curl_exec curl request returns false, curl_error return empty
提交数据到https时，需要pem证书来加密。
我们使用浏览器访问https的时候，浏览器会自动加载网站的安全证书进行加密。但是你用curl请求https时，没有通过浏览器，就只有自己手动增加一个安全证书进行加密。 $curl=curl_init();
curl_setopt ( $curl, CURLOPT_URL, $url);
curl_setopt ( $curl, CURLOPT_POST, 1 );
curl_setopt ( $curl, CURLOPT_RETURNTRANSFER, 1 );
curl_setopt ( $curl, CURLOPT_POSTFIELDS, $data );
curl_setopt ( $curl, CURLOPT_TIMEOUT, 2);
// 为保证服务器之间数据传输的安全性，所有的https方式调用，必须使用下面2行代码打开ssl安全校验。
curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($curl, CURLOPT_SSL_VERIFYHOST, false);
$value = curl_exec($curl);
curl_close($curl);So you can get to the
`0` normal access
`1` wrong protocol is not supported by the protocol. This version cURL does not support this agreement.
2 `` failed initialization code initialization failed.
3` URL incorrectly formatted `URL is malformed. Syntax is incorrect.
4 `` request protocol error
5 `` can not resolve the proxy agent can not resolve. Unable to resolve a given proxy host.
6 `` can not resolve the host address can not resolve the host. Unable to resolve the given remote host.
7 'Unable to connect to host `can not connect to the host.
8` remote server is not abnormal response by `FTP server. cURL can not parse the data sent by the server.
9 `` FTP access to a resource error Access is denied. The server refuses to sign or can not obtain a particular resource or directory you want. Most likely you are attempting to enter a directory on the server does not exist.
11` FTP password error `FTP abnormal PASS reply. cURL can not be resolved to send a response to the request of the PASS.
13 'erroneous results `FTP unusual in PASV response, cURL can not be resolved to send a response to the PASV request.
14` FTP command `FTP PASV response to abnormal 227 format. cURL can not resolve 227 lines sent by the server.
15 'internal fault `FTP can not connect to the host. Unable to resolve host IP acquired in the 227 line.
17 'is set to binary `FTP transfer mode can not be set to binary transmission. You can not change the transmission mode to binary.
File transfer 18` `short or greater than the expected part of the file. Only part of the file is transmitted.
19` RETR command transfer is complete `FTP can not download / access a given file, RETR (or similar) command failed.
21 `` FTP quote command completed successfully error. quote command returns an error from the server.
22` return to normal `HTTP page not found. The requested URL could not find or return another 400 or more errors HTTP. This return code only appears in the use of the -f / - fail option in the future.
23 '' written data write failure error. cURL can not write to the local file system, or similar purposes.
25 `` FTP upload not start not STOR file. Server rejected the STOR operation for FTP upload.
26 'callback error `read error. Read all kinds of problems.
27 'memory allocation request fails `out of memory. Memory allocation request fails.
`28` access timeout operation timed out. Arrived at the designated time-out period conditions.
30` FTP port error `FTP PORT failed. PORT command failed. Not all servers support FTP PORT command, try using (PASV) transfer instead of passive!
31` FTP error `FTP REST command can not be used. REST command failed. This command is used to recover FTP transfers.
33 'does not support the request `HTTP range error. range "command" does not work.
34` internal error occurred `HTTP POST error. POST requests internal error.
35` SSL / TLS handshake failure `SSL connection errors. SSL handshake failed.
36` download can not be recovered `FTP resume damaged. Earlier this download can not continue to be suspended.
`37` file permission error file can not be read. Unable to open file. Permissions issue?
38` LDAP can be non-binding `LDAP not binding. LDAP bind (bind) operation failed.
39` LDAP search fails `LDAP search fails.
41 'function does not find `function can not be found. LDAP can not find the necessary functions.
42 'abort callback `terminated by the callback. Application informed cURL terminate the operation.
43 'Internal Error' internal error. It made an incorrect parameter to call the function.
`45` Interface error interface error. Specified outgoing interface could not be used.
47` too many redirects `too many redirects. cURL reached the maximum limit set by following the redirect with
48 'does not recognize the option `An unknown TELNET options.
`49` TELNET malformed malformed telnet options.
`Peer SSL certificate SSL certificate of the remote server 51 'of the MD5 or SSH fingerprint is not OK.
52 'server returns nothing `server without any response, the case is considered to be a mistake here.
`53` encryption engine is not found can not find the SSL encryption engine.
54` set the default SSL encryption fails `SSL encryption engine can not be set as the default.
`55` not send network data network to send data failed.
Receiving network data `56` failure failed in the receiving network data.
57`
58` local client certificate `local certificate in question.
`59` can not use a password can not be used to specify the SSL password.
60 'credentials could not be verified `peer certificate can not be known CA certificate validation.
61` Unrecognized transfer encoding `Unrecognized transfer encoding.
62` invalid LDAP URL` invalid LDAP URL.
`63` file exceeds the maximum size exceeds the maximum file size.
64` FTP SSL level `Fail Fail requirements of FTP.
`65` rewinding operation failed rewinding transmitting the data required (rewind) fails.
`66` SSL engine failed to initialize SSL engine failure.
`67` server rejects the login user name, password or similar information is not accepted, cURL login fails.
68` file not found 'file not found on the TFTP server.
69` no authority `TFTP server permissions problem.
70 'beyond the `TFTP server server disk space is insufficient disk space.
71 'illegal' illegal operation TFTP TFTP operation.
72 'ID` unknown unknown TFTP transfer TFTP transfer number (ID).
`73` file already exists file already exists (TFTP).
74` `No such user error TFTP server (TFTP).
75` character conversion fails `character conversion failed.
76 'callback' needs must be recorded character conversion function.
77` CA certificate authority `read SSL certificate problems (path? Access rights?).
78` URL referenced in the resources do not exist `URL referenced resource does not exist.
79` error occurred during the SSH session `SSH session An unknown error occurred.
80 '' can not close the SSL connection fails to shut down the SSL connection.
81` service is not ready
82 'Could not load file' can not load CRL CRL file is missing or incorrectly formatted (increase in version 7.19.0 in).
`83` issuer check fails to issue the check fails (the increase in version 7.19.0).