基于libcurl的开发

0.Reference

官网：https://curl.se/

B站阅读的小哥的视频

知乎的一片好文

安装文档

libculr对http中的参数的设定-忽略或者需要

libcurl中CURLOPT_WRITEFUNCTION设置回调函数-将查询的值写入文件

curl将查询的值写入内存的写法

libcurl使用方法简介

Libcurl实现HTTP/HTTPS客户端（支持get、post、保持session）

1.简介

libcurl是一个跨平台的开源网络协议库，支持http, https, rtsp等多种协议。libcurl同样支持HTTPS证书授权，HTTP POST, HTTP PUT, FTP 上传, HTTP基本表单上传，代理，cookies,和用户认证。

官网地址 http://curl.haxx.se/

libcurl主要提供了两种发送HTTP请求的方式，分别是easy interface方式和multi interface方式，前者是采用阻塞的方式发送单条请求，后者采用组合的方式可以一次性发送多条请求数据，且多个下载请求是异步进行的。

2.重要接口

3.curl_easy_perform的返回值

response=curl_easy_perform(curl);
response返回的状态值

#include <curl/curl.h>enum CURLcode
{CURLE_OK = 0,CURLE_UNSUPPORTED_PROTOCOL, /* 1 */CURLE_FAILED_INIT, /* 2 */CURLE_URL_MALFORMAT, /* 3 */CURLE_OBSOLETE4, /* 4 - NOT USED */CURLE_COULDNT_RESOLVE_PROXY, /* 5 */CURLE_COULDNT_RESOLVE_HOST, /* 6 */CURLE_COULDNT_CONNECT, /* 7 */CURLE_FTP_WEIRD_SERVER_REPLY, /* 8 */CURLE_REMOTE_ACCESS_DENIED, /* 9 a service was denied by the serverdue to lack of access - when login failsthis is not returned. */CURLE_OBSOLETE10, /* 10 - NOT USED */CURLE_FTP_WEIRD_PASS_REPLY, /* 11 */CURLE_OBSOLETE12, /* 12 - NOT USED */CURLE_FTP_WEIRD_PASV_REPLY, /* 13 */CURLE_FTP_WEIRD_227_FORMAT, /* 14 */CURLE_FTP_CANT_GET_HOST, /* 15 */CURLE_OBSOLETE16, /* 16 - NOT USED */CURLE_FTP_COULDNT_SET_TYPE, /* 17 */CURLE_PARTIAL_FILE, /* 18 */CURLE_FTP_COULDNT_RETR_FILE, /* 19 */CURLE_OBSOLETE20, /* 20 - NOT USED */CURLE_QUOTE_ERROR, /* 21 - quote command failure */CURLE_HTTP_RETURNED_ERROR, /* 22 */CURLE_WRITE_ERROR, /* 23 */CURLE_OBSOLETE24, /* 24 - NOT USED */CURLE_UPLOAD_FAILED, /* 25 - failed upload "command" */CURLE_READ_ERROR, /* 26 - couldn't open/read from file */CURLE_OUT_OF_MEMORY, /* 27 *//* Note: CURLE_OUT_OF_MEMORY may sometimes indicate a conversion errorinstead of a memory allocation error if CURL_DOES_CONVERSIONSis defined*/CURLE_OPERATION_TIMEDOUT, /* 28 - the timeout time was reached */CURLE_OBSOLETE29, /* 29 - NOT USED */CURLE_FTP_PORT_FAILED, /* 30 - FTP PORT operation failed */CURLE_FTP_COULDNT_USE_REST, /* 31 - the REST command failed */CURLE_OBSOLETE32, /* 32 - NOT USED */CURLE_RANGE_ERROR, /* 33 - RANGE "command" didn't work */CURLE_HTTP_POST_ERROR, /* 34 */CURLE_SSL_CONNECT_ERROR, /* 35 - wrong when connecting with SSL */CURLE_BAD_DOWNLOAD_RESUME, /* 36 - couldn't resume download */CURLE_FILE_COULDNT_READ_FILE, /* 37 */CURLE_LDAP_CANNOT_BIND, /* 38 */CURLE_LDAP_SEARCH_FAILED, /* 39 */CURLE_OBSOLETE40, /* 40 - NOT USED */CURLE_FUNCTION_NOT_FOUND, /* 41 */CURLE_ABORTED_BY_CALLBACK, /* 42 */CURLE_BAD_FUNCTION_ARGUMENT, /* 43 */CURLE_OBSOLETE44, /* 44 - NOT USED */CURLE_INTERFACE_FAILED, /* 45 - CURLOPT_INTERFACE failed */CURLE_OBSOLETE46, /* 46 - NOT USED */CURLE_TOO_MANY_REDIRECTS, /* 47 - catch endless re-direct loops */CURLE_UNKNOWN_TELNET_OPTION, /* 48 - User specified an unknown option */CURLE_TELNET_OPTION_SYNTAX, /* 49 - Malformed telnet option */CURLE_OBSOLETE50, /* 50 - NOT USED */CURLE_PEER_FAILED_VERIFICATION, /* 51 - peer's certificate or fingerprintwasn't verified fine */CURLE_GOT_NOTHING, /* 52 - when this is a specific error */CURLE_SSL_ENGINE_NOTFOUND, /* 53 - SSL crypto engine not found */CURLE_SSL_ENGINE_SETFAILED, /* 54 - can not set SSL crypto engine asdefault */CURLE_SEND_ERROR, /* 55 - failed sending network data */CURLE_RECV_ERROR, /* 56 - failure in receiving network data */CURLE_OBSOLETE57, /* 57 - NOT IN USE */CURLE_SSL_CERTPROBLEM, /* 58 - problem with the local certificate */CURLE_SSL_CIPHER, /* 59 - couldn't use specified cipher */CURLE_SSL_CACERT, /* 60 - problem with the CA cert (path?) */CURLE_BAD_CONTENT_ENCODING, /* 61 - Unrecognized transfer encoding */CURLE_LDAP_INVALID_URL, /* 62 - Invalid LDAP URL */CURLE_FILESIZE_EXCEEDED, /* 63 - Maximum file size exceeded */CURLE_USE_SSL_FAILED, /* 64 - Requested FTP SSL level failed */CURLE_SEND_FAIL_REWIND, /* 65 - Sending the data requires a rewindthat failed */CURLE_SSL_ENGINE_INITFAILED, /* 66 - failed to initialise ENGINE */CURLE_LOGIN_DENIED, /* 67 - user, password or similar was notaccepted and we failed to login */CURLE_TFTP_NOTFOUND, /* 68 - file not found on server */CURLE_TFTP_PERM, /* 69 - permission problem on server */CURLE_REMOTE_DISK_FULL, /* 70 - out of disk space on server */CURLE_TFTP_ILLEGAL, /* 71 - Illegal TFTP operation */CURLE_TFTP_UNKNOWNID, /* 72 - Unknown transfer ID */CURLE_REMOTE_FILE_EXISTS, /* 73 - File already exists */CURLE_TFTP_NOSUCHUSER, /* 74 - No such user */CURLE_CONV_FAILED, /* 75 - conversion failed */CURLE_CONV_REQD, /* 76 - caller must register conversioncallbacks using curl_easy_setopt optionsCURLOPT_CONV_FROM_NETWORK_FUNCTION,CURLOPT_CONV_TO_NETWORK_FUNCTION, andCURLOPT_CONV_FROM_UTF8_FUNCTION */CURLE_SSL_CACERT_BADFILE, /* 77 - could not load CACERT file, missingor wrong format */CURLE_REMOTE_FILE_NOT_FOUND, /* 78 - remote file not found */CURLE_SSH, /* 79 - error from the SSH layer, somewhatgeneric so the error message will be ofinterest when this has happened */CURLE_SSL_SHUTDOWN_FAILED, /* 80 - Failed to shut down the SSLconnection */CURLE_AGAIN, /* 81 - socket is not ready for send/recv,wait till it's ready and try again (Addedin 7.18.2) */CURLE_SSL_CRL_BADFILE, /* 82 - could not load CRL file, missing orwrong format (Added in 7.19.0) */CURLE_SSL_ISSUER_ERROR, /* 83 - Issuer check failed.  (Added in7.19.0) */CURL_LAST /* never use! */
};

4. HTTPS参数

(1)CURL_VERIFY_PEER

该参数含义是验证HTTPS请求对象的合法性，就是用第三方证书机构颁发的CA数字证书来解密服务端返回的证书，来验证其合法性。可在编译时就将CA数字证书编译进去，也可以通过参数CURLOPT_CAINFO 或者CURLOPT_CAPATH设置根证书。默认值为1。

(2)CURL_VERIFY_HOST

该参数主要用于https请求时返回的证书是否与请求的域名相符合，避免被中间着篡改证书文件。默认值为2。

如果不想验证PEER和HOST的安全性，可以通过设置以下内容来实现：

curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, 0L);//忽略证书检查

curl_easy_setopt(curl, CURLOPT_SSL_VERIFYHOST, 0L);

5.开发示例

5.1 获取html内容

代码：

#include <stdio.h>
#include <curl/curl.h>
#include <stdlib.h>
#include <iostream>
using namespace std;
int main(int argc, char *argv[])
{CURL *curl;   //定义CURL类型的指针CURLcode res; //定义CURLcode类型的变量，保存返回状态码if (argc != 2){printf("Usage : file <url>;\n");exit(1);}curl = curl_easy_init(); //初始化一个CURL类型的指针if (curl != NULL){//设置curl选项. 其中CURLOPT_URL是让用户指 定url. argv[1]中存放的命令行传进来的网址curl_easy_setopt(curl, CURLOPT_URL, argv[1]);curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, 0L);curl_easy_setopt(curl, CURLOPT_SSL_VERIFYHOST, 0L);//调用curl_easy_perform 执行我们的设置.并进行相关的操作. 在这 里只在屏幕上显示出来.res = curl_easy_perform(curl);cout << "res is " << res << endl;//清除curl操作.curl_easy_cleanup(curl);}return 0;
}

编译命令：g++ getHtml.cpp -lcurl

命令行执行命令： ./getHtml https://192.168.244.139/api/projects/