Add a schema checking concept to the web app.

This starts the concept of a schema checker, similar to
zerver/lib/validator.py on the server.  We can use this
to validate incoming data.  Our server should filter most
of our incoming data, but it's useful to have client-side
checking to defend against things like upgrade
regressions (i.e. what if we change the name of the field
on the server side without updating all client uses).

.eslintrc.json

@@ -10,6 +10,7 @@
         "$": false,
         "_": false,
         "run_test": false,
+        "schema": false,
         "jQuery": false,
         "Spinner": false,
         "Handlebars": false,

frontend_tests/node_tests/schema.js

@@ -0,0 +1,59 @@
+zrequire('schema');
+
+run_test('basics', () => {
+    assert.equal(schema.check_string('x', 'fred'), undefined);
+    assert.equal(schema.check_string('x', [1,2]), 'x is not a string');
+
+    const fields = {
+        foo: schema.check_string,
+        bar: schema.check_string,
+    };
+
+    const check_rec = (val) => {
+        return schema.check_record('my_rec', val, fields);
+    };
+
+    assert.equal(
+        check_rec({foo: 'apple', bar: 'banana'}),
+        undefined
+    );
+
+    assert.equal(
+        check_rec('bogus'),
+        'my_rec is not a record'
+    );
+
+    assert.equal(
+        check_rec({foo: 'apple'}),
+        'in my_rec bar is missing'
+    );
+
+    assert.equal(
+        check_rec({}),
+        'in my_rec bar is missing, foo is missing'
+    );
+
+    assert.equal(
+        check_rec({foo: 'apple', bar: 42}),
+        'in my_rec bar is not a string'
+    );
+
+    const check_array = (val) => {
+        return schema.check_array('lst', val, schema.check_string);
+    };
+
+    assert.equal(
+        check_array(['foo', 'bar']),
+        undefined
+    );
+
+    assert.equal(
+        check_array('foo'),
+        'lst is not an array'
+    );
+
+    assert.equal(
+        check_array(['foo', 3]),
+        'in lst we found an item where item is not a string'
+    );
+});

static/js/schema.js

@@ -0,0 +1,65 @@
+var schema = (function () {
+
+var exports = {};
+
+/*
+
+These runtime schema validators are defensive and
+should always succeed, so we don't necessarily want
+to translate these.  These are very similar to server
+side validators in zerver/lib/validator.py.
+
+*/
+
+exports.check_string = function (var_name, val) {
+    if (!_.isString(val)) {
+        return var_name + ' is not a string';
+    }
+};
+
+exports.check_record = function (var_name, val, fields) {
+    if (!_.isObject(val)) {
+        return var_name + ' is not a record';
+    }
+
+    var field_results = _.map(fields, function (f, field_name) {
+        if (val[field_name] === undefined) {
+            return field_name + ' is missing';
+        }
+        return f(field_name, val[field_name]);
+    });
+
+    var msg = _.filter(field_results).sort().join(', ');
+
+    if (msg) {
+        return 'in ' + var_name + ' ' + msg;
+    }
+};
+
+exports.check_array = function (var_name, val, checker) {
+    if (!_.isArray(val)) {
+        return var_name + ' is not an array';
+    }
+
+    var msg;
+
+    _.find(val, function (item) {
+        var res = checker('item', item);
+
+        if (res) {
+            msg = res;
+            return msg;
+        }
+    });
+
+    if (msg) {
+        return 'in ' + var_name + ' we found an item where ' + msg;
+    }
+};
+
+return exports;
+
+}());
+if (typeof module !== 'undefined') {
+    module.exports = schema;
+}

tools/test-js-with-node

@@ -54,6 +54,7 @@ enforce_fully_covered = {
     'static/js/reactions.js',
     'static/js/recent_senders.js',
     'static/js/rtl.js',
+    'static/js/schema.js',
     'static/js/scroll_util.js',
     'static/js/search_suggestion.js',
     # Removed because we're migrating code from uncovered other settings pages to here.

zproject/settings.py

@@ -929,6 +929,7 @@ JS_SPECS = {
             'templates/compiled.js',
             'js/feature_flags.js',
             'js/loading.js',
+            'js/schema.js',
             'js/util.js',
             'js/keydown_util.js',
             'js/lightbox_canvas.js',