--- JSON-XS/README 2007/03/24 01:15:22 1.5 +++ JSON-XS/README 2007/11/13 22:59:08 1.20 @@ -1,15 +1,20 @@ NAME JSON::XS - JSON serialising/deserialising, done correctly and fast + JSON::XS - 正しくて高速な JSON + シリアライザ/デシリアライザ + (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html) + SYNOPSIS use JSON::XS; - # exported functions, croak on error + # exported functions, they croak on error + # and expect/generate UTF-8 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; - # oo-interface + # OO-interface $coder = JSON::XS->new->ascii->pretty->allow_nonref; $pretty_printed_unencoded = $coder->encode ($perl_scalar); @@ -32,17 +37,18 @@ vice versa. FEATURES - * correct handling of unicode issues + * correct Unicode handling This module knows how to handle Unicode, and even documents how and when it does so. * round-trip integrity When you serialise a perl data structure using only datatypes supported by JSON, the deserialised data structure is identical on - the Perl level. (e.g. the string "2.0" doesn't suddenly become "2"). + the Perl level. (e.g. the string "2.0" doesn't suddenly become "2" + just because it looks like a number). * strict checking of JSON correctness - There is no guessing, no generating of illegal JSON strings by + There is no guessing, no generating of illegal JSON texts by default, and only JSON is accepted as input by default (the latter is a security feature). @@ -55,31 +61,85 @@ interface. * reasonably versatile output formats - You can choose between the most compact guarenteed single-line + You can choose between the most compact guaranteed single-line format possible (nice for simple line-based protocols), a pure-ascii - format (for when your transport is not 8-bit clean), or a - pretty-printed format (for when you want to read that stuff). Or you - can combine those features in whatever way you like. + format (for when your transport is not 8-bit clean, still supports + the whole Unicode range), or a pretty-printed format (for when you + want to read that stuff). Or you can combine those features in + whatever way you like. FUNCTIONAL INTERFACE - The following convinience methods are provided by this module. They are + The following convenience methods are provided by this module. They are exported by default: - $json_string = to_json $perl_scalar - Converts the given Perl data structure (a simple scalar or a - reference to a hash or array) to a UTF-8 encoded, binary string - (that is, the string contains octets only). Croaks on error. + $json_text = to_json $perl_scalar + Converts the given Perl data structure to a UTF-8 encoded, binary + string (that is, the string contains octets only). Croaks on error. + + This function call is functionally identical to: - This function call is functionally identical to - "JSON::XS->new->utf8->encode ($perl_scalar)". + $json_text = JSON::XS->new->utf8->encode ($perl_scalar) - $perl_scalar = from_json $json_string + except being faster. + + $perl_scalar = from_json $json_text The opposite of "to_json": expects an UTF-8 (binary) string and - tries to parse that as an UTF-8 encoded JSON string, returning the - resulting simple scalar or reference. Croaks on error. + tries to parse that as an UTF-8 encoded JSON text, returning the + resulting reference. Croaks on error. + + This function call is functionally identical to: - This function call is functionally identical to - "JSON::XS->new->utf8->decode ($json_string)". + $perl_scalar = JSON::XS->new->utf8->decode ($json_text) + + 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. + + 1. Perl strings can store characters with ordinal values > 255. + This enables you to store Unicode characters as single characters in + a Perl string - very natural. + + 2. Perl does *not* associate an encoding with your strings. + Unless you force it to, e.g. when matching it against a regex, or + printing the scalar to a file, in which case Perl either interprets + your string as locale-encoded text, octets/binary, or as Unicode, + depending on various settings. In no case is an encoding stored + together with your data, it is *use* that decides encoding, not any + magical metadata. + + 3. The internal utf-8 flag has no meaning with regards to the encoding + of your string. + Just ignore that flag unless you debug a Perl bug, a module written + in XS or want to dive into the internals of perl. Otherwise it will + only confuse you, as, despite the name, it says nothing about how + your string is encoded. You can have Unicode strings with that flag + set, with that flag clear, and you can have binary data with that + flag set and that flag clear. Other possibilities exist, too. + + If you didn't know about that flag, just the better, pretend it + doesn't exist. + + 4. A "Unicode String" is simply a string where each character can be + validly interpreted as a Unicode codepoint. + If you have UTF-8 encoded data, it is no longer a Unicode string, + but a Unicode string encoded in UTF-8, giving you a binary string. + + 5. A string containing "high" (> 255) character values is *not* a UTF-8 + string. + It's a fact. Learn to live with it. + + I hope this helps :) OBJECT-ORIENTED INTERFACE The object oriented interface lets you configure your own encoding or @@ -93,36 +153,79 @@ The mutators for flags all return the JSON object again and thus calls can be chained: - my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]}) + my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]}) => {"a": [1, 2]} $json = $json->ascii ([$enable]) If $enable is true (or missing), then the "encode" method will not - generate characters outside the code range 0..127. Any unicode - characters outside that range will be escaped using either a single - \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, - as per RFC4627. + generate characters outside the code range 0..127 (which is ASCII). + Any Unicode characters outside that range will be escaped using + either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL + escape sequence, as per RFC4627. The resulting encoded JSON text can + be treated as a native Unicode string, an ascii-encoded, + latin1-encoded or UTF-8 encoded string, or any other superset of + ASCII. If $enable is false, then the "encode" method will not escape - Unicode characters unless necessary. + Unicode characters unless required by the JSON syntax or other + flags. This results in a faster and more compact format. - JSON::XS->new->ascii (1)->encode (chr 0x10401) - => \ud801\udc01 + The main use for this flag is to produce JSON texts that can be + transmitted over a 7-bit channel, as the encoded JSON texts will not + contain any 8 bit characters. + + JSON::XS->new->ascii (1)->encode ([chr 0x10401]) + => ["\ud801\udc01"] + + $json = $json->latin1 ([$enable]) + If $enable is true (or missing), then the "encode" method will + encode the resulting JSON text as latin1 (or iso-8859-1), escaping + any characters outside the code range 0..255. The resulting string + can be treated as a latin1-encoded JSON text or a native Unicode + string. The "decode" method will not be affected in any way by this + flag, as "decode" by default expects Unicode, which is a strict + superset of latin1. + + If $enable is false, then the "encode" method will not escape + Unicode characters unless required by the JSON syntax or other + flags. + + The main use for this flag is efficiently encoding binary data as + JSON text, as most octets will not be escaped, resulting in a + smaller encoded size. The disadvantage is that the resulting JSON + text is encoded in latin1 (and must correctly be treated as such + when storing and transferring), a rare encoding for JSON. It is + therefore most useful when you want to store data structures known + to contain binary data efficiently in files or databases, not when + talking to other JSON encoders/decoders. + + JSON::XS->new->latin1->encode (["\x{89}\x{abc}"] + => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not) $json = $json->utf8 ([$enable]) If $enable is true (or missing), then the "encode" method will - encode the JSON string into UTF-8, as required by many protocols, + encode the JSON result into UTF-8, as required by many protocols, while the "decode" method expects to be handled an UTF-8-encoded string. Please note that UTF-8-encoded strings do not contain any characters outside the range 0..255, they are thus useful for - bytewise/binary I/O. + bytewise/binary I/O. In future versions, enabling this option might + enable autodetection of the UTF-16 and UTF-32 encoding families, as + described in RFC4627. If $enable is false, then the "encode" method will return the JSON - string as a (non-encoded) unicode string, while "decode" expects - thus a unicode string. Any decoding or encoding (e.g. to UTF-8 or + string as a (non-encoded) Unicode string, while "decode" expects + thus a Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs to be done yourself, e.g. using the Encode module. - Example, output UTF-16-encoded JSON: + Example, output UTF-16BE-encoded JSON: + + use Encode; + $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); + + Example, decode UTF-32LE-encoded JSON: + + use Encode; + $object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext); $json = $json->pretty ([$enable]) This enables (or disables) all of the "indent", "space_before" and @@ -143,14 +246,13 @@ $json = $json->indent ([$enable]) If $enable is true (or missing), then the "encode" method will use a multiline format as output, putting every array member or - object/hash key-value pair into its own line, identing them + object/hash key-value pair into its own line, indenting them properly. If $enable is false, no newlines or indenting will be produced, and - the resulting JSON strings is guarenteed not to contain any - "newlines". + the resulting JSON text is guaranteed not to contain any "newlines". - This setting has no effect when decoding JSON strings. + This setting has no effect when decoding JSON texts. $json = $json->space_before ([$enable]) If $enable is true (or missing), then the "encode" method will add @@ -160,7 +262,7 @@ If $enable is false, then the "encode" method will not add any extra space at those places. - This setting has no effect when decoding JSON strings. You will also + This setting has no effect when decoding JSON texts. You will also most likely combine this setting with "space_after". Example, space_before enabled, space_after and indent disabled: @@ -176,12 +278,51 @@ If $enable is false, then the "encode" method will not add any extra space at those places. - This setting has no effect when decoding JSON strings. + This setting has no effect when decoding JSON texts. Example, space_before and indent disabled, space_after enabled: {"key": "value"} + $json = $json->relaxed ([$enable]) + If $enable is true (or missing), then "decode" will accept some + extensions to normal JSON syntax (see below). "encode" will not be + affected in anyway. *Be aware that this option makes you accept + invalid JSON texts as if they were valid!*. I suggest only to use + this option to parse application-specific files written by humans + (configuration files, resource files etc.) + + If $enable is false (the default), then "decode" will only accept + valid JSON texts. + + Currently accepted extensions are: + + * list items can have an end-comma + JSON *separates* array elements and key-value pairs with commas. + This can be annoying if you write JSON texts manually and want + to be able to quickly append elements, so this extension accepts + comma at the end of such items not just between them: + + [ + 1, + 2, <- this comma not normally allowed + ] + { + "k1": "v1", + "k2": "v2", <- this comma not normally allowed + } + + * shell-style '#'-comments + Whenever JSON allows whitespace, shell-style comments are + additionally allowed. They are terminated by the first + carriage-return or line-feed character, after which more + white-space and comments are allowed. + + [ + 1, # this comment not allowed in JSON + # neither this one... + ] + $json = $json->canonical ([$enable]) If $enable is true (or missing), then the "encode" method will output JSON objects by sorting their keys. This is adding a @@ -192,12 +333,12 @@ between runs of the same script). This option is useful if you want the same data structure to be - encoded as the same JSON string (given the same overall settings). - If it is disabled, the same hash migh be encoded differently even if + encoded as the same JSON text (given the same overall settings). If + it is disabled, the same hash might be encoded differently even if contains the same data, as key-value pairs have no inherent ordering in Perl. - This setting has no effect when decoding JSON strings. + This setting has no effect when decoding JSON texts. $json = $json->allow_nonref ([$enable]) If $enable is true (or missing), then the "encode" method can @@ -206,7 +347,7 @@ "decode" will accept those JSON values instead of croaking. If $enable is false, then the "encode" method will croak if it isn't - passed an arrayref or hashref, as JSON strings must either be an + passed an arrayref or hashref, as JSON texts must either be an object or array. Likewise, "decode" will croak if given something that is not a JSON object or array. @@ -216,15 +357,130 @@ JSON::XS->new->allow_nonref->encode ("Hello, World!") => "Hello, World!" + $json = $json->allow_blessed ([$enable]) + 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". + + If $enable is false (the default), then "encode" will throw an + exception when it encounters a blessed object. + + $json = $json->convert_blessed ([$enable]) + 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. + + 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 + way. "TO_JSON" must take care of not causing an endless recursion + cycle (== crash) in this case. The name of "TO_JSON" was chosen + because other methods called by the Perl core (== not by the user of + the object) are usually in upper case letters and to avoid + collisions with the "to_json" function. + + 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, then the "allow_blessed" setting will decide + what to do when a blessed object is found. + + $json = $json->filter_json_object ([$coderef->($hashref)]) + When $coderef is specified, it will be called from "decode" each + time it decodes a JSON object. The only argument is a reference to + the newly-created hash. If the code references returns a single + scalar (which need not be a reference), this value (i.e. a copy of + that scalar to avoid aliasing) is inserted into the deserialised + data structure. If it returns an empty list (NOTE: *not* "undef", + which is a valid scalar), the original deserialised hash will be + inserted. This setting can slow down decoding considerably. + + When $coderef is omitted or undefined, any existing callback will be + removed and "decode" will not change the deserialised hash in any + way. + + Example, convert all JSON objects into the integer 5: + + my $js = JSON::XS->new->filter_json_object (sub { 5 }); + # returns [5] + $js->decode ('[{}]') + # throw an exception because allow_nonref is not enabled + # so a lone 5 is not allowed. + $js->decode ('{"a":1, "b":2}'); + + $json = $json->filter_json_single_key_object ($key [=> + $coderef->($value)]) + Works remotely similar to "filter_json_object", but is only called + for JSON objects having a single key named $key. + + This $coderef is called before the one specified via + "filter_json_object", if any. It gets passed the single value in the + JSON object. If it returns a single value, it will be inserted into + the data structure. If it returns nothing (not even "undef" but the + empty list), the callback from "filter_json_object" will be called + next, as if no single-key callback were specified. + + If $coderef is omitted or undefined, the corresponding callback will + be disabled. There can only ever be one callback for a given key. + + As this callback gets called less often then the + "filter_json_object" one, decoding speed will not usually suffer as + much. Therefore, single-key objects make excellent targets to + serialise Perl objects into, especially as single-key JSON objects + are as close to the type-tagged value concept as JSON gets (it's + basically an ID/VALUE tuple). Of course, JSON does not support this + in any way, so you need to make sure your data never looks like a + serialised Perl hash. + + Typical names for the single object key are "__class_whatever__", or + "$__dollars_are_rarely_used__$" or "}ugly_brace_placement", or even + things like "__class_md5sum(classname)__", to reduce the risk of + clashing with real hashes. + + Example, decode JSON objects of the form "{ "__widget__" => }" + into the corresponding $WIDGET{} object: + + # return whatever is in $WIDGET{5}: + JSON::XS + ->new + ->filter_json_single_key_object (__widget__ => sub { + $WIDGET{ $_[0] } + }) + ->decode ('{"__widget__": 5') + + # this can be used with a TO_JSON method in some "widget" class + # for serialisation to json: + sub WidgetBase::TO_JSON { + my ($self) = @_; + + unless ($self->{id}) { + $self->{id} = ..get..some..id..; + $WIDGET{$self->{id}} = $self; + } + + { __widget__ => $self->{id} } + } + $json = $json->shrink ([$enable]) Perl usually over-allocates memory a bit when allocating space for strings. This flag optionally resizes strings generated by either "encode" or "decode" to their minimum size possible. This can save - memory when your JSON strings are either very very long or you have + memory when your JSON texts are either very very long or you have many short strings. It will also try to downgrade any strings to octet-form if possible: perl stores strings internally either in an encoding called UTF-X or in octet-form. The latter cannot store - everything but uses less space in general. + everything but uses less space in general (and some buggy Perl or C + code might even rely on that internal representation being used). + + The actual definition of what shrink does might change in future + versions, but it will always try to save space at the expense of + time. If $enable is true (or missing), the string returned by "encode" will be shrunk-to-fit, while all strings generated by "decode" will @@ -238,7 +494,43 @@ or floats internally (there is no difference on the Perl level), saving space. - $json_string = $json->encode ($perl_scalar) + $json = $json->max_depth ([$maximum_nesting_depth]) + Sets the maximum nesting level (default 512) accepted while encoding + or decoding. If the JSON text or Perl data structure has an equal or + higher nesting level then this limit, then the encoder and decoder + will stop and croak at that point. + + Nesting level is defined by number of hash- or arrayrefs that the + encoder needs to traverse to reach a given point or the number of + "{" or "[" characters without their matching closing parenthesis + crossed to reach a given character in a string. + + Setting the maximum depth to one disallows any nesting, so that + ensures that the object is only a single hash/object or array. + + The argument to "max_depth" will be rounded up to the next highest + power of two. If no argument is given, the highest possible setting + will be used, which is rarely useful. + + See SECURITY CONSIDERATIONS, below, for more info on why this is + useful. + + $json = $json->max_size ([$maximum_string_size]) + Set the maximum length a JSON text may have (in bytes) where + decoding is being attempted. The default is 0, meaning no limit. + When "decode" is called on a string longer then this number of + characters it will not attempt to decode the string but throw an + exception. This setting has no effect on "encode" (yet). + + The argument to "max_size" will be rounded up to the next highest + power of two (so may be more than requested). If no argument is + given, the limit check will be deactivated (same as when 0 is + specified). + + See SECURITY CONSIDERATIONS, below, for more info on why this is + 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, @@ -247,15 +539,27 @@ become JSON "null" values. Neither "true" nor "false" values will be generated. - $perl_scalar = $json->decode ($json_string) - The opposite of "encode": expects a JSON string and tries to parse - it, returning the resulting simple scalar or reference. 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 + object, it will silently stop parsing there and return the number of + 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. + + JSON::XS->new->decode_prefix ("[1] the tail") + => ([], 3) + MAPPING This section describes how JSON::XS maps Perl values to JSON values and vice versa. These mappings are designed to "do the right thing" in most @@ -263,14 +567,14 @@ (what you put in comes out as something equivalent). For the more enlightened: note that in the following descriptions, - lowercase *perl* refers to the Perl interpreter, while uppcercase *Perl* + lowercase *perl* refers to the Perl interpreter, while uppercase *Perl* refers to the abstract Perl language itself. JSON -> PERL object A JSON object becomes a reference to a hash in Perl. No ordering of - object keys is preserved (JSON does not preserver object key - ordering itself). + object keys is preserved (JSON does not preserve object key ordering + itself). array A JSON array becomes a reference to an array in Perl. @@ -281,18 +585,31 @@ so no manual decoding is necessary. number - A JSON number becomes either an integer or numeric (floating point) - scalar in perl, depending on its range and any fractional parts. On - the Perl level, there is no difference between those as Perl handles - all the conversion details, but an integer may take slightly less - memory and might represent more values exactly than (floating point) - numbers. + A JSON number becomes either an integer, numeric (floating point) or + string scalar in perl, depending on its range and any fractional + parts. On the Perl level, there is no difference between those as + Perl handles all the conversion details, but an integer may take + slightly less memory and might represent more values exactly than + (floating point) numbers. + + If the number consists of digits only, JSON::XS will try to + represent it as an integer value. If that fails, it will try to + 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. + + Numbers containing a fractional or exponential part will always be + represented as numeric (floating point) values, possibly at a loss + of precision. + + This might create round-tripping problems as numbers might become + strings, but as Perl is typeless there is no other way to do it. true, false - These JSON atoms become 0, 1, respectively. Information is lost in - this process. Future versions might represent those values - differently, but they will be guarenteed to act like these integers - would normally in Perl. + 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. null A JSON null atom becomes "undef" in Perl. @@ -304,17 +621,32 @@ hash references Perl hash references become JSON objects. As there is no inherent - ordering in hash keys, 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. + 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. array references Perl array references become JSON arrays. + 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 + readability. + + to_json [\0,JSON::XS::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. + blessed objects Blessed objects are not allowed. JSON::XS currently tries to encode their underlying representation (hash- or arrayref), but this @@ -339,24 +671,21 @@ # undef becomes null to_json [undef] # yields [null] - You can force the type to be a string by stringifying it: + You can force the type to be a JSON string by stringifying it: my $x = 3.1; # some variable containing a number "$x"; # stringified $x .= ""; # another, more awkward way to stringify print $x; # perl does it for you, too, quite often - You can force the type to be a number by numifying it: + You can force the type to be a JSON number by numifying it: my $x = "3"; # some variable containing a string $x += 0; # numify it, ensuring it will be dumped as a number - $x *= 1; # same thing, the choise is yours. - - You can not currently output JSON booleans or force the type in - other, less obscure, ways. Tell me if you need this capability. + $x *= 1; # same thing, the choice is yours. - circular data structures - Those will be encoded until memory or stackspace runs out. + You can not currently force the type in other, less obscure, ways. + Tell me if you need this capability. COMPARISON As already mentioned, this module was created because none of the @@ -368,12 +697,12 @@ JSON 1.07 Slow (but very portable, as it is written in pure Perl). - Undocumented/buggy Unicode handling (how JSON handles unicode values - is undocumented. One can get far by feeding it unicode strings and - doing en-/decoding oneself, but unicode escapes are not working + Undocumented/buggy Unicode handling (how JSON handles Unicode values + is undocumented. One can get far by feeding it Unicode strings and + doing en-/decoding oneself, but Unicode escapes are not working properly). - No roundtripping (strings get clobbered if they look like numbers, + No round-tripping (strings get clobbered if they look like numbers, e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that will decode into the number 2. @@ -382,13 +711,13 @@ Undocumented/buggy Unicode handling. - No roundtripping. + No round-tripping. Has problems handling many Perl values (e.g. regex results and other magic values will make it croak). Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" - which is not a valid JSON string. + which is not a valid JSON text. Unmaintained (maintainer unresponsive for many months, bugs are not getting fixed). @@ -399,15 +728,15 @@ Very inflexible (no human-readable format supported, format pretty much undocumented. I need at least a format for easy reading by humans and a single-line compact format for use in a protocol, and - preferably a way to generate ASCII-only JSON strings). + preferably a way to generate ASCII-only JSON texts). Completely broken (and confusingly documented) Unicode handling - (unicode escapes are not working properly, you need to set + (Unicode escapes are not working properly, you need to set ImplicitUnicode to *different* values on en- and decoding to get symmetric behaviour). - No roundtripping (simple cases work, but this depends on wether the - scalar value was used in a numeric context or not). + No round-tripping (simple cases work, but this depends on whether + the scalar value was used in a numeric context or not). Dumping hashes may skip hash values depending on iterator state. @@ -416,7 +745,7 @@ Does not check input for validity (i.e. will accept non-JSON input and return "something" instead of raising an exception. This is a - security issue: imagine two banks transfering money between each + security issue: imagine two banks transferring money between each other using JSON. One bank might parse a given non-JSON request and deduct money, while the other might reject the transaction with a syntax error. While a good protocol will at least recover, that is @@ -425,76 +754,158 @@ JSON::DWIW 0.04 Very fast. Very natural. Very nice. - Undocumented unicode handling (but the best of the pack. Unicode + Undocumented Unicode handling (but the best of the pack. Unicode escapes still don't get parsed properly). Very inflexible. - No roundtripping. + No round-tripping. - Does not generate valid JSON (key strings are often unquoted, empty - keys result in nothing being output) + Does not generate valid JSON texts (key strings are often unquoted, + empty keys result in nothing being output) Does not check input for validity. + JSON and YAML + You often hear that JSON is a subset (or a close subset) of YAML. This + is, however, a mass hysteria and very far from the truth. In general, + there is no way to configure JSON::XS to output a data structure as + valid YAML. + + If you really must use JSON::XS to generate YAML, you should use this + algorithm (subject to change in future versions): + + my $to_yaml = JSON::XS->new->utf8->space_after (1); + my $yaml = $to_yaml->encode ($ref) . "\n"; + + 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, so you should make sure that your hash + keys are noticeably shorter than the 1024 characters YAML allows. + + There might be other incompatibilities that I am not aware of. In + general you should not try to generate YAML with a JSON generator or + vice versa, or try to parse JSON with a YAML parser or vice versa: + chances are high that you will run into severe interoperability + problems. + 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 in the JSON::XS distribution, to make it easy to compare on your own system. - First comes a comparison between various modules using a very short JSON - string (83 bytes), showing the number of encodes/decodes per second - (JSON::XS is the functional interface, while JSON::XS/2 is the OO - interface with pretty-printing and hashkey sorting enabled). Higher is - better: + First comes a comparison between various modules using a very short + single-line JSON string: + + {"method": "handleMessage", "params": ["user1", "we were just talking"], \ + "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} + 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: + + Storable | 15779.925 | 14169.946 | + -----------+------------+------------+ module | encode | decode | -----------|------------|------------| - JSON | 14006 | 6820 | - JSON::DWIW | 200937 | 120386 | - JSON::PC | 85065 | 129366 | - JSON::Syck | 59898 | 44232 | - JSON::XS | 1171478 | 342435 | - JSON::XS/2 | 730760 | 328714 | + JSON | 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 6 times faster than than JSON::DWIW and about 80 - times faster than JSON, even with pretty-printing and key sorting. + 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 + compares favourably to Storable for small amounts of data. Using a longer test string (roughly 18KB, generated from Yahoo! Locals search API (http://nanoref.com/yahooapis/mgPdGg): module | encode | decode | -----------|------------|------------| - JSON | 673 | 38 | - JSON::DWIW | 5271 | 770 | - JSON::PC | 9901 | 2491 | - JSON::Syck | 2360 | 786 | - JSON::XS | 37398 | 3202 | - JSON::XS/2 | 13765 | 3153 | + JSON | 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 | -----------+------------+------------+ - Again, JSON::XS leads by far in the encoding case, while still beating - every other module in the decoding case. + Again, JSON::XS leads by far (except for Storable which non-surprisingly + decodes faster). - On large strings containing lots of unicode characters, some modules - (such as JSON::PC) decode faster than JSON::XS, but the result will be - broken due to missing unicode handling. Others refuse to decode or - encode properly, so it was impossible to prepare a fair comparison table - for that case. - -RESOURCE LIMITS - JSON::XS does not impose any limits on the size of JSON texts or Perl - values they represent - if your machine can handle it, JSON::XS will - encode or decode it. Future versions might optionally impose structure - depth and memory use resource limits. + On large strings containing lots of high Unicode characters, some + modules (such as JSON::PC) seem to decode faster than JSON::XS, but the + result will be broken due to missing (or wrong) Unicode handling. Others + refuse to decode or encode properly, so it was impossible to prepare a + fair comparison table for that case. + +SECURITY CONSIDERATIONS + When you are using JSON in a protocol, talking to untrusted potentially + hostile creatures requires relatively few measures. + + First of all, your JSON decoder should be secure, that is, should not + have any buffer overflows. Obviously, this module should ensure that and + I am trying hard on making that true, but you never know. + + Second, you need to avoid resource-starving attacks. That means you + should limit the size of JSON texts you accept, or make sure then when + your resources run out, that's just fine (e.g. by using a separate + process that can crash safely). The size of a JSON text in octets or + characters is usually a good indication of the size of the resources + required to decode it into a Perl structure. While JSON::XS can check + the size of the JSON text, it might be too late when you already have it + in memory, so you might want to check the size before you accept the + string. + + Third, JSON::XS recurses using the C stack when decoding objects and + arrays. The C stack is a limited resource: for instance, on my amd64 + machine with 8MB of stack size I can decode around 180k nested arrays + but only 14k nested JSON objects (due to perl itself recursing deeply on + croak to free the temporary). If that is exceeded, the program crashes. + to be conservative, the default nesting limit is set to 512. If your + process has a smaller stack, you should adjust this setting accordingly + with the "max_depth" method. + + And last but least, something else could bomb you that I forgot to think + of. In that case, you get to keep the pieces. I am always open for + hints, though... + + 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 doing + security right). + +THREADS + This module is *not* guaranteed to be thread safe and there are no plans + to change this until Perl gets thread support (as opposed to the + horribly slow so-called "threads" which are simply slow and bloated + process simulations - use fork, its *much* faster, cheaper, better). + + (It might actually work, but you have been warned). BUGS While the goal of this module is to be correct, that unfortunately does not mean its bug-free, only that I think its design is bug-free. It is - still very young and not well-tested. If you keep reporting bugs they - will be fixed swiftly, though. + still relatively early in its development. If you keep reporting bugs + they will be fixed swiftly, though. + + Please refrain from using rt.cpan.org or any other bug reporting + service. I put the contact address into my modules for a reason. AUTHOR Marc Lehmann