fix parsing of read preference tags

Author: baileympearson

src/connection_string.ts

@@ -228,7 +228,7 @@ function toRecord(value: string): Record<string, any> {
   return record;
 }
 
-class CaseInsensitiveMap extends Map<string, any> {
+class CaseInsensitiveMap<Value = any> extends Map<string, Value> {
   constructor(entries: Array<[string, any]> = []) {
     super(entries.map(([k, v]) => [k.toLowerCase(), v]));
   }
@@ -262,7 +262,7 @@ export function parseOptions(
   const mongoOptions = Object.create(null);
   mongoOptions.hosts = isSRV ? [] : hosts.map(HostAddress.fromString);
 
-  const urlOptions = new CaseInsensitiveMap();
+  const urlOptions = new CaseInsensitiveMap<any[]>();
 
   if (url.pathname !== '/' && url.pathname !== '') {
     const dbName = decodeURIComponent(
@@ -326,13 +326,16 @@ export function parseOptions(
   for (const key of allKeys) {
     const values = [];
     if (objectOptions.has(key)) {
-      values.push(objectOptions.get(key));
+      const options = [objectOptions.get(key)].flat();
+      values.push(...options);
     }
     if (urlOptions.has(key)) {
-      values.push(...urlOptions.get(key));
+      const options = urlOptions.get(key) ?? [];
+      values.push(...options);
     }
     if (DEFAULT_OPTIONS.has(key)) {
-      values.push(DEFAULT_OPTIONS.get(key));
+      const options = [DEFAULT_OPTIONS.get(key)].flat();
+      values.push(...options);
     }
     allOptions.set(key, values);
   }
@@ -478,12 +481,11 @@ export function parseOptions(
     throw new MongoParseError('Can only specify both of proxy username/password or neither');
   }
 
-  if (
-    urlOptions.get('proxyHost')?.length > 1 ||
-    urlOptions.get('proxyPort')?.length > 1 ||
-    urlOptions.get('proxyUsername')?.length > 1 ||
-    urlOptions.get('proxyPassword')?.length > 1
-  ) {
+  const proxyOptions = ['proxyHost', 'proxyPort', 'proxyUsername', 'proxyPassword'].map(
+    key => urlOptions.get(key) ?? []
+  );
+
+  if (proxyOptions.some(options => options.length > 1)) {
     throw new MongoParseError(
       'Proxy options cannot be specified multiple times in the connection string'
     );

test/unit/connection_string.test.ts

@@ -46,11 +46,20 @@ describe('Connection String', function () {
     expect(options.hosts[0].port).to.equal(27017);
   });
 
-  it('should parse multiple readPreferenceTags', function () {
-    const options = parseOptions(
-      'mongodb://hostname?readPreferenceTags=bar:foo&readPreferenceTags=baz:bar'
-    );
-    expect(options.readPreference.tags).to.deep.equal([{ bar: 'foo' }, { baz: 'bar' }]);
+  context('readPreferenceTags', function () {
+    it('should parse multiple readPreferenceTags when passed in the uri', () => {
+      const options = parseOptions(
+        'mongodb://hostname?readPreferenceTags=bar:foo&readPreferenceTags=baz:bar'
+      );
+      expect(options.readPreference.tags).to.deep.equal([{ bar: 'foo' }, { baz: 'bar' }]);
+    });
+
+    it('should parse multiple readPreferenceTags when passed in options object', () => {
+      const options = parseOptions('mongodb://hostname?', {
+        readPreferenceTags: [{ bar: 'foo' }, { baz: 'bar' }]
+      });
+      expect(options.readPreference.tags).to.deep.equal([{ bar: 'foo' }, { baz: 'bar' }]);
+    });
   });
 
   it('should parse boolean values', function () {