request &request, protocols::http::Response &response) {
    std::cout << "Header middleware: URL = " << request.getURL() << std::endl;
    return true;
}

bool responseMiddle(const protocols::http::Request &request, protocols::http::Response &response) {
    std::cout << "Response middleware triggered" << std::endl;
    return true;
}

ServerHandler<void> handler(protocols::http::Request &request, protocols::http::Response &response) {
    res.setStatus(200)
       .setMessage("OK")
       .addHeader("Content-Type", "text/plain")
       .setBody("Hello with middleware!\n");
    co_return;
}

int main() {
    Server server("../config/config.toml");

    // Global middleware applies to all requests
    server.addMiddleware(protocols::http::MiddlewarePhase::HEADER, globalMiddle);

    // Route-specific middleware
    server.handle({"GET"}, "/hello", handler)
          .addMiddleware(protocols::http::MiddlewarePhase::HEADER, headerMiddle)
          .addMiddleware(protocols::http::MiddlewarePhase::RESPONSE, responseMiddle);

    server.run();
}

Userdata

It is possible to save user data between middlewares, it is cleared upon new request response cycle

struct UserData {
    std::string name;
    int age;
};

bool headerMiddle(const protocols::http::Request &request, protocols::http::Response &response) {
    request.user_data = UserData{"John", 30};
    return true;
}

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Behavior

1. Settings middleware always runs first as soon as url or pseudo headers are parsed.
2. Global middleware and Header middleware runs once headers are parsed. In the same order first global, then route specific
3. Body middleware runs if the request body type is chunked.
4. Response middleware runs right before sending back data.
5. If any middleware returns false, the pipeline stops and no further handlers are executed, the response will be sent.