C语言实现HTTP下载-优快云博客

本文链接：https://blog.youkuaiyun.com/Yellow_Bug/article/details/6575470

本文详细介绍了使用C语言实现HTTP下载的功能，包括解析URL、封装请求报头、发送请求、接收响应报头和开始下载等关键步骤，并提供了一个跨平台的实现代码示例。

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很早就有这个想法了，知道今天才实现了一下，参考了周立发的《《C语言实现HTTP下载例子》》和林超旗整理的《《HTTP协议详解》》，特此谢谢！由于今天时间有限，所以大概的实现了一下(目前只在ubuntu环境下测试的)，跨平台部分还需要完善，后面会陆续整理出完整的版本。代码如下：

头文件

/* $Id: httpdownload.h, v1.0.0, 2011.6.28, YellowBug $ $@@: http下载 */ #ifndef PENQ_HTTP_DOWNLOAD_H_ #define PENQ_HTTP_DOWNLOAD_H_ #include <stdio.h> #include <stdlib.h> #include <string.h> #include <errno.h> #if defined(__GNUC__) #include <sys/types.h> #include <sys/socket.h> #include <unistd.h> #include <netinet/in.h> #include <arpa/inet.h> #include <netdb.h> #include <time.h> #define PATH_SPLIT '/' typedef int HSOCKET; #define closesocket(s) close(s) #elif defined(_WIN32) #include <windows.h> #include <winsock2.h> #define PATH_SPLIT '//' typedef SOCKET HSOCKET; #endif #define DEF_HTTP_PORT 80 #define HTTP_MAX_PATH 260 #define HTTP_MAX_REQUESTHEAD 1024 #define HTTP_MAX_RESPONSEHEAD 2048 #define HTTP_DOWN_PERSIZE 128 #define HTTP_FLUSH_BLOCK 1024 /* $@@ 下载状态 $@ HDL_URLERR: 提供的url非法 $@ HDL_SERVERFAL: 根据host地址无法找到主机 $@ HDL_TIMEOUT: 连接下载地址超时 $@ HDL_READYOK: 连接下载地址成功,准备下载 $@ HDL_DOWNING: 正在下载 $@ HDL_DISCONN: 断开连接了 $@ HDL_FINISH: 下载完成 */ enum { HDL_URLERR = 0xe0, HDL_SERVERFAL = 0xe1, HDL_SOCKFAL = 0xe2, HDL_SNDREQERR = 0xe3, HDL_SERVERERR = 0xe4, HDL_CRLOCFILEFAL = 0xe5, HDL_TIMEOUT = 0x100, HDL_NORESPONSE = 0x101, HDL_READYOK = 0x104, HDL_DOWNING = 0x105, HDL_DISCONN = 0x106, HDL_FINISH = 0x107 }; /* $@@ 下载回调函数,主要用于监听下载过程 $@ 第一个参数: 下载标识符号(上面枚举中的值) $@ 第二个参数: 需要下载的总字节数 $@ 第三个参数: 已经下载的总字节数 $@ 第四个参数: 距离上一次下载的时间戳(毫秒) $@ 返回值: 下次下载的字节数(0: 表示默认值, 小于0则下载中断, 大于0则位下次下载指定的字节) */ typedef int (*HTTPDOWNLOAD_CALLBACK)(int, unsigned int, unsigned int, unsigned int); /* $@@ 通过指定的url下载资源 $@ url: 下载资源地址 $@ filepath: 存储在本地的路径(如果为NULL则存储在当前目录) $@ filename: 存储的文件名(如果为NULL则位url中分析的文件名) $@ http_func: 下载过程监听函数(如果为NULL则不监听下载过程) */ void pq_http_download(const char *url, const char *filepath, const char *filename, HTTPDOWNLOAD_CALLBACK http_func); #endif /* #ifndef PENQ_HTTP_DOWNLOAD_H_ */ /* END */

实现:

/* $Id: httpdownload.c, v1.0.0, 2011.6.28, YellowBug $ $@@: http下载 */ #include "httpdownload.h" #define HERROR(exp, err) do { / if (exp) { / printf("(%s,%d) %s/n", __FILE__, __LINE__, #exp); / if(S_http_callback) S_http_callback((err), 0, 0, 0); / exit(1); / } / } while(0) #define HCALLBACK(a, b, c, d) (S_http_callback ? S_http_callback((a), (b), (c), (d)) : 0) /* $@@ 文件域的局部变量 */ static HTTPDOWNLOAD_CALLBACK S_http_callback = NULL; static const char * S_request_head = "GET %s HTTP/1.1/r/n" / "Accept: */*/r/n" / "Accept-Language: zh-cn/r/n" / "User-Agent: Molliza/4.0(compatible;MSIE6.0;windows NT 5.0)/r/n" / "Host: %s/r/n" / "Connection: close/r/n/r/n"; #if defined(__GNUC__) unsigned int get_tick() { struct timeval tv; gettimeofday(&tv, NULL); return (unsigned int)(tv.tv_sec*1000+tv.tv_usec/1000); } #elif defined(_WIN32) #define get_tick() GetTickCount() #endif /* $@@ 从指定长度(len0)的字符串的右端开始找到第一个位ch的字符 */ static char * r_strchr(const char *p, int len, char ch) { int last_pos = -1; int i = 0; while ( *(p+i) != '/0' ) { if ( *(p+i) == ch ) last_pos = i; if ( ++i >= len ) break; } return last_pos >= 0 ? (char *)(p+last_pos) : NULL; } /* $@@ 解析url，分析出web地址,端口号,下载的资源名称 */ static void parse_url(const char *url, char *web, int *port, char *filepath, char *filename) { int web_len = 0; int web_start = 0; int file_len = 0; int file_start = 0; int path_len = 0; int path_start = 0; char *pa = NULL; char *pb = NULL; if ( !strncmp(url, "http://", 7) ) web_start = 7; else if ( !strncmp(url, "https://", 8) ) web_start = 8; pa = strchr(url+web_start, '/'); pb = strchr(url+web_start, ':'); /* 获取web */ if ( pa ) { web_len = (int)(pa - (url+web_start)); } else { if ( pb ) web_len = pb - (url+web_start); else web_len = strlen(url+web_start); } HERROR(0 == web_len, HDL_URLERR); memcpy(web, url+web_start, web_len); web[web_len] = '/0'; /* 获取filename */ if ( pb ) { pa = r_strchr(url+web_start, (int)(pb-(url+web_start)), '/'); file_len = (int)(pb - pa - 1); file_start = (int)(pa + 1 - url); *port = atoi(pb+1); } else { pa = r_strchr(url+web_start, strlen(url+web_start), '/'); HERROR(NULL == pa, HDL_URLERR); file_len = strlen(pa+1); file_start = (int)(pa + 1 - url); *port = DEF_HTTP_PORT; } HERROR(NULL == pa, HDL_URLERR); memcpy(filename, url+file_start, file_len); filename[file_len] = '/0'; /* 获取filepath */ path_start = web_start + web_len; path_len = file_start - path_start + file_len; memcpy(filepath, url+web_start+web_len, file_start - path_start + file_len); filepath[path_len] = '/0'; } /* $@@ 封装request报头 */ int package_request(char *request, const char *web, const char *filepath) { int n = sprintf(request, S_request_head, filepath, web); request[n] = '/0'; return n; } /* $@@ 发送请求报头 */ int send_request(HSOCKET sock, const char *buf, int n) { int already_bytes = 0; int per_bytes = 0; while ( already_bytes < n ) { per_bytes = send(sock, buf+already_bytes, n-already_bytes, 0); if ( per_bytes < 0 ) { break; } else if ( 0 == per_bytes ) { HCALLBACK(HDL_DISCONN, 0, 0, 0); break; } else already_bytes += per_bytes; } return already_bytes; } /* $@@ 获取响应报头(状态行和消息报头) */ int get_response_head(HSOCKET sock, char *response, int max) { int total_bytes = 0; int per_bytes = 0; int over_flag = 0; char ch; do { per_bytes = recv(sock, &ch, 1, 0); if ( per_bytes < 0 ) break; else if ( 0 == per_bytes ) { HCALLBACK(HDL_DISCONN, 0, 0, 0); break; } else { if ( '/r' == ch || '/n' == ch ) over_flag++; else over_flag = 0; response[total_bytes] = ch; if ( total_bytes >= max ) break; else total_bytes += per_bytes; } } while ( over_flag < 4 ); response[total_bytes] = '/0'; return total_bytes; } void parse_response_head(char *response, int n, int *server_status, unsigned int *down_total) { int i = 1; char *pstatus = strstr(response, "HTTP/1.1"); char *plen = strstr(response, "Content-Length:"); printf("%s/n", response); if ( pstatus ) { pstatus += strlen("HTTP/1.1"); i = 1; while ( *(pstatus+i) == ' ' ) ++i; *server_status = atoi(pstatus+i); } else *server_status = 0; if ( plen ) { plen += strlen("Content-Length:"); i = 1; while ( *(plen+i) == ' ' ) ++i; *down_total = (unsigned int)atoi(plen+i); } else *down_total = 0; printf("status: %d/n", *server_status); printf("total: %u/n", *down_total); } /* $@@ 创建本地文件 */ FILE * create_local_file(const char *local_path, const char *local_file, const char *remote_file) { int len = strlen(local_path); static char filename[HTTP_MAX_PATH+1]; if ( local_path[len-1] != PATH_SPLIT ) { if ( local_file ) len = sprintf(filename, "%s%c%s", local_path, PATH_SPLIT, local_file); else len = sprintf(filename, "%s%c%s", local_path, PATH_SPLIT, remote_file); } else { if ( local_file ) len = sprintf(filename, "%s%s", local_path, local_file); else len = sprintf(filename, "%s%s", local_path, remote_file); } filename[len] = '/0'; printf("ready to create local file: %s/n", filename); return fopen(filename, "wb+"); } /* $@@ 开始下载 */ void start_download(HSOCKET sock, unsigned int total_bytes, FILE *stream) { unsigned int already_bytes; int per_bytes; int flush_bytes; unsigned int total_tim; unsigned int per_tim; static char buf[HTTP_DOWN_PERSIZE]; do { per_tim = get_tick(); per_bytes = recv(sock, buf, HTTP_DOWN_PERSIZE, 0); per_tim = get_tick() - per_tim; if ( per_bytes < 0 ) break; else if ( 0 == per_bytes ) { HCALLBACK(HDL_DISCONN, total_bytes, already_bytes, 0); break; } else { fwrite(buf, 1, per_bytes, stream); already_bytes += (unsigned int)per_bytes; flush_bytes += per_bytes; if ( flush_bytes >= HTTP_FLUSH_BLOCK ) { fflush(stream); flush_bytes = 0; } HCALLBACK(HDL_DOWNING, total_bytes, already_bytes, per_tim); } } while ( already_bytes < total_bytes ); if ( flush_bytes > 0 ) fflush(stream); HCALLBACK(HDL_FINISH, total_bytes, already_bytes, total_tim); } void pq_http_download(const char *url, const char *local_path, const char *local_file, HTTPDOWNLOAD_CALLBACK http_func) { int port; char web[HTTP_MAX_PATH+1]; char remote_path[HTTP_MAX_PATH+1]; char remote_file[HTTP_MAX_PATH+1]; char request[HTTP_MAX_REQUESTHEAD+1]; char response_head[HTTP_MAX_RESPONSEHEAD+1]; int request_len = 0; int response_len = 0; unsigned int down_total = 0; int server_status = 404; HSOCKET sock = -1; struct hostent *host = NULL; struct sockaddr_in server_addr; FILE *stream = NULL; S_http_callback = http_func; parse_url(url, web, &port, remote_path, remote_file); request_len = package_request(request, web, remote_path); host = gethostbyname(web); HERROR(NULL==host, HDL_SERVERFAL); sock = socket(AF_INET, SOCK_STREAM, 0); HERROR(-1==sock, HDL_SOCKFAL); memset(&server_addr, 0, sizeof(server_addr)); server_addr.sin_family = AF_INET; server_addr.sin_port = htons(port); server_addr.sin_addr = *((struct in_addr *)host->h_addr); HERROR(-1==connect(sock, (struct sockaddr *)&server_addr, sizeof(struct sockaddr)), HDL_TIMEOUT); HERROR(request_len != send_request(sock, request, request_len), HDL_SNDREQERR); response_len = get_response_head(sock, response_head, HTTP_MAX_RESPONSEHEAD); HERROR(response_len <= 0, HDL_NORESPONSE); parse_response_head(response_head, response_len, &server_status, &down_total); switch ( server_status ) { case 200: if ( down_total > 0 ) { stream = create_local_file(local_path, local_file, remote_file); HERROR(NULL == stream, HDL_CRLOCFILEFAL); HCALLBACK(HDL_READYOK, down_total, 0, 0); start_download(sock, down_total, stream); fclose(stream); } else { HCALLBACK(HDL_FINISH, 0, 0, 0); } default: HCALLBACK(HDL_SERVERERR, 0, 0, 0); } closesocket(sock); } /* END */

测试代码:

#include <stdio.h> #include "httpdownload.h" int http_callback(int status, unsigned int total_bytes, unsigned int already_bytes, unsigned int tim) { switch ( status ) { case HDL_READYOK: printf("ready to download, total.bytes=%u/n", total_bytes); break; case HDL_DOWNING: printf("downloading... (%u/%u) bytes/n", already_bytes, total_bytes); break; case HDL_FINISH: printf("download finish! download total.bytes=%u/n", already_bytes); break; default: printf("status: %#x/n", status); } return 0; } int main(int argc, char *argv[]) { pq_http_download(argv[1], argv[2], NULL, http_callback); }

后期可能会多设置几种回调函数区分，错误机制也会多考虑改进一下。