SIGPIPE的产生

当一个进程向已经收到RST的socket写数据时，SIGPIPE信号会被发送给该进程。

以下是一段服务端向客户端发送响应报文的代码，第13行调用write向fd写入报文首部，第21行调用write向fd写入报文主体。若客户端连接断开，第一次write后，fd会收到RST，第二次write将产生SIGPIPE信号。

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void serve_static(int fd, char *filename, int filesize)
{
    int srcfd;
    char *srcp, filetype[MAXLINE], buf[MAXBUF];
 
    /* Send response headers to client */
    get_filetype(filename, filetype);
    sprintf(buf, "HTTP/1.0 200 OK\r\n");
    sprintf(buf, "%sServer: Tiny Web Server\r\n", buf);
    sprintf(buf, "%sConnection: close\r\n", buf);
    sprintf(buf, "%sContent-length: %d\r\n", buf, filesize);
    sprintf(buf, "%sContent-type: %s\r\n\r\n", buf, filetype);
    Rio_writen(fd, buf, strlen(buf));
    printf("Response headers:\n");
    printf("%s", buf);

    /* Send response body to client */
    srcfd = Open(filename, O_RDONLY, 0);
    srcp = Mmap(0, filesize, PROT_READ, MAP_PRIVATE, srcfd, 0);
    Close(srcfd);
    Rio_writen(fd, srcp, filesize);
    Munmap(srcp, filesize);
}