List of common cURL Error Codes

Below is the list of most common error codes and its meaning in cURL.

cURL Error Code	cURLcode	Description
0	CURLE_OK	All fine. Proceed as usual.
1	CURLE_UNSUPPORTED_PROTOCOL	The URL you passed to libcurl used a protocol that this libcurl does not support.
2	CURLE_FAILED_INIT	Early initialization code failed.
3	CURLE_URL_MALFORMAT	The URL was not properly formatted.
4	CURLE_NOT_BUILT_IN	A requested feature, protocol, or option was not found built-in in this libcurl due to a build-time decision.
5	CURLE_COULDNT_RESOLVE_PROXY	Could not resolve the proxy host.
6	CURLE_COULDNT_RESOLVE_HOST	Could not resolve the host.
7	CURLE_COULDNT_CONNECT	Failed to connect to host or proxy.
8	CURLE_WEIRD_SERVER_REPLY	The server sent data libcurl could not parse.
9	CURLE_REMOTE_ACCESS_DENIED	We were denied access to the resource given in the URL.
10	CURLE_FTP_ACCEPT_FAILED	While waiting for the server to connect back when an active FTP session is used, an error code was sent over the control connection or similar.
11	CURLE_FTP_WEIRD_PASS_REPLY	After having sent the FTP password to the server, libcurl expects a proper reply. This error code indicates that an unexpected code was returned.
12	CURLE_FTP_ACCEPT_TIMEOUT	During an active FTP session while waiting for the server to connect, the CURLOPT_ACCEPTTIMEOUT_MS (or the internal default) timeout expired.
13	CURLE_FTP_WEIRD_PASV_REPLY	libcurl failed to get a sensible result back from the server as a response to either a PASV or a EPSV command. The server is flawed.
14	CURLE_FTP_WEIRD_227_FORMAT	FTP servers return a 227-line as a response to a PASV command. If libcurl fails to parse that line, this return code is passed back.
15	CURLE_FTP_CANT_GET_HOST	An internal failure to lookup the host used for the new connection.
16	CURLE_HTTP2	A problem was detected in the HTTP2 framing layer.
17	CURLE_FTP_COULDNT_SET_TYPE	Received an error when trying to set the transfer mode to binary or ASCII.
18	CURLE_PARTIAL_FILE	A file transfer was shorter or larger than expected.
19	CURLE_FTP_COULDNT_RETR_FILE	This was either a weird reply to a 'RETR' command or a zero byte transfer complete.
21	CURLE_QUOTE_ERROR	When sending custom "QUOTE" commands to the remote server, one of the commands returned an error code that was 400 or higher (for FTP) or otherwise indicated unsuccessful completion of the command.
22	CURLE_HTTP_RETURNED_ERROR	This is returned if CURLOPT_FAILONERROR is set TRUE and the HTTP server returns an error code that is >= 400.
23	CURLE_WRITE_ERROR	An error occurred when writing received data to a local file, or an error was returned to libcurl from a write callback.
25	CURLE_UPLOAD_FAILED	Failed starting the upload. For FTP, the server typically denied the STOR command. The error buffer usually contains the server's explanation for this.
26	CURLE_READ_ERROR	There was a problem reading a local file or an error returned by the read callback.
27	CURLE_OUT_OF_MEMORY	A memory allocation request failed.
28	CURLE_OPERATION_TIMEDOUT	Operation timeout. The specified time-out period was reached according to the conditions.
30	CURLE_FTP_PORT_FAILED	The FTP PORT command returned an error.
31	CURLE_FTP_COULDNT_USE_REST	The FTP REST command returned an error.
33	CURLE_RANGE_ERROR	The server does not support or accept range requests.
34	CURLE_HTTP_POST_ERROR	An odd error that mainly occurs due to internal confusion.
35	CURLE_SSL_CONNECT_ERROR	A problem occurred somewhere in the SSL/TLS handshake.
36	CURLE_BAD_DOWNLOAD_RESUME	The download could not be resumed because the specified offset was out of the file boundary.
37	CURLE_FILE_COULDNT_READ_FILE	A file given with FILE:// could not be opened.
38	CURLE_LDAP_CANNOT_BIND	LDAP cannot bind. LDAP bind operation failed.
39	CURLE_LDAP_SEARCH_FAILED	LDAP search failed.
41	CURLE_FUNCTION_NOT_FOUND	Function not found. A required zlib function was not found.
42	CURLE_ABORTED_BY_CALLBACK	Aborted by callback. A callback returned "abort" to libcurl.
43	CURLE_BAD_FUNCTION_ARGUMENT	A function was called with a bad parameter.
45	CURLE_INTERFACE_FAILED	Interface error. A specified outgoing interface could not be used.
47	CURLE_TOO_MANY_REDIRECTS	Too many redirects. When following redirects, libcurl hit the maximum amount.
48	CURLE_UNKNOWN_OPTION	An option passed to libcurl is not recognized/known.
49	CURLE_SETOPT_OPTION_SYNTAX	An option passed in to a setopt was wrongly formatted.
50-51	Obsolete errors	Not used in modern versions.
52	CURLE_GOT_NOTHING	Nothing was returned from the server, and getting nothing is considered an error.
53	CURLE_SSL_ENGINE_NOTFOUND	The specified crypto engine was not found.
54	CURLE_SSL_ENGINE_SETFAILED	Failed setting the selected SSL crypto engine as default.
55	CURLE_SEND_ERROR	Failed sending network data.
56	CURLE_RECV_ERROR	Failure with receiving network data.
57	Obsolete error	Not used in modern versions.
58	CURLE_SSL_CERTPROBLEM	Problem with the local client certificate.
59	CURLE_SSL_CIPHER	Could not use the specified cipher.
60	CURLE_PEER_FAILED_VERIFICATION	The remote server's SSL certificate or SSH fingerprint was deemed not OK.
61	CURLE_BAD_CONTENT_ENCODING	Unrecognized transfer encoding.
62	Obsolete error	Not used in modern versions.
63	CURLE_FILESIZE_EXCEEDED	Maximum file size exceeded.
64	CURLE_USE_SSL_FAILED	Requested FTP SSL level failed.
65	CURLE_SEND_FAIL_REWIND	When doing a send operation, curl had to rewind the data to retransmit, but the rewinding operation failed.
66	CURLE_SSL_ENGINE_INITFAILED	Initiating the SSL Engine failed.
67	CURLE_LOGIN_DENIED	The remote server denied curl to login (Added in 7.13.1).
68	CURLE_TFTP_NOTFOUND	File not found on TFTP server.
69	CURLE_TFTP_PERM	Permission problem on TFTP server.
70	CURLE_REMOTE_DISK_FULL	Out of disk space on the server.
71	CURLE_TFTP_ILLEGAL	Illegal TFTP operation.
72	CURLE_TFTP_UNKNOWNID	Unknown TFTP transfer ID.
73	CURLE_REMOTE_FILE_EXISTS	File already exists and will not be overwritten.
74	CURLE_TFTP_NOSUCHUSER	This error should never be returned by a properly functioning TFTP server.
75-76	Obsolete errors	Not used in modern versions.
77	CURLE_SSL_CACERT_BADFILE	Problem with reading the SSL CA cert (path? access rights?)
78	CURLE_REMOTE_FILE_NOT_FOUND	The resource referenced in the URL does not exist.
79	CURLE_SSH	An unspecified error occurred during the SSH session.
80	CURLE_SSL_SHUTDOWN_FAILED	Failed to shut down the SSL connection.
81	CURLE_AGAIN	Socket is not ready for send/recv; wait till it's ready and try again. (Added in 7.18.2)
82	CURLE_SSL_CRL_BADFILE	Failed to load CRL file (Added in 7.19.0)
83	CURLE_SSL_ISSUER_ERROR	Issuer check failed (Added in 7.19.0)
84	CURLE_FTP_PRET_FAILED	The FTP server does not understand the PRET command at all or does not support the given argument. Be careful when using CURLOPT_CUSTOMREQUEST; a custom LIST command will be sent with the PRET command before PASV as well. (Added in 7.20.0)
85	CURLE_RTSP_CSEQ_ERROR	Mismatch of RTSP CSeq numbers.
86	CURLE_RTSP_SESSION_ERROR	Mismatch of RTSP Session Identifiers.
87	CURLE_FTP_BAD_FILE_LIST	Unable to parse FTP file list (during FTP wildcard downloading).
88	CURLE_CHUNK_FAILED	Chunk callback reported an error.
89	CURLE_NO_CONNECTION_AVAILABLE	(For internal use only, will never be returned by libcurl) No connection available, the session will be queued. (Added in 7.30.0)
90	CURLE_SSL_PINNEDPUBKEYNOTMATCH	Failed to match the pinned key specified with CURLOPT_PINNEDPUBLICKEY.
91	CURLE_SSL_INVALIDCERTSTATUS	Status returned failure when asked with CURLOPT_SSL_VERIFYSTATUS.
92	CURLE_HTTP2_STREAM	Stream error in the HTTP/2 framing layer.
93	CURLE_RECURSIVE_API_CALL	An API function was called from inside a callback.
94	CURLE_AUTH_ERROR	An authentication function returned an error.
95	CURLE_HTTP3	A problem was detected in the HTTP/3 layer. This is somewhat generic and can be one out of several problems; see the error buffer for details.
96	CURLE_QUIC_CONNECT_ERROR	QUIC connection error. This error may be caused by an SSL library error. QUIC is the protocol used for HTTP/3 transfers.
97	CURLE_PROXY	Proxy handshake error. CURLINFO_PROXY_ERROR provides extra details on the specific problem.
98	CURLE_SSL_CLIENTCERT	SSL Client Certificate required.
99	CURLE_UNRECOVERABLE_POLL	An internal call to poll() or select() returned an error that is not recoverable.

Reference: https://curl.se/libcurl/c/libcurl-errors.html

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