lander/src/http_loop/http_loop_res.c

#include "http_loop.h"
#include "log.h"

static const char *http_response_format = "HTTP/1.1 %i %s\n"
                                          "Server: lander/" LANDER_VERSION "\n"
                                          "Content-Length: %lu\n";

/*
 * This function precalculates the size of the total buffer required using
 * snprintf. When this function is called with a buf size of 0, it never tries
 * to write any data, but it does return the amount of bytes that would be
 * written.
 */
void http_loop_init_header(http_response *res) {
  if (res->status == 0) {
    res->status = http_ok;
  }

  const char *response_type_name =
      http_status_names[res->status / 100 - 1][res->status % 100];

  // First we calculate the size of the start of the header
  int buf_size = snprintf(NULL, 0, http_response_format, res->status,
                          response_type_name, res->body.expected_len);

  // We add each header's required size
  for (size_t i = 0; i < res->header_count; i++) {
    buf_size +=
        snprintf(NULL, 0, "%s: %s\n", http_header_names[res->headers[i].type],
                 res->headers[i].value);
  }

  // The + 1 is required to store the final null byte, but we will replace it
  // with the required final newline
  char *buf = malloc(buf_size + 1);
  buf_size = sprintf(buf, http_response_format, res->status, response_type_name,
                     res->body.expected_len);

  for (size_t i = 0; i < res->header_count; i++) {
    buf_size +=
        sprintf(&buf[buf_size], "%s: %s\n",
                http_header_names[res->headers[i].type], res->headers[i].value);
  }

  buf[buf_size] = '\n';

  res->head = buf;
  res->head_len = buf_size + 1;
}

void http_loop_write_response(event_loop_conn *conn) {
  http_response *res = &((http_loop_ctx *)conn->ctx)->res;

  // Create head response
  if (res->head == NULL) {
    http_loop_init_header(res);
  }

  // The final iteration marks the end of the response, after which we reset the
  // context so a next request can be processed
  if (res->head_written == res->head_len &&
      res->body.expected_len == res->body.len) {
    http_loop_ctx_reset(conn->ctx);
    conn->state = event_loop_conn_state_req;
    return;
  }

  if (res->head_written < res->head_len) {
    size_t bytes_to_write = MIN(res->head_len - res->head_written,
                                EVENT_LOOP_BUFFER_SIZE - conn->wbuf_size);
    memcpy(&conn->wbuf[conn->wbuf_size], &res->head[res->head_written],
           bytes_to_write);

    conn->wbuf_size += bytes_to_write;
    res->head_written += bytes_to_write;
  }

  if (res->body.len < res->body.expected_len) {
    size_t bytes_to_write = MIN(res->body.expected_len - res->body.len,
                                EVENT_LOOP_BUFFER_SIZE - conn->wbuf_size);
    size_t bytes_written;

    switch (res->body.type) {
    case http_body_buf:
      memcpy(&conn->wbuf[conn->wbuf_size], &(res->body.buf)[res->body.len],
             bytes_to_write);
      conn->wbuf_size += bytes_to_write;
      res->body.len += bytes_to_write;
      break;
    case http_body_file:
      bytes_written = fread(&conn->wbuf[conn->wbuf_size], sizeof(uint8_t),
                            bytes_to_write, res->body.file);
      conn->wbuf_size += bytes_written;
      res->body.len += bytes_written;
      break;
    }
  }
}