--- CBOR-XS/README 2013/12/01 17:10:42 1.12 +++ CBOR-XS/README 2016/02/08 04:37:12 1.16 @@ -180,8 +180,13 @@ If $enable is false (the default), then "decode" will throw an error when it encounters a self-referential/cyclic data structure. + FUTURE DIRECTION: the motivation behind this option is to avoid + *real* cycles - future versions of this module might chose to decode + cyclic data structures using weak references when this option is + off, instead of throwing an error. + This option does not affect "encode" in any way - shared values and - references will always be decoded properly if present. + references will always be encoded properly if present. $cbor = $cbor->pack_strings ([$enable]) $enabled = $cbor->get_pack_strings @@ -289,6 +294,64 @@ CBOR::XS->new->decode_prefix ("......") => ("...", 3) + INCREMENTAL PARSING + In some cases, there is the need for incremental parsing of JSON texts. + While this module always has to keep both CBOR text and resulting Perl + data structure in memory at one time, it does allow you to parse a CBOR + stream incrementally, using a similar to using "decode_prefix" to see if + a full CBOR object is available, but is much more efficient. + + It basically works by parsing as much of a CBOR string as possible - if + the CBOR data is not complete yet, the pasrer will remember where it + was, to be able to restart when more data has been accumulated. Once + enough data is available to either decode a complete CBOR value or raise + an error, a real decode will be attempted. + + A typical use case would be a network protocol that consists of sending + and receiving CBOR-encoded messages. The solution that works with CBOR + and about anything else is by prepending a length to every CBOR value, + so the receiver knows how many octets to read. More compact (and + slightly slower) would be to just send CBOR values back-to-back, as + "CBOR::XS" knows where a CBOR value ends, and doesn't need an explicit + length. + + The following methods help with this: + + @decoded = $cbor->incr_parse ($buffer) + This method attempts to decode exactly one CBOR value from the + beginning of the given $buffer. The value is removed from the + $buffer on success. When $buffer doesn't contain a complete value + yet, it returns nothing. Finally, when the $buffer doesn't start + with something that could ever be a valid CBOR value, it raises an + exception, just as "decode" would. In the latter case the decoder + state is undefined and must be reset before being able to parse + further. + + This method modifies the $buffer in place. When no CBOR value can be + decoded, the decoder stores the current string offset. On the next + call, continues decoding at the place where it stopped before. For + this to make sense, the $buffer must begin with the same octets as + on previous unsuccessful calls. + + You can call this method in scalar context, in which case it either + returns a decoded value or "undef". This makes it impossible to + distinguish between CBOR null values (which decode to "undef") and + an unsuccessful decode, which is often acceptable. + + @decoded = $cbor->incr_parse_multiple ($buffer) + Same as "incr_parse", but attempts to decode as many CBOR values as + possible in one go, instead of at most one. Calls to "incr_parse" + and "incr_parse_multiple" can be interleaved. + + $cbor->incr_reset + Resets the incremental decoder. This throws away any saved state, so + that subsequent calls to "incr_parse" or "incr_parse_multiple" start + to parse a new CBOR value from the beginning of the $buffer again. + + This method can be caled at any time, but it *must* be called if you + want to change your $buffer or there was a decoding error and you + want to reuse the $cbor object for future incremental parsings. + MAPPING This section describes how CBOR::XS maps Perl values to CBOR values and vice versa. These mappings are designed to "do the right thing" in most @@ -633,7 +696,7 @@ objects using the "FREEZE/THAW" methods (the Types::Serialier object serialisation protocol). See "OBJECT SERIALISATION" for details. - 28, 29 (shareable, sharedref, L ) + 28, 29 (shareable, sharedref, ) These tags are automatically decoded when encountered (and they do not result in a cyclic data structure, see "allow_cycles"), resulting in shared values in the decoded object. They are only @@ -652,7 +715,7 @@ considered too unimportant to be supported in the encoder. The decoder, however, will decode these values as shared values. - 256, 25 (stringref-namespace, stringref, L + 256, 25 (stringref-namespace, stringref, ) These tags are automatically decoded when encountered. They are only encoded, however, when "pack_strings" is enabled. @@ -778,7 +841,8 @@ LIMITATIONS ON PERLS WITHOUT 64-BIT INTEGER SUPPORT On perls that were built without 64 bit integer support (these are rare - nowadays, even on 32 bit architectures), support for any kind of 64 bit + nowadays, even on 32 bit architectures, as all major Perl distributions + are built with 64 bit integer support), support for any kind of 64 bit integer in CBOR is very limited - most likely, these 64 bit values will be truncated, corrupted, or otherwise not decoded correctly. This also includes string, array and map sizes that are stored as 64 bit integers.