diff --git a/libs/protoutil/include/android/util/ProtoOutputStream.h b/libs/protoutil/include/android/util/ProtoOutputStream.h
index 49ec169..0f1cced 100644
--- a/libs/protoutil/include/android/util/ProtoOutputStream.h
+++ b/libs/protoutil/include/android/util/ProtoOutputStream.h
@@ -37,7 +37,7 @@
 class ProtoOutputStream
 {
 public:
-    ProtoOutputStream(int fd);
+    ProtoOutputStream();
     ~ProtoOutputStream();
 
     /**
@@ -60,13 +60,19 @@
     void end(long long token);
 
     /**
-     * Flushes the protobuf data out.
+     * Flushes the protobuf data out to given fd.
      */
-    bool flush();
+    size_t size();
+    EncodedBuffer::iterator data();
+    bool flush(int fd);
+
+    // Please don't use the following functions to dump protos unless you are sure about it.
+    void writeRawVarint(uint64_t varint);
+    void writeLengthDelimitedHeader(uint32_t id, size_t size);
+    void writeRawByte(uint8_t byte);
 
 private:
     EncodedBuffer mBuffer;
-    int mFd;
     size_t mCopyBegin;
     bool mCompact;
     int mDepth;
diff --git a/libs/protoutil/src/ProtoOutputStream.cpp b/libs/protoutil/src/ProtoOutputStream.cpp
index e9ca0dc..15144ac 100644
--- a/libs/protoutil/src/ProtoOutputStream.cpp
+++ b/libs/protoutil/src/ProtoOutputStream.cpp
@@ -70,9 +70,8 @@
 const uint64_t FIELD_COUNT_REPEATED = 2ULL << FIELD_COUNT_SHIFT;
 const uint64_t FIELD_COUNT_PACKED = 4ULL << FIELD_COUNT_SHIFT;
 
-ProtoOutputStream::ProtoOutputStream(int fd)
+ProtoOutputStream::ProtoOutputStream()
         :mBuffer(),
-         mFd(fd),
          mCopyBegin(0),
          mCompact(false),
          mDepth(0),
@@ -483,6 +482,13 @@
     return true;
 }
 
+size_t
+ProtoOutputStream::size()
+{
+    compact();
+    return mBuffer.size();
+}
+
 static bool write_all(int fd, uint8_t const* buf, size_t size)
 {
     while (size > 0) {
@@ -497,19 +503,47 @@
 }
 
 bool
-ProtoOutputStream::flush()
+ProtoOutputStream::flush(int fd)
 {
-    if (mFd < 0) return false;
+    if (fd < 0) return false;
     if (!compact()) return false;
 
     EncodedBuffer::iterator it = mBuffer.begin();
     while (it.readBuffer() != NULL) {
-        if (!write_all(mFd, it.readBuffer(), it.currentToRead())) return false;
+        if (!write_all(fd, it.readBuffer(), it.currentToRead())) return false;
         it.rp()->move(it.currentToRead());
     }
     return true;
 }
 
+EncodedBuffer::iterator
+ProtoOutputStream::data()
+{
+    compact();
+    return mBuffer.begin();
+}
+
+void
+ProtoOutputStream::writeRawVarint(uint64_t varint)
+{
+    mBuffer.writeRawVarint64(varint);
+}
+
+void
+ProtoOutputStream::writeLengthDelimitedHeader(uint32_t id, size_t size)
+{
+    mBuffer.writeHeader(id, WIRE_TYPE_LENGTH_DELIMITED);
+    // reserves 64 bits for length delimited fields, if first field is negative, compact it.
+    mBuffer.writeRawFixed32(size);
+    mBuffer.writeRawFixed32(size);
+}
+
+void
+ProtoOutputStream::writeRawByte(uint8_t byte)
+{
+    mBuffer.writeRawByte(byte);
+}
+
 
 // =========================================================================
 // Private functions
@@ -639,9 +673,7 @@
 ProtoOutputStream::writeUtf8StringImpl(uint32_t id, const char* val, size_t size)
 {
     if (val == NULL || size == 0) return;
-    mBuffer.writeHeader(id, WIRE_TYPE_LENGTH_DELIMITED);
-    mBuffer.writeRawFixed32(size);
-    mBuffer.writeRawFixed32(size);
+    writeLengthDelimitedHeader(id, size);
     for (size_t i=0; i<size; i++) {
         mBuffer.writeRawByte((uint8_t)val[i]);
     }