wip

internal/fileutil/checksum.go

@@ -0,0 +1,39 @@
+package fileutil
+
+import (
+	"errors"
+	"io/fs"
+	"os"
+	"syscall"
+
+	"github.com/pomerium/pomerium/internal/hashutil"
+)
+
+// StatCheckSum returns a checksum of the file info. It is valid to run this
+// function against a file path that doesn't exist and an error will not be returned.
+// The file path, size, modification time, device id and inode id are used to compute
+// the hash. Any change to this data, even if the underlying file contents are the
+// same, will result in a new checksum, and vice-versa, if the underlying contents
+// change, but none of the other data does, the checksum will be the same.
+func StatCheckSum(filePath string) (uint64, error) {
+	d := hashutil.NewDigestWithSeed(7968108)
+	d.WriteStringWithLen(filePath)
+
+	for _, fn := range []func(string) (os.FileInfo, error){os.Stat, os.Lstat} {
+		fi, err := fn(filePath)
+		if errors.Is(err, fs.ErrNotExist) {
+			_, _ = d.Write([]byte{0})
+		} else if err != nil {
+			return 0, err
+		} else {
+			d.WriteInt64(fi.Size())
+			d.WriteInt64(fi.ModTime().Unix())
+			if s, ok := fi.Sys().(*syscall.Stat_t); ok {
+				d.WriteUint64(s.Dev)
+				d.WriteUint64(s.Ino)
+			}
+		}
+	}
+
+	return d.Sum64(), nil
+}

internal/hashutil/hashutil.go

@@ -40,6 +40,14 @@ func NewDigest() *Digest {
 	return &d
 }
 
+// NewDigestWithSeed creates a new digest using the given seed.
+func NewDigestWithSeed(seed uint64) *Digest {
+	var d Digest
+	d.Hasher = *xxh3.NewSeed(seed)
+	d.Reset()
+	return &d
+}
+
 // WriteStringWithLen writes the string's length, then its contents to the hash.
 func (d *Digest) WriteStringWithLen(s string) {
 	d.WriteInt32(int32(len(s)))