Replace RowsFromResultReader with ScanRow function

query_test.go

@@ -1367,7 +1367,7 @@ func TestQueryCloseBefore(t *testing.T) {
 	assert.True(t, pgconn.SafeToRetry(err))
 }
 
-func TestRowsFromResultReader(t *testing.T) {
+func TestScanRow(t *testing.T) {
 	t.Parallel()
 
 	conn := mustConnectString(t, os.Getenv("PGX_TEST_DATABASE"))
@@ -1377,26 +1377,19 @@ func TestRowsFromResultReader(t *testing.T) {
 
 	var sum, rowCount int32
 
-	rows := pgx.RowsFromResultReader(conn.ConnInfo(), resultReader)
-	defer rows.Close()
-
-	for rows.Next() {
+	for resultReader.NextRow() {
 		var n int32
-		rows.Scan(&n)
+		err := pgx.ScanRow(conn.ConnInfo(), resultReader.FieldDescriptions(), resultReader.Values(), &n)
+		assert.NoError(t, err)
 		sum += n
 		rowCount++
 	}
 
-	if rows.Err() != nil {
-		t.Fatalf("conn.Query failed: %v", rows.Err())
-	}
+	_, err := resultReader.Close()
 
-	if rowCount != 10 {
-		t.Error("wrong number of rows")
-	}
-	if sum != 55 {
-		t.Error("Wrong values returned")
-	}
+	require.NoError(t, err)
+	assert.EqualValues(t, 10, rowCount)
+	assert.EqualValues(t, 55, sum)
 }
 
 func TestConnSimpleProtocol(t *testing.T) {

rows.go

@@ -174,27 +174,12 @@ func (rows *connRows) Next() bool {
 }
 
 func (rows *connRows) Scan(dest ...interface{}) error {
-	if len(rows.FieldDescriptions()) != len(dest) {
-		err := errors.Errorf("Scan received wrong number of arguments, got %d but expected %d", len(dest), len(rows.FieldDescriptions()))
+	err := ScanRow(rows.connInfo, rows.FieldDescriptions(), rows.values, dest...)
+	if err != nil {
 		rows.fatal(err)
 		return err
 	}
 
-	for i, d := range dest {
-		buf := rows.values[i]
-		fd := &rows.FieldDescriptions()[i]
-
-		if d == nil {
-			continue
-		}
-
-		err := rows.connInfo.Scan(fd.DataTypeOID, fd.Format, buf, d)
-		if err != nil {
-			rows.fatal(scanArgError{col: i, err: err})
-			return err
-		}
-	}
-
 	return nil
 }
 
@@ -254,7 +239,7 @@ func (rows *connRows) Values() ([]interface{}, error) {
 }
 
 func (rows *connRows) RawValues() [][]byte {
-	return rows.resultReader.Values()
+	return rows.values
 }
 
 type scanArgError struct {
@@ -266,14 +251,31 @@ func (e scanArgError) Error() string {
 	return fmt.Sprintf("can't scan into dest[%d]: %v", e.col, e.err)
 }
 
-// RowsFromResultReader wraps a *pgconn.ResultReader in a Rows wrapper so a more convenient scanning interface can be
-// used.
+// ScanRow decodes raw row data into dest. This is a low level function used internally to to implement the Rows
+// interface Scan method. It can be used to scan rows read from the lower level pgconn interface.
 //
-// In most cases, the appropriate pgx query methods should be used instead of sending a query with pgconn and reading
-// the results with pgx.
-func RowsFromResultReader(connInfo *pgtype.ConnInfo, rr *pgconn.ResultReader) Rows {
-	return &connRows{
-		connInfo:     connInfo,
-		resultReader: rr,
+// connInfo - OID to Go type mapping.
+// fieldDescriptions - OID and format of values
+// values - the raw data as returned from the PostgreSQL server
+// dest - the destination that values will be decoded into
+func ScanRow(connInfo *pgtype.ConnInfo, fieldDescriptions []pgproto3.FieldDescription, values [][]byte, dest ...interface{}) error {
+	if len(fieldDescriptions) != len(values) {
+		return errors.Errorf("number of field descriptions must equal number of values, got %d and %d", len(fieldDescriptions), len(values))
 	}
+	if len(fieldDescriptions) != len(dest) {
+		return errors.Errorf("number of field descriptions must equal number of destinations, got %d and %d", len(fieldDescriptions), len(dest))
+	}
+
+	for i, d := range dest {
+		if d == nil {
+			continue
+		}
+
+		err := connInfo.Scan(fieldDescriptions[i].DataTypeOID, fieldDescriptions[i].Format, values[i], d)
+		if err != nil {
+			return scanArgError{col: i, err: err}
+		}
+	}
+
+	return nil
 }