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Date: Wed, 13 Jun 2018 22:48:58 +0900
From: Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp>
To: cygwin AT cygwin DOT com
Subject: Problems of AF_INET domain socket regarding out-of-band data.
Message-Id: <20180613224858.7822b08abb75d76b72920095@nifty.ne.jp>
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Hello,

I have found a few problems of AF_INET domain socket regarding
out-of-band data.

1. recv() with MSG_OOB flag eats normal data if no OOB data
  is sent yet.

2. Calling recv() with MSG_OOB flag is blocked if no OOB data
  is sent yet.

3. Calling recv() without MSG_OOB flag after receiving OOB data
  is blocked even if received data exist in buffer. 

Regarding problem 1 and 2, POSIX states as follows about recv().
[EINVAL]
The MSG_OOB flag is set and no out-of-band data is available.
http://pubs.opengroup.org/onlinepubs/9699919799/functions/recv.html

Attached is a sample program to reproduce these problems.
Argument to this program specifies the test mode.
0: cause problem 1
2: cause problem 2
3: cause problem 3

Expected results:
debian:~/OOB> ./server_client 0
recv(OOB): Invalid argument
OOB   :  (-1)
NORMAL: 1234567890 (10)
debian:~/OOB> ./server_client 1
OOB   : A (1)
NORMAL: 1234567890 (10)
debian:~/OOB> ./server_client 2
recv(OOB): Invalid argument
OOB   :  (-1)
NORMAL: 1234567890 (10)
debian:~/OOB> ./server_client 3
OOB   : A (1)
NORMAL: 1234567890 (10)
debian:~/OOB>

Result on cygwin:
[yano AT Express5800-S70 ~/OOB]$ ./server_client 0
OOB   : 1234567890 (10)
NORMAL:  (0)
[yano AT Express5800-S70 ~/OOB]$ ./server_client 1
OOB   : A (1)
NORMAL: 1234567890 (10)
[yano AT Express5800-S70 ~/OOB]$ ./server_client 2
[yano AT Express5800-S70 ~/OOB]$ ./server_client 3
OOB   : A (1)
[yano AT Express5800-S70 ~/OOB]$

Only the result of test mode 1 is as expected.

I have confirmed this occurs in both latest 32bit and 64 bit
cygwin.

-- 
Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp>

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#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <string.h>
#include <signal.h>
#include <sys/wait.h>

#define PORT	12345
#define HOST	"127.0.0.1"

int server(int mode)
{
	int sock0, sock1;
	struct sockaddr_in addr;
	struct sockaddr_in client;
	socklen_t len;

	/* Create a socket */
	sock0 = socket(AF_INET, SOCK_STREAM, 0);
	if (sock0 < 0) {
		perror("socket");
		return -1;
	}

	/* Bind */
	addr.sin_family = AF_INET;
	addr.sin_port = htons(PORT);
	addr.sin_addr.s_addr = INADDR_ANY;
	if (bind(sock0, (struct sockaddr *)&addr, sizeof(addr)) < 0) {
		perror("bind");
		return -1;
	}

	/* Wait for connection from client */
	if (listen(sock0, 1) < 0) {
		perror("listen");
		return -1;
	}

	/* Accept connection */
	len = sizeof(client);
	sock1 = accept(sock0, (struct sockaddr *)&client, &len);
	if (sock1 < 0) {
		perror("accept");
		return -1;
	}

	/* Send normal data */
	if (send(sock1, "1234567890", 10, 0) < 0) {
		perror("send");
		return -1;
	}
	if (mode & 1) {
		/* Send out-of-band data */
		if (send(sock1, "A", 1, MSG_OOB) < 0) {
			perror("send(OOB)");
			return -1;
		}
	}

	/* Wait for receiving all data at client side */
	usleep(200000);

	if (mode & 2) {
		return -1; /* return -1 to kill client */
	}

	/* Close client socket */
	close(sock1);

	/* Close socket for listen */
	close(sock0);

	return 0;
}

int client()
{
	struct sockaddr_in server;
	int sock;
	char buf[256];
	int n;

	/* Create a socket */
	sock = socket(AF_INET, SOCK_STREAM, 0);
	if (sock < 0) {
		perror("sock");
		return -1;
	}

	/* Setting for connection */
	server.sin_family = AF_INET;
	server.sin_port = htons(PORT);
	server.sin_addr.s_addr = inet_addr(HOST);

	/* Connect to server */
	if (connect(sock, (struct sockaddr *)&server, sizeof(server)) < 0) {
		perror("connect");
		return -1;
	}

	/* Wait for sending all data at server side */
	usleep(100000);

	/* Receive out-of-band data from server */
	memset(buf, 0, sizeof(buf));
	n = recv(sock, buf, sizeof(buf), MSG_OOB);
	if (n<0) {
		perror("recv(OOB)");
	}
	printf("OOB   : %s (%d)\n", buf, n);
	/* Receive normal data from server */
	memset(buf, 0, sizeof(buf));
	n = recv(sock, buf, sizeof(buf), 0);
	if (n<0) {
		perror("recv");
	}
	printf("NORMAL: %s (%d)\n", buf, n);

	/* Close socket */
	close(sock);

	return 0;
}

int main(int argc, char *argv[])
{
	int mode = 0;
	pid_t pid;

	if (argc >= 2) {
		mode = atoi(argv[1]);
	}

	pid = fork();
	if (pid) {
		if (server(mode) < 0) kill(pid, SIGTERM);
		wait(NULL);
	} else {
		return client();
	}
	return 0;
}


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