Improve reliability of custom spelling dictionary file.

chrome/browser/spellchecker/spellcheck_custom_dictionary.cc

Index: chrome/browser/spellchecker/spellcheck_custom_dictionary.cc
diff --git a/chrome/browser/spellchecker/spellcheck_custom_dictionary.cc b/chrome/browser/spellchecker/spellcheck_custom_dictionary.cc
index 4510332e59e3032ee7b35bf26f640ff6f3f2885c..588e3675c2fa3d8e22620f578cd497abef322e16 100644
--- a/chrome/browser/spellchecker/spellcheck_custom_dictionary.cc
+++ b/chrome/browser/spellchecker/spellcheck_custom_dictionary.cc
@@ -7,6 +7,8 @@
 #include <functional>
 
 #include "base/file_util.h"
+#include "base/files/important_file_writer.h"
+#include "base/md5.h"
 #include "base/string_split.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/common/chrome_constants.h"
@@ -17,6 +19,41 @@
 using content::BrowserThread;
 using chrome::spellcheck_common::WordList;
 
+namespace {
+
+const FilePath::CharType BACKUP_EXTENSION[] = FILE_PATH_LITERAL("backup");
+const char CHECKSUM_PREFIX[] = "checksum_v1 = ";
+
+// Loads the lines from the file at |file_path| into the |lines| container. If
+// the file has a valid checksum, then returns |true|. If the file has an
+// invalid checksum, then returns |false| and clears |lines|.
+bool LoadFile(FilePath file_path, std::vector<std::string>* lines) {
+  lines->clear();
+  std::string contents;
+  file_util::ReadFileToString(file_path, &contents);
+  size_t pos = contents.rfind(CHECKSUM_PREFIX);
+  if (pos != std::string::npos) {
+    std::string checksum = contents.substr(pos + strlen(CHECKSUM_PREFIX));
+    contents = contents.substr(0, pos);
+    if (checksum != base::MD5String(contents))
+      return false;
+  }
+  TrimWhitespaceASCII(contents, TRIM_ALL, &contents);
+  base::SplitString(contents, '\n', lines);
+  return true;
+}
+
+bool IsValidWord(const std::string& word) {
+  return IsStringUTF8(word) && word.length() <= 128 && word.length() > 0 &&
+      std::string::npos == word.find_first_of(kWhitespaceASCII);
+}
+
+bool IsInvalidWord(const std::string& word) {
+  return !IsValidWord(word);
+}
+
+}  // namespace
+
 SpellcheckCustomDictionary::SpellcheckCustomDictionary(Profile* profile)
     : SpellcheckDictionary(profile),
       custom_dictionary_path_(),
@@ -49,35 +86,21 @@ void SpellcheckCustomDictionary::LoadDictionaryIntoCustomWordList(
     WordList* custom_words) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
 
-  std::string contents;
-  file_util::ReadFileToString(custom_dictionary_path_, &contents);
-  if (contents.empty()) {
-    custom_words->clear();
+  LoadDictionaryFileReliably(custom_words);
+  if (custom_words->empty())
     return;
-  }
-
-  base::SplitString(contents, '\n', custom_words);
 
-  // Erase duplicates.
+  // Clean up the dictionary file contents by removing duplicates and invalid
+  // words.
   std::sort(custom_words->begin(), custom_words->end());
   custom_words->erase(std::unique(custom_words->begin(), custom_words->end()),
                       custom_words->end());
+  custom_words->erase(std::remove_if(custom_words->begin(),
+                                     custom_words->end(),
+                                     IsInvalidWord),
+                      custom_words->end());
 
-  // Clear out empty words.
-  custom_words->erase(remove_if(custom_words->begin(), custom_words->end(),
-    mem_fun_ref(&std::string::empty)), custom_words->end());
-
-  // Write out the clean file.
-  std::stringstream ss;
-  for (WordList::iterator it = custom_words->begin();
-       it != custom_words->end();
-       ++it) {
-    ss << *it << '\n';
-  }
-  contents = ss.str();
-  file_util::WriteFile(custom_dictionary_path_,
-                       contents.c_str(),
-                       contents.length());
+  SaveDictionaryFileReliably(*custom_words);
 }
 
 void SpellcheckCustomDictionary::SetCustomWordList(WordList* custom_words) {
@@ -87,13 +110,13 @@ void SpellcheckCustomDictionary::SetCustomWordList(WordList* custom_words) {
   if (custom_words)
     std::swap(words_, *custom_words);
 
-  std::vector<Observer*>::iterator it;
-  for (it = observers_.begin(); it != observers_.end(); ++it)
-    (*it)->OnCustomDictionaryLoaded();
+  FOR_EACH_OBSERVER(Observer, observers_, OnCustomDictionaryLoaded());
 }
 
 bool SpellcheckCustomDictionary::AddWord(const std::string& word) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  if (!IsValidWord(word))
+    return false;
 
   if (!CustomWordAddedLocally(word))
     return false;
@@ -108,9 +131,7 @@ bool SpellcheckCustomDictionary::AddWord(const std::string& word) {
     i.GetCurrentValue()->Send(new SpellCheckMsg_WordAdded(word));
   }
 
-  std::vector<Observer*>::iterator it;
-  for (it = observers_.begin(); it != observers_.end(); ++it)
-    (*it)->OnCustomDictionaryWordAdded(word);
+  FOR_EACH_OBSERVER(Observer, observers_, OnCustomDictionaryWordAdded(word));
 
   return true;
 }
@@ -118,6 +139,7 @@ bool SpellcheckCustomDictionary::AddWord(const std::string& word) {
 bool SpellcheckCustomDictionary::CustomWordAddedLocally(
     const std::string& word) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  DCHECK(IsValidWord(word));
 
   WordList::iterator it = std::find(words_.begin(), words_.end(), word);
   if (it == words_.end()) {
@@ -131,22 +153,18 @@ bool SpellcheckCustomDictionary::CustomWordAddedLocally(
 void SpellcheckCustomDictionary::WriteWordToCustomDictionary(
     const std::string& word) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+  DCHECK(IsValidWord(word));
 
-  // Stored in UTF-8.
-  DCHECK(IsStringUTF8(word));
-
-  std::string word_to_add(word + "\n");
-  if (!file_util::PathExists(custom_dictionary_path_)) {
-    file_util::WriteFile(custom_dictionary_path_, word_to_add.c_str(),
-        word_to_add.length());
-  } else {
-    file_util::AppendToFile(custom_dictionary_path_, word_to_add.c_str(),
-        word_to_add.length());
-  }
+  WordList custom_words;
+  LoadDictionaryFileReliably(&custom_words);
+  custom_words.push_back(word);
+  SaveDictionaryFileReliably(custom_words);
 }
 
 bool SpellcheckCustomDictionary::RemoveWord(const std::string& word) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  if (!IsValidWord(word))
+    return false;
 
   if (!CustomWordRemovedLocally(word))
     return false;
@@ -161,9 +179,7 @@ bool SpellcheckCustomDictionary::RemoveWord(const std::string& word) {
     i.GetCurrentValue()->Send(new SpellCheckMsg_WordRemoved(word));
   }
 
-  std::vector<Observer*>::iterator it;
-  for (it = observers_.begin(); it != observers_.end(); ++it)
-    (*it)->OnCustomDictionaryWordRemoved(word);
+  FOR_EACH_OBSERVER(Observer, observers_, OnCustomDictionaryWordRemoved(word));
 
   return true;
 }
@@ -171,6 +187,7 @@ bool SpellcheckCustomDictionary::RemoveWord(const std::string& word) {
 bool SpellcheckCustomDictionary::CustomWordRemovedLocally(
     const std::string& word) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  DCHECK(IsValidWord(word));
 
   WordList::iterator it = std::find(words_.begin(), words_.end(), word);
   if (it != words_.end()) {
@@ -183,40 +200,32 @@ bool SpellcheckCustomDictionary::CustomWordRemovedLocally(
 void SpellcheckCustomDictionary::EraseWordFromCustomDictionary(
     const std::string& word) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
-  DCHECK(IsStringUTF8(word));
+  DCHECK(IsValidWord(word));
 
   WordList custom_words;
-  LoadDictionaryIntoCustomWordList(&custom_words);
-
-  const char empty[] = {'\0'};
-  const char separator[] = {'\n', '\0'};
-  file_util::WriteFile(custom_dictionary_path_, empty, 0);
-  for (WordList::iterator it = custom_words.begin();
-      it != custom_words.end();
-      ++it) {
-    std::string word_to_add = *it;
-    if (word.compare(word_to_add) != 0) {
-      file_util::AppendToFile(custom_dictionary_path_, word_to_add.c_str(),
-          word_to_add.length());
-      file_util::AppendToFile(custom_dictionary_path_, separator, 1);
-    }
-  }
+  LoadDictionaryFileReliably(&custom_words);
+  if (custom_words.empty())
+    return;
+
+  WordList::iterator it = std::find(custom_words.begin(),
+                                    custom_words.end(),
+                                    word);
+  if (it != custom_words.end())
+    custom_words.erase(it);
+
+  SaveDictionaryFileReliably(custom_words);
 }
 
 void SpellcheckCustomDictionary::AddObserver(Observer* observer) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 
-  observers_.push_back(observer);
+  observers_.AddObserver(observer);
 }
 
 void SpellcheckCustomDictionary::RemoveObserver(Observer* observer) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 
-  std::vector<Observer*>::iterator it = std::find(observers_.begin(),
-                                                  observers_.end(),
-                                                  observer);
-  if (it != observers_.end())
-    observers_.erase(it);
+  observers_.RemoveObserver(observer);
 }
 
 WordList* SpellcheckCustomDictionary::LoadDictionary() {
@@ -234,3 +243,43 @@ void SpellcheckCustomDictionary::SetCustomWordListAndDelete(
   SetCustomWordList(custom_words);
   delete custom_words;
 }
+
+void SpellcheckCustomDictionary::LoadDictionaryFileReliably(
+    WordList* custom_words) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+
+  // Load the contents and verify the checksum.
+  if (LoadFile(custom_dictionary_path_, custom_words))
+    return;
+
+  // Checksum is not valid. See if there's a backup.
+  FilePath backup = custom_dictionary_path_.AddExtension(BACKUP_EXTENSION);
+  if (!file_util::PathExists(backup))
+    return;
+
+  // Load the backup and verify its checksum.
+  if (!LoadFile(backup, custom_words))
+    return;
+
+  // Backup checksum is valid. Restore the backup.
+  file_util::CopyFile(backup, custom_dictionary_path_);
+}
+
+void SpellcheckCustomDictionary::SaveDictionaryFileReliably(
+    const WordList& custom_words) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+
+  std::stringstream content;
+  for (WordList::const_iterator it = custom_words.begin();
+       it != custom_words.end();
+       ++it) {
+    content << *it << '\n';
+  }
+  std::string checksum = base::MD5String(content.str());
+  content << CHECKSUM_PREFIX << checksum;
+
+  file_util::CopyFile(custom_dictionary_path_,
+                      custom_dictionary_path_.AddExtension(BACKUP_EXTENSION));
+  base::ImportantFileWriter::WriteFileAtomically(custom_dictionary_path_,
+                                                 content.str());
+}