A, LibCurl basic programming framework
2. calls curl_easy_init to () function to get the pointer type easy interface
3. Invoke of curl_easy_setopt () Set transfer option
according of curl_easy_setopt () transfer option is set to achieve a user callback function to accomplish specific tasks
5. call curl_easy_perform () function to complete the transfer task
6. call curl_easy_cleanup () to release memory
provided in the whole process over curl_easy_setopt ( ) is the most critical parameter, almost all programs have to use the libcurl it.
1.CURLcode curl_global_init (long flags);
Description:
This function can only be used once. (In fact, still reusable after calling curl_global_cleanup function)
If this function is not called when curl_easy_init function call, it is automatically called by speaking libcurl library, so the next best multi-threaded initiative to call this function in order to prevent multiple threads when curl_easy_init invocation.
Parameters: flags
CURL_GLOBAL_ALL // initialize all possible calls.
CURL_GLOBAL_SSL // initialize supports Secure Sockets Layer.
Win32 CURL_GLOBAL_WIN32 // initialize the socket library.
CURL_GLOBAL_NOTHING // no additional initialization.
Description: At the end libcurl used for clean-up work to do to curl_global_init. Similar to the function of close.
Description:
curl_easy_init used to initialize a CURL pointer of (somewhat like a pointer to the same type of return FILE) appropriate use curl_easy_cleanup clean up at the end of the function call.
General curl_easy_init mean a session start it. It returns a easy_handle (CURL * objects) are generally used in functions easy series.
; Description:
. This call is used to end a conversation with curl_easy_init combined with
parameters:
the CURL pointer type.
CURLoption option, parameter); Description: This function is most important almost all of the curl program must use it frequently it tells curl library program will have to see how the behavior of such a.... web page html code and other parameters (this function somewhat like ioctl function):.
1 CURL pointer of type
2 CURLoption various types of options (both defined in the curl.h Curry, man can also view)
3 this parameter is the parameter either a pointer to a function, can also be a pointer to an object, it can be a long type variable. it is what it depends on the second parameter.
the value of this parameter CURLoption a lot. You can view the specific man pages.
The Option up and running parameters:.
CURL type of pointer.
parameters This section describes curl_easy_setopt in with http relevant. This function is a very important function curl, curl all the settings are done in the function, the function of numerous setting options, note that this section only describes some common options.
callback function prototype: size_t function (PTR void *, size_t size, size_t of nmemb, void * Stream); function libcurl data received after the call, so the function of the stored data do functions such as handling download file.
callback function prototype is size_t function (void * ptr, size_t size, size_t nmemb, void * stream); http header after libcurl data received once the function call.
will call the function CURLOPT_READFUNCTION specified when libCurl need to read data to a remote host,
CURLOPT_TIMEOUT since the transmission time, CURLOPT_CONNECTIONTIMEOUT connection waiting time is provided
set relocation URL
HTTP settings. Char * CURLOPT_RANGE specify parameters passed to libcurl, for RANGE http header field in the domain, for example:
represents the first 500 bytes: bytes = 0-499
represents the second 500 bytes: bytes = 500-999
indicates that the last 500 byte: bytes = -500
represents the range of the subsequent 500 bytes: bytes = 500-
first and last bytes: bytes = 0-0, -1
specify several ranges: bytes = 500-600,601-999
CURLOPT_RESUME_FROM a long argument passed to libcurl, specify the offset you want to start passing.
This function is to complete all the options curl_easy_setopt specified in this section focuses on curl_easy_perform return value. Return 0 means everything ok, representatives of non-zero error. The main error code Description:
1.CURLE_OK
task is completed everything
2.CURLE_UNSUPPORTED_PROTOCOL
unsupported protocol, designated by the head of the URL
3.CURLE_COULDNT_CONNECT
can not connect to a remote host or proxy
4.CURLE_REMOTE_ACCESS_DENIED
access was denied
5.CURLE_HTTP_RETURNED_ERROR
Http return an error
6 .CURLE_READ_ERROR
read local file errors
when transmitting http request using libcurl, it will automatically add some http header. We can replace manually CURLOPT_HTTPHEADER properties, add or delete HTTP message headers.
Host
HTTP1.1 (most http1.0) versions require clients to request this information first.
Pragma
"NO-Cache." It means you can not buffer data.
The Accept
"* / *." It denotes allowed to receive any type of data.
Expect
When submitting a request to the server in HTTP POST manner, the message header libcurl is set as "100-continue", it requires the server to process the request before the formal, returns a "OK" message. If the POST data is small, libcurl may not set the message header.
HTTP protocol provides the message header, the request header is used to tell the server how to handle the request; response message header tells the browser how to process the received data. In libcurl, you can freely add these headers:
struct curl_slist *headers=NULL; /*init to NULL is important*/ headers = curl_slist_append (headers, "the Accept: * / *");
headers = curl_slist_append (headers, "Pragma: NO-Cache");
headers = curl_slist_append (headers, "the Host: HTTP 1.1");
of curl_easy_setopt (easyhandle, CURLOPT_HTTPHEADER, headers);
curl_easy_perform (easyhandle); / * Transfer HTTP * /
/ * Free the header List * /; curl_slist_free_all (headers)
to delete the message header
for an existing message header, provided it is empty, libcurl transmission request this message will not be submitted at the same head:
headers = curl_slist_append (headers, "the Accept:");
Seven multi-threading issues
first a basic principle: that should never share the same libcurl handle (CURL * objects) between threads, or whether it is easy handle multi handle (this article only describes easy_handle). A thread can only use a handle.
Eight, libcurl does not work when
a transmission failure is always a reason. You might set the wrong attribute some of libcurl or not properly understand the meaning of certain properties, or the remote host to return some content can not be properly resolved.
There is a golden rule to address these problems: The CURLOPT_VERBOSE property to 1, libcurl outputs some details of the communication process. If you are using the http protocol, the first request / response header will be output. The CURLOPT_HEADER set to 1, the header information will appear in the content of the message.
Of course, it is undeniable that, libcurl there bug.
If you are more understanding of the relevant agreements, in the use of libcurl, less likely to make mistakes.
Nine, on a password
when the client sends a request to the server, many protocols require a user name and password. libcurl provides several ways to set them.
Some protocol support in the URL directly specify a username and password, like: protocol: // user: [email protected]/path/. libcurl correctly identify this user name and password in the URL and performs a corresponding operation. If there are special characters in the user name and password you provided, first of all it should be URL encoded.
You can also set up a user name and password by CURLOPT_USERPWD property. Parameters such as the format "user: password" string:
curl_easy_setopt (easy_handle, CURLOPT_USERPWD, "user_name: password") ;
sometimes when accessing the proxy server, may from time to time requires a user name and password for user authentication. In this case, libcurl provides another property CURLOPT_PROXYUSERPWD:
curl_easy_setopt (easy_handle, CURLOPT_PROXYUSERPWD, "user_name: password");
In the UNIX platform, access to the FTP user name and password may be stored in $ HOME / .netrc file. libcurl support to obtain a user name and password directly from the file:
curl_easy_setopt (easy_handle, CURLOPT_NETRC, 1L);
when using SSL, may be required to provide a private key for secure transmission of data, the private key is set by CURLOPT_KEYPASSWD:
curl_easy_setopt(easy_handle, CURLOPT_KEYPASSWD, "keypassword");
Ten, HTTP validation
when using the HTTP protocol, a client there are many ways to provide authentication information to the server. The default authentication method is HTTP "Basic", it username and password in clear text, stored after Base64 encoded in the HTTP request header, to the server. Of course, this is not very safe.
The current version of libcurl authentication methods are supported: basic, Digest, NTLM, Negotiate , GSS-Negotiate and SPNEGO. : (Translator sigh: Web engage in so many years, do not necessarily know Http authentication methods, it is ashamed.) You can set a specific authentication by CURLOPT_HTTPAUTH property
; curl_easy_setopt (easy_handle, CURLOPT_HTTPAUTH, CURLAUTH_DIGEST
) when sending authentication information to the proxy server , provided by authentication CURLOPT_PROXYAUTH:
of curl_easy_setopt (easy_handle, CURLOPT_PROXYAUTH, CURLAUTH_NTLM);
may be provided a variety of authentication (through bitwise aND), the use of 'CURLAUTH_ANY' may choose any libcurl will allow it supports authentication simultaneously. Or by a variety of authentication CURLOPT_HTTPAUTH CURLOPT_PROXYAUTH property settings, libcurl it will choose one that is the best way to communicate with the server at run time:
of curl_easy_setopt (easy_handle, CURLOPT_HTTPAUTH, CURLAUTH_DIGEST | CURLAUTH_BASIC);
// of curl_easy_setopt (easy_handle, CURLOPT_HTTPAUTH, CURLAUTH_ANY);