Properly abort CopyFrom on reader error

pgconn.go

@@ -876,11 +876,10 @@ 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
-		}
+	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))
 
@@ -898,12 +897,16 @@ func (pgConn *PgConn) CopyFrom(ctx context.Context, r io.Reader, sql string) (Co
 				return "", preferContextOverNetTimeoutError(ctx, err)
 			}
 		}
+	}
 
-	// Send copy done
 	buf = buf[:0]
+	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()