compose: Display error for non-admin trying to post to announce_only stream.

Partially fixes #4708.
Implements a first version (v1) for the feature. The next step would be
to allow admins to toggle `is_announcement_only` in the UI.

frontend_tests/node_tests/compose.js

@@ -296,6 +296,33 @@ run_test('validate_stream_message', () => {
     assert($("#compose-all-everyone").visible());
 });
 
+run_test('test_validate_stream_message_announcement_only', () => {
+    // This test is in continuation with test_validate but it has been seperated out
+    // for better readabilty. Their relative position of execution should not be changed.
+    // Although the position with respect to test_validate_stream_message does not matter
+    // as `get_announcement_only` is reset at the end.
+    global.page_params.is_admin = false;
+    var sub = {
+        stream_id: 102,
+        name: 'stream102',
+        subscribed: true,
+        announcement_only: true,
+    };
+    stream_data.get_announcement_only = function () {
+        return true;
+    };
+    compose_state.subject('subject102');
+    stream_data.add_sub('stream102', sub);
+    assert(!compose.validate());
+    assert.equal($('#compose-error-msg').html(), i18n.t("Only organization admins are allowed to post to this stream."));
+
+    // reset `get_announcement_only` so that any tests occurung after this
+    // do not reproduce this error.
+    stream_data.get_announcement_only = function () {
+        return false;
+    };
+});
+
 run_test('markdown_shortcuts', () => {
     var queryCommandEnabled = true;
     var event = {

frontend_tests/node_tests/stream_data.js

@@ -32,6 +32,7 @@ run_test('basics', () => {
         stream_id: 2,
         in_home_view: true,
         invite_only: true,
+        is_announcement_only: true,
     };
     var test = {
         subscribed: true,
@@ -61,6 +62,9 @@ run_test('basics', () => {
 
     assert(stream_data.get_invite_only('social'));
     assert(!stream_data.get_invite_only('unknown'));
+    assert(stream_data.get_announcement_only('social'));
+    assert(!stream_data.get_announcement_only('unknown'));
+
     assert.equal(stream_data.get_color('social'), 'red');
     assert.equal(stream_data.get_color('unknown'), global.stream_color.default_color);
 

static/js/compose.js

@@ -511,6 +511,16 @@ function validate_stream_message_announce(stream_name) {
     return true;
 }
 
+function validate_stream_message_announcement_only(stream_name) {
+    // Only allow realm admins to post to announcement_only streams.
+    var is_announcement_only = stream_data.get_announcement_only(stream_name);
+    if (is_announcement_only && !page_params.is_admin) {
+        compose_error(i18n.t("Only organization admins are allowed to post to this stream."));
+        return false;
+    }
+    return true;
+}
+
 exports.validation_error = function (error_type, stream_name) {
     var response;
 
@@ -557,6 +567,10 @@ function validate_stream_message() {
         }
     }
 
+    if (!validate_stream_message_announcement_only(stream_name)) {
+        return false;
+    }
+
     // If both `@all` is mentioned and it's in `#announce`, just validate
     // for `@all`. Users shouldn't have to hit "yes" more than once.
     if (util.is_all_or_everyone_mentioned(compose_state.message_content()) &&

static/js/stream_data.js

@@ -276,6 +276,14 @@ exports.get_invite_only = function (stream_name) {
     return sub.invite_only;
 };
 
+exports.get_announcement_only = function (stream_name) {
+    var sub = exports.get_sub(stream_name);
+    if (sub === undefined) {
+        return false;
+    }
+    return sub.is_announcement_only;
+};
+
 var default_stream_ids = new Dict();
 
 exports.set_realm_default_streams = function (realm_default_streams) {