Added custom rest error type (#271)

restapi.go

@@ -169,7 +169,7 @@ func (s *Session) request(method, urlStr, contentType string, b []byte, sequence
 		response, err = s.request(method, urlStr, contentType, b, sequence)
 
 	default: // Error condition
-		err = fmt.Errorf("HTTP %s, %s", resp.Status, response)
+		err = newRestError(req, resp, response)
 	}
 
 	return

structs.go

@@ -502,6 +502,12 @@ type UserGuildSettingsEdit struct {
 	ChannelOverrides     map[string]*UserGuildSettingsChannelOverride `json:"channel_overrides"`
 }
 
+// An APIErrorMessage is an api error message returned from discord
+type APIErrorMessage struct {
+	Code    int    `json:"code"`
+	Message string `json:"message"`
+}
+
 // ChannelPinsUpdate stores data for the channel pins update event
 type ChannelPinsUpdate struct {
 	LastPinTimestamp string `json:"last_pin_timestamp"`

types.go

@@ -10,6 +10,9 @@
 package discordgo
 
 import (
+	"encoding/json"
+	"fmt"
+	"net/http"
 	"time"
 )
 
@@ -21,3 +24,35 @@ type Timestamp string
 func (t Timestamp) Parse() (time.Time, error) {
 	return time.Parse(time.RFC3339, string(t))
 }
+
+// RESTError stores error information about a request with a bad response code.
+// Message is not always present, there are cases where api calls can fail
+// without returning a json message.
+type RESTError struct {
+	Request      *http.Request
+	Response     *http.Response
+	ResponseBody []byte
+
+	Message *APIErrorMessage // Message may be nil.
+}
+
+func newRestError(req *http.Request, resp *http.Response, body []byte) *RESTError {
+	restErr := &RESTError{
+		Request:      req,
+		Response:     resp,
+		ResponseBody: body,
+	}
+
+	// Attempt to decode the error and assume no message was provided if it fails
+	var msg *APIErrorMessage
+	err := json.Unmarshal(body, &msg)
+	if err == nil {
+		restErr.Message = msg
+	}
+
+	return restErr
+}
+
+func (r RESTError) Error() string {
+	return fmt.Sprintf("HTTP %s, %s", r.Response.Status, r.ResponseBody)
+}