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。

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

#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 server due to lack of access - when login fails this 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 error instead of a memory allocation error if CURL_DOES_CONVERSIONS is 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 fingerprint wasn'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 as default */ 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 rewind that failed */ CURLE_SSL_ENGINE_INITFAILED, /* 66 - failed to initialise ENGINE */ CURLE_LOGIN_DENIED, /* 67 - user, password or similar was not accepted 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 conversion callbacks using curl_easy_setopt options CURLOPT_CONV_FROM_NETWORK_FUNCTION, CURLOPT_CONV_TO_NETWORK_FUNCTION, and CURLOPT_CONV_FROM_UTF8_FUNCTION */ CURLE_SSL_CACERT_BADFILE, /* 77 - could not load CACERT file, missing or wrong format */ CURLE_REMOTE_FILE_NOT_FOUND, /* 78 - remote file not found */ CURLE_SSH, /* 79 - error from the SSH layer, somewhat generic so the error message will be of interest when this has happened */ 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 (Added in 7.18.2) */ CURLE_SSL_CRL_BADFILE, /* 82 - could not load CRL file, missing or wrong format (Added in 7.19.0) */ CURLE_SSL_ISSUER_ERROR, /* 83 - Issuer check failed. (Added in 7.19.0) */ 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/