| … | |
… | |
| 330 | and you need to know where the first CBOR string ends amd the next one |
330 | and you need to know where the first CBOR string ends amd the next one |
| 331 | starts. |
331 | starts. |
| 332 | |
332 | |
| 333 | CBOR::XS->new->decode_prefix ("......") |
333 | CBOR::XS->new->decode_prefix ("......") |
| 334 | => ("...", 3) |
334 | => ("...", 3) |
|
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335 | |
|
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336 | =back |
|
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337 | |
|
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338 | =head2 INCREMENTAL PARSING |
|
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339 | |
|
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340 | In some cases, there is the need for incremental parsing of JSON |
|
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341 | texts. While this module always has to keep both CBOR text and resulting |
|
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342 | Perl data structure in memory at one time, it does allow you to parse a |
|
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343 | CBOR stream incrementally, using a similar to using "decode_prefix" to see |
|
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344 | if a full CBOR object is available, but is much more efficient. |
|
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345 | |
|
|
346 | It basically works by parsing as much of a CBOR string as possible - if |
|
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347 | the CBOR data is not complete yet, the pasrer will remember where it was, |
|
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348 | to be able to restart when more data has been accumulated. Once enough |
|
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349 | data is available to either decode a complete CBOR value or raise an |
|
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350 | error, a real decode will be attempted. |
|
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351 | |
|
|
352 | A typical use case would be a network protocol that consists of sending |
|
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353 | and receiving CBOR-encoded messages. The solution that works with CBOR and |
|
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354 | about anything else is by prepending a length to every CBOR value, so the |
|
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355 | receiver knows how many octets to read. More compact (and slightly slower) |
|
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356 | would be to just send CBOR values back-to-back, as C<CBOR::XS> knows where |
|
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357 | a CBOR value ends, and doesn't need an explicit length. |
|
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358 | |
|
|
359 | The following methods help with this: |
|
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360 | |
|
|
361 | =over 4 |
|
|
362 | |
|
|
363 | =item @decoded = $cbor->incr_parse ($buffer) |
|
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364 | |
|
|
365 | This method attempts to decode exactly one CBOR value from the beginning |
|
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366 | of the given C<$buffer>. The value is removed from the C<$buffer> on |
|
|
367 | success. When C<$buffer> doesn't contain a complete value yet, it returns |
|
|
368 | nothing. Finally, when the C<$buffer> doesn't start with something |
|
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369 | that could ever be a valid CBOR value, it raises an exception, just as |
|
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370 | C<decode> would. In the latter case the decoder state is undefined and |
|
|
371 | must be reset before being able to parse further. |
|
|
372 | |
|
|
373 | This method modifies the C<$buffer> in place. When no CBOR value can be |
|
|
374 | decoded, the decoder stores the current string offset. On the next call, |
|
|
375 | continues decoding at the place where it stopped before. For this to make |
|
|
376 | sense, the C<$buffer> must begin with the same octets as on previous |
|
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377 | unsuccessful calls. |
|
|
378 | |
|
|
379 | You can call this method in scalar context, in which case it either |
|
|
380 | returns a decoded value or C<undef>. This makes it impossible to |
|
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381 | distinguish between CBOR null values (which decode to C<undef>) and an |
|
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382 | unsuccessful decode, which is often acceptable. |
|
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383 | |
|
|
384 | =item @decoded = $cbor->incr_parse_multiple ($buffer) |
|
|
385 | |
|
|
386 | Same as C<incr_parse>, but attempts to decode as many CBOR values as |
|
|
387 | possible in one go, instead of at most one. Calls to C<incr_parse> and |
|
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388 | C<incr_parse_multiple> can be interleaved. |
|
|
389 | |
|
|
390 | =item $cbor->incr_reset |
|
|
391 | |
|
|
392 | Resets the incremental decoder. This throws away any saved state, so that |
|
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393 | subsequent calls to C<incr_parse> or C<incr_parse_multiple> start to parse |
|
|
394 | a new CBOR value from the beginning of the C<$buffer> again. |
|
|
395 | |
|
|
396 | This method can be caled at any time, but it I<must> be called if you want |
|
|
397 | to change your C<$buffer> or there was a decoding error and you want to |
|
|
398 | reuse the C<$cbor> object for future incremental parsings. |
| 335 | |
399 | |
| 336 | =back |
400 | =back |
| 337 | |
401 | |
| 338 | |
402 | |
| 339 | =head1 MAPPING |
403 | =head1 MAPPING |
