--- JSON-XS/README 2009/02/19 01:13:46 1.29 +++ JSON-XS/README 2013/10/29 15:55:49 1.39 @@ -22,8 +22,8 @@ # Note that JSON version 2.0 and above will automatically use JSON::XS # if available, at virtually no speed overhead either, so you should # be able to just: - - use JSON; + + use JSON; # and do the same things, except that you have a pure-perl fallback now. @@ -58,10 +58,11 @@ * round-trip integrity When you serialise a perl data structure using only data types - supported by JSON, the deserialised data structure is identical on - the Perl level. (e.g. the string "2.0" doesn't suddenly become "2" - just because it looks like a number). There minor *are* exceptions - to this, read the MAPPING section below to learn about those. + supported by JSON and Perl, the deserialised data structure is + identical on the Perl level. (e.g. the string "2.0" doesn't suddenly + become "2" just because it looks like a number). There *are* minor + exceptions to this, read the MAPPING section below to learn about + those. * strict checking of JSON correctness @@ -78,7 +79,7 @@ * simple to use This module has both a simple functional interface as well as an - object oriented interface interface. + object oriented interface. * reasonably versatile output formats @@ -114,15 +115,6 @@ Except being faster. - $is_boolean = JSON::XS::is_bool $scalar - Returns true if the passed scalar represents either JSON::XS::true - or JSON::XS::false, two constants that act like 1 and 0, - respectively and are used to represent JSON "true" and "false" - values in Perl. - - See MAPPING, below, for more information on how JSON values are - mapped to Perl. - A FEW NOTES ON UNICODE AND PERL Since this often leads to confusion, here are a few very clear words on how Unicode works in Perl, modulo bugs. @@ -370,7 +362,8 @@ If $enable is false, then the "encode" method will output key-value pairs in the order Perl stores them (which will likely change - between runs of the same script). + between runs of the same script, and can change even within the same + run from 5.18 onwards). This option is useful if you want the same data structure to be encoded as the same JSON text (given the same overall settings). If @@ -380,6 +373,8 @@ This setting has no effect when decoding JSON texts. + This setting has currently no effect on tied hashes. + $json = $json->allow_nonref ([$enable]) $enabled = $json->get_allow_nonref If $enable is true (or missing), then the "encode" method can @@ -415,24 +410,28 @@ $json = $json->allow_blessed ([$enable]) $enabled = $json->get_allow_blessed + See "OBJECT SERIALISATION" for details. + If $enable is true (or missing), then the "encode" method will not - barf when it encounters a blessed reference. Instead, the value of - the convert_blessed option will decide whether "null" - ("convert_blessed" disabled or no "TO_JSON" method found) or a - representation of the object ("convert_blessed" enabled and - "TO_JSON" method found) is being encoded. Has no effect on "decode". + barf when it encounters a blessed reference that it cannot convert + otherwise. Instead, a JSON "null" value is encoded instead of the + object. If $enable is false (the default), then "encode" will throw an - exception when it encounters a blessed object. + exception when it encounters a blessed object that it cannot convert + otherwise. + + This setting has no effect on "decode". $json = $json->convert_blessed ([$enable]) $enabled = $json->get_convert_blessed + See "OBJECT SERIALISATION" for details. + If $enable is true (or missing), then "encode", upon encountering a blessed object, will check for the availability of the "TO_JSON" method on the object's class. If found, it will be called in scalar context and the resulting scalar will be encoded instead of the - object. If no "TO_JSON" method is found, the value of - "allow_blessed" will decide what to do. + object. The "TO_JSON" method may safely call die if it wants. If "TO_JSON" returns other blessed objects, those will be handled in the same @@ -442,12 +441,27 @@ the object) are usually in upper case letters and to avoid collisions with any "to_json" function or method. - This setting does not yet influence "decode" in any way, but in the - future, global hooks might get installed that influence "decode" and - are enabled by this setting. + If $enable is false (the default), then "encode" will not consider + this type of conversion. + + This setting has no effect on "decode". + + $json = $json->allow_tags ([$enable]) + $enabled = $json->allow_tags + See "OBJECT SERIALISATION" for details. - If $enable is false, then the "allow_blessed" setting will decide - what to do when a blessed object is found. + If $enable is true (or missing), then "encode", upon encountering a + blessed object, will check for the availability of the "FREEZE" + method on the object's class. If found, it will be used to serialise + the object into a nonstandard tagged JSON value (that JSON decoders + cannot decode). + + It also causes "decode" to parse such tagged JSON values and + deserialise them via a call to the "THAW" method. + + If $enable is false (the default), then "encode" will not consider + this type of conversion, and tagged JSON values will cause a parse + error in "decode", as if tags were not part of the grammar. $json = $json->filter_json_object ([$coderef->($hashref)]) When $coderef is specified, it will be called from "decode" each @@ -593,22 +607,13 @@ useful. $json_text = $json->encode ($perl_scalar) - Converts the given Perl data structure (a simple scalar or a - reference to a hash or array) to its JSON representation. Simple - scalars will be converted into JSON string or number sequences, - while references to arrays become JSON arrays and references to - hashes become JSON objects. Undefined Perl values (e.g. "undef") - become JSON "null" values. Neither "true" nor "false" values will be - generated. + Converts the given Perl value or data structure to its JSON + representation. Croaks on error. $perl_scalar = $json->decode ($json_text) The opposite of "encode": expects a JSON text and tries to parse it, returning the resulting simple scalar or reference. Croaks on error. - JSON numbers and strings become simple Perl scalars. JSON arrays - become Perl arrayrefs and JSON objects become Perl hashrefs. "true" - becomes 1, "false" becomes 0 and "null" becomes "undef". - ($perl_scalar, $characters) = $json->decode_prefix ($json_text) This works like the "decode" method, but instead of raising an exception when there is trailing garbage after the first JSON @@ -616,8 +621,7 @@ characters consumed so far. This is useful if your JSON texts are not delimited by an outer - protocol (which is not the brightest thing to do in the first place) - and you need to know where the JSON text ends. + protocol and you need to know where the JSON text ends. JSON::XS->new->decode_prefix ("[1] the tail") => ([], 3) @@ -635,7 +639,7 @@ JSON::XS will only attempt to parse the JSON text once it is sure it has enough text to get a decisive result, using a very simple but truly incremental parser. This means that it sometimes won't stop as early as - the full parser, for example, it doesn't detect parenthese mismatches. + the full parser, for example, it doesn't detect mismatched parentheses. The only thing it guarantees is that it starts decoding as soon as a syntactically valid JSON text has been seen. This means you need to set resource limits (e.g. "max_size") to ensure the parser will stop parsing @@ -659,7 +663,7 @@ extract exactly *one* JSON object. If that is successful, it will return this object, otherwise it will return "undef". If there is a parse error, this method will croak just as "decode" would do (one - can then use "incr_skip" to skip the errornous part). This is the + can then use "incr_skip" to skip the erroneous part). This is the most common way of using the method. And finally, in list context, it will try to extract as many objects @@ -670,6 +674,11 @@ the scalar context case. Note that in this case, any previously-parsed JSON texts will be lost. + Example: Parse some JSON arrays/objects in a given string and return + them. + + my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]"); + $lvalue_string = $json->incr_text This method returns the currently stored JSON fragment as an lvalue, that is, you can manipulate it. This *only* works when a preceding @@ -692,7 +701,7 @@ to reset the parse state. The difference to "incr_reset" is that only text until the parse - error occured is removed. + error occurred is removed. $json->incr_reset This completely resets the incremental parser, that is, after this @@ -886,7 +895,7 @@ represent it as a numeric (floating point) value if that is possible without loss of precision. Otherwise it will preserve the number as a string value (in which case you lose roundtripping ability, as the - JSON number will be re-encoded toa JSON string). + JSON number will be re-encoded to a JSON string). Numbers containing a fractional or exponential part will always be represented as numeric (floating point) values, possibly at a loss @@ -894,15 +903,35 @@ ability, but the JSON number will still be re-encoded as a JSON number). + Note that precision is not accuracy - binary floating point values + cannot represent most decimal fractions exactly, and when converting + from and to floating point, JSON::XS only guarantees precision up to + but not including the least significant bit. + true, false - These JSON atoms become "JSON::XS::true" and "JSON::XS::false", - respectively. They are overloaded to act almost exactly like the - numbers 1 and 0. You can check whether a scalar is a JSON boolean by - using the "JSON::XS::is_bool" function. + These JSON atoms become "Types::Serialiser::true" and + "Types::Serialiser::false", respectively. They are overloaded to act + almost exactly like the numbers 1 and 0. You can check whether a + scalar is a JSON boolean by using the "Types::Serialiser::is_bool" + function (after "use Types::Serialier", of course). null A JSON null atom becomes "undef" in Perl. + shell-style comments ("# *text*") + As a nonstandard extension to the JSON syntax that is enabled by the + "relaxed" setting, shell-style comments are allowed. They can start + anywhere outside strings and go till the end of the line. + + tagged values ("(*tag*)*value*"). + Another nonstandard extension to the JSON syntax, enabled with the + "allow_tags" setting, are tagged values. In this implementation, the + *tag* must be a perl package/class name encoded as a JSON string, + and the *value* must be a JSON array encoding optional constructor + arguments. + + See "OBJECT SERIALISATION", below, for details. + PERL -> JSON The mapping from Perl to JSON is slightly more difficult, as Perl is a truly typeless language, so we can only guess which JSON type is meant @@ -911,14 +940,12 @@ hash references Perl hash references become JSON objects. As there is no inherent ordering in hash keys (or JSON objects), they will usually be - encoded in a pseudo-random order that can change between runs of the - same program but stays generally the same within a single run of a - program. JSON::XS can optionally sort the hash keys (determined by - the *canonical* flag), so the same datastructure will serialise to - the same JSON text (given same settings and version of JSON::XS), - but this incurs a runtime overhead and is only rarely useful, e.g. - when you want to compare some JSON text against another for - equality. + encoded in a pseudo-random order. JSON::XS can optionally sort the + hash keys (determined by the *canonical* flag), so the same + datastructure will serialise to the same JSON text (given same + settings and version of JSON::XS), but this incurs a runtime + overhead and is only rarely useful, e.g. when you want to compare + some JSON text against another for equality. array references Perl array references become JSON arrays. @@ -926,22 +953,25 @@ other references Other unblessed references are generally not allowed and will cause an exception to be thrown, except for references to the integers 0 - and 1, which get turned into "false" and "true" atoms in JSON. You - can also use "JSON::XS::false" and "JSON::XS::true" to improve + and 1, which get turned into "false" and "true" atoms in JSON. + + Since "JSON::XS" uses the boolean model from Types::Serialiser, you + can also "use Types::Serialiser" and then use + "Types::Serialiser::false" and "Types::Serialiser::true" to improve readability. - encode_json [\0, JSON::XS::true] # yields [false,true] + use Types::Serialiser; + encode_json [\0, Types::Serialiser::true] # yields [false,true] - JSON::XS::true, JSON::XS::false - These special values become JSON true and JSON false values, - respectively. You can also use "\1" and "\0" directly if you want. + Types::Serialiser::true, Types::Serialiser::false + These special values from the Types::Serialiser module become JSON + true and JSON false values, respectively. You can also use "\1" and + "\0" directly if you want. blessed objects - Blessed objects are not directly representable in JSON. See the - "allow_blessed" and "convert_blessed" methods on various options on - how to deal with this: basically, you can choose between throwing an - exception, encoding the reference as if it weren't blessed, or - provide your own serialiser method. + Blessed objects are not directly representable in JSON, but + "JSON::XS" allows various ways of handling objects. See "OBJECT + SERIALISATION", below, for details. simple scalars Simple Perl scalars (any scalar that is not a reference) are the @@ -979,6 +1009,113 @@ Tell me if you need this capability (but don't forget to explain why it's needed :). + Note that numerical precision has the same meaning as under Perl (so + binary to decimal conversion follows the same rules as in Perl, + which can differ to other languages). Also, your perl interpreter + might expose extensions to the floating point numbers of your + platform, such as infinities or NaN's - these cannot be represented + in JSON, and it is an error to pass those in. + + OBJECT SERIALISATION + As JSON cannot directly represent Perl objects, you have to choose + between a pure JSON representation (without the ability to deserialise + the object automatically again), and a nonstandard extension to the JSON + syntax, tagged values. + + SERIALISATION + What happens when "JSON::XS" encounters a Perl object depends on the + "allow_blessed", "convert_blessed" and "allow_tags" settings, which are + used in this order: + + 1. "allow_tags" is enabled and the object has a "FREEZE" method. + In this case, "JSON::XS" uses the Types::Serialiser object + serialisation protocol to create a tagged JSON value, using a + nonstandard extension to the JSON syntax. + + This works by invoking the "FREEZE" method on the object, with the + first argument being the object to serialise, and the second + argument being the constant string "JSON" to distinguish it from + other serialisers. + + The "FREEZE" method can return any number of values (i.e. zero or + more). These values and the paclkage/classname of the object will + then be encoded as a tagged JSON value in the following format: + + ("classname")[FREEZE return values...] + + e.g.: + + ("URI")["http://www.google.com/"] + ("MyDate")[2013,10,29] + ("ImageData::JPEG")["Z3...VlCg=="] + + For example, the hypothetical "My::Object" "FREEZE" method might use + the objects "type" and "id" members to encode the object: + + sub My::Object::FREEZE { + my ($self, $serialiser) = @_; + + ($self->{type}, $self->{id}) + } + + 2. "convert_blessed" is enabled and the object has a "TO_JSON" method. + In this case, the "TO_JSON" method of the object is invoked in + scalar context. It must return a single scalar that can be directly + encoded into JSON. This scalar replaces the object in the JSON text. + + For example, the following "TO_JSON" method will convert all URI + objects to JSON strings when serialised. The fatc that these values + originally were URI objects is lost. + + sub URI::TO_JSON { + my ($uri) = @_; + $uri->as_string + } + + 3. "allow_blessed" is enabled. + The object will be serialised as a JSON null value. + + 4. none of the above + If none of the settings are enabled or the respective methods are + missing, "JSON::XS" throws an exception. + + DESERIALISATION + For deserialisation there are only two cases to consider: either + nonstandard tagging was used, in which case "allow_tags" decides, or + objects cannot be automatically be deserialised, in which case you can + use postprocessing or the "filter_json_object" or + "filter_json_single_key_object" callbacks to get some real objects our + of your JSON. + + This section only considers the tagged value case: I a tagged JSON + object is encountered during decoding and "allow_tags" is disabled, a + parse error will result (as if tagged values were not part of the + grammar). + + If "allow_tags" is enabled, "JSON::XS" will look up the "THAW" method of + the package/classname used during serialisation (it will not attempt to + load the package as a Perl module). If there is no such method, the + decoding will fail with an error. + + Otherwise, the "THAW" method is invoked with the classname as first + argument, the constant string "JSON" as second argument, and all the + values from the JSON array (the values originally returned by the + "FREEZE" method) as remaining arguments. + + The method must then return the object. While technically you can return + any Perl scalar, you might have to enable the "enable_nonref" setting to + make that work in all cases, so better return an actual blessed + reference. + + As an example, let's implement a "THAW" function that regenerates the + "My::Object" from the "FREEZE" example earlier: + + sub My::Object::THAW { + my ($class, $serialiser, $type, $id) = @_; + + $class->new (type => $type, id => $id) + } + ENCODING/CODESET FLAG NOTES The interested reader might have seen a number of flags that signify encodings or codesets - "utf8", "latin1" and "ascii". There seems to be @@ -1007,7 +1144,7 @@ When "utf8" is disabled (the default), then "encode"/"decode" generate and expect Unicode strings, that is, characters with high ordinal Unicode values (> 255) will be encoded as such characters, - and likewise such characters are decoded as-is, no canges to them + and likewise such characters are decoded as-is, no changes to them will be done, except "(re-)interpreting" them as Unicode codepoints or Unicode characters, respectively (to Perl, these are the same thing in strings unless you do funny/weird/dumb stuff). @@ -1125,7 +1262,7 @@ Another problem is that some javascript implementations reserve some property names for their own purposes (which probably makes them non-ECMAscript-compliant). For example, Iceweasel reserves the - "__proto__" property name for it's own purposes. + "__proto__" property name for its own purposes. If that is a problem, you could parse try to filter the resulting JSON output for these property strings, e.g.: @@ -1133,7 +1270,7 @@ $json =~ s/"__proto__"\s*:/"__proto__renamed":/g; This works because "__proto__" is not valid outside of strings, so every - occurence of ""__proto__"\s*:" must be a string used as property name. + occurrence of ""__proto__"\s*:" must be a string used as property name. If you know of other incompatibilities, please let me know. @@ -1153,10 +1290,10 @@ This will *usually* generate JSON texts that also parse as valid YAML. Please note that YAML has hardcoded limits on (simple) object key lengths that JSON doesn't have and also has different and incompatible - unicode handling, so you should make sure that your hash keys are - noticeably shorter than the 1024 "stream characters" YAML allows and - that you do not have characters with codepoint values outside the - Unicode BMP (basic multilingual page). YAML also does not allow "\/" + unicode character escape syntax, so you should make sure that your hash + keys are noticeably shorter than the 1024 "stream characters" YAML + allows and that you do not have characters with codepoint values outside + the Unicode BMP (basic multilingual page). YAML also does not allow "\/" sequences in strings (which JSON::XS does not *currently* generate, but other JSON generators might). @@ -1183,6 +1320,13 @@ spreading lies about the real compatibility for many *years* and trying to silence people who point out that it isn't true. + Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, + even though the incompatibilities have been documented (and are + known to Brian) for many years and the spec makes explicit claims + that YAML is a superset of JSON. It would be so easy to fix, but + apparently, bullying people and corrupting userdata is so much + easier. + SPEED It seems that JSON::XS is surprisingly fast, as shown in the following tables. They have been generated with the help of the "eg/bench" program @@ -1195,49 +1339,48 @@ {"method": "handleMessage", "params": ["user1", "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7, - true, false]} + 1, 0]} It shows the number of encodes/decodes per second (JSON::XS uses the functional interface, while JSON::XS/2 uses the OO interface with - pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink). - Higher is better: - - module | encode | decode | - -----------|------------|------------| - JSON 1.x | 4990.842 | 4088.813 | - JSON::DWIW | 51653.990 | 71575.154 | - JSON::PC | 65948.176 | 74631.744 | - JSON::PP | 8931.652 | 3817.168 | - JSON::Syck | 24877.248 | 27776.848 | - JSON::XS | 388361.481 | 227951.304 | - JSON::XS/2 | 227951.304 | 218453.333 | - JSON::XS/3 | 338250.323 | 218453.333 | - Storable | 16500.016 | 135300.129 | - -----------+------------+------------+ - - That is, JSON::XS is about five times faster than JSON::DWIW on - encoding, about three times faster on decoding, and over forty times - faster than JSON, even with pretty-printing and key sorting. It also + pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink. + JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ uses + the from_json method). Higher is better: + + module | encode | decode | + --------------|------------|------------| + JSON::DWIW/DS | 86302.551 | 102300.098 | + JSON::DWIW/FJ | 86302.551 | 75983.768 | + JSON::PP | 15827.562 | 6638.658 | + JSON::Syck | 63358.066 | 47662.545 | + JSON::XS | 511500.488 | 511500.488 | + JSON::XS/2 | 291271.111 | 388361.481 | + JSON::XS/3 | 361577.931 | 361577.931 | + Storable | 66788.280 | 265462.278 | + --------------+------------+------------+ + + That is, JSON::XS is almost six times faster than JSON::DWIW on + encoding, about five times faster on decoding, and over thirty to + seventy times faster than JSON's pure perl implementation. It also compares favourably to Storable for small amounts of data. Using a longer test string (roughly 18KB, generated from Yahoo! Locals search API (). - module | encode | decode | - -----------|------------|------------| - JSON 1.x | 55.260 | 34.971 | - JSON::DWIW | 825.228 | 1082.513 | - JSON::PC | 3571.444 | 2394.829 | - JSON::PP | 210.987 | 32.574 | - JSON::Syck | 552.551 | 787.544 | - JSON::XS | 5780.463 | 4854.519 | - JSON::XS/2 | 3869.998 | 4798.975 | - JSON::XS/3 | 5862.880 | 4798.975 | - Storable | 4445.002 | 5235.027 | - -----------+------------+------------+ + module | encode | decode | + --------------|------------|------------| + JSON::DWIW/DS | 1647.927 | 2673.916 | + JSON::DWIW/FJ | 1630.249 | 2596.128 | + JSON::PP | 400.640 | 62.311 | + JSON::Syck | 1481.040 | 1524.869 | + JSON::XS | 20661.596 | 9541.183 | + JSON::XS/2 | 10683.403 | 9416.938 | + JSON::XS/3 | 20661.596 | 9400.054 | + Storable | 19765.806 | 10000.725 | + --------------+------------+------------+ Again, JSON::XS leads by far (except for Storable which non-surprisingly - decodes faster). + decodes a bit faster). On large strings containing lots of high Unicode characters, some modules (such as JSON::PC) seem to decode faster than JSON::XS, but the @@ -1282,11 +1425,17 @@ If you are using JSON::XS to return packets to consumption by JavaScript scripts in a browser you should have a look at - to see whether - you are vulnerable to some common attack vectors (which really are - browser design bugs, but it is still you who will have to deal with it, - as major browser developers care only for features, not about getting - security right). + + to see whether you are vulnerable to some common attack vectors (which + really are browser design bugs, but it is still you who will have to + deal with it, as major browser developers care only for features, not + about getting security right). + +INTEROPERABILITY WITH OTHER MODULES + "JSON::XS" uses the Types::Serialiser module to provide boolean + constants. That means that the JSON true and false values will be + comaptible to true and false values of iother modules that do the same, + such as JSON::PP and CBOR::XS. THREADS This module is *not* guaranteed to be thread safe and there are no plans @@ -1296,6 +1445,22 @@ (It might actually work, but you have been warned). +THE PERILS OF SETLOCALE + Sometimes people avoid the Perl locale support and directly call the + system's setlocale function with "LC_ALL". + + This breaks both perl and modules such as JSON::XS, as stringification + of numbers no longer works correctly (e.g. "$x = 0.1; print "$x"+1" + might print 1, and JSON::XS might output illegal JSON as JSON::XS relies + on perl to stringify numbers). + + The solution is simple: don't call "setlocale", or use it for only those + categories you need, such as "LC_MESSAGES" or "LC_CTYPE". + + If you need "LC_NUMERIC", you should enable it only around the code that + actually needs it (avoiding stringification of numbers), and restore it + afterwards. + BUGS While the goal of this module is to be correct, that unfortunately does not mean it's bug-free, only that I think its design is bug-free. If you