fix: skip service containers with an empty image (#1074)

GitHub Actions skips services whose image evaluates to an empty string, enabling conditional services via expressions like `image: ${{ matrix.image || '' }}`. Here such a service failed the job at `docker create`. Skip them before container creation, using GitHub's log message verbatim, and add a regression test.

Reviewed-on: https://gitea.com/gitea/runner/pulls/1074
Reviewed-by: Nicolas <bircni@icloud.com>
Co-authored-by: silverwind <me@silverwind.io>

Dockerfile

@@ -17,14 +17,14 @@ RUN make clean && make build
 ### DIND VARIANT
 #
 #
-FROM docker:29.6.0-dind AS dind
+FROM docker:29.6.1-dind AS dind
 
 ARG VERSION=dev
 
 LABEL org.opencontainers.image.source="https://gitea.com/gitea/runner"
 LABEL org.opencontainers.image.version="${VERSION}"
 
-RUN apk add --no-cache s6 bash git tzdata
+RUN apk add --no-cache s6 bash git tzdata nftables
 
 COPY --from=builder /opt/src/runner/gitea-runner /usr/local/bin/gitea-runner
 COPY scripts/run.sh /usr/local/bin/run.sh
@@ -37,7 +37,7 @@ ENTRYPOINT ["s6-svscan","/etc/s6"]
 ### DIND-ROOTLESS VARIANT
 #
 #
-FROM docker:29.6.0-dind-rootless AS dind-rootless
+FROM docker:29.6.1-dind-rootless AS dind-rootless
 
 ARG VERSION=dev
 
@@ -45,7 +45,7 @@ LABEL org.opencontainers.image.source="https://gitea.com/gitea/runner"
 LABEL org.opencontainers.image.version="${VERSION}"
 
 USER root
-RUN apk add --no-cache s6 bash git tzdata
+RUN apk add --no-cache s6 bash git tzdata nftables
 
 COPY --from=builder /opt/src/runner/gitea-runner /usr/local/bin/gitea-runner
 COPY scripts/run.sh /usr/local/bin/run.sh

act/runner/action_composite.go

@@ -8,6 +8,7 @@ import (
 	"context"
 	"errors"
 	"regexp"
+	"slices"
 	"strconv"
 	"strings"
 
@@ -85,6 +86,19 @@ func newCompositeRunContext(ctx context.Context, parent *RunContext, step action
 	return compositerc
 }
 
+// appendUniqueMasks appends the masks from src to dst, skipping any mask that
+// is already present in dst. This prevents the parent RunContext's Masks slice
+// from growing exponentially when composite actions are nested or repeated,
+// since each composite RunContext is seeded with its parent's masks.
+func appendUniqueMasks(dst, src []string) []string {
+	for _, m := range src {
+		if !slices.Contains(dst, m) {
+			dst = append(dst, m)
+		}
+	}
+	return dst
+}
+
 func execAsComposite(step actionStep) common.Executor {
 	rc := step.getRunContext()
 	action := step.getActionModel()
@@ -110,7 +124,11 @@ func execAsComposite(step actionStep) common.Executor {
 			}, eval.Interpolate(ctx, output.Value))
 		}
 
-		rc.Masks = append(rc.Masks, compositeRC.Masks...)
+		// compositeRC.Masks is seeded with rc.Masks (see newCompositeRunContext)
+		// and may have additional masks appended while the composite action runs.
+		// Only append masks that are not already present, otherwise nested or
+		// repeated composite actions grow rc.Masks exponentially.
+		rc.Masks = appendUniqueMasks(rc.Masks, compositeRC.Masks)
 		rc.ExtraPath = compositeRC.ExtraPath
 		// compositeRC.Env is dirty, contains INPUT_ and merged step env, only rely on compositeRC.GlobalEnv
 		mergeIntoMap := mergeIntoMapCaseSensitive

act/runner/action_composite_test.go

@@ -0,0 +1,70 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package runner
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestAppendUniqueMasks(t *testing.T) {
+	tests := []struct {
+		name string
+		dst  []string
+		src  []string
+		want []string
+	}{
+		{
+			name: "appends new masks",
+			dst:  []string{"a"},
+			src:  []string{"b", "c"},
+			want: []string{"a", "b", "c"},
+		},
+		{
+			name: "skips masks already present",
+			dst:  []string{"a", "b"},
+			src:  []string{"a", "b"},
+			want: []string{"a", "b"},
+		},
+		{
+			name: "deduplicates within src",
+			dst:  []string{"a"},
+			src:  []string{"b", "b", "a"},
+			want: []string{"a", "b"},
+		},
+		{
+			name: "empty src leaves dst unchanged",
+			dst:  []string{"a"},
+			src:  nil,
+			want: []string{"a"},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			assert.Equal(t, tt.want, appendUniqueMasks(tt.dst, tt.src))
+		})
+	}
+}
+
+// TestAppendUniqueMasksNoExponentialGrowth reproduces the exponential growth of
+// the parent's Masks slice observed with nested/repeated composite actions. A
+// composite RunContext is seeded with its parent's masks and the whole seeded
+// slice was previously appended back into the parent, doubling its length on
+// every composite action.
+func TestAppendUniqueMasksNoExponentialGrowth(t *testing.T) {
+	parentMasks := []string{"secret"}
+
+	for range 20 {
+		// compositeRC.Masks starts as a copy of the parent's masks (it is
+		// seeded with parent.Masks in newCompositeRunContext).
+		compositeMasks := make([]string, len(parentMasks))
+		copy(compositeMasks, parentMasks)
+
+		parentMasks = appendUniqueMasks(parentMasks, compositeMasks)
+	}
+
+	assert.Equal(t, []string{"secret"}, parentMasks)
+}

act/runner/run_context.go

@@ -379,6 +379,13 @@ func (rc *RunContext) startJobContainer() common.Executor {
 
 		// add service containers
 		for serviceID, spec := range rc.Run.Job().Services {
+			// GitHub compatibility: skip services whose image evaluates to an
+			// empty string, enabling conditional services via expressions
+			serviceImage := rc.ExprEval.Interpolate(ctx, spec.Image)
+			if serviceImage == "" {
+				logger.Infof("The service '%s' will not be started because the container definition has an empty image.", serviceID)
+				continue
+			}
 			// interpolate env
 			interpolatedEnvs := make(map[string]string, len(spec.Env))
 			for k, v := range spec.Env {
@@ -417,7 +424,7 @@ func (rc *RunContext) startJobContainer() common.Executor {
 			c := container.NewContainer(&container.NewContainerInput{
 				Name:           serviceContainerName,
 				WorkingDir:     ext.ToContainerPath(rc.Config.Workdir),
-				Image:          rc.ExprEval.Interpolate(ctx, spec.Image),
+				Image:          serviceImage,
 				Username:       username,
 				Password:       password,
 				Cmd:            interpolatedCmd,

act/runner/runner_test.go

@@ -303,6 +303,7 @@ func TestRunEvent(t *testing.T) {
 		// services
 		{workdir, "services", "push", "", platforms, secrets},
 		{workdir, "services-with-container", "push", "", platforms, secrets},
+		{workdir, "services-empty-image", "push", "", platforms, secrets},
 
 		// local remote action overrides
 		{workdir, "local-remote-action-overrides", "push", "", platforms, secrets},

act/runner/testdata/services-empty-image/push.yml

@@ -0,0 +1,10 @@
+name: services-empty-image
+on: push
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    services:
+      db:
+        image: ${{ false && 'postgres:16' || '' }}
+    steps:
+      - run: echo "empty-image service was skipped"

go.mod

@@ -11,7 +11,7 @@ require (
 	github.com/containerd/errdefs v1.0.0
 	github.com/creack/pty v1.1.24
 	github.com/distribution/reference v0.6.0
-	github.com/docker/cli v29.6.0+incompatible
+	github.com/docker/cli v29.6.1+incompatible
 	github.com/docker/go-connections v0.7.0
 	github.com/go-git/go-billy/v5 v5.9.0
 	github.com/go-git/go-git/v5 v5.19.1
@@ -29,6 +29,7 @@ require (
 	github.com/opencontainers/selinux v1.15.1
 	github.com/pkg/errors v0.9.1
 	github.com/prometheus/client_golang v1.23.2
+	github.com/prometheus/client_model v0.6.2
 	github.com/rhysd/actionlint v1.7.12
 	github.com/sirupsen/logrus v1.9.4
 	github.com/spf13/cobra v1.10.2
@@ -37,7 +38,7 @@ require (
 	github.com/timshannon/bolthold v0.0.0-20240314194003-30aac6950928
 	go.etcd.io/bbolt v1.5.0
 	go.yaml.in/yaml/v4 v4.0.0-rc.3
-	golang.org/x/sys v0.46.0
+	golang.org/x/sys v0.47.0
 	golang.org/x/term v0.44.0
 	google.golang.org/protobuf v1.36.11
 	gotest.tools/v3 v3.5.2
@@ -84,7 +85,6 @@ require (
 	github.com/opencontainers/go-digest v1.0.0 // indirect
 	github.com/pjbgf/sha1cd v0.6.0 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
-	github.com/prometheus/client_model v0.6.2 // indirect
 	github.com/prometheus/common v0.66.1 // indirect
 	github.com/prometheus/procfs v0.17.0 // indirect
 	github.com/robfig/cron/v3 v3.0.1 // indirect

go.sum

@@ -51,6 +51,8 @@ github.com/docker/cli v29.5.3+incompatible h1:nbEFfz774vBwQ5KRYv7c/AghjReqnGISvr
 github.com/docker/cli v29.5.3+incompatible/go.mod h1:JLrzqnKDaYBop7H2jaqPtU4hHvMKP+vjCwu2uszcLI8=
 github.com/docker/cli v29.6.0+incompatible h1:nw9himxMMZ7eIeherJNlKQq+acnlzGgHd+4uf10QRSc=
 github.com/docker/cli v29.6.0+incompatible/go.mod h1:JLrzqnKDaYBop7H2jaqPtU4hHvMKP+vjCwu2uszcLI8=
+github.com/docker/cli v29.6.1+incompatible h1:oO7F4nn3Ovr/5TlfTUWFbMwBSS/B7Xs6Epv26gBrUP8=
+github.com/docker/cli v29.6.1+incompatible/go.mod h1:JLrzqnKDaYBop7H2jaqPtU4hHvMKP+vjCwu2uszcLI8=
 github.com/docker/docker-credential-helpers v0.9.6 h1:cT2PbRPSlnMmNTfT2TDMXRyQ1KMWHG7xoTLBcn1ZNv0=
 github.com/docker/docker-credential-helpers v0.9.6/go.mod h1:v1S+hepowrQXITkEfw6o4+BMbGot02wiKpzWhGUZK6c=
 github.com/docker/go-connections v0.7.0 h1:6SsRfJddP22WMrCkj19x9WKjEDTB+ahsdiGYf0mN39c=
@@ -260,6 +262,8 @@ golang.org/x/sys v0.4.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.15.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
 golang.org/x/sys v0.46.0 h1:noSf2Fq6F8DBgS+LysIkx7rIExoNHJsxOAtPp4rthXw=
 golang.org/x/sys v0.46.0/go.mod h1:4GL1E5IUh+htKOUEOaiffhrAeqysfVGipDYzABqnCmw=
+golang.org/x/sys v0.47.0 h1:o7XGOvZQCADBQQ4Y7VNq2dRWQR7JmOUW8Kxx4ZsNgWs=
+golang.org/x/sys v0.47.0/go.mod h1:4GL1E5IUh+htKOUEOaiffhrAeqysfVGipDYzABqnCmw=
 golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
 golang.org/x/term v0.44.0 h1:0rLvDRCtNj0gZkyIXhCyOb2OAzEhLVqc4B+hrsBhrmc=
 golang.org/x/term v0.44.0/go.mod h1:7ze4MdzUzLXpSAoFP1H0bOI9aXDqveSvatT5vKcFh2Y=

internal/pkg/config/config.example.yaml

@@ -110,6 +110,11 @@ cache:
   dir: ""
   # Outbound IP or hostname that job containers use to reach this runner's cache server.
   # Leave empty to detect automatically. 0.0.0.0 is not valid here.
+  # If the runner itself runs in Docker, automatic detection can choose an
+  # address on the runner container's network that job containers cannot reach
+  # when the runner creates a separate per-job network. In that case, set this
+  # to a hostname/IP reachable from job containers, and set port to a fixed
+  # published port or put the job containers on a shared Docker network.
   # Ignored when external_server is set.
   host: ""
   # Port for the built-in cache server. 0 picks a random free port.
@@ -133,6 +138,8 @@ container:
   # Specifies the network to which the container will connect.
   # Could be host, bridge or the name of a custom network.
   # If it's empty, runner will create a network automatically.
+  # For dockerized runners using the built-in cache server, a custom shared
+  # network can be required so job containers can reach cache.host/cache.port.
   # Deprecated: `network_mode` is still accepted for old configs; use `network` instead.
   network: ""
   # network_create_options only apply when `network` is left empty and the runner