Add pgconn.CheckConn

internal/nbconn/nbconn.go

@@ -13,6 +13,7 @@ package nbconn
 import (
 	"crypto/tls"
 	"errors"
+	"io"
 	"net"
 	"os"
 	"sync"
@@ -46,11 +47,16 @@ func (*wouldBlockError) Error() string {
 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 must be called to actually write to the
-// underlying connection.
+// 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 sucessfully read bytes until the read would block.
+	BufferReadUntilBlock() error
 }
 
 // NetConn is a non-blocking net.Conn wrapper. It implements net.Conn.
@@ -303,24 +309,35 @@ func (c *NetConn) flush() error {
 	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)
+		}
+
+		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 {
-			buf := iobufpool.Get(8 * 1024)
-			n, err := c.nonblockingRead(buf)
-			if n > 0 {
-				buf = buf[:n]
-				c.readQueue.pushBack(buf)
-			}
-
+			err := c.BufferReadUntilBlock()
 			if err != nil {
-				if !errors.Is(err, ErrWouldBlock) {
-					errChan <- err
-					return
-				}
+				errChan <- err
+				return
 			}
 
 			select {
@@ -456,6 +473,11 @@ func (c *NetConn) realNonblockingRead(b []byte) (n int, err error) {
 		return n, err
 	}
 
+	// syscall read did not return an error and 0 bytes were read means EOF.
+	if n == 0 {
+		return 0, io.EOF
+	}
+
 	return n, nil
 }
 
@@ -494,6 +516,7 @@ type TLSConn struct {
 
 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() }

internal/nbconn/nbconn_test.go

@@ -2,6 +2,7 @@ package nbconn_test
 
 import (
 	"crypto/tls"
+	"errors"
 	"io"
 	"net"
 	"strings"
@@ -345,6 +346,34 @@ func TestNonBlockingRead(t *testing.T) {
 	})
 }
 
+func TestBufferNonBlockingRead(t *testing.T) {
+	testVariants(t, func(t *testing.T, conn nbconn.Conn, remote net.Conn) {
+		err := conn.BufferReadUntilBlock()
+		require.NoError(t, err)
+
+		errChan := make(chan error, 1)
+		go func() {
+			_, err := remote.Write([]byte("okay"))
+			errChan <- err
+		}()
+
+		for i := 0; i < 1000; i++ {
+			err = conn.BufferReadUntilBlock()
+			if !errors.Is(err, nbconn.ErrWouldBlock) {
+				break
+			}
+			time.Sleep(time.Millisecond)
+		}
+		require.NoError(t, err)
+
+		buf := make([]byte, 4)
+		n, err := conn.Read(buf)
+		require.NoError(t, err)
+		require.EqualValues(t, 4, n)
+		require.Equal(t, []byte("okay"), buf)
+	})
+}
+
 func TestReadPreviouslyBuffered(t *testing.T) {
 	testVariants(t, func(t *testing.T, conn nbconn.Conn, remote net.Conn) {