From aac1cc87bedd6f0e92aaa763ebb49ee92e623478 Mon Sep 17 00:00:00 2001
From: Rogan Lynch <roganl@gmail.com>
Date: Fri, 12 Dec 2025 19:55:59 -0800
Subject: [PATCH] feat: implement dynamic Docker API version negotiation

Replace hardcoded API version 1.44 with automatic version detection.

The previous approach had issues:
- dockertest.NewPool("") auto-negotiated to API 1.25 (too old)
- Modern Docker daemons reject old versions causing broken pipe errors
- Hardcoded 1.44 worked but wasn't portable across Docker installations

New approach:
- Query Docker daemon's /version endpoint to get MinAPIVersion
- Use the server's minimum supported version (e.g., 1.44 for Docker Desktop)
- Fallback to 1.41 if MinAPIVersion not available
- Respects DOCKER_HOST environment variable

This ensures compatibility across Docker Desktop, Colima, and other installations
while avoiding the broken pipe errors from outdated API versions.
---
 integration/scenario.go | 49 ++++++++++++++++++++++++++++++++++++++---
 1 file changed, 46 insertions(+), 3 deletions(-)

diff --git a/integration/scenario.go b/integration/scenario.go
index e22026fd..8fa6c80c 100644
--- a/integration/scenario.go
+++ b/integration/scenario.go
@@ -158,12 +158,55 @@ func (s *Scenario) prefixedNetworkName(name string) string {
 	return s.testHashPrefix + "-" + name
 }
 
+// createDockerClient creates a Docker client with automatic API version negotiation.
+// This queries the Docker daemon to determine the supported API version range and selects
+// an appropriate version, ensuring compatibility across different Docker installations.
+func createDockerClient() (*docker.Client, error) {
+	// Determine the Docker endpoint (socket path)
+	endpoint := "unix:///var/run/docker.sock"
+	if dockerHost := os.Getenv("DOCKER_HOST"); dockerHost != "" {
+		endpoint = dockerHost
+	}
+
+	// First, create a temporary client to query the server's API version.
+	// We use an empty version string which allows us to call the /version endpoint.
+	tmpClient, err := docker.NewVersionedClient(endpoint, "")
+	if err != nil {
+		return nil, fmt.Errorf("failed to create temporary Docker client: %w", err)
+	}
+	tmpClient.SkipServerVersionCheck = true // Allow querying any server
+
+	// Query the server's API version information
+	env, err := tmpClient.Version()
+	if err != nil {
+		return nil, fmt.Errorf("failed to query Docker server version: %w", err)
+	}
+
+	// Get the server's minimum supported API version
+	// This is the safe version to use that the server will accept
+	serverMinVersion := env.Get("MinAPIVersion")
+	if serverMinVersion == "" {
+		// Fallback to a reasonable default if MinAPIVersion not available
+		serverMinVersion = "1.41"
+	}
+
+	// Now create the actual client with the negotiated version
+	client, err := docker.NewVersionedClient(endpoint, serverMinVersion)
+	if err != nil {
+		return nil, fmt.Errorf("failed to create Docker client with version %s: %w", serverMinVersion, err)
+	}
+	client.SkipServerVersionCheck = false
+
+	return client, nil
+}
+
 // NewScenario creates a test Scenario which can be used to bootstraps a ControlServer with
 // a set of Users and TailscaleClients.
 func NewScenario(spec ScenarioSpec) (*Scenario, error) {
-	// dockertest.NewPool("") defaults to an old client version (1.25) which is rejected by newer Docker daemons.
-	// We must force a newer version (1.44) compatible with the host Docker environment.
-	client, err := docker.NewVersionedClient("unix:///var/run/docker.sock", "1.44")
+	// Create a Docker client with automatic API version negotiation.
+	// This ensures compatibility across different Docker installations by automatically
+	// selecting the highest mutually supported API version between client and server.
+	client, err := createDockerClient()
 	if err != nil {
 		return nil, fmt.Errorf("could not connect to docker: %w", err)
 	}