register path overrides with libc_bio, install fonts.xml

src/main-executable/libc_bio_path_overrides.c

@@ -0,0 +1,112 @@
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include <fontconfig/fontconfig.h>
+
+/* helpers */
+static bool starts_with(const char *string, const char *substring)
+{
+	return !strncmp(string, substring, strlen(substring));
+}
+
+static bool ends_with(const char *str, const char *suffix) {
+	if (!str || !suffix)
+		return 0;
+
+	size_t str_len = strlen(str);
+	size_t suffix_len = strlen(suffix);
+	if (suffix_len > str_len) return 0;
+	return (strcmp(str + (str_len - suffix_len), suffix) == 0);
+}
+
+static bool file_exists(char *path) {
+	return (!access(path, F_OK));
+}
+
+/* use fontconfig to find a font */
+static char * get_font_path(char *filename) {
+	int ret;
+
+	/* just load the list once on first call to this function */
+	static FcFontSet *font_set = NULL;
+	if(!font_set) {
+		ret = FcInit();
+		if (!ret)
+			return NULL;
+
+		// match all fonts
+		FcPattern *pattern = FcPatternCreate();
+		if (!pattern)
+			return NULL;
+
+		FcObjectSet *object_set = FcObjectSetBuild(FC_FILE, NULL);
+		if (!object_set) {
+			FcPatternDestroy(pattern);
+			return NULL;
+		}
+
+		// Retrieve the list of fonts
+		font_set = FcFontList(NULL, pattern, object_set);
+		if (!font_set) {
+			FcObjectSetDestroy(object_set);
+			FcPatternDestroy(pattern);
+			return NULL;
+		}
+	}
+
+	for (int i = 0; i < font_set->nfont; i++) {
+		FcPattern *font = font_set->fonts[i];
+		FcChar8 *file = NULL;
+		if (FcPatternGetString(font, FC_FILE, 0, &file) == FcResultMatch && file) {
+			if (ends_with((char *)file, filename)) {
+				return (char *)file;
+			}
+		}
+	}
+
+	return NULL;
+}
+
+static char *fonts_overrides[] = {
+	"/etc/fonts.xml",
+	/* INSTALL_DATADIR will be something like /usr/local/share */
+	INSTALL_DATADIR"/atl/system/etc/fonts.xml",
+	NULL,
+};
+
+bool apply_path_overrides(char **path) {
+	bool free_path = false;
+
+	/* TODO: read the overrides from a config file */
+	/* TODO: compare with canonicalized path */
+	if(!strcmp(*path, "/system/etc/fonts.xml")) {
+		for(char **override = fonts_overrides; *override; override++) {
+			if(file_exists(*override)) {
+				*path = *override;
+				break;
+			}
+		}
+	}
+
+	/* AOSP seems to put all the fonts in `/system/fonts`. On a standard Linux distro, the font
+	 * could be anywhere, so we need to get all the fonts fontconfig knows about and check
+	 * if the filename matches. */
+	if(starts_with(*path, "/system/fonts/")) {
+		char *font_filename = strchr(*path + 8, '/'); // after /fonts
+		char *new_path = get_font_path(font_filename);
+		if(new_path)
+			*path = new_path;
+		else
+			fprintf(stderr, "%s: !!! app trying to access a font at >%s<, but there is no >%s< in the fontconfig cache\n", __func__, *path, font_filename);
+	}
+
+	if (starts_with(*path, "/system/") || starts_with(*path, "/data/")) {
+		fprintf(stderr, "%s: !!! app trying to access >%s<, which will certainly fail\n", __func__, *path);
+		fflush(stderr);
+	}
+
+	return free_path;
+}

src/main-executable/libc_bio_path_overrides.h

@@ -0,0 +1,6 @@
+#ifndef LIBC_BIO_PATH_OVERIDES_H
+#define LIBC_BIO_PATH_OVERIDES_H
+
+bool apply_path_overrides(char **path);
+
+#endif

src/main-executable/main.c

@@ -10,6 +10,7 @@
 #include "../api-impl-jni/app/android_app_Activity.h"
 
 #include "back_button.h"
+#include "libc_bio_path_overrides.h"
 
 #include <dlfcn.h>
 #include <errno.h>
@@ -720,6 +721,9 @@ void init_cmd_parameters(GApplication *app, struct jni_callback_data *d)
 void init__r_debug();
 void remove_ongoing_notifications();
 
+typedef bool (apply_path_overrides_func_type)(char **);
+void libc_bio_set_apply_path_overrides_func(apply_path_overrides_func_type *func);
+
 int main(int argc, char **argv)
 {
 	GtkApplication *app;
@@ -732,6 +736,8 @@ int main(int argc, char **argv)
 	// for correct functionality
 	setenv("LC_ALL", "C.UTF-8", 1);
 
+	libc_bio_set_apply_path_overrides_func(apply_path_overrides);
+
 	struct jni_callback_data *callback_data = malloc(sizeof(struct jni_callback_data));
 	callback_data->apk_main_activity_class = NULL;
 	callback_data->apk_instrumentation_class = NULL;