Bind and connect to Unix domain sockets using relative paths (#1192)

Author: edigaryev

Sources/tart/Commands/Exec.swift

@@ -47,8 +47,16 @@ struct Exec: AsyncParsableCommand {
       try! group.syncShutdownGracefully()
     }
 
+    // Change the current working directory to a VM's base directory
+    // to work around Unix domain socket 104 byte limitation [1]
+    //
+    // [1]: https://blog.8-p.info/en/2020/06/11/unix-domain-socket-length/
+    if let baseURL = vmDir.controlSocketURL.baseURL {
+      FileManager.default.changeCurrentDirectoryPath(baseURL.path())
+    }
+
     let channel = try GRPCChannelPool.with(
-      target: .unixDomainSocket(vmDir.controlSocketURL.path()),
+      target: .unixDomainSocket(vmDir.controlSocketURL.relativePath),
       transportSecurity: .plaintext,
       eventLoopGroup: group,
     )

Sources/tart/Commands/IP.swift

@@ -68,7 +68,15 @@ struct IP: AsyncParsableCommand {
           throw RuntimeError.Generic("Cannot perform IP resolution via Tart Guest Agent when control socket URL is not set")
         }
 
-        if let ip = try await AgentResolver.ResolveIP(controlSocketURL) {
+        // Change the current working directory to a VM's base directory
+        // to work around Unix domain socket 104 byte limitation [1]
+        //
+        // [1]: https://blog.8-p.info/en/2020/06/11/unix-domain-socket-length/
+        if let baseURL = controlSocketURL.baseURL {
+          FileManager.default.changeCurrentDirectoryPath(baseURL.path())
+        }
+
+        if let ip = try await AgentResolver.ResolveIP(controlSocketURL.relativePath) {
           return ip
         }
       }

Sources/tart/ControlSocket.swift

@@ -21,8 +21,16 @@ class ControlSocket {
     // if any, otherwise we may get the "address already in use" error
     try? FileManager.default.removeItem(atPath: controlSocketURL.path())
 
+    // Change the current working directory to a VM's base directory
+    // to work around Unix domain socket 104 byte limitation [1]
+    //
+    // [1]: https://blog.8-p.info/en/2020/06/11/unix-domain-socket-length/
+    if let baseURL = controlSocketURL.baseURL {
+      FileManager.default.changeCurrentDirectoryPath(baseURL.path())
+    }
+
     let serverChannel = try await ServerBootstrap(group: eventLoopGroup)
-      .bind(unixDomainSocketPath: controlSocketURL.path()) { childChannel in
+      .bind(unixDomainSocketPath: controlSocketURL.relativePath) { childChannel in
         childChannel.eventLoop.makeCompletedFuture {
           return try NIOAsyncChannel<ByteBuffer, ByteBuffer>(
             wrappingChannelSynchronously: childChannel

Sources/tart/MACAddressResolver/AgentResolver.swift

@@ -6,23 +6,23 @@ import Cirruslabs_TartGuestAgent_Apple_Swift
 import Cirruslabs_TartGuestAgent_Grpc_Swift
 
 class AgentResolver {
-  static func ResolveIP(_ controlSocketURL: URL) async throws -> IPv4Address? {
+  static func ResolveIP(_ controlSocketPath: String) async throws -> IPv4Address? {
     do {
-      return try await resolveIP(controlSocketURL)
+      return try await resolveIP(controlSocketPath)
     } catch let error as GRPCConnectionPoolError {
       return nil
     }
   }
 
-  private static func resolveIP(_ controlSocketURL: URL) async throws -> IPv4Address? {
+  private static func resolveIP(_ controlSocketPath: String) async throws -> IPv4Address? {
     // Create a gRPC channel connected to the VM's control socket
     let group = MultiThreadedEventLoopGroup(numberOfThreads: 1)
     defer {
       try! group.syncShutdownGracefully()
     }
 
     let channel = try GRPCChannelPool.with(
-      target: .unixDomainSocket(controlSocketURL.path()),
+      target: .unixDomainSocket(controlSocketPath),
       transportSecurity: .plaintext,
       eventLoopGroup: group,
     )

Sources/tart/VMDirectory.swift

@@ -27,7 +27,7 @@ struct VMDirectory: Prunable {
     baseURL.appendingPathComponent("manifest.json")
   }
   var controlSocketURL: URL {
-    baseURL.appendingPathComponent("control.sock")
+    URL(fileURLWithPath: "control.sock", relativeTo: baseURL)
   }
 
   var explicitlyPulledMark: URL {