111 lines
2.3 KiB
C
111 lines
2.3 KiB
C
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/* Example only. Do not run in production. */
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#include <stdio.h>
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#include <unistd.h>
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#include <stdlib.h>
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#include <stdint.h>
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#include <string.h>
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#include <errno.h>
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#include <sys/types.h>
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#include <sys/socket.h>
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#include <netinet/in.h>
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#include <arpa/inet.h>
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struct entry {
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uint8_t pubkey[32];
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uint32_t ip;
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uint16_t port;
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};
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enum { MAX_ENTRIES = 65536, PORT = 49918 };
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static struct entry entries[MAX_ENTRIES];
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static unsigned int next_entry;
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/* XX: this should use a hash table */
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static struct entry *find_entry(uint8_t key[32])
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{
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int i;
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for (i = 0; i < MAX_ENTRIES; ++i) {
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if (!memcmp(entries[i].pubkey, key, 32))
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return &entries[i];
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}
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return NULL;
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}
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/* XX: this is obviously vulnerable to DoS */
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static struct entry *find_or_insert_entry(uint8_t key[32])
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{
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struct entry *entry = find_entry(key);
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if (!entry) {
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entry = &entries[next_entry++ % MAX_ENTRIES];
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memcpy(entry->pubkey, key, 32);
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}
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return entry;
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}
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int main(int argc, char *argv[])
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{
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struct sockaddr_in addr = {
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.sin_family = AF_INET,
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.sin_addr = { .s_addr = htonl(INADDR_ANY) },
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.sin_port = htons(PORT)
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};
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struct {
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uint8_t my_pubkey[32];
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uint8_t their_pubkey[32];
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} __attribute__((packed)) packet;
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struct {
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uint32_t ip;
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uint16_t port;
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} __attribute__((packed)) reply;
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struct entry *entry;
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socklen_t len;
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ssize_t retlen;
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int optval;
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int sock = socket(AF_INET, SOCK_DGRAM, 0);
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if (sock < 0) {
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perror("socket");
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return errno;
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}
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optval = 1;
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if (setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &optval, sizeof(optval)) < 0) {
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perror("setsockopt");
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return errno;
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}
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if (bind(sock, (struct sockaddr *)&addr, sizeof(addr)) < 0) {
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perror("bind");
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return errno;
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}
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for (;;) {
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len = sizeof(addr);
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if (recvfrom(sock, &packet, sizeof(packet), 0, (struct sockaddr *)&addr, &len) != sizeof(packet)) {
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perror("recvfrom");
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continue;
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}
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entry = find_or_insert_entry(packet.my_pubkey);
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entry->ip = addr.sin_addr.s_addr;
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entry->port = addr.sin_port;
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entry = find_entry(packet.their_pubkey);
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if (entry) {
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reply.ip = entry->ip;
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reply.port = entry->port;
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if (sendto(sock, &reply, sizeof(reply), 0, (struct sockaddr *)&addr, len) < 0) {
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perror("sendto");
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continue;
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}
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} else {
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if (sendto(sock, NULL, 0, 0, (struct sockaddr *)&addr, len) < 0) {
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perror("sendto");
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continue;
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}
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}
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}
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close(sock);
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return 0;
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}
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