send_fd.cpp

Author: codeduckerxyx

ch13/send_fd.cpp

@@ -0,0 +1,84 @@
+#include <sys/socket.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <assert.h>
+#include <string.h>
+
+static const int CONTROL_LEN = CMSG_LEN( sizeof(int) );
+/* 发送文件描述符，fd参数是用来传递信息的UNIX域socket，fd_to_send参数是待发送的文件描述符 */
+void send_fd( int fd, int fd_to_send ){
+    struct iovec iov[1];
+    struct msghdr msg;
+    char buf[0];
+
+    iov[0].iov_base = buf;
+    iov[0].iov_len = 1;
+    msg.msg_name = NULL;
+    msg.msg_namelen = 0;
+    msg.msg_iov = iov;
+    msg.msg_iovlen = 1;
+
+    cmsghdr cm;
+    cm.cmsg_len = CONTROL_LEN;
+    cm.cmsg_level = SOL_SOCKET;
+    cm.cmsg_type = SCM_RIGHTS;
+    *(int *)CMSG_DATA( &cm ) = fd_to_send;
+    msg.msg_control = &cm;  /* 设置辅助数据 */
+    msg.msg_controllen = CONTROL_LEN;
+
+    sendmsg( fd, &msg, 0 );
+}
+
+/* 接收目标文件描述符 */
+int recv_fd( int fd ){
+    struct iovec iov[1];
+    struct msghdr msg;
+    char buf[0];
+
+    iov[0].iov_base = buf;
+    iov[0].iov_len = 1;
+    msg.msg_name = NULL;
+    msg.msg_namelen = 0;
+    msg.msg_iov = iov;
+    msg.msg_iovlen = 1;
+
+    cmsghdr cm;
+    msg.msg_control = &cm;
+    msg.msg_controllen = CONTROL_LEN;
+
+    recvmsg( fd,&msg,0 );
+
+    int fd_to_read = *(int *)CMSG_DATA( &cm );
+    return fd_to_read;
+}
+
+
+int main(){
+    int pipefd[2];
+    int fd_to_pass = 0;
+    /* 创建父亲，子进程间的管道，文件描述符pipefd[0]和pipefd[1]都是UNIX域socket */
+    int ret = socketpair( PF_UNIX, SOCK_DGRAM, 0, pipefd  );
+    assert( ret != -1 );
+
+    pid_t pid = fork();
+    assert( pid>=0 );
+
+    if( pid == 0 ){
+        close( pipefd[0] );
+        fd_to_pass = open( "test.txt", O_RDWR, 0666 );
+        /* 子进程通过管道将文件描述符发送到父进程。如果文件test.txt打开失败，则子进程将标准输入文件描述符发送到父进程 */
+        send_fd( pipefd[1], ( fd_to_pass > 0 ) ? fd_to_pass : 0 );
+        close( fd_to_pass );
+        exit(0);
+    }
+
+    close( pipefd[1] );
+    fd_to_pass = recv_fd( pipefd[0] );  /* 父进程从管道接收目标文件描述符 */
+    char buf[1024];
+    memset( buf, '\0', 1024 );  /* 读目标文件描述符，以验证其有效性 */
+    read( fd_to_pass, buf, 1024 );
+    printf("I got fd %d and data %s\n", fd_to_pass, buf);
+    close( fd_to_pass );
+}