get port number from envvar

src/main.c

@@ -1,5 +1,54 @@
 #include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+
+const char *LOCALHOST = "127.0.0.1";
+
+int read_env_int(const char *var) {
+    const char* port_str = getenv(var);
+
+    if (port_str == NULL) {
+        fprintf(stderr, "error: %s environment variable not set.\n", var);
+        exit(EXIT_FAILURE);
+    }
+
+    char* endptr;
+    long val = strtol(port_str, &endptr, 10);
+    if (endptr == port_str || *endptr != '\0') {
+        fprintf(stderr, "error: invalid number format for %s.\n", var);
+        exit(EXIT_FAILURE);
+    }
+    return (int)val;
+}
+
+int rcon_connect(int port) {
+    int sockfd = socket(AF_INET, SOCK_STREAM, 0);
+    if (sockfd < 0) {
+        perror("socket creation failed");
+        exit(EXIT_FAILURE);
+    }
+
+    struct sockaddr_in server_addr;
+    memset(&server_addr, 0, sizeof(server_addr));
+    server_addr.sin_family = AF_INET;
+    server_addr.sin_port = htons(port);
+    inet_pton(AF_INET, LOCALHOST, &server_addr.sin_addr);
+
+    if (connect(sockfd, (struct sockaddr *)&server_addr, sizeof(server_addr)) < 0) {
+        perror("connection failed");
+        exit(EXIT_FAILURE);
+    }
+    printf("connected to rcon server\n");
+    return sockfd;
+}
 
 int main(int argc, char **argv) {
-    printf("hello");
+    const int PORT_NUM = read_env_int("RCON_PORT_NUMBER");
+    printf("port: %d\n", PORT_NUM);
+
+    rcon_connect(PORT_NUM);
 }