Build only the subdirectory a service asks for

cmd/wodby/ci/build/build.go

@@ -141,7 +141,9 @@ var Cmd = &cobra.Command{
 		for _, appServiceBuildConfig := range appServiceBuildConfigs {
 			buildArgs := make(map[string]string)
 			var redactValues []string
-			buildArgs["COPY_FROM"] = opts.from
+			// A service can narrow the build to a subdirectory of the context, so
+			// the flags give the roots and the service gives the path within them.
+			buildArgs["COPY_FROM"] = joinCopyPath(opts.from, appServiceBuildConfig.CopyFrom)
 			buildArgs["WODBY_BASE_IMAGE"] = appServiceBuildConfig.Image
 			buildFiles := newBuildFiles(context, appServiceBuildConfig.Name, opts.dockerfile)
 			cacheFrom, cacheTo, err := resolveCacheOptions(config, appServiceBuildConfig.Name, opts)
@@ -172,7 +174,7 @@ var Cmd = &cobra.Command{
 					return errors.WithStack(err)
 				}
 				dockerfile = string(d)
-				if err := addDockerfileBuildArgs(buildArgs, dockerfile, appServiceBuildConfig, opts.to, logger, &redactValues); err != nil {
+				if err := addDockerfileBuildArgs(buildArgs, dockerfile, appServiceBuildConfig, joinCopyPath(opts.to, appServiceBuildConfig.CopyTo), logger, &redactValues); err != nil {
 					return errors.WithStack(err)
 				}
 			} else if fileExists(buildFiles.dockerfilePath) {
@@ -183,21 +185,21 @@ var Cmd = &cobra.Command{
 					return errors.WithStack(err)
 				}
 				dockerfile = string(d)
-				if err := addDockerfileBuildArgs(buildArgs, dockerfile, appServiceBuildConfig, opts.to, logger, &redactValues); err != nil {
+				if err := addDockerfileBuildArgs(buildArgs, dockerfile, appServiceBuildConfig, joinCopyPath(opts.to, appServiceBuildConfig.CopyTo), logger, &redactValues); err != nil {
 					return errors.WithStack(err)
 				}
 			} else {
 				if appServiceBuildConfig.Dockerfile != nil {
 					dockerfileSource = dockerfileSourceService
 					fmt.Println("Dockerfile provided by app service")
 					dockerfile = *appServiceBuildConfig.Dockerfile
-					if err := addDockerfileBuildArgs(buildArgs, dockerfile, appServiceBuildConfig, opts.to, logger, &redactValues); err != nil {
+					if err := addDockerfileBuildArgs(buildArgs, dockerfile, appServiceBuildConfig, joinCopyPath(opts.to, appServiceBuildConfig.CopyTo), logger, &redactValues); err != nil {
 						return errors.WithStack(err)
 					}
 				} else {
 					dockerfileSource = dockerfileSourceDefault
 					fmt.Println("No Dockerfile provided by app service, using the default")
-					buildArgs["COPY_TO"] = opts.to
+					buildArgs["COPY_TO"] = joinCopyPath(opts.to, appServiceBuildConfig.CopyTo)
 					// Replace default image user in dockerfile template.
 					defaultUser, err := dockerClient.GetImageDefaultUser(appServiceBuildConfig.Image)
 					if err != nil {
@@ -347,6 +349,24 @@ func dockerfileContentHash(dockerfile string) string {
 	return "sha256:" + hex.EncodeToString(sum[:])
 }
 
+// joinCopyPath places a service's copy subdirectory under the root given by the
+// --from/--to flags. An empty subdirectory leaves the root untouched, which is
+// the default whole-context build.
+func joinCopyPath(root string, subdir string) string {
+	if subdir == "" {
+		if root == "" {
+			return "."
+		}
+
+		return root
+	}
+	if root == "" {
+		root = "."
+	}
+
+	return path.Join(root, subdir)
+}
+
 func authoredDockerfile(source string) bool {
 	return source == dockerfileSourceFlag || source == dockerfileSourceContext
 }

cmd/wodby/ci/build/build_test.go

@@ -468,3 +468,27 @@ func TestDockerfileContentHash(t *testing.T) {
 		t.Fatalf("dockerfileContentHash(\"\") = %q, want empty", dockerfileContentHash(""))
 	}
 }
+
+func TestJoinCopyPath(t *testing.T) {
+	for _, tc := range []struct {
+		name   string
+		root   string
+		subdir string
+		want   string
+	}{
+		{name: "default root, no subdir", root: ".", subdir: "", want: "."},
+		{name: "default root with subdir", root: ".", subdir: "web", want: "web"},
+		{name: "explicit root with subdir", root: "static", subdir: "web", want: "static/web"},
+		{name: "absolute destination with subdir", root: "/var/www/html", subdir: "web", want: "/var/www/html/web"},
+		{name: "explicit root, no subdir", root: "static", subdir: "", want: "static"},
+		{name: "empty root, no subdir", root: "", subdir: "", want: "."},
+		{name: "empty root with subdir", root: "", subdir: "web", want: "web"},
+		{name: "nested subdir", root: ".", subdir: "apps/web", want: "apps/web"},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			if got := joinCopyPath(tc.root, tc.subdir); got != tc.want {
+				t.Fatalf("joinCopyPath(%q, %q) = %q, want %q", tc.root, tc.subdir, got, tc.want)
+			}
+		})
+	}
+}

pkg/types/build.go

@@ -25,14 +25,18 @@ type (
 		Services           []*AppServiceBuildConfig `json:"services"`
 	}
 	AppServiceBuildConfig struct {
-		Name         string                `json:"name"`
-		Title        string                `json:"title"`
-		Image        string                `json:"image"`
-		Managed      bool                  `json:"managed"`
-		Main         bool                  `json:"main"`
-		Dockerfile   *string               `json:"dockerfile"`
-		Dockerignore *string               `json:"dockerignore"`
-		Args         []*AppServiceBuildArg `json:"args"`
+		Name         string  `json:"name"`
+		Title        string  `json:"title"`
+		Image        string  `json:"image"`
+		Managed      bool    `json:"managed"`
+		Main         bool    `json:"main"`
+		Dockerfile   *string `json:"dockerfile"`
+		Dockerignore *string `json:"dockerignore"`
+		// CopyFrom and CopyTo narrow the build to a subdirectory, relative to the
+		// --from and --to paths. Empty means copy the whole context.
+		CopyFrom string                `json:"copyFrom"`
+		CopyTo   string                `json:"copyTo"`
+		Args     []*AppServiceBuildArg `json:"args"`
 	}
 	AppServiceBuildArg struct {
 		Name   string `json:"name"`