Description:
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Note that the script below with the CURLOPT_BUFFERSIZE commented illustrates the problem. Uncommenting the CURLOPT_BUFFERSIZE line that sets a 4096 buffer size resolves the problem. 

This appears to confirm the issue report libssh2 #50 (see https://github.com/libssh2/libssh2/issues/50). We encountered timeout failures on our sftp transfers immediately upon upgrading from PHP 5.6.17 to 5.6.18 that seems to have problems with SFTP transfers when using the default buffer size.


Test script:
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$curl = curl_init();
curl_setopt($curl, CURLOPT_URL, $remote);
curl_setopt($curl, CURLOPT_PROTOCOLS, CURLPROTO_SFTP);
curl_setopt($curl, CURLOPT_SSH_AUTH_TYPES, CURLSSH_AUTH_PUBLICKEY);
curl_setopt($curl, CURLOPT_SSH_PRIVATE_KEYFILE, $keysFolder.$keyFileName);         curl_setopt($curl, CURLOPT_KEYPASSWD, $password);                                  //curl_setopt($curl, CURLOPT_BUFFERSIZE, 4096);
curl_setopt($curl, CURLOPT_RETURNTRANSFER, 1);
$data = curl_exec($curl);
$info = curl_getinfo($curl);
myPrintArray($info);