database/sql: make Rows.Scan properly wrap underlying errors
The prior implementation used the format verb %v which unfortunately
improperly wrapped any underlying scanner errors, and we couldn't use
errors.Is nor errors.As. This change fixes that by using the %w verb.
Added a unit to ensure that both error sub string matching works, but
also that errors.Is works as expected.
Fixes #38099
Change-Id: Iea667041dd8081d961246f77f2542330417292dc
Reviewed-on: https://go-review.googlesource.com/c/go/+/248337
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
Reviewed-by: Daniel Theophanes <kardianos@gmail.com>
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
diff --git a/src/database/sql/sql.go b/src/database/sql/sql.go
index b3d0653..0b85db6 100644
--- a/src/database/sql/sql.go
+++ b/src/database/sql/sql.go
@@ -3110,6 +3110,9 @@
// "select cursor(select * from my_table) from dual", into a
// *Rows value that can itself be scanned from. The parent
// select query will close any cursor *Rows if the parent *Rows is closed.
+//
+// If any of the first arguments implementing Scanner returns an error,
+// that error will be wrapped in the returned error
func (rs *Rows) Scan(dest ...interface{}) error {
rs.closemu.RLock()
@@ -3133,7 +3136,7 @@
for i, sv := range rs.lastcols {
err := convertAssignRows(dest[i], sv, rs)
if err != nil {
- return fmt.Errorf(`sql: Scan error on column index %d, name %q: %v`, i, rs.rowsi.Columns()[i], err)
+ return fmt.Errorf(`sql: Scan error on column index %d, name %q: %w`, i, rs.rowsi.Columns()[i], err)
}
}
return nil
diff --git a/src/database/sql/sql_test.go b/src/database/sql/sql_test.go
index 5727f0d..762d42f 100644
--- a/src/database/sql/sql_test.go
+++ b/src/database/sql/sql_test.go
@@ -4149,6 +4149,41 @@
}
}
+type alwaysErrScanner struct{}
+
+var errTestScanWrap = errors.New("errTestScanWrap")
+
+func (alwaysErrScanner) Scan(interface{}) error {
+ return errTestScanWrap
+}
+
+// Issue 38099: Ensure that Rows.Scan properly wraps underlying errors.
+func TestRowsScanProperlyWrapsErrors(t *testing.T) {
+ db := newTestDB(t, "people")
+ defer closeDB(t, db)
+
+ rows, err := db.Query("SELECT|people|age|")
+ if err != nil {
+ t.Fatalf("Query: %v", err)
+ }
+
+ var res alwaysErrScanner
+
+ for rows.Next() {
+ err = rows.Scan(&res)
+ if err == nil {
+ t.Fatal("expecting back an error")
+ }
+ if !errors.Is(err, errTestScanWrap) {
+ t.Fatalf("errors.Is mismatch\n%v\nWant: %v", err, errTestScanWrap)
+ }
+ // Ensure that error substring matching still correctly works.
+ if !strings.Contains(err.Error(), errTestScanWrap.Error()) {
+ t.Fatalf("Error %v does not contain %v", err, errTestScanWrap)
+ }
+ }
+}
+
// badConn implements a bad driver.Conn, for TestBadDriver.
// The Exec method panics.
type badConn struct{}
