Allow for overriding default dependency source

dependency_cache.go

@@ -164,15 +164,17 @@ type RequestModifierFunc func(request *http.Request) (*http.Request, error)
 func (d *DependencyCache) Artifact(dependency BuildpackDependency, mods ...RequestModifierFunc) (*os.File, error) {
 
 	var (
-		actual   BuildpackDependency
-		artifact string
-		file     string
-		uri      = dependency.URI
-		urlP     *url.URL
+		actual    BuildpackDependency
+		artifact  string
+		file      string
+		isBinding bool
+		uri       = dependency.URI
+		urlP      *url.URL
 	)
 
 	for d, u := range d.Mappings {
 		if d == dependency.SHA256 {
+			isBinding = true
 			uri = u
 			break
 		}
@@ -184,6 +186,10 @@ func (d *DependencyCache) Artifact(dependency BuildpackDependency, mods ...Reque
 		return nil, fmt.Errorf("unable to parse URI. see DEBUG log level")
 	}
 
+	if !isBinding {
+		d.overrideDependencySource(urlP)
+	}
+
 	if dependency.SHA256 == "" {
 		d.Logger.Headerf("%s Dependency has no SHA256. Skipping cache.",
 			color.New(color.FgYellow, color.Bold).Sprint("Warning:"))
@@ -363,3 +369,20 @@ func (DependencyCache) verify(path string, expected string) error {
 
 	return nil
 }
+
+func (d DependencyCache) overrideDependencySource(urlD *url.URL) {
+	dependencySourceOverride := sherpa.GetEnvWithDefault("BP_DEPENDENCY_SOURCE_OVERRIDE", "")
+	if dependencySourceOverride != "" {
+		d.Logger.Infof("variable BP_DEPENDENCY_SOURCE_OVERRIDE found. overriding download uri.")
+		urlOverride, err := url.ParseRequestURI(dependencySourceOverride)
+		if err == nil {
+			urlD.Scheme = urlOverride.Scheme
+			urlD.User = urlOverride.User
+			urlD.Host = urlOverride.Host
+			urlD.Path = urlOverride.Path + urlD.Path
+		} else {
+			d.Logger.Debugf("environment variable BP_DEPENDENCY_SOURCE_OVERRIDE could not be parsed. value: %s\n%w", dependencySourceOverride, err)
+			d.Logger.Infof("ignoring invalid variable BP_DEPENDENCY_SOURCE_OVERRIDE. continuing without override...")
+		}
+	}
+}

dependency_cache_test.go

@@ -298,6 +298,28 @@ func testDependencyCache(t *testing.T, context spec.G, it spec.S) {
 			})
 		})
 
+		context("source is overridden", func() {
+			serverOverride := ghttp.NewServer()
+			url, _ := url.Parse(serverOverride.URL())
+
+			it.Before(func() {
+				t.Setenv("BP_DEPENDENCY_SOURCE_OVERRIDE", url.Scheme+"://"+"username:password@"+url.Host+"/foo/bar")
+			})
+
+			it("downloads from override source", func() {
+				serverOverride.AppendHandlers(ghttp.CombineHandlers(
+					ghttp.VerifyBasicAuth("username", "password"),
+					ghttp.VerifyRequest(http.MethodGet, "/foo/bar/test-path", ""),
+					ghttp.RespondWith(http.StatusOK, "test-fixture"),
+				))
+
+				a, err := dependencyCache.Artifact(dependency)
+				Expect(err).NotTo(HaveOccurred())
+
+				Expect(io.ReadAll(a)).To(Equal([]byte("test-fixture")))
+			})
+		})
+
 		it("fails with invalid SHA256", func() {
 			server.AppendHandlers(ghttp.RespondWith(http.StatusOK, "invalid-fixture"))