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- // Copyright 2015 Google Inc. All rights reserved.
- //
- // 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 parse constructs martian modifiers from JSON messages.
- package parse
-
- import (
- "encoding/json"
- "fmt"
- "sync"
-
- "github.com/google/martian"
- )
-
- // ModifierType is the HTTP message type.
- type ModifierType string
-
- const (
- // Request modifies an HTTP request.
- Request ModifierType = "request"
- // Response modifies an HTTP response.
- Response ModifierType = "response"
- )
-
- // Result holds the parsed modifier and its type.
- type Result struct {
- reqmod martian.RequestModifier
- resmod martian.ResponseModifier
- }
-
- // NewResult returns a new parse.Result for a given interface{} that implements a modifier
- // and a slice of scopes to generate the result for.
- //
- // Returns nil, error if a given modifier does not support a given scope
- func NewResult(mod interface{}, scope []ModifierType) (*Result, error) {
- reqmod, reqOk := mod.(martian.RequestModifier)
- resmod, resOk := mod.(martian.ResponseModifier)
- result := &Result{}
- if scope == nil {
- result.reqmod = reqmod
- result.resmod = resmod
- return result, nil
- }
-
- for _, s := range scope {
- switch s {
- case Request:
- if !reqOk {
- return nil, fmt.Errorf("parse: invalid scope %q for modifier", "request")
- }
-
- result.reqmod = reqmod
- case Response:
- if !resOk {
- return nil, fmt.Errorf("parse: invalid scope %q for modifier", "response")
- }
-
- result.resmod = resmod
- default:
- return nil, fmt.Errorf("parse: invalid scope: %s not in [%q, %q]", s, "request", "response")
- }
- }
-
- return result, nil
- }
-
- // RequestModifier returns the parsed RequestModifier.
- //
- // Returns nil if the message has no request modifier.
- func (r *Result) RequestModifier() martian.RequestModifier {
- return r.reqmod
- }
-
- // ResponseModifier returns the parsed ResponseModifier.
- //
- // Returns nil if the message has no response modifier.
- func (r *Result) ResponseModifier() martian.ResponseModifier {
- return r.resmod
- }
-
- var (
- parseMu sync.RWMutex
- parseFuncs = make(map[string]func(b []byte) (*Result, error))
- )
-
- // ErrUnknownModifier is the error returned when the message does not
- // contain a field representing a known modifier type.
- type ErrUnknownModifier struct {
- name string
- }
-
- // Error returns a formatted error message for an ErrUnknownModifier.
- func (e ErrUnknownModifier) Error() string {
- return fmt.Sprintf("parse: unknown modifier: %s", e.name)
- }
-
- // Register registers a parsing function for name that will be used to unmarshal
- // a JSON message into the appropriate modifier.
- func Register(name string, parseFunc func(b []byte) (*Result, error)) {
- parseMu.Lock()
- defer parseMu.Unlock()
-
- parseFuncs[name] = parseFunc
- }
-
- // FromJSON parses a Modifier JSON message by looking up the named modifier in parseFuncs
- // and passing its modifier to the registered parseFunc. Returns a parse.Result containing
- // the top-level parsed modifier. If no parser has been registered with the given name
- // it returns an error of type ErrUnknownModifier.
- func FromJSON(b []byte) (*Result, error) {
- msg := make(map[string]json.RawMessage)
- if err := json.Unmarshal(b, &msg); err != nil {
- return nil, err
- }
-
- if len(msg) != 1 {
- ks := ""
- for k := range msg {
- ks += ", " + k
- }
-
- return nil, fmt.Errorf("parse: expected one modifier, received %d: %s", len(msg), ks)
- }
-
- parseMu.RLock()
- defer parseMu.RUnlock()
- for k, m := range msg {
- parseFunc, ok := parseFuncs[k]
- if !ok {
- return nil, ErrUnknownModifier{name: k}
- }
- return parseFunc(m)
- }
-
- return nil, fmt.Errorf("parse: no modifiers found: %v", msg)
- }
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