Add non-blocking IO

This eliminates an edge case that can cause a deadlock and is a
prerequisite to cheaply testing connection liveness and to recoving a
connection after a timeout.

jackc/pgconn#27

Squashed commit of the following:

commit 0d7b0dd
Author: Jack Christensen <jack@jackchristensen.com>
Date:   Sat Jun 25 13:15:05 2022 -0500

    Add test for non-blocking IO preventing deadlock

commit 79d68d2
Author: Jack Christensen <jack@jackchristensen.com>
Date:   Sat Jun 18 18:23:24 2022 -0500

    Release CopyFrom buf when done

commit 95a4313
Author: Jack Christensen <jack@jackchristensen.com>
Date:   Sat Jun 18 18:22:32 2022 -0500

    Avoid allocations with non-blocking write

commit 6b63cee
Author: Jack Christensen <jack@jackchristensen.com>
Date:   Sat Jun 18 17:46:49 2022 -0500

    Simplify iobufpool usage

commit 60ecdda
Author: Jack Christensen <jack@jackchristensen.com>
Date:   Sat Jun 18 11:51:59 2022 -0500

    Add true non-blocking IO

commit 7dd26a3
Author: Jack Christensen <jack@jackchristensen.com>
Date:   Sat Jun 4 20:28:23 2022 -0500

    Fix block when reading more than buffered

commit afa7022
Author: Jack Christensen <jack@jackchristensen.com>
Date:   Sat Jun 4 20:10:23 2022 -0500

    More TLS support

commit 51655bf
Author: Jack Christensen <jack@jackchristensen.com>
Date:   Sat Jun 4 17:46:00 2022 -0500

    Steps toward TLS

commit 2b80beb
Author: Jack Christensen <jack@jackchristensen.com>
Date:   Sat Jun 4 13:06:29 2022 -0500

    Litle more TLS support

commit 765b2c6
Author: Jack Christensen <jack@jackchristensen.com>
Date:   Sat Jun 4 12:29:30 2022 -0500

    Add testing of TLS

commit 5b64432
Author: Jack Christensen <jack@jackchristensen.com>
Date:   Sat Jun 4 09:48:19 2022 -0500

    Introduce testVariants in prep for TLS

commit ecebd7b
Author: Jack Christensen <jack@jackchristensen.com>
Date:   Sat Jun 4 09:32:14 2022 -0500

    Handle and test read of previously buffered data

commit 09c64d8
Author: Jack Christensen <jack@jackchristensen.com>
Date:   Sat Jun 4 09:04:48 2022 -0500

    Rename nbbconn to nbconn

commit 73398bc
Author: Jack Christensen <jack@jackchristensen.com>
Date:   Sat Jun 4 08:59:53 2022 -0500

    Remove backup files

commit f1df39a
Author: Jack Christensen <jack@jackchristensen.com>
Date:   Sat Jun 4 08:58:05 2022 -0500

    Initial passing tests

commit ea3cdab
Author: Jack Christensen <jack@jackchristensen.com>
Date:   Sat Jun 4 08:38:57 2022 -0500

    Fix connect timeout

commit ca22396
Author: Jack Christensen <jack@jackchristensen.com>
Date:   Thu Jun 2 19:32:55 2022 -0500

    wip

commit 2e7b46d
Author: Jack Christensen <jack@jackchristensen.com>
Date:   Mon May 30 08:32:43 2022 -0500

    Update comments

commit 7d04dc5
Author: Jack Christensen <jack@jackchristensen.com>
Date:   Sat May 28 19:43:23 2022 -0500

    Fix broken test

commit bf1edc7
Author: Jack Christensen <jack@jackchristensen.com>
Date:   Sat May 28 19:40:33 2022 -0500

    fixed putting wrong size bufs

commit 1f7a855
Author: Jack Christensen <jack@jackchristensen.com>
Date:   Sat May 28 18:13:47 2022 -0500

    initial not quite working non-blocking conn

internal/iobufpool/iobufpool.go

@@ -14,33 +14,44 @@ func init() {
 	}
 }
 
-// Get gets a []byte with len >= size and len <= size*2.
+// Get gets a []byte of len size with cap <= size*2.
 func Get(size int) []byte {
-	i := poolIdx(size)
+	i := getPoolIdx(size)
 	if i >= len(pools) {
 		return make([]byte, size)
 	}
-	return pools[i].Get().([]byte)
+	return pools[i].Get().([]byte)[:size]
+}
+
+func getPoolIdx(size int) int {
+	size--
+	size >>= minPoolExpOf2
+	i := 0
+	for size > 0 {
+		size >>= 1
+		i++
+	}
+
+	return i
 }
 
 // Put returns buf to the pool.
 func Put(buf []byte) {
-	i := poolIdx(len(buf))
-	if i >= len(pools) {
+	i := putPoolIdx(cap(buf))
+	if i < 0 {
 		return
 	}
 
 	pools[i].Put(buf)
 }
 
-func poolIdx(size int) int {
-	size--
-	size >>= minPoolExpOf2
-	i := 0
-	for size > 0 {
-		size >>= 1
-		i++
+func putPoolIdx(size int) int {
+	minPoolSize := 1 << minPoolExpOf2
+	for i := range pools {
+		if size == minPoolSize<<i {
+			return i
+		}
 	}
 
-	return i
+	return -1
 }

internal/iobufpool/iobufpool_internal_test.go

@@ -30,7 +30,7 @@ func TestPoolIdx(t *testing.T) {
 		{size: 8388609, expected: 16},
 	}
 	for _, tt := range tests {
-		idx := poolIdx(tt.size)
+		idx := getPoolIdx(tt.size)
 		assert.Equalf(t, tt.expected, idx, "size: %d", tt.size)
 	}
 }

internal/iobufpool/iobufpool_test.go

@@ -5,31 +5,74 @@ import (
 
 	"github.com/jackc/pgx/v5/internal/iobufpool"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
-func TestGet(t *testing.T) {
+func TestGetCap(t *testing.T) {
 	tests := []struct {
 		requestedLen int
-		expectedLen  int
+		expectedCap  int
 	}{
-		{requestedLen: 0, expectedLen: 256},
-		{requestedLen: 128, expectedLen: 256},
-		{requestedLen: 255, expectedLen: 256},
-		{requestedLen: 256, expectedLen: 256},
-		{requestedLen: 257, expectedLen: 512},
-		{requestedLen: 511, expectedLen: 512},
-		{requestedLen: 512, expectedLen: 512},
-		{requestedLen: 513, expectedLen: 1024},
-		{requestedLen: 1023, expectedLen: 1024},
-		{requestedLen: 1024, expectedLen: 1024},
-		{requestedLen: 33554431, expectedLen: 33554432},
-		{requestedLen: 33554432, expectedLen: 33554432},
+		{requestedLen: 0, expectedCap: 256},
+		{requestedLen: 128, expectedCap: 256},
+		{requestedLen: 255, expectedCap: 256},
+		{requestedLen: 256, expectedCap: 256},
+		{requestedLen: 257, expectedCap: 512},
+		{requestedLen: 511, expectedCap: 512},
+		{requestedLen: 512, expectedCap: 512},
+		{requestedLen: 513, expectedCap: 1024},
+		{requestedLen: 1023, expectedCap: 1024},
+		{requestedLen: 1024, expectedCap: 1024},
+		{requestedLen: 33554431, expectedCap: 33554432},
+		{requestedLen: 33554432, expectedCap: 33554432},
 
 		// Above 32 MiB skip the pool and allocate exactly the requested size.
-		{requestedLen: 33554433, expectedLen: 33554433},
+		{requestedLen: 33554433, expectedCap: 33554433},
 	}
 	for _, tt := range tests {
 		buf := iobufpool.Get(tt.requestedLen)
-		assert.Equalf(t, tt.expectedLen, len(buf), "requestedLen: %d", tt.requestedLen)
+		assert.Equalf(t, tt.requestedLen, len(buf), "bad len for requestedLen: %d", len(buf), tt.requestedLen)
+		assert.Equalf(t, tt.expectedCap, cap(buf), "bad cap for requestedLen: %d", tt.requestedLen)
 	}
 }
+
+func TestPutHandlesWrongSizedBuffers(t *testing.T) {
+	for putBufSize := range []int{0, 1, 128, 250, 256, 257, 1023, 1024, 1025, 1 << 28} {
+		putBuf := make([]byte, putBufSize)
+		iobufpool.Put(putBuf)
+
+		tests := []struct {
+			requestedLen int
+			expectedCap  int
+		}{
+			{requestedLen: 0, expectedCap: 256},
+			{requestedLen: 128, expectedCap: 256},
+			{requestedLen: 255, expectedCap: 256},
+			{requestedLen: 256, expectedCap: 256},
+			{requestedLen: 257, expectedCap: 512},
+			{requestedLen: 511, expectedCap: 512},
+			{requestedLen: 512, expectedCap: 512},
+			{requestedLen: 513, expectedCap: 1024},
+			{requestedLen: 1023, expectedCap: 1024},
+			{requestedLen: 1024, expectedCap: 1024},
+			{requestedLen: 33554431, expectedCap: 33554432},
+			{requestedLen: 33554432, expectedCap: 33554432},
+
+			// Above 32 MiB skip the pool and allocate exactly the requested size.
+			{requestedLen: 33554433, expectedCap: 33554433},
+		}
+		for _, tt := range tests {
+			getBuf := iobufpool.Get(tt.requestedLen)
+			assert.Equalf(t, tt.requestedLen, len(getBuf), "len(putBuf): %d, requestedLen: %d", len(putBuf), tt.requestedLen)
+			assert.Equalf(t, tt.expectedCap, cap(getBuf), "cap(putBuf): %d, requestedLen: %d", cap(putBuf), tt.requestedLen)
+		}
+	}
+}
+
+func TestPutGetBufferReuse(t *testing.T) {
+	buf := iobufpool.Get(4)
+	buf[0] = 1
+	iobufpool.Put(buf)
+	buf = iobufpool.Get(4)
+	require.Equal(t, byte(1), buf[0])
+}

internal/nbconn/bufferqueue.go

@@ -0,0 +1,70 @@
+package nbconn
+
+import (
+	"sync"
+)
+
+const minBufferQueueLen = 8
+
+type bufferQueue struct {
+	lock  sync.Mutex
+	queue [][]byte
+	r, w  int
+}
+
+func (bq *bufferQueue) pushBack(buf []byte) {
+	bq.lock.Lock()
+	defer bq.lock.Unlock()
+
+	if bq.w >= len(bq.queue) {
+		bq.growQueue()
+	}
+	bq.queue[bq.w] = buf
+	bq.w++
+}
+
+func (bq *bufferQueue) pushFront(buf []byte) {
+	bq.lock.Lock()
+	defer bq.lock.Unlock()
+
+	if bq.w >= len(bq.queue) {
+		bq.growQueue()
+	}
+	copy(bq.queue[bq.r+1:bq.w+1], bq.queue[bq.r:bq.w])
+	bq.queue[bq.r] = buf
+	bq.w++
+}
+
+func (bq *bufferQueue) popFront() []byte {
+	bq.lock.Lock()
+	defer bq.lock.Unlock()
+
+	if bq.r == bq.w {
+		return nil
+	}
+
+	buf := bq.queue[bq.r]
+	bq.queue[bq.r] = nil // Clear reference so it can be garbage collected.
+	bq.r++
+
+	if bq.r == bq.w {
+		bq.r = 0
+		bq.w = 0
+		if len(bq.queue) > minBufferQueueLen {
+			bq.queue = make([][]byte, minBufferQueueLen)
+		}
+	}
+
+	return buf
+}
+
+func (bq *bufferQueue) growQueue() {
+	desiredLen := (len(bq.queue) + 1) * 3 / 2
+	if desiredLen < minBufferQueueLen {
+		desiredLen = minBufferQueueLen
+	}
+
+	newQueue := make([][]byte, desiredLen)
+	copy(newQueue, bq.queue)
+	bq.queue = newQueue
+}