clientcompat.twirp.go

// Code generated by protoc-gen-twirp v5.5.2, DO NOT EDIT.
// source: clientcompat.proto

/*
Package clientcompat is a generated twirp stub package.
This code was generated with github.com/twitchtv/twirp/protoc-gen-twirp v5.5.2.

It is generated from these files:
	clientcompat.proto
*/
package clientcompat

import bytes "bytes"
import strings "strings"
import context "context"
import fmt "fmt"
import ioutil "io/ioutil"
import http "net/http"

import jsonpb "github.com/golang/protobuf/jsonpb"
import proto "github.com/golang/protobuf/proto"
import twirp "github.com/twitchtv/twirp"
import ctxsetters "github.com/twitchtv/twirp/ctxsetters"

// Imports only used by utility functions:
import io "io"
import strconv "strconv"
import json "encoding/json"
import url "net/url"

// =======================
// CompatService Interface
// =======================

type CompatService interface {
	Method(context.Context, *Req) (*Resp, error)

	NoopMethod(context.Context, *Empty) (*Empty, error)
}

// =============================
// CompatService Protobuf Client
// =============================

type compatServiceProtobufClient struct {
	client HTTPClient
	urls   [2]string
}

// NewCompatServiceProtobufClient creates a Protobuf client that implements the CompatService interface.
// It communicates using Protobuf and can be configured with a custom HTTPClient.
func NewCompatServiceProtobufClient(addr string, client HTTPClient) CompatService {
	prefix := urlBase(addr) + CompatServicePathPrefix
	urls := [2]string{
		prefix + "Method",
		prefix + "NoopMethod",
	}
	if httpClient, ok := client.(*http.Client); ok {
		return &compatServiceProtobufClient{
			client: withoutRedirects(httpClient),
			urls:   urls,
		}
	}
	return &compatServiceProtobufClient{
		client: client,
		urls:   urls,
	}
}

func (c *compatServiceProtobufClient) Method(ctx context.Context, in *Req) (*Resp, error) {
	ctx = ctxsetters.WithPackageName(ctx, "twirp.clientcompat")
	ctx = ctxsetters.WithServiceName(ctx, "CompatService")
	ctx = ctxsetters.WithMethodName(ctx, "Method")
	out := new(Resp)
	err := doProtobufRequest(ctx, c.client, c.urls[0], in, out)
	if err != nil {
		return nil, err
	}
	return out, nil
}

func (c *compatServiceProtobufClient) NoopMethod(ctx context.Context, in *Empty) (*Empty, error) {
	ctx = ctxsetters.WithPackageName(ctx, "twirp.clientcompat")
	ctx = ctxsetters.WithServiceName(ctx, "CompatService")
	ctx = ctxsetters.WithMethodName(ctx, "NoopMethod")
	out := new(Empty)
	err := doProtobufRequest(ctx, c.client, c.urls[1], in, out)
	if err != nil {
		return nil, err
	}
	return out, nil
}

// =========================
// CompatService JSON Client
// =========================

type compatServiceJSONClient struct {
	client HTTPClient
	urls   [2]string
}

// NewCompatServiceJSONClient creates a JSON client that implements the CompatService interface.
// It communicates using JSON and can be configured with a custom HTTPClient.
func NewCompatServiceJSONClient(addr string, client HTTPClient) CompatService {
	prefix := urlBase(addr) + CompatServicePathPrefix
	urls := [2]string{
		prefix + "Method",
		prefix + "NoopMethod",
	}
	if httpClient, ok := client.(*http.Client); ok {
		return &compatServiceJSONClient{
			client: withoutRedirects(httpClient),
			urls:   urls,
		}
	}
	return &compatServiceJSONClient{
		client: client,
		urls:   urls,
	}
}

func (c *compatServiceJSONClient) Method(ctx context.Context, in *Req) (*Resp, error) {
	ctx = ctxsetters.WithPackageName(ctx, "twirp.clientcompat")
	ctx = ctxsetters.WithServiceName(ctx, "CompatService")
	ctx = ctxsetters.WithMethodName(ctx, "Method")
	out := new(Resp)
	err := doJSONRequest(ctx, c.client, c.urls[0], in, out)
	if err != nil {
		return nil, err
	}
	return out, nil
}

func (c *compatServiceJSONClient) NoopMethod(ctx context.Context, in *Empty) (*Empty, error) {
	ctx = ctxsetters.WithPackageName(ctx, "twirp.clientcompat")
	ctx = ctxsetters.WithServiceName(ctx, "CompatService")
	ctx = ctxsetters.WithMethodName(ctx, "NoopMethod")
	out := new(Empty)
	err := doJSONRequest(ctx, c.client, c.urls[1], in, out)
	if err != nil {
		return nil, err
	}
	return out, nil
}

// ============================
// CompatService Server Handler
// ============================

type compatServiceServer struct {
	CompatService
	hooks *twirp.ServerHooks
}

func NewCompatServiceServer(svc CompatService, hooks *twirp.ServerHooks) TwirpServer {
	return &compatServiceServer{
		CompatService: svc,
		hooks:         hooks,
	}
}

// writeError writes an HTTP response with a valid Twirp error format, and triggers hooks.
// If err is not a twirp.Error, it will get wrapped with twirp.InternalErrorWith(err)
func (s *compatServiceServer) writeError(ctx context.Context, resp http.ResponseWriter, err error) {
	writeError(ctx, resp, err, s.hooks)
}

// CompatServicePathPrefix is used for all URL paths on a twirp CompatService server.
// Requests are always: POST CompatServicePathPrefix/method
// It can be used in an HTTP mux to route twirp requests along with non-twirp requests on other routes.
const CompatServicePathPrefix = "/twirp/twirp.clientcompat.CompatService/"

func (s *compatServiceServer) ServeHTTP(resp http.ResponseWriter, req *http.Request) {
	ctx := req.Context()
	ctx = ctxsetters.WithPackageName(ctx, "twirp.clientcompat")
	ctx = ctxsetters.WithServiceName(ctx, "CompatService")
	ctx = ctxsetters.WithResponseWriter(ctx, resp)

	var err error
	ctx, err = callRequestReceived(ctx, s.hooks)
	if err != nil {
		s.writeError(ctx, resp, err)
		return
	}

	if req.Method != "POST" {
		msg := fmt.Sprintf("unsupported method %q (only POST is allowed)", req.Method)
		err = badRouteError(msg, req.Method, req.URL.Path)
		s.writeError(ctx, resp, err)
		return
	}

	switch req.URL.Path {
	case "/twirp/twirp.clientcompat.CompatService/Method":
		s.serveMethod(ctx, resp, req)
		return
	case "/twirp/twirp.clientcompat.CompatService/NoopMethod":
		s.serveNoopMethod(ctx, resp, req)
		return
	default:
		msg := fmt.Sprintf("no handler for path %q", req.URL.Path)
		err = badRouteError(msg, req.Method, req.URL.Path)
		s.writeError(ctx, resp, err)
		return
	}
}

func (s *compatServiceServer) serveMethod(ctx context.Context, resp http.ResponseWriter, req *http.Request) {
	header := req.Header.Get("Content-Type")
	i := strings.Index(header, ";")
	if i == -1 {
		i = len(header)
	}
	switch strings.TrimSpace(strings.ToLower(header[:i])) {
	case "application/json":
		s.serveMethodJSON(ctx, resp, req)
	case "application/protobuf":
		s.serveMethodProtobuf(ctx, resp, req)
	default:
		msg := fmt.Sprintf("unexpected Content-Type: %q", req.Header.Get("Content-Type"))
		twerr := badRouteError(msg, req.Method, req.URL.Path)
		s.writeError(ctx, resp, twerr)
	}
}

func (s *compatServiceServer) serveMethodJSON(ctx context.Context, resp http.ResponseWriter, req *http.Request) {
	var err error
	ctx = ctxsetters.WithMethodName(ctx, "Method")
	ctx, err = callRequestRouted(ctx, s.hooks)
	if err != nil {
		s.writeError(ctx, resp, err)
		return
	}

	reqContent := new(Req)
	unmarshaler := jsonpb.Unmarshaler{AllowUnknownFields: true}
	if err = unmarshaler.Unmarshal(req.Body, reqContent); err != nil {
		err = wrapErr(err, "failed to parse request json")
		s.writeError(ctx, resp, twirp.InternalErrorWith(err))
		return
	}

	// Call service method
	var respContent *Resp
	func() {
		defer func() {
			// In case of a panic, serve a 500 error and then panic.
			if r := recover(); r != nil {
				s.writeError(ctx, resp, twirp.InternalError("Internal service panic"))
				panic(r)
			}
		}()
		respContent, err = s.CompatService.Method(ctx, reqContent)
	}()

	if err != nil {
		s.writeError(ctx, resp, err)
		return
	}
	if respContent == nil {
		s.writeError(ctx, resp, twirp.InternalError("received a nil *Resp and nil error while calling Method. nil responses are not supported"))
		return
	}

	ctx = callResponsePrepared(ctx, s.hooks)

	var buf bytes.Buffer
	marshaler := &jsonpb.Marshaler{OrigName: true}
	if err = marshaler.Marshal(&buf, respContent); err != nil {
		err = wrapErr(err, "failed to marshal json response")
		s.writeError(ctx, resp, twirp.InternalErrorWith(err))
		return
	}

	ctx = ctxsetters.WithStatusCode(ctx, http.StatusOK)
	resp.Header().Set("Content-Type", "application/json")
	resp.WriteHeader(http.StatusOK)

	respBytes := buf.Bytes()
	if n, err := resp.Write(respBytes); err != nil {
		msg := fmt.Sprintf("failed to write response, %d of %d bytes written: %s", n, len(respBytes), err.Error())
		twerr := twirp.NewError(twirp.Unknown, msg)
		callError(ctx, s.hooks, twerr)
	}
	callResponseSent(ctx, s.hooks)
}

func (s *compatServiceServer) serveMethodProtobuf(ctx context.Context, resp http.ResponseWriter, req *http.Request) {
	var err error
	ctx = ctxsetters.WithMethodName(ctx, "Method")
	ctx, err = callRequestRouted(ctx, s.hooks)
	if err != nil {
		s.writeError(ctx, resp, err)
		return
	}

	buf, err := ioutil.ReadAll(req.Body)
	if err != nil {
		err = wrapErr(err, "failed to read request body")
		s.writeError(ctx, resp, twirp.InternalErrorWith(err))
		return
	}
	reqContent := new(Req)
	if err = proto.Unmarshal(buf, reqContent); err != nil {
		err = wrapErr(err, "failed to parse request proto")
		s.writeError(ctx, resp, twirp.InternalErrorWith(err))
		return
	}

	// Call service method
	var respContent *Resp
	func() {
		defer func() {
			// In case of a panic, serve a 500 error and then panic.
			if r := recover(); r != nil {
				s.writeError(ctx, resp, twirp.InternalError("Internal service panic"))
				panic(r)
			}
		}()
		respContent, err = s.CompatService.Method(ctx, reqContent)
	}()

	if err != nil {
		s.writeError(ctx, resp, err)
		return
	}
	if respContent == nil {
		s.writeError(ctx, resp, twirp.InternalError("received a nil *Resp and nil error while calling Method. nil responses are not supported"))
		return
	}

	ctx = callResponsePrepared(ctx, s.hooks)

	respBytes, err := proto.Marshal(respContent)
	if err != nil {
		err = wrapErr(err, "failed to marshal proto response")
		s.writeError(ctx, resp, twirp.InternalErrorWith(err))
		return
	}

	ctx = ctxsetters.WithStatusCode(ctx, http.StatusOK)
	resp.Header().Set("Content-Type", "application/protobuf")
	resp.WriteHeader(http.StatusOK)
	if n, err := resp.Write(respBytes); err != nil {
		msg := fmt.Sprintf("failed to write response, %d of %d bytes written: %s", n, len(respBytes), err.Error())
		twerr := twirp.NewError(twirp.Unknown, msg)
		callError(ctx, s.hooks, twerr)
	}
	callResponseSent(ctx, s.hooks)
}

func (s *compatServiceServer) serveNoopMethod(ctx context.Context, resp http.ResponseWriter, req *http.Request) {
	header := req.Header.Get("Content-Type")
	i := strings.Index(header, ";")
	if i == -1 {
		i = len(header)
	}
	switch strings.TrimSpace(strings.ToLower(header[:i])) {
	case "application/json":
		s.serveNoopMethodJSON(ctx, resp, req)
	case "application/protobuf":
		s.serveNoopMethodProtobuf(ctx, resp, req)
	default:
		msg := fmt.Sprintf("unexpected Content-Type: %q", req.Header.Get("Content-Type"))
		twerr := badRouteError(msg, req.Method, req.URL.Path)
		s.writeError(ctx, resp, twerr)
	}
}

func (s *compatServiceServer) serveNoopMethodJSON(ctx context.Context, resp http.ResponseWriter, req *http.Request) {
	var err error
	ctx = ctxsetters.WithMethodName(ctx, "NoopMethod")
	ctx, err = callRequestRouted(ctx, s.hooks)
	if err != nil {
		s.writeError(ctx, resp, err)
		return
	}

	reqContent := new(Empty)
	unmarshaler := jsonpb.Unmarshaler{AllowUnknownFields: true}
	if err = unmarshaler.Unmarshal(req.Body, reqContent); err != nil {
		err = wrapErr(err, "failed to parse request json")
		s.writeError(ctx, resp, twirp.InternalErrorWith(err))
		return
	}

	// Call service method
	var respContent *Empty
	func() {
		defer func() {
			// In case of a panic, serve a 500 error and then panic.
			if r := recover(); r != nil {
				s.writeError(ctx, resp, twirp.InternalError("Internal service panic"))
				panic(r)
			}
		}()
		respContent, err = s.CompatService.NoopMethod(ctx, reqContent)
	}()

	if err != nil {
		s.writeError(ctx, resp, err)
		return
	}
	if respContent == nil {
		s.writeError(ctx, resp, twirp.InternalError("received a nil *Empty and nil error while calling NoopMethod. nil responses are not supported"))
		return
	}

	ctx = callResponsePrepared(ctx, s.hooks)

	var buf bytes.Buffer
	marshaler := &jsonpb.Marshaler{OrigName: true}
	if err = marshaler.Marshal(&buf, respContent); err != nil {
		err = wrapErr(err, "failed to marshal json response")
		s.writeError(ctx, resp, twirp.InternalErrorWith(err))
		return
	}

	ctx = ctxsetters.WithStatusCode(ctx, http.StatusOK)
	resp.Header().Set("Content-Type", "application/json")
	resp.WriteHeader(http.StatusOK)

	respBytes := buf.Bytes()
	if n, err := resp.Write(respBytes); err != nil {
		msg := fmt.Sprintf("failed to write response, %d of %d bytes written: %s", n, len(respBytes), err.Error())
		twerr := twirp.NewError(twirp.Unknown, msg)
		callError(ctx, s.hooks, twerr)
	}
	callResponseSent(ctx, s.hooks)
}

func (s *compatServiceServer) serveNoopMethodProtobuf(ctx context.Context, resp http.ResponseWriter, req *http.Request) {
	var err error
	ctx = ctxsetters.WithMethodName(ctx, "NoopMethod")
	ctx, err = callRequestRouted(ctx, s.hooks)
	if err != nil {
		s.writeError(ctx, resp, err)
		return
	}

	buf, err := ioutil.ReadAll(req.Body)
	if err != nil {
		err = wrapErr(err, "failed to read request body")
		s.writeError(ctx, resp, twirp.InternalErrorWith(err))
		return
	}
	reqContent := new(Empty)
	if err = proto.Unmarshal(buf, reqContent); err != nil {
		err = wrapErr(err, "failed to parse request proto")
		s.writeError(ctx, resp, twirp.InternalErrorWith(err))
		return
	}

	// Call service method
	var respContent *Empty
	func() {
		defer func() {
			// In case of a panic, serve a 500 error and then panic.
			if r := recover(); r != nil {
				s.writeError(ctx, resp, twirp.InternalError("Internal service panic"))
				panic(r)
			}
		}()
		respContent, err = s.CompatService.NoopMethod(ctx, reqContent)
	}()

	if err != nil {
		s.writeError(ctx, resp, err)
		return
	}
	if respContent == nil {
		s.writeError(ctx, resp, twirp.InternalError("received a nil *Empty and nil error while calling NoopMethod. nil responses are not supported"))
		return
	}

	ctx = callResponsePrepared(ctx, s.hooks)

	respBytes, err := proto.Marshal(respContent)
	if err != nil {
		err = wrapErr(err, "failed to marshal proto response")
		s.writeError(ctx, resp, twirp.InternalErrorWith(err))
		return
	}

	ctx = ctxsetters.WithStatusCode(ctx, http.StatusOK)
	resp.Header().Set("Content-Type", "application/protobuf")
	resp.WriteHeader(http.StatusOK)
	if n, err := resp.Write(respBytes); err != nil {
		msg := fmt.Sprintf("failed to write response, %d of %d bytes written: %s", n, len(respBytes), err.Error())
		twerr := twirp.NewError(twirp.Unknown, msg)
		callError(ctx, s.hooks, twerr)
	}
	callResponseSent(ctx, s.hooks)
}

func (s *compatServiceServer) ServiceDescriptor() ([]byte, int) {
	return twirpFileDescriptor0, 0
}

func (s *compatServiceServer) ProtocGenTwirpVersion() string {
	return "v5.5.2"
}

// =====
// Utils
// =====

// HTTPClient is the interface used by generated clients to send HTTP requests.
// It is fulfilled by *(net/http).Client, which is sufficient for most users.
// Users can provide their own implementation for special retry policies.
//
// HTTPClient implementations should not follow redirects. Redirects are
// automatically disabled if *(net/http).Client is passed to client
// constructors. See the withoutRedirects function in this file for more
// details.
type HTTPClient interface {
	Do(req *http.Request) (*http.Response, error)
}

// TwirpServer is the interface generated server structs will support: they're
// HTTP handlers with additional methods for accessing metadata about the
// service. Those accessors are a low-level API for building reflection tools.
// Most people can think of TwirpServers as just http.Handlers.
type TwirpServer interface {
	http.Handler
	// ServiceDescriptor returns gzipped bytes describing the .proto file that
	// this service was generated from. Once unzipped, the bytes can be
	// unmarshalled as a
	// github.com/golang/protobuf/protoc-gen-go/descriptor.FileDescriptorProto.
	//
	// The returned integer is the index of this particular service within that
	// FileDescriptorProto's 'Service' slice of ServiceDescriptorProtos. This is a
	// low-level field, expected to be used for reflection.
	ServiceDescriptor() ([]byte, int)
	// ProtocGenTwirpVersion is the semantic version string of the version of
	// twirp used to generate this file.
	ProtocGenTwirpVersion() string
}

// WriteError writes an HTTP response with a valid Twirp error format.
// If err is not a twirp.Error, it will get wrapped with twirp.InternalErrorWith(err)
func WriteError(resp http.ResponseWriter, err error) {
	writeError(context.Background(), resp, err, nil)
}

// writeError writes Twirp errors in the response and triggers hooks.
func writeError(ctx context.Context, resp http.ResponseWriter, err error, hooks *twirp.ServerHooks) {
	// Non-twirp errors are wrapped as Internal (default)
	twerr, ok := err.(twirp.Error)
	if !ok {
		twerr = twirp.InternalErrorWith(err)
	}

	statusCode := twirp.ServerHTTPStatusFromErrorCode(twerr.Code())
	ctx = ctxsetters.WithStatusCode(ctx, statusCode)
	ctx = callError(ctx, hooks, twerr)

	resp.Header().Set("Content-Type", "application/json") // Error responses are always JSON (instead of protobuf)
	resp.WriteHeader(statusCode)                          // HTTP response status code

	respBody := marshalErrorToJSON(twerr)
	_, writeErr := resp.Write(respBody)
	if writeErr != nil {
		// We have three options here. We could log the error, call the Error
		// hook, or just silently ignore the error.
		//
		// Logging is unacceptable because we don't have a user-controlled
		// logger; writing out to stderr without permission is too rude.
		//
		// Calling the Error hook would confuse users: it would mean the Error
		// hook got called twice for one request, which is likely to lead to
		// duplicated log messages and metrics, no matter how well we document
		// the behavior.
		//
		// Silently ignoring the error is our least-bad option. It's highly
		// likely that the connection is broken and the original 'err' says
		// so anyway.
		_ = writeErr
	}

	callResponseSent(ctx, hooks)
}

// urlBase helps ensure that addr specifies a scheme. If it is unparsable
// as a URL, it returns addr unchanged.
func urlBase(addr string) string {
	// If the addr specifies a scheme, use it. If not, default to
	// http. If url.Parse fails on it, return it unchanged.
	url, err := url.Parse(addr)
	if err != nil {
		return addr
	}
	if url.Scheme == "" {
		url.Scheme = "http"
	}
	return url.String()
}

// getCustomHTTPReqHeaders retrieves a copy of any headers that are set in
// a context through the twirp.WithHTTPRequestHeaders function.
// If there are no headers set, or if they have the wrong type, nil is returned.
func getCustomHTTPReqHeaders(ctx context.Context) http.Header {
	header, ok := twirp.HTTPRequestHeaders(ctx)
	if !ok || header == nil {
		return nil
	}
	copied := make(http.Header)
	for k, vv := range header {
		if vv == nil {
			copied[k] = nil
			continue
		}
		copied[k] = make([]string, len(vv))
		copy(copied[k], vv)
	}
	return copied
}

// newRequest makes an http.Request from a client, adding common headers.
func newRequest(ctx context.Context, url string, reqBody io.Reader, contentType string) (*http.Request, error) {
	req, err := http.NewRequest("POST", url, reqBody)
	if err != nil {
		return nil, err
	}
	req = req.WithContext(ctx)
	if customHeader := getCustomHTTPReqHeaders(ctx); customHeader != nil {
		req.Header = customHeader
	}
	req.Header.Set("Accept", contentType)
	req.Header.Set("Content-Type", contentType)
	req.Header.Set("Twirp-Version", "v5.5.2")
	return req, nil
}

// JSON serialization for errors
type twerrJSON struct {
	Code string            `json:"code"`
	Msg  string            `json:"msg"`
	Meta map[string]string `json:"meta,omitempty"`
}

// marshalErrorToJSON returns JSON from a twirp.Error, that can be used as HTTP error response body.
// If serialization fails, it will use a descriptive Internal error instead.
func marshalErrorToJSON(twerr twirp.Error) []byte {
	// make sure that msg is not too large
	msg := twerr.Msg()
	if len(msg) > 1e6 {
		msg = msg[:1e6]
	}

	tj := twerrJSON{
		Code: string(twerr.Code()),
		Msg:  msg,
		Meta: twerr.MetaMap(),
	}

	buf, err := json.Marshal(&tj)
	if err != nil {
		buf = []byte("{\"type\": \"" + twirp.Internal + "\", \"msg\": \"There was an error but it could not be serialized into JSON\"}") // fallback
	}

	return buf
}

// errorFromResponse builds a twirp.Error from a non-200 HTTP response.
// If the response has a valid serialized Twirp error, then it's returned.
// If not, the response status code is used to generate a similar twirp
// error. See twirpErrorFromIntermediary for more info on intermediary errors.
func errorFromResponse(resp *http.Response) twirp.Error {
	statusCode := resp.StatusCode
	statusText := http.StatusText(statusCode)

	if isHTTPRedirect(statusCode) {
		// Unexpected redirect: it must be an error from an intermediary.
		// Twirp clients don't follow redirects automatically, Twirp only handles
		// POST requests, redirects should only happen on GET and HEAD requests.
		location := resp.Header.Get("Location")
		msg := fmt.Sprintf("unexpected HTTP status code %d %q received, Location=%q", statusCode, statusText, location)
		return twirpErrorFromIntermediary(statusCode, msg, location)
	}

	respBodyBytes, err := ioutil.ReadAll(resp.Body)
	if err != nil {
		return clientError("failed to read server error response body", err)
	}
	var tj twerrJSON
	if err := json.Unmarshal(respBodyBytes, &tj); err != nil {
		// Invalid JSON response; it must be an error from an intermediary.
		msg := fmt.Sprintf("Error from intermediary with HTTP status code %d %q", statusCode, statusText)
		return twirpErrorFromIntermediary(statusCode, msg, string(respBodyBytes))
	}

	errorCode := twirp.ErrorCode(tj.Code)
	if !twirp.IsValidErrorCode(errorCode) {
		msg := "invalid type returned from server error response: " + tj.Code
		return twirp.InternalError(msg)
	}

	twerr := twirp.NewError(errorCode, tj.Msg)
	for k, v := range tj.Meta {
		twerr = twerr.WithMeta(k, v)
	}
	return twerr
}

// twirpErrorFromIntermediary maps HTTP errors from non-twirp sources to twirp errors.
// The mapping is similar to gRPC: https://github.com/grpc/grpc/blob/master/doc/http-grpc-status-mapping.md.
// Returned twirp Errors have some additional metadata for inspection.
func twirpErrorFromIntermediary(status int, msg string, bodyOrLocation string) twirp.Error {
	var code twirp.ErrorCode
	if isHTTPRedirect(status) { // 3xx
		code = twirp.Internal
	} else {
		switch status {
		case 400: // Bad Request
			code = twirp.Internal
		case 401: // Unauthorized
			code = twirp.Unauthenticated
		case 403: // Forbidden
			code = twirp.PermissionDenied
		case 404: // Not Found
			code = twirp.BadRoute
		case 429, 502, 503, 504: // Too Many Requests, Bad Gateway, Service Unavailable, Gateway Timeout
			code = twirp.Unavailable
		default: // All other codes
			code = twirp.Unknown
		}
	}

	twerr := twirp.NewError(code, msg)
	twerr = twerr.WithMeta("http_error_from_intermediary", "true") // to easily know if this error was from intermediary
	twerr = twerr.WithMeta("status_code", strconv.Itoa(status))
	if isHTTPRedirect(status) {
		twerr = twerr.WithMeta("location", bodyOrLocation)
	} else {
		twerr = twerr.WithMeta("body", bodyOrLocation)
	}
	return twerr
}
func isHTTPRedirect(status int) bool {
	return status >= 300 && status <= 399
}

// wrappedError implements the github.com/pkg/errors.Causer interface, allowing errors to be
// examined for their root cause.
type wrappedError struct {
	msg   string
	cause error
}

func wrapErr(err error, msg string) error { return &wrappedError{msg: msg, cause: err} }
func (e *wrappedError) Cause() error      { return e.cause }
func (e *wrappedError) Error() string     { return e.msg + ": " + e.cause.Error() }

// clientError adds consistency to errors generated in the client
func clientError(desc string, err error) twirp.Error {
	return twirp.InternalErrorWith(wrapErr(err, desc))
}

// badRouteError is used when the twirp server cannot route a request
func badRouteError(msg string, method, url string) twirp.Error {
	err := twirp.NewError(twirp.BadRoute, msg)
	err = err.WithMeta("twirp_invalid_route", method+" "+url)
	return err
}

// The standard library will, by default, redirect requests (including POSTs) if it gets a 302 or
// 303 response, and also 301s in go1.8. It redirects by making a second request, changing the
// method to GET and removing the body. This produces very confusing error messages, so instead we
// set a redirect policy that always errors. This stops Go from executing the redirect.
//
// We have to be a little careful in case the user-provided http.Client has its own CheckRedirect
// policy - if so, we'll run through that policy first.
//
// Because this requires modifying the http.Client, we make a new copy of the client and return it.
func withoutRedirects(in *http.Client) *http.Client {
	copy := *in
	copy.CheckRedirect = func(req *http.Request, via []*http.Request) error {
		if in.CheckRedirect != nil {
			// Run the input's redirect if it exists, in case it has side effects, but ignore any error it
			// returns, since we want to use ErrUseLastResponse.
			err := in.CheckRedirect(req, via)
			_ = err // Silly, but this makes sure generated code passes errcheck -blank, which some people use.
		}
		return http.ErrUseLastResponse
	}
	return &copy
}

// doProtobufRequest is common code to make a request to the remote twirp service.
func doProtobufRequest(ctx context.Context, client HTTPClient, url string, in, out proto.Message) (err error) {
	reqBodyBytes, err := proto.Marshal(in)
	if err != nil {
		return clientError("failed to marshal proto request", err)
	}
	reqBody := bytes.NewBuffer(reqBodyBytes)
	if err = ctx.Err(); err != nil {
		return clientError("aborted because context was done", err)
	}

	req, err := newRequest(ctx, url, reqBody, "application/protobuf")
	if err != nil {
		return clientError("could not build request", err)
	}
	resp, err := client.Do(req)
	if err != nil {
		return clientError("failed to do request", err)
	}

	defer func() {
		cerr := resp.Body.Close()
		if err == nil && cerr != nil {
			err = clientError("failed to close response body", cerr)
		}
	}()

	if err = ctx.Err(); err != nil {
		return clientError("aborted because context was done", err)
	}

	if resp.StatusCode != 200 {
		return errorFromResponse(resp)
	}

	respBodyBytes, err := ioutil.ReadAll(resp.Body)
	if err != nil {
		return clientError("failed to read response body", err)
	}
	if err = ctx.Err(); err != nil {
		return clientError("aborted because context was done", err)
	}

	if err = proto.Unmarshal(respBodyBytes, out); err != nil {
		return clientError("failed to unmarshal proto response", err)
	}
	return nil
}

// doJSONRequest is common code to make a request to the remote twirp service.
func doJSONRequest(ctx context.Context, client HTTPClient, url string, in, out proto.Message) (err error) {
	reqBody := bytes.NewBuffer(nil)
	marshaler := &jsonpb.Marshaler{OrigName: true}
	if err = marshaler.Marshal(reqBody, in); err != nil {
		return clientError("failed to marshal json request", err)
	}
	if err = ctx.Err(); err != nil {
		return clientError("aborted because context was done", err)
	}

	req, err := newRequest(ctx, url, reqBody, "application/json")
	if err != nil {
		return clientError("could not build request", err)
	}
	resp, err := client.Do(req)
	if err != nil {
		return clientError("failed to do request", err)
	}

	defer func() {
		cerr := resp.Body.Close()
		if err == nil && cerr != nil {
			err = clientError("failed to close response body", cerr)
		}
	}()

	if err = ctx.Err(); err != nil {
		return clientError("aborted because context was done", err)
	}

	if resp.StatusCode != 200 {
		return errorFromResponse(resp)
	}

	unmarshaler := jsonpb.Unmarshaler{AllowUnknownFields: true}
	if err = unmarshaler.Unmarshal(resp.Body, out); err != nil {
		return clientError("failed to unmarshal json response", err)
	}
	if err = ctx.Err(); err != nil {
		return clientError("aborted because context was done", err)
	}
	return nil
}

// Call twirp.ServerHooks.RequestReceived if the hook is available
func callRequestReceived(ctx context.Context, h *twirp.ServerHooks) (context.Context, error) {
	if h == nil || h.RequestReceived == nil {
		return ctx, nil
	}
	return h.RequestReceived(ctx)
}

// Call twirp.ServerHooks.RequestRouted if the hook is available
func callRequestRouted(ctx context.Context, h *twirp.ServerHooks) (context.Context, error) {
	if h == nil || h.RequestRouted == nil {
		return ctx, nil
	}
	return h.RequestRouted(ctx)
}

// Call twirp.ServerHooks.ResponsePrepared if the hook is available
func callResponsePrepared(ctx context.Context, h *twirp.ServerHooks) context.Context {
	if h == nil || h.ResponsePrepared == nil {
		return ctx
	}
	return h.ResponsePrepared(ctx)
}

// Call twirp.ServerHooks.ResponseSent if the hook is available
func callResponseSent(ctx context.Context, h *twirp.ServerHooks) {
	if h == nil || h.ResponseSent == nil {
		return
	}
	h.ResponseSent(ctx)
}

// Call twirp.ServerHooks.Error if the hook is available
func callError(ctx context.Context, h *twirp.ServerHooks, err twirp.Error) context.Context {
	if h == nil || h.Error == nil {
		return ctx
	}
	return h.Error(ctx, err)
}

var twirpFileDescriptor0 = []byte{
	// 276 bytes of a gzipped FileDescriptorProto
	0x1f, 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02, 0xff, 0x74, 0x91, 0xc1, 0x4e, 0x83, 0x40,
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	0xe4, 0x01, 0x00, 0x00,
}