--- JSON-XS/README 2007/11/13 22:59:08 1.20 +++ JSON-XS/README 2013/10/29 15:55:49 1.39 @@ -1,8 +1,7 @@ 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 + 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 @@ -11,8 +10,8 @@ # 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; + $utf8_encoded_json_text = encode_json $perl_hash_or_arrayref; + $perl_hash_or_arrayref = decode_json $utf8_encoded_json_text; # OO-interface @@ -20,49 +19,72 @@ $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. + DESCRIPTION This module converts Perl data structures to JSON and vice versa. Its primary goal is to be *correct* and its secondary goal is to be *fast*. 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. FEATURES - * 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" - just because it looks like a number). + * correct Unicode handling + + This module knows how to handle Unicode, documents how and when it + does so, and even documents what "correct" means. + + * round-trip integrity + + When you serialise a perl data structure using only data types + supported by JSON and Perl, the deserialised data structure is + identical on the Perl level. (e.g. the string "2.0" doesn't suddenly + become "2" just because it looks like a number). There *are* minor + exceptions to this, read the MAPPING section below to learn about + those. + + * strict checking of JSON correctness - * strict checking of JSON correctness 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). - * fast - Compared to other JSON modules, this module compares favourably in - terms of speed, too. - - * simple to use - This module has both a simple functional interface as well as an OO - interface. - - * reasonably versatile output formats - You can choose between the most compact guaranteed single-line - format possible (nice for simple line-based protocols), a pure-ascii + * fast + + Compared to other JSON modules and other serialisers such as + Storable, this module usually compares favourably in terms of speed, + too. + + * simple to use + + This module has both a simple functional interface as well as an + object oriented interface. + + * reasonably versatile output formats + + 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 stuff). Or you can combine those features in @@ -72,7 +94,7 @@ The following convenience methods are provided by this module. They are exported by default: - $json_text = to_json $perl_scalar + $json_text = encode_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. @@ -80,10 +102,10 @@ $json_text = JSON::XS->new->utf8->encode ($perl_scalar) - except being faster. + Except being faster. - $perl_scalar = from_json $json_text - The opposite of "to_json": expects an UTF-8 (binary) string and + $perl_scalar = decode_json $json_text + The opposite of "encode_json": 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. @@ -91,16 +113,7 @@ $perl_scalar = JSON::XS->new->utf8->decode ($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. + Except being faster. A FEW NOTES ON UNICODE AND PERL Since this often leads to confusion, here are a few very clear words on @@ -111,12 +124,12 @@ 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 + ... 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 *use* that decides encoding, not any - magical metadata. + magical meta data. 3. The internal utf-8 flag has no meaning with regards to the encoding of your string. @@ -131,7 +144,7 @@ doesn't exist. 4. A "Unicode String" is simply a string where each character can be - validly interpreted as a Unicode codepoint. + 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. @@ -157,6 +170,7 @@ => {"a": [1, 2]} $json = $json->ascii ([$enable]) + $enabled = $json->get_ascii If $enable is true (or missing), then the "encode" method will not generate characters outside the code range 0..127 (which is ASCII). Any Unicode characters outside that range will be escaped using @@ -170,6 +184,9 @@ Unicode characters unless required by the JSON syntax or other flags. This results in a faster and more compact format. + See also the section *ENCODING/CODESET FLAG NOTES* 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. @@ -178,6 +195,7 @@ => ["\ud801\udc01"] $json = $json->latin1 ([$enable]) + $enabled = $json->get_latin1 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 @@ -190,6 +208,9 @@ Unicode characters unless required by the JSON syntax or other flags. + See also the section *ENCODING/CODESET FLAG NOTES* 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 @@ -203,6 +224,7 @@ => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not) $json = $json->utf8 ([$enable]) + $enabled = $json->get_utf8 If $enable is true (or missing), then the "encode" method will encode the JSON result into UTF-8, as required by many protocols, while the "decode" method expects to be handled an UTF-8-encoded @@ -217,6 +239,9 @@ 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 *ENCODING/CODESET FLAG NOTES* later in this + document. + Example, output UTF-16BE-encoded JSON: use Encode; @@ -244,6 +269,7 @@ } $json = $json->indent ([$enable]) + $enabled = $json->get_indent 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, indenting them @@ -255,6 +281,7 @@ This setting has no effect when decoding JSON texts. $json = $json->space_before ([$enable]) + $enabled = $json->get_space_before If $enable is true (or missing), then the "encode" method will add an extra optional space before the ":" separating keys from values in JSON objects. @@ -270,6 +297,7 @@ {"key" :"value"} $json = $json->space_after ([$enable]) + $enabled = $json->get_space_after If $enable is true (or missing), then the "encode" method will add an extra optional space after the ":" separating keys from values in JSON objects and extra whitespace after the "," separating key-value @@ -285,6 +313,7 @@ {"key": "value"} $json = $json->relaxed ([$enable]) + $enabled = $json->get_relaxed 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 @@ -297,7 +326,8 @@ Currently accepted extensions are: - * list items can have an end-comma + * 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 @@ -312,7 +342,8 @@ "k2": "v2", <- this comma not normally allowed } - * shell-style '#'-comments + * 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 @@ -324,13 +355,15 @@ ] $json = $json->canonical ([$enable]) + $enabled = $json->get_canonical If $enable is true (or missing), then the "encode" method will output JSON objects by sorting their keys. This is adding a comparatively high overhead. If $enable is false, then the "encode" method will output key-value pairs in the order Perl stores them (which will likely change - between runs of the same script). + between runs of the same script, and can change even within the same + run from 5.18 onwards). This option is useful if you want the same data structure to be encoded as the same JSON text (given the same overall settings). If @@ -340,7 +373,10 @@ This setting has no effect when decoding JSON texts. + This setting has currently no effect on tied hashes. + $json = $json->allow_nonref ([$enable]) + $enabled = $json->get_allow_nonref If $enable is true (or missing), then the "encode" method can convert a non-reference into its corresponding string, number or null JSON value, which is an extension to RFC4627. Likewise, @@ -357,24 +393,45 @@ JSON::XS->new->allow_nonref->encode ("Hello, World!") => "Hello, World!" + $json = $json->allow_unknown ([$enable]) + $enabled = $json->get_allow_unknown + If $enable is true (or missing), then "encode" will *not* throw an + exception when it encounters values it cannot represent in JSON (for + example, filehandles) but instead will encode a JSON "null" value. + Note that blessed objects are not included here and are handled + separately by c. + + If $enable is false (the default), then "encode" will throw an + exception when it encounters anything it cannot encode as JSON. + + This option does not affect "decode" in any way, and it is + recommended to leave it off unless you know your communications + partner. + $json = $json->allow_blessed ([$enable]) + $enabled = $json->get_allow_blessed + See "OBJECT SERIALISATION" for details. + If $enable is true (or missing), then the "encode" method will not - barf when it encounters a blessed reference. Instead, the value of - the convert_blessed option will decide whether "null" - ("convert_blessed" disabled or no "to_json" method found) or a - representation of the object ("convert_blessed" enabled and - "to_json" method found) is being encoded. Has no effect on "decode". + barf when it encounters a blessed reference that it cannot convert + otherwise. Instead, a JSON "null" value is encoded instead of the + object. If $enable is false (the default), then "encode" will throw an - exception when it encounters a blessed object. + exception when it encounters a blessed object that it cannot convert + otherwise. + + This setting has no effect on "decode". $json = $json->convert_blessed ([$enable]) + $enabled = $json->get_convert_blessed + See "OBJECT SERIALISATION" for details. + If $enable is true (or missing), then "encode", upon encountering a blessed object, will check for the availability of the "TO_JSON" method on the object's class. If found, it will be called in scalar context and the resulting scalar will be encoded instead of the - object. If no "TO_JSON" method is found, the value of - "allow_blessed" will decide what to do. + object. The "TO_JSON" method may safely call die if it wants. If "TO_JSON" returns other blessed objects, those will be handled in the same @@ -382,14 +439,29 @@ 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. + collisions with any "to_json" function or method. + + If $enable is false (the default), then "encode" will not consider + this type of conversion. - 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. + This setting has no effect on "decode". - If $enable is false, then the "allow_blessed" setting will decide - what to do when a blessed object is found. + $json = $json->allow_tags ([$enable]) + $enabled = $json->allow_tags + See "OBJECT SERIALISATION" for details. + + If $enable is true (or missing), then "encode", upon encountering a + blessed object, will check for the availability of the "FREEZE" + method on the object's class. If found, it will be used to serialise + the object into a nonstandard tagged JSON value (that JSON decoders + cannot decode). + + It also causes "decode" to parse such tagged JSON values and + deserialise them via a call to the "THAW" method. + + If $enable is false (the default), then "encode" will not consider + this type of conversion, and tagged JSON values will cause a parse + error in "decode", as if tags were not part of the grammar. $json = $json->filter_json_object ([$coderef->($hashref)]) When $coderef is specified, it will be called from "decode" each @@ -468,6 +540,7 @@ } $json = $json->shrink ([$enable]) + $enabled = $json->get_shrink 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 @@ -495,10 +568,11 @@ saving space. $json = $json->max_depth ([$maximum_nesting_depth]) + $max_depth = $json->get_max_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. + 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 @@ -508,45 +582,38 @@ 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. + 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. $json = $json->max_size ([$maximum_string_size]) + $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 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 + When "decode" 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 "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). + 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, - while references to arrays become JSON arrays and references to - hashes become JSON objects. Undefined Perl values (e.g. "undef") - become JSON "null" values. Neither "true" nor "false" values will be - generated. + Converts the given Perl value or data structure to its JSON + representation. Croaks on error. $perl_scalar = $json->decode ($json_text) The opposite of "encode": expects a JSON text and tries to parse it, returning the resulting simple scalar or reference. Croaks on error. - JSON numbers and strings become simple Perl scalars. JSON arrays - become Perl arrayrefs and JSON objects become Perl hashrefs. "true" - becomes 1, "false" becomes 0 and "null" becomes "undef". - ($perl_scalar, $characters) = $json->decode_prefix ($json_text) This works like the "decode" method, but instead of raising an exception when there is trailing garbage after the first JSON @@ -554,12 +621,243 @@ characters consumed so far. This is useful if your JSON texts are not delimited by an outer - protocol (which is not the brightest thing to do in the first place) - and you need to know where the JSON text ends. + protocol and you need to know where the JSON text ends. JSON::XS->new->decode_prefix ("[1] the tail") => ([], 3) +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 "decode_prefix" 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 mismatched parentheses. + The only thing it guarantees is that it starts decoding as soon as a + syntactically valid JSON text has been seen. This means you need to set + resource limits (e.g. "max_size") to ensure the parser will stop parsing + in the presence if syntax errors. + + The following methods implement this incremental parser. + + [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 $string is given, then this string is appended to the already + existing JSON fragment stored in the $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 *one* JSON object. If that is successful, it will + return this object, otherwise it will return "undef". If there is a + parse error, this method will croak just as "decode" would do (one + can then use "incr_skip" to skip the erroneous part). This is the + most common way of using the method. + + And finally, in list context, it will try to extract as many objects + 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. + + Example: Parse some JSON arrays/objects in a given string and return + them. + + my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]"); + + $lvalue_string = $json->incr_text + This method returns the currently stored JSON fragment as an lvalue, + that is, you can manipulate it. This *only* works when a preceding + call to "incr_parse" in *scalar context* 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 *will* 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). + + $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 + "incr_parse" 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 "incr_reset" is that only text until the parse + error occurred is removed. + + $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. + + LIMITATIONS + All options that affect decoding are supported, except "allow_nonref". + 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 1 a single JSON number, or is it simply the + start of 12? Or is 12 a single JSON number, or the concatenation of 1 + and 2? In neither case you can tell, and this is why JSON::XS takes the + conservative route and disallows this case. + + EXAMPLES + Some examples will make all this clearer. First, a simple example that + works similarly to "decode_prefix": 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 "telnet"...). + + 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. "[1],[2], + [3]"). To parse them, we have to skip the commas between the JSON texts, + and here is where the lvalue-ness of "incr_text" 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 :). + 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 @@ -590,30 +888,50 @@ 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. + 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. + a string value (in which case you lose roundtripping ability, as the + JSON number will be re-encoded to a JSON string). Numbers containing a fractional or exponential part will always be represented as numeric (floating point) values, possibly at a loss - 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. + of precision (in which case you might lose perfect roundtripping + ability, but the JSON number will still be re-encoded as a JSON + number). + + Note that precision is not accuracy - binary floating point values + cannot represent most decimal fractions exactly, and when converting + from and to floating point, JSON::XS only guarantees precision up to + but not including the least significant bit. true, false - These JSON atoms become "JSON::XS::true" and "JSON::XS::false", - respectively. They are overloaded to act almost exactly like the - numbers 1 and 0. You can check whether a scalar is a JSON boolean by - using the "JSON::XS::is_bool" function. + These JSON atoms become "Types::Serialiser::true" and + "Types::Serialiser::false", respectively. They are overloaded to act + almost exactly like the numbers 1 and 0. You can check whether a + scalar is a JSON boolean by using the "Types::Serialiser::is_bool" + function (after "use Types::Serialier", of course). null A JSON null atom becomes "undef" in Perl. + shell-style comments ("# *text*") + As a nonstandard extension to the JSON syntax that is enabled by the + "relaxed" setting, shell-style comments are allowed. They can start + anywhere outside strings and go till the end of the line. + + tagged values ("(*tag*)*value*"). + Another nonstandard extension to the JSON syntax, enabled with the + "allow_tags" setting, are tagged values. In this implementation, the + *tag* must be a perl package/class name encoded as a JSON string, + and the *value* must be a JSON array encoding optional constructor + arguments. + + See "OBJECT SERIALISATION", below, for details. + PERL -> JSON The mapping from Perl to JSON is slightly more difficult, as Perl is a truly typeless language, so we can only guess which JSON type is meant @@ -622,14 +940,12 @@ hash references Perl hash references become JSON objects. As there is no inherent ordering in hash keys (or JSON objects), they will usually be - encoded in a pseudo-random order that can change between runs of the - same program but stays generally the same within a single run of a - program. JSON::XS can optionally sort the hash keys (determined by - the *canonical* flag), so the same datastructure will serialise to - the same JSON text (given same settings and version of JSON::XS), - but this incurs a runtime overhead and is only rarely useful, e.g. - when you want to compare some JSON text against another for - equality. + encoded in a pseudo-random order. JSON::XS can optionally sort the + hash keys (determined by the *canonical* flag), so the same + datastructure will serialise to the same JSON text (given same + settings and version of JSON::XS), but this incurs a runtime + overhead and is only rarely useful, e.g. when you want to compare + some JSON text against another for equality. array references Perl array references become JSON arrays. @@ -637,39 +953,44 @@ other references Other unblessed references are generally not allowed and will cause an exception to be thrown, except for references to the integers 0 - and 1, which get turned into "false" and "true" atoms in JSON. You - can also use "JSON::XS::false" and "JSON::XS::true" to improve + and 1, which get turned into "false" and "true" atoms in JSON. + + Since "JSON::XS" uses the boolean model from Types::Serialiser, you + can also "use Types::Serialiser" and then use + "Types::Serialiser::false" and "Types::Serialiser::true" to improve readability. - to_json [\0,JSON::XS::true] # yields [false,true] + use Types::Serialiser; + encode_json [\0, Types::Serialiser::true] # yields [false,true] - JSON::XS::true, JSON::XS::false - These special values become JSON true and JSON false values, - respectively. You can also use "\1" and "\0" directly if you want. + Types::Serialiser::true, Types::Serialiser::false + These special values from the Types::Serialiser module become JSON + true and JSON false values, respectively. You can also use "\1" and + "\0" directly if you want. blessed objects - Blessed objects are not 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, but + "JSON::XS" allows various ways of handling objects. See "OBJECT + SERIALISATION", below, for details. simple scalars Simple Perl scalars (any scalar that is not a reference) are the 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 + scalars as JSON "null" 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 JSON string by stringifying it: @@ -685,92 +1006,280 @@ $x *= 1; # same thing, the choice is yours. 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 - 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 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 - properly). - - 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. - - JSON::PC 0.01 - Very fast. - - Undocumented/buggy Unicode handling. - - No round-tripping. + Tell me if you need this capability (but don't forget to explain why + it's needed :). - Has problems handling many Perl values (e.g. regex results and other - magic values will make it croak). + Note that numerical precision has the same meaning as under Perl (so + binary to decimal conversion follows the same rules as in Perl, + which can differ to other languages). Also, your perl interpreter + might expose extensions to the floating point numbers of your + platform, such as infinities or NaN's - these cannot be represented + in JSON, and it is an error to pass those in. + + OBJECT SERIALISATION + As JSON cannot directly represent Perl objects, you have to choose + between a pure JSON representation (without the ability to deserialise + the object automatically again), and a nonstandard extension to the JSON + syntax, tagged values. + + SERIALISATION + What happens when "JSON::XS" encounters a Perl object depends on the + "allow_blessed", "convert_blessed" and "allow_tags" settings, which are + used in this order: + + 1. "allow_tags" is enabled and the object has a "FREEZE" method. + In this case, "JSON::XS" uses the Types::Serialiser object + serialisation protocol to create a tagged JSON value, using a + nonstandard extension to the JSON syntax. + + This works by invoking the "FREEZE" method on the object, with the + first argument being the object to serialise, and the second + argument being the constant string "JSON" to distinguish it from + other serialisers. + + The "FREEZE" method can return any number of values (i.e. zero or + more). These values and the paclkage/classname of the object will + then be encoded as a tagged JSON value in the following format: + + ("classname")[FREEZE return values...] + + e.g.: + + ("URI")["http://www.google.com/"] + ("MyDate")[2013,10,29] + ("ImageData::JPEG")["Z3...VlCg=="] - Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" - which is not a valid JSON text. + For example, the hypothetical "My::Object" "FREEZE" method might use + the objects "type" and "id" members to encode the object: - Unmaintained (maintainer unresponsive for many months, bugs are not - getting fixed). + sub My::Object::FREEZE { + my ($self, $serialiser) = @_; - JSON::Syck 0.21 - Very buggy (often crashes). - - Very inflexible (no human-readable format supported, format pretty - much undocumented. I need at least a format for easy reading by - humans and a single-line compact format for use in a protocol, and - preferably a way to generate ASCII-only JSON texts). - - Completely broken (and confusingly documented) Unicode handling - (Unicode escapes are not working properly, you need to set - ImplicitUnicode to *different* values on en- and decoding to get - symmetric behaviour). - - No round-tripping (simple cases work, but this depends on whether - the scalar value was used in a numeric context or not). - - Dumping hashes may skip hash values depending on iterator state. - - Unmaintained (maintainer unresponsive for many months, bugs are not - getting fixed). - - Does not check input for validity (i.e. will accept non-JSON input - and return "something" instead of raising an exception. This is a - security issue: imagine two banks transferring money between each - other using JSON. One bank might parse a given non-JSON request and - deduct money, while the other might reject the transaction with a - syntax error. While a good protocol will at least recover, that is - extra unnecessary work and the transaction will still not succeed). + ($self->{type}, $self->{id}) + } - JSON::DWIW 0.04 - Very fast. Very natural. Very nice. + 2. "convert_blessed" is enabled and the object has a "TO_JSON" method. + In this case, the "TO_JSON" method of the object is invoked in + scalar context. It must return a single scalar that can be directly + encoded into JSON. This scalar replaces the object in the JSON text. + + For example, the following "TO_JSON" method will convert all URI + objects to JSON strings when serialised. The fatc that these values + originally were URI objects is lost. + + sub URI::TO_JSON { + my ($uri) = @_; + $uri->as_string + } - Undocumented Unicode handling (but the best of the pack. Unicode - escapes still don't get parsed properly). + 3. "allow_blessed" is enabled. + The object will be serialised as a JSON null value. - Very inflexible. + 4. none of the above + If none of the settings are enabled or the respective methods are + missing, "JSON::XS" throws an exception. + + DESERIALISATION + For deserialisation there are only two cases to consider: either + nonstandard tagging was used, in which case "allow_tags" decides, or + objects cannot be automatically be deserialised, in which case you can + use postprocessing or the "filter_json_object" or + "filter_json_single_key_object" callbacks to get some real objects our + of your JSON. + + This section only considers the tagged value case: I a tagged JSON + object is encountered during decoding and "allow_tags" is disabled, a + parse error will result (as if tagged values were not part of the + grammar). + + If "allow_tags" is enabled, "JSON::XS" will look up the "THAW" method of + the package/classname used during serialisation (it will not attempt to + load the package as a Perl module). If there is no such method, the + decoding will fail with an error. + + Otherwise, the "THAW" method is invoked with the classname as first + argument, the constant string "JSON" as second argument, and all the + values from the JSON array (the values originally returned by the + "FREEZE" method) as remaining arguments. + + The method must then return the object. While technically you can return + any Perl scalar, you might have to enable the "enable_nonref" setting to + make that work in all cases, so better return an actual blessed + reference. + + As an example, let's implement a "THAW" function that regenerates the + "My::Object" from the "FREEZE" example earlier: + + sub My::Object::THAW { + my ($class, $serialiser, $type, $id) = @_; + + $class->new (type => $type, id => $id) + } + +ENCODING/CODESET FLAG NOTES + The interested reader might have seen a number of flags that signify + encodings or codesets - "utf8", "latin1" and "ascii". There seems to be + some confusion on what these do, so here is a short comparison: + + "utf8" controls whether the JSON text created by "encode" (and expected + by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only + control whether "encode" 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 + "encode" and "decode", 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 *encodes* 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 *and* + encodings at the same time, which can be confusing. + + "utf8" flag disabled + When "utf8" is disabled (the default), then "encode"/"decode" + generate and expect Unicode strings, that is, characters with high + ordinal Unicode values (> 255) will be encoded as such characters, + and likewise such characters are decoded as-is, no changes to them + will be done, except "(re-)interpreting" them as Unicode codepoints + or Unicode characters, respectively (to Perl, these are the same + thing in strings unless you do funny/weird/dumb stuff). + + 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). + + "utf8" flag enabled + If the "utf8"-flag is enabled, "encode"/"decode" 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 "utf8" 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. + + "latin1" or "ascii" flags enabled + With "latin1" (or "ascii") enabled, "encode" will escape characters + with ordinal values > 255 (> 127 with "ascii") and encode the + remaining characters as specified by the "utf8" flag. + + If "utf8" 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 "utf8" is enabled, you still get a correct UTF-8-encoded string, + regardless of these flags, just some more characters will be escaped + using "\uXXXX" then before. + + Note that ISO-8859-1-*encoded* 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 + *codeset* being a subset of Unicode), while ASCII is. + + Surprisingly, "decode" will ignore these flags and so treat all + input values as governed by the "utf8" 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 "latin1" nor "ascii" are incompatible with the "utf8" + flag - they only govern when the JSON output engine escapes a + character or not. + + The main use for "latin1" is to relatively efficiently store binary + data as JSON, at the expense of breaking compatibility with most + JSON decoders. + + The main use for "ascii" 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. + + JSON and ECMAscript + 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". + + However, JSON is not a subset (and also not a superset of course) of + ECMAscript (the standard) or javascript (whatever browsers actually + implement). + + If you want to use javascript's "eval" function to "parse" JSON, you + might run into parse errors for valid JSON texts, or the resulting data + structure might not be queryable: + + 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 "eval": + + use JSON::XS; + + print encode_json [chr 0x2028]; + + The right fix for this is to use a proper JSON parser in your javascript + programs, and not rely on "eval" (see for example Douglas Crockford's + json2.js parser). + + If this is not an option, you can, as a stop-gap measure, simply encode + to ASCII-only JSON: + + use JSON::XS; + + print JSON::XS->new->ascii->encode ([chr 0x2028]); + + 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.: + + # 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; + + Note that *this is a bad idea*: 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 "eval" naively simply *will* cause problems. + + Another problem is that some javascript implementations reserve some + property names for their own purposes (which probably makes them + non-ECMAscript-compliant). For example, Iceweasel reserves the + "__proto__" property name for its own purposes. + + If that is a problem, you could parse try to filter the resulting JSON + output for these property strings, e.g.: - No round-tripping. + $json =~ s/"__proto__"\s*:/"__proto__renamed":/g; - Does not generate valid JSON texts (key strings are often unquoted, - empty keys result in nothing being output) + This works because "__proto__" is not valid outside of strings, so every + occurrence of ""__proto__"\s*:" must be a string used as property name. - Does not check input for validity. + If you know of other incompatibilities, please let me know. 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. + 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: *in general, there is no way to + configure JSON::XS to output a data structure as valid YAML* that works + in all cases. If you really must use JSON::XS to generate YAML, you should use this algorithm (subject to change in future versions): @@ -778,16 +1287,45 @@ 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. + 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 + lengths that JSON doesn't have and also has different and incompatible + unicode character escape syntax, so you should make sure that your hash + keys are noticeably shorter than the 1024 "stream characters" YAML + allows and that you do not have characters with codepoint values outside + the Unicode BMP (basic multilingual page). YAML also does not allow "\/" + sequences in strings (which JSON::XS does not *currently* generate, but + other JSON generators might). + + 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. + chances are high that you will run into severe interoperability problems + when you least expect it. + + (*) 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)*complete and worthless idiot*(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 *years* and + trying to silence people who point out that it isn't true. + + Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, + even though the incompatibilities have been documented (and are + known to Brian) for many years and the spec makes explicit claims + that YAML is a superset of JSON. It would be so easy to fix, but + apparently, bullying people and corrupting userdata is so much + easier. SPEED It seems that JSON::XS is surprisingly fast, as shown in the following @@ -796,54 +1334,53 @@ system. First comes a comparison between various modules using a very short - single-line JSON string: + single-line JSON string (also available at + ). - {"method": "handleMessage", "params": ["user1", "we were just talking"], \ - "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} + {"method": "handleMessage", "params": ["user1", + "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7, + 1, 0]} It shows the number of encodes/decodes per second (JSON::XS uses the functional interface, while JSON::XS/2 uses the OO interface with - pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink). - Higher is better: - - Storable | 15779.925 | 14169.946 | - -----------+------------+------------+ - module | encode | decode | - -----------|------------|------------| - 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 about five times faster than JSON::DWIW on - encoding, about three times faster on decoding, and over forty times - faster than JSON, even with pretty-printing and key sorting. It also + pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink. + JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ uses + the from_json method). Higher is better: + + module | encode | decode | + --------------|------------|------------| + JSON::DWIW/DS | 86302.551 | 102300.098 | + JSON::DWIW/FJ | 86302.551 | 75983.768 | + JSON::PP | 15827.562 | 6638.658 | + JSON::Syck | 63358.066 | 47662.545 | + JSON::XS | 511500.488 | 511500.488 | + JSON::XS/2 | 291271.111 | 388361.481 | + JSON::XS/3 | 361577.931 | 361577.931 | + Storable | 66788.280 | 265462.278 | + --------------+------------+------------+ + + That is, JSON::XS is almost six times faster than JSON::DWIW on + encoding, about five times faster on decoding, and over thirty to + seventy times faster than JSON's pure perl implementation. It also compares favourably to Storable for small amounts of data. Using a longer test string (roughly 18KB, generated from Yahoo! Locals - search API (http://nanoref.com/yahooapis/mgPdGg): + search API (). - module | encode | decode | - -----------|------------|------------| - 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 | - -----------+------------+------------+ + module | encode | decode | + --------------|------------|------------| + JSON::DWIW/DS | 1647.927 | 2673.916 | + JSON::DWIW/FJ | 1630.249 | 2596.128 | + JSON::PP | 400.640 | 62.311 | + JSON::Syck | 1481.040 | 1524.869 | + JSON::XS | 20661.596 | 9541.183 | + JSON::XS/2 | 10683.403 | 9416.938 | + JSON::XS/3 | 20661.596 | 9400.054 | + Storable | 19765.806 | 10000.725 | + --------------+------------+------------+ Again, JSON::XS leads by far (except for Storable which non-surprisingly - decodes faster). + decodes a bit faster). On large strings containing lots of high Unicode characters, some modules (such as JSON::PC) seem to decode faster than JSON::XS, but the @@ -874,39 +1411,67 @@ 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 + 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... + 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 - 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). + + to see whether you are vulnerable to some common attack vectors (which + really are browser design bugs, but it is still you who will have to + deal with it, as major browser developers care only for features, not + about getting security right). + +INTEROPERABILITY WITH OTHER MODULES + "JSON::XS" uses the Types::Serialiser module to provide boolean + constants. That means that the JSON true and false values will be + comaptible to true and false values of iother modules that do the same, + such as JSON::PP and CBOR::XS. THREADS This module is *not* guaranteed to be thread safe and there are no plans 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). + process simulations - use fork, it's *much* faster, cheaper, better). (It might actually work, but you have been warned). +THE PERILS OF SETLOCALE + Sometimes people avoid the Perl locale support and directly call the + system's setlocale function with "LC_ALL". + + This breaks both perl and modules such as JSON::XS, as stringification + of numbers no longer works correctly (e.g. "$x = 0.1; print "$x"+1" + might print 1, and JSON::XS might output illegal JSON as JSON::XS relies + on perl to stringify numbers). + + The solution is simple: don't call "setlocale", or use it for only those + categories you need, such as "LC_MESSAGES" or "LC_CTYPE". + + If you need "LC_NUMERIC", you should enable it only around the code that + actually needs it (avoiding stringification of numbers), and restore it + afterwards. + BUGS While the goal of this module is to be correct, that unfortunately does - not mean 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. +SEE ALSO + The json_xs command line utility for quick experiments. + AUTHOR Marc Lehmann http://home.schmorp.de/