carlosascari/http_res

Memory efficient HTTP Response parser written in C. Pure functional programming

HTTP Response Parser

A memory efficient http parser written in c. No memory allocation or buffers. Pure functional programming.

• Handles chunked transfer-encoding
• Zero memory allocation or temporary buffers
• Only depends on: string.h and stdlib.h
• Naturaly fast
• Very simple; easy for you to snatch

This is a naive, no thrills, no fluff, implementation of a http response parser.

Assumptions are made:

• You are not feeding it NULL as a source
• The source buffer may or may not be complete
• The response data is standards compliant; there is no error detection.

Usage

Say you have a response data buffer and its size available, for all these examples.

The buffer may or may not have the completed response.

int response_size;
char* response = GET_THAT_HTTP_RESPONSE_DATA(&response_size);

Get the status line

int status_line_size;

char* status_line = http_res_parse_status_line(response, response_size, &status_line_size);

if (status_line == NULL) {
  printf("Buffer not ready; doesn't have the status line available");
  return -1;
}

for (char* p = status_line; p != status_line + status_line_size; p++) {
   printf("%c", *p);
}

Get the headers

int headers_size;

char* headers = http_res_parse_headers(response, response_size, &headers_size);

if (headers == NULL) {
  printf("Buffer not ready; doesn't have headers available");
  return -2;
}

for (char* p = headers; p != headers + headers_size; p++) {
   printf("%c", *p);
}

Get a particular header value

Header field is case-insensitive

int header_value_size;

char* header_value = http_res_parse_header(response, response_size, "content-length", &header_value_size);

if (header_value == NULL) {
  printf("Header does not exist or data is not complete");
  return -3;
}

for (char* p = header_value; p != header_value + header_value_size; p++) {
   printf("%c", *p);
}

Get response body

Note that if the response has a chunked transfer-encoding, the body will include chunk size information for each chunk, the last empty chunk and trailer information. This function works best when transfer-encoding is not chunked.

int body_size;

char* body = http_res_parse_body(response, response_size, &body_size);

if (body == NULL) {
  printf("Buffer not ready and/or body data is not available");
  return -4;
}

for (char* p = body; p != body + body_size; p++) {
   printf("%c", *p);
}

Get a chunked encoded response body

Will work with chunked encoding responses and non-chunk encoded responses.

We have to use a destination buffer in order to merge all the chunks together, while at the same time removing their header information.

char body = malloc(response_size); // Will be smaller, unless response has not completed

int body_size = http_res_copy_body(body, response, response_size);

if (body_size == 0) {
  printf("buffer not ready; body data is not available");
  return -5;
}

if (body_size == -1) {
  printf("buffer not ready; chunks are missing!");
  return -6;
}

for (char* p = body; p != body + body_size; p++) {
   printf("%c", *p);
}

How to compile

Its plain c, nothing fancy.

Just include the header

#include "http_res.h"

License

MIT