Using CURLOPT_WRITEFUNCTION along with CURLOPT_HEADERFUNCTION

[Daniel Stenberg via curl-users]

On Fri, 26 Mar 2021, kent williams via curl-users wrote:

First: there's a dedicated mailing list for libcurl that's usually more
suitable for libcurl topics: curl-library

So, naturally, I get a request to allow both at once.  The catch is that if
you turn on CURLOPT_HEADER, the headers always go into the data sent to the
CURLOPT_WRITEFUNCTION.

If you want them separate, why force the headers into the same callback?

I have a solution but it feels kind of wonky. The CURLOPT_WRITEFUNCTION
buffers all the data it gets, and checks it for "\r\n\r\n"  Once it sees
that, it knows the headers are done, and writes the rest of the data to file.

... or you would just use *separate* callbacks as libcurl already split the
headers from the body for you?

I didn't find a CURLOPT that tells libcurl "don't send headers to the
CURLOPT_WRITEFUNCTION."

That's the default behavior. You changed it by setting CURLOPT_HEADER to 1.
You can switch it off again by setting CURLOPT_HEADER to 0.

I also didn't see any guarantee that the CURLOPT_WRITEFUNCTION can depend on
its data being null-terminated strings, a line at a time, though that
certainly is what I observed.

I think this quote from the man page is pretty clear on this topic:

The data passed to this function will not be null-terminated!

And also: the data provided in the write callback is not "strings" at all. It
is binary data that might be text at times.