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adding support for nonstandard map key in the decoder #266

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Merged
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Feb 21, 2025
Merged

adding support for nonstandard map key in the decoder #266

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25 changes: 14 additions & 11 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -145,17 +145,20 @@ NodeJS `Buffer` is also acceptable because it is a subclass of `Uint8Array`.

#### `DecoderOptions`

| 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) |
| 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) |
| mapKeyConverter | MapKeyConverterType | throw exception if key is not string or number |

`MapKeyConverterType` is defined as `(key: unknown) => string | number`.

To skip UTF-8 decoding of strings, `rawStrings` can be set to `true`. In this case, strings are decoded into `Uint8Array`.

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21 changes: 15 additions & 6 deletions src/Decoder.ts
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Expand Up @@ -68,6 +68,13 @@ export type DecoderOptions<ContextType = undefined> = Readonly<
* `null` is a special value to disable the use of the key decoder at all.
*/
keyDecoder: KeyDecoder | null;

/**
* A function to convert decoded map key to a valid JS key type.
*
* Defaults to a function that throws an error if the key is not a string or a number.
*/
mapKeyConverter: (key: unknown) => MapKeyType;
}>
> &
ContextOf<ContextType>;
Expand All @@ -78,8 +85,11 @@ const STATE_MAP_VALUE = "map_value";

type MapKeyType = string | number;

const isValidMapKeyType = (key: unknown): key is MapKeyType => {
return typeof key === "string" || typeof key === "number";
const mapKeyConverter = (key: unknown): MapKeyType => {
if (typeof key === "string" || typeof key === "number") {
return key;
}
throw new DecodeError("The type of key must be string or number but " + typeof key);
};

type StackMapState = {
Expand Down Expand Up @@ -213,6 +223,7 @@ export class Decoder<ContextType = undefined> {
private readonly maxMapLength: number;
private readonly maxExtLength: number;
private readonly keyDecoder: KeyDecoder | null;
private readonly mapKeyConverter: (key: unknown) => MapKeyType;

private totalPos = 0;
private pos = 0;
Expand All @@ -236,6 +247,7 @@ export class Decoder<ContextType = undefined> {
this.maxMapLength = options?.maxMapLength ?? UINT32_MAX;
this.maxExtLength = options?.maxExtLength ?? UINT32_MAX;
this.keyDecoder = options?.keyDecoder !== undefined ? options.keyDecoder : sharedCachedKeyDecoder;
this.mapKeyConverter = options?.mapKeyConverter ?? mapKeyConverter;
}

private clone(): Decoder<ContextType> {
Expand Down Expand Up @@ -631,14 +643,11 @@ export class Decoder<ContextType = undefined> {
continue DECODE;
}
} else if (state.type === STATE_MAP_KEY) {
if (!isValidMapKeyType(object)) {
throw new DecodeError("The type of key must be string or number but " + typeof object);
}
if (object === "__proto__") {
throw new DecodeError("The key __proto__ is not allowed");
}

state.key = object;
state.key = this.mapKeyConverter(object);
state.type = STATE_MAP_VALUE;
continue DECODE;
} else {
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15 changes: 15 additions & 0 deletions test/decodeAsync.test.ts
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Expand Up @@ -36,6 +36,21 @@ describe("decodeAsync", () => {
assert.deepStrictEqual(object, { "foo": "bar" });
});

it("decodes fixmap {'[1, 2]': 'baz'} with custom map key converter", async () => {
const createStream = async function* () {
yield [0x81]; // fixmap size=1
yield encode([1, 2]);
yield encode("baz");
};

const object = await decodeAsync(createStream(), {
mapKeyConverter: (key) => JSON.stringify(key),
});

const key = JSON.stringify([1, 2]);
assert.deepStrictEqual(object, { [key]: "baz" });
});

it("decodes multi-byte integer byte-by-byte", async () => {
const createStream = async function* () {
yield [0xcd]; // uint 16
Expand Down
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