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fix: add backtracking to opt decoding #979

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crusso wants to merge 8 commits into from
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fix: add backtracking to opt decoding #979

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da86365
add backtracking to opt decoding
crusso Mar 17, 2025
d950e3f
basic tests of variant defaulting under opt
crusso Mar 17, 2025
258b313
comments
crusso Mar 17, 2025
afdafdc
appease linter
crusso Mar 17, 2025
e366eb6
Merge branch 'main' into claudio/variant-fix
crusso Mar 17, 2025
a126068
Update packages/candid/src/idl.ts
crusso Mar 18, 2025
d68a380
Update packages/candid/src/idl.test.ts
crusso Mar 18, 2025
64820d3
fix merged suggestions
crusso Mar 18, 2025
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28 changes: 28 additions & 0 deletions packages/candid/src/idl.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -698,3 +698,31 @@ test('should decode matching optional fields if wire type contains additional fi
b: ['123'],
});
});


test('IDL opt variant decoding', () => {
testDecode(
IDL.Record({a: IDL.Opt(IDL.Variant({ x: IDL.Null, y: IDL.Null, z: IDL.Null }))}),
{a: [{ x: null }]},
'4449444c036c0161016e026b03787f797f7a7f01000100', // Motoko: {a = ?#x} : {a : ?{#x;#y;#z}}
'same variant under opt x',
);
testDecode(
IDL.Record({a: IDL.Opt(IDL.Variant({ x: IDL.Null, y: IDL.Null, z: IDL.Null }))}),
{a: [{ z: null}]},
'4449444c036c0161016e026b03787f797f7a7f01000102', // Motoko: {a = ?#z} : {a : ?{#x;#y;#z}}
'same variant under opt z',
);
testDecode(
IDL.Record({a: IDL.Opt(IDL.Variant({ x: IDL.Null, y: IDL.Null }))}),
{a: [{ x: null }]},
'4449444c036c0161016e026b03787f797f7a7f01000100', // Motoko: {a = ?#x} : {a : ?{#x;#y;#z}}
'extended variant under opt expected tag',
);
testDecode(
IDL.Record({a: IDL.Opt(IDL.Variant({ x: IDL.Null, y: IDL.Null }))}),
{a: []},
'4449444c036c0161016e026b03787f797f7a7f01000102', // Motoko: {a = ?#z} : {a : ?{#x;#y;#z}}
'extended variant under opt unexpected tag - defaulting',
);
});
15 changes: 13 additions & 2 deletions packages/candid/src/idl.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -921,8 +921,19 @@ export class OptClass<T> extends ConstructType<[T] | []> {
switch (safeReadUint8(b)) {
case 0:
return [];
case 1:
return [this._type.decodeValue(b, opt._type)];
case 1: {
const checkpoint = b.save();
try {
const v = this._type.decodeValue(b, opt._type)
return [v];
} catch (e : any) {
b.restore(checkpoint);
// skip value at wire type (to advance b)
const v = opt._type.decodeValue(b, opt._type)
// retun none
return [];
}
}
default:
throw new Error('Not an option value');
}
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15 changes: 15 additions & 0 deletions packages/candid/src/utils/buffer.ts
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Expand Up @@ -38,6 +38,21 @@ export class PipeArrayBuffer {
*/
private _view: Uint8Array;

/**
* Save a checkpoint of the reading view (for backtracking)
*/
public save() : Uint8Array {
return this._view;
}

/**
* Restore a checkpoint of the reading view (for backtracking)
* @param checkPoint a previously saved checkpoint
*/
public restore(checkPoint: Uint8Array) {
this._view = checkPoint;
}

/**
* The actual buffer containing the bytes.
* @private
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