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/* SPDX-License-Identifier: GPL-3.0-or-later */
#include "p2p.h"
#include <errno.h>
#include <netinet/in.h>
#include <stdint.h>
#include <sys/poll.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <unistd.h>
// Create a UDP socket with DF set.
static int create_socket() {
int sockfd = socket(AF_INET, SOCK_DGRAM, 0);
if (sockfd < 0) {
return -1;
}
int value = IP_PMTUDISC_DO;
if (setsockopt(sockfd, IPPROTO_IP, IP_MTU_DISCOVER, &value, sizeof(value)) < 0) {
close(sockfd);
return -1;
}
return sockfd;
}
int p2p_bind(uint16_t port, in_addr_t ip) {
int sockfd = create_socket();
if (sockfd < 0) {
goto err;
}
struct sockaddr_in local_addr = {
.sin_family = AF_INET,
.sin_port = htons(port),
.sin_addr = { .s_addr = INADDR_ANY },
};
if (bind(sockfd, (struct sockaddr*) &local_addr, sizeof(local_addr)) < 0) {
goto err_close;
}
while (true) {
// Wait for handshake from peer
struct sockaddr_in remote_addr;
socklen_t remote_addr_len = sizeof(remote_addr);
uint8_t handshake[1];
ssize_t handshake_len = recvfrom(sockfd, handshake, sizeof(handshake), 0,
(struct sockaddr*) &remote_addr, &remote_addr_len);
if (handshake_len < 0) {
goto err_close;
}
if (handshake_len != 1 || *handshake != '?') {
// Malformed handshake, ignore
continue;
}
if (remote_addr.sin_addr.s_addr != ip) {
// Wrong peer, reject handshake
sendto(sockfd, "N", 1, 0, (struct sockaddr*) &remote_addr, remote_addr_len);
continue;
}
// Accept handshake and lock into peer
if (connect(sockfd, (struct sockaddr*) &remote_addr, remote_addr_len) < 0) {
goto err_close;
}
if (send(sockfd, "Y", 1, 0) < 0) {
goto err_close;
}
break;
}
return sockfd;
err_close:
close(sockfd);
err:
return -1;
}
int p2p_connect(uint16_t port, in_addr_t ip, int timeout) {
int sockfd = create_socket();
if (sockfd < 0) {
goto err;
}
struct sockaddr_in remote_addr = {
.sin_family = AF_INET,
.sin_port = htons(port),
.sin_addr = { .s_addr = ip },
};
if (connect(sockfd, (struct sockaddr*) &remote_addr, sizeof(remote_addr)) < 0) {
goto err_close;
}
// Perform handshake
if (send(sockfd, "?", 1, 0) < 0) {
goto err_close;
}
struct pollfd pfd = {
.fd = sockfd,
.events = POLLIN,
};
int ret = poll(&pfd, 1, timeout);
if (ret < 0) {
goto err_close;
} else if (ret == 0) {
errno = ETIMEDOUT;
goto err_close;
}
uint8_t handshake[1];
ssize_t handshake_len = recv(sockfd, handshake, sizeof(handshake), 0);
if (handshake_len < 0) {
goto err_close;
} else if (handshake_len != 1 || *handshake != 'Y') {
errno = ECONNREFUSED;
goto err_close;
}
return sockfd;
err_close:
close(sockfd);
err:
return -1;
}
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