Allow decoding raw strings

README.md

@@ -148,12 +148,15 @@ Name|Type|Default
 extensionCodec | ExtensionCodec | `ExtensionCodec.defaultCodec`
 context | user-defined | -
 useBigInt64 | boolean | false
+rawStrings | boolean | false
 maxStrLength | number | `4_294_967_295` (UINT32_MAX)
 maxBinLength | number | `4_294_967_295` (UINT32_MAX)
 maxArrayLength | number | `4_294_967_295` (UINT32_MAX)
 maxMapLength | number | `4_294_967_295` (UINT32_MAX)
 maxExtLength | number | `4_294_967_295` (UINT32_MAX)
 
+To skip UTF-8 decoding of strings, `rawStrings` can be set to `true`. In this case, strings are decoded into `Uint8Array`.
+
 You can use `max${Type}Length` to limit the length of each type decoded.
 
 ### `decodeMulti(buffer: ArrayLike<number> | BufferSource, options?: DecoderOptions): Generator<unknown, void, unknown>`
@@ -498,18 +501,19 @@ null, undefined|nil|null (*1)
 boolean (true, false)|bool family|boolean (true, false)
 number (53-bit int)|int family|number
 number (64-bit float)|float family|number
-string|str family|string
-ArrayBufferView |bin family|Uint8Array (*2)
+string|str family|string (*2)
+ArrayBufferView |bin family|Uint8Array (*3)
 Array|array family|Array
-Object|map family|Object (*3)
-Date|timestamp ext family|Date (*4)
-bigint|N/A|N/A (*5)
+Object|map family|Object (4)
+Date|timestamp ext family|Date (*5)
+bigint|N/A|N/A (*6)
 
 * *1 Both `null` and `undefined` are mapped to `nil` (`0xC0`) type, and are decoded into `null`
-* *2 Any `ArrayBufferView`s including NodeJS's `Buffer` are mapped to `bin` family, and are decoded into `Uint8Array`
-* *3 In handling `Object`, it is regarded as `Record<string, unknown>` in terms of TypeScript
-* *4 MessagePack timestamps may have nanoseconds, which will lost when it is decoded into JavaScript `Date`. This behavior can be overridden by registering `-1` for the extension codec.
-* *5 bigint is not supported in `useBigInt64: false` mode, but you can define an extension codec for it.
+* *2 If you'd like to skip UTF-8 decoding of strings, set `rawStrings: true`. In this case, strings are decoded into `Uint8Array`.
+* *3 Any `ArrayBufferView`s including NodeJS's `Buffer` are mapped to `bin` family, and are decoded into `Uint8Array`
+* *4 In handling `Object`, it is regarded as `Record<string, unknown>` in terms of TypeScript
+* *5 MessagePack timestamps may have nanoseconds, which will lost when it is decoded into JavaScript `Date`. This behavior can be overridden by registering `-1` for the extension codec.
+* *6 bigint is not supported in `useBigInt64: false` mode, but you can define an extension codec for it.
 
 If you set `useBigInt64: true`, the following mapping is used:
 
@@ -519,15 +523,15 @@ null, undefined|nil|null
 boolean (true, false)|bool family|boolean (true, false)
 **number (32-bit int)**|int family|number
 **number (except for the above)**|float family|number
-**bigint**|int64 / uint64|bigint (*6)
+**bigint**|int64 / uint64|bigint (*7)
 string|str family|string
 ArrayBufferView |bin family|Uint8Array
 Array|array family|Array
 Object|map family|Object
 Date|timestamp ext family|Date
 
 
-* *6 If the bigint is larger than the max value of uint64 or smaller than the min value of int64, then the behavior is undefined.
+* *7 If the bigint is larger than the max value of uint64 or smaller than the min value of int64, then the behavior is undefined.
 
 ## Prerequisites
 

src/Decoder.ts

@@ -20,6 +20,17 @@ export type DecoderOptions<ContextType = undefined> = Readonly<
      */
     useBigInt64: boolean;
 
+    /**
+     * By default, string values will be decoded as UTF-8 strings. However, if this option is true,
+     * string values will be returned as Uint8Arrays without additional decoding.
+     * 
+     * This is useful if the strings may contain invalid UTF-8 sequences.
+     * 
+     * Note that this option only applies to string values, not map keys. Additionally, when
+     * enabled, raw string length is limited by the maxBinLength option.
+     */
+    rawStrings: boolean;
+
     /**
      * Maximum string length.
      *
@@ -195,6 +206,7 @@ export class Decoder<ContextType = undefined> {
   private readonly extensionCodec: ExtensionCodecType<ContextType>;
   private readonly context: ContextType;
   private readonly useBigInt64: boolean;
+  private readonly rawStrings: boolean;
   private readonly maxStrLength: number;
   private readonly maxBinLength: number;
   private readonly maxArrayLength: number;
@@ -215,6 +227,7 @@ export class Decoder<ContextType = undefined> {
     this.context = (options as { context: ContextType } | undefined)?.context as ContextType; // needs a type assertion because EncoderOptions has no context property when ContextType is undefined
 
     this.useBigInt64 = options?.useBigInt64 ?? false;
+    this.rawStrings = options?.rawStrings ?? false;
     this.maxStrLength = options?.maxStrLength ?? UINT32_MAX;
     this.maxBinLength = options?.maxBinLength ?? UINT32_MAX;
     this.maxArrayLength = options?.maxArrayLength ?? UINT32_MAX;
@@ -399,7 +412,7 @@ export class Decoder<ContextType = undefined> {
         } else {
           // fixstr (101x xxxx) 0xa0 - 0xbf
           const byteLength = headByte - 0xa0;
-          object = this.decodeUtf8String(byteLength, 0);
+          object = this.decodeString(byteLength, 0);
         }
       } else if (headByte === 0xc0) {
         // nil
@@ -451,15 +464,15 @@ export class Decoder<ContextType = undefined> {
       } else if (headByte === 0xd9) {
         // str 8
         const byteLength = this.lookU8();
-        object = this.decodeUtf8String(byteLength, 1);
+        object = this.decodeString(byteLength, 1);
       } else if (headByte === 0xda) {
         // str 16
         const byteLength = this.lookU16();
-        object = this.decodeUtf8String(byteLength, 2);
+        object = this.decodeString(byteLength, 2);
       } else if (headByte === 0xdb) {
         // str 32
         const byteLength = this.lookU32();
-        object = this.decodeUtf8String(byteLength, 4);
+        object = this.decodeString(byteLength, 4);
       } else if (headByte === 0xdc) {
         // array 16
         const size = this.readU16();
@@ -637,6 +650,13 @@ export class Decoder<ContextType = undefined> {
     this.stack.pushArrayState(size);
   }
 
+  private decodeString(byteLength: number, headerOffset: number): string | Uint8Array {
+    if (!this.rawStrings || this.stateIsMapKey()) {
+      return this.decodeUtf8String(byteLength, headerOffset);
+    }
+    return this.decodeBinary(byteLength, headerOffset);
+  }
+
   private decodeUtf8String(byteLength: number, headerOffset: number): string {
     if (byteLength > this.maxStrLength) {
       throw new DecodeError(

test/decode-raw-strings.test.ts

@@ -0,0 +1,43 @@
+import assert from "assert";
+import { encode, decode } from "../src";
+import type { DecoderOptions } from "../src";
+
+describe("decode with rawStrings specified", () => {
+  const options = { rawStrings: true } satisfies DecoderOptions;
+
+  it("decodes string as binary", () => {
+    const actual = decode(encode("foo"), options);
+    const expected = Uint8Array.from([0x66, 0x6f, 0x6f]);
+    assert.deepStrictEqual(actual, expected);
+  });
+
+  it("decodes invalid UTF-8 string as binary", () => {
+    const invalidUtf8String = Uint8Array.from([61, 180, 118, 220, 39, 166, 43, 68, 219, 116, 105, 84, 121, 46, 122, 136, 233, 221, 15, 174, 247, 19, 50, 176, 184, 221, 66, 188, 171, 36, 135, 121]);
+    const encoded = Uint8Array.from([196, 32, 61, 180, 118, 220, 39, 166, 43, 68, 219, 116, 105, 84, 121, 46, 122, 136, 233, 221, 15, 174, 247, 19, 50, 176, 184, 221, 66, 188, 171, 36, 135, 121]);
+
+    const actual = decode(encoded, options);
+    assert.deepStrictEqual(actual, invalidUtf8String);
+  });
+
+  it("decodes object keys as strings", () => {
+    const actual = decode(encode({ key: "foo" }), options);
+    const expected = { key: Uint8Array.from([0x66, 0x6f, 0x6f]) };
+    assert.deepStrictEqual(actual, expected);
+  });
+
+  it("ignores maxStrLength", () => {
+    const lengthLimitedOptions = { ...options, maxStrLength: 1 } satisfies DecoderOptions;
+
+    const actual = decode(encode("foo"), lengthLimitedOptions);
+    const expected = Uint8Array.from([0x66, 0x6f, 0x6f]);
+    assert.deepStrictEqual(actual, expected);
+  });
+
+  it("respects maxBinLength", () => {
+    const lengthLimitedOptions = { ...options, maxBinLength: 1 } satisfies DecoderOptions;
+
+    assert.throws(() => {
+      decode(encode("foo"), lengthLimitedOptions);
+    }, /max length exceeded/i);
+  });
+});