Properly abort CopyFrom on reader error

pgconn.go

@@ -876,34 +876,37 @@ func (pgConn *PgConn) CopyFrom(ctx context.Context, r io.Reader, sql string) (Co
 	buf = make([]byte, 0, 65536)
 	buf = append(buf, 'd')
 	sp := len(buf)
-	for {
-		n, err := r.Read(buf[5:cap(buf)])
-		if err == io.EOF && n == 0 {
-			break
-		}
-		buf = buf[0 : n+5]
-		pgio.SetInt32(buf[sp:], int32(n+4))
+	var readErr error
+	for readErr == nil {
+		n, readErr = r.Read(buf[5:cap(buf)])
+		if n > 0 {
+			buf = buf[0 : n+5]
+			pgio.SetInt32(buf[sp:], int32(n+4))
 
-		_, err = pgConn.conn.Write(buf)
-		if err != nil {
-			// Partially sent messages are a fatal error for the connection. If nothing was sent it might be possible to
-			// recover the connection with a CopyFail, but that could be rather complicated and error prone. Simpler just to
-			// close the connection.
-			pgConn.conn.Close()
-			pgConn.closed = true
+			_, err = pgConn.conn.Write(buf)
+			if err != nil {
+				// Partially sent messages are a fatal error for the connection. If nothing was sent it might be possible to
+				// recover the connection with a CopyFail, but that could be rather complicated and error prone. Simpler just to
+				// close the connection.
+				pgConn.conn.Close()
+				pgConn.closed = true
 
-			cleanupContextDeadline()
-			<-pgConn.controller
+				cleanupContextDeadline()
+				<-pgConn.controller
 
-			return "", preferContextOverNetTimeoutError(ctx, err)
+				return "", preferContextOverNetTimeoutError(ctx, err)
+			}
 		}
 	}
 
-	// Send copy done
 	buf = buf[:0]
-	copyDone := &pgproto3.CopyDone{}
-	buf = copyDone.Encode(buf)
-
+	if readErr == io.EOF {
+		copyDone := &pgproto3.CopyDone{}
+		buf = copyDone.Encode(buf)
+	} else {
+		copyFail := &pgproto3.CopyFail{Error: readErr.Error()}
+		buf = copyFail.Encode(buf)
+	}
 	_, err = pgConn.conn.Write(buf)
 	if err != nil {
 		pgConn.conn.Close()