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}
diff --git a/webrtc/base/bytebuffer.cc b/webrtc/base/bytebuffer.cc
index cf4ce42..9730ff2 100644
--- a/webrtc/base/bytebuffer.cc
+++ b/webrtc/base/bytebuffer.cc
@@ -88,6 +88,20 @@
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::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;