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package goa
import (
// Keys used to store data in context.
const (
reqKey key = iota + 1
type (
// RequestData provides access to the underlying HTTP request.
RequestData struct {
// Payload returns the decoded request body.
Payload interface{}
// Params contains the raw values for the parameters defined in the design including
// path parameters, query string parameters and header parameters.
Params url.Values
// ResponseData provides access to the underlying HTTP response.
ResponseData struct {
// The service used to encode the response.
Service *Service
// ErrorCode is the code of the error returned by the action if any.
ErrorCode string
// Status is the response HTTP status code.
Status int
// Length is the response body length.
Length int
// key is the type used to store internal values in the context.
// Context provides typed accessor methods to these values.
key int
// NewContext builds a new goa request context.
// If ctx is nil then context.Background() is used.
func NewContext(ctx context.Context, rw http.ResponseWriter, req *http.Request, params url.Values) context.Context {
if ctx == nil {
ctx = context.Background()
request := &RequestData{Request: req, Params: params}
response := &ResponseData{ResponseWriter: rw}
ctx = context.WithValue(ctx, respKey, response)
ctx = context.WithValue(ctx, reqKey, request)
return ctx
// WithAction creates a context with the given action name.
func WithAction(ctx context.Context, action string) context.Context {
return context.WithValue(ctx, actionKey, action)
// WithLogger sets the request context logger and returns the resulting new context.
func WithLogger(ctx context.Context, logger LogAdapter) context.Context {
return context.WithValue(ctx, logKey, logger)
// WithLogContext instantiates a new logger by appending the given key/value pairs to the context
// logger and setting the resulting logger in the context.
func WithLogContext(ctx context.Context, keyvals ...interface{}) context.Context {
logger := ContextLogger(ctx)
if logger == nil {
return ctx
nl := logger.New(keyvals...)
return WithLogger(ctx, nl)
// WithError creates a context with the given error.
func WithError(ctx context.Context, err error) context.Context {
return context.WithValue(ctx, errKey, err)
// ContextController extracts the controller name from the given context.
func ContextController(ctx context.Context) string {
if c := ctx.Value(ctrlKey); c != nil {
return c.(string)
return "<unknown>"
// ContextAction extracts the action name from the given context.
func ContextAction(ctx context.Context) string {
if a := ctx.Value(actionKey); a != nil {
return a.(string)
return "<unknown>"
// ContextRequest extracts the request data from the given context.
func ContextRequest(ctx context.Context) *RequestData {
if r := ctx.Value(reqKey); r != nil {
return r.(*RequestData)
return nil
// ContextResponse extracts the response data from the given context.
func ContextResponse(ctx context.Context) *ResponseData {
if r := ctx.Value(respKey); r != nil {
return r.(*ResponseData)
return nil
// ContextLogger extracts the logger from the given context.
func ContextLogger(ctx context.Context) LogAdapter {
if v := ctx.Value(logKey); v != nil {
return v.(LogAdapter)
return nil
// ContextError extracts the error from the given context.
func ContextError(ctx context.Context) error {
if err := ctx.Value(errKey); err != nil {
return err.(error)
return nil
// SwitchWriter overrides the underlying response writer. It returns the response
// writer that was previously set.
func (r *ResponseData) SwitchWriter(rw http.ResponseWriter) http.ResponseWriter {
rwo := r.ResponseWriter
r.ResponseWriter = rw
return rwo
// Written returns true if the response was written, false otherwise.
func (r *ResponseData) Written() bool {
return r.Status != 0
// WriteHeader records the response status code and calls the underlying writer.
func (r *ResponseData) WriteHeader(status int) {
go IncrCounter([]string{"goa", "response", strconv.Itoa(status)}, 1.0)
r.Status = status
// Write records the amount of data written and calls the underlying writer.
func (r *ResponseData) Write(b []byte) (int, error) {
if !r.Written() {
r.Length += len(b)
return r.ResponseWriter.Write(b)