linux_msg_peek.c
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	melifaro
	Jan 8 2022, 1:47 PM

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linux_msg_peek.c
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	/*
	*
	*/

	#include <string.h>
	#include <stdlib.h>
	#include <errno.h>
	#include <sys/types.h>
	#include <unistd.h>
	#include <stdio.h>
	#include <arpa/inet.h>
	#include <sys/socket.h>
	#include <assert.h>


	struct sd {
	int family;
	int type;
	int proto;
	struct sockaddr *sa;
	int sa_len;
	};

	static int
	bind_socket(struct sd *sd)
	{
	struct sockaddr_in *sin;
	struct sockaddr_in6 *sin6;
	int error, s;

	s = socket(sd->family, sd->type, sd->proto);
	printf("socket(%d,%d,%d) -> %d \| %s\n", sd->family, sd->type, sd->proto, s, strerror(errno));

	for (int i = 0; i < 10; i++) {
	int port = htons(32768 + random() % 4096);
	error = 0;

	switch (sd->family) {
	case AF_INET:
	sin = (struct sockaddr_in *)sd->sa;
	memset(sin, 0, sizeof(struct sockaddr_in));
	sin->sin_family = AF_INET;
	inet_pton(AF_INET, "127.0.0.1", &sin->sin_addr);
	sin->sin_port = htons(port);
	sd->sa_len = sizeof(struct sockaddr_in);
	break;
	case AF_INET6:
	sin6 = (struct sockaddr_in6 *)sd->sa;
	memset(sin6, 0, sizeof(struct sockaddr_in6));
	sin6->sin6_family = AF_INET6;
	inet_pton(AF_INET6, "::1", &sin6->sin6_addr);
	sin6->sin6_port = htons(port);
	sd->sa_len = sizeof(struct sockaddr_in6);
	break;
	}
	error = bind(s, sd->sa, sd->sa_len);
	printf("bind(fd#%d) -> %d \| %s\n", s, error, strerror(errno));
	if (error != EADDRINUSE)
	break;
	}

	if (error != 0) {
	close(s);
	return (0);
	}

	return (s);
	}

	static void
	test_msg_peek_sd(int s, struct sd *sd)
	{
	int c = socket(sd->family, sd->type, sd->proto);

	int databuf_len = 1024;
	char *databuf = malloc(databuf_len);
	memset(databuf, 0xFF, databuf_len);

	char *rxbuf = malloc(databuf_len);
	memset(databuf, 0, databuf_len);

	int peek_len = 128;
	memset(databuf, 0xEE, peek_len);

	int len;


	len = sendto(c, databuf, databuf_len, 0, sd->sa, sd->sa_len);
	printf("sendto(fd#%d) -> %d\n", c, len);

	char sabuf[32];
	struct iovec iov = {
	.iov_base = rxbuf,
	.iov_len = peek_len,
	};
	struct msghdr msg = {
	.msg_name = sabuf,
	.msg_namelen = sizeof(sabuf),
	.msg_iov = &iov,
	.msg_iovlen = 1,
	};

	errno = 0;
	len = recvmsg(s, &msg, MSG_PEEK);
	printf("recvmsg(fd#%d) -> %d \| errno %s\n", s, len, strerror(errno));
	assert(len == peek_len);
	assert(memcmp(rxbuf, databuf, len) == 0);

	iov.iov_len = databuf_len;

	len = recvmsg(s, &msg, 0);
	printf("recvmsg(fd#%d) -> %d \| errno %s\n", s, len, strerror(errno));
	assert(len == databuf_len);
	assert(memcmp(rxbuf, databuf, len) == 0);

	free(databuf);
	free(rxbuf);
	}


	static void
	test_msg_peek()
	{
	char sa_buffer[32];

	struct sd sd = {
	.family = AF_INET,
	.type = SOCK_DGRAM,
	.proto = IPPROTO_UDP,
	.sa = (struct sockaddr *)sa_buffer,
	};

	int s = bind_socket(&sd);
	test_msg_peek_sd(s, &sd);
	}



	int main()
	{
	test_msg_peek();

	return (0);
	}

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