nghttp2 の HPACK エンコードの例です

hpack_encode.c

#include <stdio.h>
#include <nghttp2/nghttp2.h>

// https://nghttp2.org/documentation/tutorial-hpack.html

#define MAKE_NV(K, V)                                                          \
  {                                                                            \
    (uint8_t *)K, (uint8_t *)V, sizeof(K) - 1, sizeof(V) - 1,                  \
        NGHTTP2_NV_FLAG_NONE                                                   \
  }

int main() {
  size_t i;
  size_t sum;
  size_t nvlen;
  uint8_t *buf;
  size_t buflen;
  size_t outlen;
  int rv;
  nghttp2_hd_deflater *deflater;

  nghttp2_nv nva[] = {
      MAKE_NV(":scheme", "https"), MAKE_NV(":authority", "example.org"),
      MAKE_NV(":path", "/"), MAKE_NV("user-agent", "libnghttp2"),
      MAKE_NV("accept-encoding", "gzip, deflate")};

  nvlen = sizeof(nva) / sizeof(nva[0]);

  sum = 0;

  for (i = 0; i < nvlen; ++i) {
    sum += nva[i].namelen + nva[i].valuelen;
  }

  printf("Input (%zu byte(s)):\n\n", sum);

  for (i = 0; i < nvlen; ++i) {
    fwrite(nva[i].name, 1, nva[i].namelen, stdout);
    printf(": ");
    fwrite(nva[i].value, 1, nva[i].valuelen, stdout);
    printf("\n");
  }

  rv = nghttp2_hd_deflate_new(&deflater, 4096);

  buflen = nghttp2_hd_deflate_bound(deflater, nva, nvlen);
  buf = malloc(buflen);
  rv = nghttp2_hd_deflate_hd(deflater, buf, buflen, nva, nvlen);
  outlen = (size_t)rv;

  printf("\nDeflate (%zu byte(s), ratio %.02f):\n\n", outlen,
         sum == 0 ? 0 : (double)outlen / (double)sum);

  for (i = 0; i < outlen; ++i) {
    if ((i & 0x0fu) == 0) {
      printf("%08zX: ", i);
    }

    printf("%02X ", buf[i]);

    if (((i + 1) & 0x0fu) == 0) {
      printf("\n");
    }
  }

  printf("\n\nInflate:\n\n");

  free(buf);
  nghttp2_hd_deflate_del(deflater);

  return 0;
}

result.txt

zig run test.c -lc -lnghttp2

Input (87 byte(s)):

:scheme: https
:authority: example.org
:path: /
user-agent: libnghttp2
accept-encoding: gzip, deflate

Deflate (22 byte(s), ratio 0.25):

00000000: 87 41 88 2F 91 D3 5D 05 5C F6 4D 84 7A 87 A0 D1 
00000010: D5 34 E9 4D 62 90 

Inflate: