CURLcode
Almost all "easy" interface functions return a CURLcode error code. No matter what, using the curl_easy_setopt option CURLOPT_ERRORBUFFER is a good idea as it will give you a human readable error string that may offer more details about the cause of the error than just the error code. curl_easy_strerror can be called to get an error string from a given CURLcode number.
几乎所有的easy接口函数会返回CURLcode类型的错误码。
无论如何，使用curl_easy_setopt(handle, CURLOPT_ERRORBUFFER)来获取一个人类可读的错误原因字符串，
会比仅仅获取一个错误码要好。
curl_easy_strerror函数可以通过error_code来获取错误原因字符串。
CURLcode is one of the following:
CURLcode错误码如下：
CURLE_OK (0)
All fine. Proceed as usual.
正常
CURLE_UNSUPPORTED_PROTOCOL (1)
The URL you passed to libcurl used a protocol that this libcurl does not support. The support might be a compile-time option that you didn't use, it can be a misspelled protocol string or just a protocol libcurl has no code for.
协议不支持
CURLE_FAILED_INIT (2)
Very early initialization code failed. This is likely to be an internal error or problem, or a resource problem where something fundamental couldn't get done at init time.
初始化失败
CURLE_URL_MALFORMAT (3)
The URL was not properly formatted.
URL未格式化
CURLE_NOT_BUILT_IN (4)
A requested feature, protocol or option was not found built-in in this libcurl due to a build-time decision. This means that a feature or option was not enabled or explicitly disabled when libcurl was built and in order to get it to function you have to get a rebuilt libcurl.
特性、OPTION、协议未识别
CURLE_COULDNT_RESOLVE_PROXY (5)
Couldn't resolve proxy. The given proxy host could not be resolved.
代理无法解析
CURLE_COULDNT_RESOLVE_HOST (6)
Couldn't resolve host. The given remote host was not resolved.
HOST无法解析
CURLE_COULDNT_CONNECT (7)
Failed to connect() to host or proxy.
host或者代理无法连接
CURLE_FTP_WEIRD_SERVER_REPLY (8)
After connecting to a FTP server, libcurl expects to get a certain reply back. This error code implies that it got a strange or bad reply. The given remote server is probably not an OK FTP server.
CURLE_REMOTE_ACCESS_DENIED (9)
We were denied access to the resource given in the URL. For FTP, this occurs while trying to change to the remote directory.
远程资源拒绝访问
CURLE_FTP_ACCEPT_FAILED (10)
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.
CURLE_FTP_WEIRD_PASS_REPLY (11)
After having sent the FTP password to the server, libcurl expects a proper reply. This error code indicates that an unexpected code was returned.
CURLE_FTP_ACCEPT_TIMEOUT (12)
During an active FTP session while waiting for the server to connect, the CURLOPT_ACCEPTTIMOUT_MS(3) (or the internal default) timeout expired.
CURLE_FTP_WEIRD_PASV_REPLY (13)
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.
CURLE_FTP_WEIRD_227_FORMAT (14)
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.
CURLE_FTP_CANT_GET_HOST (15)
An internal failure to lookup the host used for the new connection.
CURLE_HTTP2 (16)
A problem was detected in the HTTP2 framing layer. This is somewhat generic and can be one out of several problems, see the error buffer for details.
http2框架层中出现问题，可以通过error buffer查看详细信息
CURLE_FTP_COULDNT_SET_TYPE (17)
Received an error when trying to set the transfer mode to binary or ASCII.
CURLE_PARTIAL_FILE (18)
A file transfer was shorter or larger than expected. This happens when the server first reports an expected transfer size, and then delivers data that doesn't match the previously given size.
文件传输长度异常。
实际获取到的文件长度和服务器第一次说明文件的长度不符。
CURLE_FTP_COULDNT_RETR_FILE (19)
This was either a weird reply to a 'RETR' command or a zero byte transfer complete.
CURLE_QUOTE_ERROR (21)
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.
当发送QUOTE命令到远程服务器时，服务器返回400或者更大的错误码。
CURLE_HTTP_RETURNED_ERROR (22)
This is returned if CURLOPT_FAILONERROR is set TRUE and the HTTP server returns an error code that is >= 400.
如果设置了CURLOPT_FAILONERROR属性为true，并且服务器返回的http code >= 400
CURLE_WRITE_ERROR (23)
An error occurred when writing received data to a local file, or an error was returned to libcurl from a write callback.
写入本地文件或者写回调错误
CURLE_UPLOAD_FAILED (25)
Failed starting the upload. For FTP, the server typically denied the STOR command. The error buffer usually contains the server's explanation for this.
上传失败
CURLE_READ_ERROR (26)
There was a problem reading a local file or an error returned by the read callback.
读取本地文件或者读回调错误
CURLE_OUT_OF_MEMORY (27)
A memory allocation request failed. This is serious badness and things are severely screwed up if this ever occurs.
内存分配失败
CURLE_OPERATION_TIMEDOUT (28)
Operation timeout. The specified time-out period was reached according to the conditions.
操作超时。
CURLE_FTP_PORT_FAILED (30)
The FTP PORT command returned error. This mostly happens when you haven't specified a good enough address for libcurl to use. See CURLOPT_FTPPORT.
CURLE_FTP_COULDNT_USE_REST (31)
The FTP REST command returned error. This should never happen if the server is sane.
CURLE_RANGE_ERROR (33)
The server does not support or accept range requests.
服务器不支持或接受range方式
CURLE_HTTP_POST_ERROR (34)
This is an odd error that mainly occurs due to internal confusion.
POST错误
CURLE_SSL_CONNECT_ERROR (35)
A problem occurred somewhere in the SSL/TLS handshake. You really want the error buffer and read the message there as it pinpoints the problem slightly more. Could be certificates (file formats, paths, permissions), passwords, and others.
SSL连接错误
CURLE_BAD_DOWNLOAD_RESUME (36)
The download could not be resumed because the specified offset was out of the file boundary.
下载无法被恢复，因为指定的offset超出了文件大小
CURLE_FILE_COULDNT_READ_FILE (37)
A file given with FILE:// couldn't be opened. Most likely because the file path doesn't identify an existing file. Did you check file permissions?
文件不存在、或者权限错误
CURLE_LDAP_CANNOT_BIND (38)
LDAP cannot bind. LDAP bind operation failed.
CURLE_LDAP_SEARCH_FAILED (39)
LDAP search failed.
CURLE_FUNCTION_NOT_FOUND (41)
Function not found. A required zlib function was not found.
CURLE_ABORTED_BY_CALLBACK (42)
Aborted by callback. A callback returned "abort" to libcurl.
回调报错
CURLE_BAD_FUNCTION_ARGUMENT (43)
Internal error. A function was called with a bad parameter.
函数调用参数出错
CURLE_INTERFACE_FAILED (45)
Interface error. A specified outgoing interface could not be used. Set which interface to use for outgoing connections' source IP address with CURLOPT_INTERFACE.
接口错误，指定的外部接口无法被调用。
CURLE_TOO_MANY_REDIRECTS (47)
Too many redirects. When following redirects, libcurl hit the maximum amount. Set your limit with CURLOPT_MAXREDIRS.
重定向次数过多。当自动跟随重定向时，达到了最大跳转次数。
可以通过CURLOPT_MAXREDIRS设置重定向次数。
CURLE_UNKNOWN_OPTION (48)
An option passed to libcurl is not recognized/known. Refer to the appropriate documentation. This is most likely a problem in the program that uses libcurl. The error buffer might contain more specific information about which exact option it concerns.
OPTION未识别。
CURLE_TELNET_OPTION_SYNTAX (49)
A telnet option string was Illegally formatted.
CURLE_PEER_FAILED_VERIFICATION (51)
The remote server's SSL certificate or SSH md5 fingerprint was deemed not OK.
CURLE_GOT_NOTHING (52)
Nothing was returned from the server, and under the circumstances, getting nothing is considered an error.
服务器什么都没返回
CURLE_SSL_ENGINE_NOTFOUND (53)
The specified crypto engine wasn't found.
CURLE_SSL_ENGINE_SETFAILED (54)
Failed setting the selected SSL crypto engine as default!
CURLE_SEND_ERROR (55)
Failed sending network data.
发送数据失败
CURLE_RECV_ERROR (56)
Failure with receiving network data.
接受数据失败
CURLE_SSL_CERTPROBLEM (58)
problem with the local client certificate.
CURLE_SSL_CIPHER (59)
Couldn't use specified cipher.
CURLE_SSL_CACERT (60)
Peer certificate cannot be authenticated with known CA certificates.
CURLE_BAD_CONTENT_ENCODING (61)
Unrecognized transfer encoding.
传输编码不识别
CURLE_LDAP_INVALID_URL (62)
Invalid LDAP URL.
CURLE_FILESIZE_EXCEEDED (63)
Maximum file size exceeded.
超过最大文件大小
CURLE_USE_SSL_FAILED (64)
Requested FTP SSL level failed.
CURLE_SEND_FAIL_REWIND (65)
When doing a send operation curl had to rewind the data to retransmit, but the rewinding operation failed.
rewind操作失败
CURLE_SSL_ENGINE_INITFAILED (66)
Initiating the SSL Engine failed.
CURLE_LOGIN_DENIED (67)
The remote server denied curl to login (Added in 7.13.1)
CURLE_TFTP_NOTFOUND (68)
File not found on TFTP server.
CURLE_TFTP_PERM (69)
Permission problem on TFTP server.
CURLE_REMOTE_DISK_FULL (70)
Out of disk space on the server.
CURLE_TFTP_ILLEGAL (71)
Illegal TFTP operation.
CURLE_TFTP_UNKNOWNID (72)
Unknown TFTP transfer ID.
CURLE_REMOTE_FILE_EXISTS (73)
File already exists and will not be overwritten.
CURLE_TFTP_NOSUCHUSER (74)
This error should never be returned by a properly functioning TFTP server.
CURLE_CONV_FAILED (75)
Character conversion failed.
CURLE_CONV_REQD (76)
Caller must register conversion callbacks.
CURLE_SSL_CACERT_BADFILE (77)
Problem with reading the SSL CA cert (path? access rights?)
CURLE_REMOTE_FILE_NOT_FOUND (78)
The resource referenced in the URL does not exist.
CURLE_SSH (79)
An unspecified error occurred during the SSH session.
CURLE_SSL_SHUTDOWN_FAILED (80)
Failed to shut down the SSL connection.
CURLE_AGAIN (81)
Socket is not ready for send/recv wait till it's ready and try again. This return code is only returned from curl_easy_recv and curl_easy_send (Added in 7.18.2)
socket未准备好，无法进行读写操作。
只有curl_easy_recv和curl_easy_send会返回这个错误。
CURLE_SSL_CRL_BADFILE (82)
Failed to load CRL file (Added in 7.19.0)
CURLE_SSL_ISSUER_ERROR (83)
Issuer check failed (Added in 7.19.0)
CURLE_FTP_PRET_FAILED (84)
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 PRET CMD before PASV as well. (Added in 7.20.0)
CURLE_RTSP_CSEQ_ERROR (85)
Mismatch of RTSP CSeq numbers.
CURLE_RTSP_SESSION_ERROR (86)
Mismatch of RTSP Session Identifiers.
CURLE_FTP_BAD_FILE_LIST (87)
Unable to parse FTP file list (during FTP wildcard downloading).
CURLE_CHUNK_FAILED (88)
Chunk callback reported error.
Chunk回调错误
CURLE_NO_CONNECTION_AVAILABLE (89)
(For internal use only, will never be returned by libcurl) No connection available, the session will be queued. (added in 7.30.0)
CURLE_OBSOLETE*
These error codes will never be returned. They were used in an old libcurl version and are currently unused.
CURLMcode
This is the generic return code used by functions in the libcurl multi interface. Also consider curl_multi_strerror.
multi接口返回
CURLM_CALL_MULTI_PERFORM (-1)
This is not really an error. It means you should call curl_multi_perform again without doing select() or similar in between. Before version 7.20.0 this could be returned by curl_multi_perform, but in later versions this return code is never used.
这不算是个错误。这代表你可以不需要做类似select之类的操作，直接再次调用curl_multi_perform。
在7.20.0版本前curl_multi_perform会返回，在之后的版本就不再使用了。
CURLM_OK (0)
Things are fine.
一切正常
CURLM_BAD_HANDLE (1)
The passed-in handle is not a valid CURLM handle.
传入的Mutli handle无效。
CURLM_BAD_EASY_HANDLE (2)
An easy handle was not good/valid. It could mean that it isn't an easy handle at all, or possibly that the handle already is in used by this or another multi handle.
easy handle无效。
可能这不是一个easy handle，或者这个easy handle已经存在与这个multi handle中或其他multi handle中。
CURLM_OUT_OF_MEMORY (3)
You are doomed.
你完了。。
CURLM_INTERNAL_ERROR (4)
This can only be returned if libcurl bugs. Please report it to us!
内部错误
CURLM_BAD_SOCKET (5)
The passed-in socket is not a valid one that libcurl already knows about. (Added in 7.15.4)
传入的socket无效。
CURLM_UNKNOWN_OPTION (6)
curl_multi_setopt() with unsupported option (Added in 7.15.4)
curl_multi_setopt不支持这个选项。
CURLM_ADDED_ALREADY (7)
An easy handle already added to a multi handle was attempted to get added a second time. (Added in 7.32.1)
easy handle已经存在于multi handle中，无法添加
CURLSHcode
The "share" interface will return a CURLSHcode to indicate when an error has occurred. Also consider curl_share_strerror.
CURLSHE_OK (0)
All fine. Proceed as usual.
CURLSHE_BAD_OPTION (1)
An invalid option was passed to the function.
CURLSHE_IN_USE (2)
The share object is currently in use.
CURLSHE_INVALID (3)
An invalid share object was passed to the function.
CURLSHE_NOMEM (4)
Not enough memory was available. (Added in 7.12.0)
CURLSHE_NOT_BUILT_IN (5)
The requested sharing could not be done because the library you use don't have that particular feature enabled. (Added in 7.23.0)