是否有C语言版本http3 api使用示例呢？

[wdj55556]

目前我在开发一个基于tquic的传输软件，在使用http3的c api时遇到了一些困难，例如http3_headers_t 该如何构造，它是http3_header_t的数组指针吗？ http3_recv_body函数正常应该是在on_stream_data中调用吗？以及http3_conn_process_streams函数正确的调用时机是什么?

[wangfuyu]

1. 应用层无需构造http3_headers_t，此结构体内部细节应用层无需关注（构造和解析均由TQUIC协议栈完成），应用程序在回调on_stream_headers函数内，调用http3_for_each_header解析http3_headers_t对象即可，TQUIC协议栈会通过http3_for_each_header入参中的cb回显每个头域细节（name-value及各自的长度）。
2. 应用层发送HTTP/3头域（请求或响应）时，需要先将应用层的头域集合转换为http3_header_t数组，然后调用http3_send_headers接口写入TQUIC协议栈；发送头域逻辑编写示例，仅供参考（以下代码是C++编写，部分内容省略）：

struct HeaderBuffer {
  unsigned off = 0;
  char buf[UINT16_MAX];
};

// Set offset for HTTP/3 header
static inline void QuicHeaderSetOffset(http3_header_t *hdr, char *buf, size_t name_len,
                                       size_t val_len) {
  memset(hdr, 0, sizeof(*hdr));
  hdr->name = reinterpret_cast<uint8_t *>(buf);
  hdr->name_len = name_len;
  hdr->value = reinterpret_cast<uint8_t *>(buf + name_len);
  hdr->value_len = val_len;
}

// Fill HTTP/3 header with given name and value
static int HeaderSetPtr(http3_header_t *hdr, struct HeaderBuffer *header_buf, const char *name,
                        size_t name_len, const char *val, size_t val_len) {
  if (header_buf->off + name_len + val_len > sizeof(header_buf->buf)) {
    LOG(ERROR) << "HeaderSetPtr failed, header_buf->off: " << header_buf->off
               << ", name_len: " << name_len << ", val_len: " << val_len
               << ", buf size: " << sizeof(header_buf->buf);
    return -1;
  }

  memcpy(header_buf->buf + header_buf->off, name, name_len);
  memcpy(header_buf->buf + header_buf->off + name_len, val, val_len);

  QuicHeaderSetOffset(hdr, header_buf->buf + header_buf->off, name_len, val_len);
  header_buf->off += name_len + val_len;

  return 0;
}


// Construct HTTP/3 response headers
static int QuicConstructResponseHeaders(quic_stream_ctx *stream_ctx, const http::Context &ctx,
                                        struct HeaderBuffer *header_buf,
                                        http3_header_t *headers_arr, size_t *headers_count) {
  // 
  // omit some code
  //
  
  int cnt = 0;

  for (const auto &mit : http_headers) {
    const auto &cur_value = mit.second.Get();
    std::string key = mit.first;

    if (HeaderSetPtr(&headers_arr[cnt++], header_buf, key.c_str(), key.size(), cur_value.c_str(),
                     cur_value.size()) != 0) {
      LOG(ERROR) << "HeaderSetPtr failed, key: " << key << ", value: " << cur_value;
      return -1;
    }
  }

  LOG_DEBUG() << "quic construct response headers success" << ", header count: " << cnt;

  *headers_count = cnt;
  return 0;
}

// Send HTTP/3 headers by TQUIC
// Note: TQUIC do not support client mode, so flag must be kRspHeader
static int64_t QuicSendHeader(const http::Context &ctx, bool fin) {
  size_t num = ctx.header_map().size();
  size_t headers_count = 0;
  struct HeaderBuffer header_buf;
  // Note: +1 for :status header
  http3_header_t *headers_arr = new http3_header_t[num + 1];

  // 1. Construct HTTP/3 headers
  if (QuicConstructResponseHeaders(ctx, &header_buf, headers_arr, &headers_count) !=
      0) {
    LOG(ERROR) << "QuicConstructResponseHeaders failed";
    delete[] headers_arr;
    return -1;
  }

  // 2. Send HTTP/3 headers
  int rc = http3_send_headers(..., headers_arr, headers_count, fin);
  // After send headers, we can delete headers array, no matter success or not,
  // because TQUIC will copy headers array to its internal buffer in need.
  delete[] headers_arr;

  // Omit some code
  
}

3. http3_recv_body仅在on_stream_data回调中使用，从TQUIC协议栈读取HTTP/3 body；
4. http3_conn_process_streams函数建议在以下逻辑中调用：
   1）quic层的新流回调，也就是on_stream_created内；
   2）quic层的readable回调，也就是on_stream_readable内；
   3）quic层的writable回调，也就是on_stream_writable内，且流ID为非请求流时调用即可；
   4）quic层的流关闭回调，也就是on_stream_closed内，且流ID为非请求流时调用即可；

总之，针对http3_conn_process_streams接口，仅需记住它的主要功能是驱动TQUIC处理某一连接的HTTP/3层的流数据即可。