消息有一个标题部分和一个由空行分隔的消息正文。即使没有消息正文，也始终需要空白行。标头以命令开头，并具有由冒号和空格分隔的键值对的附加行。如果有消息正文，它可以是您想要的任何内容。
标题中的行和标题末尾的空白行必须以回车和换行对结束（请参阅HTTP header line break style），这就是为什么这些行末尾有 \r\n。
URL 的格式为http://host:port/path?query_string
向网站提交请求有两种主要方式：
-
GET：查询字符串是可选的，但如果指定，则必须相当短。因此，标头可能只是 GET 命令，没有别的。示例消息可能是：
GET /path?query_string HTTP/1.0\r\n
\r\n
-
POST：通常在查询字符串中的内容是在消息正文中。因此，标头需要包含 Content-Type: 和 Content-Length: 属性以及 POST 命令。示例消息可能是：
POST /path HTTP/1.0\r\n
Content-Type: text/plain\r\n
Content-Length: 12\r\n
\r\n
query_string
所以，回答您的问题：如果您有兴趣发布到的 URL 是 http://api.somesite.com/apikey=ARG1&command=ARG2，那么没有正文或查询字符串，因此，没有理由发布，因为没有任何内容可放入消息，因此无需在 Content-Type: 和 Content-Length: 中放入任何内容：
如果你真的想的话，我想你可以发布。在这种情况下，您的消息将如下所示：
POST /apikey=ARG1&command=ARG2 HTTP/1.0\r\n
\r\n
所以要发送 C 程序需要的消息：
- 创建一个套接字
- 查找 IP 地址
- 打开套接字
- 发送请求
- 等待回复
- 关闭套接字
发送和接收调用不一定会发送/接收您提供给它们的所有数据 - 它们将返回实际发送/接收的字节数。您可以循环调用它们并发送/接收消息的其余部分。
我在这个示例中没有做的是任何类型的真正错误检查 - 当出现故障时，我只是退出程序。让我知道它是否适合您：
#include <stdio.h> /* printf, sprintf */
#include <stdlib.h> /* exit */
#include <unistd.h> /* read, write, close */
#include <string.h> /* memcpy, memset */
#include <sys/socket.h> /* socket, connect */
#include <netinet/in.h> /* struct sockaddr_in, struct sockaddr */
#include <netdb.h> /* struct hostent, gethostbyname */
void error(const char *msg) { perror(msg); exit(0); }
int main(int argc,char *argv[])
{
/* first what are we going to send and where are we going to send it? */
int portno = 80;
char *host = "api.somesite.com";
char *message_fmt = "POST /apikey=%s&command=%s HTTP/1.0\r\n\r\n";
struct hostent *server;
struct sockaddr_in serv_addr;
int sockfd, bytes, sent, received, total;
char message[1024],response[4096];
if (argc < 3) { puts("Parameters: <apikey> <command>"); exit(0); }
/* fill in the parameters */
sprintf(message,message_fmt,argv[1],argv[2]);
printf("Request:\n%s\n",message);
/* create the socket */
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd < 0) error("ERROR opening socket");
/* lookup the ip address */
server = gethostbyname(host);
if (server == NULL) error("ERROR, no such host");
/* fill in the structure */
memset(&serv_addr,0,sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
serv_addr.sin_port = htons(portno);
memcpy(&serv_addr.sin_addr.s_addr,server->h_addr,server->h_length);
/* connect the socket */
if (connect(sockfd,(struct sockaddr *)&serv_addr,sizeof(serv_addr)) < 0)
error("ERROR connecting");
/* send the request */
total = strlen(message);
sent = 0;
do {
bytes = write(sockfd,message+sent,total-sent);
if (bytes < 0)
error("ERROR writing message to socket");
if (bytes == 0)
break;
sent+=bytes;
} while (sent < total);
/* receive the response */
memset(response,0,sizeof(response));
total = sizeof(response)-1;
received = 0;
do {
bytes = read(sockfd,response+received,total-received);
if (bytes < 0)
error("ERROR reading response from socket");
if (bytes == 0)
break;
received+=bytes;
} while (received < total);
/*
* if the number of received bytes is the total size of the
* array then we have run out of space to store the response
* and it hasn't all arrived yet - so that's a bad thing
*/
if (received == total)
error("ERROR storing complete response from socket");
/* close the socket */
close(sockfd);
/* process response */
printf("Response:\n%s\n",response);
return 0;
}
就像另一个答案指出的那样，4096 字节并不是一个很大的响应。我随机选择了这个数字，假设对您的请求的响应会很短。如果它可以很大，您有两种选择：
- 从响应中读取 Content-Length: 标头，然后动态分配足够的内存来保存整个响应。
- 在片段到达时将响应写入文件
回答 cmets 中提出的问题的其他信息：
如果您想在消息正文中发布数据怎么办？然后您确实需要包含 Content-Type: 和 Content-Length: 标头。 Content-Length: 是分隔标题和正文的空白行之后所有内容的实际长度。
这是一个采用以下命令行参数的示例：
- 主持人
- 端口
- 命令（GET 或 POST）
- 路径（不包括查询数据）
- 查询数据（GET 放入查询字符串，POST 放入正文）
- 标题列表（内容长度：如果使用 POST，则为自动）
因此，对于您将运行的原始问题：
a.out api.somesite.com 80 GET "/apikey=ARG1&command=ARG2"
对于您将运行的 cmets 中提出的问题：
a.out api.somesite.com 80 POST / "name=ARG1&value=ARG2" "Content-Type: application/x-www-form-urlencoded"
代码如下：
#include <stdio.h> /* printf, sprintf */
#include <stdlib.h> /* exit, atoi, malloc, free */
#include <unistd.h> /* read, write, close */
#include <string.h> /* memcpy, memset */
#include <sys/socket.h> /* socket, connect */
#include <netinet/in.h> /* struct sockaddr_in, struct sockaddr */
#include <netdb.h> /* struct hostent, gethostbyname */
void error(const char *msg) { perror(msg); exit(0); }
int main(int argc,char *argv[])
{
int i;
/* first where are we going to send it? */
int portno = atoi(argv[2])>0?atoi(argv[2]):80;
char *host = strlen(argv[1])>0?argv[1]:"localhost";
struct hostent *server;
struct sockaddr_in serv_addr;
int sockfd, bytes, sent, received, total, message_size;
char *message, response[4096];
if (argc < 5) { puts("Parameters: <host> <port> <method> <path> [<data> [<headers>]]"); exit(0); }
/* How big is the message? */
message_size=0;
if(!strcmp(argv[3],"GET"))
{
message_size+=strlen("%s %s%s%s HTTP/1.0\r\n"); /* method */
message_size+=strlen(argv[3]); /* path */
message_size+=strlen(argv[4]); /* headers */
if(argc>5)
message_size+=strlen(argv[5]); /* query string */
for(i=6;i<argc;i++) /* headers */
message_size+=strlen(argv[i])+strlen("\r\n");
message_size+=strlen("\r\n"); /* blank line */
}
else
{
message_size+=strlen("%s %s HTTP/1.0\r\n");
message_size+=strlen(argv[3]); /* method */
message_size+=strlen(argv[4]); /* path */
for(i=6;i<argc;i++) /* headers */
message_size+=strlen(argv[i])+strlen("\r\n");
if(argc>5)
message_size+=strlen("Content-Length: %d\r\n")+10; /* content length */
message_size+=strlen("\r\n"); /* blank line */
if(argc>5)
message_size+=strlen(argv[5]); /* body */
}
/* allocate space for the message */
message=malloc(message_size);
/* fill in the parameters */
if(!strcmp(argv[3],"GET"))
{
if(argc>5)
sprintf(message,"%s %s%s%s HTTP/1.0\r\n",
strlen(argv[3])>0?argv[3]:"GET", /* method */
strlen(argv[4])>0?argv[4]:"/", /* path */
strlen(argv[5])>0?"?":"", /* ? */
strlen(argv[5])>0?argv[5]:""); /* query string */
else
sprintf(message,"%s %s HTTP/1.0\r\n",
strlen(argv[3])>0?argv[3]:"GET", /* method */
strlen(argv[4])>0?argv[4]:"/"); /* path */
for(i=6;i<argc;i++) /* headers */
{strcat(message,argv[i]);strcat(message,"\r\n");}
strcat(message,"\r\n"); /* blank line */
}
else
{
sprintf(message,"%s %s HTTP/1.0\r\n",
strlen(argv[3])>0?argv[3]:"POST", /* method */
strlen(argv[4])>0?argv[4]:"/"); /* path */
for(i=6;i<argc;i++) /* headers */
{strcat(message,argv[i]);strcat(message,"\r\n");}
if(argc>5)
sprintf(message+strlen(message),"Content-Length: %d\r\n",strlen(argv[5]));
strcat(message,"\r\n"); /* blank line */
if(argc>5)
strcat(message,argv[5]); /* body */
}
/* What are we going to send? */
printf("Request:\n%s\n",message);
/* create the socket */
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd < 0) error("ERROR opening socket");
/* lookup the ip address */
server = gethostbyname(host);
if (server == NULL) error("ERROR, no such host");
/* fill in the structure */
memset(&serv_addr,0,sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
serv_addr.sin_port = htons(portno);
memcpy(&serv_addr.sin_addr.s_addr,server->h_addr,server->h_length);
/* connect the socket */
if (connect(sockfd,(struct sockaddr *)&serv_addr,sizeof(serv_addr)) < 0)
error("ERROR connecting");
/* send the request */
total = strlen(message);
sent = 0;
do {
bytes = write(sockfd,message+sent,total-sent);
if (bytes < 0)
error("ERROR writing message to socket");
if (bytes == 0)
break;
sent+=bytes;
} while (sent < total);
/* receive the response */
memset(response,0,sizeof(response));
total = sizeof(response)-1;
received = 0;
do {
bytes = read(sockfd,response+received,total-received);
if (bytes < 0)
error("ERROR reading response from socket");
if (bytes == 0)
break;
received+=bytes;
} while (received < total);
/*
* if the number of received bytes is the total size of the
* array then we have run out of space to store the response
* and it hasn't all arrived yet - so that's a bad thing
*/
if (received == total)
error("ERROR storing complete response from socket");
/* close the socket */
close(sockfd);
/* process response */
printf("Response:\n%s\n",response);
free(message);
return 0;
}