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wired guide

Streaming a large body

A response body larger than body_out is produced in rounds. This page serves 1 MiB, and the client prints its length and SHA-256.

Code

main.c
#define WIRED_MAIN
#include "wired.h"


#define BODY_SIZE (1024 * 1024)


/* A body bigger than body_out goes out over several rounds: each call fills
 * what fits starting at offset and sets *more until the whole body is sent.
 * Byte i of the body is (u8)i. */
static int on_request(
    void*                       ctx,
    const wired_h3reqdrive_req* req,
    u64                         offset,
    wired_obuf*                 body_out,
    const char**                content_type,
    int*                        more,
    u64*                        total_size) {
  (void)ctx;
  (void)req;
  u64 n = BODY_SIZE - offset;
  if (n > body_out->cap) n = body_out->cap;
  for (u64 i = 0; i < n; i++) body_out->p[i] = (u8)(offset + i);
  body_out->len = n;
  *more         = offset + n < BODY_SIZE;
  *total_size   = BODY_SIZE;
  *content_type = "application/octet-stream";
  return 1;
}


int wired_main(int argc, char** argv) {
  /* Fixed demo identity (self-signed certificate; never for production). */
  static wired_srvboot_demo_keys keys;
  wired_srvboot_id               id;
  wired_srvboot_demo(&id, &keys, 0x50, "guide-h3");


  u16 port                 = (u16)wired_cliargs_int(argc, argv, "--port", 4433);
  wired_srvrun_handler h   = {.cb = on_request};
  wired_srvrun_obs     obs = {0};
  return wired_server_run(port, &id, h, obs) ? 0 : 1;
}

Output

Terminal window
$ ./h3-streaming --port 4433
conn closed by peer (CONNECTION_CLOSE)
Terminal window
$ probe h3get 127.0.0.1:4433 /big
GET /big status=200 content-type=application/octet-stream bytes=1048576 sha256=fbbab289f7f94b25736c58be46a994c441fd02552cc6022352e3d86d2fab7c83

How it works

Section titled “How it works”
  • The handler is called again for the same request while it sets *more = 1. offset is the number of body bytes already sent.
  • Each round writes at most body_out->cap bytes, starting at offset.
  • *total_size gives the full body length up front, so the response can announce it before every byte exists. It is read on the first round only.