database/sql: use driver.ColumnConverter everywhere consistently

It was only being used for (*Stmt).Exec, not Query, and not for
the same two methods on *DB.

This unifies (*Stmt).Exec's old inline code into the old
subsetArgs function, renaming it in the process (changing the
old word "subset" to "driver", mostly converted earlier)

Fixes #3640

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/6258045

src/pkg/database/sql/convert.go

@@ -14,19 +14,61 @@ import (
 	"strconv"
 )
 
-// subsetTypeArgs takes a slice of arguments from callers of the sql
-// package and converts them into a slice of the driver package's
-// "subset types".
-func subsetTypeArgs(args []interface{}) ([]driver.Value, error) {
-	out := make([]driver.Value, len(args))
+// driverArgs converts arguments from callers of Stmt.Exec and
+// Stmt.Query into driver Values.
+//
+// The statement si may be nil, if no statement is available.
+func driverArgs(si driver.Stmt, args []interface{}) ([]driver.Value, error) {
+	dargs := make([]driver.Value, len(args))
+	cc, ok := si.(driver.ColumnConverter)
+
+	// Normal path, for a driver.Stmt that is not a ColumnConverter.
+	if !ok {
 		for n, arg := range args {
 			var err error
-		out[n], err = driver.DefaultParameterConverter.ConvertValue(arg)
+			dargs[n], err = driver.DefaultParameterConverter.ConvertValue(arg)
+			if err != nil {
+				return nil, fmt.Errorf("sql: converting Exec argument #%d's type: %v", n, err)
+			}
+		}
+		return dargs, nil
+	}
+
+	// Let the Stmt convert its own arguments.
+	for n, arg := range args {
+		// First, see if the value itself knows how to convert
+		// itself to a driver type.  For example, a NullString
+		// struct changing into a string or nil.
+		if svi, ok := arg.(driver.Valuer); ok {
+			sv, err := svi.Value()
 			if err != nil {
-			return nil, fmt.Errorf("sql: converting argument #%d's type: %v", n+1, err)
+				return nil, fmt.Errorf("sql: argument index %d from Value: %v", n, err)
+			}
+			if !driver.IsValue(sv) {
+				return nil, fmt.Errorf("sql: argument index %d: non-subset type %T returned from Value", n, sv)
 			}
+			arg = sv
 		}
-	return out, nil
+
+		// Second, ask the column to sanity check itself. For
+		// example, drivers might use this to make sure that
+		// an int64 values being inserted into a 16-bit
+		// integer field is in range (before getting
+		// truncated), or that a nil can't go into a NOT NULL
+		// column before going across the network to get the
+		// same error.
+		var err error
+		dargs[n], err = cc.ColumnConverter(n).ConvertValue(arg)
+		if err != nil {
+			return nil, fmt.Errorf("sql: converting argument #%d's type: %v", n, err)
+		}
+		if !driver.IsValue(dargs[n]) {
+			return nil, fmt.Errorf("sql: driver ColumnConverter error converted %T to unsupported type %T",
+				arg, dargs[n])
+		}
+	}
+
+	return dargs, nil
 }
 
 // convertAssign copies to dest the value in src, converting it if possible.

src/pkg/database/sql/fakedb_test.go

@@ -383,6 +383,9 @@ func (c *fakeConn) Prepare(query string) (driver.Stmt, error) {
 }
 
 func (s *fakeStmt) ColumnConverter(idx int) driver.ValueConverter {
+	if len(s.placeholderConverter) == 0 {
+		return driver.DefaultParameterConverter
+	}
 	return s.placeholderConverter[idx]
 }
 
@@ -598,6 +601,28 @@ func (rc *rowsCursor) Next(dest []driver.Value) error {
 	return nil
 }
 
+// fakeDriverString is like driver.String, but indirects pointers like
+// DefaultValueConverter.
+//
+// This could be surprising behavior to retroactively apply to
+// driver.String now that Go1 is out, but this is convenient for
+// our TestPointerParamsAndScans.
+//
+type fakeDriverString struct{}
+
+func (fakeDriverString) ConvertValue(v interface{}) (driver.Value, error) {
+	switch c := v.(type) {
+	case string, []byte:
+		return v, nil
+	case *string:
+		if c == nil {
+			return nil, nil
+		}
+		return *c, nil
+	}
+	return fmt.Sprintf("%v", v), nil
+}
+
 func converterForType(typ string) driver.ValueConverter {
 	switch typ {
 	case "bool":
@@ -607,9 +632,9 @@ func converterForType(typ string) driver.ValueConverter {
 	case "int32":
 		return driver.Int32
 	case "string":
-		return driver.NotNull{Converter: driver.String}
+		return driver.NotNull{Converter: fakeDriverString{}}
 	case "nullstring":
-		return driver.Null{Converter: driver.String}
+		return driver.Null{Converter: fakeDriverString{}}
 	case "int64":
 		// TODO(coopernurse): add type-specific converter
 		return driver.NotNull{Converter: driver.DefaultParameterConverter}

src/pkg/database/sql/sql.go

@@ -326,13 +326,10 @@ func (db *DB) prepare(query string) (stmt *Stmt, err error) {
 
 // Exec executes a query without returning any rows.
 func (db *DB) Exec(query string, args ...interface{}) (Result, error) {
-	sargs, err := subsetTypeArgs(args)
-	if err != nil {
-		return nil, err
-	}
 	var res Result
+	var err error
 	for i := 0; i < 10; i++ {
-		res, err = db.exec(query, sargs)
+		res, err = db.exec(query, args)
 		if err != driver.ErrBadConn {
 			break
 		}
@@ -340,7 +337,7 @@ func (db *DB) Exec(query string, args ...interface{}) (Result, error) {
 	return res, err
 }
 
-func (db *DB) exec(query string, sargs []driver.Value) (res Result, err error) {
+func (db *DB) exec(query string, args []interface{}) (res Result, err error) {
 	ci, err := db.conn()
 	if err != nil {
 		return nil, err
@@ -348,7 +345,11 @@ func (db *DB) exec(query string, sargs []driver.Value) (res Result, err error) {
 	defer db.putConn(ci, err)
 
 	if execer, ok := ci.(driver.Execer); ok {
-		resi, err := execer.Exec(query, sargs)
+		dargs, err := driverArgs(nil, args)
+		if err != nil {
+			return nil, err
+		}
+		resi, err := execer.Exec(query, dargs)
 		if err != driver.ErrSkip {
 			if err != nil {
 				return nil, err
@@ -363,7 +364,12 @@ func (db *DB) exec(query string, sargs []driver.Value) (res Result, err error) {
 	}
 	defer sti.Close()
 
-	resi, err := sti.Exec(sargs)
+	dargs, err := driverArgs(sti, args)
+	if err != nil {
+		return nil, err
+	}
+
+	resi, err := sti.Exec(dargs)
 	if err != nil {
 		return nil, err
 	}
@@ -577,13 +583,12 @@ func (tx *Tx) Exec(query string, args ...interface{}) (Result, error) {
 	}
 	defer tx.releaseConn()
 
-	sargs, err := subsetTypeArgs(args)
+	if execer, ok := ci.(driver.Execer); ok {
+		dargs, err := driverArgs(nil, args)
 		if err != nil {
 			return nil, err
 		}
-
-	if execer, ok := ci.(driver.Execer); ok {
-		resi, err := execer.Exec(query, sargs)
+		resi, err := execer.Exec(query, dargs)
 		if err == nil {
 			return result{resi}, nil
 		}
@@ -598,7 +603,12 @@ func (tx *Tx) Exec(query string, args ...interface{}) (Result, error) {
 	}
 	defer sti.Close()
 
-	resi, err := sti.Exec(sargs)
+	dargs, err := driverArgs(sti, args)
+	if err != nil {
+		return nil, err
+	}
+
+	resi, err := sti.Exec(dargs)
 	if err != nil {
 		return nil, err
 	}
@@ -674,51 +684,12 @@ func (s *Stmt) Exec(args ...interface{}) (Result, error) {
 		return nil, fmt.Errorf("sql: expected %d arguments, got %d", want, len(args))
 	}
 
-	sargs := make([]driver.Value, len(args))
-
-	// Convert args to subset types.
-	if cc, ok := si.(driver.ColumnConverter); ok {
-		for n, arg := range args {
-			// First, see if the value itself knows how to convert
-			// itself to a driver type.  For example, a NullString
-			// struct changing into a string or nil.
-			if svi, ok := arg.(driver.Valuer); ok {
-				sv, err := svi.Value()
+	dargs, err := driverArgs(si, args)
 	if err != nil {
-					return nil, fmt.Errorf("sql: argument index %d from Value: %v", n, err)
-				}
-				if !driver.IsValue(sv) {
-					return nil, fmt.Errorf("sql: argument index %d: non-subset type %T returned from Value", n, sv)
-				}
-				arg = sv
-			}
-
-			// Second, ask the column to sanity check itself. For
-			// example, drivers might use this to make sure that
-			// an int64 values being inserted into a 16-bit
-			// integer field is in range (before getting
-			// truncated), or that a nil can't go into a NOT NULL
-			// column before going across the network to get the
-			// same error.
-			sargs[n], err = cc.ColumnConverter(n).ConvertValue(arg)
-			if err != nil {
-				return nil, fmt.Errorf("sql: converting Exec argument #%d's type: %v", n, err)
-			}
-			if !driver.IsValue(sargs[n]) {
-				return nil, fmt.Errorf("sql: driver ColumnConverter error converted %T to unsupported type %T",
-					arg, sargs[n])
-			}
-		}
-	} else {
-		for n, arg := range args {
-			sargs[n], err = driver.DefaultParameterConverter.ConvertValue(arg)
-			if err != nil {
-				return nil, fmt.Errorf("sql: converting Exec argument #%d's type: %v", n, err)
-			}
-		}
+		return nil, err
 	}
 
-	resi, err := si.Exec(sargs)
+	resi, err := si.Exec(dargs)
 	if err != nil {
 		return nil, err
 	}
@@ -805,11 +776,13 @@ func (s *Stmt) Query(args ...interface{}) (*Rows, error) {
 	if want := si.NumInput(); want != -1 && len(args) != want {
 		return nil, fmt.Errorf("sql: statement expects %d inputs; got %d", si.NumInput(), len(args))
 	}
-	sargs, err := subsetTypeArgs(args)
+
+	dargs, err := driverArgs(si, args)
 	if err != nil {
 		return nil, err
 	}
-	rowsi, err := si.Query(sargs)
+
+	rowsi, err := si.Query(dargs)
 	if err != nil {
 		releaseConn(err)
 		return nil, err

src/pkg/database/sql/sql_test.go

@@ -306,8 +306,8 @@ func TestExec(t *testing.T) {
 		{[]interface{}{7, 9}, ""},
 
 		// Invalid conversions:
-		{[]interface{}{"Brad", int64(0xFFFFFFFF)}, "sql: converting Exec argument #1's type: sql/driver: value 4294967295 overflows int32"},
-		{[]interface{}{"Brad", "strconv fail"}, "sql: converting Exec argument #1's type: sql/driver: value \"strconv fail\" can't be converted to int32"},
+		{[]interface{}{"Brad", int64(0xFFFFFFFF)}, "sql: converting argument #1's type: sql/driver: value 4294967295 overflows int32"},
+		{[]interface{}{"Brad", "strconv fail"}, "sql: converting argument #1's type: sql/driver: value \"strconv fail\" can't be converted to int32"},
 
 		// Wrong number of args:
 		{[]interface{}{}, "sql: expected 2 arguments, got 0"},