Merge pull request coreos#148 from chancez/improve_json_unmarshal_err

Check response content-type to improve message if cannot decode as JSON

Author: chancez

jwks.go

@@ -2,7 +2,6 @@ package oidc
 
 import (
 	"context"
-	"encoding/json"
 	"errors"
 	"fmt"
 	"io/ioutil"
@@ -182,14 +181,16 @@ func (r *remoteKeySet) updateKeys() ([]jose.JSONWebKey, time.Time, error) {
 
 	body, err := ioutil.ReadAll(resp.Body)
 	if err != nil {
-		return nil, time.Time{}, fmt.Errorf("oidc: read response body: %v", err)
+		return nil, time.Time{}, fmt.Errorf("unable to read response body: %v", err)
 	}
+
 	if resp.StatusCode != http.StatusOK {
 		return nil, time.Time{}, fmt.Errorf("oidc: get keys failed: %s %s", resp.Status, body)
 	}
 
 	var keySet jose.JSONWebKeySet
-	if err := json.Unmarshal(body, &keySet); err != nil {
+	err = unmarshalResp(resp, body, &keySet)
+	if err != nil {
 		return nil, time.Time{}, fmt.Errorf("oidc: failed to decode keys: %v %s", err, body)
 	}
 

oidc.go

@@ -7,6 +7,7 @@ import (
 	"errors"
 	"fmt"
 	"io/ioutil"
+	"mime"
 	"net/http"
 	"strings"
 	"time"
@@ -93,18 +94,23 @@ func NewProvider(ctx context.Context, issuer string) (*Provider, error) {
 	if err != nil {
 		return nil, err
 	}
+	defer resp.Body.Close()
+
 	body, err := ioutil.ReadAll(resp.Body)
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("unable to read response body: %v", err)
 	}
+
 	if resp.StatusCode != http.StatusOK {
 		return nil, fmt.Errorf("%s: %s", resp.Status, body)
 	}
-	defer resp.Body.Close()
+
 	var p providerJSON
-	if err := json.Unmarshal(body, &p); err != nil {
+	err = unmarshalResp(resp, body, &p)
+	if err != nil {
 		return nil, fmt.Errorf("oidc: failed to decode provider discovery object: %v", err)
 	}
+
 	if p.Issuer != issuer {
 		return nil, fmt.Errorf("oidc: issuer did not match the issuer returned by provider, expected %q got %q", issuer, p.Issuer)
 	}
@@ -307,3 +313,16 @@ func (j *jsonTime) UnmarshalJSON(b []byte) error {
 	*j = jsonTime(time.Unix(unix, 0))
 	return nil
 }
+
+func unmarshalResp(r *http.Response, body []byte, v interface{}) error {
+	err := json.Unmarshal(body, &v)
+	if err == nil {
+		return nil
+	}
+	ct := r.Header.Get("Content-Type")
+	mediaType, _, parseErr := mime.ParseMediaType(ct)
+	if parseErr == nil && mediaType == "application/json" {
+		return fmt.Errorf("got Content-Type = application/json, but could not unmarshal as JSON: %v", err)
+	}
+	return fmt.Errorf("expected Content-Type = application/json, got %q: %v", ct, err)
+}