CNB_BUILDPACK_DIR (RFC #36)

This change causes the buildpack's path to be determined first by reading CNB_BUILDPACK_DIR if it exists. If it does not, fall back to trimming argv[0]. The fallback is temporary and can be removed once the lifecycle supports the primary behavior. [buildpacks/rfcs#49] Signed-off-by: Ben Hale <[email protected]>
buildpacks · Apr 22, 2020 · f24419c · f24419c
1 parent 8b98016
commit f24419c
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Showing 4 changed files with 45 additions and 4 deletions.
diff --git a/build.go b/build.go
@@ -133,7 +133,11 @@ func Build(builder Builder, options ...Option) {
 		logger.Debug(ApplicationPathFormatter(ctx.Application.Path))
 	}
 
-	ctx.Buildpack.Path = filepath.Clean(strings.TrimSuffix(config.arguments[0], filepath.Join("bin", "build")))
+	if s, ok := os.LookupEnv("CNB_BUILDPACK_DIR"); ok {
+		ctx.Buildpack.Path = filepath.Clean(s)
+	} else {  // TODO: Remove branch once lifecycle has been updated to support this
+		ctx.Buildpack.Path = filepath.Clean(strings.TrimSuffix(config.arguments[0], filepath.Join("bin", "build")))
+	}
 	if logger.IsDebugEnabled() {
 		logger.Debug(BuildpackPathFormatter(ctx.Buildpack.Path))
 	}

diff --git a/build_test.go b/build_test.go
@@ -61,6 +61,7 @@ func testBuild(t *testing.T, context spec.G, it spec.S) {
 
 		buildpackPath, err = ioutil.TempDir("", "build-buildpack-path")
 		Expect(err).NotTo(HaveOccurred())
+		Expect(os.Setenv("CNB_BUILDPACK_DIR", buildpackPath)).To(Succeed())
 
 		Expect(ioutil.WriteFile(filepath.Join(buildpackPath, "buildpack.toml"),
 			[]byte(`
@@ -105,7 +106,7 @@ test-key = "test-value"
 			0644),
 		).To(Succeed())
 
-		commandPath = filepath.Join(buildpackPath, "bin", "build")
+		commandPath = filepath.Join("bin", "build")
 
 		environmentWriter = &mocks.EnvironmentWriter{}
 		environmentWriter.On("Write", mock.Anything, mock.Anything).Return(nil)
@@ -158,6 +159,7 @@ test-key = "test-value"
 
 	it.After(func() {
 		Expect(os.Chdir(workingDir)).To(Succeed())
+		Expect(os.Unsetenv("CNB_BUILDPACK_DIR")).To(Succeed())
 		Expect(os.Unsetenv("CNB_STACK_ID")).To(Succeed())
 
 		Expect(os.RemoveAll(applicationPath)).To(Succeed())
@@ -256,6 +258,20 @@ test-key = "test-value"
 		Expect(ctx.StackID).To(Equal("test-stack-id"))
 	})
 
+	it("extracts buildpack path from command path if CNB_BUILDPACK_PATH is not set", func() {
+		Expect(os.Unsetenv("CNB_BUILDPACK_DIR")).To(Succeed())
+
+		builder.On("Build", mock.Anything).Return(libcnb.NewBuildResult(), nil)
+
+		libcnb.Build(builder,
+			libcnb.WithArguments([]string{filepath.Join(buildpackPath, commandPath), layersPath, platformPath, buildpackPlanPath}),
+		)
+
+		ctx := builder.Calls[0].Arguments[0].(libcnb.BuildContext)
+
+		Expect(ctx.Buildpack.Path).To(Equal(buildpackPath))
+	})
+
 	it("handles error from BuildFunc", func() {
 		builder.On("Build", mock.Anything).Return(libcnb.NewBuildResult(), fmt.Errorf("test-error"))
 

diff --git a/detect.go b/detect.go
@@ -97,7 +97,11 @@ func Detect(detector Detector, options ...Option) {
 		logger.Debug(ApplicationPathFormatter(ctx.Application.Path))
 	}
 
-	ctx.Buildpack.Path = filepath.Clean(strings.TrimSuffix(config.arguments[0], filepath.Join("bin", "detect")))
+	if s, ok := os.LookupEnv("CNB_BUILDPACK_DIR"); ok {
+		ctx.Buildpack.Path = filepath.Clean(s)
+	} else {  // TODO: Remove branch once lifecycle has been updated to support this
+		ctx.Buildpack.Path = filepath.Clean(strings.TrimSuffix(config.arguments[0], filepath.Join("bin", "detect")))
+	}
 	if logger.IsDebugEnabled() {
 		logger.Debug(BuildpackPathFormatter(ctx.Buildpack.Path))
 	}

diff --git a/detect_test.go b/detect_test.go
@@ -56,6 +56,7 @@ func testDetect(t *testing.T, context spec.G, it spec.S) {
 
 		buildpackPath, err = ioutil.TempDir("", "detect-buildpack-path")
 		Expect(err).NotTo(HaveOccurred())
+		Expect(os.Setenv("CNB_BUILDPACK_DIR", buildpackPath)).To(Succeed())
 
 		Expect(ioutil.WriteFile(filepath.Join(buildpackPath, "buildpack.toml"),
 			[]byte(`
@@ -88,7 +89,7 @@ test-key = "test-value"
 		Expect(f.Close()).NotTo(HaveOccurred())
 		buildPlanPath = f.Name()
 
-		commandPath = filepath.Join(buildpackPath, "bin", "detect")
+		commandPath = filepath.Join("bin", "detect")
 
 		detector = &mocks.Detector{}
 
@@ -129,6 +130,7 @@ test-key = "test-value"
 
 	it.After(func() {
 		Expect(os.Chdir(workingDir)).To(Succeed())
+		Expect(os.Unsetenv("CNB_BUILDPACK_DIR")).To(Succeed())
 		Expect(os.Unsetenv("CNB_STACK_ID")).To(Succeed())
 
 		Expect(os.RemoveAll(applicationPath)).To(Succeed())
@@ -216,6 +218,21 @@ test-key = "test-value"
 		Expect(ctx.StackID).To(Equal("test-stack-id"))
 	})
 
+	it("extracts buildpack path from command path if CNB_BUILDPACK_PATH is not set", func() {
+		Expect(os.Unsetenv("CNB_BUILDPACK_DIR")).To(Succeed())
+
+		detector.On("Detect", mock.Anything).Return(libcnb.DetectResult{}, nil)
+
+		libcnb.Detect(detector,
+			libcnb.WithArguments([]string{filepath.Join(buildpackPath, commandPath), platformPath, buildPlanPath}),
+			libcnb.WithExitHandler(exitHandler),
+		)
+
+		ctx := detector.Calls[0].Arguments[0].(libcnb.DetectContext)
+
+		Expect(ctx.Buildpack.Path).To(Equal(buildpackPath))
+	})
+
 	it("handles error from DetectFunc", func() {
 		detector.On("Detect", mock.Anything).Return(libcnb.DetectResult{}, fmt.Errorf("test-error"))