feat: add GITEA_DOCKER_WORKSPACE and container cleanup (#1204)

1. Add `GITEA_DOCKER_WORKSPACE` which holds the workspace path as the daemon sees it, enabling `${GITEA_DOCKER_WORKSPACE:-.}/data:/app/data` in a compose file without having to resort to `bind_workdir` (which causes much more problems like breaking `actions/cache` because of unstable workspace paths).
2. Add container/network/volume cleanup for containers started within jobs, for example via `docker compose` inside a job. It works by running a lightweight docker socket proxy and injecting a `com.gitea.runner.job` label into every container creation and that label is used to remove containers started by that job at the end. Perf impact of this is near-zero.

Docs: https://gitea.com/gitea/docs/pulls/535

Assisted by Claude (Fable 5.1).
Co-authored-by: bircni <bircni@icloud.com>
Reviewed-on: https://gitea.com/gitea/runner/pulls/1204
Reviewed-by: bircni <bircni@icloud.com>
Co-authored-by: silverwind <me@silverwind.io>

README.md

@@ -266,6 +266,17 @@ A job in a container reaches a service by its id on the job network, on the port
 
 Unlike GitHub, a job whose steps run on the host (a `host` label without `container:`) starts no service containers, so `job.services` and `job.container` stay empty. Give such a job a `container:` when it needs services.
 
+#### Docker from a job (`GITEA_DOCKER_WORKSPACE`)
+
+A container a job starts through the Docker socket cannot bind-mount the workspace by the job's own path, the daemon does not have it. `GITEA_DOCKER_WORKSPACE` holds the path the daemon sees. Use it as the prefix of workspace binds, with `.` as the fallback for local use, here in a `docker-compose.yaml`:
+
+```yaml
+volumes:
+  - ${GITEA_DOCKER_WORKSPACE:-.}/data:/app/data
+```
+
+Containers, networks and volumes a job creates through the socket are removed when the job ends. Both apply to jobs in containers, on the host `.` already works.
+
 #### Proxy
 
 Set these variables in the runner's environment, with systemd `Environment=`, `docker run -e`, or Kubernetes `env:`:

act/container/container_types.go

@@ -75,6 +75,17 @@ const (
 // fragment, missingContainerError composes it into the message every operation shares.
 var ErrContainerNotFound = errors.New("does not exist")
 
+// DockerProxy is a job's docker socket, fronting the daemon's for the job's lifetime.
+type DockerProxy struct {
+	Socket string
+	close  func(context.Context) error
+}
+
+// Close removes what the job created through the socket, then stops serving it.
+func (p *DockerProxy) Close(ctx context.Context) error {
+	return p.close(ctx)
+}
+
 // Info is a snapshot of a container, as of one inspect.
 type Info struct {
 	ID       string
@@ -84,6 +95,7 @@ type Info struct {
 	// HealthOutput is the last healthcheck probe's output.
 	HealthOutput string
 	Ports        map[string]string // container port ("5432") to the host port it is published on
+	Mounts       map[string]string // container path to its source on the daemon
 }
 
 // Container for managing docker run containers

act/container/docker_proxy.go

@@ -0,0 +1,276 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+//go:build !(WITHOUT_DOCKER || !(linux || darwin || windows || netbsd))
+
+package container
+
+import (
+	"bytes"
+	"context"
+	"crypto/sha256"
+	"encoding/hex"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net"
+	"net/http"
+	"net/http/httputil"
+	"os"
+	"path/filepath"
+	"regexp"
+	"strings"
+	"sync"
+	"time"
+
+	"gitea.com/gitea/runner/act/common"
+
+	cerrdefs "github.com/containerd/errdefs"
+	"github.com/moby/moby/api/types/container"
+	"github.com/moby/moby/api/types/mount"
+	"github.com/moby/moby/client"
+)
+
+const (
+	jobLabel      = "com.gitea.runner.job"
+	maxCreateBody = 8 << 20
+)
+
+var (
+	createPath    = regexp.MustCompile(`^(/v[0-9.]+)?/(containers|networks|volumes)/create$`)
+	rawStreamPath = regexp.MustCompile(`^(/v[0-9.]+)?/(containers/[^/]+/attach|exec/[^/]+/start)$`)
+	proxyProbe    struct {
+		sync.Mutex
+		decided bool
+		dir     string
+	}
+)
+
+// DockerProxyDir returns where job proxy sockets live, "" while undecided or when the daemon cannot open the runner's files.
+func DockerProxyDir(ctx context.Context) string {
+	proxyProbe.Lock()
+	defer proxyProbe.Unlock()
+	if proxyProbe.decided {
+		return proxyProbe.dir
+	}
+	dir := filepath.Join(os.TempDir(), "gitea-runner-docker")
+	ok, err := daemonSeesDir(ctx, dir)
+	if err != nil {
+		common.Logger(ctx).Debugf("docker proxy probe postponed: %v", err)
+		return ""
+	}
+	proxyProbe.decided = true
+	if ok {
+		proxyProbe.dir = dir
+	} else {
+		common.Logger(ctx).Infof("the docker daemon cannot reach the runner's filesystem, jobs get the daemon socket directly")
+	}
+	return proxyProbe.dir
+}
+
+func daemonSeesDir(ctx context.Context, dir string) (bool, error) {
+	if err := os.MkdirAll(dir, 0o700); err != nil {
+		return false, err
+	}
+	probe := filepath.Join(dir, "probe")
+	if err := os.WriteFile(probe, nil, 0o600); err != nil {
+		return false, err
+	}
+	cli, err := GetDockerClient(ctx)
+	if err != nil {
+		return false, err
+	}
+	defer cli.Close()
+	images, err := cli.ImageList(ctx, client.ImageListOptions{})
+	if err != nil {
+		return false, err
+	}
+	if len(images.Items) == 0 {
+		return false, errors.New("no image to probe with yet")
+	}
+	// creating validates that a bind source exists on the daemon's side, nothing is started
+	created, err := cli.ContainerCreate(ctx, client.ContainerCreateOptions{
+		Config:     &container.Config{Image: images.Items[0].ID, Cmd: []string{"true"}},
+		HostConfig: &container.HostConfig{Mounts: []mount.Mount{{Type: mount.TypeBind, Source: probe, Target: "/gitea-runner-probe"}}},
+	})
+	if cerrdefs.IsInvalidArgument(err) {
+		return false, nil
+	}
+	if err != nil {
+		return false, err
+	}
+	_, err = cli.ContainerRemove(ctx, created.ID, client.ContainerRemoveOptions{Force: true})
+	return true, err
+}
+
+// StartDockerProxy serves a job's docker socket in dir, labelling what the job creates through it.
+func StartDockerProxy(daemonSocket, dir, job string) (*DockerProxy, error) {
+	if err := os.MkdirAll(dir, 0o700); err != nil {
+		return nil, err
+	}
+	digest := sha256.Sum256([]byte(job))
+	socket := filepath.Join(dir, hex.EncodeToString(digest[:8])+".sock")
+	_ = os.Remove(socket)
+	listener, err := net.Listen("unix", socket)
+	if err != nil {
+		return nil, err
+	}
+	if info, err := os.Stat(daemonSocket); err == nil {
+		_ = os.Chmod(socket, info.Mode().Perm())
+	}
+	dial := func(ctx context.Context, _, _ string) (net.Conn, error) {
+		return (&net.Dialer{}).DialContext(ctx, "unix", daemonSocket)
+	}
+	transport := &http.Transport{DialContext: dial}
+	forward := &httputil.ReverseProxy{
+		Rewrite: func(r *httputil.ProxyRequest) {
+			r.Out.URL.Scheme = "http"
+			r.Out.URL.Host = "docker"
+		},
+		Transport: transport,
+	}
+	server := &http.Server{ReadHeaderTimeout: 30 * time.Second, Handler: http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		switch {
+		case r.Method != http.MethodPost:
+		case createPath.MatchString(r.URL.Path):
+			if err := addLabel(r, job); err != nil {
+				http.Error(w, err.Error(), http.StatusBadRequest)
+				return
+			}
+		case rawStreamPath.MatchString(r.URL.Path):
+			tunnel(w, r, dial)
+			return
+		}
+		forward.ServeHTTP(w, r)
+	})}
+	go func() { _ = server.Serve(listener) }()
+	return &DockerProxy{Socket: socket, close: func(ctx context.Context) error {
+		err := removeJobResources(ctx, job)
+		_ = server.Close()
+		transport.CloseIdleConnections()
+		_ = os.Remove(socket)
+		return err
+	}}, nil
+}
+
+func addLabel(r *http.Request, job string) error {
+	body, err := io.ReadAll(io.LimitReader(r.Body, maxCreateBody+1))
+	if err != nil {
+		return err
+	}
+	if len(body) > maxCreateBody {
+		return errors.New("create request too large")
+	}
+	if len(bytes.TrimSpace(body)) == 0 {
+		r.Body = io.NopCloser(bytes.NewReader(body))
+		return nil
+	}
+	var fields map[string]json.RawMessage
+	if err := json.Unmarshal(body, &fields); err != nil {
+		return fmt.Errorf("invalid create request: %w", err)
+	}
+	key := "Labels"
+	for name := range fields {
+		if strings.EqualFold(name, key) {
+			key = name
+			break
+		}
+	}
+	labels := map[string]string{}
+	if raw := fields[key]; len(raw) > 0 && string(raw) != "null" {
+		if err := json.Unmarshal(raw, &labels); err != nil {
+			return fmt.Errorf("invalid create request: %w", err)
+		}
+	}
+	labels[jobLabel] = job
+	if fields[key], err = json.Marshal(labels); err != nil {
+		return err
+	}
+	if body, err = json.Marshal(fields); err != nil {
+		return err
+	}
+	r.Body = io.NopCloser(bytes.NewReader(body))
+	r.ContentLength = int64(len(body))
+	r.TransferEncoding = nil
+	return nil
+}
+
+// tunnel splices attach and exec streams, which the daemon hijacks with or without an HTTP upgrade
+func tunnel(w http.ResponseWriter, r *http.Request, dial func(context.Context, string, string) (net.Conn, error)) {
+	hijacker, ok := w.(http.Hijacker)
+	if !ok {
+		http.Error(w, "connection cannot be hijacked", http.StatusInternalServerError)
+		return
+	}
+	upstream, err := dial(r.Context(), "", "")
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusBadGateway)
+		return
+	}
+	defer upstream.Close()
+	if err := r.Write(upstream); err != nil {
+		http.Error(w, err.Error(), http.StatusBadGateway)
+		return
+	}
+	downstream, buffered, err := hijacker.Hijack()
+	if err != nil {
+		return
+	}
+	defer downstream.Close()
+	if _, err := io.CopyN(upstream, buffered, int64(buffered.Reader.Buffered())); err != nil {
+		return
+	}
+	done := make(chan struct{}, 2)
+	go func() {
+		_, _ = io.Copy(upstream, downstream)
+		done <- struct{}{}
+	}()
+	go func() {
+		_, _ = io.Copy(downstream, upstream)
+		done <- struct{}{}
+	}()
+	<-done
+}
+
+func removeJobResources(ctx context.Context, job string) error {
+	cli, err := GetDockerClient(ctx)
+	if err != nil {
+		return err
+	}
+	defer cli.Close()
+	return removeLabelled(ctx, cli, job)
+}
+
+func removeLabelled(ctx context.Context, cli client.APIClient, job string) error {
+	logger := common.Logger(ctx)
+	filters := make(client.Filters).Add("label", jobLabel+"="+job)
+	containers, err := cli.ContainerList(ctx, client.ContainerListOptions{All: true, Filters: filters})
+	if err != nil {
+		return err
+	}
+	var errs []error
+	for _, c := range containers.Items {
+		logger.Infof("removing container %s the job left behind", strings.TrimPrefix(strings.Join(c.Names, ","), "/"))
+		errs = append(errs, (&containerReference{cli: cli, id: c.ID}).remove()(ctx))
+	}
+	networks, err := cli.NetworkList(ctx, client.NetworkListOptions{Filters: filters})
+	if err != nil {
+		return errors.Join(append(errs, err)...)
+	}
+	for _, n := range networks.Items {
+		if _, err := cli.NetworkRemove(ctx, n.ID, client.NetworkRemoveOptions{}); err != nil && !cerrdefs.IsNotFound(err) {
+			errs = append(errs, fmt.Errorf("failed to remove network %s: %w", n.Name, err))
+		}
+	}
+	volumes, err := cli.VolumeList(ctx, client.VolumeListOptions{Filters: filters})
+	if err != nil {
+		return errors.Join(append(errs, err)...)
+	}
+	for _, v := range volumes.Items {
+		if _, err := cli.VolumeRemove(ctx, v.Name, client.VolumeRemoveOptions{}); err != nil && !cerrdefs.IsNotFound(err) {
+			errs = append(errs, fmt.Errorf("failed to remove volume %s: %w", v.Name, err))
+		}
+	}
+	return errors.Join(errs...)
+}

act/container/docker_proxy_test.go

@@ -0,0 +1,270 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+//go:build !(WITHOUT_DOCKER || !(linux || darwin || windows || netbsd))
+
+package container
+
+import (
+	"archive/tar"
+	"bufio"
+	"bytes"
+	"context"
+	"encoding/json"
+	"io"
+	"net"
+	"net/http"
+	"path/filepath"
+	"strings"
+	"testing"
+	"time"
+
+	cerrdefs "github.com/containerd/errdefs"
+	"github.com/moby/moby/api/types/container"
+	"github.com/moby/moby/api/types/network"
+	"github.com/moby/moby/api/types/volume"
+	mobyclient "github.com/moby/moby/client"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/mock"
+	"github.com/stretchr/testify/require"
+)
+
+func (m *mockDockerClient) VolumeList(ctx context.Context, opts mobyclient.VolumeListOptions) (mobyclient.VolumeListResult, error) {
+	args := m.Called(ctx, opts)
+	return args.Get(0).(mobyclient.VolumeListResult), args.Error(1)
+}
+
+func (m *mockDockerClient) VolumeRemove(ctx context.Context, id string, opts mobyclient.VolumeRemoveOptions) (mobyclient.VolumeRemoveResult, error) {
+	args := m.Called(ctx, id, opts)
+	return args.Get(0).(mobyclient.VolumeRemoveResult), args.Error(1)
+}
+
+// unix socket paths are limited to about a hundred bytes, which the default macOS TMPDIR exceeds
+func shortTempDir(t testing.TB) string {
+	t.Helper()
+	t.Setenv("TMPDIR", "/tmp")
+	return t.TempDir()
+}
+
+func daemonSocketPath(t testing.TB, cli mobyclient.APIClient) string {
+	t.Helper()
+	host := cli.DaemonHost()
+	if !strings.HasPrefix(host, "unix://") {
+		t.Skipf("skipping: daemon at %s is not a unix socket", host)
+	}
+	return strings.TrimPrefix(host, "unix://")
+}
+
+func TestDockerProxy(t *testing.T) {
+	bodies := make(chan []byte, 8)
+	daemonSocket := filepath.Join(shortTempDir(t), "d.sock")
+	listener, err := net.Listen("unix", daemonSocket)
+	require.NoError(t, err)
+	daemon := &http.Server{ReadHeaderTimeout: time.Second, Handler: http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		switch {
+		case strings.HasSuffix(r.URL.Path, "/create"):
+			body, _ := io.ReadAll(r.Body)
+			bodies <- body
+			w.WriteHeader(http.StatusCreated)
+		case strings.HasSuffix(r.URL.Path, "/start"):
+			conn, buffered, err := w.(http.Hijacker).Hijack()
+			if err != nil {
+				return
+			}
+			defer conn.Close()
+			_, _ = conn.Write([]byte("HTTP/1.1 200 OK\r\nContent-Type: application/vnd.docker.raw-stream\r\n\r\n"))
+			_, _ = io.Copy(conn, buffered)
+		default:
+			w.Header().Set("Api-Version", "1.47")
+			_, _ = w.Write([]byte("OK " + r.Method + " " + r.URL.Path))
+		}
+	})}
+	go func() { _ = daemon.Serve(listener) }()
+	t.Cleanup(func() { _ = daemon.Close() })
+	proxy, err := StartDockerProxy(daemonSocket, shortTempDir(t), "job-1")
+	require.NoError(t, err)
+	client := &http.Client{Transport: &http.Transport{DialContext: func(ctx context.Context, _, _ string) (net.Conn, error) {
+		return (&net.Dialer{}).DialContext(ctx, "unix", proxy.Socket)
+	}}}
+
+	t.Run("labels creates", func(t *testing.T) {
+		for path, body := range map[string]string{
+			"/v1.47/containers/create": `{"Image":"alpine","Labels":{"own":"1"}}`,
+			"/networks/create":         `{"Name":"n"}`,
+			"/volumes/create":          `{"Name":"v","labels":null}`,
+		} {
+			resp, err := client.Post("http://docker"+path, "application/json", strings.NewReader(body))
+			require.NoError(t, err)
+			resp.Body.Close()
+			assert.Equal(t, http.StatusCreated, resp.StatusCode)
+
+			var got map[string]json.RawMessage
+			require.NoError(t, json.Unmarshal(<-bodies, &got))
+			key := "Labels"
+			if _, ok := got["labels"]; ok {
+				key = "labels"
+			}
+			var labels map[string]string
+			require.NoError(t, json.Unmarshal(got[key], &labels))
+			assert.Equal(t, "job-1", labels[jobLabel], path)
+			if strings.Contains(body, "own") {
+				assert.Equal(t, "1", labels["own"])
+				assert.JSONEq(t, `"alpine"`, string(got["Image"]))
+			}
+		}
+	})
+
+	t.Run("passes other requests through", func(t *testing.T) {
+		resp, err := client.Get("http://docker/v1.47/_ping")
+		require.NoError(t, err)
+		defer resp.Body.Close()
+		body, _ := io.ReadAll(resp.Body)
+		assert.Equal(t, "1.47", resp.Header.Get("Api-Version"))
+		assert.Equal(t, "OK GET /v1.47/_ping", string(body))
+	})
+
+	t.Run("tunnels raw streams", func(t *testing.T) {
+		conn, err := net.Dial("unix", proxy.Socket)
+		require.NoError(t, err)
+		defer conn.Close()
+		_, err = conn.Write([]byte("POST /v1.47/exec/abc/start HTTP/1.1\r\nHost: docker\r\nContent-Length: 2\r\n\r\n{}ping\n"))
+		require.NoError(t, err)
+		reader := bufio.NewReader(conn)
+		resp, err := http.ReadResponse(reader, nil)
+		require.NoError(t, err)
+		defer resp.Body.Close()
+		assert.Equal(t, "application/vnd.docker.raw-stream", resp.Header.Get("Content-Type"))
+		echoed, err := reader.ReadString('\n')
+		require.NoError(t, err)
+		assert.Equal(t, "{}ping\n", echoed)
+	})
+}
+
+func TestRemoveLabelledRemovesContainersNetworksAndVolumes(t *testing.T) {
+	ctx := context.Background()
+	filters := make(mobyclient.Filters).Add("label", jobLabel+"=job-1")
+	cli := &mockDockerClient{}
+	cli.On("ContainerList", ctx, mobyclient.ContainerListOptions{All: true, Filters: filters}).
+		Return(mobyclient.ContainerListResult{Items: []container.Summary{{ID: "c1", Names: []string{"/app"}}}}, nil)
+	cli.On("ContainerKill", ctx, "c1", mock.Anything).Return(mobyclient.ContainerKillResult{}, nil)
+	cli.On("ContainerRemove", ctx, "c1", mobyclient.ContainerRemoveOptions{RemoveVolumes: true, Force: true}).
+		Return(mobyclient.ContainerRemoveResult{}, nil)
+	cli.On("NetworkList", ctx, mobyclient.NetworkListOptions{Filters: filters}).
+		Return(mobyclient.NetworkListResult{Items: []network.Summary{{ID: "n1", Name: "app_default"}}}, nil)
+	cli.On("NetworkRemove", ctx, "n1", mock.Anything).Return(mobyclient.NetworkRemoveResult{}, nil)
+	cli.On("VolumeList", ctx, mobyclient.VolumeListOptions{Filters: filters}).
+		Return(mobyclient.VolumeListResult{Items: []volume.Volume{{Name: "app_data"}}}, nil)
+	cli.On("VolumeRemove", ctx, "app_data", mobyclient.VolumeRemoveOptions{}).Return(mobyclient.VolumeRemoveResult{}, nil)
+
+	require.NoError(t, removeLabelled(ctx, cli, "job-1"))
+	cli.AssertExpectations(t)
+}
+
+func TestDockerProxyWithDaemon(t *testing.T) {
+	requireDocker(t)
+	ctx := context.Background()
+	require.NoError(t, NewDockerPullExecutor(NewDockerPullExecutorInput{Image: "alpine"})(ctx))
+	direct, err := GetDockerClient(ctx)
+	require.NoError(t, err)
+	defer direct.Close()
+	dir := shortTempDir(t)
+	seen, err := daemonSeesDir(ctx, dir)
+	require.NoError(t, err)
+	t.Logf("daemon sees the runner's filesystem: %v", seen)
+
+	job := "proxy-test-" + t.Name()
+	proxy, err := StartDockerProxy(daemonSocketPath(t, direct), dir, job)
+	require.NoError(t, err)
+	viaProxy, err := mobyclient.New(mobyclient.WithHost("unix://" + proxy.Socket))
+	require.NoError(t, err)
+	defer viaProxy.Close()
+
+	created, err := viaProxy.ContainerCreate(ctx, mobyclient.ContainerCreateOptions{
+		Config: &container.Config{Image: "alpine", Cmd: []string{"sleep", "300"}, Labels: map[string]string{"own": "1"}},
+	})
+	require.NoError(t, err)
+	t.Cleanup(func() { _, _ = direct.ContainerRemove(ctx, created.ID, mobyclient.ContainerRemoveOptions{Force: true}) })
+	_, err = viaProxy.ContainerStart(ctx, created.ID, mobyclient.ContainerStartOptions{})
+	require.NoError(t, err)
+	net, err := viaProxy.NetworkCreate(ctx, job, mobyclient.NetworkCreateOptions{})
+	require.NoError(t, err)
+	t.Cleanup(func() { _, _ = direct.NetworkRemove(ctx, net.ID, mobyclient.NetworkRemoveOptions{}) })
+	_, err = viaProxy.VolumeCreate(ctx, mobyclient.VolumeCreateOptions{Name: job})
+	require.NoError(t, err)
+	t.Cleanup(func() { _, _ = direct.VolumeRemove(ctx, job, mobyclient.VolumeRemoveOptions{Force: true}) })
+
+	inspected, err := direct.ContainerInspect(ctx, created.ID, mobyclient.ContainerInspectOptions{})
+	require.NoError(t, err)
+	assert.Equal(t, map[string]string{"own": "1", jobLabel: job}, inspected.Container.Config.Labels)
+	vol, err := direct.VolumeInspect(ctx, job, mobyclient.VolumeInspectOptions{})
+	require.NoError(t, err)
+	assert.Equal(t, job, vol.Volume.Labels[jobLabel])
+
+	exec, err := viaProxy.ExecCreate(ctx, created.ID, mobyclient.ExecCreateOptions{Cmd: []string{"cat"}, AttachStdin: true, AttachStdout: true, TTY: true})
+	require.NoError(t, err)
+	attached, err := viaProxy.ExecAttach(ctx, exec.ID, mobyclient.ExecAttachOptions{TTY: true})
+	require.NoError(t, err)
+	_, err = attached.Conn.Write([]byte("hello\n"))
+	require.NoError(t, err)
+	echoed, err := attached.Reader.ReadString('\n')
+	require.NoError(t, err)
+	assert.Equal(t, "hello\r\n", echoed)
+	attached.Close()
+
+	require.NoError(t, proxy.Close(ctx))
+	_, err = direct.ContainerInspect(ctx, created.ID, mobyclient.ContainerInspectOptions{})
+	assert.True(t, cerrdefs.IsNotFound(err))
+	_, err = direct.NetworkInspect(ctx, net.ID, mobyclient.NetworkInspectOptions{})
+	assert.True(t, cerrdefs.IsNotFound(err))
+	_, err = direct.VolumeInspect(ctx, job, mobyclient.VolumeInspectOptions{})
+	assert.True(t, cerrdefs.IsNotFound(err))
+}
+
+func BenchmarkDockerProxy(b *testing.B) {
+	ctx := context.Background()
+	direct, err := GetDockerClient(ctx)
+	require.NoError(b, err)
+	defer direct.Close()
+	if _, err := direct.Ping(ctx, mobyclient.PingOptions{}); err != nil {
+		b.Skipf("docker daemon unreachable: %v", err)
+	}
+	proxy, err := StartDockerProxy(daemonSocketPath(b, direct), shortTempDir(b), "bench")
+	require.NoError(b, err)
+	defer func() { _ = proxy.Close(ctx) }()
+	viaProxy, err := mobyclient.New(mobyclient.WithHost("unix://" + proxy.Socket))
+	require.NoError(b, err)
+	defer viaProxy.Close()
+
+	require.NoError(b, NewDockerPullExecutor(NewDockerPullExecutorInput{Image: "alpine"})(ctx))
+	created, err := direct.ContainerCreate(ctx, mobyclient.ContainerCreateOptions{Config: &container.Config{Image: "alpine", Cmd: []string{"sleep", "600"}}})
+	require.NoError(b, err)
+	defer func() { _, _ = direct.ContainerRemove(ctx, created.ID, mobyclient.ContainerRemoveOptions{Force: true}) }()
+	_, err = direct.ContainerStart(ctx, created.ID, mobyclient.ContainerStartOptions{})
+	require.NoError(b, err)
+
+	var archive bytes.Buffer
+	writer := tar.NewWriter(&archive)
+	payload := make([]byte, 64<<20)
+	require.NoError(b, writer.WriteHeader(&tar.Header{Name: "blob", Mode: 0o600, Size: int64(len(payload))}))
+	_, _ = writer.Write(payload)
+	require.NoError(b, writer.Close())
+
+	for name, cli := range map[string]mobyclient.APIClient{"direct": direct, "proxy": viaProxy} {
+		b.Run("ping/"+name, func(b *testing.B) {
+			for b.Loop() {
+				if _, err := cli.Ping(ctx, mobyclient.PingOptions{}); err != nil {
+					b.Fatal(err)
+				}
+			}
+		})
+		b.Run("copy64MiB/"+name, func(b *testing.B) {
+			b.SetBytes(int64(archive.Len()))
+			for b.Loop() {
+				_, err := cli.CopyToContainer(ctx, created.ID, mobyclient.CopyToContainerOptions{DestinationPath: "/tmp", Content: bytes.NewReader(archive.Bytes())})
+				if err != nil {
+					b.Fatal(err)
+				}
+			}
+		})
+	}
+}

act/container/docker_run.go

@@ -252,6 +252,10 @@ func containerInfoFromInspect(inspect container.InspectResponse) *Info {
 		ID:     inspect.ID,
 		Health: HealthNone,
 		Ports:  map[string]string{}, // an empty map, never null, in the expression context
+		Mounts: make(map[string]string, len(inspect.Mounts)),
+	}
+	for _, mountPoint := range inspect.Mounts {
+		info.Mounts[mountPoint.Destination] = mountPoint.Source
 	}
 
 	if state := inspect.State; state != nil {

act/container/docker_run_test.go

@@ -801,6 +801,20 @@ func TestContainerInfoFromInspect(t *testing.T) {
 		assert.Equal(t, "abc123", info.ID)
 		assert.Equal(t, HealthNone, info.Health)
 	})
+
+	t.Run("reports the mount sources by container path", func(t *testing.T) {
+		info := containerInfoFromInspect(container.InspectResponse{
+			Mounts: []container.MountPoint{
+				{Type: mount.TypeVolume, Name: "job", Source: "/var/lib/docker/volumes/job/_data", Destination: "/workspace/owner/repo"},
+				{Type: mount.TypeBind, Source: "/var/run/docker.sock", Destination: "/var/run/docker.sock"},
+			},
+		})
+
+		assert.Equal(t, map[string]string{
+			"/workspace/owner/repo": "/var/lib/docker/volumes/job/_data",
+			"/var/run/docker.sock":  "/var/run/docker.sock",
+		}, info.Mounts)
+	})
 }
 
 func TestMergeContainerConfigsVolumesReplaceRunnerMounts(t *testing.T) {

act/container/docker_stub.go

@@ -29,6 +29,14 @@ func RemoveImage(ctx context.Context, imageName string, force, pruneChildren boo
 	return false, errors.New("Unsupported Operation")
 }
 
+func DockerProxyDir(ctx context.Context) string {
+	return ""
+}
+
+func StartDockerProxy(daemonSocket, dir, job string) (*DockerProxy, error) {
+	return nil, errors.New("Unsupported Operation")
+}
+
 // NewDockerBuildExecutor function to create a run executor for the container
 func NewDockerBuildExecutor(input NewDockerBuildExecutorInput) common.Executor {
 	return func(ctx context.Context) error {

act/runner/run_context.go

@@ -96,6 +96,7 @@ type RunContext struct {
 	jobContainerID string
 	hasBash        *bool // memoized implicit-shell probe, only set on the top-level RunContext
 	jobNetworkName string
+	dockerProxy    *container.DockerProxy
 	// stepEnv is a copy of the running step's environment, so that workflow commands parsed out
 	// of the container's output can be judged against it. Written by runStepExecutor and read on
 	// the log-writer goroutine, hence unsecureCommandMu, which also guards unsecureCommandErr.
@@ -253,11 +254,38 @@ func (rc *RunContext) validVolumes() []string {
 	if rc.Config.BindWorkdir {
 		volumes = append(volumes, rc.Config.Workdir)
 	}
+	if rc.dockerProxy != nil {
+		volumes = append(volumes, rc.dockerProxy.Socket)
+	}
 	// TODO: add a new configuration to control whether the docker daemon can be mounted
 	return append(volumes, name, name+"-env",
 		getDockerDaemonSocketMountPath(rc.containerDaemonSocket()))
 }
 
+func (rc *RunContext) jobDockerSocket() string {
+	if rc.dockerProxy != nil {
+		return rc.dockerProxy.Socket
+	}
+	return getDockerDaemonSocketMountPath(rc.containerDaemonSocket())
+}
+
+func (rc *RunContext) startDockerProxy(ctx context.Context) {
+	daemonSocket := rc.containerDaemonSocket()
+	if daemonSocket == "-" || strings.HasPrefix(strings.ToLower(daemonSocket), "npipe://") {
+		return
+	}
+	dir := container.DockerProxyDir(ctx)
+	if dir == "" {
+		return
+	}
+	proxy, err := container.StartDockerProxy(getDockerDaemonSocketMountPath(daemonSocket), dir, rc.jobContainerName())
+	if err != nil {
+		common.Logger(ctx).Warnf("docker proxy not started, the job gets the daemon socket directly: %v", err)
+		return
+	}
+	rc.dockerProxy = proxy
+}
+
 // toolCache returns the tool cache path the job sees, relocatable through RUNNER_TOOL_CACHE.
 func (rc *RunContext) toolCache(fallback string) string {
 	if path := rc.GetEnv()["RUNNER_TOOL_CACHE"]; path != "" {
@@ -327,8 +355,8 @@ func (rc *RunContext) GetBindsAndMounts() ([]string, map[string]string, error) {
 	// the runner's own mounts below yield to the targets the job claims
 	binds, mounts, claimed := splitVolumes(volumes)
 
-	if daemonSocket := rc.containerDaemonSocket(); daemonSocket != "-" && !claimed["/var/run/docker.sock"] {
-		binds = append(binds, getDockerDaemonSocketMountPath(daemonSocket)+":/var/run/docker.sock")
+	if rc.containerDaemonSocket() != "-" && !claimed["/var/run/docker.sock"] {
+		binds = append(binds, rc.jobDockerSocket()+":/var/run/docker.sock")
 	}
 	if rc.Config.SharedToolCache {
 		if toolCache := rc.toolCache(container.DefaultToolCache); !claimed[toolCache] {
@@ -455,6 +483,7 @@ func (rc *RunContext) startJobContainer() common.Executor {
 		// For gitea, to support --volumes-from <container_name_or_id> in options.
 		// We need to set the container name to the environment variable.
 		rc.Env["JOB_CONTAINER_NAME"] = name
+		rc.startDockerProxy(ctx)
 
 		envList := make([]string, 0)
 
@@ -651,6 +680,12 @@ func (rc *RunContext) cleanupJobResources(networkName string, createAndDeleteNet
 				logger.Errorf("Error while cleaning services: %v", err)
 			}
 		}
+		if rc.dockerProxy != nil {
+			if err := rc.dockerProxy.Close(ctx); err != nil {
+				logger.Errorf("Error while removing what the job created: %v", err)
+			}
+			rc.dockerProxy = nil
+		}
 		if removeJobContainer {
 			// after the containers using them, services can hold these via `--volumes-from`
 			name := rc.jobContainerName()
@@ -914,6 +949,9 @@ func (rc *RunContext) captureJobContainerInfo() common.Executor {
 			return nil
 		}
 		rc.jobContainerID = info.ID
+		if source := info.Mounts[rc.githubWorkspace()]; source != "" {
+			rc.Env["GITEA_DOCKER_WORKSPACE"] = source
+		}
 		return nil
 	}
 }

act/runner/run_context_test.go

@@ -1294,6 +1294,29 @@ func TestGetJobContextReportsContainers(t *testing.T) {
 	}, jobContext.Services)
 }
 
+func TestCaptureJobContainerInfoExportsDockerWorkspace(t *testing.T) {
+	job := &containerMock{}
+	job.On("Inspect", mock.Anything).Return(&container.Info{
+		ID:     "job-container-id",
+		Mounts: map[string]string{"/workspace/owner/repo": "/var/lib/docker/volumes/job/_data"},
+	}, nil)
+	rc := &RunContext{
+		Config:       &Config{Workdir: "/workspace/owner/repo/"},
+		Env:          map[string]string{},
+		JobContainer: job,
+	}
+
+	require.NoError(t, rc.captureJobContainerInfo()(context.Background()))
+
+	assert.Equal(t, "job-container-id", rc.jobContainerID)
+	assert.Equal(t, "/var/lib/docker/volumes/job/_data", rc.Env["GITEA_DOCKER_WORKSPACE"])
+
+	rc.Config.Workdir = "/elsewhere"
+	rc.Env = map[string]string{}
+	require.NoError(t, rc.captureJobContainerInfo()(context.Background()))
+	assert.NotContains(t, rc.Env, "GITEA_DOCKER_WORKSPACE")
+}
+
 // A job that never started a container reports an empty context, not a placeholder.
 func TestGetJobContextWithoutContainer(t *testing.T) {
 	jobContext := (&RunContext{}).getJobContext()

internal/pkg/config/config.example.yaml

@@ -256,11 +256,10 @@ container:
   #require_docker: false
   # Timeout to wait for the docker daemon to be reachable, if docker is required by require_docker or runner
   #docker_timeout: 0s
-  # Bind the workspace to the host filesystem instead of using Docker volumes.
-  # This is required for Docker-in-Docker (DinD) setups when jobs use docker compose
-  # with bind mounts (e.g., ".:/app"), as volume-based workspaces are not accessible
-  # from the DinD daemon's filesystem. When enabled, ensure the workspace parent
-  # directory is also mounted into the runner container.
+  # Mount the workspace from a host directory instead of a Docker volume, so jobs
+  # can bind-mount it by its own path into sibling containers (".:/app" in docker
+  # compose). Not needed when workflows use the GITEA_DOCKER_WORKSPACE variable.
+  # The workspace parent directory must be mounted into the runner container.
   #bind_workdir: false
   # How long a job waits for a service container that declares a healthcheck to become
   # healthy. A negative value (e.g. -1s) starts the steps without waiting.

internal/pkg/config/config.go

@@ -157,7 +157,7 @@ type Container struct {
 	ForceRebuild         bool                          `yaml:"force_rebuild"`          // Rebuild docker image(s) even if already present
 	RequireDocker        bool                          `yaml:"require_docker"`         // Always require a reachable docker daemon, even if not required by runner
 	DockerTimeout        time.Duration                 `yaml:"docker_timeout"`         // Timeout to wait for the docker daemon to be reachable, if docker is required by require_docker or runner
-	BindWorkdir          bool                          `yaml:"bind_workdir"`           // BindWorkdir binds the workspace to the host filesystem instead of using Docker volumes. Required for DinD when jobs use docker compose with bind mounts.
+	BindWorkdir          bool                          `yaml:"bind_workdir"`           // BindWorkdir mounts the workspace from a host directory instead of a Docker volume.
 	ServiceReadyTimeout  time.Duration                 `yaml:"service_ready_timeout"`  // ServiceReadyTimeout bounds how long a job waits for a service container that declares a healthcheck to report healthy. Negative disables waiting.
 }