How to get a substring up to "\r\n\r\n"

Question

I have the following string:

HTTP/1.1 200 OK
Date: Tue, 06 Dec 2011 11:53:22 GMT
Server: Apache/2.2.14 (Ubuntu)
X-Powered-By: PHP/5.3.2-1ubuntu4.9
Vary: Accept-Encoding
Content-Encoding: gzip
Content-Length: 48
Content-Type: text/html

��(�ͱ���I�O����H�����ч��
                          �4�@��AQ������t

I want to extract up to the "\r\n\r\n", discarding the binary data. I.e. :

HTTP/1.1 200 OK
Date: Tue, 06 Dec 2011 11:53:22 GMT
Server: Apache/2.2.14 (Ubuntu)
X-Powered-By: PHP/5.3.2-1ubuntu4.9
Vary: Accept-Encoding
Content-Encoding: gzip
Content-Length: 48
Content-Type: text/html

How to do this in C?

Cyclonecode · Accepted Answer · 2020-08-06T23:00:32.137

This could easily be done by simple finding the first two sequential linebreaks, since this terminates the header, and then copy everything upto that point to a separate buffer:

// Find the end of the header, which is terminated
// by two line breaks
char* end = strstr(header, "\r\n\r\n");
char* buffer = 0;
if (end) {
    // Allocate memory to hold the entire header
    buffer = malloc((end - header) + 1);
    if (buffer) {
        // Copy header to buffer
        memcpy(buffer, header, end - header);
        // NULL terminate the buffer
        buffer[end - header] = 0;
        // Do something with the buffer here
    
        // Don't forget to release the allocated memory
        free(buffer);
    }
}

Shouldn't that be alloc((end - header) + 1) so that the 0x00 is also stored in valid allocated memory? — Folkert van Heusden, Dec 06 '11 at 12:50

score 1 · Answer 2 · answered Dec 06 '11 at 12:46

1

You could use the strstr function.

But be aware that there exist good C libraries for HTTP client (like libcurl) and for HTTP server (like onion) sides. And that HTTP is complex in its details.

answered Dec 06 '11 at 12:46

Basile Starynkevitch

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I tried strstr, but it returns a pointer to the binary data! `strstr(buf,"\r\n\r\n")` - how to overcome this? – Eamorr Dec 06 '11 at 12:48
Of course it does, you'll need to manipulate everything UP TO the pointer returned by strstr (see @Krister Andersson post below) – KevinDTimm Dec 06 '11 at 12:53

How to get a substring up to "\r\n\r\n"

2 Answers2