Fix Windows non-blocking I/O for CopyFrom

Created based on discussion here: https://github.com/jackc/pgx/pull/1525#pullrequestreview-1344511991

Fixes https://github.com/jackc/pgx/issues/1552

copy_from.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"context"
 	"fmt"
+	"github.com/jackc/pgx/v5/internal/nbconn"
 	"io"
 
 	"github.com/jackc/pgx/v5/internal/pgio"
@@ -134,6 +135,17 @@ func (ct *copyFrom) run(ctx context.Context) (int64, error) {
 	r, w := io.Pipe()
 	doneChan := make(chan struct{})
 
+	if realNbConn, ok := ct.conn.pgConn.Conn().(*nbconn.NetConn); ok {
+		if err := realNbConn.SetBlockingMode(false); err != nil {
+			return 0, fmt.Errorf("cannot set socket non-blocking mode: %w", err)
+		}
+
+		defer func() {
+			// TODO: Deal with it
+			_ = realNbConn.SetBlockingMode(true)
+		}()
+	}
+
 	go func() {
 		defer close(doneChan)
 

internal/nbconn/nbconn.go

@@ -96,6 +96,9 @@ type NetConn struct {
 
 	writeDeadlineLock sync.Mutex
 	writeDeadline     time.Time
+
+	// Indicates that underlying socket connection mode set to be non-blocking
+	isNonBlocking bool
 }
 
 func NewNetConn(conn net.Conn, fakeNonBlockingIO bool) *NetConn {

internal/nbconn/nbconn_real_non_block.go

@@ -79,3 +79,8 @@ func (c *NetConn) realNonblockingRead(b []byte) (n int, err error) {
 
 	return n, nil
 }
+
+func (c *NetConn) SetBlockingMode(blocking bool) error {
+	// for UNIX do nothing
+	return nil
+}

internal/nbconn/nbconn_real_non_block_windows.go

@@ -43,10 +43,12 @@ func setSockMode(fd uintptr, mode sockMode) error {
 func (c *NetConn) realNonblockingWrite(b []byte) (n int, err error) {
 	if c.nonblockWriteFunc == nil {
 		c.nonblockWriteFunc = func(fd uintptr) (done bool) {
-			// Make sock non-blocking
-			if err := setSockMode(fd, sockModeNonBlocking); err != nil {
-				c.nonblockWriteErr = err
-				return true
+			if !c.isNonBlocking {
+				// Make sock non-blocking
+				if err := setSockMode(fd, sockModeNonBlocking); err != nil {
+					c.nonblockWriteErr = err
+					return true
+				}
 			}
 
 			var written uint32
@@ -56,10 +58,12 @@ func (c *NetConn) realNonblockingWrite(b []byte) (n int, err error) {
 			c.nonblockWriteErr = syscall.WSASend(syscall.Handle(fd), &buf, 1, &written, 0, nil, nil)
 			c.nonblockWriteN = int(written)
 
-			// Make sock blocking again
-			if err := setSockMode(fd, sockModeBlocking); err != nil {
-				c.nonblockWriteErr = err
-				return true
+			if !c.isNonBlocking {
+				// Make sock blocking again
+				if err := setSockMode(fd, sockModeBlocking); err != nil {
+					c.nonblockWriteErr = err
+					return true
+				}
 			}
 
 			return true
@@ -94,10 +98,12 @@ func (c *NetConn) realNonblockingWrite(b []byte) (n int, err error) {
 func (c *NetConn) realNonblockingRead(b []byte) (n int, err error) {
 	if c.nonblockReadFunc == nil {
 		c.nonblockReadFunc = func(fd uintptr) (done bool) {
-			// Make sock non-blocking
-			if err := setSockMode(fd, sockModeNonBlocking); err != nil {
-				c.nonblockReadErr = err
-				return true
+			if !c.isNonBlocking {
+				// Make sock non-blocking
+				if err := setSockMode(fd, sockModeNonBlocking); err != nil {
+					c.nonblockReadErr = err
+					return true
+				}
 			}
 
 			var read uint32
@@ -108,10 +114,12 @@ func (c *NetConn) realNonblockingRead(b []byte) (n int, err error) {
 			c.nonblockReadErr = syscall.WSARecv(syscall.Handle(fd), &buf, 1, &read, &flags, nil, nil)
 			c.nonblockReadN = int(read)
 
-			// Make sock blocking again
-			if err := setSockMode(fd, sockModeBlocking); err != nil {
-				c.nonblockReadErr = err
-				return true
+			if !c.isNonBlocking {
+				// Make sock blocking again
+				if err := setSockMode(fd, sockModeBlocking); err != nil {
+					c.nonblockReadErr = err
+					return true
+				}
 			}
 
 			return true
@@ -147,3 +155,22 @@ func (c *NetConn) realNonblockingRead(b []byte) (n int, err error) {
 
 	return n, nil
 }
+
+func (c *NetConn) SetBlockingMode(blocking bool) error {
+	mode := sockModeNonBlocking
+	if blocking {
+		mode = sockModeBlocking
+	}
+
+	var err error
+
+	c.rawConn.Control(func(fd uintptr) {
+		err = setSockMode(fd, mode)
+	})
+
+	if err == nil {
+		c.isNonBlocking = !blocking
+	}
+
+	return err
+}