internal/redirect: add redirect from go.dev/cs to cs.opensource.google

This change makes it so that go.dev/cs redirects to
cs.opensource.google/go while keeping any path and URL parameter intact.
This allows users to link code within cs.opensource.google/go using
go.dev/cs.

As a special case, go.dev/cs/search/ has also been added. Anything that
comes after /search/ will be used as the Code Search query parameter
within the "go" project in cs.opensource.google/search. This allows
users to search within the codebase in one go from their browser's URL
bar.

Change-Id: I1eae8c2e0d18c7e94bc85cced81404716f29ed99
Reviewed-on: https://go-review.googlesource.com/c/website/+/722560
Reviewed-by: Alan Donovan <adonovan@google.com>
Reviewed-by: Nicholas Husin <husin@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

2 files changed, 43 insertions, 0 deletions

diff --git a/internal/redirect/redirect.go b/internal/redirect/redirect.go
index e12455b8..d3e242d2 100644
--- a/internal/redirect/redirect.go
+++ b/internal/redirect/redirect.go
@@ -13,6 +13,7 @@ import (
 	"fmt"
 	"html/template"
 	"net/http"
+	"net/url"
 	"regexp"
 	"strconv"
 	"strings"
@@ -44,6 +45,7 @@ func Register(mux *http.ServeMux) {
 	// NB: /src/pkg (sans trailing slash) is the index of packages.
 	mux.HandleFunc("/src/pkg/", srcPkgHandler)
 	mux.HandleFunc("/cl/", clHandler)
+	mux.HandleFunc("/cs/", csHandler)
 	mux.HandleFunc("/change/", changeHandler)
 	mux.HandleFunc("/design/", designHandler)
 }
@@ -101,6 +103,7 @@ var redirects = map[string]string{
 	"/build":      "https://build.golang.org",
 	"/change":     "https://go.googlesource.com/go",
 	"/cl":         "https://go-review.googlesource.com",
+	"/cs":         "https://cs.opensource.google/go",
 	"/cmd/godoc/": "https://pkg.go.dev/golang.org/x/tools/cmd/godoc",
 	"/issue":      "https://github.com/golang/go/issues",
 	"/issues":     "https://github.com/golang/go/issues",
@@ -372,3 +375,33 @@ func designHandler(w http.ResponseWriter, r *http.Request) {
 	target := "https://go.googlesource.com/proposal/+/master/design/" + name + ".md"
 	http.Redirect(w, r, target, http.StatusFound)
 }
+
+func csHandler(w http.ResponseWriter, r *http.Request) {
+	path, ok := strings.CutPrefix(r.URL.Path, "/cs/")
+	if !ok || path == "" {
+		http.Redirect(w, r, "/cs", http.StatusFound)
+		return
+	}
+
+	// /cs/search/<query> redirects to cs.opensource.google/search. <query>
+	// represents Code Search syntax which we will automatically put as part of
+	// the URL query parameter for convenience. The search will always be
+	// scoped to "go".
+	if query, ok := strings.CutPrefix(path, "search/"); ok {
+		target := "https://cs.opensource.google/search?ss=go"
+		if query != "" {
+			target += "&q=" + url.QueryEscape(query)
+		}
+		http.Redirect(w, r, target, http.StatusFound)
+		return
+	}
+
+	// Any other /cs/ redirects to cs.opensource.google/go while keeping the
+	// path and URL query intact.
+	target := "https://cs.opensource.google/go/"
+	target += path
+	if query := r.URL.RawQuery; query != "" {
+		target += "?" + query
+	}
+	http.Redirect(w, r, target, http.StatusFound)
+}
diff --git a/internal/redirect/redirect_test.go b/internal/redirect/redirect_test.go
index 10d4de05..e7e2cd9d 100644
--- a/internal/redirect/redirect_test.go
+++ b/internal/redirect/redirect_test.go
@@ -108,6 +108,16 @@ func TestRedirects(t *testing.T) {
 		// And verify we're using the "bigEnoughAssumeRietveld" value:
 		"/cl/3999999": {302, "https://go-review.googlesource.com/3999999"},
 		"/cl/4000000": {302, "https://codereview.appspot.com/4000000"},
+
+		"/cs":           {301, "https://cs.opensource.google/go"},
+		"/cs/":          {302, "/cs"},
+		"/cs/x/pkgsite": {302, "https://cs.opensource.google/go/x/pkgsite"},
+		"/cs/x/net/+/master:http/httpguts/httplex.go;l=57-69;drc=0a24555f5cc06e8caf23d84a4f8b7102dcab838e": {302, "https://cs.opensource.google/go/x/net/+/master:http/httpguts/httplex.go;l=57-69;drc=0a24555f5cc06e8caf23d84a4f8b7102dcab838e"},
+
+		"/cs/search/":                          {302, "https://cs.opensource.google/search?ss=go"},
+		"/cs/search/f:test.go":                 {302, "https://cs.opensource.google/search?ss=go&q=f%3Atest.go"},
+		"/cs/search/func:Bench AND f:bench.go": {302, "https://cs.opensource.google/search?ss=go&q=func%3ABench+AND+f%3Abench.go"},
+		"/cs/search/\"&\"":                     {302, "https://cs.opensource.google/search?ss=go&q=%22%26%22"},
 	}
 
 	mux := http.NewServeMux()