Allow Asset Overriding

mods/CMakeLists.txt

@@ -22,6 +22,9 @@ target_link_libraries(screenshot GLESv1_CM freeimage)
 add_library(extra SHARED src/extra.c src/extra.cpp src/cxx11_util.cpp)
 target_link_libraries(extra core dl server screenshot)
 
+add_library(override SHARED src/override.c)
+target_link_libraries(override dl)
+
 find_package(glfw3 3.3 REQUIRED)
 
 add_library(compat SHARED src/compat.c)

mods/src/override.c

@@ -0,0 +1,70 @@
+#define _GNU_SOURCE
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdarg.h>
+
+#include <unistd.h>
+#include <fcntl.h>
+
+#include <libcore/libcore.h>
+
+static int starts_with(const char *s, const char *t) {
+    return strncmp(s, t, strlen(t)) == 0;
+}
+
+static char *get_override_path(const char *filename) {
+    // Get Asset Override Path
+    char *overrides = NULL;
+    asprintf(&overrides, "%s/.minecraft/overrides", getenv("HOME"));
+    // Get data Path
+    char *data = NULL;
+    char *cwd = getcwd(NULL, 0);
+    asprintf(&data, "%s/data", cwd);
+    free(cwd);
+    // Get Full Path
+    char *new_path = NULL;
+    char *full_path = realpath(filename, NULL);
+    if (full_path != NULL) {
+        if (starts_with(full_path, data)) {
+            asprintf(&new_path, "%s%s", overrides, &full_path[strlen(data)]);
+            if (access(new_path, F_OK) == -1) {
+                free(new_path);
+                new_path = NULL;
+            }
+        }
+        free(full_path);
+    }
+    // Free Variables
+    free(overrides);
+    free(data);
+    // Return
+    return new_path;
+}
+
+HOOK(fopen, FILE *, (const char *filename, const char *mode)) {
+    char *new_path = get_override_path(filename);
+    // Open File
+    ensure_fopen();
+    FILE *file = (*real_fopen)(new_path != NULL ? new_path : filename, mode);
+    // Free Data
+    if (new_path != NULL) {
+        free(new_path);
+    }
+    // Return File
+    return file;
+}
+
+HOOK(fopen64, FILE *, (const char *filename, const char *mode)) {
+    char *new_path = get_override_path(filename);
+    // Open File
+    ensure_fopen64();
+    FILE *file = (*real_fopen64)(new_path != NULL ? new_path : filename, mode);
+    // Free Data
+    if (new_path != NULL) {
+        free(new_path);
+    }
+    // Return File
+    return file;
+}