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default_dispatcher.go
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/
default_dispatcher.go
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// Copyright 2020 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package safehttp
import (
"encoding/json"
"fmt"
"github.com/google/safehtml"
"github.com/google/safehtml/template"
"io"
"net/http"
)
// DefaultDispatcher is responsible for writing safe responses.
type DefaultDispatcher struct{}
// ContentType returns the Content-Type of a response if it's deemed safe and
// an error otherwise.
func (DefaultDispatcher) ContentType(resp Response) (string, error) {
switch x := resp.(type) {
case safehtml.HTML:
return "text/html; charset=utf-8", nil
case TemplateResponse:
_, ok := (*x.Template).(*template.Template)
if !ok {
return "", fmt.Errorf("%T is not a safe response type, a Content-Type cannot be provided", resp)
}
return "text/html; charset=utf-8", nil
case JSONResponse:
return "application/json; charset=utf-8", nil
default:
return "", fmt.Errorf("%T is not a safe response type, a Content-Type cannot be provided", resp)
}
}
// Write writes the response to the http.ResponseWriter if it's deemed safe.
// A safe response is either safe HTML, a JSON object or safe HTML template. It
// will return a non-nil error if the response is deemed unsafe or if writing
// operation fails.
func (DefaultDispatcher) Write(rw http.ResponseWriter, resp Response) error {
switch x := resp.(type) {
case JSONResponse:
io.WriteString(rw, ")]}',\n") // Break parsing of JavaScript in order to prevent XSSI.
return json.NewEncoder(rw).Encode(x.Data)
case TemplateResponse:
t, ok := (*x.Template).(*template.Template)
if !ok {
return fmt.Errorf("%T is not a safe template and it cannot be parsed and written", t)
}
if len(x.FuncMap) == 0 {
return t.Execute(rw, x.Data)
}
cloned, err := t.Clone()
if err != nil {
return err
}
return cloned.Funcs(x.FuncMap).Execute(rw, x.Data)
case safehtml.HTML:
_, err := io.WriteString(rw, x.String())
return err
default:
return fmt.Errorf("%T is not a safe response type and it cannot be written", resp)
}
}