When parsing a TLV with variable-length data ( choice

Error parsing TLV with variable length data (array, choice) about binary-parser HOT 5 CLOSED

wpyoga commented on June 3, 2024

Error parsing TLV with variable length data (array, choice)

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Comments (5)

keichi commented on June 3, 2024

Sorry for the unclarity, you need to call useContextVars() on the top-level parser. If you change

const parser = new Parser().array('data', {

const parser = new Parser().useContextVars().array('data', {

This works:

const Parser = require('binary-parser').Parser;

const buf = Buffer.from('a1012aa2027ab8a30460713d44ff03414243a401ff', 'hex');

const parser = new Parser().useContextVars().array('data', {
  readUntil: 'eof',
  type: new Parser()
    .uint8('type')
    .uint8('length')
    .choice('value', {
      tag: 'type',
      choices: {
        0xa1: new Parser().uint8('_a1'),
        0xa2: new Parser().uint16be('_a2'),
        0xa3: new Parser().buffer('_a3', { length: '$parent.length' }),
        0xa4: new Parser().uint8('_a4'),
      },
      defaultChoice: new Parser().buffer('other', { length: '$parent.length' }),
    }),
});

console.dir(parser.parse(buf), { depth: null });

Output:

{
  data: [
    { type: 161, length: 1, value: { _a1: 42 } },
    { type: 162, length: 2, value: { _a2: 31416 } },
    {
      type: 163,
      length: 4,
      value: { _a3: Buffer(4) [Uint8Array] [ 96, 113, 61, 68 ] }
    },
    {
      type: 255,
      length: 3,
      value: { other: Buffer(3) [Uint8Array] [ 65, 66, 67 ] }
    },
    { type: 164, length: 1, value: { _a4: 255 } }
  ]
}

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wpyoga commented on June 3, 2024

I see... your solution works. I'm curious though, does this mean useContextVars() have to declared at the very top level parser, and at that level only?

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keichi commented on June 3, 2024

Yes, you have to declare it at the top level. If you call it at the lower levels it's simply ignored. This is required because the top-level parser has to know if the context vars is enabled as it sets$root.

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keichi commented on June 3, 2024

Closing since your initial problem seems resolved. Feel free to reopen if needed.

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wpyoga commented on June 3, 2024

I see, thank you for the explanation.

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