quic: CRYPTO stream handling

CRYPTO frames carry TLS handshake messages.

Add a cryptoStream type which manages the TLS handshake stream,
including retransmission of lost data, processing out-of-order
received data, etc.

For golang/go#58547

Change-Id: I8defa38e22d9c1bb8753f3a44d5ae0853fa56de8
Reviewed-on: https://go-review.googlesource.com/c/net/+/510616
Reviewed-by: Jonathan Amsterdam <jba@google.com>
Run-TryBot: Damien Neil <dneil@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

Author: neild

internal/quic/crypto_stream.go

@@ -0,0 +1,159 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build go1.21
+
+package quic
+
+// "Implementations MUST support buffering at least 4096 bytes of data
+// received in out-of-order CRYPTO frames."
+// https://www.rfc-editor.org/rfc/rfc9000.html#section-7.5-2
+//
+// 4096 is too small for real-world cases, however, so we allow more.
+const cryptoBufferSize = 1 << 20
+
+// A cryptoStream is the stream of data passed in CRYPTO frames.
+// There is one cryptoStream per packet number space.
+type cryptoStream struct {
+	// CRYPTO data received from the peer.
+	in    pipe
+	inset rangeset[int64] // bytes received
+
+	// CRYPTO data queued for transmission to the peer.
+	out       pipe
+	outunsent rangeset[int64] // bytes in need of sending
+	outacked  rangeset[int64] // bytes acked by peer
+}
+
+// handleCrypto processes data received in a CRYPTO frame.
+func (s *cryptoStream) handleCrypto(off int64, b []byte, f func([]byte) error) error {
+	end := off + int64(len(b))
+	if end-s.inset.min() > cryptoBufferSize {
+		return localTransportError(errCryptoBufferExceeded)
+	}
+	s.inset.add(off, end)
+	if off == s.in.start {
+		// Fast path: This is the next chunk of data in the stream,
+		// so just handle it immediately.
+		if err := f(b); err != nil {
+			return err
+		}
+		s.in.discardBefore(end)
+	} else {
+		// This is either data we've already processed,
+		// data we can't process yet, or a mix of both.
+		s.in.writeAt(b, off)
+	}
+	// s.in.start is the next byte in sequence.
+	// If it's in s.inset, we have bytes to provide.
+	// If it isn't, we don't--we're either out of data,
+	// or only have data that comes after the next byte.
+	if !s.inset.contains(s.in.start) {
+		return nil
+	}
+	// size is the size of the first contiguous chunk of bytes
+	// that have not been processed yet.
+	size := int(s.inset[0].end - s.in.start)
+	if size <= 0 {
+		return nil
+	}
+	err := s.in.read(s.in.start, size, f)
+	s.in.discardBefore(s.inset[0].end)
+	return err
+}
+
+// write queues data for sending to the peer.
+// It does not block or limit the amount of buffered data.
+// QUIC connections don't communicate the amount of CRYPTO data they are willing to buffer,
+// so we send what we have and the peer can close the connection if it is too much.
+func (s *cryptoStream) write(b []byte) {
+	start := s.out.end
+	s.out.writeAt(b, start)
+	s.outunsent.add(start, s.out.end)
+}
+
+// ackOrLoss reports that an CRYPTO frame sent by us has been acknowledged by the peer, or lost.
+func (s *cryptoStream) ackOrLoss(start, end int64, fate packetFate) {
+	switch fate {
+	case packetAcked:
+		s.outacked.add(start, end)
+		s.outunsent.sub(start, end)
+		// If this ack is for data at the start of the send buffer, we can now discard it.
+		if s.outacked.contains(s.out.start) {
+			s.out.discardBefore(s.outacked[0].end)
+		}
+	case packetLost:
+		// Mark everything lost, but not previously acked, as needing retransmission.
+		// We do this by adding all the lost bytes to outunsent, and then
+		// removing everything already acked.
+		s.outunsent.add(start, end)
+		for _, a := range s.outacked {
+			s.outunsent.sub(a.start, a.end)
+		}
+	}
+}
+
+// dataToSend reports what data should be sent in CRYPTO frames to the peer.
+// It calls f with each range of data to send.
+// f uses sendData to get the bytes to send, and returns the number of bytes sent.
+// dataToSend calls f until no data is left, or f returns 0.
+//
+// This function is unusually indirect (why not just return a []byte,
+// or implement io.Reader?).
+//
+// Returning a []byte to the caller either requires that we store the
+// data to send contiguously (which we don't), allocate a temporary buffer
+// and copy into it (inefficient), or return less data than we have available
+// (requires complexity to avoid unnecessarily breaking data across frames).
+//
+// Accepting a []byte from the caller (io.Reader) makes packet construction
+// difficult. Since CRYPTO data is encoded with a varint length prefix, the
+// location of the data depends on the length of the data. (We could hardcode
+// a 2-byte length, of course.)
+//
+// Instead, we tell the caller how much data is, the caller figures out where
+// to put it (and possibly decides that it doesn't have space for this data
+// in the packet after all), and the caller then makes a separate call to
+// copy the data it wants into position.
+func (s *cryptoStream) dataToSend(pto bool, f func(off, size int64) (sent int64)) {
+	for {
+		var off, size int64
+		if pto {
+			// On PTO, resend unacked data that fits in the probe packet.
+			// For simplicity, we send the range starting at s.out.start
+			// (which is definitely unacked, or else we would have discarded it)
+			// up to the next acked byte (if any).
+			//
+			// This may miss unacked data starting after that acked byte,
+			// but avoids resending data the peer has acked.
+			off = s.out.start
+			end := s.out.end
+			for _, r := range s.outacked {
+				if r.start > off {
+					end = r.start
+					break
+				}
+			}
+			size = end - s.out.start
+		} else if s.outunsent.numRanges() > 0 {
+			off = s.outunsent.min()
+			size = s.outunsent[0].size()
+		}
+		if size == 0 {
+			return
+		}
+		n := f(off, size)
+		if n == 0 || pto {
+			return
+		}
+	}
+}
+
+// sendData fills b with data to send to the peer, starting at off,
+// and marks the data as sent. The caller must have already ascertained
+// that there is data to send in this region using dataToSend.
+func (s *cryptoStream) sendData(off int64, b []byte) {
+	s.out.copy(off, b)
+	s.outunsent.sub(off, off+int64(len(b)))
+}