--- JSON-XS/README 2007/08/27 02:03:23 1.17 +++ JSON-XS/README 2007/12/05 10:59:27 1.22 @@ -1,14 +1,18 @@ NAME JSON::XS - JSON serialising/deserialising, done correctly and fast + JSON::XS - 正しくて高速な JSON + シリアライザ/デシリアライザ + (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html) + SYNOPSIS use JSON::XS; # exported functions, 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 @@ -16,11 +20,27 @@ $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 overriden) with no overhead due to emulation (by inheritign + 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 @@ -33,7 +53,7 @@ vice versa. FEATURES - * correct unicode handling + * correct Unicode handling This module knows how to handle Unicode, and even documents how and when it does so. @@ -57,21 +77,20 @@ interface. * reasonably versatile output formats - You can choose between the most compact guarenteed single-line + You can choose between the most compact guaranteed single-line format possible (nice for simple line-based protocols), a pure-ascii format (for when your transport is not 8-bit clean, still supports - the whole unicode range), or a pretty-printed format (for when you + the whole Unicode range), or a pretty-printed format (for when you want to read that stuff). Or you can combine those features in whatever way you like. FUNCTIONAL INTERFACE - The following convinience methods are provided by this module. They are + The following convenience methods are provided by this module. They are exported by default: - $json_text = to_json $perl_scalar - Converts the given Perl data structure (a simple scalar or a - reference to a hash or array) to a UTF-8 encoded, binary string - (that is, the string contains octets only). Croaks on error. + $json_text = 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. This function call is functionally identical to: @@ -79,10 +98,10 @@ 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 simple scalar or reference. Croaks on error. + resulting reference. Croaks on error. This function call is functionally identical to: @@ -99,6 +118,45 @@ See MAPPING, below, for more information on how JSON values are mapped to Perl. +A FEW NOTES ON UNICODE AND PERL + Since this often leads to confusion, here are a few very clear words on + how Unicode works in Perl, modulo bugs. + + 1. Perl strings can store characters with ordinal values > 255. + This enables you to store Unicode characters as single characters in + a Perl string - very natural. + + 2. Perl does *not* associate an encoding with your strings. + Unless you force it to, e.g. when matching it against a regex, or + printing the scalar to a file, in which case Perl either interprets + your string as locale-encoded text, octets/binary, or as Unicode, + depending on various settings. In no case is an encoding stored + together with your data, it is *use* that decides encoding, not any + magical metadata. + + 3. The internal utf-8 flag has no meaning with regards to the encoding + of your string. + Just ignore that flag unless you debug a Perl bug, a module written + in XS or want to dive into the internals of perl. Otherwise it will + only confuse you, as, despite the name, it says nothing about how + your string is encoded. You can have Unicode strings with that flag + set, with that flag clear, and you can have binary data with that + flag set and that flag clear. Other possibilities exist, too. + + If you didn't know about that flag, just the better, pretend it + doesn't exist. + + 4. A "Unicode String" is simply a string where each character can be + validly interpreted as a Unicode codepoint. + If you have UTF-8 encoded data, it is no longer a Unicode string, + but a Unicode string encoded in UTF-8, giving you a binary string. + + 5. A string containing "high" (> 255) character values is *not* a UTF-8 + string. + It's a fact. Learn to live with it. + + I hope this helps :) + OBJECT-ORIENTED INTERFACE The object oriented interface lets you configure your own encoding or decoding style, within the limits of supported formats. @@ -115,12 +173,13 @@ => {"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 + Any Unicode characters outside that range will be escaped using either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, as per RFC4627. The resulting encoded JSON text can - be treated as a native unicode string, an ascii-encoded, + be treated as a native Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string, or any other superset of ASCII. @@ -136,12 +195,13 @@ => ["\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 - can be treated as a latin1-encoded JSON text or a native unicode + can be treated as a latin1-encoded JSON text or a native Unicode string. The "decode" method will not be affected in any way by this - flag, as "decode" by default expects unicode, which is a strict + flag, as "decode" by default expects Unicode, which is a strict superset of latin1. If $enable is false, then the "encode" method will not escape @@ -152,7 +212,7 @@ 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 transfering), a rare encoding for JSON. It is + 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. @@ -161,6 +221,7 @@ => ["\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 @@ -171,8 +232,8 @@ described in RFC4627. If $enable is false, then the "encode" method will return the JSON - string as a (non-encoded) unicode string, while "decode" expects - thus a unicode string. Any decoding or encoding (e.g. to UTF-8 or + string as a (non-encoded) Unicode string, while "decode" expects + thus a Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs to be done yourself, e.g. using the Encode module. Example, output UTF-16BE-encoded JSON: @@ -202,17 +263,19 @@ } $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, identing them + object/hash key-value pair into its own line, indenting them properly. If $enable is false, no newlines or indenting will be produced, and - the resulting JSON text is guarenteed not to contain any "newlines". + the resulting JSON text is guaranteed not to contain any "newlines". This setting has no effect when decoding JSON 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. @@ -228,6 +291,7 @@ {"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 @@ -243,6 +307,7 @@ {"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 @@ -270,7 +335,19 @@ "k2": "v2", <- this comma not normally allowed } + * shell-style '#'-comments + Whenever JSON allows whitespace, shell-style comments are + additionally allowed. They are terminated by the first + carriage-return or line-feed character, after which more + white-space and comments are allowed. + + [ + 1, # this comment not allowed in JSON + # neither this one... + ] + $json = $json->canonical ([$enable]) + $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. @@ -281,13 +358,14 @@ 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 + it is disabled, the same hash might be encoded differently even if contains the same data, as key-value pairs have no inherent ordering in Perl. This setting has no effect when decoding JSON texts. $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, @@ -305,17 +383,19 @@ => "Hello, World!" $json = $json->allow_blessed ([$enable]) + $enabled = $json->get_allow_blessed 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 wether "null" - ("convert_blessed" disabled or no "to_json" method found) or a + 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". + "TO_JSON" method found) is being encoded. Has no effect on "decode". If $enable is false (the default), then "encode" will throw an exception when it encounters a blessed object. $json = $json->convert_blessed ([$enable]) + $enabled = $json->get_convert_blessed 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 @@ -329,7 +409,7 @@ 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. This setting does not yet influence "decode" in any way, but in the future, global hooks might get installed that influence "decode" and @@ -380,7 +460,7 @@ "filter_json_object" one, decoding speed will not usually suffer as much. Therefore, single-key objects make excellent targets to serialise Perl objects into, especially as single-key JSON objects - are as close to the type-tagged value concept as JSON gets (its + 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. @@ -415,6 +495,7 @@ } $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 @@ -442,6 +523,7 @@ 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 @@ -463,6 +545,7 @@ 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 @@ -514,14 +597,14 @@ (what you put in comes out as something equivalent). For the more enlightened: note that in the following descriptions, - lowercase *perl* refers to the Perl interpreter, while uppcercase *Perl* + lowercase *perl* refers to the Perl interpreter, while uppercase *Perl* refers to the abstract Perl language itself. JSON -> PERL object A JSON object becomes a reference to a hash in Perl. No ordering of - object keys is preserved (JSON does not preserver object key - ordering itself). + object keys is preserved (JSON does not preserve object key ordering + itself). array A JSON array becomes a reference to an array in Perl. @@ -555,7 +638,7 @@ 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 wether a scalar is a JSON boolean by + numbers 1 and 0. You can check whether a scalar is a JSON boolean by using the "JSON::XS::is_bool" function. null @@ -588,11 +671,11 @@ can also use "JSON::XS::false" and "JSON::XS::true" to improve readability. - to_json [\0,JSON::XS::true] # yields [false,true] + encode_json [\0,JSON::XS::true] # yields [false,true] JSON::XS::true, JSON::XS::false These special values become JSON true and JSON false values, - respectively. You cna alos use "\1" and "\0" directly if you want. + 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 @@ -607,32 +690,32 @@ 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. COMPARISON As already mentioned, this module was created because none of the @@ -644,12 +727,12 @@ JSON 1.07 Slow (but very portable, as it is written in pure Perl). - Undocumented/buggy Unicode handling (how JSON handles unicode values - is undocumented. One can get far by feeding it unicode strings and - doing en-/decoding oneself, but unicode escapes are not working + Undocumented/buggy Unicode handling (how JSON handles Unicode values + is undocumented. One can get far by feeding it Unicode strings and + doing en-/decoding oneself, but Unicode escapes are not working properly). - No roundtripping (strings get clobbered if they look like numbers, + No round-tripping (strings get clobbered if they look like numbers, e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that will decode into the number 2. @@ -658,7 +741,7 @@ Undocumented/buggy Unicode handling. - No roundtripping. + No round-tripping. Has problems handling many Perl values (e.g. regex results and other magic values will make it croak). @@ -678,12 +761,12 @@ preferably a way to generate ASCII-only JSON texts). Completely broken (and confusingly documented) Unicode handling - (unicode escapes are not working properly, you need to set + (Unicode escapes are not working properly, you need to set ImplicitUnicode to *different* values on en- and decoding to get symmetric behaviour). - No roundtripping (simple cases work, but this depends on wether the - scalar value was used in a numeric context or not). + No round-tripping (simple cases work, but this depends on whether + the scalar value was used in a numeric context or not). Dumping hashes may skip hash values depending on iterator state. @@ -692,7 +775,7 @@ Does not check input for validity (i.e. will accept non-JSON input and return "something" instead of raising an exception. This is a - security issue: imagine two banks transfering money between each + security issue: imagine two banks transferring money between each other using JSON. One bank might parse a given non-JSON request and deduct money, while the other might reject the transaction with a syntax error. While a good protocol will at least recover, that is @@ -701,12 +784,12 @@ JSON::DWIW 0.04 Very fast. Very natural. Very nice. - Undocumented unicode handling (but the best of the pack. Unicode + Undocumented Unicode handling (but the best of the pack. Unicode escapes still don't get parsed properly). Very inflexible. - No roundtripping. + No round-tripping. Does not generate valid JSON texts (key strings are often unquoted, empty keys result in nothing being output) @@ -728,7 +811,7 @@ 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 noticably shorter than the 1024 characters YAML allows. + 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 @@ -753,11 +836,9 @@ 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 1.x | 4990.842 | 4088.813 | JSON::DWIW | 51653.990 | 71575.154 | JSON::PC | 65948.176 | 74631.744 | JSON::PP | 8931.652 | 3817.168 | @@ -769,7 +850,7 @@ -----------+------------+------------+ That is, JSON::XS is about five times faster than JSON::DWIW on - encoding, about three times faster on decoding, and over fourty times + 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. @@ -778,7 +859,7 @@ module | encode | decode | -----------|------------|------------| - JSON | 55.260 | 34.971 | + 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 | @@ -792,9 +873,9 @@ Again, JSON::XS leads by far (except for Storable which non-surprisingly decodes faster). - On large strings containing lots of high unicode characters, some + 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 + result will be broken due to missing (or wrong) Unicode handling. Others refuse to decode or encode properly, so it was impossible to prepare a fair comparison table for that case. @@ -808,7 +889,7 @@ 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 + your resources run out, that's just fine (e.g. by using a separate process that can crash safely). The size of a JSON text in octets or characters is usually a good indication of the size of the resources required to decode it into a Perl structure. While JSON::XS can check @@ -829,20 +910,31 @@ of. In that case, you get to keep the pieces. I am always open for hints, though... - If you are using JSON::XS to return packets to consumption by javascript + 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 wether + to see whether you are vulnerable to some common attack vectors (which really are browser design bugs, but it is still you who will have to deal with it, as major browser developers care only for features, not about doing security right). +THREADS + This module is *not* guaranteed to be thread safe and there are no plans + to change this until Perl gets thread support (as opposed to the + horribly slow so-called "threads" which are simply slow and bloated + process simulations - use fork, its *much* faster, cheaper, better). + + (It might actually work, but you have been warned). + BUGS While the goal of this module is to be correct, that unfortunately does not mean its bug-free, only that I think its design is bug-free. It is still relatively early in its development. If you keep reporting bugs they will be fixed swiftly, though. + Please refrain from using rt.cpan.org or any other bug reporting + service. I put the contact address into my modules for a reason. + AUTHOR Marc Lehmann http://home.schmorp.de/