feat(http2_channel.dart): add support for prefixPath in ClientChannel…

… to allow setting a prefix path for all requests

feat(http2_connection.dart): add support for prefixPath in Http2ClientConnection to include a prefix path in request paths
feat(xhr_transport.dart): update requestUri construction to include prefixPath in XhrClientConnection
feat(web_channel.dart): add validation for prefixPath in GrpcWebClientChannel to ensure it starts and ends with /

lib/src/client/http2_channel.dart

@@ -30,18 +30,23 @@ class ClientChannel extends ClientChannelBase {
   /// case it can be a Unix Domain Socket address.
   final Object host;
   final int port;
+  final String prefixPath;
   final ChannelOptions options;
 
   ClientChannel(
     this.host, {
     this.port = 443,
+    this.prefixPath = '',
     this.options = const ChannelOptions(),
     super.channelShutdownHandler,
-  });
+  }) : assert(
+            prefixPath.isEmpty ||
+                prefixPath.isNotEmpty && !prefixPath.endsWith('/'),
+            'prefixPath must be empty or does not start and end with /');
 
   @override
   ClientConnection createConnection() =>
-      Http2ClientConnection(host, port, options);
+      Http2ClientConnection(host, port, options, prefixPath: '/$prefixPath');
 }
 
 class ClientTransportConnectorChannel extends ClientChannelBase {

lib/src/client/http2_connection.dart

@@ -62,11 +62,15 @@ class Http2ClientConnection implements connection.ClientConnection {
 
   ClientKeepAlive? keepAliveManager;
 
-  Http2ClientConnection(Object host, int port, this.options)
+  final String prefixPath;
+
+  Http2ClientConnection(Object host, int port, this.options,
+      {this.prefixPath = ''})
       : _transportConnector = SocketTransportConnector(host, port, options);
 
   Http2ClientConnection.fromClientTransportConnector(
-      this._transportConnector, this.options);
+      this._transportConnector, this.options,
+      {this.prefixPath = ''});
 
   ChannelCredentials get credentials => options.credentials;
 
@@ -178,7 +182,7 @@ class Http2ClientConnection implements connection.ClientConnection {
     final headers = createCallHeaders(
       credentials.isSecure,
       _transportConnector.authority,
-      path,
+      prefixPath + path,
       timeout,
       metadata,
       compressionCodec,

lib/src/client/transport/xhr_transport.dart

@@ -180,12 +180,7 @@ class XhrClientConnection implements ClientConnection {
       metadata['X-Grpc-Web'] = '1';
     }
 
-    if (prefixPath.isNotEmpty && prefixPath.endsWith('/')) {
-      throw ArgumentError.value(
-          prefixPath, 'prefixPath', 'must not end with a slash');
-    }
-
-    var requestUri = uri.resolve('$prefixPath$path');
+    var requestUri = uri.resolve(prefixPath + path);
     if (callOptions is WebCallOptions &&
         callOptions.bypassCorsPreflight == true) {
       requestUri = cors.moveHttpHeadersToQueryParam(metadata, requestUri);

lib/src/client/web_channel.dart

@@ -25,7 +25,11 @@ class GrpcWebClientChannel extends ClientChannelBase {
   final String prefixPath;
 
   GrpcWebClientChannel.xhr(this.uri,
-      {this.prefixPath = '', super.channelShutdownHandler});
+      {this.prefixPath = '', super.channelShutdownHandler})
+      : assert(
+            prefixPath.isEmpty ||
+                prefixPath.isNotEmpty && !prefixPath.endsWith('/'),
+            'prefixPath must be empty or does not start and end with /');
 
   @override
   ClientConnection createConnection() {