Ensure files and links have missing parent dirs created. Support hard…

… links

Signed-off-by: Jose R. Gonzalez <komish@flutes.dev>

internal/engine/engine.go

@@ -412,6 +412,13 @@ func untar(ctx context.Context, dst string, r io.Reader) error {
 
 		// if it's a file create it
 		case tar.TypeReg:
+			// If the file's parent dir doesn't exist, create it.
+			dirname := filepath.Dir(target)
+			if _, err := os.Stat(dirname); err != nil {
+				if err := os.MkdirAll(dirname, 0o755); err != nil {
+					return err
+				}
+			}
 			f, err := os.OpenFile(target, os.O_CREATE|os.O_RDWR, os.FileMode(header.Mode))
 			if err != nil {
 				return err
@@ -428,16 +435,44 @@ func untar(ctx context.Context, dst string, r io.Reader) error {
 			f.Close()
 
 			// if it's a link create it
-		case tar.TypeSymlink:
-			err := os.Symlink(header.Linkname, filepath.Join(dst, header.Name))
+		case tar.TypeSymlink, tar.TypeLink:
+			ln := os.Symlink
+			if header.Typeflag == tar.TypeLink {
+				ln = os.Link
+			}
+
+			oldNoBase, newNoBase := resolveLinkPaths(header.Linkname, header.Name)
+			old := filepath.Join(dst, oldNoBase)
+			new := filepath.Join(dst, newNoBase)
+			// Create the new link's directory if it doesn't exist.
+			dirname := filepath.Dir(new)
+			if _, err := os.Stat(dirname); err != nil {
+				if err := os.MkdirAll(dirname, 0o755); err != nil {
+					return err
+				}
+			}
+			err := ln(old, new)
 			if err != nil {
-				logger.V(log.DBG).Info(fmt.Sprintf("Error creating link: %s. Ignoring.", header.Name))
+				logger.V(log.DBG).Info(fmt.Sprintf("Error creating link: %s. Ignoring.", header.Name), "link", new, "linkedTo", old)
 				continue
 			}
 		}
 	}
 }
 
+// resolveLinkPaths resolves relative pathing in linkname relative to filename.
+// Relative link names are resolved such that the linkname is no longer relative
+// to filename. E.g etc/c/foo -> ../../usr/lib/foo would become etc/c/foo and usr/lib/foo,
+// making both paths relative to their shared base.
+func resolveLinkPaths(oldname, newname string) (string, string) {
+	if !strings.HasPrefix(oldname, "..") {
+		return oldname, newname
+	}
+
+	linkDir := filepath.Dir(newname)
+	return filepath.Join(linkDir, oldname), newname
+}
+
 // writeCertImage takes imageRef and writes it to disk as JSON representing a pyxis.CertImage
 // struct. The file is written at path certification.DefaultCertImageFilename.
 //

internal/engine/engine_test.go

@@ -379,6 +379,20 @@ var _ = Describe("Check Name Queries", func() {
 	})
 })
 
+var _ = Describe("Link Path Resolution", func() {
+	DescribeTable(
+		"Link targets should resolve correctly",
+		func(old, new, expectedOld, expectedNew string) {
+			resO, resN := resolveLinkPaths(old, new)
+			Expect(resO).To(Equal(expectedOld))
+			Expect(resN).To(Equal(expectedNew))
+		},
+		Entry("Up one level", "../var/lib/file", "etc/file", "var/lib/file", "etc/file"),
+		Entry("Up two levels", "../../var/lib/file", "etc/foo/file", "var/lib/file", "etc/foo/file"),
+		Entry("Up no levels", "var/lib/file", "etc/file", "var/lib/file", "etc/file"),
+	)
+})
+
 // writeTarball writes a tar archive to out with filename containing contents at the base path
 // with extra bytes written at the end of length extraBytes.
 // note: this should only be used as a helper function in tests