Add opensearch endpoint and handler

internal/opensearch_handler.go

@@ -0,0 +1,35 @@
+package internal
+
+import (
+	"fmt"
+	"net/http"
+
+	"github.com/julienschmidt/httprouter"
+)
+
+const OpenSearchTemplate string = `<?xml version="1.0" encoding="UTF-8"?>
+<OpenSearchDescription xmlns="http://a9.com/-/spec/opensearch/1.1/">
+  <ShortName>%s</ShortName>
+  <Description>%s</Description>
+  <Tags>search</Tags>
+  <Contact>%s</Contact>
+  <Url type="text/html" method="get" template="%s?q={searchTerms}"/>
+</OpenSearchDescription>
+`
+
+// OpenSearchHandler ...
+func (s *Server) OpenSearchHandler() httprouter.Handle {
+	return func(w http.ResponseWriter, r *http.Request, _ httprouter.Params) {
+		w.Header().Set("Content-Type", "text/xml")
+
+		w.Write(
+			[]byte(fmt.Sprintf(
+				OpenSearchTemplate,
+				s.config.Name,
+				s.config.Description,
+				s.config.AdminEmail,
+				s.config.BaseURL,
+			)),
+		)
+	}
+}