--- JSON-XS/XS.pm 2007/03/29 02:45:49 1.25 +++ JSON-XS/XS.pm 2009/02/22 10:13:16 1.119 @@ -2,6 +2,11 @@ JSON::XS - JSON serialising/deserialising, done correctly and fast +=encoding utf-8 + +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) + =head1 SYNOPSIS use JSON::XS; @@ -9,12 +14,8 @@ # 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; - - # objToJson and jsonToObj aliases to to_json and from_json - # are exported for compatibility to the JSON module, - # but should not be used in new code. + $utf8_encoded_json_text = encode_json $perl_hash_or_arrayref; + $perl_hash_or_arrayref = decode_json $utf8_encoded_json_text; # OO-interface @@ -22,20 +23,34 @@ $pretty_printed_unencoded = $coder->encode ($perl_scalar); $perl_scalar = $coder->decode ($unicode_json_text); + # 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; + + # and do the same things, except that you have a pure-perl fallback now. + =head1 DESCRIPTION This module converts Perl data structures to JSON and vice versa. Its primary goal is to be I and its secondary goal is to be I. To reach the latter goal it was written in C. +Beginning with version 2.0 of the JSON module, when both JSON and +JSON::XS are installed, then JSON will fall back on JSON::XS (this can be +overridden) with no overhead due to emulation (by inheriting constructor +and methods). If JSON::XS is not available, it will fall back to the +compatible JSON::PP module as backend, so using JSON instead of JSON::XS +gives you a portable JSON API that can be fast when you need and doesn't +require a C compiler when that is a problem. + As this is the n-th-something JSON module on CPAN, what was the reason to write yet another JSON module? While it seems there are many JSON modules, none of them correctly handle all corner cases, and in most cases their maintainers are unresponsive, gone missing, or not listening to bug reports for other reasons. -See COMPARISON, below, for a comparison to some other JSON modules. - See MAPPING, below, on how JSON::XS maps perl values to JSON values and vice versa. @@ -43,17 +58,18 @@ =over 4 -=item * correct unicode handling +=item * correct Unicode handling -This module knows how to handle Unicode, and even documents how and when -it does so. +This module knows how to handle Unicode, documents how and when it does +so, and even documents what "correct" means. =item * round-trip integrity -When you serialise a perl data structure using only datatypes supported +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). +like a number). There minor I exceptions to this, read the MAPPING +section below to learn about those. =item * strict checking of JSON correctness @@ -63,20 +79,20 @@ =item * fast -Compared to other JSON modules, this module compares favourably in terms -of speed, too. +Compared to other JSON modules and other serialisers such as Storable, +this module usually compares favourably in terms of speed, too. =item * simple to use -This module has both a simple functional interface as well as an OO -interface. +This module has both a simple functional interface as well as an object +oriented interface interface. =item * reasonably versatile output formats -You can choose between the most compact guarenteed single-line format -possible (nice for simple line-based protocols), a pure-ascii format +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, still supports the whole -unicode range), or a pretty-printed format (for when you want to read that +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. =back @@ -85,52 +101,116 @@ package JSON::XS; +no warnings; use strict; -BEGIN { - our $VERSION = '1.0'; - our @ISA = qw(Exporter); +our $VERSION = '2.232'; +our @ISA = qw(Exporter); - our @EXPORT = qw(to_json from_json objToJson jsonToObj); - require Exporter; +our @EXPORT = qw(encode_json decode_json to_json from_json); - require XSLoader; - XSLoader::load JSON::XS::, $VERSION; +sub to_json($) { + require Carp; + Carp::croak ("JSON::XS::to_json has been renamed to encode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call"); } +sub from_json($) { + require Carp; + Carp::croak ("JSON::XS::from_json has been renamed to decode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call"); +} + +use Exporter; +use XSLoader; + =head1 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: =over 4 -=item $json_text = to_json $perl_scalar +=item $json_text = encode_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. +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: $json_text = JSON::XS->new->utf8->encode ($perl_scalar) -except being faster. +Except being faster. -=item $perl_scalar = from_json $json_text +=item $perl_scalar = decode_json $json_text -The opposite of C: expects an UTF-8 (binary) string and tries to -parse that as an UTF-8 encoded JSON text, returning the resulting simple -scalar or reference. Croaks on error. +The opposite of C: expects an UTF-8 (binary) string and 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: $perl_scalar = JSON::XS->new->utf8->decode ($json_text) -except being faster. +Except being faster. + +=item $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 C<1> and C<0>, respectively +and are used to represent JSON C and C values in Perl. + +See MAPPING, below, for more information on how JSON values are mapped to +Perl. + +=back + + +=head1 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. + +=over 4 + +=item 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. + +=item 2. Perl does I associate an encoding with your strings. + +... until 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 I that decides encoding, not any magical meta data. + +=item 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. + +=item 4. A "Unicode String" is simply a string where each character can be +validly interpreted as a Unicode code point. + +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. + +=item 5. A string containing "high" (> 255) character values is I a UTF-8 string. + +It's a fact. Learn to live with it. =back +I hope this helps :) + =head1 OBJECT-ORIENTED INTERFACE @@ -152,21 +232,62 @@ =item $json = $json->ascii ([$enable]) +=item $enabled = $json->get_ascii + If C<$enable> is true (or missing), then the C method will not generate characters outside the code range C<0..127> (which is ASCII). Any -unicode characters outside that range will be escaped using either a +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. +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 C<$enable> is false, then the C method will not escape Unicode -characters unless required by the JSON syntax. This results in a faster -and more compact format. +characters unless required by the JSON syntax or other flags. This results +in a faster and more compact format. + +See also the section I later in this +document. + +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"] +=item $json = $json->latin1 ([$enable]) + +=item $enabled = $json->get_latin1 + +If C<$enable> is true (or missing), then the C method will encode +the resulting JSON text as latin1 (or iso-8859-1), escaping any characters +outside the code range C<0..255>. The resulting string can be treated as a +latin1-encoded JSON text or a native Unicode string. The C method +will not be affected in any way by this flag, as C by default +expects Unicode, which is a strict superset of latin1. + +If C<$enable> is false, then the C method will not escape Unicode +characters unless required by the JSON syntax or other flags. + +See also the section I later in this +document. + +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) + =item $json = $json->utf8 ([$enable]) +=item $enabled = $json->get_utf8 + If C<$enable> is true (or missing), then the C method will encode the JSON result into UTF-8, as required by many protocols, while the C method expects to be handled an UTF-8-encoded string. Please @@ -176,10 +297,13 @@ and UTF-32 encoding families, as described in RFC4627. If C<$enable> is false, then the C method will return the JSON -string as a (non-encoded) unicode string, while C expects thus a -unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs +string as a (non-encoded) Unicode string, while C 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. +See also the section I later in this +document. + Example, output UTF-16BE-encoded JSON: use Encode; @@ -209,17 +333,21 @@ =item $json = $json->indent ([$enable]) +=item $enabled = $json->get_indent + If C<$enable> is true (or missing), then the C method will use a multiline format as output, putting every array member or object/hash key-value pair -into its own line, identing them properly. +into its own line, indenting them properly. If C<$enable> is false, no newlines or indenting will be produced, and the -resulting JSON text is guarenteed not to contain any C. +resulting JSON text is guaranteed not to contain any C. This setting has no effect when decoding JSON texts. =item $json = $json->space_before ([$enable]) +=item $enabled = $json->get_space_before + If C<$enable> is true (or missing), then the C method will add an extra optional space before the C<:> separating keys from values in JSON objects. @@ -235,6 +363,8 @@ =item $json = $json->space_after ([$enable]) +=item $enabled = $json->get_space_after + If C<$enable> is true (or missing), then the C method will add an extra optional space after the C<:> separating keys from values in JSON objects and extra whitespace after the C<,> separating key-value pairs and array @@ -249,8 +379,57 @@ {"key": "value"} +=item $json = $json->relaxed ([$enable]) + +=item $enabled = $json->get_relaxed + +If C<$enable> is true (or missing), then C will accept some +extensions to normal JSON syntax (see below). C will not be +affected in anyway. I. I suggest only to use this option to +parse application-specific files written by humans (configuration files, +resource files etc.) + +If C<$enable> is false (the default), then C will only accept +valid JSON texts. + +Currently accepted extensions are: + +=over 4 + +=item * list items can have an end-comma + +JSON I 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 + } + +=item * 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... + ] + +=back + =item $json = $json->canonical ([$enable]) +=item $enabled = $json->get_canonical + If C<$enable> is true (or missing), then the C method will output JSON objects by sorting their keys. This is adding a comparatively high overhead. @@ -260,13 +439,15 @@ 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 it is disabled, -the same hash migh be encoded differently even if contains the same data, +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 texts. =item $json = $json->allow_nonref ([$enable]) +=item $enabled = $json->get_allow_nonref + If C<$enable> is true (or missing), then the C method can convert a non-reference into its corresponding string, number or null JSON value, which is an extension to RFC4627. Likewise, C will accept those JSON @@ -283,8 +464,142 @@ JSON::XS->new->allow_nonref->encode ("Hello, World!") => "Hello, World!" +=item $json = $json->allow_unknown ([$enable]) + +=item $enabled = $json->get_allow_unknown + +If C<$enable> is true (or missing), then C will I throw an +exception when it encounters values it cannot represent in JSON (for +example, filehandles) but instead will encode a JSON C value. Note +that blessed objects are not included here and are handled separately by +c. + +If C<$enable> is false (the default), then C will throw an +exception when it encounters anything it cannot encode as JSON. + +This option does not affect C in any way, and it is recommended to +leave it off unless you know your communications partner. + +=item $json = $json->allow_blessed ([$enable]) + +=item $enabled = $json->get_allow_blessed + +If C<$enable> is true (or missing), then the C method will not +barf when it encounters a blessed reference. Instead, the value of the +B option will decide whether C (C +disabled or no C method found) or a representation of the +object (C enabled and C method found) is being +encoded. Has no effect on C. + +If C<$enable> is false (the default), then C will throw an +exception when it encounters a blessed object. + +=item $json = $json->convert_blessed ([$enable]) + +=item $enabled = $json->get_convert_blessed + +If C<$enable> is true (or missing), then C, upon encountering a +blessed object, will check for the availability of the C 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 +C method is found, the value of C will decide what +to do. + +The C method may safely call die if it wants. If C +returns other blessed objects, those will be handled in the same +way. C must take care of not causing an endless recursion cycle +(== crash) in this case. The name of C 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 any C +function or method. + +This setting does not yet influence C in any way, but in the +future, global hooks might get installed that influence C and are +enabled by this setting. + +If C<$enable> is false, then the C setting will decide what +to do when a blessed object is found. + +=item $json = $json->filter_json_object ([$coderef->($hashref)]) + +When C<$coderef> is specified, it will be called from C 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: I C, which is a valid scalar), the +original deserialised hash will be inserted. This setting can slow down +decoding considerably. + +When C<$coderef> is omitted or undefined, any existing callback will +be removed and C 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}'); + +=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)]) + +Works remotely similar to C, but is only called for +JSON objects having a single key named C<$key>. + +This C<$coderef> is called before the one specified via +C, 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 C but the empty list), +the callback from C will be called next, as if no +single-key callback were specified. + +If C<$coderef> is omitted or undefined, the corresponding callback will be +disabled. There can only ever be one callback for a given key. + +As this callback gets called less often then the C +one, decoding speed will not usually suffer as much. Therefore, single-key +objects make excellent targets to serialise Perl objects into, especially +as single-key JSON objects are as close to the type-tagged value concept +as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not +support this in any way, so you need to make sure your data never looks +like a serialised Perl hash. + +Typical names for the single object key are C<__class_whatever__>, or +C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even +things like C<__class_md5sum(classname)__>, to reduce the risk of clashing +with real hashes. + +Example, decode JSON objects of the form C<< { "__widget__" => } >> +into the corresponding C<< $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} } + } + =item $json = $json->shrink ([$enable]) +=item $enabled = $json->get_shrink + Perl usually over-allocates memory a bit when allocating space for strings. This flag optionally resizes strings generated by either C or C to their minimum size possible. This can save @@ -311,10 +626,12 @@ =item $json = $json->max_depth ([$maximum_nesting_depth]) -Sets the maximum nesting level (default C<4096>) 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. +=item $max_depth = $json->get_max_depth + +Sets the maximum nesting level (default C<512>) accepted while encoding +or decoding. If a higher nesting level is detected in JSON text or a Perl +data structure, 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 C<{> or C<[> @@ -324,8 +641,27 @@ 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 C will be rounded up to the next nearest power -of two. +If no argument is given, the highest possible setting will be used, which +is rarely useful. + +Note that nesting is implemented by recursion in C. The default value has +been chosen to be as large as typical operating systems allow without +crashing. + +See SECURITY CONSIDERATIONS, below, for more info on why this is useful. + +=item $json = $json->max_size ([$maximum_string_size]) + +=item $max_size = $json->get_max_size + +Set the maximum length a JSON text may have (in bytes) where decoding is +being attempted. The default is C<0>, meaning no limit. When C +is called on a string that is longer then this many bytes, it will not +attempt to decode the string but throw an exception. This setting has no +effect on C (yet). + +If no argument is given, the limit check will be deactivated (same as when +C<0> is specified). See SECURITY CONSIDERATIONS, below, for more info on why this is useful. @@ -347,8 +683,261 @@ Perl arrayrefs and JSON objects become Perl hashrefs. C becomes C<1>, C becomes C<0> and C becomes C. +=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text) + +This works like the C 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) + +=back + + +=head1 INCREMENTAL PARSING + +In some cases, there is the need for incremental parsing of JSON +texts. While this module always has to keep both JSON text and resulting +Perl data structure in memory at one time, it does allow you to parse a +JSON stream incrementally. It does so by accumulating text until it has +a full JSON object, which it then can decode. This process is similar to +using C to see if a full JSON object is available, but +is much more efficient (and can be implemented with a minimum of method +calls). + +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 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. C) to ensure the parser will stop +parsing in the presence if syntax errors. + +The following methods implement this incremental parser. + +=over 4 + +=item [void, scalar or list context] = $json->incr_parse ([$string]) + +This is the central parsing function. It can both append new text and +extract objects from the stream accumulated so far (both of these +functions are optional). + +If C<$string> is given, then this string is appended to the already +existing JSON fragment stored in the C<$json> object. + +After that, if the function is called in void context, it will simply +return without doing anything further. This can be used to add more text +in as many chunks as you want. + +If the method is called in scalar context, then it will try to extract +exactly I JSON object. If that is successful, it will return this +object, otherwise it will return C. If there is a parse error, +this method will croak just as C would do (one can then use +C to skip the errornous part). This is the most common way of +using the method. + +And finally, in list context, it will try to extract as many objects +from the stream as it can find and return them, or the empty list +otherwise. For this to work, there must be no separators between the JSON +objects or arrays, instead they must be concatenated back-to-back. If +an error occurs, an exception will be raised as in the scalar context +case. Note that in this case, any previously-parsed JSON texts will be +lost. + +=item $lvalue_string = $json->incr_text + +This method returns the currently stored JSON fragment as an lvalue, that +is, you can manipulate it. This I works when a preceding call to +C in I successfully returned an object. Under +all other circumstances you must not call this function (I mean it. +although in simple tests it might actually work, it I fail under +real world conditions). As a special exception, you can also call this +method before having parsed anything. + +This function is useful in two cases: a) finding the trailing text after a +JSON object or b) parsing multiple JSON objects separated by non-JSON text +(such as commas). + +=item $json->incr_skip + +This will reset the state of the incremental parser and will remove +the parsed text from the input buffer so far. This is useful after +C died, in which case the input buffer and incremental parser +state is left unchanged, to skip the text parsed so far and to reset the +parse state. + +The difference to C is that only text until the parse error +occured is removed. + +=item $json->incr_reset + +This completely resets the incremental parser, that is, after this call, +it will be as if the parser had never parsed anything. + +This is useful if you want to repeatedly parse JSON objects and want to +ignore any trailing data, which means you have to reset the parser after +each successful decode. + =back +=head2 LIMITATIONS + +All options that affect decoding are supported, except +C. The reason for this is that it cannot be made to +work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate +them back to back and still decode them perfectly. This does not hold true +for JSON numbers, however. + +For example, is the string C<1> a single JSON number, or is it simply the +start of C<12>? Or is C<12> a single JSON number, or the concatenation +of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS +takes the conservative route and disallows this case. + +=head2 EXAMPLES + +Some examples will make all this clearer. First, a simple example that +works similarly to C: We want to decode the JSON object at +the start of a string and identify the portion after the JSON object: + + my $text = "[1,2,3] hello"; + + my $json = new JSON::XS; + + my $obj = $json->incr_parse ($text) + or die "expected JSON object or array at beginning of string"; + + my $tail = $json->incr_text; + # $tail now contains " hello" + +Easy, isn't it? + +Now for a more complicated example: Imagine a hypothetical protocol where +you read some requests from a TCP stream, and each request is a JSON +array, without any separation between them (in fact, it is often useful to +use newlines as "separators", as these get interpreted as whitespace at +the start of the JSON text, which makes it possible to test said protocol +with C...). + +Here is how you'd do it (it is trivial to write this in an event-based +manner): + + my $json = new JSON::XS; + + # read some data from the socket + while (sysread $socket, my $buf, 4096) { + + # split and decode as many requests as possible + for my $request ($json->incr_parse ($buf)) { + # act on the $request + } + } + +Another complicated example: Assume you have a string with JSON objects +or arrays, all separated by (optional) comma characters (e.g. C<[1],[2], +[3]>). To parse them, we have to skip the commas between the JSON texts, +and here is where the lvalue-ness of C comes in useful: + + my $text = "[1],[2], [3]"; + my $json = new JSON::XS; + + # void context, so no parsing done + $json->incr_parse ($text); + + # now extract as many objects as possible. note the + # use of scalar context so incr_text can be called. + while (my $obj = $json->incr_parse) { + # do something with $obj + + # now skip the optional comma + $json->incr_text =~ s/^ \s* , //x; + } + +Now lets go for a very complex example: Assume that you have a gigantic +JSON array-of-objects, many gigabytes in size, and you want to parse it, +but you cannot load it into memory fully (this has actually happened in +the real world :). + +Well, you lost, you have to implement your own JSON parser. But JSON::XS +can still help you: You implement a (very simple) array parser and let +JSON decode the array elements, which are all full JSON objects on their +own (this wouldn't work if the array elements could be JSON numbers, for +example): + + my $json = new JSON::XS; + + # open the monster + open my $fh, "incr_parse ($buf); # void context, so no parsing + + # Exit the loop once we found and removed(!) the initial "[". + # In essence, we are (ab-)using the $json object as a simple scalar + # we append data to. + last if $json->incr_text =~ s/^ \s* \[ //x; + } + + # now we have the skipped the initial "[", so continue + # parsing all the elements. + for (;;) { + # in this loop we read data until we got a single JSON object + for (;;) { + if (my $obj = $json->incr_parse) { + # do something with $obj + last; + } + + # add more data + sysread $fh, my $buf, 65536 + or die "read error: $!"; + $json->incr_parse ($buf); # void context, so no parsing + } + + # in this loop we read data until we either found and parsed the + # separating "," between elements, or the final "]" + for (;;) { + # first skip whitespace + $json->incr_text =~ s/^\s*//; + + # if we find "]", we are done + if ($json->incr_text =~ s/^\]//) { + print "finished.\n"; + exit; + } + + # if we find ",", we can continue with the next element + if ($json->incr_text =~ s/^,//) { + last; + } + + # if we find anything else, we have a parse error! + if (length $json->incr_text) { + die "parse error near ", $json->incr_text; + } + + # else add more data + sysread $fh, my $buf, 65536 + or die "read error: $!"; + $json->incr_parse ($buf); # void context, so no parsing + } + +This is a complex example, but most of the complexity comes from the fact +that we are trying to be correct (bear with me if I am wrong, I never ran +the above example :). + + =head1 MAPPING @@ -358,9 +947,10 @@ (what you put in comes out as something equivalent). For the more enlightened: note that in the following descriptions, -lowercase I refers to the Perl interpreter, while uppcercase I +lowercase I refers to the Perl interpreter, while uppercase I refers to the abstract Perl language itself. + =head2 JSON -> PERL =over 4 @@ -368,7 +958,7 @@ =item 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). +keys is preserved (JSON does not preserve object key ordering itself). =item array @@ -382,18 +972,30 @@ =item 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 (in +which case you lose roundtripping ability, as the JSON number will be +re-encoded toa JSON string). + +Numbers containing a fractional or exponential part will always be +represented as numeric (floating point) values, possibly at a loss of +precision (in which case you might lose perfect roundtripping ability, but +the JSON number will still be re-encoded as a JSON number). =item true, false -These JSON atoms become C<0>, C<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 C and C, +respectively. They are overloaded to act almost exactly like the numbers +C<1> and C<0>. You can check whether a scalar is a JSON boolean by using +the C function. =item null @@ -401,6 +1003,7 @@ =back + =head2 PERL -> JSON The mapping from Perl to JSON is slightly more difficult, as Perl is a @@ -432,142 +1035,277 @@ C<1>, which get turned into C and C atoms in JSON. You can also use C and C to improve readability. - to_json [\0,JSON::XS::true] # yields [false,true] + encode_json [\0, JSON::XS::true] # yields [false,true] + +=item JSON::XS::true, JSON::XS::false + +These special values become JSON true and JSON false values, +respectively. You can also use C<\1> and C<\0> directly if you want. =item blessed objects -Blessed objects are not allowed. JSON::XS currently tries to encode their -underlying representation (hash- or arrayref), but this behaviour might -change in future versions. +Blessed objects are not directly representable in JSON. See the +C and C 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. =item simple scalars Simple Perl scalars (any scalar that is not a reference) are the most difficult objects to encode: JSON::XS will encode undefined scalars as -JSON null value, scalars that have last been used in a string context -before encoding as JSON strings and anything else as number value: +JSON C values, scalars that have last been used in a string context +before encoding as JSON strings, and anything else as number value: # dump as number - to_json [2] # yields [2] - to_json [-3.0e17] # yields [-3e+17] - my $value = 5; to_json [$value] # yields [5] + encode_json [2] # yields [2] + encode_json [-3.0e17] # yields [-3e+17] + my $value = 5; encode_json [$value] # yields [5] # used as string, so dump as string print $value; - to_json [$value] # yields ["5"] + encode_json [$value] # yields ["5"] # undef becomes null - to_json [undef] # yields [null] + encode_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. + $x *= 1; # same thing, the choice 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. +You can not currently force the type in other, less obscure, ways. Tell me +if you need this capability (but don't forget to explain why it's needed +:). + +=back -=item circular data structures -Those will be encoded until memory or stackspace runs out. +=head1 ENCODING/CODESET FLAG NOTES + +The interested reader might have seen a number of flags that signify +encodings or codesets - C, C and C. There seems to be +some confusion on what these do, so here is a short comparison: + +C controls whether the JSON text created by C (and expected +by C) is UTF-8 encoded or not, while C and C only +control whether C escapes character values outside their respective +codeset range. Neither of these flags conflict with each other, although +some combinations make less sense than others. + +Care has been taken to make all flags symmetrical with respect to +C and C, that is, texts encoded with any combination of +these flag values will be correctly decoded when the same flags are used +- in general, if you use different flag settings while encoding vs. when +decoding you likely have a bug somewhere. + +Below comes a verbose discussion of these flags. Note that a "codeset" is +simply an abstract set of character-codepoint pairs, while an encoding +takes those codepoint numbers and I them, in our case into +octets. Unicode is (among other things) a codeset, UTF-8 is an encoding, +and ISO-8859-1 (= latin 1) and ASCII are both codesets I encodings at +the same time, which can be confusing. + +=over 4 + +=item C flag disabled + +When C is disabled (the default), then C/C 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 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). + +This is useful when you want to do the encoding yourself (e.g. when you +want to have UTF-16 encoded JSON texts) or when some other layer does +the encoding for you (for example, when printing to a terminal using a +filehandle that transparently encodes to UTF-8 you certainly do NOT want +to UTF-8 encode your data first and have Perl encode it another time). + +=item C flag enabled + +If the C-flag is enabled, C/C will encode all +characters using the corresponding UTF-8 multi-byte sequence, and will +expect your input strings to be encoded as UTF-8, that is, no "character" +of the input string must have any value > 255, as UTF-8 does not allow +that. + +The C flag therefore switches between two modes: disabled means you +will get a Unicode string in Perl, enabled means you get an UTF-8 encoded +octet/binary string in Perl. + +=item C or C flags enabled + +With C (or C) enabled, C will escape characters +with ordinal values > 255 (> 127 with C) and encode the remaining +characters as specified by the C flag. + +If C is disabled, then the result is also correctly encoded in those +character sets (as both are proper subsets of Unicode, meaning that a +Unicode string with all character values < 256 is the same thing as a +ISO-8859-1 string, and a Unicode string with all character values < 128 is +the same thing as an ASCII string in Perl). + +If C is enabled, you still get a correct UTF-8-encoded string, +regardless of these flags, just some more characters will be escaped using +C<\uXXXX> then before. + +Note that ISO-8859-1-I strings are not compatible with UTF-8 +encoding, while ASCII-encoded strings are. That is because the ISO-8859-1 +encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I being +a subset of Unicode), while ASCII is. + +Surprisingly, C will ignore these flags and so treat all input +values as governed by the C flag. If it is disabled, this allows you +to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of +Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings. + +So neither C nor C are incompatible with the C flag - +they only govern when the JSON output engine escapes a character or not. + +The main use for C is to relatively efficiently store binary data +as JSON, at the expense of breaking compatibility with most JSON decoders. + +The main use for C is to force the output to not contain characters +with values > 127, which means you can interpret the resulting string +as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and +8-bit-encoding, and still get the same data structure back. This is useful +when your channel for JSON transfer is not 8-bit clean or the encoding +might be mangled in between (e.g. in mail), and works because ASCII is a +proper subset of most 8-bit and multibyte encodings in use in the world. =back -=head1 COMPARISON +=head2 JSON and ECMAscript -As already mentioned, this module was created because none of the existing -JSON modules could be made to work correctly. First I will describe the -problems (or pleasures) I encountered with various existing JSON modules, -followed by some benchmark values. JSON::XS was designed not to suffer -from any of these problems or limitations. +JSON syntax is based on how literals are represented in javascript (the +not-standardised predecessor of ECMAscript) which is presumably why it is +called "JavaScript Object Notation". -=over 4 +However, JSON is not a subset (and also not a superset of course) of +ECMAscript (the standard) or javascript (whatever browsers actually +implement). -=item JSON 1.07 +If you want to use javascript's C function to "parse" JSON, you +might run into parse errors for valid JSON texts, or the resulting data +structure might not be queryable: -Slow (but very portable, as it is written in pure Perl). +One of the problems is that U+2028 and U+2029 are valid characters inside +JSON strings, but are not allowed in ECMAscript string literals, so the +following Perl fragment will not output something that can be guaranteed +to be parsable by javascript's C: -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). + use JSON::XS; -No roundtripping (strings get clobbered if they look like numbers, e.g. -the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will -decode into the number 2. + print encode_json [chr 0x2028]; -=item JSON::PC 0.01 +The right fix for this is to use a proper JSON parser in your javascript +programs, and not rely on C (see for example Douglas Crockford's +F parser). -Very fast. +If this is not an option, you can, as a stop-gap measure, simply encode to +ASCII-only JSON: -Undocumented/buggy Unicode handling. + use JSON::XS; -No roundtripping. + print JSON::XS->new->ascii->encode ([chr 0x2028]); -Has problems handling many Perl values (e.g. regex results and other magic -values will make it croak). +Note that this will enlarge the resulting JSON text quite a bit if you +have many non-ASCII characters. You might be tempted to run some regexes +to only escape U+2028 and U+2029, e.g.: -Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}> -which is not a valid JSON text. + # DO NOT USE THIS! + my $json = JSON::XS->new->utf8->encode ([chr 0x2028]); + $json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028 + $json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029 + print $json; -Unmaintained (maintainer unresponsive for many months, bugs are not -getting fixed). +Note that I: the above only works for U+2028 and +U+2029 and thus only for fully ECMAscript-compliant parsers. Many existing +javascript implementations, however, have issues with other characters as +well - using C naively simply I cause problems. -=item JSON::Syck 0.21 +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 +C<__proto__> property name for it's own purposes. -Very buggy (often crashes). +If that is a problem, you could parse try to filter the resulting JSON +output for these property strings, e.g.: -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 texts). + $json =~ s/"__proto__"\s*:/"__proto__renamed":/g; -Completely broken (and confusingly documented) Unicode handling (unicode -escapes are not working properly, you need to set ImplicitUnicode to -I values on en- and decoding to get symmetric behaviour). +This works because C<__proto__> is not valid outside of strings, so every +occurence of C<"__proto__"\s*:> must be a string used as property name. -No roundtripping (simple cases work, but this depends on wether the scalar -value was used in a numeric context or not). +If you know of other incompatibilities, please let me know. -Dumping hashes may skip hash values depending on iterator state. -Unmaintained (maintainer unresponsive for many months, bugs are not -getting fixed). +=head2 JSON and YAML -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 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 extra unnecessary work and -the transaction will still not succeed). +You often hear that JSON is a subset of YAML. This is, however, a mass +hysteria(*) and very far from the truth (as of the time of this writing), +so let me state it clearly: I that works in all +cases. -=item JSON::DWIW 0.04 +If you really must use JSON::XS to generate YAML, you should use this +algorithm (subject to change in future versions): -Very fast. Very natural. Very nice. + my $to_yaml = JSON::XS->new->utf8->space_after (1); + my $yaml = $to_yaml->encode ($ref) . "\n"; -Undocumented unicode handling (but the best of the pack. Unicode escapes -still don't get parsed properly). +This will I 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 C<\/> sequences in +strings (which JSON::XS does not I generate, but other JSON +generators might). -Very inflexible. +There might be other incompatibilities that I am not aware of (or the YAML +specification has been changed yet again - it does so quite often). 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 when you +least expect it. -No roundtripping. +=over 4 -Does not generate valid JSON texts (key strings are often unquoted, empty keys -result in nothing being output) +=item (*) -Does not check input for validity. +I have been pressured multiple times by Brian Ingerson (one of the +authors of the YAML specification) to remove this paragraph, despite him +acknowledging that the actual incompatibilities exist. As I was personally +bitten by this "JSON is YAML" lie, I refused and said I will continue to +educate people about these issues, so others do not run into the same +problem again and again. After this, Brian called me a (quote)I(unquote). + +In my opinion, instead of pressuring and insulting people who actually +clarify issues with YAML and the wrong statements of some of its +proponents, I would kindly suggest reading the JSON spec (which is not +that difficult or long) and finally make YAML compatible to it, and +educating users about the changes, instead of spreading lies about the +real compatibility for many I and trying to silence people who +point out that it isn't true. =back + =head2 SPEED It seems that JSON::XS is surprisingly fast, as shown in the following @@ -575,47 +1313,59 @@ 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: - - {"method": "handleMessage", "params": ["user1", "we were just talking"], "id": null} - -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). Higher is better: +First comes a comparison between various modules using +a very short single-line JSON string (also available at +L). + + {"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: module | encode | decode | -----------|------------|------------| - JSON | 11488.516 | 7823.035 | - JSON::DWIW | 94708.054 | 129094.260 | - JSON::PC | 63884.157 | 128528.212 | - JSON::Syck | 34898.677 | 42096.911 | - JSON::XS | 654027.064 | 396423.669 | - JSON::XS/2 | 371564.190 | 371725.613 | + 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 more than six times faster than JSON::DWIW on -encoding, more than three times faster on decoding, and about thirty 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): +search API (L). module | encode | decode | -----------|------------|------------| - JSON | 273.023 | 44.674 | - JSON::DWIW | 1089.383 | 1145.704 | - JSON::PC | 3097.419 | 2393.921 | - JSON::Syck | 514.060 | 843.053 | - JSON::XS | 6479.668 | 3636.364 | - JSON::XS/2 | 3774.221 | 3599.124 | + 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 | -----------+------------+------------+ -Again, JSON::XS leads by far. +Again, JSON::XS leads by far (except for Storable which non-surprisingly +decodes faster). -On large strings containing lots of high unicode characters, some modules +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 +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. @@ -631,38 +1381,87 @@ 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, thats just fine (e.g. by using a separate process that +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. +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. If that is exceeded, the program -crashes. Thats why the default nesting limit is set to 4096. If your -process has a smaller stack, you should adjust this setting accordingly -with the C 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 alway sopen for hints, -though... +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 +C method. + +Something else could bomb you, too, that I forgot to think of. In that +case, you get to keep the pieces. I am always open for hints, though... + +Also keep in mind that JSON::XS might leak contents of your Perl data +structures in its error messages, so when you serialise sensitive +information you might want to make sure that exceptions thrown by JSON::XS +will not end up in front of untrusted eyes. + +If you are using JSON::XS to return packets to consumption +by JavaScript scripts in a browser you should have a look at +L 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). + + +=head1 THREADS + +This module is I 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, it's I faster, cheaper, better). + +(It might actually work, but you have been warned). =head1 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 relatively early in its development. If you keep reporting bugs they -will be fixed swiftly, though. +not mean it's bug-free, only that I think its design is bug-free. 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. =cut -sub true() { \1 } -sub false() { \0 } +our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" }; +our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" }; + +sub true() { $true } +sub false() { $false } + +sub is_bool($) { + UNIVERSAL::isa $_[0], "JSON::XS::Boolean" +# or UNIVERSAL::isa $_[0], "JSON::Literal" +} + +XSLoader::load "JSON::XS", $VERSION; + +package JSON::XS::Boolean; + +use overload + "0+" => sub { ${$_[0]} }, + "++" => sub { $_[0] = ${$_[0]} + 1 }, + "--" => sub { $_[0] = ${$_[0]} - 1 }, + fallback => 1; 1; +=head1 SEE ALSO + +The F command line utility for quick experiments. + =head1 AUTHOR Marc Lehmann