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/
json_bind.go
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/
json_bind.go
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// Copyright 2020 the Exposure Notifications Verification Server authors
//
// 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
//
// http://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 controller
import (
"encoding/json"
"errors"
"fmt"
"io"
"net/http"
"strings"
)
const (
// Max request size of 64KB. None of the current API requests for this
// server are near that limit. Prevents us from unnecessarily parsing JSON
// payloads that are much large than we anticipate.
maxBodyBytes = 64_000
)
// BindJSON provides a common implementation of JSON unmarshaling with well defined error handling.
func BindJSON(w http.ResponseWriter, r *http.Request, data interface{}) error {
if !IsJSONContentType(r) {
return fmt.Errorf("content-type is not application/json")
}
defer r.Body.Close()
r.Body = http.MaxBytesReader(w, r.Body, maxBodyBytes)
d := json.NewDecoder(r.Body)
d.DisallowUnknownFields()
if err := d.Decode(&data); err != nil {
var syntaxErr *json.SyntaxError
var unmarshalError *json.UnmarshalTypeError
switch {
case errors.As(err, &syntaxErr):
return fmt.Errorf("malformed json at position %d", syntaxErr.Offset)
case errors.Is(err, io.ErrUnexpectedEOF):
return fmt.Errorf("malformed json")
case errors.As(err, &unmarshalError):
return fmt.Errorf("invalid value %q at position %d", unmarshalError.Field, unmarshalError.Offset)
case strings.HasPrefix(err.Error(), "json: unknown field"):
fieldName := strings.TrimPrefix(err.Error(), "json: unknown field ")
return fmt.Errorf("unknown field %q", fieldName)
case errors.Is(err, io.EOF):
return fmt.Errorf("body must not be empty")
case err.Error() == "http: request body too large":
return err
default:
return fmt.Errorf("failed to decode json: %w", err)
}
}
if d.More() {
return fmt.Errorf("body must contain only one JSON object")
}
return nil
}