minecraft: query and parse player positions

src/main.c

@@ -1,8 +1,13 @@
+/*
+ *  main.c - Main entry point for the wamf executable.
+ */
+
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>
 
 #include "rcon.h"
+#include "minecraft.h"
 
 const char *LOCALHOST = "127.0.0.1";
 
@@ -42,17 +47,31 @@ int main(void) {
         exit(EXIT_FAILURE);
     }
 
-    const char *get_player_positions_cmd = "execute as @a run data get entity @s Pos";
-    printf("\nexecuting command: %s\n", get_player_positions_cmd);
-    char *response = rcon_command_multipacket(sockfd, get_player_positions_cmd);
-
-    if (response) {
-        printf("\n=== player positions ===\n");
-        printf("%s\n", response);
-    } else {
-        fprintf(stderr, "failed to get player positions\n");
+    player_entity_t* entities = malloc(sizeof(player_entity_t) * 20);
+    if (!entities) {
+        perror("malloc failed");
+        close(sockfd);
+        exit(EXIT_FAILURE);
     }
 
+    if (query_player_entities(sockfd, 20, entities) < 0) {
+        fprintf(stderr, "failed to query player entities\n");
+        free(entities);
+        close(sockfd);
+        exit(EXIT_FAILURE);
+    }
+
+    printf("\n=== player positions ===\n");
+    for (size_t i = 0; i < 20 && entities[i].name != NULL; i++) {
+        printf("%s: (%.2f, %.2f, %.2f)\n", entities[i].name, entities[i].x, entities[i].y, entities[i].z);
+    }
+
+    for (size_t i = 0; i < 20; i++) {
+        free_player_entity(&entities[i]);
+    }
+
+    free(entities);
+
     close(sockfd);
     return 0;
 }

src/minecraft.c

@@ -0,0 +1,103 @@
+/*
+ *  minecraft.c - Minecraft specific RCON client implementation
+ *
+ * This file implements some Minecraft-specific RCON commands and utilities,
+ * such as parsing player position data.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "minecraft.h"
+#include "rcon.h"
+
+void free_player_entity(player_entity_t *entity) {
+  if (entity->name) {
+    free(entity->name);
+    entity->name = NULL;
+  }
+}
+
+// Parses lines of of the format:
+//   <user> has the following entity data: [-1234.1234567891234d, 71.0d,
+//   113.0000000000001d]
+int parse_player_entity(const char *response, player_entity_t *entity) {
+  const char *prefix = " has the following entity data: [";
+  char *prefix_pos = strstr(response, prefix);
+  if (!prefix_pos) {
+    fprintf(stderr, "invalid response format: missing prefix\n");
+    return -1;
+  }
+
+  size_t name_len = prefix_pos - response;
+  entity->name = malloc(name_len + 1);
+  if (!entity->name) {
+    perror("malloc failed");
+    return -1;
+  }
+  strncpy(entity->name, response, name_len);
+  entity->name[name_len] = '\0';
+
+  const char *coords_start = prefix_pos + strlen(prefix);
+  const char *coords_end = strchr(coords_start, ']');
+  if (!coords_end) {
+    fprintf(stderr, "invalid response format: missing closing bracket\n");
+    free(entity->name);
+    return -1;
+  }
+
+  char coords_str[256];
+  size_t coords_len = coords_end - coords_start;
+  if (coords_len >= sizeof(coords_str)) {
+    fprintf(stderr, "coordinates string too long\n");
+    free(entity->name);
+    return -1;
+  }
+  strncpy(coords_str, coords_start, coords_len);
+  coords_str[coords_len] = '\0';
+
+  if (sscanf(coords_str, "%lfd, %lfd, %lfd", &entity->x, &entity->y,
+             &entity->z) != 3) {
+    fprintf(stderr, "invalid coordinates format\n");
+    free(entity->name);
+    return -1;
+  }
+
+  return 0;
+}
+
+int query_player_entities(int sockfd, size_t max_entities,
+                          player_entity_t *entities) {
+  char *response = rcon_command_multipacket(
+      sockfd, "execute as @a run data get entity @s Pos");
+  if (!response) {
+    fprintf(stderr, "failed to execute command\n");
+    return -1;
+  }
+
+  size_t entity_count = 0;
+  for (size_t i = 0; i < max_entities; i++) {
+    char *line = strtok(response, "\n");
+    if (!line)
+      break;
+    printf("parsing line: '%s'\n", line);
+
+    if (parse_player_entity(line, &entities[entity_count]) == 0) {
+      entity_count++;
+    } else {
+      fprintf(stderr, "failed to parse player entity from line: %s\n", line);
+    }
+  };
+
+  if (entity_count == max_entities) {
+    fprintf(
+        stderr,
+        "warning: more player entities in response than provided space for\n");
+  }
+
+  // WARNING: response is not malloced :skull: - don't free it!
+  // free(response);
+
+  return (int)entity_count;
+}

src/minecraft.h

@@ -0,0 +1,15 @@
+#include <stddef.h>
+
+typedef struct {
+  char *name;
+  double x;
+  double y;
+  double z;
+} player_entity_t;
+
+void free_player_entity(player_entity_t *entity);
+
+int parse_player_entity(const char *response, player_entity_t *entity);
+
+int query_player_entities(int sockfd, size_t entities_size,
+                          player_entity_t *entities);

src/rcon.c

@@ -1,3 +1,9 @@
+/*
+ * rcon.c - RCON client implementation
+ *
+ * This file implements some basic functions for communicating with arbitrary RCON servers.
+ */
+
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>