internal/frontend: add frontend server endpoint for proxying play.golang.org/share

This change adds a /play handler that mirrors requests
to play.golang.org/share which is used in implementing playground
integration in the frontend. This change also adds a test that
includes a mock server using net/httptest to check for proper
status codes.

Updates golang/go#36865

Change-Id: Ia3e902808534189ada747b270fed908e766c224b
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/241164
Reviewed-by: Julie Qiu <[email protected]>
Reviewed-by: Jonathan Amsterdam <[email protected]>

Author: Miguel Acero

internal/frontend/playground.go

@@ -0,0 +1,58 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package frontend
+
+import (
+	"io"
+	"net/http"
+
+	"golang.org/x/pkgsite/internal/log"
+)
+
+// playgroundURL is the playground endpoint used for share links.
+const playgroundURL = "https://play.golang.org"
+
+// handlePlay handles requests that mirror play.golang.org/share.
+func (s *Server) handlePlay(w http.ResponseWriter, r *http.Request) {
+	makeFetchPlayRequest(w, r, playgroundURL)
+}
+
+func httpErrorStatus(w http.ResponseWriter, status int) {
+	http.Error(w, http.StatusText(status), status)
+}
+
+func makeFetchPlayRequest(w http.ResponseWriter, r *http.Request, pgURL string) {
+	ctx := r.Context()
+	if r.Method != http.MethodPost {
+		httpErrorStatus(w, http.StatusMethodNotAllowed)
+		return
+	}
+	req, err := http.NewRequest("POST", pgURL+"/share", r.Body)
+	if err != nil {
+		log.Errorf(ctx, "ERROR share error: %v", err)
+		httpErrorStatus(w, http.StatusInternalServerError)
+		return
+	}
+	req.Header.Set("Content-Type", "text/plain; charset=utf-8")
+	req = req.WithContext(r.Context())
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		log.Errorf(ctx, "ERROR share error: %v", err)
+		httpErrorStatus(w, http.StatusInternalServerError)
+		return
+	}
+	copyHeader := func(k string) {
+		if v := resp.Header.Get(k); v != "" {
+			w.Header().Set(k, v)
+		}
+	}
+	copyHeader("Content-Type")
+	copyHeader("Content-Length")
+	defer resp.Body.Close()
+	w.WriteHeader(resp.StatusCode)
+	if _, err := io.Copy(w, resp.Body); err != nil {
+		log.Errorf(ctx, "ERROR writing shareId: %v", err)
+	}
+}

internal/frontend/playground_test.go

@@ -0,0 +1,97 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package frontend
+
+import (
+	"io"
+	"io/ioutil"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+)
+
+const shareID = "arbitraryShareID"
+
+func TestPlaygroundShare(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != http.MethodPost {
+			http.Error(w, "Expected a POST", http.StatusMethodNotAllowed)
+		}
+		_, err := io.WriteString(w, shareID)
+		if err != nil {
+			t.Fatal(err)
+		}
+	}))
+	defer ts.Close()
+
+	testCases := []struct {
+		pgURL   string
+		method  string
+		desc    string
+		body    string
+		code    int
+		shareID string
+	}{
+		{
+			pgURL:  ts.URL,
+			method: http.MethodPost,
+			desc:   "Share endpoint: for Hello World func",
+			body: `package main
+import (
+	"fmt"
+)
+
+func main() {
+	fmt.Println("Hello, playground")
+}`,
+			code: http.StatusOK,
+		},
+		{
+			pgURL:  ts.URL,
+			method: http.MethodGet,
+			desc:   "Share endpoint: Failed GET Request, Accept POST only",
+			body:   "",
+			code:   http.StatusMethodNotAllowed,
+		},
+		{
+			pgURL:  "/*?",
+			method: http.MethodPost,
+			desc:   "Share endpoint: Malformed URL returns internal server error",
+			body:   "",
+			code:   http.StatusInternalServerError,
+		},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.desc, func(t *testing.T) {
+			body := strings.NewReader(tc.body)
+
+			req, err := http.NewRequest(tc.method, "/play", body)
+			if err != nil {
+				t.Fatal(err)
+			}
+			req.Header.Set("Content-Type", "text/plain; charset=utf-8")
+			w := httptest.NewRecorder()
+			makeFetchPlayRequest(w, req, tc.pgURL)
+
+			res := w.Result()
+
+			if got, want := res.StatusCode, tc.code; got != want {
+				t.Errorf("Status Code = %d; want %d", got, want)
+			}
+
+			if res.StatusCode >= 200 && res.StatusCode < 300 {
+				body, err := ioutil.ReadAll(res.Body)
+				if err != nil {
+					t.Fatal(err)
+				}
+
+				if string(body) != shareID {
+					t.Errorf("body = %s; want %s", body, shareID)
+				}
+			}
+		})
+	}
+}

internal/frontend/server.go

@@ -102,6 +102,7 @@ func (s *Server) Install(handle func(string, http.Handler), redisClient *redis.C
 		http.ServeFile(w, r, fmt.Sprintf("%s/img/favicon.ico", http.Dir(s.staticPath.String())))
 	}))
 	handle("/fetch/", fetchHandler)
+	handle("/play/", http.HandlerFunc(s.handlePlay))
 	handle("/pkg/", http.HandlerFunc(s.handlePackageDetailsRedirect))
 	handle("/search", searchHandler)
 	handle("/search-help", s.staticPageHandler("search_help.tmpl", "Search Help - go.dev"))