[英]C socket server and Python socket client "Resource temporarily unavailable"
I am creating a C server and Python client for UNIX domain datagram sockets (UDS) IPC on Ubuntu 18.04. 我的场景是: Python 作为使用 fork-execv 创建的子进程运行,其中 C 是父进程。 Python 客户端在 socket.recvfrom 上阻塞,直到 C 服务器发送数据。 When the C server sends data to the Python client then C will block on recvfrom until Python sends data to C with sendto.
我已经将 UDS 用于 C 客户端和 C 服务器没有问题,但是 C-Python 设置导致了一些问题。 对于这个 Python 版本,我从https://lloydrochester.com/post/c/unix-domain-socket-datagram的示例中工作。
我在 C 中创建一个服务器套接字并绑定到它; 它返回文件描述符 5:
int64_t * create_socket_server(struct sockaddr_un svaddr, int64_t retvals[])
{
int sfd, j;
ssize_t numBytes;
socklen_t len;
char buf[BUF_SIZE];
retvals[0] = 0;
retvals[1] = 0;
sfd = socket(AF_UNIX, SOCK_DGRAM, 0); /* Create server socket
if (sfd == -1)
return retvals;
if (remove(SV_SOCK_PATH) == -1 && errno != ENOENT)
return retvals;
memset(&svaddr, 0, sizeof(struct sockaddr_un));
svaddr.sun_family = AF_UNIX;
strncpy(svaddr.sun_path, SV_SOCK_PATH, sizeof(svaddr.sun_path) - 1);
if (bind(sfd, (struct sockaddr *) &svaddr, sizeof(struct sockaddr_un)) == -1)
return retvals;
retvals[0] = sfd;
retvals[1] = (int64_t)&svaddr;
return retvals;
}
我没有在 C 端创建或显式连接到客户端套接字。
在 Python 端,我绑定到客户端套接字。 这是我的 Python 代码,按照引用的示例,但有所改动以适合我的用例:
#!/usr/bin/python3
import socket
import os, os.path
csock_file = "/tmp/py_sock"
ssock_file = "/tmp/ud_ucase"
if os.path.exists(csock_file):
os.remove(csock_file)
csock = socket.socket(socket.AF_UNIX, socket.SOCK_DGRAM)
csock.bind(csock_file) # Bind to the server socket
return_msg = "Got it"
while True:
(bytes, address) = csock.recvfrom(720)
msg = bytes.decode('utf-8')
print("Python received")
if msg != "Code_99":
print('address:',address,'received:',msg)
csock.sendto(str.encode(return_msg), ssock_file)
if msg == "Code_99":
print("closing")
#Close the socket
I want recvfrom to be blocking in both Python and C because Python should block until C sends, but when I leave it at blocking (the default) then Python blocks both processes when it calls (bytes, address) = csock.recvfrom(720) ,并且 C 无法继续。
如果我使用 csock.setblocking(False) 将其设置为非阻塞,我会收到以下错误消息:
(bytes, address) = csock.recvfrom(720)
BlockingIOError: [Errno 11] Resource temporarily unavailable
所以我的问题是为什么 Python 会阻止这两个进程,为什么我会在非阻塞模式下收到该错误消息?
谢谢你的帮助。
为什么 Python 会阻止这两个进程?
当您的客户端使用recvfrom
等待服务器的响应时,您的服务器什么也没做,因此服务器也会在其recvfrom
处阻塞。
为什么我在非阻塞模式下会收到该错误消息?
您的服务器/客户端可能不像您引用的那样强大(即来自lloydrochester.com )。 几个零件坏了,导致整个东西坏了。 其中一些只是关于 C 郎,如变量声明, Function 返回等。还有一些是关于网络编程的,如Buffer Sizing , Socket Internals等,不一一列举并一一分析。 最好通读K&R和BSD 套接字以彻底修复它们。
但是,根据您的代码,这是一个相对简单的实现,如下所示。 此外,您可能希望将server_alice.c第 48 行中的回复消息更改为Code_99
。
Ubuntu 18.04
gcc 7.5.0
Python 3.6.9
#include <sys/un.h>
#include <sys/socket.h>
#include <ctype.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>
#define BUF_SIZE 720
#define SV_SOCK_PATH "ssock"
int create_socket_server(int *sfd_ptr, struct sockaddr_un *svaddr_ptr);
int main(int argc, char *argv[]) {
struct sockaddr_un svaddr, claddr;
int sfd, j;
ssize_t numBytes;
socklen_t len;
char buf[BUF_SIZE];
int64_t retvals[2];
if (create_socket_server(&sfd, &svaddr) == 0)
printf("create_socket_server...DONE\n");
else exit(0);
for (;;) {
len = sizeof(struct sockaddr);
printf("waiting clients...\n");
numBytes = recvfrom(sfd, buf, BUF_SIZE, 0, (struct sockaddr *) &claddr, &len);
if (numBytes == -1) {
fprintf(stderr, "error recvfrom");
return 4;
}
claddr.sun_path[len - sizeof(sa_family_t) - 1] = 0;
buf[numBytes] = '\0';
fprintf(stdout, "server received %ld bytes from %s, they are: \x1b[32m%s\x1b[0m\n", (long) numBytes,
claddr.sun_path, buf);
for (j = 0; j < numBytes; j++) {
buf[j] = toupper((unsigned char) buf[j]);
}
// char *reply_msg="Code_99"; # different reply message
char *reply_msg = "Hello Bob~ This is a message: blablablabla";
j = sendto(sfd, reply_msg, strlen(reply_msg), 0, (struct sockaddr *) &claddr, len);
if (j != strlen(reply_msg)) {
fprintf(stderr, "error sendto %s", strerror(errno));
}
}
exit(EXIT_SUCCESS);
}
/* Your create_socket_server, with a few changes */
int create_socket_server(int *sfd_ptr, struct sockaddr_un *svaddr_ptr) {
struct sockaddr_un svaddr;
int sfd = socket(AF_UNIX, SOCK_DGRAM, 0); // Create server socket
if (sfd == -1)
return -1;
if (remove(SV_SOCK_PATH) == -1 && errno != ENOENT)
return -1;
memset(&svaddr, 0, sizeof(struct sockaddr_un));
svaddr.sun_family = AF_UNIX;
strncpy(svaddr.sun_path, SV_SOCK_PATH, sizeof(svaddr.sun_path) - 1);
if (bind(sfd, (struct sockaddr *) &svaddr, sizeof(struct sockaddr_un)) == -1)
return -1;
memcpy(sfd_ptr, &sfd, sizeof(int));
memcpy(svaddr_ptr, &svaddr, sizeof(struct sockaddr_un));
return 0;
}
#!/usr/bin/python3
import socket
import os, os.path
csock_file = "./csock"
ssock_file = "./ssock"
if os.path.exists(csock_file):
os.remove(csock_file)
csock = socket.socket(socket.AF_UNIX, socket.SOCK_DGRAM)
csock.bind(csock_file) # Bind to the server socket
return_msg = "Got it"
csock.sendto(str.encode("Hello Alice! I'm coming!"), ssock_file)
# while True: # ! CATION ! If 'while(true)', there will be infinite message sending back and forth!
(bytes, address) = csock.recvfrom(720)
msg = bytes.decode('utf-8')
if msg != "Code_99":
print('address: ', address, 'received: ', msg)
csock.sendto(str.encode(return_msg), ssock_file)
if msg == "Code_99":
print("closing")
csock.close()
$ gcc server_alice.c && ./a.out
create_socket_server...DONE
waiting clients...
server received 24 bytes from ./csock, they are: Hello Alice! I'm coming!
waiting clients...
server received 6 bytes from ./csock, they are: Got it
waiting clients...
$ python3 client_bob.py
address: ssock received: Hello Bob~ This is a message: blablablabla
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