detect preferences errors

chrome/common/json_value_serializer.cc

Index: chrome/common/json_value_serializer.cc
diff --git a/chrome/common/json_value_serializer.cc b/chrome/common/json_value_serializer.cc
index 1e739e6bde24e31c612bb7b00859f6710d1734d0..df92afda457d54056e501086bfb2ec575eec32c4 100644
--- a/chrome/common/json_value_serializer.cc
+++ b/chrome/common/json_value_serializer.cc
@@ -9,6 +9,11 @@
 #include "base/json/json_writer.h"
 #include "base/string_util.h"
 
+const char* JSONFileValueSerializer::kAccessDenied = "Access denied.";
+const char* JSONFileValueSerializer::kCannotReadFile = "Can't read file.";
+const char* JSONFileValueSerializer::kFileLocked = "File locked.";
+const char* JSONFileValueSerializer::kNoSuchFile = "File doesn't exist.";
+
 JSONStringValueSerializer::~JSONStringValueSerializer() {}
 
 bool JSONStringValueSerializer::Serialize(const Value& root) {
@@ -19,13 +24,15 @@ bool JSONStringValueSerializer::Serialize(const Value& root) {
   return true;
 }
 
-Value* JSONStringValueSerializer::Deserialize(std::string* error_message) {
+Value* JSONStringValueSerializer::Deserialize(int* error_code,
+                                              std::string* error_str) {
   if (!json_string_)
     return NULL;
 
   return base::JSONReader::ReadAndReturnError(*json_string_,
                                               allow_trailing_comma_,
-                                              error_message);
+                                              error_code,
+                                              error_str);
 }
 
 /******* File Serializer *******/
@@ -47,11 +54,55 @@ bool JSONFileValueSerializer::Serialize(const Value& root) {
   return true;
 }
 
-Value* JSONFileValueSerializer::Deserialize(std::string* error_message) {
+int JSONFileValueSerializer::ReadFileToString(std::string* json_string) {
+  DCHECK(json_string);
+  if (!file_util::ReadFileToString(json_file_path_, json_string)) {
+#if defined(OS_WIN)
+    int error = ::GetLastError();
+    if (error == ERROR_SHARING_VIOLATION || error == ERROR_LOCK_VIOLATION) {
+      return JSON_FILE_LOCKED;
+    } else if (error == ERROR_ACCESS_DENIED) {
+      return JSON_ACCESS_DENIED;
+    }
+#endif
+    if (!file_util::PathExists(json_file_path_))
+      return JSON_NO_SUCH_FILE;
+    else
+      return JSON_CANNOT_READ_FILE;
+  }
+  return JSON_NO_ERROR;
+}
+
+const char* JSONFileValueSerializer::GetErrorMessageForCode(int error_code) {
+  switch (error_code) {
+    case JSON_NO_ERROR:
+      return "";
+    case JSON_ACCESS_DENIED:
+      return kAccessDenied;
+    case JSON_CANNOT_READ_FILE:
+      return kCannotReadFile;
+    case JSON_FILE_LOCKED:
+      return kFileLocked;
+    case JSON_NO_SUCH_FILE:
+      return kNoSuchFile;
+    default:
+      NOTREACHED();
+      return "";
+  }
+}
+
+Value* JSONFileValueSerializer::Deserialize(int* error_code,
+                                            std::string* error_str) {
   std::string json_string;
-  if (!file_util::ReadFileToString(json_file_path_, &json_string)) {
+  int error = ReadFileToString(&json_string);
+  if (error != JSON_NO_ERROR) {
+    if (error_code)
+      *error_code = error;
+    if (error_str)
+      *error_str = GetErrorMessageForCode(error);
     return NULL;
   }
+
   JSONStringValueSerializer serializer(json_string);
-  return serializer.Deserialize(error_message);
+  return serializer.Deserialize(error_code, error_str);
 }