implemented 11-docker-build-runtime.md: added optional Docker-based build execution with configuration, per-branch runtime selection, image rebuild on input changes, Gradle cache volume, and ownership repair; updated docs and configuration

2026-07-07 13:49:08 +02:00
parent 73221a8b8b
commit e869b46cbf
14 changed files with 836 additions and 5 deletions
@@ -185,7 +185,8 @@ class BuildExecutor(
                Files.newOutputStream(build.runningBuild.liveLogFile).use { liveLog ->
                    writeLiveLogHeader(liveLog, build.runningBuild, branchConfig, workspace)
                    if (branchConfig.cleanCommand.isNotBlank()) {
-                        val cleanExitCode = runCommand(build, branchConfig.cleanCommand, workspace, stdoutLog, stderrLog, liveLog)
+                        val cleanExitCode =
+                            runCommand(build, branchConfig, branchConfig.cleanCommand, workspace, stdoutLog, stderrLog, liveLog)
                        if (cleanExitCode != 0) {
                            return cleanExitCode
                        }
@@ -193,7 +194,7 @@ class BuildExecutor(
                    if (build.cancelled.get()) {
                        return CANCELLED_EXIT_CODE
                    }
-                    return runCommand(build, branchConfig.buildCommand, workspace, stdoutLog, stderrLog, liveLog)
+                    return runCommand(build, branchConfig, branchConfig.buildCommand, workspace, stdoutLog, stderrLog, liveLog)
                }
            }
        }
@@ -201,13 +202,21 @@ class BuildExecutor(

    private fun runCommand(
        build: ActiveBuild,
+        branchConfig: BranchConfig,
        command: String,
        workspace: Path,
        stdoutLog: OutputStream,
        stderrLog: OutputStream,
        liveLog: OutputStream,
    ): Int {
-        val process = buildRunner.start(command, workspace, mapOf("branch" to build.runningBuild.branch))
+        val process =
+            buildRunner.start(
+                command = command,
+                workingDir = workspace,
+                environment = mapOf("branch" to build.runningBuild.branch),
+                repoDir = build.workingDir,
+                branchConfig = branchConfig,
+            )
        build.process = process
        if (build.cancelled.get()) {
            destroyProcessTree(process)
@@ -1,18 +1,23 @@
 package de.hoennig.gittally.build

+import de.hoennig.gittally.config.BranchConfig
+import org.springframework.context.annotation.Primary
 import org.springframework.stereotype.Component
 import java.nio.file.Path

 /**
 * Starts a single build or clean command and hands the [Process] back to the caller,
 * which owns log streaming and process-tree termination.
- * Native shell execution for now; a Docker runner can plug in later (step 11).
+ * [repoDir] and [branchConfig] let implementations derive per-repository resources
+ * and per-branch settings (step 11: Docker runtime).
 */
 interface BuildRunner {
    fun start(
        command: String,
        workingDir: Path,
        environment: Map<String, String>,
+        repoDir: Path = workingDir,
+        branchConfig: BranchConfig = BranchConfig(),
    ): Process
 }

@@ -22,6 +27,8 @@ class ProcessBuildRunner : BuildRunner {
        command: String,
        workingDir: Path,
        environment: Map<String, String>,
+        repoDir: Path,
+        branchConfig: BranchConfig,
    ): Process {
        val processBuilder = ProcessBuilder("bash", "-c", command)
        processBuilder.directory(workingDir.toFile())
@@ -29,3 +36,25 @@ class ProcessBuildRunner : BuildRunner {
        return processBuilder.start()
    }
 }
+
+/**
+ * Selects the runtime per branch: Docker when `branches.<name>.docker.enabled`,
+ * native shell execution otherwise (the unchanged default).
+ */
+@Primary
+@Component
+class DispatchingBuildRunner(
+    private val processBuildRunner: ProcessBuildRunner,
+    private val dockerBuildRunner: DockerBuildRunner,
+) : BuildRunner {
+    override fun start(
+        command: String,
+        workingDir: Path,
+        environment: Map<String, String>,
+        repoDir: Path,
+        branchConfig: BranchConfig,
+    ): Process {
+        val runner = if (branchConfig.docker.enabled) dockerBuildRunner else processBuildRunner
+        return runner.start(command, workingDir, environment, repoDir, branchConfig)
+    }
+}
@@ -0,0 +1,292 @@
+package de.hoennig.gittally.build
+
+import de.hoennig.gittally.config.BranchConfig
+import de.hoennig.gittally.config.DockerConfig
+import de.hoennig.gittally.git.GitCommandRunner
+import org.slf4j.LoggerFactory
+import org.springframework.stereotype.Component
+import java.nio.file.Path
+
+/**
+ * Runs build commands inside a Docker container (legacy `--docker` mode), shelling
+ * out to the `docker` CLI via the generic [GitCommandRunner] process wrapper —
+ * consistent with the git gateway; no Docker SDK dependency.
+ *
+ * Auxiliary steps run synchronously before each command: stale container cleanup
+ * (once per process), image ensure (rebuild when the Dockerfile inputs changed,
+ * tracked via the [DockerImageInputs.INPUTS_LABEL] image label), and the per-repo
+ * Gradle cache volume. The returned [Process] is the attached `docker run` client
+ * (`--init`, so termination signals reach the build inside the container); the
+ * executor streams and terminates it like a native build. Ownership of `build/`
+ * and `.gradle/` is repaired to the host user inside the same container run.
+ */
+@Component
+class DockerBuildRunner(
+    private val commandRunner: GitCommandRunner,
+    private val socketLocator: DockerSocketLocator,
+) : BuildRunner {
+    private val log = LoggerFactory.getLogger(DockerBuildRunner::class.java)
+
+    /** Volumes already prepared by this process, keyed by volume and image. */
+    private val preparedVolumes = mutableSetOf<String>()
+
+    private var staleContainersCleaned = false
+
+    /** Replaceable process launcher so unit tests can capture the assembled `docker run` argv. */
+    internal var processStarter: (List<String>, Path) -> Process = { command, dir ->
+        ProcessBuilder(command).directory(dir.toFile()).start()
+    }
+
+    override fun start(
+        command: String,
+        workingDir: Path,
+        environment: Map<String, String>,
+        repoDir: Path,
+        branchConfig: BranchConfig,
+    ): Process {
+        val docker = branchConfig.docker
+        require(docker.image.isNotBlank()) { "branches.<name>.docker.image must be set when docker.enabled is true" }
+        val repoKey = ArtifactKeys.repoKey(repoDir)
+        cleanupStaleContainersOnce(repoKey, repoDir)
+        ensureImage(docker, repoDir)
+        val uid = id("-u", repoDir)
+        val gid = id("-g", repoDir)
+        val volume = gradleVolumeName(repoKey)
+        prepareGradleVolume(volume, docker.image, uid, gid, repoDir)
+        val containerName = containerName(repoKey, environment["branch"])
+        removeContainer(containerName, repoDir)
+        val runCommand =
+            runArgs(
+                command = command,
+                workspace = workingDir.toAbsolutePath().normalize(),
+                environment = environment,
+                docker = docker,
+                repoKey = repoKey,
+                containerName = containerName,
+                volume = volume,
+                uid = uid,
+                gid = gid,
+            )
+        return processStarter(runCommand, repoDir)
+    }
+
+    /**
+     * Legacy `ensure_docker_build_image`: without a configured Dockerfile the image
+     * is used as-is (pulled by `docker run` on demand); otherwise it is (re)built
+     * whenever it is missing or its build-inputs label no longer matches.
+     */
+    private fun ensureImage(
+        docker: DockerConfig,
+        repoDir: Path,
+    ) {
+        if (docker.dockerfile.isBlank()) {
+            return
+        }
+        val dockerfileHash = DockerImageInputs.dockerfileSha256(repoDir.resolve(docker.dockerfile))
+        val inputsHash = DockerImageInputs.inputsSha256(dockerfileHash, docker.dockerfile, docker.context)
+        val inspect =
+            commandRunner.run(
+                listOf("docker", "image", "inspect", docker.image, "--format", INSPECT_INPUTS_LABEL_FORMAT),
+                repoDir,
+            )
+        if (inspect.isSuccess && inspect.stdout.trim() == inputsHash) {
+            return
+        }
+        log.info("building Docker image {} from {}", docker.image, docker.dockerfile)
+        commandRunner.runOrThrow(
+            listOf(
+                "docker",
+                "build",
+                "--label",
+                "org.gittally.dockerfile=${docker.dockerfile}",
+                "--label",
+                "org.gittally.dockerfile-sha256=$dockerfileHash",
+                "--label",
+                "org.gittally.build-context=${docker.context}",
+                "--label",
+                "${DockerImageInputs.INPUTS_LABEL}=$inputsHash",
+                "-t",
+                docker.image,
+                "-f",
+                docker.dockerfile,
+                docker.context,
+            ),
+            repoDir,
+        )
+    }
+
+    /**
+     * Legacy `prepare_docker_gradle_volume`: create the per-repo Gradle cache volume
+     * and chown it to the host user — once per process and image.
+     */
+    @Synchronized
+    private fun prepareGradleVolume(
+        volume: String,
+        image: String,
+        uid: String,
+        gid: String,
+        repoDir: Path,
+    ) {
+        val key = "$volume@$image"
+        if (key in preparedVolumes) {
+            return
+        }
+        commandRunner.runOrThrow(listOf("docker", "volume", "create", volume), repoDir)
+        commandRunner.runOrThrow(
+            listOf(
+                "docker",
+                "run",
+                "--rm",
+                "--user",
+                "0",
+                "--volume",
+                "$volume:/gradle-user-home",
+                image,
+                "sh",
+                "-c",
+                VOLUME_PREPARE_SCRIPT,
+                "sh",
+                uid,
+                gid,
+            ),
+            repoDir,
+        )
+        preparedVolumes += key
+    }
+
+    /**
+     * Legacy `cleanup_stale_build_runtime`, run before the first Docker build of this
+     * process instead of at daemon startup, so hosts that never build in Docker never
+     * see a docker call: force-remove all leftover build containers of this repository.
+     */
+    @Synchronized
+    private fun cleanupStaleContainersOnce(
+        repoKey: String,
+        repoDir: Path,
+    ) {
+        if (staleContainersCleaned) {
+            return
+        }
+        staleContainersCleaned = true
+        val listing =
+            commandRunner.run(
+                listOf(
+                    "docker",
+                    "ps",
+                    "-aq",
+                    "--filter",
+                    "label=$GITTALLY_LABEL=true",
+                    "--filter",
+                    "label=$GITTALLY_LABEL.repository=$repoKey",
+                    "--filter",
+                    "label=$GITTALLY_LABEL.role=build",
+                ),
+                repoDir,
+            )
+        if (!listing.isSuccess) {
+            log.warn("could not list stale build containers: {}", listing.stderr.trim())
+            return
+        }
+        val containers = listing.lines()
+        if (containers.isEmpty()) {
+            return
+        }
+        log.info("removing {} stale build container(s)", containers.size)
+        commandRunner.run(listOf("docker", "rm", "-f") + containers, repoDir)
+    }
+
+    private fun removeContainer(
+        containerName: String,
+        repoDir: Path,
+    ) {
+        commandRunner.run(listOf("docker", "rm", "-f", containerName), repoDir)
+    }
+
+    private fun runArgs(
+        command: String,
+        workspace: Path,
+        environment: Map<String, String>,
+        docker: DockerConfig,
+        repoKey: String,
+        containerName: String,
+        volume: String,
+        uid: String,
+        gid: String,
+    ): List<String> {
+        val socket = socketLocator.locate(uid)
+        val args = mutableListOf("docker", "run", "--rm", "--init", "--name", containerName)
+        args +=
+            listOf(
+                "--label",
+                "$GITTALLY_LABEL=true",
+                "--label",
+                "$GITTALLY_LABEL.repository=$repoKey",
+                "--label",
+                "$GITTALLY_LABEL.role=build",
+            )
+        args += listOf("--workdir", "$workspace", "--volume", "$workspace:$workspace")
+        args += listOf("--volume", "$volume:/gradle-user-home")
+        args += listOf("--env", "HOME=/tmp/docker-home", "--env", "GRADLE_USER_HOME=/gradle-user-home")
+        for ((key, value) in environment) {
+            args += listOf("--env", "$key=$value")
+        }
+        for ((key, value) in docker.env) {
+            args += listOf("--env", "$key=$value")
+        }
+        if (docker.network.isNotBlank()) {
+            args += listOf("--network", docker.network)
+        }
+        if (socket != null) {
+            args += listOf("--volume", "${socket.path}:/var/run/docker.sock")
+            args += listOf("--env", "TESTCONTAINERS_DOCKER_SOCKET_OVERRIDE=/var/run/docker.sock")
+            args += listOf("--env", "DOCKER_HOST=unix:///var/run/docker.sock")
+            if (!socket.rootless && socket.gid != null) {
+                args += listOf("--group-add", socket.gid.toString())
+            }
+        }
+        args += listOf("--user", if (socket?.rootless == true) uid else "0")
+        val hostOverride = if (docker.network == "host") "localhost" else "host.docker.internal"
+        args += listOf("--env", "TESTCONTAINERS_HOST_OVERRIDE=$hostOverride")
+        if (docker.network != "host") {
+            args += listOf("--add-host", "host.docker.internal:host-gateway")
+        }
+        args += docker.image
+        args += listOf("sh", "-c", OWNERSHIP_REPAIR_SCRIPT, "sh", uid, gid, command)
+        return args
+    }
+
+    private fun id(
+        flag: String,
+        repoDir: Path,
+    ): String = commandRunner.runOrThrow(listOf("id", flag), repoDir).stdout.trim()
+
+    companion object {
+        /** Container label namespace; legacy used `org.hostsharing.gittally`. */
+        const val GITTALLY_LABEL = "org.hoennig.gittally"
+
+        fun gradleVolumeName(repoKey: String): String = "gittally-gradle-$repoKey"
+
+        fun containerName(
+            repoKey: String,
+            branch: String?,
+        ): String = "gittally-build-$repoKey" + (branch?.let { "-${ArtifactKeys.branchKey(it)}" } ?: "")
+
+        private val INSPECT_INPUTS_LABEL_FORMAT = """{{ index .Config.Labels "${DockerImageInputs.INPUTS_LABEL}" }}"""
+
+        /** Legacy `prepare_docker_gradle_volume` container script, verbatim. */
+        private const val VOLUME_PREPARE_SCRIPT =
+            "mkdir -p /gradle-user-home/wrapper/dists && chown -R \"\$1:\$2\" /gradle-user-home && chmod -R u+rwX /gradle-user-home"
+
+        /**
+         * Runs the build command and then repairs the workspace ownership (legacy
+         * `repair_docker_workspace_ownership`) inside the same container, preserving
+         * the build's exit code.
+         */
+        private const val OWNERSHIP_REPAIR_SCRIPT =
+            "bash -c \"\$3\"; build_exit=\$?; " +
+                "for path in build .gradle; do " +
+                "if [ -e \"\$path\" ]; then chown -R \"\$1:\$2\" \"\$path\" && chmod -R u+rwX \"\$path\"; fi; " +
+                "done; " +
+                "exit \$build_exit"
+    }
+}
@@ -0,0 +1,28 @@
+package de.hoennig.gittally.build
+
+import java.nio.file.Files
+import java.nio.file.Path
+import java.security.MessageDigest
+
+/**
+ * Staleness checksum of the Docker image build inputs, compatible with legacy
+ * `docker_build_inputs_sha256`: the SHA-256 of the Dockerfile contents combined
+ * with the configured Dockerfile and context paths, stored as an image label.
+ */
+object DockerImageInputs {
+    const val INPUTS_LABEL = "org.gittally.build-inputs-sha256"
+
+    fun dockerfileSha256(dockerfile: Path): String = sha256Hex(Files.readAllBytes(dockerfile))
+
+    fun inputsSha256(
+        dockerfileHash: String,
+        dockerfile: String,
+        context: String,
+    ): String = sha256Hex("$dockerfileHash\n$dockerfile\n$context\n".toByteArray())
+
+    private fun sha256Hex(bytes: ByteArray): String =
+        MessageDigest
+            .getInstance("SHA-256")
+            .digest(bytes)
+            .joinToString("") { "%02x".format(it) }
+}
@@ -0,0 +1,46 @@
+package de.hoennig.gittally.build
+
+import org.springframework.stereotype.Component
+import java.nio.file.Files
+import java.nio.file.Path
+import java.nio.file.Paths
+
+/** The host-side Docker socket a build container should talk to. */
+data class DockerSocket(
+    val path: Path,
+    /** True for a rootless daemon socket (`/run/user/<uid>/docker.sock`); the container then runs as the host user. */
+    val rootless: Boolean,
+    /** Group id owning the socket, for `--group-add` on rootful daemons; null when unavailable. */
+    val gid: Long?,
+)
+
+/**
+ * Port of the legacy socket detection: a unix `DOCKER_HOST` wins, then the rootless
+ * user socket, then the system socket. Returns null when no unix socket exists
+ * (e.g. a tcp:// daemon); the build container then runs without a socket mount.
+ */
+@Component
+class DockerSocketLocator {
+    fun locate(uid: String): DockerSocket? {
+        val dockerHost = System.getenv("DOCKER_HOST").orEmpty()
+        val rootlessPath = Paths.get("/run/user/$uid/docker.sock")
+        val path =
+            when {
+                dockerHost.startsWith("unix://") -> Paths.get(dockerHost.removePrefix("unix://"))
+                dockerHost.isNotEmpty() -> return null
+                Files.exists(rootlessPath) -> rootlessPath
+                else -> Paths.get("/var/run/docker.sock")
+            }
+        if (!Files.exists(path)) {
+            return null
+        }
+        return DockerSocket(path = path, rootless = path == rootlessPath, gid = socketGid(path))
+    }
+
+    private fun socketGid(path: Path): Long? =
+        try {
+            (Files.getAttribute(path, "unix:gid") as? Number)?.toLong()
+        } catch (_: Exception) {
+            null
+        }
+}
@@ -153,6 +153,13 @@ class InitCommand(
                autoBuild:
                  enabled: false        # whether to rebuild on schedule
                  times: ["01:00"]      # UTC times HH:MM for scheduled builds
+                docker:
+                  enabled: false        # run clean/build commands in a Docker container instead of natively
+                  image: ""             # image for the build container; required when enabled
+                  dockerfile: ""        # Dockerfile to (re)build the image from when missing or stale; empty pulls the image as-is
+                  context: "."          # Docker build context used with dockerfile
+                  network: ""           # Docker network mode for the build container; empty = Docker default
+                  env: {}               # additional environment variables set inside the build container
            """.trimIndent()
        file.toFile().writeText(content + "\n")
        println("created ${file.toFile().relativeTo(normalizedWorkingDir.toFile())}")
@@ -58,6 +58,22 @@ data class BranchConfig(
    val stdoutLog: String = "build.stdout.log",
    val stderrLog: String = "build.stderr.log",
    val autoBuild: AutoBuildConfig = AutoBuildConfig(),
+    val docker: DockerConfig = DockerConfig(),
+)
+
+data class DockerConfig(
+    /** Run the clean and build commands in a Docker container instead of natively. */
+    val enabled: Boolean = false,
+    /** Image for the build container; required when [enabled]. */
+    val image: String = "",
+    /** Dockerfile to build [image] from when it is missing or stale; empty uses [image] as-is (pulled on demand). */
+    val dockerfile: String = "",
+    /** Docker build context used with [dockerfile]. */
+    val context: String = ".",
+    /** Docker network mode for the build container; empty uses Docker's default network. */
+    val network: String = "",
+    /** Additional environment variables set inside the build container. */
+    val env: Map<String, String> = emptyMap(),
 )

 data class AutoBuildConfig(
@@ -0,0 +1,42 @@
+package de.hoennig.gittally.build
+
+import de.hoennig.gittally.config.BranchConfig
+import de.hoennig.gittally.config.DockerConfig
+import io.kotest.core.spec.style.FunSpec
+import io.kotest.matchers.shouldBe
+import io.mockk.Called
+import io.mockk.clearMocks
+import io.mockk.every
+import io.mockk.mockk
+import io.mockk.verify
+import java.nio.file.Paths
+
+class DispatchingBuildRunnerTest : FunSpec() {
+    private val processBuildRunner = mockk<ProcessBuildRunner>()
+    private val dockerBuildRunner = mockk<DockerBuildRunner>()
+    private val dispatcher = DispatchingBuildRunner(processBuildRunner, dockerBuildRunner)
+    private val process = mockk<Process>()
+    private val dir = Paths.get(".")
+
+    init {
+        beforeEach { clearMocks(processBuildRunner, dockerBuildRunner) }
+
+        test("runs natively by default") {
+            val branchConfig = BranchConfig()
+            every { processBuildRunner.start("cmd", dir, emptyMap(), dir, branchConfig) } returns process
+
+            dispatcher.start("cmd", dir, emptyMap(), dir, branchConfig) shouldBe process
+
+            verify { dockerBuildRunner wasNot Called }
+        }
+
+        test("runs in Docker when the branch enables it") {
+            val branchConfig = BranchConfig(docker = DockerConfig(enabled = true, image = "build-env:latest"))
+            every { dockerBuildRunner.start("cmd", dir, emptyMap(), dir, branchConfig) } returns process
+
+            dispatcher.start("cmd", dir, emptyMap(), dir, branchConfig) shouldBe process
+
+            verify { processBuildRunner wasNot Called }
+        }
+    }
+}
@@ -0,0 +1,248 @@
+package de.hoennig.gittally.build
+
+import de.hoennig.gittally.config.BranchConfig
+import de.hoennig.gittally.config.DockerConfig
+import de.hoennig.gittally.git.GitCommandResult
+import de.hoennig.gittally.git.GitCommandRunner
+import io.kotest.assertions.throwables.shouldThrow
+import io.kotest.core.spec.style.FunSpec
+import io.kotest.matchers.collections.shouldContain
+import io.kotest.matchers.collections.shouldNotContain
+import io.kotest.matchers.shouldBe
+import io.kotest.matchers.string.shouldContain
+import io.mockk.clearMocks
+import io.mockk.every
+import io.mockk.mockk
+import io.mockk.verify
+import java.nio.file.Files
+import java.nio.file.Path
+import java.nio.file.Paths
+
+class DockerBuildRunnerTest : FunSpec() {
+    private val commandRunner = mockk<GitCommandRunner>()
+    private val socketLocator = mockk<DockerSocketLocator>()
+    private lateinit var runner: DockerBuildRunner
+    private lateinit var repoDir: Path
+    private lateinit var workspace: Path
+    private val captured = mutableListOf<List<String>>()
+
+    private fun dockerBranchConfig(
+        image: String = "build-env:latest",
+        dockerfile: String = "",
+        network: String = "",
+        env: Map<String, String> = emptyMap(),
+    ): BranchConfig =
+        BranchConfig(
+            docker =
+                DockerConfig(
+                    enabled = true,
+                    image = image,
+                    dockerfile = dockerfile,
+                    network = network,
+                    env = env,
+                ),
+        )
+
+    init {
+        beforeEach {
+            clearMocks(commandRunner, socketLocator)
+            captured.clear()
+            repoDir = Files.createTempDirectory("gittally-docker-runner")
+            workspace = repoDir.resolve("workspace")
+            every { commandRunner.run(any(), any(), any()) } returns GitCommandResult(0, "", "")
+            every { commandRunner.runOrThrow(any(), any(), any()) } returns GitCommandResult(0, "", "")
+            every { commandRunner.runOrThrow(listOf("id", "-u"), any(), any()) } returns GitCommandResult(0, "1000\n", "")
+            every { commandRunner.runOrThrow(listOf("id", "-g"), any(), any()) } returns GitCommandResult(0, "1001\n", "")
+            every { socketLocator.locate("1000") } returns
+                DockerSocket(Paths.get("/var/run/docker.sock"), rootless = false, gid = 999L)
+            runner = DockerBuildRunner(commandRunner, socketLocator)
+            runner.processStarter = { command, _ ->
+                captured += command
+                ProcessBuilder("true").start()
+            }
+        }
+
+        test("assembles the exact docker run command (rootful socket, default network)") {
+            val branchConfig = dockerBranchConfig(env = mapOf("FOO" to "bar"))
+
+            runner.start("./gradlew test", workspace, mapOf("branch" to "main"), repoDir, branchConfig)
+
+            val repoKey = ArtifactKeys.repoKey(repoDir)
+            val args = captured.single()
+            val script = args[args.size - 5]
+            args shouldBe
+                listOf(
+                    "docker",
+                    "run",
+                    "--rm",
+                    "--init",
+                    "--name",
+                    "gittally-build-$repoKey-${ArtifactKeys.branchKey("main")}",
+                    "--label",
+                    "org.hoennig.gittally=true",
+                    "--label",
+                    "org.hoennig.gittally.repository=$repoKey",
+                    "--label",
+                    "org.hoennig.gittally.role=build",
+                    "--workdir",
+                    "$workspace",
+                    "--volume",
+                    "$workspace:$workspace",
+                    "--volume",
+                    "gittally-gradle-$repoKey:/gradle-user-home",
+                    "--env",
+                    "HOME=/tmp/docker-home",
+                    "--env",
+                    "GRADLE_USER_HOME=/gradle-user-home",
+                    "--env",
+                    "branch=main",
+                    "--env",
+                    "FOO=bar",
+                    "--volume",
+                    "/var/run/docker.sock:/var/run/docker.sock",
+                    "--env",
+                    "TESTCONTAINERS_DOCKER_SOCKET_OVERRIDE=/var/run/docker.sock",
+                    "--env",
+                    "DOCKER_HOST=unix:///var/run/docker.sock",
+                    "--group-add",
+                    "999",
+                    "--user",
+                    "0",
+                    "--env",
+                    "TESTCONTAINERS_HOST_OVERRIDE=host.docker.internal",
+                    "--add-host",
+                    "host.docker.internal:host-gateway",
+                    "build-env:latest",
+                    "sh",
+                    "-c",
+                    script,
+                    "sh",
+                    "1000",
+                    "1001",
+                    "./gradlew test",
+                )
+            script shouldContain "bash -c \"\$3\""
+            script shouldContain "chown -R \"\$1:\$2\""
+            script shouldContain "exit \$build_exit"
+        }
+
+        test("a rootless socket runs the container as the host user without group-add") {
+            every { socketLocator.locate("1000") } returns
+                DockerSocket(Paths.get("/run/user/1000/docker.sock"), rootless = true, gid = 998L)
+
+            runner.start("./gradlew test", workspace, mapOf("branch" to "main"), repoDir, dockerBranchConfig())
+
+            val args = captured.single()
+            args shouldContain "/run/user/1000/docker.sock:/var/run/docker.sock"
+            args[args.indexOf("--user") + 1] shouldBe "1000"
+            args shouldNotContain "--group-add"
+        }
+
+        test("host network keeps Testcontainers on localhost without add-host") {
+            runner.start("./gradlew test", workspace, mapOf("branch" to "main"), repoDir, dockerBranchConfig(network = "host"))
+
+            val args = captured.single()
+            args[args.indexOf("--network") + 1] shouldBe "host"
+            args shouldContain "TESTCONTAINERS_HOST_OVERRIDE=localhost"
+            args shouldNotContain "--add-host"
+        }
+
+        test("without a docker socket the container runs without socket mount as root") {
+            every { socketLocator.locate("1000") } returns null
+
+            runner.start("./gradlew test", workspace, mapOf("branch" to "main"), repoDir, dockerBranchConfig())
+
+            val args = captured.single()
+            args shouldNotContain "/var/run/docker.sock:/var/run/docker.sock"
+            args shouldNotContain "DOCKER_HOST=unix:///var/run/docker.sock"
+            args[args.indexOf("--user") + 1] shouldBe "0"
+        }
+
+        test("builds a missing image from the Dockerfile with the input labels") {
+            Files.writeString(repoDir.resolve("Dockerfile"), "FROM eclipse-temurin:21\n")
+            every { commandRunner.run(match { it.take(3) == listOf("docker", "image", "inspect") }, any(), any()) } returns
+                GitCommandResult(1, "", "no such image")
+
+            runner.start("./gradlew test", workspace, mapOf("branch" to "main"), repoDir, dockerBranchConfig(dockerfile = "Dockerfile"))
+
+            val dockerfileHash = DockerImageInputs.dockerfileSha256(repoDir.resolve("Dockerfile"))
+            val inputsHash = DockerImageInputs.inputsSha256(dockerfileHash, "Dockerfile", ".")
+            verify {
+                commandRunner.runOrThrow(
+                    listOf(
+                        "docker",
+                        "build",
+                        "--label",
+                        "org.gittally.dockerfile=Dockerfile",
+                        "--label",
+                        "org.gittally.dockerfile-sha256=$dockerfileHash",
+                        "--label",
+                        "org.gittally.build-context=.",
+                        "--label",
+                        "org.gittally.build-inputs-sha256=$inputsHash",
+                        "-t",
+                        "build-env:latest",
+                        "-f",
+                        "Dockerfile",
+                        ".",
+                    ),
+                    repoDir,
+                )
+            }
+        }
+
+        test("skips the image build when the build-inputs label still matches") {
+            Files.writeString(repoDir.resolve("Dockerfile"), "FROM eclipse-temurin:21\n")
+            val dockerfileHash = DockerImageInputs.dockerfileSha256(repoDir.resolve("Dockerfile"))
+            val inputsHash = DockerImageInputs.inputsSha256(dockerfileHash, "Dockerfile", ".")
+            every { commandRunner.run(match { it.take(3) == listOf("docker", "image", "inspect") }, any(), any()) } returns
+                GitCommandResult(0, "$inputsHash\n", "")
+
+            runner.start("./gradlew test", workspace, mapOf("branch" to "main"), repoDir, dockerBranchConfig(dockerfile = "Dockerfile"))
+
+            verify(exactly = 0) {
+                commandRunner.runOrThrow(match { it.take(2) == listOf("docker", "build") }, any(), any())
+            }
+        }
+
+        test("prepares the gradle cache volume once but removes the container before every command") {
+            val branchConfig = dockerBranchConfig()
+
+            runner.start("./gradlew clean", workspace, mapOf("branch" to "main"), repoDir, branchConfig)
+            runner.start("./gradlew test", workspace, mapOf("branch" to "main"), repoDir, branchConfig)
+
+            val repoKey = ArtifactKeys.repoKey(repoDir)
+            verify(exactly = 1) {
+                commandRunner.runOrThrow(listOf("docker", "volume", "create", "gittally-gradle-$repoKey"), repoDir)
+            }
+            verify(exactly = 2) {
+                commandRunner.run(
+                    listOf("docker", "rm", "-f", "gittally-build-$repoKey-${ArtifactKeys.branchKey("main")}"),
+                    repoDir,
+                )
+            }
+        }
+
+        test("removes stale labelled build containers once, before the first docker build") {
+            every { commandRunner.run(match { it.take(3) == listOf("docker", "ps", "-aq") }, any(), any()) } returns
+                GitCommandResult(0, "abc\ndef\n", "")
+
+            runner.start("./gradlew clean", workspace, mapOf("branch" to "main"), repoDir, dockerBranchConfig())
+            runner.start("./gradlew test", workspace, mapOf("branch" to "main"), repoDir, dockerBranchConfig())
+
+            verify(exactly = 1) { commandRunner.run(match { it.take(3) == listOf("docker", "ps", "-aq") }, any(), any()) }
+            verify { commandRunner.run(listOf("docker", "rm", "-f", "abc", "def"), repoDir) }
+        }
+
+        test("fails without a configured image") {
+            val branchConfig = BranchConfig(docker = DockerConfig(enabled = true))
+
+            val exception =
+                shouldThrow<IllegalArgumentException> {
+                    runner.start("./gradlew test", workspace, mapOf("branch" to "main"), repoDir, branchConfig)
+                }
+
+            exception.message shouldContain "docker.image"
+        }
+    }
+}
@@ -0,0 +1,51 @@
+package de.hoennig.gittally.build
+
+import io.kotest.core.spec.style.FunSpec
+import io.kotest.matchers.shouldBe
+import io.kotest.matchers.shouldNotBe
+import io.kotest.matchers.string.shouldMatch
+import java.nio.file.Files
+
+class DockerImageInputsTest : FunSpec() {
+    init {
+        test("dockerfileSha256 is a stable hex checksum of the file contents") {
+            val dir = Files.createTempDirectory("gittally-docker-inputs")
+            val dockerfile = dir.resolve("Dockerfile")
+            Files.writeString(dockerfile, "FROM eclipse-temurin:21\n")
+
+            val hash = DockerImageInputs.dockerfileSha256(dockerfile)
+
+            hash shouldMatch Regex("[0-9a-f]{64}")
+            DockerImageInputs.dockerfileSha256(dockerfile) shouldBe hash
+        }
+
+        test("inputs checksum changes when the Dockerfile contents change") {
+            val dir = Files.createTempDirectory("gittally-docker-inputs")
+            val dockerfile = dir.resolve("Dockerfile")
+            Files.writeString(dockerfile, "FROM eclipse-temurin:21\n")
+            val before =
+                DockerImageInputs.inputsSha256(
+                    DockerImageInputs.dockerfileSha256(dockerfile),
+                    "Dockerfile",
+                    ".",
+                )
+
+            Files.writeString(dockerfile, "FROM eclipse-temurin:22\n")
+
+            DockerImageInputs.inputsSha256(
+                DockerImageInputs.dockerfileSha256(dockerfile),
+                "Dockerfile",
+                ".",
+            ) shouldNotBe before
+        }
+
+        test("inputs checksum changes when the Dockerfile path or the context change") {
+            val dockerfileHash = "0".repeat(64)
+            val base = DockerImageInputs.inputsSha256(dockerfileHash, "ci/Dockerfile", "ci")
+
+            DockerImageInputs.inputsSha256(dockerfileHash, "other/Dockerfile", "ci") shouldNotBe base
+            DockerImageInputs.inputsSha256(dockerfileHash, "ci/Dockerfile", "other") shouldNotBe base
+            DockerImageInputs.inputsSha256(dockerfileHash, "ci/Dockerfile", "ci") shouldBe base
+        }
+    }
+}