Read a peer's submit and receipt message ids into one notation before comparing them

src/sms-id.ts

@@ -0,0 +1,32 @@
+/** The notation a peer writes message ids in. */
+export type SmsIdFormat = 'decimal' | 'hex';
+
+/** The notation per place the peer writes an id. An omitted place is left as it arrived. */
+export type SmsIdFormats = {
+	receipt?: SmsIdFormat | undefined;
+	submitResp?: SmsIdFormat | undefined;
+};
+
+export function isSmsIdFormat(value: unknown): value is SmsIdFormat {
+	return value === 'decimal' || value === 'hex';
+}
+
+// SMPP 3.4 caps message_id at 64 octets, and BigInt on a longer string is a peer-controlled cost.
+const maxIdLength = 64;
+
+const notations = {
+	decimal: { digits: /^[0-9]+$/, prefix: '' },
+	hex: { digits: /^[0-9a-f]+$/i, prefix: '0x' },
+};
+
+/**
+ * The id as a plain decimal value, so an SMSC that answers a submit in one notation and writes the
+ * receipt in another still correlates. An id the notation cannot read is left as it arrived.
+ */
+export function normaliseSmsId(id: string, format: SmsIdFormat | undefined): string {
+	if (format === undefined || id.length > maxIdLength) return id;
+
+	const { digits, prefix } = notations[format];
+
+	return digits.test(id) ? BigInt(`${prefix}${id}`).toString(10) : id;
+}