Add support for setting start script name

Refs: paketo-buildpacks/npm-start#292

Signed-off-by: Michael Dawson <[email protected]>

package_json.go

@@ -10,10 +10,12 @@ import (
 // PackageJSON represents the contents of a package.json file.
 type PackageJSON struct {
 	Scripts struct {
-		PostStart string `json:"poststart"`
-		PreStart  string `json:"prestart"`
-		Start     string `json:"start"`
-	} `json:"scripts"`
+		PostStart string
+		PreStart  string
+		Start     string
+	}
+
+	AllScripts map[string]string `json:"scripts"`
 }
 
 // ParsePackageJSON parses the contents of a package.json file.
@@ -30,11 +32,24 @@ func ParsePackageJSON(path string) (PackageJSON, error) {
 		return PackageJSON{}, fmt.Errorf("unable to decode package.json %w", err)
 	}
 
+	startScriptName := os.Getenv(StartScriptNameEnvName)
+	if startScriptName == "" {
+		startScriptName = "start"
+	} else {
+		if pkg.AllScripts[startScriptName] == "" {
+			return PackageJSON{}, fmt.Errorf("no script entry with name \"%s\" exists", startScriptName)
+		}
+	}
+
+	pkg.Scripts.Start = pkg.AllScripts[startScriptName]
+	pkg.Scripts.PreStart = pkg.AllScripts["prestart"]
+	pkg.Scripts.PostStart = pkg.AllScripts["poststart"]
+
 	return pkg, nil
 }
 
 // HasStartScript indicates the presence of a start script in the package.json
-// file.
+// file or as defined by .
 func (pj PackageJSON) HasStartScript() bool {
 	return pj.Scripts.Start != ""
 }

package_json_test.go

@@ -29,7 +29,8 @@ func testPackageJSON(t *testing.T, context spec.G, it spec.S) {
 			"scripts": {
 				"poststart": "echo \"poststart\"",
 				"prestart": "echo \"prestart\"",
-				"start": "echo \"start\" && node server.js"
+				"start": "echo \"start\" && node server.js",
+				"serve": "echo \"about to serve\" && node app.js"
 			}
 		}`), 0600)).To(Succeed())
 	})
@@ -45,6 +46,37 @@ func testPackageJSON(t *testing.T, context spec.G, it spec.S) {
 		})
 	})
 
+	context("when parsing a valid package.json poststart and prestart are optional", func() {
+		it.Before(func() {
+			Expect(os.WriteFile(filePath, []byte(`{
+				"scripts": {
+					"start": "echo \"start\" && node server.js"
+				}
+			}`), 0600)).To(Succeed())
+		})
+
+		it("successfully extracts the scripts information", func() {
+			pkg, err := libnodejs.ParsePackageJSON(path)
+			Expect(err).NotTo(HaveOccurred())
+
+			Expect(pkg.Scripts.Start).To(ContainSubstring(`echo "start" && node server.js`))
+			Expect(pkg.Scripts.PreStart).To(Equal(``))
+			Expect(pkg.Scripts.PostStart).To(Equal(``))
+		})
+	})
+
+	context("when parsing a valid package.json with BP_NPM_START_SCRIPT", func() {
+		it("successfully extracts the scripts information", func() {
+			t.Setenv("BP_NPM_START_SCRIPT", "serve")
+			pkg, err := libnodejs.ParsePackageJSON(path)
+			Expect(err).NotTo(HaveOccurred())
+
+			Expect(pkg.Scripts.Start).To(ContainSubstring(`echo "about to serve" && node app.js`))
+			Expect(pkg.Scripts.PreStart).To(Equal(`echo "prestart"`))
+			Expect(pkg.Scripts.PostStart).To(Equal(`echo "poststart"`))
+		})
+	})
+
 	context("failure cases", func() {
 		context("when the package.json is not a valid json file", func() {
 			it.Before(func() {
@@ -63,6 +95,24 @@ func testPackageJSON(t *testing.T, context spec.G, it spec.S) {
 				Expect(err).To(HaveOccurred())
 			})
 		})
+
+		context("when parsing a valid package.json with BP_NPM_START_SCRIPT and script does not exist", func() {
+			it.Before(func() {
+				Expect(os.WriteFile(filePath, []byte(`{
+					"scripts": {
+						"poststart": "echo \"poststart\"",
+						"prestart": "echo \"prestart\"",
+						"start": "echo \"start\" && node server.js"
+					}
+				}`), 0600)).To(Succeed())
+			})
+
+			it("fails to extracts the script information", func() {
+				t.Setenv("BP_NPM_START_SCRIPT", "serve")
+				_, err := libnodejs.ParsePackageJSON(path)
+				Expect(err).To(MatchError(ContainSubstring("no script entry with name \"serve\" exists")))
+			})
+		})
 	})
 
 	context("HasStartScript", func() {
@@ -75,6 +125,24 @@ func testPackageJSON(t *testing.T, context spec.G, it spec.S) {
 			})
 		})
 
+		context("when a start script is present and BP_NPM_START_SCRIPT is used", func() {
+			it.Before(func() {
+				Expect(os.WriteFile(filePath, []byte(`{
+					"scripts": {
+						"serve": "echo \"start\" && node server.js"
+					}
+				}`), 0600)).To(Succeed())
+			})
+
+			it("indicates that the package.json file has a start script", func() {
+				t.Setenv("BP_NPM_START_SCRIPT", "serve")
+				pkg, err := libnodejs.ParsePackageJSON(path)
+				Expect(err).NotTo(HaveOccurred())
+
+				Expect(pkg.HasStartScript()).To(BeTrue())
+			})
+		})
+
 		context("when a start script is NOT present", func() {
 			it.Before(func() {
 				Expect(os.WriteFile(filePath, []byte(`{}`), 0600)).To(Succeed())

spec_constants.go

@@ -1,3 +1,4 @@
 package libnodejs
 
 const ProjectPathEnvName = "BP_NODE_PROJECT_PATH"
+const StartScriptNameEnvName = "BP_NPM_START_SCRIPT"