frontend: Set up opensearchdescription aka Tab To Search

This used to work on godoc.org, let's set it up for pkg.go.dev too. golang/go#58133

Author: Jille

internal/frontend/server.go

@@ -193,6 +193,7 @@ Disallow: /fetch/*
 Sitemap: https://pkg.go.dev/sitemap/index.xml
 `))
 }))
+handle("/opensearch.xml", s.opensearchHandler())
 s.installDebugHandlers(handle)
 }
 
@@ -466,6 +467,21 @@ func (s *Server) aboutHandler() http.HandlerFunc {
 })
 }
 
+func (s *Server) opensearchHandler() http.HandlerFunc {
+return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+w.Header().Set("Content-Type", "application/opensearchdescription+xml")
+http.ServeContent(w, r, "", time.Time{}, strings.NewReader(`<?xml version="1.0"?>
+<OpenSearchDescription xmlns="http://a9.com/-/spec/opensearch/1.1/">
+ <InputEncoding>UTF-8</InputEncoding>
+ <ShortName>Go Packages</ShortName>
+ <Description>Go Packages: Go Package Documentation</Description>
+ <Url type="text/html" method="get" template="https://` + r.Host + `/search?q={searchTerms}"/>
+ <Url type="application/opensearchdescription+xml" rel="self" template="https://` + r.Host + `/opensearch.xml"/>
+</OpenSearchDescription>
+`))
+})
+}
+
 // newBasePage returns a base page for the given request and title.
 func (s *Server) newBasePage(r *http.Request, title string) basePage {
 q := rawSearchQuery(r)

static/frontend/frontend.tmpl

@@ -30,6 +30,7 @@
  <link rel="shortcut icon" href="/static/shared/icon/favicon.ico">
  {{block "canonical" .}}{{end}}
  <link href="/static/frontend/frontend.min.css?version={{.AppVersionLabel}}" rel="stylesheet">
+ <link type="application/opensearchdescription+xml" rel="search" href="/opensearch.xml?version={{.AppVersionLabel}}" title="Go Packages" />
  {{block "title" .}}
  <title>Go Packages</title>
  {{end}}