feat(quoted_string): add isQdtext function

Author: TomokiMiyauci

README.md

@@ -582,6 +582,28 @@ assert(isTchar("*!~"));
 assertFalse(isToken(""));
 ```
 
+## Quoted Strings
+
+Compliant with
+[RFC 9110, 5.6.4. Quoted Strings](https://www.rfc-editor.org/rfc/rfc9110.html#section-5.6.4).
+
+### isQdtext
+
+Whether the input is
+[qdtext](https://www.rfc-editor.org/rfc/rfc9110.html#section-5.6.4-2) or not.
+
+```ts
+import { isQdtext } from "https://deno.land/x/http_utils@$VERSION/quoted_string.ts";
+import {
+  assert,
+  assertFalse,
+} from "https://deno.land/std@$VERSION/testing/asserts.ts";
+
+assert(isQdtext("\t"));
+assert(isQdtext("\xFF"));
+assertFalse(isQdtext(`"`));
+```
+
 ## License
 
 Copyright © 2023-present [httpland](https://github.com/httpland).

quoted_string.ts

@@ -0,0 +1,32 @@
+// Copyright 2023-latest the httpland authors. All rights reserved. MIT license.
+// This module is browser compatible.
+
+// export function isQuotedString(input: string): input is QuotedString {
+// }
+
+/**
+ * ```abnf
+ * obs-text = %x80-FF
+ * qdtext   = HTAB / SP / %x21 / %x23-5B / %x5D-7E / obs-text
+ * ```
+ */
+const reQdtext = /^[\t \x21\x23-\x5B\x5D-\x7E\x80-\xFF]$/;
+
+/** Whether the input is [qdtext](https://www.rfc-editor.org/rfc/rfc9110.html#section-5.6.4-2) or not.
+ *
+ * @example
+ * ```ts
+ * import { isQdtext } from "https://deno.land/x/http_utils@$VERSION/quoted_string.ts";
+ * import {
+ *   assert,
+ *   assertFalse,
+ * } from "https://deno.land/std@$VERSION/testing/asserts.ts";
+ *
+ * assert(isQdtext("\t"));
+ * assert(isQdtext("\xFF"));
+ * assertFalse(isQdtext(`"`));
+ * ```
+ */
+export function isQdtext(input: string): boolean {
+  return reQdtext.test(input);
+}

quoted_string_test.ts

@@ -0,0 +1,70 @@
+import { isQdtext } from "./quoted_string.ts";
+import {
+  assert,
+  assertEquals,
+  assertFalse,
+  assertThrows,
+  describe,
+  it,
+} from "./_dev_deps.ts";
+
+function charRange(start: string, end: string): string[] {
+  if (end < start) throw RangeError();
+
+  return Array.from(new Array(end.charCodeAt(0) - start.charCodeAt(0) + 1)).map(
+    (
+      _,
+      i,
+    ) => String.fromCharCode(start.charCodeAt(0) + i),
+  );
+}
+
+describe("charRange", () => {
+  it("should throw error is the range is invalid", () => {
+    const table: [string, string, string[]][] = [
+      ["A", "C", ["A", "B", "C"]],
+      ["A", "A", ["A"]],
+      ["\x21", "\x24", ["\x21", "\x22", "\x23", "\x24"]],
+    ];
+
+    table.forEach(([start, end, expected]) => {
+      assertEquals(charRange(start, end), expected);
+    });
+  });
+
+  it("should throw error is the range is invalid", () => {
+    assertThrows(() => charRange("b", "a"));
+  });
+});
+
+describe("describe", () => {
+  it("should return true", () => {
+    const table: string[] = [
+      "\t",
+      " ",
+      "\x21",
+      ...charRange("\x23", "\x5B"),
+      ...charRange("\x5D", "\x7E"),
+      ...charRange("\x80", "\xFF"),
+    ];
+
+    table.forEach((input) => {
+      assert(isQdtext(input));
+    });
+  });
+
+  it("should return false", () => {
+    const table: string[] = [
+      "",
+      ...charRange("\x00", "\x08"), // \x09 is "\t"
+      ...charRange("\x10", "\x19"), // \x20 is " "
+      "\x22",
+      "\xFF" + 1,
+      "\x22\x22",
+    ];
+
+    table.forEach((input) => {
+      assertFalse(isQdtext(input), input);
+    });
+  });
+});