How to know when the HTTP headers part is ended?

Question

The server returns the HTTP headers and binary file; something like this:

HTTP/1.1 200 OK
Date: Thu, 28 Jun 2012 22:11:14 GMT
Server: Apache/2.2.3 (Red Hat)
Set-Cookie: JSESSIONID=blabla; Path=/
Pragma: no-cache
Cache-Control: must-revalidate, no-store
Expires: Thu, 01 Jan 1970 00:00:00 GMT
Content-disposition: inline; filename="foo.pdf"
Content-Length: 6231119
Connection: close
Content-Type: application/pdf

%PDF-1.6
%âãÏÓ
5989 0 obj
<</Linearized 1/L 6231119/O 5992/E 371504/N 1498/T 6111290/H [ 55176 6052]>>
endobj

xref
5989 2744
0000000016 00000 n
0000061228 00000 n
0000061378 00000 n

I want to copy only the binary file. But how to know when the headers part is ended? I tried check check if the line contains a \r\n\r\n but looks like this standard does not applies to server response, only to client. This given:

Content-disposition: inline; filename="foo.pdf"
Content-Length: 6231119
Connection: close
Content-Type: application/pdf

%PDF-1.6
%âãÏÓ
5989 0 obj
<</Linearized 1/L 6231119/O 5992/E 371504/N 1498/T 6111290/H [ 55176 6052]>>
endobj

xref
5989 2744
0000000016 00000 n

Here is the C Code:

while((readed = recv(sock, buffer, 128, 0)) > 0) {

    if(isnheader == 0 && strstr(buffer, "\r\n\r\n") != NULL)
        isnheader = 1;

        if(isnheader) 
          fwrite(buffer, 1, readed, fp);
}

UPDATE:

I put a continue control into my if-statement:

if(isnheader == 0 && strstr(buffer, "\r\n\r\n") != NULL) {
    isnheader = 1;
    continue;
}

Well, it works as expected. But as @Alnitak have mentioned, it's not safe.

Answer 1

The header and the body are supposed to be separated by \r\n\r\n (section 4.1 of RFC 2616)

However some servers might omit the \r and only send \n lines, particularly if they fail to sanitise any CGI supplied headers to ensure that they include the \r.

You also need to consider how you're chunking your reads - it's perfectly possible that the separator might span your 128 byte chunks, which will stop the strstr call from working.