initial commit

.gitignore

@@ -0,0 +1,6 @@
+.vscode
+CMakeFiles
+CMakeCache.txt
+Makefile
+*.cmake
+udptracker

CMakeLists.txt

@@ -0,0 +1,8 @@
+cmake_minimum_required(VERSION 3.10)
+project(udptracker)
+
+set(SOURCES
+    udptracker.c
+)
+
+add_executable(udptracker ${SOURCES})

udptracker.c

@@ -0,0 +1,142 @@
+#include <stdio.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#include <time.h>
+#include <errno.h>
+#include <netdb.h>
+#include <arpa/inet.h>
+#include <sys/socket.h>
+
+#define INIT_CONNECTION_ID  0x41727101980ULL
+#define ACTION_CONNECT      0
+#define ACTION_ANNOUNCE     1
+#define ANNOUNCE_NUMWANT    -1
+
+struct connect_request_s {
+    uint64_t connection_id;
+    uint32_t action;
+    uint32_t transaction_id;
+} __attribute__((packed));
+
+struct connect_response_s {
+    uint32_t action;
+    uint32_t transaction_id;
+    uint64_t connection_id;
+} __attribute__((packed));
+
+struct announce_request_s {
+    uint64_t connection_id;
+    uint32_t action;
+    uint32_t transaction_id;
+    uint8_t info_hash[20];
+    uint8_t peer_id[20];
+    uint64_t downloaded;
+    uint64_t left;
+    uint64_t uploaded;
+    uint32_t event;
+    uint32_t ip_address;
+    uint32_t key;
+    int32_t numwant;
+    uint16_t port;
+} __attribute__((packed));
+
+struct announce_response_s {
+    uint32_t action;
+    uint32_t transaction_id;
+    uint32_t interval;
+    uint32_t leechers;
+    uint32_t seeders;
+} __attribute__((packed));
+
+struct peer_s {
+    uint32_t ip_address;
+    uint16_t port;
+} __attribute__((packed));
+
+static void _sendto(int sockfd, const void* data, size_t size,
+    const struct sockaddr* paddr, socklen_t socklen)
+{
+    ssize_t sent = sendto(sockfd, data, size, 0, paddr, socklen);
+    if (sent == -1)
+    {
+        fprintf(stderr, "sendto errno %d error %s\n",
+            errno, strerror(errno));
+    }
+}
+
+static ssize_t _recvfrom(int sockfd, void* data, size_t size,
+    struct sockaddr* paddr, socklen_t* socklen)
+{
+    ssize_t read = recvfrom(sockfd, data, size, 0, paddr, socklen);
+    if (read == -1)
+    {
+        fprintf(stderr, "recvfrom errno %d error %s\n",
+            errno, strerror(errno));
+    }
+
+    return read;
+}
+
+int main(int argc, char** argv)
+{
+    if (argc < 3)
+    {
+        fprintf(stderr, "%s <host> <port>\n", argv[0]);
+        return 1;
+    }
+
+    struct hostent* host = gethostbyname(argv[1]);
+    if (!host)
+    {
+        fprintf(stderr, "Host not found: %d\n", errno);
+        return 1;
+    }
+
+    if (host->h_addrtype == AF_INET6)
+    {
+        char buf[48] = {0};
+        fprintf(stderr, "IPv6 not supported yet: %s\n",
+            inet_ntop(AF_INET6, host->h_addr_list[0], buf, 48));
+        return 1;
+    }
+
+    struct sockaddr_in addr = {0};
+    struct sockaddr* paddr = (struct sockaddr*)&addr;
+    socklen_t addrlen = sizeof(addr);
+    addr.sin_family = host->h_addrtype;
+    memcpy(&addr.sin_addr, host->h_addr_list[0], addrlen);
+    addr.sin_port = htons(atoi(argv[2]));
+
+    printf("%s\t%d\n", inet_ntoa(addr.sin_addr), ntohs(addr.sin_port));
+
+    int sockfd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
+
+    srand(time(NULL));
+    uint64_t connection_id = INIT_CONNECTION_ID;
+    uint32_t transaction_id = rand();
+    printf("connect\ttransaction\t%u\n", transaction_id);
+    {
+        struct connect_request_s req = {
+            .connection_id = __bswap_64(INIT_CONNECTION_ID),
+            .action = __bswap_32(ACTION_CONNECT),
+            .transaction_id = transaction_id
+        };
+        _sendto(sockfd, &req, sizeof(req), paddr, addrlen);
+
+        struct connect_response_s res = {0};
+        _recvfrom(sockfd, &res, sizeof(res), paddr, &addrlen);
+        res.action = __bswap_32(res.action);
+        res.transaction_id = __bswap_32(res.transaction_id);
+        res.connection_id = __bswap_64(res.connection_id);
+        printf("%u\t%u\t%lu\n", res.action,
+            res.transaction_id, res.connection_id);
+
+        connection_id = res.connection_id;
+    }
+
+    close(sockfd);
+
+    return 0;
+}