logtail: add ParsePrivateID

logtail/id.go

@@ -8,6 +8,7 @@
 	"crypto/rand"
 	"crypto/sha256"
 	"encoding/hex"
+	"errors"
 	"fmt"
 )
 
@@ -37,6 +38,23 @@ func (id PrivateID) MarshalText() ([]byte, error) {
 	return b, nil
 }
 
+// ParsePrivateID returns a PrivateID from its hex (String) representation.
+func ParsePrivateID(s string) (PrivateID, error) {
+	if len(s) != 64 {
+		return PrivateID{}, errors.New("invalid length")
+	}
+	var p PrivateID
+	for i := range p {
+		a, ok1 := fromHexChar(s[i*2+0])
+		b, ok2 := fromHexChar(s[i*2+1])
+		if !ok1 || !ok2 {
+			return PrivateID{}, errors.New("invalid hex character")
+		}
+		p[i] = (a << 4) | b
+	}
+	return p, nil
+}
+
 func (id *PrivateID) UnmarshalText(s []byte) error {
 	b, err := hex.DecodeString(string(s))
 	if err != nil {
@@ -101,3 +119,17 @@ func (id PublicID) String() string {
 	}
 	return string(b)
 }
+
+// fromHexChar converts a hex character into its value and a success flag.
+func fromHexChar(c byte) (byte, bool) {
+	switch {
+	case '0' <= c && c <= '9':
+		return c - '0', true
+	case 'a' <= c && c <= 'f':
+		return c - 'a' + 10, true
+	case 'A' <= c && c <= 'F':
+		return c - 'A' + 10, true
+	}
+
+	return 0, false
+}

logtail/id_test.go

@@ -51,4 +51,12 @@ func TestIDs(t *testing.T) {
 	if id1.String() != id3.String() {
 		t.Fatalf("id1.String()=%v does not match id3.String()=%v", id1.String(), id3.String())
 	}
+
+	id4, err := ParsePrivateID(id1.String())
+	if err != nil {
+		t.Fatalf("failed to ParsePrivateID(%q): %v", id1.String(), err)
+	}
+	if id1 != id4 {
+		t.Fatalf("ParsePrivateID returned different id")
+	}
 }