fix: #2146

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Co-authored-by: <[email protected]>

pgtype/json.go

@@ -143,10 +143,12 @@ func (c *JSONCodec) PlanScan(m *Map, oid uint32, format int16, target any) ScanP
  case BytesScanner:
  return scanPlanBinaryBytesToBytesScanner{}
 
+ }
+
  // Cannot rely on sql.Scanner being handled later because scanPlanJSONToJSONUnmarshal will take precedence.
  //
  // https:/jackc/pgx/issues/1418
- case sql.Scanner:
+ if isSQLScanner(target) {
  return &scanPlanSQLScanner{formatCode: format}
  }
 
@@ -155,6 +157,20 @@ func (c *JSONCodec) PlanScan(m *Map, oid uint32, format int16, target any) ScanP
  }
 }
 
+// we need to check if the target is a pointer to a sql.Scanner (or any of the pointer ref tree implements a sql.Scanner).
+//
+// https:/jackc/pgx/issues/2146
+func isSQLScanner(v any) bool {
+ val := reflect.ValueOf(v)
+ for val.Kind() == reflect.Ptr {
+ if _, ok := val.Interface().(sql.Scanner); ok {
+ return true
+ }
+ val = val.Elem()
+ }
+ return false
+}
+
 type scanPlanAnyToString struct{}
 
 func (scanPlanAnyToString) Scan(src []byte, dst any) error {

pgtype/json_test.go

@@ -63,6 +63,8 @@ func TestJSONCodec(t *testing.T) {
 
  // Test driver.Valuer is used before json.Marshaler (https:/jackc/pgx/issues/1805)
  {Issue1805(7), new(Issue1805), isExpectedEq(Issue1805(7))},
+ // Test driver.Scanner is used before json.Unmarshaler (https:/jackc/pgx/issues/2146)
+ {Issue2146(7), new(*Issue2146), isPtrExpectedEq(Issue2146(7))},
  })
 
  pgxtest.RunValueRoundTripTests(context.Background(), t, defaultConnTestRunner, pgxtest.KnownOIDQueryExecModes, "json", []pgxtest.ValueRoundTripTest{
@@ -109,6 +111,31 @@ func (i Issue1805) MarshalJSON() ([]byte, error) {
  return nil, errors.New("MarshalJSON called")
 }
 
+type Issue2146 int
+
+func (i *Issue2146) Scan(src any) error {
+ var source []byte
+ switch src.(type) {
+ case string:
+ source = []byte(src.(string))
+ case []byte:
+ source = src.([]byte)
+ default:
+ return errors.New("unknown source type")
+ }
+ var newI int
+ if err := json.Unmarshal(source, &newI); err != nil {
+ return err
+ }
+ *i = Issue2146(newI + 1)
+ return nil
+}
+
+func (i Issue2146) Value() (driver.Value, error) {
+ b, err := json.Marshal(int(i - 1))
+ return string(b), err
+}
+
 // https:/jackc/pgx/issues/1273#issuecomment-1221414648
 func TestJSONCodecUnmarshalSQLNull(t *testing.T) {
  defaultConnTestRunner.RunTest(context.Background(), t, func(ctx context.Context, t testing.TB, conn *pgx.Conn) {

pgtype/pgtype.go

@@ -396,7 +396,12 @@ type scanPlanSQLScanner struct {
 }
 
 func (plan *scanPlanSQLScanner) Scan(src []byte, dst any) error {
- scanner := dst.(sql.Scanner)
+ scanner := getSQLScanner(dst)
+
+ if scanner == nil {
+ return fmt.Errorf("cannot scan into %T", dst)
+ }
+
  if src == nil {
  // This is necessary because interface value []byte:nil does not equal nil:nil for the binary format path and the
  // text format path would be converted to empty string.
@@ -408,6 +413,21 @@ func (plan *scanPlanSQLScanner) Scan(src []byte, dst any) error {
  }
 }
 
+// we don't know if the target is a sql.Scanner or a pointer on a sql.Scanner, so we need to check recursively
+func getSQLScanner(target any) sql.Scanner {
+ val := reflect.ValueOf(target)
+ for val.Kind() == reflect.Ptr {
+ if _, ok := val.Interface().(sql.Scanner); ok {
+ if val.IsNil() {
+ val.Set(reflect.New(val.Type().Elem()))
+ }
+ return val.Interface().(sql.Scanner)
+ }
+ val = val.Elem()
+ }
+ return nil
+}
+
 type scanPlanString struct{}
 
 func (scanPlanString) Scan(src []byte, dst any) error {

pgtype/pgtype_test.go

@@ -9,6 +9,7 @@ import (
  "fmt"
  "net"
  "os"
+ "reflect"
  "regexp"
  "strconv"
  "testing"
@@ -631,3 +632,10 @@ func isExpectedEq(a any) func(any) bool {
  return a == v
  }
 }
+
+func isPtrExpectedEq(a any) func(any) bool {
+ return func(v any) bool {
+ val := reflect.ValueOf(v)
+ return a == val.Elem().Interface()
+ }
+}