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| 286 | protocol and you need to know where the first CBOR string ends amd |
286 | protocol and you need to know where the first CBOR string ends amd |
| 287 | the next one starts. |
287 | the next one starts. |
| 288 | |
288 | |
| 289 | CBOR::XS->new->decode_prefix ("......") |
289 | CBOR::XS->new->decode_prefix ("......") |
| 290 | => ("...", 3) |
290 | => ("...", 3) |
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291 | |
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292 | INCREMENTAL PARSING |
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293 | In some cases, there is the need for incremental parsing of JSON texts. |
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294 | While this module always has to keep both CBOR text and resulting Perl |
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295 | data structure in memory at one time, it does allow you to parse a CBOR |
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296 | stream incrementally, using a similar to using "decode_prefix" to see if |
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297 | a full CBOR object is available, but is much more efficient. |
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298 | |
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299 | It basically works by parsing as much of a CBOR string as possible - if |
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300 | the CBOR data is not complete yet, the pasrer will remember where it |
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301 | was, to be able to restart when more data has been accumulated. Once |
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302 | enough data is available to either decode a complete CBOR value or raise |
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303 | an error, a real decode will be attempted. |
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304 | |
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305 | A typical use case would be a network protocol that consists of sending |
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306 | and receiving CBOR-encoded messages. The solution that works with CBOR |
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307 | and about anything else is by prepending a length to every CBOR value, |
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308 | so the receiver knows how many octets to read. More compact (and |
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309 | slightly slower) would be to just send CBOR values back-to-back, as |
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310 | "CBOR::XS" knows where a CBOR value ends, and doesn't need an explicit |
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311 | length. |
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312 | |
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313 | The following methods help with this: |
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314 | |
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315 | @decoded = $cbor->incr_parse ($buffer) |
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316 | This method attempts to decode exactly one CBOR value from the |
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317 | beginning of the given $buffer. The value is removed from the |
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318 | $buffer on success. When $buffer doesn't contain a complete value |
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319 | yet, it returns nothing. Finally, when the $buffer doesn't start |
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320 | with something that could ever be a valid CBOR value, it raises an |
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321 | exception, just as "decode" would. In the latter case the decoder |
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322 | state is undefined and must be reset before being able to parse |
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323 | further. |
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324 | |
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325 | This method modifies the $buffer in place. When no CBOR value can be |
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326 | decoded, the decoder stores the current string offset. On the next |
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327 | call, continues decoding at the place where it stopped before. For |
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328 | this to make sense, the $buffer must begin with the same octets as |
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329 | on previous unsuccessful calls. |
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330 | |
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331 | You can call this method in scalar context, in which case it either |
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332 | returns a decoded value or "undef". This makes it impossible to |
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333 | distinguish between CBOR null values (which decode to "undef") and |
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334 | an unsuccessful decode, which is often acceptable. |
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335 | |
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336 | @decoded = $cbor->incr_parse_multiple ($buffer) |
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337 | Same as "incr_parse", but attempts to decode as many CBOR values as |
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338 | possible in one go, instead of at most one. Calls to "incr_parse" |
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339 | and "incr_parse_multiple" can be interleaved. |
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340 | |
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341 | $cbor->incr_reset |
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342 | Resets the incremental decoder. This throws away any saved state, so |
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343 | that subsequent calls to "incr_parse" or "incr_parse_multiple" start |
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344 | to parse a new CBOR value from the beginning of the $buffer again. |
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345 | |
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346 | This method can be caled at any time, but it *must* be called if you |
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347 | want to change your $buffer or there was a decoding error and you |
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348 | want to reuse the $cbor object for future incremental parsings. |
| 291 | |
349 | |
| 292 | MAPPING |
350 | MAPPING |
| 293 | This section describes how CBOR::XS maps Perl values to CBOR values and |
351 | This section describes how CBOR::XS maps Perl values to CBOR values and |
| 294 | vice versa. These mappings are designed to "do the right thing" in most |
352 | vice versa. These mappings are designed to "do the right thing" in most |
| 295 | circumstances automatically, preserving round-tripping characteristics |
353 | circumstances automatically, preserving round-tripping characteristics |
