p2p/rlpx: reduce allocation and syscalls (ethereum#22899)

This change significantly improves the performance of RLPx message reads
and writes. In the previous implementation, reading and writing of
message frames performed multiple reads and writes on the underlying
network connection, and allocated a new []byte buffer for every read.

In the new implementation, reads and writes re-use buffers, and perform
much fewer system calls on the underlying connection. This doubles the
theoretically achievable throughput on a single connection, as shown by
the benchmark result:

    name             old speed      new speed       delta
    Throughput-8     70.3MB/s ± 0%  155.4MB/s ± 0%  +121.11%  (p=0.000 n=9+8)

The change also removes support for the legacy, pre-EIP-8 handshake encoding.
As of May 2021, no actively maintained client sends this format.

p2p/rlpx/buffer.go

@@ -0,0 +1,127 @@
+// Copyright 2021 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package rlpx
+
+import (
+	"io"
+)
+
+// readBuffer implements buffering for network reads. This type is similar to bufio.Reader,
+// with two crucial differences: the buffer slice is exposed, and the buffer keeps all
+// read data available until reset.
+//
+// How to use this type:
+//
+// Keep a readBuffer b alongside the underlying network connection. When reading a packet
+// from the connection, first call b.reset(). This empties b.data. Now perform reads
+// through b.read() until the end of the packet is reached. The complete packet data is
+// now available in b.data.
+type readBuffer struct {
+	data []byte
+	end  int
+}
+
+// reset removes all processed data which was read since the last call to reset.
+// After reset, len(b.data) is zero.
+func (b *readBuffer) reset() {
+	unprocessed := b.end - len(b.data)
+	copy(b.data[:unprocessed], b.data[len(b.data):b.end])
+	b.end = unprocessed
+	b.data = b.data[:0]
+}
+
+// read reads at least n bytes from r, returning the bytes.
+// The returned slice is valid until the next call to reset.
+func (b *readBuffer) read(r io.Reader, n int) ([]byte, error) {
+	offset := len(b.data)
+	have := b.end - len(b.data)
+
+	// If n bytes are available in the buffer, there is no need to read from r at all.
+	if have >= n {
+		b.data = b.data[:offset+n]
+		return b.data[offset : offset+n], nil
+	}
+
+	// Make buffer space available.
+	need := n - have
+	b.grow(need)
+
+	// Read.
+	rn, err := io.ReadAtLeast(r, b.data[b.end:cap(b.data)], need)
+	if err != nil {
+		return nil, err
+	}
+	b.end += rn
+	b.data = b.data[:offset+n]
+	return b.data[offset : offset+n], nil
+}
+
+// grow ensures the buffer has at least n bytes of unused space.
+func (b *readBuffer) grow(n int) {
+	if cap(b.data)-b.end >= n {
+		return
+	}
+	need := n - (cap(b.data) - b.end)
+	offset := len(b.data)
+	b.data = append(b.data[:cap(b.data)], make([]byte, need)...)
+	b.data = b.data[:offset]
+}
+
+// writeBuffer implements buffering for network writes. This is essentially
+// a convenience wrapper around a byte slice.
+type writeBuffer struct {
+	data []byte
+}
+
+func (b *writeBuffer) reset() {
+	b.data = b.data[:0]
+}
+
+func (b *writeBuffer) appendZero(n int) []byte {
+	offset := len(b.data)
+	b.data = append(b.data, make([]byte, n)...)
+	return b.data[offset : offset+n]
+}
+
+func (b *writeBuffer) Write(data []byte) (int, error) {
+	b.data = append(b.data, data...)
+	return len(data), nil
+}
+
+const maxUint24 = int(^uint32(0) >> 8)
+
+func readUint24(b []byte) uint32 {
+	return uint32(b[2]) | uint32(b[1])<<8 | uint32(b[0])<<16
+}
+
+func putUint24(v uint32, b []byte) {
+	b[0] = byte(v >> 16)
+	b[1] = byte(v >> 8)
+	b[2] = byte(v)
+}
+
+// growslice ensures b has the wanted length by either expanding it to its capacity
+// or allocating a new slice if b has insufficient capacity.
+func growslice(b []byte, wantLength int) []byte {
+	if len(b) >= wantLength {
+		return b
+	}
+	if cap(b) >= wantLength {
+		return b[:cap(b)]
+	}
+	return make([]byte, wantLength)
+}

p2p/rlpx/buffer_test.go

@@ -0,0 +1,51 @@
+// Copyright 2021 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package rlpx
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/ethereum/go-ethereum/common/hexutil"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestReadBufferReset(t *testing.T) {
+	reader := bytes.NewReader(hexutil.MustDecode("0x010202030303040505"))
+	var b readBuffer
+
+	s1, _ := b.read(reader, 1)
+	s2, _ := b.read(reader, 2)
+	s3, _ := b.read(reader, 3)
+
+	assert.Equal(t, []byte{1}, s1)
+	assert.Equal(t, []byte{2, 2}, s2)
+	assert.Equal(t, []byte{3, 3, 3}, s3)
+
+	b.reset()
+
+	s4, _ := b.read(reader, 1)
+	s5, _ := b.read(reader, 2)
+
+	assert.Equal(t, []byte{4}, s4)
+	assert.Equal(t, []byte{5, 5}, s5)
+
+	s6, err := b.read(reader, 2)
+
+	assert.EqualError(t, err, "EOF")
+	assert.Nil(t, s6)
+}