Implement POST with get fallback for Query/QueryRange

api/client.go

@@ -58,6 +58,28 @@ 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.

api/client_test.go

@@ -14,9 +14,14 @@
 package api
 
 import (
+	"context"
+	"encoding/json"
 	"net/http"
+	"net/http/httptest"
 	"net/url"
 	"testing"
+
+	"github.com/prometheus/tsdb/testutil"
 )
 
 func TestConfig(t *testing.T) {
@@ -111,3 +116,70 @@ func TestClientURL(t *testing.T) {
 		}
 	}
 }
+
+func TestDoGetFallback(t *testing.T) {
+	v := url.Values{"a": []string{"1", "2"}}
+
+	type testResponse struct {
+		Values string
+		Method string
+	}
+
+	// Start a local HTTP server.
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
+		req.ParseForm()
+		r := &testResponse{
+			Values: req.Form.Encode(),
+			Method: req.Method,
+		}
+
+		body, _ := json.Marshal(r)
+
+		if req.Method == http.MethodPost {
+			if req.URL.Path == "/blockPost" {
+				http.Error(w, string(body), http.StatusMethodNotAllowed)
+				return
+			}
+		}
+
+		w.Write(body)
+	}))
+	// Close the server when test finishes.
+	defer server.Close()
+
+	u, err := url.Parse(server.URL)
+	testutil.Ok(t, err)
+	client := &httpClient{client: *(server.Client())}
+
+	// Do a post, and ensure that the post succeeds.
+	_, b, err := DoGetFallback(client, context.TODO(), u, v)
+	if err != nil {
+		t.Fatalf("Error doing local request: %v", err)
+	}
+	resp := &testResponse{}
+	if err := json.Unmarshal(b, resp); err != nil {
+		testutil.Ok(t, err)
+	}
+	if resp.Method != http.MethodPost {
+		t.Fatalf("Mismatch method")
+	}
+	if resp.Values != v.Encode() {
+		t.Fatalf("Mismatch in values")
+	}
+
+	// Do a fallbcak to a get.
+	u.Path = "/blockPost"
+	_, b, err = DoGetFallback(client, context.TODO(), u, v)
+	if err != nil {
+		t.Fatalf("Error doing local request: %v", err)
+	}
+	if err := json.Unmarshal(b, resp); err != nil {
+		testutil.Ok(t, err)
+	}
+	if resp.Method != http.MethodGet {
+		t.Fatalf("Mismatch method")
+	}
+	if resp.Values != v.Encode() {
+		t.Fatalf("Mismatch in values")
+	}
+}

api/prometheus/v1/api.go

@@ -540,12 +540,7 @@ 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
 	}
@@ -571,14 +566,7 @@ 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
 	}

api/prometheus/v1/api_test.go

@@ -179,7 +179,7 @@ func TestAPIs(t *testing.T) {
 				},
 			},
 
-			reqMethod: "GET",
+			reqMethod: "POST",
 			reqPath:   "/api/v1/query",
 			reqParam: url.Values{
 				"query": []string{"2"},
@@ -194,7 +194,7 @@ 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"},
@@ -212,7 +212,7 @@ func TestAPIs(t *testing.T) {
 				Detail: "some body",
 			},
 
-			reqMethod: "GET",
+			reqMethod: "POST",
 			reqPath:   "/api/v1/query",
 			reqParam: url.Values{
 				"query": []string{"2"},
@@ -230,7 +230,7 @@ func TestAPIs(t *testing.T) {
 				Detail: "some body",
 			},
 
-			reqMethod: "GET",
+			reqMethod: "POST",
 			reqPath:   "/api/v1/query",
 			reqParam: url.Values{
 				"query": []string{"2"},
@@ -247,7 +247,7 @@ 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"},

go.mod

@@ -6,4 +6,5 @@ require (
 	github.com/prometheus/client_model v0.0.0-20190129233127-fd36f4220a90
 	github.com/prometheus/common v0.3.0
 	github.com/prometheus/procfs v0.0.0-20190412120340-e22ddced7142
+	github.com/prometheus/tsdb v0.7.1
 )

go.sum

@@ -1,12 +1,18 @@
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+github.com/cespare/xxhash v1.1.0/go.mod h1:XrSqR1VqqWfGrhpAt58auRo0WTKS1nRRg3ghfAqPWnc=
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+github.com/go-logfmt/logfmt v0.3.0 h1:8HUsc87TaSWLKwrnumgC8/YconD2fJQsRJAsWaPg2ic=
 github.com/go-logfmt/logfmt v0.3.0/go.mod h1:Qt1PoO58o5twSAckw1HlFXLmHsOX5/0LbT9GBnD5lWE=
+github.com/go-stack/stack v1.8.0 h1:5SgMzNM5HxrEjV0ww2lTmX6E2Izsfxas4+YHWRs3Lsk=
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 github.com/golang/protobuf v1.2.0 h1:P3YflyNX/ehuJFLhxviNdFxQPkGK5cDcApsge1SqnvM=
@@ -15,23 +21,29 @@ github.com/golang/protobuf v1.3.1 h1:YF8+flBXS5eO826T4nzqPrxfhQThhXl0YzfuUPu4SBg
 github.com/golang/protobuf v1.3.1/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5yJMmIC1U=
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+github.com/kr/logfmt v0.0.0-20140226030751-b84e30acd515 h1:T+h1c/A9Gawja4Y9mFVWj2vyii2bbUNDw3kt9VxK2EY=
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+github.com/spaolacci/murmur3 v0.0.0-20180118202830-f09979ecbc72/go.mod h1:JwIasOWyU6f++ZhiEuf87xNszmSA2myDM2Kzu9HwQUA=
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@@ -41,6 +53,7 @@ golang.org/x/sync v0.0.0-20181108010431-42b317875d0f/go.mod h1:RxMgew5VJxzue5/jJ
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