From d06690eb9022871475d9f30e1fdc389b22abdf77 Mon Sep 17 00:00:00 2001
From: Thomas Jackson <jacksontj.89@gmail.com>
Date: Tue, 23 Apr 2019 16:40:27 -0700
Subject: [PATCH] Implement POST with get fallback for Query/QueryRange

Signed-off-by: Thomas Jackson <jacksontj.89@gmail.com>

Fixes #428
---
 api/client.go                 | 22 ++++++++++++++++++++++
 api/prometheus/v1/api.go      | 16 ++--------------
 api/prometheus/v1/api_test.go | 10 +++++-----
 3 files changed, 29 insertions(+), 19 deletions(-)

diff --git a/api/client.go b/api/client.go
index 9d5b1879c..b12d6617b 100644
--- a/api/client.go
+++ b/api/client.go
@@ -60,6 +60,28 @@ type Client interface {
 	Do(context.Context, *http.Request) (*http.Response, []byte, error)
 }
 
+// DoGetFallback will attempt to do the request as-is, and on a 405 it will fallback to a GET request
+func DoGetFallback(c Client, ctx context.Context, u *url.URL, args url.Values) (*http.Response, []byte, error) {
+	req, err := http.NewRequest(http.MethodPost, u.String(), strings.NewReader(args.Encode()))
+	if err != nil {
+		return nil, nil, err
+	}
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+
+	resp, body, err := c.Do(ctx, req)
+	if resp != nil && resp.StatusCode == http.StatusMethodNotAllowed {
+		u.RawQuery = args.Encode()
+		req, err = http.NewRequest(http.MethodGet, u.String(), nil)
+		if err != nil {
+			return nil, nil, err
+		}
+
+	} else {
+		return resp, body, err
+	}
+	return c.Do(ctx, req)
+}
+
 // NewClient returns a new Client.
 //
 // It is safe to use the returned Client from multiple goroutines.
diff --git a/api/prometheus/v1/api.go b/api/prometheus/v1/api.go
index c0481797e..32aa49f0c 100644
--- a/api/prometheus/v1/api.go
+++ b/api/prometheus/v1/api.go
@@ -542,12 +542,7 @@ func (h *httpAPI) Query(ctx context.Context, query string, ts time.Time) (model.
 
 	u.RawQuery = q.Encode()
 
-	req, err := http.NewRequest(http.MethodGet, u.String(), nil)
-	if err != nil {
-		return nil, err
-	}
-
-	_, body, err := h.client.Do(ctx, req)
+	_, body, err := api.DoGetFallback(h.client, ctx, u, q)
 	if err != nil {
 		return nil, err
 	}
@@ -573,14 +568,7 @@ func (h *httpAPI) QueryRange(ctx context.Context, query string, r Range) (model.
 	q.Set("end", end)
 	q.Set("step", step)
 
-	u.RawQuery = q.Encode()
-
-	req, err := http.NewRequest(http.MethodGet, u.String(), nil)
-	if err != nil {
-		return nil, err
-	}
-
-	_, body, err := h.client.Do(ctx, req)
+	_, body, err := api.DoGetFallback(h.client, ctx, u, q)
 	if err != nil {
 		return nil, err
 	}
diff --git a/api/prometheus/v1/api_test.go b/api/prometheus/v1/api_test.go
index fec170ede..ca5c5a745 100644
--- a/api/prometheus/v1/api_test.go
+++ b/api/prometheus/v1/api_test.go
@@ -181,7 +181,7 @@ func TestAPIs(t *testing.T) {
 				},
 			},
 
-			reqMethod: "GET",
+			reqMethod: "POST",
 			reqPath:   "/api/v1/query",
 			reqParam: url.Values{
 				"query": []string{"2"},
@@ -196,7 +196,7 @@ func TestAPIs(t *testing.T) {
 			do:    doQuery("2", testTime),
 			inErr: fmt.Errorf("some error"),
 
-			reqMethod: "GET",
+			reqMethod: "POST",
 			reqPath:   "/api/v1/query",
 			reqParam: url.Values{
 				"query": []string{"2"},
@@ -214,7 +214,7 @@ func TestAPIs(t *testing.T) {
 				Detail: "some body",
 			},
 
-			reqMethod: "GET",
+			reqMethod: "POST",
 			reqPath:   "/api/v1/query",
 			reqParam: url.Values{
 				"query": []string{"2"},
@@ -232,7 +232,7 @@ func TestAPIs(t *testing.T) {
 				Detail: "some body",
 			},
 
-			reqMethod: "GET",
+			reqMethod: "POST",
 			reqPath:   "/api/v1/query",
 			reqParam: url.Values{
 				"query": []string{"2"},
@@ -249,7 +249,7 @@ func TestAPIs(t *testing.T) {
 			}),
 			inErr: fmt.Errorf("some error"),
 
-			reqMethod: "GET",
+			reqMethod: "POST",
 			reqPath:   "/api/v1/query_range",
 			reqParam: url.Values{
 				"query": []string{"2"},