Implement file:// downloads for artifacts

This can be used with dependency mapping bindings to volume mount in external pre-cached artifacts.

Signed-off-by: Daniel Mikusa <dmikusa@vmware.com>

dependency_cache.go

@@ -23,6 +23,7 @@ import (
 	"io"
 	"io/ioutil"
 	"net/http"
+	"net/url"
 	"os"
 	"path/filepath"
 	"reflect"
@@ -187,6 +188,43 @@ func (d *DependencyCache) Artifact(dependency BuildpackDependency, mods ...Reque
 }
 
 func (d DependencyCache) download(uri string, destination string, mods ...RequestModifierFunc) error {
+	url, err := url.Parse(uri)
+	if err != nil {
+		return fmt.Errorf("unable to parse URI %s\n%w", uri, err)
+	}
+
+	if url.Scheme == "file" {
+		return d.downloadFile(url.Path, destination, mods...)
+	}
+
+	return d.downloadHttp(uri, destination, mods...)
+}
+
+func (d DependencyCache) downloadFile(source string, destination string, mods ...RequestModifierFunc) error {
+	if err := os.MkdirAll(filepath.Dir(destination), 0755); err != nil {
+		return fmt.Errorf("unable to make directory %s\n%w", filepath.Dir(destination), err)
+	}
+
+	out, err := os.OpenFile(destination, os.O_CREATE|os.O_TRUNC|os.O_WRONLY, 0644)
+	if err != nil {
+		return fmt.Errorf("unable to open destination file %s\n%w", destination, err)
+	}
+	defer out.Close()
+
+	input, err := os.Open(source)
+	if err != nil {
+		return fmt.Errorf("unable to open source file %s\n%w", source, err)
+	}
+	defer out.Close()
+
+	if _, err := io.Copy(out, input); err != nil {
+		return fmt.Errorf("unable to copy from %s to %s\n%w", source, destination, err)
+	}
+
+	return nil
+}
+
+func (d DependencyCache) downloadHttp(uri string, destination string, mods ...RequestModifierFunc) error {
 	req, err := http.NewRequest("GET", uri, nil)
 	if err != nil {
 		return fmt.Errorf("unable to create new GET request for %s\n%w", uri, err)

dependency_cache_test.go

@@ -223,7 +223,7 @@ func testDependencyCache(t *testing.T, context spec.G, it spec.S) {
 			Expect(ioutil.ReadAll(a)).To(Equal([]byte("test-fixture")))
 		})
 
-		context("uri is overridden", func() {
+		context("uri is overridden HTTP", func() {
 			it.Before(func() {
 				dependencyCache.Mappings = map[string]string{
 					dependency.SHA256: fmt.Sprintf("%s/override-path", server.URL()),
@@ -243,6 +243,26 @@ func testDependencyCache(t *testing.T, context spec.G, it spec.S) {
 			})
 		})
 
+		context("uri is overridden FILE", func() {
+			it.Before(func() {
+				sourcePath, err := ioutil.TempDir("", "dependency-source-path")
+				Expect(err).NotTo(HaveOccurred())
+				sourceFile := filepath.Join(sourcePath, "source-file")
+				Expect(ioutil.WriteFile(sourceFile, []byte("test-fixture"), 0644)).ToNot(HaveOccurred())
+
+				dependencyCache.Mappings = map[string]string{
+					dependency.SHA256: fmt.Sprintf("file://%s", sourceFile),
+				}
+			})
+
+			it("downloads from override filesystem", func() {
+				a, err := dependencyCache.Artifact(dependency)
+				Expect(err).NotTo(HaveOccurred())
+
+				Expect(ioutil.ReadAll(a)).To(Equal([]byte("test-fixture")))
+			})
+		})
+
 		it("fails with invalid SHA256", func() {
 			server.AppendHandlers(ghttp.RespondWith(http.StatusOK, "invalid-fixture"))