HashFromPathname

Author: Karrick S. McDermott

internal/fs/hash.go

@@ -0,0 +1,93 @@
+package fs
+
+import (
+	"crypto/sha256"
+	"fmt"
+	"io"
+	"os"
+	"strconv"
+
+	"github.com/pkg/errors"
+)
+
+// HashFromPathname returns a hash of the specified file or directory, ignoring
+// all file system objects named, `vendor` and their descendants. This function
+// follows symbolic links.
+func HashFromPathname(pathname string) (hash string, err error) {
+	fi, err := os.Stat(pathname)
+	if err != nil {
+		return "", errors.Wrap(err, "could not stat")
+	}
+	if fi.IsDir() {
+		return hashFromDirectory(pathname, fi)
+	}
+	return hashFromFile(pathname, fi)
+}
+
+func hashFromFile(pathname string, fi os.FileInfo) (hash string, err error) {
+	fh, err := os.Open(pathname)
+	if err != nil {
+		return "", errors.Wrap(err, "could not open")
+	}
+	defer func() {
+		err = errors.Wrap(fh.Close(), "could not close")
+	}()
+
+	h := sha256.New()
+	_, _ = h.Write([]byte(strconv.FormatInt(fi.Size(), 10)))
+
+	if _, err = io.Copy(h, fh); err != nil {
+		err = errors.Wrap(err, "could not read file")
+		return
+	}
+
+	hash = fmt.Sprintf("%x", h.Sum(nil))
+	return
+}
+
+func hashFromDirectory(pathname string, fi os.FileInfo) (hash string, err error) {
+	const maxFileInfos = 32
+
+	fh, err := os.Open(pathname)
+	if err != nil {
+		return hash, errors.Wrap(err, "could not open")
+	}
+	defer func() {
+		err = errors.Wrap(fh.Close(), "could not close")
+	}()
+
+	h := sha256.New()
+
+	// NOTE: Chunk through file system objects to prevent allocating too much
+	// memory for directories with tens of thousands of child objects.
+	for {
+		var children []os.FileInfo
+		var childHash string
+
+		children, err = fh.Readdir(maxFileInfos)
+		if err != nil {
+			if err == io.EOF {
+				err = nil
+				break
+			}
+			return hash, errors.Wrap(err, "could not read directory")
+		}
+		for _, child := range children {
+			switch child.Name() {
+			case ".", "..", "vendor":
+				// skip
+			default:
+				childPathname := pathname + string(os.PathSeparator) + child.Name()
+				if childHash, err = HashFromPathname(childPathname); err != nil {
+					err = errors.Wrap(err, "could not compute hash from pathname")
+					return
+				}
+				_, _ = h.Write([]byte(childPathname))
+				_, _ = h.Write([]byte(childHash))
+			}
+		}
+	}
+
+	hash = fmt.Sprintf("%x", h.Sum(nil))
+	return
+}

internal/fs/hash_test.go

@@ -0,0 +1,27 @@
+package fs
+
+import (
+	"testing"
+)
+
+func TestHashFromPathnameWithFile(t *testing.T) {
+	actual, err := HashFromPathname("testdata/blob")
+	if err != nil {
+		t.Fatal(err)
+	}
+	expected := "825dc11fe41d8f604ab48a8cd6cecf304005bd82fd0228a6e411e992d4d03a08"
+	if actual != expected {
+		t.Errorf("Actual:\n\t%#q\nExpected:\n\t%#q", actual, expected)
+	}
+}
+
+func TestHashFromPathnameWithDirectory(t *testing.T) {
+	actual, err := HashFromPathname("testdata/recursive")
+	if err != nil {
+		t.Fatal(err)
+	}
+	expected := "9b3a1f1f63c0c54860799cc5464a3c380a697a3ec49ca103a62d9c09ad9fedf8"
+	if actual != expected {
+		t.Errorf("Actual:\n\t%#q\nExpected:\n\t%#q", actual, expected)
+	}
+}

internal/fs/testdata/blob

@@ -0,0 +1,7 @@
+fjdkal;fdjskc
+xzc
+axc
+fdsf
+adsf
+das
+fd

internal/fs/testdata/recursive/blob

@@ -0,0 +1,7 @@
+fjdkal;fdjskc
+xzc
+axc
+fdsf
+adsf
+das
+fd

internal/fs/testdata/recursive/emptyFile

@@ -0,0 +1,3 @@
+fjdsakl;fd
+vcafcds
+vca

internal/fs/testdata/recursive/foo/bar

@@ -0,0 +1 @@
+this file ought to be skipped