fix: support bracketed IPv6 runtime URLs

dotnet/src/Client.cs

@@ -177,7 +177,7 @@ public CopilotClient(CopilotClientOptions? options = null)
                     throw new ArgumentException("GitHubToken and UseLoggedInUser cannot be combined with RuntimeConnection.ForUri (the existing runtime manages its own auth).", nameof(options));
                 }
                 var parsed = ParseRuntimeUrl(uri.Url);
-                _optionsHost = parsed.Host;
+                _optionsHost = parsed.Host.Trim('[', ']');
                 _optionsPort = parsed.Port;
                 break;
 
@@ -308,7 +308,7 @@ private static RuntimeConnection ResolveDefaultConnection(CopilotClientOptions o
     /// <summary>
     /// Parses a runtime URL into a URI with host and port.
     /// </summary>
-    /// <param name="url">The URL to parse. Supports formats: "port", "host:port", "http://host:port".</param>
+    /// <param name="url">The URL to parse. Supports formats: "port", "host:port", "[ipv6]:port", "http://host:port".</param>
     private static Uri ParseRuntimeUrl(string url)
     {
         // If it's just a port number, treat as localhost

dotnet/test/Unit/RuntimeConnectionUrlParsingTests.cs

@@ -0,0 +1,42 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *--------------------------------------------------------------------------------------------*/
+
+using Xunit;
+using System.Reflection;
+
+namespace GitHub.Copilot.Test.Unit;
+
+public class RuntimeConnectionUrlParsingTests
+{
+    [Fact]
+    public void ForUri_ParsesBracketedIpv6HostPort()
+    {
+        var client = new CopilotClient(new CopilotClientOptions
+        {
+            Connection = RuntimeConnection.ForUri("[::1]:9000")
+        });
+
+        Assert.Equal("::1", GetPrivateField<string>(client, "_optionsHost"));
+        Assert.Equal(9000, GetPrivateField<int?>(client, "_optionsPort"));
+    }
+
+    [Fact]
+    public void ForUri_ParsesHttpIpv6HostPort()
+    {
+        var client = new CopilotClient(new CopilotClientOptions
+        {
+            Connection = RuntimeConnection.ForUri("http://[::1]:7000")
+        });
+
+        Assert.Equal("::1", GetPrivateField<string>(client, "_optionsHost"));
+        Assert.Equal(7000, GetPrivateField<int?>(client, "_optionsPort"));
+    }
+
+    private static T? GetPrivateField<T>(object instance, string name)
+    {
+        var field = instance.GetType().GetField(name, BindingFlags.Instance | BindingFlags.NonPublic);
+        Assert.NotNull(field);
+        return (T?)field.GetValue(instance);
+    }
+}

go/client.go

@@ -36,6 +36,7 @@ import (
 	"fmt"
 	"log"
 	"net"
+	"net/netip"
 	"os"
 	"os/exec"
 	"path/filepath"
@@ -401,29 +402,45 @@ func setEnvValue(env []string, key string, value string) []string {
 
 // parseCLIURL parses a CLI URL into host and port components.
 //
-// Supports formats: "host:port", "http://host:port", "https://host:port", or just "port".
+// Supports formats: "host:port", "[ipv6]:port", "http://host:port", "https://host:port", or just "port".
 // Panics if the URL format is invalid or the port is out of range.
 func parseCLIURL(url string) (string, int) {
 	// Remove protocol if present
 	cleanURL, _ := strings.CutPrefix(url, "https://")
 	cleanURL, _ = strings.CutPrefix(cleanURL, "http://")
 
+	// Use the standard parser only for the bracketed IPv6 form. Keep the
+	// existing host:port parsing behavior for all other inputs.
+	if strings.HasPrefix(cleanURL, "[") {
+		host, portStr, err := net.SplitHostPort(cleanURL)
+		if err != nil {
+			panic(fmt.Sprintf("Invalid port in URIConnection: %s", url))
+		}
+		addr, err := netip.ParseAddr(host)
+		if err != nil || !addr.Is6() {
+			panic(fmt.Sprintf("Invalid URIConnection format: %s", url))
+		}
+		port, err := strconv.Atoi(portStr)
+		if err != nil || port <= 0 || port > 65535 {
+			panic(fmt.Sprintf("Invalid port in URIConnection: %s", url))
+		}
+		return host, port
+	}
+
 	// Parse host:port or port format
 	var host string
 	var portStr string
 	if before, after, found := strings.Cut(cleanURL, ":"); found {
 		host = before
 		portStr = after
 	} else {
-		// Only port provided
-		portStr = before
+		portStr = cleanURL
 	}
 
 	if host == "" {
 		host = "localhost"
 	}
 
-	// Validate port
 	port, err := strconv.Atoi(portStr)
 	if err != nil || port <= 0 || port > 65535 {
 		panic(fmt.Sprintf("Invalid port in URIConnection: %s", url))

go/client_test.go

@@ -78,6 +78,15 @@ func TestClient_URLParsing(t *testing.T) {
 		}
 	})
 
+	t.Run("should parse bracketed IPv6 host:port URL format", func(t *testing.T) {
+		client := NewClient(&ClientOptions{
+			Connection: URIConnection{URL: "[::1]:9000"},
+		})
+		if client.actualPort != 9000 || client.actualHost != "::1" {
+			t.Errorf("Expected [::1]:9000, got %s:%d", client.actualHost, client.actualPort)
+		}
+	})
+
 	t.Run("should parse http://host:port URL format", func(t *testing.T) {
 		client := NewClient(&ClientOptions{
 			Connection: URIConnection{URL: "http://localhost:7000"},
@@ -87,6 +96,24 @@ func TestClient_URLParsing(t *testing.T) {
 		}
 	})
 
+	t.Run("should parse http://[ipv6]:port URL format", func(t *testing.T) {
+		client := NewClient(&ClientOptions{
+			Connection: URIConnection{URL: "http://[::1]:7000"},
+		})
+		if client.actualPort != 7000 || client.actualHost != "::1" {
+			t.Errorf("Expected [::1]:7000, got %s:%d", client.actualHost, client.actualPort)
+		}
+	})
+
+	t.Run("should panic for bracketed non-IPv6 host", func(t *testing.T) {
+		defer func() {
+			if r := recover(); r == nil {
+				t.Error("Expected panic for invalid bracketed host")
+			}
+		}()
+		NewClient(&ClientOptions{Connection: URIConnection{URL: "[not-ipv6]:1234"}})
+	})
+
 	t.Run("should parse https://host:port URL format", func(t *testing.T) {
 		client := NewClient(&ClientOptions{
 			Connection: URIConnection{URL: "https://example.com:443"},

java/sdk/src/main/java/com/github/copilot/CopilotClient.java

@@ -221,7 +221,10 @@ public CopilotClient(CopilotClientOptions options) {
         // Parse CliUrl if provided
         if (this.options.getCliUrl() != null && !this.options.getCliUrl().isEmpty()) {
             URI uri = CliServerManager.parseCliUrl(this.options.getCliUrl());
-            this.optionsHost = uri.getHost();
+            String host = uri.getHost();
+            this.optionsHost = host != null && host.startsWith("[") && host.endsWith("]")
+                    ? host.substring(1, host.length() - 1)
+                    : host;
             this.optionsPort = uri.getPort();
         } else {
             this.optionsHost = null;

java/sdk/src/test/java/com/github/copilot/CliServerManagerTest.java

@@ -93,6 +93,13 @@ void parseCliUrlWithHttpsPrefix() {
         assertEquals("https://secure.host:443", uri.toString());
     }
 
+    @Test
+    void parseCliUrlWithBracketedIpv6() {
+        URI uri = CliServerManager.parseCliUrl("[::1]:4321");
+        assertNotNull(uri.getHost());
+        assertEquals(4321, uri.getPort());
+    }
+
     @Test
     void parseCliUrlWithHostOnly() {
         URI uri = CliServerManager.parseCliUrl("copilot.example.com");

java/sdk/src/test/java/com/github/copilot/CopilotClientTest.java

@@ -179,6 +179,15 @@ void testCliUrlOnlyConstruction() {
         client.close();
     }
 
+    @Test
+    void testBracketedIpv6CliUrlNormalizesHost() throws Exception {
+        try (var client = new CopilotClient(new CopilotClientOptions().setCliUrl("[::1]:4321"))) {
+            Field hostField = CopilotClient.class.getDeclaredField("optionsHost");
+            hostField.setAccessible(true);
+            assertEquals("::1", hostField.get(client));
+        }
+    }
+
     @Test
     void testCliUrlMutualExclusionWithCliPath() {
         var options = new CopilotClientOptions().setCliUrl("localhost:3000").setCliPath("/path/to/cli");

nodejs/src/client.ts

@@ -14,7 +14,7 @@
 import { spawn, type ChildProcess } from "node:child_process";
 import { randomUUID } from "node:crypto";
 import { existsSync } from "node:fs";
-import { Socket } from "node:net";
+import { isIPv6, Socket } from "node:net";
 import { dirname, isAbsolute, join, resolve } from "node:path";
 import {
     createMessageConnection,
@@ -748,22 +748,38 @@ export class CopilotClient {
 
     /**
      * Parse CLI URL into host and port
-     * Supports formats: "host:port", "http://host:port", "https://host:port", or just "port"
+     * Supports formats: "host:port", "[ipv6]:port", "http://host:port", "https://host:port", or just "port"
      */
     private parseCliUrl(url: string): { host: string; port: number } {
         // Remove protocol if present
-        let cleanUrl = url.replace(/^https?:\/\//, "");
+        const cleanUrl = url.replace(/^https?:\/\//, "");
 
         // Check if it's just a port number
         if (/^\d+$/.test(cleanUrl)) {
             return { host: "localhost", port: parseInt(cleanUrl, 10) };
         }
 
+        // Handle the canonical bracketed IPv6 host:port form without changing
+        // the existing parser behavior for other inputs.
+        const ipv6Match = cleanUrl.match(/^\[([^\]]+)\]:(\d+)$/);
+        if (ipv6Match) {
+            const host = ipv6Match[1];
+            if (!isIPv6(host)) {
+                throw new Error(`Invalid cliUrl format: ${url}`);
+            }
+
+            const port = parseInt(ipv6Match[2], 10);
+            if (isNaN(port) || port <= 0 || port > 65535) {
+                throw new Error(`Invalid port in cliUrl: ${url}`);
+            }
+            return { host, port };
+        }
+
         // Parse host:port format
         const parts = cleanUrl.split(":");
         if (parts.length !== 2) {
             throw new Error(
-                `Invalid cliUrl format: ${url}. Expected "host:port", "http://host:port", or "port"`
+                `Invalid cliUrl format: ${url}. Expected "host:port", "[ipv6]:port", "http://host:port", or "port"`
             );
         }
 

nodejs/test/client.test.ts

@@ -2627,6 +2627,17 @@ describe("CopilotClient", () => {
             expect((client as any).isExternalServer).toBe(true);
         });
 
+        it("should parse bracketed IPv6 host:port URL format", () => {
+            const client = new CopilotClient({
+                connection: RuntimeConnection.forUri("[::1]:9000"),
+                logLevel: "error",
+            });
+
+            expect((client as any).runtimePort).toBe(9000);
+            expect((client as any).actualHost).toBe("::1");
+            expect((client as any).isExternalServer).toBe(true);
+        });
+
         it("should parse http://host:port URL format", () => {
             const client = new CopilotClient({
                 connection: RuntimeConnection.forUri("http://localhost:7000"),
@@ -2638,6 +2649,26 @@ describe("CopilotClient", () => {
             expect((client as any).isExternalServer).toBe(true);
         });
 
+        it("should parse http://[ipv6]:port URL format", () => {
+            const client = new CopilotClient({
+                connection: RuntimeConnection.forUri("http://[::1]:7000"),
+                logLevel: "error",
+            });
+
+            expect((client as any).runtimePort).toBe(7000);
+            expect((client as any).actualHost).toBe("::1");
+            expect((client as any).isExternalServer).toBe(true);
+        });
+
+        it("should reject a bracketed non-IPv6 host", () => {
+            expect(() => {
+                new CopilotClient({
+                    connection: RuntimeConnection.forUri("[not-ipv6]:1234"),
+                    logLevel: "error",
+                });
+            }).toThrow(/Invalid cliUrl format/);
+        });
+
         it("should parse https://host:port URL format", () => {
             const client = new CopilotClient({
                 connection: RuntimeConnection.forUri("https://example.com:443"),

python/copilot/client.py

@@ -16,6 +16,7 @@
 
 import asyncio
 import inspect
+import ipaddress
 import logging
 import os
 import re
@@ -1838,8 +1839,8 @@ def _parse_cli_url(self, url: str) -> tuple[str, int]:
         """
         Parse CLI URL into host and port.
 
-        Supports formats: "host:port", "http://host:port", "https://host:port",
-        or just "port".
+        Supports formats: "host:port", "[ipv6]:port", "http://host:port",
+        "https://host:port", or just "port".
 
         Args:
             url: The CLI URL to parse.
@@ -1850,9 +1851,6 @@ def _parse_cli_url(self, url: str) -> tuple[str, int]:
         Raises:
             ValueError: If the URL format is invalid or the port is out of range.
         """
-        import re
-
-        # Remove protocol if present
         clean_url = re.sub(r"^https?://", "", url)
 
         # Check if it's just a port number
@@ -1862,14 +1860,24 @@ def _parse_cli_url(self, url: str) -> tuple[str, int]:
                 raise ValueError(f"Invalid port in cli_url: {url}")
             return ("localhost", port)
 
-        # Parse host:port format
-        parts = clean_url.split(":")
-        if len(parts) != 2:
-            raise ValueError(f"Invalid cli_url format: {url}")
+        ipv6_match = re.match(r"^\[([^\]]+)\]:(.*)$", clean_url)
+        if ipv6_match:
+            host = ipv6_match.group(1)
+            port_text = ipv6_match.group(2)
+            try:
+                ipaddress.IPv6Address(host)
+            except ValueError as e:
+                raise ValueError(f"Invalid cli_url format: {url}") from e
+        else:
+            # Parse host:port format
+            parts = clean_url.split(":")
+            if len(parts) != 2:
+                raise ValueError(f"Invalid cli_url format: {url}")
+            host = parts[0] if parts[0] else "localhost"
+            port_text = parts[1]
 
-        host = parts[0] if parts[0] else "localhost"
         try:
-            port = int(parts[1])
+            port = int(port_text)
         except ValueError as e:
             raise ValueError(f"Invalid port in cli_url: {url}") from e
 
@@ -4631,22 +4639,22 @@ async def _connect_via_tcp(self) -> None:
         if not self._runtime_port:
             raise RuntimeError("Server port not available")
 
-        # Create a TCP socket connection with timeout
+        # Create a TCP socket connection with timeout. create_connection resolves
+        # both IPv4 and IPv6 addresses instead of forcing AF_INET.
         import socket
 
         # Connection timeout constant
         TCP_CONNECTION_TIMEOUT = 10  # seconds
 
-        sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
-        sock.settimeout(TCP_CONNECTION_TIMEOUT)
-
         try:
             tcp_connect_start = time.perf_counter()
             logger.info(
                 "CopilotClient._connect_via_tcp connecting to CLI server",
                 extra={"host": self._actual_host, "port": self._runtime_port},
             )
-            sock.connect((self._actual_host, self._runtime_port))
+            sock = socket.create_connection(
+                (self._actual_host, self._runtime_port), timeout=TCP_CONNECTION_TIMEOUT
+            )
             sock.settimeout(None)  # Remove timeout after connection
             log_timing(
                 logger,