From 90f902c3ab312eeb9de2fc7a8b9f6852e2c2bcec Mon Sep 17 00:00:00 2001
From: Marcin Owsiany <marcin@owsiany.pl>
Date: Fri, 12 Oct 2018 09:13:12 +0200
Subject: [PATCH] Add a way to return the body of a 5xx response.

Fixes: #479.
Signed-off-by: Marcin Owsiany <marcin@owsiany.pl>
---
 api/prometheus/v1/api.go      | 10 ++++----
 api/prometheus/v1/api_test.go | 44 +++++++++++++++++++++++++++++++----
 2 files changed, 45 insertions(+), 9 deletions(-)

diff --git a/api/prometheus/v1/api.go b/api/prometheus/v1/api.go
index 6a19fac12..702a78e94 100644
--- a/api/prometheus/v1/api.go
+++ b/api/prometheus/v1/api.go
@@ -69,8 +69,9 @@ const (
 
 // Error is an error returned by the API.
 type Error struct {
-	Type ErrorType
-	Msg  string
+	Type   ErrorType
+	Msg    string
+	Detail string
 }
 
 func (e *Error) Error() string {
@@ -470,8 +471,9 @@ func (c apiClient) Do(ctx context.Context, req *http.Request) (*http.Response, [
 
 	if code/100 != 2 && !apiError(code) {
 		return resp, body, &Error{
-			Type: ErrBadResponse,
-			Msg:  fmt.Sprintf("bad response code %d", resp.StatusCode),
+			Type:   ErrBadResponse,
+			Msg:    fmt.Sprintf("bad response code %d", resp.StatusCode),
+			Detail: string(body),
 		}
 	}
 
diff --git a/api/prometheus/v1/api_test.go b/api/prometheus/v1/api_test.go
index 1f7fda7f9..58ae38746 100644
--- a/api/prometheus/v1/api_test.go
+++ b/api/prometheus/v1/api_test.go
@@ -30,15 +30,17 @@ import (
 )
 
 type apiTest struct {
-	do    func() (interface{}, error)
-	inErr error
-	inRes interface{}
+	do     func() (interface{}, error)
+	inErr  error
+	inCode int
+	inRes  interface{}
 
 	reqPath   string
 	reqParam  url.Values
 	reqMethod string
 	res       interface{}
 	err       error
+	errCheck  func(error) error
 }
 
 type apiTestClient struct {
@@ -75,7 +77,9 @@ func (c *apiTestClient) Do(ctx context.Context, req *http.Request) (*http.Respon
 	}
 
 	resp := &http.Response{}
-	if test.inErr != nil {
+	if test.inCode != 0 {
+		resp.StatusCode = test.inCode
+	} else if test.inErr != nil {
 		resp.StatusCode = statusAPIError
 	} else {
 		resp.StatusCode = http.StatusOK
@@ -194,6 +198,30 @@ func TestAPIs(t *testing.T) {
 			},
 			err: fmt.Errorf("some error"),
 		},
+		{
+			do:     doQuery("2", testTime),
+			inRes:  "some body",
+			inCode: 500,
+			inErr: &Error{
+				Type:   ErrBadResponse,
+				Msg:    "bad response code: 500",
+				Detail: "a body",
+			},
+
+			reqMethod: "GET",
+			reqPath:   "/api/v1/query",
+			reqParam: url.Values{
+				"query": []string{"2"},
+				"time":  []string{testTime.Format(time.RFC3339Nano)},
+			},
+			errCheck: func(err error) error {
+				apiErr := err.(*Error)
+				if apiErr.Detail != "a body" {
+					return fmt.Errorf("%q should be %q", apiErr.Detail, "a body")
+				}
+				return nil
+			},
+		},
 
 		{
 			do: doQueryRange("2", Range{
@@ -503,7 +531,13 @@ func TestAPIs(t *testing.T) {
 
 		res, err := test.do()
 
-		if test.err != nil {
+		if test.errCheck != nil {
+			err = test.errCheck(err)
+			if err != nil {
+				t.Errorf("returned error is wrong: %s", err)
+			}
+			continue
+		} else if test.err != nil {
 			if err == nil {
 				t.Errorf("expected error %q but got none", test.err)
 				continue