{send,recv}_packet: embed last padding byte in package struct and fix sizes accordingly

src/main.c

@@ -18,10 +18,16 @@ const char *LOCALHOST = "127.0.0.1";
 #define SERVERDATA_RESPONSE_VALUE 0
 
 typedef struct {
+    // size of the remainder of the packet
     int32_t size;
+    // packet id (client sets, server echoes, -1 on auth failure)
     int32_t id;
+    // packet type (see the SERVERDATA_* constants)
     int32_t type;
+    // null-terminated command string (for auth and exec) or response string (from server)
     char body[4096];
+    // yet another null byte after the body (required by protocol)
+    uint8_t _padding;
 } rcon_packet_t;
 
 int read_env_int(const char *var) {
@@ -73,10 +79,9 @@ int rcon_connect(int port) {
 }
 
 void send_packet(int sockfd, int32_t id, int32_t type, const char *body) {
-    int body_len = strlen(body);
-    int32_t size = 10 + body_len;
+    size_t body_len = strlen(body);
 
-    size_t packet_size = sizeof(int32_t) + size;
+    size_t packet_size = sizeof(int32_t) * 3 + body_len + 2;
     unsigned char *packet = malloc(packet_size);
     if (!packet) {
         perror("malloc failed");
@@ -93,8 +98,8 @@ void send_packet(int sockfd, int32_t id, int32_t type, const char *body) {
     memcpy(packet + 8, &type_, sizeof(int32_t));
 
     memcpy(packet + 12, body, body_len);
-    packet[12 + body_len] = 0;
-    packet[12 + body_len + 1] = 0;
+    packet[3 * sizeof(int32_t) + body_len] = 0;
+    packet[3 * sizeof(int32_t) + body_len + 1] = 0;
 
     ssize_t sent = send(sockfd, packet, packet_size, 0);
     if (sent < 0) {
@@ -139,14 +144,20 @@ int recv_packet(int sockfd, rcon_packet_t *packet) {
     }
     packet->type = le32toh(packet->type);
 
-    int body_size = packet->size - 10;
+    int body_size = packet->size - sizeof(int32_t) * 2 - 2;
     if (body_size > 0 && body_size < (int)sizeof(packet->body)) {
-        bytes = recv(sockfd, packet->body, body_size + 2, MSG_WAITALL);
+        bytes = recv(sockfd, packet->body, body_size, MSG_WAITALL);
         if (bytes <= 0) {
             perror("recv body failed");
             return -1;
         }
         packet->body[body_size] = '\0';
+
+        bytes = recv(sockfd, &packet->_padding, 1, MSG_WAITALL);
+        if (bytes <= 0) {
+            perror("recv padding failed");
+            return -1;
+        }
     } else {
         packet->size = sizeof(int32_t) * 2 + 2;
         packet->body[0] = '\0';