1 files changed, 297 insertions, 0 deletions
diff --git a/std/node/string_decoder.ts b/std/node/string_decoder.ts
new file mode 100644
index 000000000..7f167ad3c
--- /dev/null
+++ b/std/node/string_decoder.ts
@@ -0,0 +1,297 @@
+// Copyright Joyent, Inc. and other Node contributors.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the
+// "Software"), to deal in the Software without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Software, and to permit
+// persons to whom the Software is furnished to do so, subject to the
+// following conditions:
+//
+// The above copyright notice and this permission notice shall be included
+// in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
+// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+// USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+import { Buffer } from "./buffer.ts";
+import { normalizeEncoding as castEncoding, notImplemented } from "./_utils.ts";
+
+enum NotImplemented {
+  "ascii",
+  "latin1",
+  "utf16le",
+}
+
+function normalizeEncoding(enc?: string): string {
+  const encoding = castEncoding(enc ?? null);
+  if (encoding && encoding in NotImplemented) notImplemented(encoding);
+  if (!encoding && typeof enc === "string" && enc.toLowerCase() !== "raw")
+    throw new Error(`Unknown encoding: ${enc}`);
+  return String(encoding);
+}
+/*
+ * Checks the type of a UTF-8 byte, whether it's ASCII, a leading byte, or a
+ * continuation byte. If an invalid byte is detected, -2 is returned.
+ * */
+function utf8CheckByte(byte: number): number {
+  if (byte <= 0x7f) return 0;
+  else if (byte >> 5 === 0x06) return 2;
+  else if (byte >> 4 === 0x0e) return 3;
+  else if (byte >> 3 === 0x1e) return 4;
+  return byte >> 6 === 0x02 ? -1 : -2;
+}
+
+/*
+ * Checks at most 3 bytes at the end of a Buffer in order to detect an
+ * incomplete multi-byte UTF-8 character. The total number of bytes (2, 3, or 4)
+ * needed to complete the UTF-8 character (if applicable) are returned.
+ * */
+function utf8CheckIncomplete(
+  self: StringDecoderBase,
+  buf: Buffer,
+  i: number
+): number {
+  let j = buf.length - 1;
+  if (j < i) return 0;
+  let nb = utf8CheckByte(buf[j]);
+  if (nb >= 0) {
+    if (nb > 0) self.lastNeed = nb - 1;
+    return nb;
+  }
+  if (--j < i || nb === -2) return 0;
+  nb = utf8CheckByte(buf[j]);
+  if (nb >= 0) {
+    if (nb > 0) self.lastNeed = nb - 2;
+    return nb;
+  }
+  if (--j < i || nb === -2) return 0;
+  nb = utf8CheckByte(buf[j]);
+  if (nb >= 0) {
+    if (nb > 0) {
+      if (nb === 2) nb = 0;
+      else self.lastNeed = nb - 3;
+    }
+    return nb;
+  }
+  return 0;
+}
+
+/*
+ * Validates as many continuation bytes for a multi-byte UTF-8 character as
+ * needed or are available. If we see a non-continuation byte where we expect
+ * one, we "replace" the validated continuation bytes we've seen so far with
+ * a single UTF-8 replacement character ('\ufffd'), to match v8's UTF-8 decoding
+ * behavior. The continuation byte check is included three times in the case
+ * where all of the continuation bytes for a character exist in the same buffer.
+ * It is also done this way as a slight performance increase instead of using a
+ * loop.
+ * */
+function utf8CheckExtraBytes(
+  self: StringDecoderBase,
+  buf: Buffer
+): string | undefined {
+  if ((buf[0] & 0xc0) !== 0x80) {
+    self.lastNeed = 0;
+    return "\ufffd";
+  }
+  if (self.lastNeed > 1 && buf.length > 1) {
+    if ((buf[1] & 0xc0) !== 0x80) {
+      self.lastNeed = 1;
+      return "\ufffd";
+    }
+    if (self.lastNeed > 2 && buf.length > 2) {
+      if ((buf[2] & 0xc0) !== 0x80) {
+        self.lastNeed = 2;
+        return "\ufffd";
+      }
+    }
+  }
+}
+
+/*
+ * Attempts to complete a multi-byte UTF-8 character using bytes from a Buffer.
+ * */
+function utf8FillLastComplete(
+  this: StringDecoderBase,
+  buf: Buffer
+): string | undefined {
+  const p = this.lastTotal - this.lastNeed;
+  const r = utf8CheckExtraBytes(this, buf);
+  if (r !== undefined) return r;
+  if (this.lastNeed <= buf.length) {
+    buf.copy(this.lastChar, p, 0, this.lastNeed);
+    return this.lastChar.toString(this.encoding, 0, this.lastTotal);
+  }
+  buf.copy(this.lastChar, p, 0, buf.length);
+  this.lastNeed -= buf.length;
+}
+
+/*
+ * Attempts to complete a partial non-UTF-8 character using bytes from a Buffer
+ * */
+function utf8FillLastIncomplete(
+  this: StringDecoderBase,
+  buf: Buffer
+): string | undefined {
+  if (this.lastNeed <= buf.length) {
+    buf.copy(this.lastChar, this.lastTotal - this.lastNeed, 0, this.lastNeed);
+    return this.lastChar.toString(this.encoding, 0, this.lastTotal);
+  }
+  buf.copy(this.lastChar, this.lastTotal - this.lastNeed, 0, buf.length);
+  this.lastNeed -= buf.length;
+}
+
+/*
+ * Returns all complete UTF-8 characters in a Buffer. If the Buffer ended on a
+ * partial character, the character's bytes are buffered until the required
+ * number of bytes are available.
+ * */
+function utf8Text(this: StringDecoderBase, buf: Buffer, i: number): string {
+  const total = utf8CheckIncomplete(this, buf, i);
+  if (!this.lastNeed) return buf.toString("utf8", i);
+  this.lastTotal = total;
+  const end = buf.length - (total - this.lastNeed);
+  buf.copy(this.lastChar, 0, end);
+  return buf.toString("utf8", i, end);
+}
+
+/*
+ * For UTF-8, a replacement character is added when ending on a partial
+ * character.
+ * */
+function utf8End(this: Utf8Decoder, buf?: Buffer): string {
+  const r = buf && buf.length ? this.write(buf) : "";
+  if (this.lastNeed) return r + "\ufffd";
+  return r;
+}
+
+function utf8Write(this: Utf8Decoder | Base64Decoder, buf: Buffer): string {
+  if (buf.length === 0) return "";
+  let r;
+  let i;
+  if (this.lastNeed) {
+    r = this.fillLast(buf);
+    if (r === undefined) return "";
+    i = this.lastNeed;
+    this.lastNeed = 0;
+  } else {
+    i = 0;
+  }
+  if (i < buf.length) return r ? r + this.text(buf, i) : this.text(buf, i);
+  return r || "";
+}
+
+function base64Text(this: StringDecoderBase, buf: Buffer, i: number): string {
+  const n = (buf.length - i) % 3;
+  if (n === 0) return buf.toString("base64", i);
+  this.lastNeed = 3 - n;
+  this.lastTotal = 3;
+  if (n === 1) {
+    this.lastChar[0] = buf[buf.length - 1];
+  } else {
+    this.lastChar[0] = buf[buf.length - 2];
+    this.lastChar[1] = buf[buf.length - 1];
+  }
+  return buf.toString("base64", i, buf.length - n);
+}
+
+function base64End(this: Base64Decoder, buf?: Buffer): string {
+  const r = buf && buf.length ? this.write(buf) : "";
+  if (this.lastNeed)
+    return r + this.lastChar.toString("base64", 0, 3 - this.lastNeed);
+  return r;
+}
+
+function simpleWrite(this: StringDecoderBase, buf: Buffer): string {
+  return buf.toString(this.encoding);
+}
+
+function simpleEnd(this: GenericDecoder, buf?: Buffer): string {
+  return buf && buf.length ? this.write(buf) : "";
+}
+
+class StringDecoderBase {
+  public lastChar: Buffer;
+  public lastNeed = 0;
+  public lastTotal = 0;
+  constructor(public encoding: string, nb: number) {
+    this.lastChar = Buffer.allocUnsafe(nb);
+  }
+}
+
+class Base64Decoder extends StringDecoderBase {
+  public end = base64End;
+  public fillLast = utf8FillLastIncomplete;
+  public text = base64Text;
+  public write = utf8Write;
+
+  constructor(encoding?: string) {
+    super(normalizeEncoding(encoding), 3);
+  }
+}
+
+class GenericDecoder extends StringDecoderBase {
+  public end = simpleEnd;
+  public fillLast = undefined;
+  public text = utf8Text;
+  public write = simpleWrite;
+
+  constructor(encoding?: string) {
+    super(normalizeEncoding(encoding), 4);
+  }
+}
+
+class Utf8Decoder extends StringDecoderBase {
+  public end = utf8End;
+  public fillLast = utf8FillLastComplete;
+  public text = utf8Text;
+  public write = utf8Write;
+
+  constructor(encoding?: string) {
+    super(normalizeEncoding(encoding), 4);
+  }
+}
+
+/*
+ * StringDecoder provides an interface for efficiently splitting a series of
+ * buffers into a series of JS strings without breaking apart multi-byte
+ * characters.
+ * */
+export class StringDecoder {
+  public encoding: string;
+  public end: (buf?: Buffer) => string;
+  public fillLast: ((buf: Buffer) => string | undefined) | undefined;
+  public lastChar: Buffer;
+  public lastNeed: number;
+  public lastTotal: number;
+  public text: (buf: Buffer, n: number) => string;
+  public write: (buf: Buffer) => string;
+
+  constructor(encoding?: string) {
+    let decoder;
+    switch (encoding) {
+      case "utf8":
+        decoder = new Utf8Decoder(encoding);
+        break;
+      case "base64":
+        decoder = new Base64Decoder(encoding);
+        break;
+      default:
+        decoder = new GenericDecoder(encoding);
+    }
+    this.encoding = decoder.encoding;
+    this.end = decoder.end;
+    this.fillLast = decoder.fillLast;
+    this.lastChar = decoder.lastChar;
+    this.lastNeed = decoder.lastNeed;
+    this.lastTotal = decoder.lastTotal;
+    this.text = decoder.text;
+    this.write = decoder.write;
+  }
+}