Android app (TWA) in android/, built with podman; serve assetlinks.json for it

internal/web/pwa.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"io/fs"
 	"net/http"
+	"strings"
 )
 
 // The site installs as an app (a PWA): a web app manifest, plus the service worker in
@@ -62,6 +63,34 @@ func (s *Server) manifest(staff bool) http.HandlerFunc {
 	}
 }
 
+// assetLinks tells Chrome the Android app belongs to this site, so it opens the site full screen
+// (a Trusted Web Activity) instead of with its URL bar showing.
+func (s *Server) assetLinks(w http.ResponseWriter, r *http.Request) {
+	var certs []string
+	for _, c := range s.cfg.AndroidCerts {
+		if c = strings.ToUpper(strings.TrimSpace(c)); c != "" {
+			certs = append(certs, c)
+		}
+	}
+	if s.cfg.AndroidPackage == "" || len(certs) == 0 {
+		http.NotFound(w, r)
+		return
+	}
+	type target struct {
+		Namespace    string   `json:"namespace"`
+		PackageName  string   `json:"package_name"`
+		Fingerprints []string `json:"sha256_cert_fingerprints"`
+	}
+	type statement struct {
+		Relation []string `json:"relation"`
+		Target   target   `json:"target"`
+	}
+	writeJSON(w, http.StatusOK, []statement{{
+		Relation: []string{"delegate_permission/common.handle_all_urls"},
+		Target:   target{Namespace: "android_app", PackageName: s.cfg.AndroidPackage, Fingerprints: certs},
+	}})
+}
+
 // serviceWorker serves sw.js from the root, since a worker only controls pages under its own path.
 func serviceWorker(static fs.FS) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {