gotosocial/vendor/github.com/jackc/pgx/v5/internal/nbconn/nbconn.go

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// Package nbconn implements a non-blocking net.Conn wrapper.
//
// It is designed to solve three problems.
//
// The first is resolving the deadlock that can occur when both sides of a connection are blocked writing because all
// buffers between are full. See https://github.com/jackc/pgconn/issues/27 for discussion.
//
// The second is the inability to use a write deadline with a TLS.Conn without killing the connection.
//
// The third is to efficiently check if a connection has been closed via a non-blocking read.
package nbconn
import (
"crypto/tls"
"errors"
"net"
"os"
"sync"
"sync/atomic"
"syscall"
"time"
"github.com/jackc/pgx/v5/internal/iobufpool"
)
var errClosed = errors.New("closed")
var ErrWouldBlock = new(wouldBlockError)
const fakeNonblockingWriteWaitDuration = 100 * time.Millisecond
const minNonblockingReadWaitDuration = time.Microsecond
const maxNonblockingReadWaitDuration = 100 * time.Millisecond
// NonBlockingDeadline is a magic value that when passed to Set[Read]Deadline places the connection in non-blocking read
// mode.
var NonBlockingDeadline = time.Date(1900, 1, 1, 0, 0, 0, 608536336, time.UTC)
// disableSetDeadlineDeadline is a magic value that when passed to Set[Read|Write]Deadline causes those methods to
// ignore all future calls.
var disableSetDeadlineDeadline = time.Date(1900, 1, 1, 0, 0, 0, 968549727, time.UTC)
// wouldBlockError implements net.Error so tls.Conn will recognize ErrWouldBlock as a temporary error.
type wouldBlockError struct{}
func (*wouldBlockError) Error() string {
return "would block"
}
func (*wouldBlockError) Timeout() bool { return true }
func (*wouldBlockError) Temporary() bool { return true }
// Conn is a net.Conn where Write never blocks and always succeeds. Flush or Read must be called to actually write to
// the underlying connection.
type Conn interface {
net.Conn
// Flush flushes any buffered writes.
Flush() error
// BufferReadUntilBlock reads and buffers any successfully read bytes until the read would block.
BufferReadUntilBlock() error
}
// NetConn is a non-blocking net.Conn wrapper. It implements net.Conn.
type NetConn struct {
// 64 bit fields accessed with atomics must be at beginning of struct to guarantee alignment for certain 32-bit
// architectures. See BUGS section of https://pkg.go.dev/sync/atomic and https://github.com/jackc/pgx/issues/1288 and
// https://github.com/jackc/pgx/issues/1307. Only access with atomics
closed int64 // 0 = not closed, 1 = closed
conn net.Conn
rawConn syscall.RawConn
readQueue bufferQueue
writeQueue bufferQueue
readFlushLock sync.Mutex
// non-blocking writes with syscall.RawConn are done with a callback function. By using these fields instead of the
// callback functions closure to pass the buf argument and receive the n and err results we avoid some allocations.
nonblockWriteFunc func(fd uintptr) (done bool)
nonblockWriteBuf []byte
nonblockWriteErr error
nonblockWriteN int
// non-blocking reads with syscall.RawConn are done with a callback function. By using these fields instead of the
// callback functions closure to pass the buf argument and receive the n and err results we avoid some allocations.
nonblockReadFunc func(fd uintptr) (done bool)
nonblockReadBuf []byte
nonblockReadErr error
nonblockReadN int
readDeadlineLock sync.Mutex
readDeadline time.Time
readNonblocking bool
fakeNonBlockingShortReadCount int
fakeNonblockingReadWaitDuration time.Duration
writeDeadlineLock sync.Mutex
writeDeadline time.Time
}
func NewNetConn(conn net.Conn, fakeNonBlockingIO bool) *NetConn {
nc := &NetConn{
conn: conn,
fakeNonblockingReadWaitDuration: maxNonblockingReadWaitDuration,
}
if !fakeNonBlockingIO {
if sc, ok := conn.(syscall.Conn); ok {
if rawConn, err := sc.SyscallConn(); err == nil {
nc.rawConn = rawConn
}
}
}
return nc
}
// Read implements io.Reader.
func (c *NetConn) Read(b []byte) (n int, err error) {
if c.isClosed() {
return 0, errClosed
}
c.readFlushLock.Lock()
defer c.readFlushLock.Unlock()
err = c.flush()
if err != nil {
return 0, err
}
for n < len(b) {
buf := c.readQueue.popFront()
if buf == nil {
break
}
copiedN := copy(b[n:], *buf)
if copiedN < len(*buf) {
*buf = (*buf)[copiedN:]
c.readQueue.pushFront(buf)
} else {
iobufpool.Put(buf)
}
n += copiedN
}
// If any bytes were already buffered return them without trying to do a Read. Otherwise, when the caller is trying to
// Read up to len(b) bytes but all available bytes have already been buffered the underlying Read would block.
if n > 0 {
return n, nil
}
var readNonblocking bool
c.readDeadlineLock.Lock()
readNonblocking = c.readNonblocking
c.readDeadlineLock.Unlock()
var readN int
if readNonblocking {
readN, err = c.nonblockingRead(b[n:])
} else {
readN, err = c.conn.Read(b[n:])
}
n += readN
return n, err
}
// Write implements io.Writer. It never blocks due to buffering all writes. It will only return an error if the Conn is
// closed. Call Flush to actually write to the underlying connection.
func (c *NetConn) Write(b []byte) (n int, err error) {
if c.isClosed() {
return 0, errClosed
}
buf := iobufpool.Get(len(b))
copy(*buf, b)
c.writeQueue.pushBack(buf)
return len(b), nil
}
func (c *NetConn) Close() (err error) {
swapped := atomic.CompareAndSwapInt64(&c.closed, 0, 1)
if !swapped {
return errClosed
}
defer func() {
closeErr := c.conn.Close()
if err == nil {
err = closeErr
}
}()
c.readFlushLock.Lock()
defer c.readFlushLock.Unlock()
err = c.flush()
if err != nil {
return err
}
return nil
}
func (c *NetConn) LocalAddr() net.Addr {
return c.conn.LocalAddr()
}
func (c *NetConn) RemoteAddr() net.Addr {
return c.conn.RemoteAddr()
}
// SetDeadline is the equivalent of calling SetReadDealine(t) and SetWriteDeadline(t).
func (c *NetConn) SetDeadline(t time.Time) error {
err := c.SetReadDeadline(t)
if err != nil {
return err
}
return c.SetWriteDeadline(t)
}
// SetReadDeadline sets the read deadline as t. If t == NonBlockingDeadline then future reads will be non-blocking.
func (c *NetConn) SetReadDeadline(t time.Time) error {
if c.isClosed() {
return errClosed
}
c.readDeadlineLock.Lock()
defer c.readDeadlineLock.Unlock()
if c.readDeadline == disableSetDeadlineDeadline {
return nil
}
if t == disableSetDeadlineDeadline {
c.readDeadline = t
return nil
}
if t == NonBlockingDeadline {
c.readNonblocking = true
t = time.Time{}
} else {
c.readNonblocking = false
}
c.readDeadline = t
return c.conn.SetReadDeadline(t)
}
func (c *NetConn) SetWriteDeadline(t time.Time) error {
if c.isClosed() {
return errClosed
}
c.writeDeadlineLock.Lock()
defer c.writeDeadlineLock.Unlock()
if c.writeDeadline == disableSetDeadlineDeadline {
return nil
}
if t == disableSetDeadlineDeadline {
c.writeDeadline = t
return nil
}
c.writeDeadline = t
return c.conn.SetWriteDeadline(t)
}
func (c *NetConn) Flush() error {
if c.isClosed() {
return errClosed
}
c.readFlushLock.Lock()
defer c.readFlushLock.Unlock()
return c.flush()
}
// flush does the actual work of flushing the writeQueue. readFlushLock must already be held.
func (c *NetConn) flush() error {
var stopChan chan struct{}
var errChan chan error
defer func() {
if stopChan != nil {
select {
case stopChan <- struct{}{}:
case <-errChan:
}
}
}()
for buf := c.writeQueue.popFront(); buf != nil; buf = c.writeQueue.popFront() {
remainingBuf := *buf
for len(remainingBuf) > 0 {
n, err := c.nonblockingWrite(remainingBuf)
remainingBuf = remainingBuf[n:]
if err != nil {
if !errors.Is(err, ErrWouldBlock) {
*buf = (*buf)[:len(remainingBuf)]
copy(*buf, remainingBuf)
c.writeQueue.pushFront(buf)
return err
}
// Writing was blocked. Reading might unblock it.
if stopChan == nil {
stopChan, errChan = c.bufferNonblockingRead()
}
select {
case err := <-errChan:
stopChan = nil
return err
default:
}
}
}
iobufpool.Put(buf)
}
return nil
}
func (c *NetConn) BufferReadUntilBlock() error {
for {
buf := iobufpool.Get(8 * 1024)
n, err := c.nonblockingRead(*buf)
if n > 0 {
*buf = (*buf)[:n]
c.readQueue.pushBack(buf)
} else if n == 0 {
iobufpool.Put(buf)
}
if err != nil {
if errors.Is(err, ErrWouldBlock) {
return nil
} else {
return err
}
}
}
}
func (c *NetConn) bufferNonblockingRead() (stopChan chan struct{}, errChan chan error) {
stopChan = make(chan struct{})
errChan = make(chan error, 1)
go func() {
for {
err := c.BufferReadUntilBlock()
if err != nil {
errChan <- err
return
}
select {
case <-stopChan:
return
default:
}
}
}()
return stopChan, errChan
}
func (c *NetConn) isClosed() bool {
closed := atomic.LoadInt64(&c.closed)
return closed == 1
}
func (c *NetConn) nonblockingWrite(b []byte) (n int, err error) {
if c.rawConn == nil {
return c.fakeNonblockingWrite(b)
} else {
return c.realNonblockingWrite(b)
}
}
func (c *NetConn) fakeNonblockingWrite(b []byte) (n int, err error) {
c.writeDeadlineLock.Lock()
defer c.writeDeadlineLock.Unlock()
deadline := time.Now().Add(fakeNonblockingWriteWaitDuration)
if c.writeDeadline.IsZero() || deadline.Before(c.writeDeadline) {
err = c.conn.SetWriteDeadline(deadline)
if err != nil {
return 0, err
}
defer func() {
// Ignoring error resetting deadline as there is nothing that can reasonably be done if it fails.
c.conn.SetWriteDeadline(c.writeDeadline)
if err != nil {
if errors.Is(err, os.ErrDeadlineExceeded) {
err = ErrWouldBlock
}
}
}()
}
return c.conn.Write(b)
}
func (c *NetConn) nonblockingRead(b []byte) (n int, err error) {
if c.rawConn == nil {
return c.fakeNonblockingRead(b)
} else {
return c.realNonblockingRead(b)
}
}
func (c *NetConn) fakeNonblockingRead(b []byte) (n int, err error) {
c.readDeadlineLock.Lock()
defer c.readDeadlineLock.Unlock()
// The first 5 reads only read 1 byte at a time. This should give us 4 chances to read when we are sure the bytes are
// already in Go or the OS's receive buffer.
if c.fakeNonBlockingShortReadCount < 5 && len(b) > 0 && c.fakeNonblockingReadWaitDuration < minNonblockingReadWaitDuration {
b = b[:1]
}
startTime := time.Now()
deadline := startTime.Add(c.fakeNonblockingReadWaitDuration)
if c.readDeadline.IsZero() || deadline.Before(c.readDeadline) {
err = c.conn.SetReadDeadline(deadline)
if err != nil {
return 0, err
}
defer func() {
// If the read was successful and the wait duration is not already the minimum
if err == nil && c.fakeNonblockingReadWaitDuration > minNonblockingReadWaitDuration {
endTime := time.Now()
if n > 0 && c.fakeNonBlockingShortReadCount < 5 {
c.fakeNonBlockingShortReadCount++
}
// The wait duration should be 2x the fastest read that has occurred. This should give reasonable assurance that
// a Read deadline will not block a read before it has a chance to read data already in Go or the OS's receive
// buffer.
proposedWait := endTime.Sub(startTime) * 2
if proposedWait < minNonblockingReadWaitDuration {
proposedWait = minNonblockingReadWaitDuration
}
if proposedWait < c.fakeNonblockingReadWaitDuration {
c.fakeNonblockingReadWaitDuration = proposedWait
}
}
// Ignoring error resetting deadline as there is nothing that can reasonably be done if it fails.
c.conn.SetReadDeadline(c.readDeadline)
if err != nil {
if errors.Is(err, os.ErrDeadlineExceeded) {
err = ErrWouldBlock
}
}
}()
}
return c.conn.Read(b)
}
// syscall.Conn is interface
// TLSClient establishes a TLS connection as a client over conn using config.
//
// To avoid the first Read on the returned *TLSConn also triggering a Write due to the TLS handshake and thereby
// potentially causing a read and write deadlines to behave unexpectedly, Handshake is called explicitly before the
// *TLSConn is returned.
func TLSClient(conn *NetConn, config *tls.Config) (*TLSConn, error) {
tc := tls.Client(conn, config)
err := tc.Handshake()
if err != nil {
return nil, err
}
// Ensure last written part of Handshake is actually sent.
err = conn.Flush()
if err != nil {
return nil, err
}
return &TLSConn{
tlsConn: tc,
nbConn: conn,
}, nil
}
// TLSConn is a TLS wrapper around a *Conn. It works around a temporary write error (such as a timeout) being fatal to a
// tls.Conn.
type TLSConn struct {
tlsConn *tls.Conn
nbConn *NetConn
}
func (tc *TLSConn) Read(b []byte) (n int, err error) { return tc.tlsConn.Read(b) }
func (tc *TLSConn) Write(b []byte) (n int, err error) { return tc.tlsConn.Write(b) }
func (tc *TLSConn) BufferReadUntilBlock() error { return tc.nbConn.BufferReadUntilBlock() }
func (tc *TLSConn) Flush() error { return tc.nbConn.Flush() }
func (tc *TLSConn) LocalAddr() net.Addr { return tc.tlsConn.LocalAddr() }
func (tc *TLSConn) RemoteAddr() net.Addr { return tc.tlsConn.RemoteAddr() }
func (tc *TLSConn) Close() error {
// tls.Conn.closeNotify() sets a 5 second deadline to avoid blocking, sends a TLS alert close notification, and then
// sets the deadline to now. This causes NetConn's Close not to be able to flush the write buffer. Instead we set our
// own 5 second deadline then make all set deadlines no-op.
tc.tlsConn.SetDeadline(time.Now().Add(time.Second * 5))
tc.tlsConn.SetDeadline(disableSetDeadlineDeadline)
return tc.tlsConn.Close()
}
func (tc *TLSConn) SetDeadline(t time.Time) error { return tc.tlsConn.SetDeadline(t) }
func (tc *TLSConn) SetReadDeadline(t time.Time) error { return tc.tlsConn.SetReadDeadline(t) }
func (tc *TLSConn) SetWriteDeadline(t time.Time) error { return tc.tlsConn.SetWriteDeadline(t) }