TL;DR: As topic says - need send multipart post body ONLY after process response headers, received after established connection.
According to libcurl documentation, CURLOPT_HEADERFUNCTION gets called by libcurl as soon as it has received header data. But after simple investigation this not happened.
How to reproduce:
Callbacks:
size_t HeaderCallback(void *data, size_t size, size_t nmemb, void *userdata) {
cout << __FUNCTION__ << " " << data << '\n';
return size*nmemb;
}
static int Trace(CURL *handle, curl_infotype type, char *data, size_t size, void *userp) {
cout << __FUNCTION__ << " " <<timestamp<< ' ' << data << endl;
return 0;
}
static size_t ReadFromStateCallBack(void* dst, size_t size, size_t nmemb, void* state) {
cout << __FUNCTION__ << " " <<timestamp<< endl;
return READ();
}
Short main request body:
CURL *curl = curl_easy_init();
curl_slist* h = NULL;
const char * url = "https://upload.box.com/api/2.0/files/content";
curl_httppost *formpost=NULL;
curl_httppost *lastptr=NULL;
curl_formadd(&formpost,&lastptr,
CURLFORM_COPYNAME, "filename",
CURLFORM_CONTENTTYPE, "text/plain",
CURLFORM_FILENAME, "uploadthis.txt",
CURLFORM_STREAM, (void*)state,
CURLFORM_CONTENTSLENGTH, GetFileSize(),
CURLFORM_END);
curl_formadd(&formpost, &lastptr,
CURLFORM_COPYNAME, "parent_id",
CURLFORM_COPYCONTENTS, "0",
CURLFORM_END);
curl_easy_setopt(curl, CURLOPT_VERBOSE, 1L);
curl_easy_setopt(curl, CURLOPT_DEBUGFUNCTION, Trace);
curl_easy_setopt(curl, CURLOPT_URL, url);
curl_easy_setopt(curl, CURLOPT_POST, 1L);
curl_easy_setopt(curl, CURLOPT_HEADERFUNCTION, HeaderCallback);
curl_easy_setopt(curl, CURLOPT_READFUNCTION, ReadFromStateCallBack);
curl_easy_setopt(curl, CURLOPT_READDATA, state);
curl_easy_setopt(curl, CURLOPT_HTTPPOST, formpost);
curl_easy_setopt(curl, CURLOPT_ERRORBUFFER, err_buf);
h = curl_slist_append(h, "Expect: 100-continue");
h = curl_slist_append(h, "Authorization: Bearer WRONGTOKEN");
curl_easy_setopt(curl, CURLOPT_HTTPHEADER, h);
curl_easy_perform(curl);
curl_formfree(formpost);
And then we can recive next log(large number time since c++11 chrono epoch):
Type [0] data: [SSL Related stuff]
Type [0] data: [Done waiting for 100-continue]
ReadFromStateCallBack 1455532592078426519
...
ReadFromStateCallBack 1455532592507779449
HeaderCallback 1455532592937695923 [HTTP/1.1 100 Continue]
HeaderCallback 1455532592937713786 [Date: Mon, 15 Feb 2016 10:36:32 GMT]
Type [0] data: [Server ATS is not blacklisted]
HeaderCallback: 1455532593030759917 [HTTP/1.1 401 Unauthorized]
Additional info from Headers
And as you can see libcurl for own needs processed 100-continue header, but callback for processing headers called only after sending data.
Also it seems all necessary headers received. Example of tcpdump:
13:36:30.425361 IP 192.168.1.70.41895 > 74.112.184.85.https: Flags [S], seq 164841209, win 29200, options [mss 1460,sackOK,TS val 2164947 ecr 0,nop,wscale 7], length 0
13:36:30.639293 IP 74.112.184.85.https > 192.168.1.70.41895: Flags [S.], seq 1336121630, ack 164841210, win 14480, options [mss 1460,sackOK,TS val 2083933652 ecr 2164947,nop,wscale 7], length 0
13:36:30.639337 IP 192.168.1.70.41895 > 74.112.184.85.https: Flags [.], ack 1, win 229, options [nop,nop,TS val 2165000 ecr 2083933652], length 0
13:36:30.640031 IP 192.168.1.70.41895 > 74.112.184.85.https: Flags [P.], seq 1:297, ack 1, win 229, options [nop,nop,TS val 2165000 ecr 2083933652], length 296
13:36:30.853750 IP 74.112.184.85.https > 192.168.1.70.41895: Flags [.], ack 297, win 122, options [nop,nop,TS val 2083933866 ecr 2165000], length 0
13:36:30.861507 IP 74.112.184.85.https > 192.168.1.70.41895: Flags [P.], seq 1:2690, ack 297, win 122, options [nop,nop,TS val 2083933874 ecr 2165000], length 2689
^^^^^ - right here.
13:36:30.861524 IP 192.168.1.70.41895 > 74.112.184.85.https: Flags [.], ack 2690, win 271, options [nop,nop,TS val 2165056 ecr 2083933874], length 0
13:36:30.862654 IP 192.168.1.70.41895 > 74.112.184.85.https: Flags [P.], seq 297:423, ack 2690, win 271, options [nop,nop,TS val 2165056 ecr 2083933874], length 126
13:36:31.076949 IP 74.112.184.85.https > 192.168.1.70.41895: Flags [P.], seq 2690:2741, ack 423, win 122, options [nop,nop,TS val 2083934090 ecr 2165056], length 51
13:36:31.077286 IP 192.168.1.70.41895 > 74.112.184.85.https: Flags [P.], seq 423:693, ack 2741, win 271, options [nop,nop,TS val 2165110 ecr 2083934090], length 270
13:36:31.330808 IP 74.112.184.85.https > 192.168.1.70.41895: Flags [.], ack 693, win 130, options [nop,nop,TS val 2083934344 ecr 2165110], length 0
13:36:32.078397 IP 192.168.1.70.41895 > 74.112.184.85.https: Flags [P.], seq 693:870, ack 2741, win 271, options [nop,nop,TS val 2165360 ecr 2083934344], length 177
13:36:32.078533 IP 192.168.1.70.41895 > 74.112.184.85.https: Flags [.], seq 870:2218, ack 2741, win 271, options [nop,nop,TS val 2165360 ecr 2083934344], length 1348
repeating send data
Because of SSL connection I can`t view tcpdump with -A, to be sure that headers received in suggested part.
Software:
- libcurl(7.36)
- Compiler GCC(4.8.4)
P.S. For me it seems libcurl have wrong behavior for [RFC 2616(8.2.4)] (https://www.w3.org/Protocols/rfc2616/rfc2616-sec8.html)
P.P.S Same behavior if existed Connection: close header.