feat: Add vscodeipc subcommand for VS Code Extension (#5326)

* Add extio

* feat: Add `vscodeipc` subcommand for VS Code Extension

This enables the VS Code extension to communicate with a Coder client.
The extension will download the slim binary from `/bin/*` for the
respective client architecture and OS, then execute `coder vscodeipc`
for the connecting workspace.

* Add authentication header, improve comments, and add tests for the CLI

* Update cli/vscodeipc_test.go

Co-authored-by: Mathias Fredriksson <mafredri@gmail.com>

* Update cli/vscodeipc_test.go

Co-authored-by: Mathias Fredriksson <mafredri@gmail.com>

* Update cli/vscodeipc/vscodeipc_test.go

Co-authored-by: Mathias Fredriksson <mafredri@gmail.com>

* Fix requested changes

* Fix IPC tests

* Fix shell execution

* Fix nix flake

* Silence usage

Co-authored-by: Mathias Fredriksson <mafredri@gmail.com>

cli/vscodeipc.go

@@ -0,0 +1,88 @@
+package cli
+
+import (
+	"fmt"
+	"net"
+	"net/http"
+	"net/url"
+
+	"github.com/google/uuid"
+	"github.com/spf13/cobra"
+	"golang.org/x/xerrors"
+
+	"github.com/coder/coder/cli/cliflag"
+	"github.com/coder/coder/cli/vscodeipc"
+	"github.com/coder/coder/codersdk"
+)
+
+// vscodeipcCmd spawns a local HTTP server on the provided port that listens to messages.
+// It's made for use by the Coder VS Code extension. See: https://github.com/coder/vscode-coder
+func vscodeipcCmd() *cobra.Command {
+	var (
+		rawURL string
+		token  string
+		port   uint16
+	)
+	cmd := &cobra.Command{
+		Use:          "vscodeipc <workspace-agent>",
+		Args:         cobra.ExactArgs(1),
+		SilenceUsage: true,
+		Hidden:       true,
+		RunE: func(cmd *cobra.Command, args []string) error {
+			if rawURL == "" {
+				return xerrors.New("CODER_URL must be set!")
+			}
+			// token is validated in a header on each request to prevent
+			// unauthenticated clients from connecting.
+			if token == "" {
+				return xerrors.New("CODER_TOKEN must be set!")
+			}
+			listener, err := net.Listen("tcp", fmt.Sprintf("127.0.0.1:%d", port))
+			if err != nil {
+				return xerrors.Errorf("listen: %w", err)
+			}
+			defer listener.Close()
+			addr, ok := listener.Addr().(*net.TCPAddr)
+			if !ok {
+				return xerrors.Errorf("listener.Addr() is not a *net.TCPAddr: %T", listener.Addr())
+			}
+			url, err := url.Parse(rawURL)
+			if err != nil {
+				return err
+			}
+			agentID, err := uuid.Parse(args[0])
+			if err != nil {
+				return err
+			}
+			client := codersdk.New(url)
+			client.SetSessionToken(token)
+
+			handler, closer, err := vscodeipc.New(cmd.Context(), client, agentID, nil)
+			if err != nil {
+				return err
+			}
+			defer closer.Close()
+			// nolint:gosec
+			server := http.Server{
+				Handler: handler,
+			}
+			defer server.Close()
+			_, _ = fmt.Fprintf(cmd.OutOrStdout(), "%s\n", addr.String())
+			errChan := make(chan error, 1)
+			go func() {
+				err := server.Serve(listener)
+				errChan <- err
+			}()
+			select {
+			case <-cmd.Context().Done():
+				return cmd.Context().Err()
+			case err := <-errChan:
+				return err
+			}
+		},
+	}
+	cliflag.StringVarP(cmd.Flags(), &rawURL, "url", "u", "CODER_URL", "", "The URL of the Coder instance!")
+	cliflag.StringVarP(cmd.Flags(), &token, "token", "t", "CODER_TOKEN", "", "The session token of the user!")
+	cmd.Flags().Uint16VarP(&port, "port", "p", 0, "The port to listen on!")
+	return cmd
+}