add setloadfile and setfileexists functions to flatbuffers

to allow for custom file loaders. The targeted use case is android runtime.

(from CL 116980408)

Change-Id: I8785c0acf714fab41d8f6fc9f1c52875423b8f5b

CMakeLists.txt

@@ -26,6 +26,7 @@ set(FlatBuffers_Library_SRCS
   src/idl_parser.cpp
   src/idl_gen_text.cpp
   src/reflection.cpp
+  src/util.cpp
 )
 
 set(FlatBuffers_Compiler_SRCS
@@ -68,6 +69,7 @@ set(FlatBuffers_Sample_Text_SRCS
   include/flatbuffers/util.h
   src/idl_parser.cpp
   src/idl_gen_text.cpp
+  src/util.cpp
   samples/sample_text.cpp
   # file generated by running compiler on samples/monster.fbs
   ${CMAKE_CURRENT_BINARY_DIR}/samples/monster_generated.h

android/jni/Android.mk

@@ -33,7 +33,8 @@ include $(CLEAR_VARS)
 LOCAL_MODULE := flatbuffers_extra
 LOCAL_SRC_FILES := src/idl_parser.cpp \
                    src/idl_gen_text.cpp \
-                   src/reflection.cpp
+                   src/reflection.cpp \
+                   src/util.cpp
 LOCAL_STATIC_LIBRARIES := flatbuffers
 include $(BUILD_STATIC_LIBRARY)
 

include/flatbuffers/util.h

@@ -111,33 +111,24 @@ inline int64_t StringToUInt(const char *str, int base = 10) {
   #endif
 }
 
+typedef bool (*LoadFileFunction)(const char *filename, bool binary,
+                                 std::string *dest);
+typedef bool (*FileExistsFunction)(const char *filename);
+
+LoadFileFunction SetLoadFileFunction(LoadFileFunction load_file_function);
+
+FileExistsFunction SetFileExistsFunction(FileExistsFunction
+                                         file_exists_function);
+
+
 // Check if file "name" exists.
-inline bool FileExists(const char *name) {
-  std::ifstream ifs(name);
-  return ifs.good();
-}
+bool FileExists(const char *name);
 
 // Load file "name" into "buf" returning true if successful
 // false otherwise.  If "binary" is false data is read
 // using ifstream's text mode, otherwise data is read with
 // no transcoding.
-inline bool LoadFile(const char *name, bool binary, std::string *buf) {
-  std::ifstream ifs(name, binary ? std::ifstream::binary : std::ifstream::in);
-  if (!ifs.is_open()) return false;
-  if (binary) {
-    // The fastest way to read a file into a string.
-    ifs.seekg(0, std::ios::end);
-    (*buf).resize(static_cast<size_t>(ifs.tellg()));
-    ifs.seekg(0, std::ios::beg);
-    ifs.read(&(*buf)[0], (*buf).size());
-  } else {
-    // This is slower, but works correctly on all platforms for text files.
-    std::ostringstream oss;
-    oss << ifs.rdbuf();
-    *buf = oss.str();
-  }
-  return !ifs.bad();
-}
+bool LoadFile(const char *name, bool binary, std::string *buf);
 
 // Save data "buf" of length "len" bytes into a file
 // "name" returning true if successful, false otherwise.

src/util.cpp

+/*
+ * Copyright 2016 Google Inc. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "flatbuffers/util.h"
+
+namespace flatbuffers {
+
+bool FileExistsRaw(const char *name) {
+  std::ifstream ifs(name);
+  return ifs.good();
+}
+
+bool LoadFileRaw(const char *name, bool binary, std::string *buf) {
+  std::ifstream ifs(name, binary ? std::ifstream::binary : std::ifstream::in);
+  if (!ifs.is_open()) return false;
+  if (binary) {
+    // The fastest way to read a file into a string.
+    ifs.seekg(0, std::ios::end);
+    (*buf).resize(static_cast<size_t>(ifs.tellg()));
+    ifs.seekg(0, std::ios::beg);
+    ifs.read(&(*buf)[0], (*buf).size());
+  } else {
+    // This is slower, but works correctly on all platforms for text files.
+    std::ostringstream oss;
+    oss << ifs.rdbuf();
+    *buf = oss.str();
+  }
+  return !ifs.bad();
+}
+
+static LoadFileFunction g_load_file_function = LoadFileRaw;
+static FileExistsFunction g_file_exists_function = FileExistsRaw;
+
+bool LoadFile(const char *name, bool binary, std::string *buf) {
+  assert(g_load_file_function);
+  return g_load_file_function(name, binary, buf);
+}
+
+bool FileExists(const char *name) {
+  assert(g_file_exists_function);
+  return g_file_exists_function(name);
+}
+
+LoadFileFunction SetLoadFileFunction(LoadFileFunction load_file_function) {
+  LoadFileFunction previous_function = g_load_file_function;
+  g_load_file_function = load_file_function ? load_file_function : LoadFileRaw;
+  return previous_function;
+}
+
+FileExistsFunction SetFileExistsFunction(
+    FileExistsFunction file_exists_function) {
+  FileExistsFunction previous_function = g_file_exists_function;
+  g_file_exists_function = file_exists_function ?
+      file_exists_function : FileExistsRaw;
+  return previous_function;
+}
+
+}  // namespace flatbuffers