curl_errno

if someone need more information about curl errors
<?php
$error_codes=array(
[1] => 'CURLE_UNSUPPORTED_PROTOCOL', 
[2] => 'CURLE_FAILED_INIT', 
[3] => 'CURLE_URL_MALFORMAT', 
[4] => 'CURLE_URL_MALFORMAT_USER', 
[5] => 'CURLE_COULDNT_RESOLVE_PROXY', 
[6] => 'CURLE_COULDNT_RESOLVE_HOST', 
[7] => 'CURLE_COULDNT_CONNECT', 
[8] => 'CURLE_FTP_WEIRD_SERVER_REPLY',
[9] => 'CURLE_REMOTE_ACCESS_DENIED',
[11] => 'CURLE_FTP_WEIRD_PASS_REPLY',
[13] => 'CURLE_FTP_WEIRD_PASV_REPLY',
[14]=>'CURLE_FTP_WEIRD_227_FORMAT',
[15] => 'CURLE_FTP_CANT_GET_HOST',
[17] => 'CURLE_FTP_COULDNT_SET_TYPE',
[18] => 'CURLE_PARTIAL_FILE',
[19] => 'CURLE_FTP_COULDNT_RETR_FILE',
[21] => 'CURLE_QUOTE_ERROR',
[22] => 'CURLE_HTTP_RETURNED_ERROR',
[23] => 'CURLE_WRITE_ERROR',
[25] => 'CURLE_UPLOAD_FAILED',
[26] => 'CURLE_READ_ERROR',
[27] => 'CURLE_OUT_OF_MEMORY',
[28] => 'CURLE_OPERATION_TIMEDOUT',
[30] => 'CURLE_FTP_PORT_FAILED',
[31] => 'CURLE_FTP_COULDNT_USE_REST',
[33] => 'CURLE_RANGE_ERROR',
[34] => 'CURLE_HTTP_POST_ERROR',
[35] => 'CURLE_SSL_CONNECT_ERROR',
[36] => 'CURLE_BAD_DOWNLOAD_RESUME',
[37] => 'CURLE_FILE_COULDNT_READ_FILE',
[38] => 'CURLE_LDAP_CANNOT_BIND',
[39] => 'CURLE_LDAP_SEARCH_FAILED',
[41] => 'CURLE_FUNCTION_NOT_FOUND',
[42] => 'CURLE_ABORTED_BY_CALLBACK',
[43] => 'CURLE_BAD_FUNCTION_ARGUMENT',
[45] => 'CURLE_INTERFACE_FAILED',
[47] => 'CURLE_TOO_MANY_REDIRECTS',
[48] => 'CURLE_UNKNOWN_TELNET_OPTION',
[49] => 'CURLE_TELNET_OPTION_SYNTAX',
[51] => 'CURLE_PEER_FAILED_VERIFICATION',
[52] => 'CURLE_GOT_NOTHING',
[53] => 'CURLE_SSL_ENGINE_NOTFOUND',
[54] => 'CURLE_SSL_ENGINE_SETFAILED',
[55] => 'CURLE_SEND_ERROR',
[56] => 'CURLE_RECV_ERROR',
[58] => 'CURLE_SSL_CERTPROBLEM',
[59] => 'CURLE_SSL_CIPHER',
[60] => 'CURLE_SSL_CACERT',
[61] => 'CURLE_BAD_CONTENT_ENCODING',
[62] => 'CURLE_LDAP_INVALID_URL',
[63] => 'CURLE_FILESIZE_EXCEEDED',
[64] => 'CURLE_USE_SSL_FAILED',
[65] => 'CURLE_SEND_FAIL_REWIND',
[66] => 'CURLE_SSL_ENGINE_INITFAILED',
[67] => 'CURLE_LOGIN_DENIED',
[68] => 'CURLE_TFTP_NOTFOUND',
[69] => 'CURLE_TFTP_PERM',
[70] => 'CURLE_REMOTE_DISK_FULL',
[71] => 'CURLE_TFTP_ILLEGAL',
[72] => 'CURLE_TFTP_UNKNOWNID',
[73] => 'CURLE_REMOTE_FILE_EXISTS',
[74] => 'CURLE_TFTP_NOSUCHUSER',
[75] => 'CURLE_CONV_FAILED',
[76] => 'CURLE_CONV_REQD',
[77] => 'CURLE_SSL_CACERT_BADFILE',
[78] => 'CURLE_REMOTE_FILE_NOT_FOUND',
[79] => 'CURLE_SSH',
[80] => 'CURLE_SSL_SHUTDOWN_FAILED',
[81] => 'CURLE_AGAIN',
[82] => 'CURLE_SSL_CRL_BADFILE',
[83] => 'CURLE_SSL_ISSUER_ERROR',
[84] => 'CURLE_FTP_PRET_FAILED',
[84] => 'CURLE_FTP_PRET_FAILED',
[85] => 'CURLE_RTSP_CSEQ_ERROR',
[86] => 'CURLE_RTSP_SESSION_ERROR',
[87] => 'CURLE_FTP_BAD_FILE_LIST',
[88] => 'CURLE_CHUNK_FAILED');

?>

To coder.ua[at]gmail.com:

Please note some errors have more than one constants:

[CURLE_FTP_PARTIAL_FILE]    18
[CURLE_PARTIAL_FILE]    18

[CURLE_HTTP_NOT_FOUND]    22
[CURLE_HTTP_RETURNED_ERROR]    22

[CURLE_OPERATION_TIMEDOUT]    28
[CURLE_OPERATION_TIMEOUTED]    28

[CURLE_BAD_DOWNLOAD_RESUME]    36
[CURLE_FTP_BAD_DOWNLOAD_RESUME]    36

Note that you can detect errors using curl_multi_info_read() in the curl_multi_exec() loop that don't show up later using curl_errno().  This seems particularly true of connection errors.

The manual above only mentions how to get an error description from the cURL handle ($ch) using curl_error():
<?php
$description = curl_error($ch);
?>

But you can also get a description from the error number itself using curl_strerror():
<?php
$description = curl_strerror(curl_errno($ch));
?>

The latter can be useful if you only have access to the error number but not to the cURL handle.

All available curl error constants and values in PHP 5.4.7 on FreeBSD 8.2-RELEASE:

CURLE_UNSUPPORTED_PROTOCOL => 1
CURLE_FAILED_INIT => 2
CURLE_URL_MALFORMAT => 3
CURLE_URL_MALFORMAT_USER => 4
CURLE_COULDNT_RESOLVE_PROXY => 5
CURLE_COULDNT_RESOLVE_HOST => 6
CURLE_COULDNT_CONNECT => 7
CURLE_FTP_WEIRD_SERVER_REPLY => 8
CURLE_FTP_ACCESS_DENIED => 9
CURLE_FTP_USER_PASSWORD_INCORRECT => 10
CURLE_FTP_WEIRD_PASS_REPLY => 11
CURLE_FTP_WEIRD_USER_REPLY => 12
CURLE_FTP_WEIRD_PASV_REPLY => 13
CURLE_FTP_WEIRD_227_FORMAT => 14
CURLE_FTP_CANT_GET_HOST => 15
CURLE_FTP_CANT_RECONNECT => 16
CURLE_FTP_COULDNT_SET_BINARY => 17
CURLE_PARTIAL_FILE => 18
CURLE_FTP_COULDNT_RETR_FILE => 19
CURLE_FTP_WRITE_ERROR => 20
CURLE_FTP_QUOTE_ERROR => 21
CURLE_HTTP_NOT_FOUND => 22
CURLE_WRITE_ERROR => 23
CURLE_MALFORMAT_USER => 24
CURLE_FTP_COULDNT_STOR_FILE => 25
CURLE_READ_ERROR => 26
CURLE_OUT_OF_MEMORY => 27
CURLE_OPERATION_TIMEOUTED => 28
CURLE_FTP_COULDNT_SET_ASCII => 29
CURLE_FTP_PORT_FAILED => 30
CURLE_FTP_COULDNT_USE_REST => 31
CURLE_FTP_COULDNT_GET_SIZE => 32
CURLE_HTTP_RANGE_ERROR => 33
CURLE_HTTP_POST_ERROR => 34
CURLE_SSL_CONNECT_ERROR => 35
CURLE_FTP_BAD_DOWNLOAD_RESUME => 36
CURLE_FILE_COULDNT_READ_FILE => 37
CURLE_LDAP_CANNOT_BIND => 38
CURLE_LDAP_SEARCH_FAILED => 39
CURLE_LIBRARY_NOT_FOUND => 40
CURLE_FUNCTION_NOT_FOUND => 41
CURLE_ABORTED_BY_CALLBACK => 42
CURLE_BAD_FUNCTION_ARGUMENT => 43
CURLE_BAD_CALLING_ORDER => 44
CURLE_HTTP_PORT_FAILED => 45
CURLE_BAD_PASSWORD_ENTERED => 46
CURLE_TOO_MANY_REDIRECTS => 47
CURLE_UNKNOWN_TELNET_OPTION => 48
CURLE_TELNET_OPTION_SYNTAX => 49
CURLE_OBSOLETE => 50
CURLE_SSL_PEER_CERTIFICATE => 51
CURLE_GOT_NOTHING => 52
CURLE_SSL_ENGINE_NOTFOUND => 53
CURLE_SSL_ENGINE_SETFAILED => 54
CURLE_SEND_ERROR => 55
CURLE_RECV_ERROR => 56
CURLE_SHARE_IN_USE => 57
CURLE_SSL_CERTPROBLEM => 58
CURLE_SSL_CIPHER => 59
CURLE_SSL_CACERT => 60
CURLE_BAD_CONTENT_ENCODING => 61
CURLE_LDAP_INVALID_URL => 62
CURLE_FILESIZE_EXCEEDED => 63
CURLE_FTP_SSL_FAILED] => 64

you should look on http://php.net/manual/en/curl.constants.php for the error codes, not on the linked official curl doc. some of the error codes are different, at least the one mentioned on the other page:

in PHP the curl error number 28 is called

CURLE_OPERATION_TIMEOUTED

while in the official site is:

CURLE_OPERATION_TIMEDOUT

CURLcode v7.81 reversed array for PHP  (from \curl\include\curl\curl.h l.495)
https://gist.github.com/nono303/de1256f55e26fdbcc3e0d72e397ac4a1

/!\ ATTENTION if you are using curl multi handles

This function returns 0 in error conditions when run on curl handles accessed via curl_multi_info_read().

You must look at the data returned by curl_multi_info_read() for the true errno. The data is over there instead.

Gets a current list of all CURLE_* error constants, their applicable error messages, and their applicable error codes. Useful for making wrapper classes or for mapping cURL errors to specific Exception objects.

<?php

$list   = get_defined_constants(TRUE);
$list   = preg_grep('/^CURLE_/', array_flip($list['curl']));
$result = array();

foreach ($list as $const) {
    $result[$const] = array
    (
        'code'    => constant($const),
        'message' => curl_strerror(constant($const))
    );
}

echo "<pre>";
echo print_r($result, TRUE);
echo "</pre>";