api: Send simple User-Agent header

Fixes: #406
Fixes: #460

[chris: changed commit message; changed user-agent string; included
in image requests]

Author: sirpengi

lib/api/core.dart

@@ -80,6 +80,7 @@ class ApiConnection {
     assert(debugLog("${request.method} ${request.url}"));
 
     addAuth(request);
+    request.headers.addAll(userAgentHeader());
 
     final http.StreamedResponse response;
     try {
@@ -201,6 +202,13 @@ Map<String, String> authHeader({required String email, required String apiKey})
   };
 }
 
+Map<String, String> userAgentHeader() {
+  return {
+    // TODO(#467) include platform, platform version, and app version
+    'User-Agent': 'ZulipFlutter',
+  };
+}
+
 Map<String, String>? encodeParameters(Map<String, dynamic>? params) {
   return params?.map((k, v) =>
     MapEntry(k, v is RawParameter ? v.value : jsonEncode(v)));

lib/widgets/content.dart

@@ -853,6 +853,7 @@ class RealmContentNetworkImage extends StatelessWidget {
         if (src.origin == account.realmUrl.origin) ...authHeader(
           email: account.email, apiKey: account.apiKey,
         ),
+        ...userAgentHeader(),
       },
       cacheWidth: cacheWidth,
       cacheHeight: cacheHeight,

test/api/core_test.dart

@@ -22,7 +22,10 @@ void main() {
         check(connection.lastRequest!).isA<http.Request>()
           ..method.equals('GET')
           ..url.asString.equals('${eg.realmUrl.origin}$expectedRelativeUrl')
-          ..headers.deepEquals(authHeader(email: eg.selfAccount.email, apiKey: eg.selfAccount.apiKey))
+          ..headers.deepEquals({
+            ...authHeader(email: eg.selfAccount.email, apiKey: eg.selfAccount.apiKey),
+            ...userAgentHeader(),
+          })
           ..body.equals('');
       });
     }
@@ -52,6 +55,7 @@ void main() {
           ..url.asString.equals('${eg.realmUrl.origin}/api/v1/example/route')
           ..headers.deepEquals({
             ...authHeader(email: eg.selfAccount.email, apiKey: eg.selfAccount.apiKey),
+            ...userAgentHeader(),
             if (expectContentType)
               'content-type': 'application/x-www-form-urlencoded; charset=utf-8',
           })
@@ -82,7 +86,10 @@ void main() {
         check(connection.lastRequest!).isA<http.MultipartRequest>()
           ..method.equals('POST')
           ..url.asString.equals('${eg.realmUrl.origin}/api/v1/example/route')
-          ..headers.deepEquals(authHeader(email: eg.selfAccount.email, apiKey: eg.selfAccount.apiKey))
+          ..headers.deepEquals({
+            ...authHeader(email: eg.selfAccount.email, apiKey: eg.selfAccount.apiKey),
+            ...userAgentHeader(),
+          })
           ..fields.deepEquals({})
           ..files.single.which((it) => it
             ..field.equals('file')
@@ -114,6 +121,7 @@ void main() {
           ..url.asString.equals('${eg.realmUrl.origin}/api/v1/example/route')
           ..headers.deepEquals({
             ...authHeader(email: eg.selfAccount.email, apiKey: eg.selfAccount.apiKey),
+            ...userAgentHeader(),
             if (expectContentType)
               'content-type': 'application/x-www-form-urlencoded; charset=utf-8',
           })

test/widgets/content_test.dart

@@ -306,13 +306,16 @@ void main() {
 
     testWidgets('includes auth header if `src` on-realm', (tester) async {
       check(await actualHeaders(tester, Uri.parse('https://chat.example/image.png')))
-        .deepEquals({'Authorization': [authHeaders['Authorization']!]});
+        .deepEquals({
+          'Authorization': [authHeaders['Authorization']!],
+          'User-Agent': [userAgentHeader()['User-Agent']!],
+        });
       debugNetworkImageHttpClientProvider = null;
     });
 
     testWidgets('excludes auth header if `src` off-realm', (tester) async {
       check(await actualHeaders(tester, Uri.parse('https://other.example/image.png')))
-        .deepEquals({});
+        .deepEquals({'User-Agent': [userAgentHeader()['User-Agent']!]});
       debugNetworkImageHttpClientProvider = null;
     });