Add WriteUVarint to ByteBufferWriter and ReadUVarint to ByteBufferReader

Methods to write/read a varint as described by
https://developers.google.com/protocol-buffers/docs/encoding#varints
that will be used for a QUIC data channel.

Split from CL https://codereview.webrtc.org/1844803002/.

Review URL: https://codereview.webrtc.org/1844333006

Cr-Commit-Position: refs/heads/master@{#12322}

webrtc/base/bytebuffer.cc

@@ -88,6 +88,20 @@ void ByteBufferWriter::WriteUInt64(uint64_t val) {
   WriteBytes(reinterpret_cast<const char*>(&v), 8);
 }
 
+// Serializes an unsigned varint in the format described by
+// https://developers.google.com/protocol-buffers/docs/encoding#varints
+// with the caveat that integers are 64-bit, not 128-bit.
+void ByteBufferWriter::WriteUVarint(uint64_t val) {
+  while (val >= 0x80) {
+    // Write 7 bits at a time, then set the msb to a continuation byte (msb=1).
+    char byte = static_cast<char>(val) | 0x80;
+    WriteBytes(&byte, 1);
+    val >>= 7;
+  }
+  char last_byte = static_cast<char>(val);
+  WriteBytes(&last_byte, 1);
+}
+
 void ByteBufferWriter::WriteString(const std::string& val) {
   WriteBytes(val.c_str(), val.size());
 }
@@ -220,6 +234,29 @@ bool ByteBufferReader::ReadUInt64(uint64_t* val) {
   }
 }
 
+bool ByteBufferReader::ReadUVarint(uint64_t* val) {
+  if (!val) {
+    return false;
+  }
+  // Integers are deserialized 7 bits at a time, with each byte having a
+  // continuation byte (msb=1) if there are more bytes to be read.
+  uint64_t v = 0;
+  for (int i = 0; i < 64; i += 7) {
+    char byte;
+    if (!ReadBytes(&byte, 1)) {
+      return false;
+    }
+    // Read the first 7 bits of the byte, then offset by bits read so far.
+    v |= (static_cast<uint64_t>(byte) & 0x7F) << i;
+    // True if the msb is not a continuation byte.
+    if (static_cast<uint64_t>(byte) < 0x80) {
+      *val = v;
+      return true;
+    }
+  }
+  return false;
+}
+
 bool ByteBufferReader::ReadString(std::string* val, size_t len) {
   if (!val) return false;
 

webrtc/base/bytebuffer.h

@@ -57,6 +57,7 @@ class ByteBufferWriter : public ByteBuffer {
   void WriteUInt24(uint32_t val);
   void WriteUInt32(uint32_t val);
   void WriteUInt64(uint64_t val);
+  void WriteUVarint(uint64_t val);
   void WriteString(const std::string& val);
   void WriteBytes(const char* val, size_t len);
 
@@ -110,6 +111,7 @@ class ByteBufferReader : public ByteBuffer {
   bool ReadUInt24(uint32_t* val);
   bool ReadUInt32(uint32_t* val);
   bool ReadUInt64(uint64_t* val);
+  bool ReadUVarint(uint64_t* val);
   bool ReadBytes(char* val, size_t len);
 
   // Appends next |len| bytes from the buffer to |val|. Returns false

webrtc/base/bytebuffer_unittest.cc

@@ -196,4 +196,64 @@ TEST(ByteBufferTest, TestReadWriteBuffer) {
   }
 }
 
+TEST(ByteBufferTest, TestReadWriteUVarint) {
+  ByteBufferWriter::ByteOrder orders[2] = {ByteBufferWriter::ORDER_HOST,
+                                           ByteBufferWriter::ORDER_NETWORK};
+  for (ByteBufferWriter::ByteOrder& order : orders) {
+    ByteBufferWriter write_buffer(order);
+    size_t size = 0;
+    EXPECT_EQ(size, write_buffer.Length());
+
+    write_buffer.WriteUVarint(1u);
+    ++size;
+    EXPECT_EQ(size, write_buffer.Length());
+
+    write_buffer.WriteUVarint(2u);
+    ++size;
+    EXPECT_EQ(size, write_buffer.Length());
+
+    write_buffer.WriteUVarint(27u);
+    ++size;
+    EXPECT_EQ(size, write_buffer.Length());
+
+    write_buffer.WriteUVarint(149u);
+    size += 2;
+    EXPECT_EQ(size, write_buffer.Length());
+
+    write_buffer.WriteUVarint(68719476736u);
+    size += 6;
+    EXPECT_EQ(size, write_buffer.Length());
+
+    ByteBufferReader read_buffer(write_buffer.Data(), write_buffer.Length(),
+                                 order);
+    EXPECT_EQ(size, read_buffer.Length());
+    uint64_t val1, val2, val3, val4, val5;
+
+    ASSERT_TRUE(read_buffer.ReadUVarint(&val1));
+    EXPECT_EQ(1u, val1);
+    --size;
+    EXPECT_EQ(size, read_buffer.Length());
+
+    ASSERT_TRUE(read_buffer.ReadUVarint(&val2));
+    EXPECT_EQ(2u, val2);
+    --size;
+    EXPECT_EQ(size, read_buffer.Length());
+
+    ASSERT_TRUE(read_buffer.ReadUVarint(&val3));
+    EXPECT_EQ(27u, val3);
+    --size;
+    EXPECT_EQ(size, read_buffer.Length());
+
+    ASSERT_TRUE(read_buffer.ReadUVarint(&val4));
+    EXPECT_EQ(149u, val4);
+    size -= 2;
+    EXPECT_EQ(size, read_buffer.Length());
+
+    ASSERT_TRUE(read_buffer.ReadUVarint(&val5));
+    EXPECT_EQ(68719476736u, val5);
+    size -= 6;
+    EXPECT_EQ(size, read_buffer.Length());
+  }
+}
+
 }  // namespace rtc