Throw an error when the format can't represent the given date in formatRfc7231

Author: fabon-f

src/datetime/formatRfc7231.test.ts

@@ -32,3 +32,39 @@ test("fractional seconds", () => {
 		formatRfc7231(Temporal.Instant.from("1968-06-07T01:23:45.123456789Z")),
 	).toEqual("Fri, 07 Jun 1968 01:23:45 GMT");
 });
+
+test("valid range of year", () => {
+	expect(formatRfc7231(Temporal.Instant.from("0000-01-01T00:00:00Z"))).toEqual(
+		"Sat, 01 Jan 0000 00:00:00 GMT",
+	);
+	expect(
+		formatRfc7231(Temporal.ZonedDateTime.from("0000-01-01T00:00:00Z[UTC]")),
+	).toEqual("Sat, 01 Jan 0000 00:00:00 GMT");
+	expect(formatRfc7231(Temporal.Instant.from("9999-12-31T00:00:00Z"))).toEqual(
+		"Fri, 31 Dec 9999 00:00:00 GMT",
+	);
+	expect(
+		formatRfc7231(Temporal.ZonedDateTime.from("9999-12-31T00:00:00Z[UTC]")),
+	).toEqual("Fri, 31 Dec 9999 00:00:00 GMT");
+});
+
+test("invalid range of year", () => {
+	expect(() => {
+		formatRfc7231(Temporal.Instant.from("-000001-12-31T23:59:59Z"));
+	}).toThrow();
+	expect(() => {
+		formatRfc7231(Temporal.ZonedDateTime.from("-000001-12-31T23:59:59Z[UTC]"));
+	}).toThrow();
+	expect(() => {
+		formatRfc7231(Temporal.Instant.from("-100000-01-01T00:00:00Z"));
+	}).toThrow();
+	expect(() => {
+		formatRfc7231(Temporal.ZonedDateTime.from("-100000-01-01T00:00:00Z[UTC]"));
+	}).toThrow();
+	expect(() => {
+		formatRfc7231(Temporal.Instant.from("+010000-01-01T00:00:00Z"));
+	}).toThrow();
+	expect(() => {
+		formatRfc7231(Temporal.ZonedDateTime.from("+010000-01-01T00:00:00Z[UTC]"));
+	}).toThrow();
+});

src/datetime/formatRfc7231.ts

@@ -18,6 +18,9 @@ export function formatRfc7231(
 	// timeZone: 'UTC', calendar: 'iso8601'
 	const zdt = (isInstant(dt) ? dt : dt.toInstant()).toZonedDateTimeISO("UTC");
 	const dayOfWeek = getDayOfWeekAbbreviationFromNumber(zdt.dayOfWeek);
+	if (zdt.year < 0 || zdt.year > 9999) {
+		throw new Error(`RFC 7231 format can't represent year ${zdt.year}`);
+	}
 	const year = padLeadingZeros(zdt.year, 4);
 	const day = padLeadingZeros(zdt.day, 2);
 	const month = getMonthAbbreviationFromNumber(zdt.month);