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|
package httperr
import (
"bytes"
"encoding/json"
"io/ioutil"
"net/http"
"reflect"
)
// ClientArg is an argument to Client
type ClientArg func(xport *Transport)
// Client returns an http.Client that wraps client with
// an error handling transport.
func Client(next *http.Client, args ...ClientArg) *http.Client {
xport := Transport{Next: next.Transport}
for _, arg := range args {
arg(&xport)
}
rv := *next
rv.Transport = xport
return &rv
}
// DefaultClient returns an http.Client that wraps the default
// http.Client with an error handling transport.
func DefaultClient() *http.Client {
return Client(http.DefaultClient)
}
var _ http.RoundTripper = Transport{}
// Transport is an http.RoundTripper that intercepts responses where
// the StatusCode >= 400 and returns a Response{}.
//
// If ErrorFactory is specified it should return an error that can be used
// to unmarshal a JSON error response. This is useful when a web service
// offers structured error information. If the error structure cannot be
// unmarshalled, then a regular Response error is returned.
//
// type APIError struct {
// Code string `json:"code"`
// Message string `json:"message"`
// }
//
// func (a APIError) Error() string {
// return fmt.Sprintf("%s (%d)", a.Message, a.Code)
// }
//
// t := Transport{
// ErrorFactory: func() error {
// return &APIError{}
// },
// }
//
type Transport struct {
Next http.RoundTripper
OnError func(req *http.Request, resp *http.Response) error
}
// RoundTrip implements http.RoundTripper.
func (t Transport) RoundTrip(req *http.Request) (*http.Response, error) {
next := t.Next
if next == nil {
next = http.DefaultTransport
}
resp, err := next.RoundTrip(req)
if err != nil {
return nil, err
}
if resp.StatusCode < 400 {
return resp, nil
}
if t.OnError != nil {
if err := t.OnError(req, resp); err != nil {
return nil, err
}
}
return nil, Response(*resp)
}
// JSON returns a ClientArg that specifies a function that
// handles errors structured as a JSON object.
func JSON(errStruct error) ClientArg {
typ := reflect.TypeOf(errStruct)
if typ.Kind() != reflect.Struct {
panic("JSON() argument must be a structure")
}
e := reflect.New(typ).Interface()
_ = e.(error) // panic if errStruct
return func(xport *Transport) {
xport.OnError = func(req *http.Request, resp *http.Response) error {
defer resp.Body.Close()
body, err := ioutil.ReadAll(resp.Body)
if err != nil {
return err
}
resp.Body = ioutil.NopCloser(bytes.NewReader(body))
jsonErrValue := reflect.New(typ)
unmarshalErr := json.Unmarshal(body, jsonErrValue.Interface())
if unmarshalErr == nil {
// jsonErrValue is a *Foo if errStruct == Foo{}
return jsonErrValue.Elem().Interface().(error)
}
// we failed to unmarshal the response body, so ignore the
// JSON error and proceed as if ErrorFactory was not provided.
return Response(*resp)
}
}
}
|
