Curl_easy_perform returns CURLE_OK when HTTP/1.1 connection reuse fails

[djelinski]

I did this

I'm uploading files to HTTP/1.1 endpoint over SSL using lubcurl. I'm reusing the same easy handle to allow for connection reuse. Every now and then I'm getting CURLE_OK without accompanying HTTP response. Debug logs show the following:

We are completely uploaded and fine
TLSv1.2 (IN), TLS alert, Client hello (1):
Connection died, retrying a fresh connect
necessary data rewind wasn't possible
Closing connection 17
TLSv1.2 (OUT), TLS alert, Client hello (1):

I expected the following

curl_easy_perform should return CURLE_SEND_FAIL_REWIND

curl/libcurl version

[curl -V output]
curl 7.60.0 (i386-pc-win32) libcurl/7.60.0 OpenSSL/1.1.0h (WinSSL) zlib/1.2.11 brotli/1.0.4 WinIDN libssh2/1.8.0 nghttp2/1.32.0
Release-Date: 2018-05-16
Protocols: dict file ftp ftps gopher http https imap imaps ldap ldaps pop3 pop3s rtsp scp sftp smb smbs smtp smtps telnet tftp
Features: AsynchDNS IDN IPv6 Largefile SSPI Kerberos SPNEGO NTLM SSL libz brotli TLS-SRP HTTP2 HTTPS-proxy MultiSSL

operating system

Windows 2008R2

[bagder]

Can you please help us understand how to reproduce this? I've read the code a few times now and I can't see how it can log that message and not return an error... can you?

[djelinski]

This is a tricky one to reproduce in lab, but happens regularly in practice; the other end needs to close the connection after the initial check for dead connection but before the upload completes.
I'm reading the code now and I think this may happen when we enter this:

curl/lib/multi.c

Line 1944 in acefdd0

if(done || (result == CURLE_RECV_ERROR)) {

with done=true and result=CURLE_OK. I'll verify this on Monday.

[djelinski]

Gist of code used to reproduce:

CURL *curl;
curl = curl_easy_init();
curl_easy_setopt(curl, CURLOPT_URL, "https://s3.amazonaws.com");
curl_easy_setopt(curl, CURLOPT_VERBOSE, 1L);
curl_easy_perform(curl);
Sleep(5950); // experimental delay that usually results in the server closing connection while we upload
struct curl_slist *headers = NULL;
headers = curl_slist_append( headers, "Expect:");
curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);
curl_easy_setopt(curl, CURLOPT_UPLOAD, 1L);
curl_easy_setopt(curl, CURLOPT_INFILESIZE, 1L);
curl_easy_setopt(curl, CURLOPT_READFUNCTION, read_callback_dummy );
CURLcode result;
result = curl_easy_perform(curl);
printf("%d",(int)result); // result: 0

With read callback:

size_t read_callback_dummy(void *ptr, size_t size, size_t nmemb, void *stream)
{
static int i = 1;
if(i) {i=0;return 1;}
return 0;
}

[djelinski]

Also my comment above was apparently right; the following patch gives me CURLE_SEND_FAIL_REWIND:
djelinski@dfa8181

I don't understand the code enough to know if this is the right place for this fix or not; let me know if I should file a pull request.

[bagder]

Thanks! I think it looks like a good fix. Please submit a PR for it!