diff --git a/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_policy.cpp b/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_policy.cpp
index 2198a13..f91dd0e 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_policy.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_policy.cpp
@@ -250,7 +250,7 @@
     }
     DynamicPatriciaTrieWritingHelper writingHelper(&mBufferWithExtendableBuffer,
             &mBigramListPolicy, &mShortcutListPolicy);
-    writingHelper.writeToDictFile(filePath, mBuffer->getBuffer(), mHeaderPolicy.getSize());
+    writingHelper.writeToDictFile(filePath, &mHeaderPolicy);
 }
 
 void DynamicPatriciaTriePolicy::flushWithGC(const char *const filePath) {
diff --git a/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_policy.h b/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_policy.h
index 2cbb0ff..ebe1f32 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_policy.h
+++ b/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_policy.h
@@ -33,7 +33,7 @@
 class DynamicPatriciaTriePolicy : public DictionaryStructureWithBufferPolicy {
  public:
     DynamicPatriciaTriePolicy(const MmappedBuffer *const buffer)
-            : mBuffer(buffer), mHeaderPolicy(mBuffer->getBuffer()),
+            : mBuffer(buffer), mHeaderPolicy(mBuffer->getBuffer(), buffer->getBufferSize()),
               mBufferWithExtendableBuffer(mBuffer->getBuffer() + mHeaderPolicy.getSize(),
                       mBuffer->getBufferSize() - mHeaderPolicy.getSize()),
               mShortcutListPolicy(&mBufferWithExtendableBuffer),
diff --git a/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_writing_helper.cpp b/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_writing_helper.cpp
index a67c0d9..31178fb 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_writing_helper.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_writing_helper.cpp
@@ -24,6 +24,7 @@
 #include "suggest/policyimpl/dictionary/dynamic_patricia_trie_reading_helper.h"
 #include "suggest/policyimpl/dictionary/dynamic_patricia_trie_reading_utils.h"
 #include "suggest/policyimpl/dictionary/dynamic_patricia_trie_writing_utils.h"
+#include "suggest/policyimpl/dictionary/header/header_policy.h"
 #include "suggest/policyimpl/dictionary/patricia_trie_reading_utils.h"
 #include "suggest/policyimpl/dictionary/shortcut/dynamic_shortcut_list_policy.h"
 
@@ -137,7 +138,11 @@
 }
 
 void DynamicPatriciaTrieWritingHelper::writeToDictFile(const char *const fileName,
-        const uint8_t *const headerBuf, const int headerSize) {
+        const HeaderPolicy *const headerPolicy) {
+    BufferWithExtendableBuffer headerBuffer(0 /* originalBuffer */, 0 /* originalBufferSize */);
+    if (!headerPolicy->writeHeaderToBuffer(&headerBuffer, false /* updatesLastUpdatedTime */)) {
+        return;
+    }
     const int tmpFileNameBufSize = strlen(fileName)
             + strlen(TEMP_FILE_SUFFIX_FOR_WRITING_DICT_FILE) + 1;
     char tmpFileName[tmpFileNameBufSize];
@@ -148,7 +153,8 @@
         return;
     }
     // Write header.
-    if (fwrite(headerBuf, headerSize, 1, file) < 1) {
+    if (fwrite(headerBuffer.getBuffer(true /* usesAdditionalBuffer */),
+            headerBuffer.getTailPosition(), 1, file) < 1) {
         fclose(file);
         remove(tmpFileName);
         return;
diff --git a/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_writing_helper.h b/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_writing_helper.h
index faf7a4e..219ea98 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_writing_helper.h
+++ b/native/jni/src/suggest/policyimpl/dictionary/dynamic_patricia_trie_writing_helper.h
@@ -28,6 +28,7 @@
 class DynamicPatriciaTrieNodeReader;
 class DynamicPatriciaTrieReadingHelper;
 class DynamicShortcutListPolicy;
+class HeaderPolicy;
 
 class DynamicPatriciaTrieWritingHelper {
  public:
@@ -48,8 +49,9 @@
     // Remove a bigram relation from word0Pos to word1Pos.
     bool removeBigramWords(const int word0Pos, const int word1Pos);
 
-    void writeToDictFile(const char *const fileName, const uint8_t *const headerBuf,
-            const int headerSize);
+    void writeToDictFile(const char *const fileName, const HeaderPolicy *const headerPolicy);
+
+    void writeToDictFileWithGC(const char *const fileName, const HeaderPolicy *const headerPolicy);
 
  private:
     DISALLOW_IMPLICIT_CONSTRUCTORS(DynamicPatriciaTrieWritingHelper);
diff --git a/native/jni/src/suggest/policyimpl/dictionary/header/header_policy.cpp b/native/jni/src/suggest/policyimpl/dictionary/header/header_policy.cpp
index 196da5c..47ace23 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/header/header_policy.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/header/header_policy.cpp
@@ -17,6 +17,8 @@
 #include "suggest/policyimpl/dictionary/header/header_policy.h"
 
 #include <cstddef>
+#include <cstdio>
+#include <ctime>
 
 namespace latinime {
 
@@ -36,7 +38,7 @@
     }
     std::vector<int> keyCodePointVector;
     insertCharactersIntoVector(key, &keyCodePointVector);
-    HeaderReadingUtils::AttributeMap::const_iterator it = mAttributeMap.find(keyCodePointVector);
+    HeaderReadWriteUtils::AttributeMap::const_iterator it = mAttributeMap.find(keyCodePointVector);
     if (it == mAttributeMap.end()) {
         // The key was not found.
         outValue[0] = '?';
@@ -85,7 +87,7 @@
 bool HeaderPolicy::getAttributeValueAsInt(const char *const key, int *const outValue) const {
     std::vector<int> keyVector;
     insertCharactersIntoVector(key, &keyVector);
-    HeaderReadingUtils::AttributeMap::const_iterator it = mAttributeMap.find(keyVector);
+    HeaderReadWriteUtils::AttributeMap::const_iterator it = mAttributeMap.find(keyVector);
     if (it == mAttributeMap.end()) {
         // The key was not found.
         return false;
@@ -94,10 +96,56 @@
     return true;
 }
 
-/* static */ HeaderReadingUtils::AttributeMap HeaderPolicy::createAttributeMapAndReadAllAttributes(
-        const uint8_t *const dictBuf) {
-    HeaderReadingUtils::AttributeMap attributeMap;
-    HeaderReadingUtils::fetchAllHeaderAttributes(dictBuf, &attributeMap);
+bool HeaderPolicy::writeHeaderToBuffer(BufferWithExtendableBuffer *const bufferToWrite,
+        const bool updatesLastUpdatedTime) const {
+    int writingPos = 0;
+    if (!HeaderReadWriteUtils::writeDictionaryVersion(bufferToWrite, mDictFormatVersion,
+            &writingPos)) {
+        return false;
+    }
+    if (!HeaderReadWriteUtils::writeDictionaryFlags(bufferToWrite, mDictionaryFlags,
+            &writingPos)) {
+        return false;
+    }
+    // Temporarily writes a dummy header size.
+    int headerSizeFieldPos = writingPos;
+    if (!HeaderReadWriteUtils::writeDictionaryHeaderSize(bufferToWrite, 0 /* size */,
+            &writingPos)) {
+        return false;
+    }
+    if (updatesLastUpdatedTime) {
+        // Set current time as a last updated time.
+        HeaderReadWriteUtils::AttributeMap attributeMapTowrite(mAttributeMap);
+        std::vector<int> updatedTimekey;
+        insertCharactersIntoVector(LAST_UPDATED_TIME_KEY, &updatedTimekey);
+        const time_t currentTime = time(NULL);
+        std::vector<int> updatedTimeValue;
+        char charBuf[LARGEST_INT_DIGIT_COUNT + 1];
+        snprintf(charBuf, LARGEST_INT_DIGIT_COUNT + 1, "%ld", currentTime);
+        insertCharactersIntoVector(charBuf, &updatedTimeValue);
+        attributeMapTowrite[updatedTimekey] = updatedTimeValue;
+        if (!HeaderReadWriteUtils::writeHeaderAttributes(bufferToWrite, &attributeMapTowrite,
+                &writingPos)) {
+            return false;
+        }
+    } else {
+        if (!HeaderReadWriteUtils::writeHeaderAttributes(bufferToWrite, &mAttributeMap,
+                &writingPos)) {
+            return false;
+        }
+    }
+    // Writes an actual header size.
+    if (!HeaderReadWriteUtils::writeDictionaryHeaderSize(bufferToWrite, writingPos,
+            &headerSizeFieldPos)) {
+        return false;
+    }
+    return true;
+}
+
+/* static */ HeaderReadWriteUtils::AttributeMap
+        HeaderPolicy::createAttributeMapAndReadAllAttributes(const uint8_t *const dictBuf) {
+    HeaderReadWriteUtils::AttributeMap attributeMap;
+    HeaderReadWriteUtils::fetchAllHeaderAttributes(dictBuf, &attributeMap);
     return attributeMap;
 }
 
diff --git a/native/jni/src/suggest/policyimpl/dictionary/header/header_policy.h b/native/jni/src/suggest/policyimpl/dictionary/header/header_policy.h
index 930b475..cdad7de 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/header/header_policy.h
+++ b/native/jni/src/suggest/policyimpl/dictionary/header/header_policy.h
@@ -23,14 +23,17 @@
 #include "defines.h"
 #include "suggest/core/policy/dictionary_header_structure_policy.h"
 #include "suggest/policyimpl/dictionary/header/header_reading_utils.h"
+#include "suggest/policyimpl/dictionary/utils/format_utils.h"
 
 namespace latinime {
 
 class HeaderPolicy : public DictionaryHeaderStructurePolicy {
  public:
-    explicit HeaderPolicy(const uint8_t *const dictBuf)
-            : mDictBuf(dictBuf), mDictionaryFlags(HeaderReadingUtils::getFlags(dictBuf)),
-              mSize(HeaderReadingUtils::getHeaderSize(dictBuf)),
+    explicit HeaderPolicy(const uint8_t *const dictBuf, const int dictSize)
+            : mDictBuf(dictBuf),
+              mDictFormatVersion(FormatUtils::detectFormatVersion(dictBuf, dictSize)),
+              mDictionaryFlags(HeaderReadWriteUtils::getFlags(dictBuf)),
+              mSize(HeaderReadWriteUtils::getHeaderSize(dictBuf)),
               mAttributeMap(createAttributeMapAndReadAllAttributes(mDictBuf)),
               mMultiWordCostMultiplier(readMultipleWordCostMultiplier()),
               mUsesForgettingCurve(readUsesForgettingCurveFlag()),
@@ -43,16 +46,15 @@
     }
 
     AK_FORCE_INLINE bool supportsDynamicUpdate() const {
-        return HeaderReadingUtils::supportsDynamicUpdate(mDictionaryFlags);
+        return HeaderReadWriteUtils::supportsDynamicUpdate(mDictionaryFlags);
     }
 
     AK_FORCE_INLINE bool requiresGermanUmlautProcessing() const {
-        return HeaderReadingUtils::requiresGermanUmlautProcessing(mDictionaryFlags);
+        return HeaderReadWriteUtils::requiresGermanUmlautProcessing(mDictionaryFlags);
     }
 
     AK_FORCE_INLINE bool requiresFrenchLigatureProcessing() const {
-        return HeaderReadingUtils::requiresFrenchLigatureProcessing(
-                mDictionaryFlags);
+        return HeaderReadWriteUtils::requiresFrenchLigatureProcessing(mDictionaryFlags);
     }
 
     AK_FORCE_INLINE float getMultiWordCostMultiplier() const {
@@ -70,6 +72,9 @@
     void readHeaderValueOrQuestionMark(const char *const key,
             int *outValue, int outValueSize) const;
 
+    bool writeHeaderToBuffer(BufferWithExtendableBuffer *const bufferToWrite,
+            const bool updatesLastUpdatedTime) const;
+
  private:
     DISALLOW_IMPLICIT_CONSTRUCTORS(HeaderPolicy);
 
@@ -80,9 +85,10 @@
     static const float MULTIPLE_WORD_COST_MULTIPLIER_SCALE;
 
     const uint8_t *const mDictBuf;
-    const HeaderReadingUtils::DictionaryFlags mDictionaryFlags;
+    const FormatUtils::FORMAT_VERSION mDictFormatVersion;
+    const HeaderReadWriteUtils::DictionaryFlags mDictionaryFlags;
     const int mSize;
-    HeaderReadingUtils::AttributeMap mAttributeMap;
+    HeaderReadWriteUtils::AttributeMap mAttributeMap;
     const float mMultiWordCostMultiplier;
     const bool mUsesForgettingCurve;
     const int mLastUpdatedTime;
@@ -95,7 +101,7 @@
 
     bool getAttributeValueAsInt(const char *const key, int *const outValue) const;
 
-    static HeaderReadingUtils::AttributeMap createAttributeMapAndReadAllAttributes(
+    static HeaderReadWriteUtils::AttributeMap createAttributeMapAndReadAllAttributes(
             const uint8_t *const dictBuf);
 
     static int parseIntAttributeValue(const std::vector<int> *const attributeValue);
diff --git a/native/jni/src/suggest/policyimpl/dictionary/header/header_reading_utils.cpp b/native/jni/src/suggest/policyimpl/dictionary/header/header_reading_utils.cpp
index 186c043..705355d 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/header/header_reading_utils.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/header/header_reading_utils.cpp
@@ -19,43 +19,44 @@
 #include <vector>
 
 #include "defines.h"
+#include "suggest/policyimpl/dictionary/utils/buffer_with_extendable_buffer.h"
 #include "suggest/policyimpl/dictionary/utils/byte_array_utils.h"
 
 namespace latinime {
 
-const int HeaderReadingUtils::MAX_ATTRIBUTE_KEY_LENGTH = 256;
-const int HeaderReadingUtils::MAX_ATTRIBUTE_VALUE_LENGTH = 256;
+const int HeaderReadWriteUtils::MAX_ATTRIBUTE_KEY_LENGTH = 256;
+const int HeaderReadWriteUtils::MAX_ATTRIBUTE_VALUE_LENGTH = 256;
 
-const int HeaderReadingUtils::HEADER_MAGIC_NUMBER_SIZE = 4;
-const int HeaderReadingUtils::HEADER_DICTIONARY_VERSION_SIZE = 2;
-const int HeaderReadingUtils::HEADER_FLAG_SIZE = 2;
-const int HeaderReadingUtils::HEADER_SIZE_FIELD_SIZE = 4;
+const int HeaderReadWriteUtils::HEADER_MAGIC_NUMBER_SIZE = 4;
+const int HeaderReadWriteUtils::HEADER_DICTIONARY_VERSION_SIZE = 2;
+const int HeaderReadWriteUtils::HEADER_FLAG_SIZE = 2;
+const int HeaderReadWriteUtils::HEADER_SIZE_FIELD_SIZE = 4;
 
-const HeaderReadingUtils::DictionaryFlags HeaderReadingUtils::NO_FLAGS = 0;
+const HeaderReadWriteUtils::DictionaryFlags HeaderReadWriteUtils::NO_FLAGS = 0;
 // Flags for special processing
 // Those *must* match the flags in makedict (FormatSpec#*_PROCESSING_FLAG) or
 // something very bad (like, the apocalypse) will happen. Please update both at the same time.
-const HeaderReadingUtils::DictionaryFlags
-        HeaderReadingUtils::GERMAN_UMLAUT_PROCESSING_FLAG = 0x1;
-const HeaderReadingUtils::DictionaryFlags
-        HeaderReadingUtils::SUPPORTS_DYNAMIC_UPDATE_FLAG = 0x2;
-const HeaderReadingUtils::DictionaryFlags
-        HeaderReadingUtils::FRENCH_LIGATURE_PROCESSING_FLAG = 0x4;
+const HeaderReadWriteUtils::DictionaryFlags
+        HeaderReadWriteUtils::GERMAN_UMLAUT_PROCESSING_FLAG = 0x1;
+const HeaderReadWriteUtils::DictionaryFlags
+        HeaderReadWriteUtils::SUPPORTS_DYNAMIC_UPDATE_FLAG = 0x2;
+const HeaderReadWriteUtils::DictionaryFlags
+        HeaderReadWriteUtils::FRENCH_LIGATURE_PROCESSING_FLAG = 0x4;
 
-/* static */ int HeaderReadingUtils::getHeaderSize(const uint8_t *const dictBuf) {
+/* static */ int HeaderReadWriteUtils::getHeaderSize(const uint8_t *const dictBuf) {
     // See the format of the header in the comment in
     // BinaryDictionaryFormatUtils::detectFormatVersion()
     return ByteArrayUtils::readUint32(dictBuf, HEADER_MAGIC_NUMBER_SIZE
             + HEADER_DICTIONARY_VERSION_SIZE + HEADER_FLAG_SIZE);
 }
 
-/* static */ HeaderReadingUtils::DictionaryFlags
-        HeaderReadingUtils::getFlags(const uint8_t *const dictBuf) {
+/* static */ HeaderReadWriteUtils::DictionaryFlags
+        HeaderReadWriteUtils::getFlags(const uint8_t *const dictBuf) {
     return ByteArrayUtils::readUint16(dictBuf,
             HEADER_MAGIC_NUMBER_SIZE + HEADER_DICTIONARY_VERSION_SIZE);
 }
 
-/* static */ void HeaderReadingUtils::fetchAllHeaderAttributes(const uint8_t *const dictBuf,
+/* static */ void HeaderReadWriteUtils::fetchAllHeaderAttributes(const uint8_t *const dictBuf,
         AttributeMap *const headerAttributes) {
     const int headerSize = getHeaderSize(dictBuf);
     int pos = getHeaderOptionsPosition();
@@ -78,4 +79,53 @@
     }
 }
 
+/* static */ bool HeaderReadWriteUtils::writeDictionaryVersion(
+        BufferWithExtendableBuffer *const buffer, const FormatUtils::FORMAT_VERSION version,
+        int *const writingPos) {
+    if (!buffer->writeUintAndAdvancePosition(FormatUtils::MAGIC_NUMBER, HEADER_MAGIC_NUMBER_SIZE,
+            writingPos)) {
+        return false;
+    }
+    switch (version) {
+        case FormatUtils::VERSION_2:
+            // Version 2 dictionary writing is not supported.
+            return false;
+        case FormatUtils::VERSION_3:
+            return buffer->writeUintAndAdvancePosition(3 /* data */,
+                    HEADER_DICTIONARY_VERSION_SIZE, writingPos);
+        default:
+            return false;
+    }
+}
+
+/* static */ bool HeaderReadWriteUtils::writeDictionaryFlags(
+        BufferWithExtendableBuffer *const buffer, const DictionaryFlags flags,
+        int *const writingPos) {
+    return buffer->writeUintAndAdvancePosition(flags, HEADER_FLAG_SIZE, writingPos);
+}
+
+/* static */ bool HeaderReadWriteUtils::writeDictionaryHeaderSize(
+        BufferWithExtendableBuffer *const buffer, const int size, int *const writingPos) {
+    return buffer->writeUintAndAdvancePosition(size, HEADER_SIZE_FIELD_SIZE, writingPos);
+}
+
+/* static */ bool HeaderReadWriteUtils::writeHeaderAttributes(
+        BufferWithExtendableBuffer *const buffer, const AttributeMap *const headerAttributes,
+        int *const writingPos) {
+    for (AttributeMap::const_iterator it = headerAttributes->begin();
+            it != headerAttributes->end(); ++it) {
+        // Write a key.
+        if (!buffer->writeCodePointsAndAdvancePosition(&(it->first.at(0)), it->first.size(),
+                true /* writesTerminator */, writingPos)) {
+            return false;
+        }
+        // Write a value.
+        if (!buffer->writeCodePointsAndAdvancePosition(&(it->second.at(0)), it->second.size(),
+                true /* writesTerminator */, writingPos)) {
+            return false;
+        }
+    }
+    return true;
+}
+
 } // namespace latinime
diff --git a/native/jni/src/suggest/policyimpl/dictionary/header/header_reading_utils.h b/native/jni/src/suggest/policyimpl/dictionary/header/header_reading_utils.h
index 5716198..4b4e220 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/header/header_reading_utils.h
+++ b/native/jni/src/suggest/policyimpl/dictionary/header/header_reading_utils.h
@@ -22,10 +22,14 @@
 #include <vector>
 
 #include "defines.h"
+#include "suggest/policyimpl/dictionary/utils/format_utils.h"
 
 namespace latinime {
 
-class HeaderReadingUtils {
+class BufferWithExtendableBuffer;
+
+// TODO: Change this file name to header_read_write_utils.h.
+class HeaderReadWriteUtils {
  public:
     typedef uint16_t DictionaryFlags;
     typedef std::map<std::vector<int>, std::vector<int> > AttributeMap;
@@ -54,8 +58,20 @@
     static void fetchAllHeaderAttributes(const uint8_t *const dictBuf,
             AttributeMap *const headerAttributes);
 
+    static bool writeDictionaryVersion(BufferWithExtendableBuffer *const buffer,
+            const FormatUtils::FORMAT_VERSION version, int *const writingPos);
+
+    static bool writeDictionaryFlags(BufferWithExtendableBuffer *const buffer,
+            const DictionaryFlags flags, int *const writingPos);
+
+    static bool writeDictionaryHeaderSize(BufferWithExtendableBuffer *const buffer,
+            const int size, int *const writingPos);
+
+    static bool writeHeaderAttributes(BufferWithExtendableBuffer *const buffer,
+            const AttributeMap *const headerAttributes, int *const writingPos);
+
  private:
-    DISALLOW_IMPLICIT_CONSTRUCTORS(HeaderReadingUtils);
+    DISALLOW_IMPLICIT_CONSTRUCTORS(HeaderReadWriteUtils);
 
     static const int MAX_ATTRIBUTE_KEY_LENGTH;
     static const int MAX_ATTRIBUTE_VALUE_LENGTH;
diff --git a/native/jni/src/suggest/policyimpl/dictionary/patricia_trie_policy.h b/native/jni/src/suggest/policyimpl/dictionary/patricia_trie_policy.h
index cee3e4a..697d015 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/patricia_trie_policy.h
+++ b/native/jni/src/suggest/policyimpl/dictionary/patricia_trie_policy.h
@@ -34,7 +34,7 @@
 class PatriciaTriePolicy : public DictionaryStructureWithBufferPolicy {
  public:
     PatriciaTriePolicy(const MmappedBuffer *const buffer)
-            : mBuffer(buffer), mHeaderPolicy(mBuffer->getBuffer()),
+            : mBuffer(buffer), mHeaderPolicy(mBuffer->getBuffer(), buffer->getBufferSize()),
               mDictRoot(mBuffer->getBuffer() + mHeaderPolicy.getSize()),
               mBigramListPolicy(mDictRoot), mShortcutListPolicy(mDictRoot) {}
 
diff --git a/native/jni/src/suggest/policyimpl/dictionary/utils/format_utils.cpp b/native/jni/src/suggest/policyimpl/dictionary/utils/format_utils.cpp
index 3796c7b..1d77d5c 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/utils/format_utils.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/utils/format_utils.cpp
@@ -20,20 +20,10 @@
 
 namespace latinime {
 
-/**
- * Dictionary size
- */
-// Any file smaller than this is not a dictionary.
-const int FormatUtils::DICTIONARY_MINIMUM_SIZE = 4;
+const uint32_t FormatUtils::MAGIC_NUMBER = 0x9BC13AFE;
 
-/**
- * Format versions
- */
-// 32 bit magic number is stored at the beginning of the dictionary header to reject unsupported
-// or obsolete dictionary formats.
-const uint32_t FormatUtils::HEADER_VERSION_2_MAGIC_NUMBER = 0x9BC13AFE;
-// Magic number (4 bytes), version (2 bytes), options (2 bytes), header size (4 bytes) = 12
-const int FormatUtils::HEADER_VERSION_2_MINIMUM_SIZE = 12;
+// Magic number (4 bytes), version (2 bytes), flags (2 bytes), header size (4 bytes) = 12
+const int FormatUtils::DICTIONARY_MINIMUM_SIZE = 12;
 
 /* static */ FormatUtils::FORMAT_VERSION FormatUtils::detectFormatVersion(
         const uint8_t *const dict, const int dictSize) {
@@ -45,16 +35,10 @@
     }
     const uint32_t magicNumber = ByteArrayUtils::readUint32(dict, 0);
     switch (magicNumber) {
-        case HEADER_VERSION_2_MAGIC_NUMBER:
-            // Version 2 header are at least 12 bytes long.
-            // If this header has the version 2 magic number but is less than 12 bytes long,
-            // then it's an unknown format and we need to avoid confidently reading the next bytes.
-            if (dictSize < HEADER_VERSION_2_MINIMUM_SIZE) {
-                return UNKNOWN_VERSION;
-            }
+        case MAGIC_NUMBER:
             // Version 2 header is as follows:
             // Magic number (4 bytes) 0x9B 0xC1 0x3A 0xFE
-            // Version number (2 bytes)
+            // Dictionary format version number (2 bytes)
             // Options (2 bytes)
             // Header size (4 bytes) : integer, big endian
             if (ByteArrayUtils::readUint16(dict, 4) == 2) {
diff --git a/native/jni/src/suggest/policyimpl/dictionary/utils/format_utils.h b/native/jni/src/suggest/policyimpl/dictionary/utils/format_utils.h
index f843215..79ed0de 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/utils/format_utils.h
+++ b/native/jni/src/suggest/policyimpl/dictionary/utils/format_utils.h
@@ -34,14 +34,16 @@
         UNKNOWN_VERSION
     };
 
+    // 32 bit magic number is stored at the beginning of the dictionary header to reject
+    // unsupported or obsolete dictionary formats.
+    static const uint32_t MAGIC_NUMBER;
+
     static FORMAT_VERSION detectFormatVersion(const uint8_t *const dict, const int dictSize);
 
  private:
     DISALLOW_IMPLICIT_CONSTRUCTORS(FormatUtils);
 
     static const int DICTIONARY_MINIMUM_SIZE;
-    static const uint32_t HEADER_VERSION_2_MAGIC_NUMBER;
-    static const int HEADER_VERSION_2_MINIMUM_SIZE;
 };
 } // namespace latinime
 #endif /* LATINIME_FORMAT_UTILS_H */
diff --git a/tests/src/com/android/inputmethod/latin/BinaryDictionaryTests.java b/tests/src/com/android/inputmethod/latin/BinaryDictionaryTests.java
index d8105ba..00d76c9 100644
--- a/tests/src/com/android/inputmethod/latin/BinaryDictionaryTests.java
+++ b/tests/src/com/android/inputmethod/latin/BinaryDictionaryTests.java
@@ -358,8 +358,8 @@
                 0 /* offset */, dictFile.length(), true /* useFullEditDistance */,
                 Locale.getDefault(), TEST_LOCALE, true /* isUpdatable */);
 
-        assertEquals(-1, binaryDictionary.getFrequency("aaa"));
-        assertEquals(-1, binaryDictionary.getFrequency("abcd"));
+        assertEquals(Dictionary.NOT_A_PROBABILITY, binaryDictionary.getFrequency("aaa"));
+        assertEquals(Dictionary.NOT_A_PROBABILITY, binaryDictionary.getFrequency("abcd"));
 
         binaryDictionary.addUnigramWord("aaa", probability);
         binaryDictionary.addUnigramWord("abcd", probability);