ident: implement system identifier

Signed-off-by: Yonah <contrib@gensokyo.uk>

ident/ident.go

@@ -0,0 +1,23 @@
+// Package ident is the reference implementation of system and member
+// identifiers.
+package ident
+
+import (
+	"errors"
+	"strconv"
+)
+
+// ErrNewline is returned for identifiers found to contain newline characters.
+var ErrNewline = errors.New("identifier contains newline characters")
+
+// UnexpectedSizeError describes a malformed string representation of an
+// identifier, with unexpected length.
+type UnexpectedSizeError struct {
+	Data []byte
+	Want int
+}
+
+func (e *UnexpectedSizeError) Error() string {
+	return "got " + strconv.Itoa(len(e.Data)) + " bytes for " +
+		"a " + strconv.Itoa(e.Want) + "-byte identifier"
+}