--- JSON-XS/README 2007/08/28 02:06:06 1.18 +++ JSON-XS/README 2008/03/19 22:31:00 1.23 @@ -1,14 +1,17 @@ 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 +19,27 @@ $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 @@ -33,45 +52,52 @@ vice versa. FEATURES - * correct unicode handling - This module knows how to handle Unicode, and even documents how and - when it does so. + * 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 - * 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). + just because it looks like a number). There minor *are* 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. + * fast + + Compared to other JSON modules and other serialisers such as + Storable, this module usually compares favourably in terms of speed, + too. - * reasonably versatile output formats - You can choose between the most compact guarenteed single-line + * simple to use + + This module has both a simple functional interface as well as an + objetc oriented interface 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 + 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 +105,10 @@ 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 +125,45 @@ 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. + ... 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 meta data. + + 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 +180,13 @@ => {"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. @@ -128,6 +194,9 @@ 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. @@ -136,23 +205,27 @@ => ["\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 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 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 +234,7 @@ => ["\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 @@ -171,10 +245,13 @@ 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. + See also the section *ENCODING/CODESET FLAG NOTES* later in this + document. + Example, output UTF-16BE-encoded JSON: use Encode; @@ -202,17 +279,19 @@ } $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 +307,7 @@ {"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 +323,7 @@ {"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 @@ -255,7 +336,8 @@ 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 @@ -270,7 +352,8 @@ "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 @@ -282,6 +365,7 @@ ] $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. @@ -292,13 +376,14 @@ 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, @@ -316,17 +401,19 @@ => "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 @@ -340,7 +427,7 @@ 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 @@ -391,7 +478,7 @@ "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. @@ -426,6 +513,7 @@ } $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 @@ -453,6 +541,7 @@ 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 @@ -474,6 +563,7 @@ 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 @@ -525,14 +615,14 @@ (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. @@ -548,25 +638,25 @@ 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 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. - - 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). 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 @@ -599,51 +689,149 @@ 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 - their underlying representation (hash- or arrayref), but this - behaviour might change in future versions. + Blessed objects are not directly representable in JSON. See the + "allow_blessed" and "convert_blessed" methods on various options on + how to deal with this: basically, you can choose between throwing an + exception, encoding the reference as if it weren't blessed, or + provide your own serialiser method. 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 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 + its needed :). + +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 wether the JSON text created by "encode" (and expected + by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only + control wether "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 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). + + "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. COMPARISON As already mentioned, this module was created because none of the @@ -652,15 +840,26 @@ JSON modules, followed by some benchmark values. JSON::XS was designed not to suffer from any of these problems or limitations. + JSON 2.xx + A marvellous piece of engineering, this module either uses JSON::XS + directly when available (so will be 100% compatible with it, + including speed), or it uses JSON::PP, which is basically JSON::XS + translated to Pure Perl, which should be 100% compatible with + JSON::XS, just a bit slower. + + You cannot really lose by using this module, especially as it tries + very hard to work even with ancient Perl versions, while JSON::XS + does not. + 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. @@ -669,7 +868,7 @@ 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). @@ -689,12 +888,12 @@ 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. @@ -703,7 +902,7 @@ 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 @@ -712,12 +911,12 @@ 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) @@ -725,10 +924,11 @@ Does not check input for validity. JSON and YAML - You often hear that JSON is a subset (or a close subset) of YAML. This - is, however, a mass hysteria and very far from the truth. In general, - there is no way to configure JSON::XS to output a data structure as - valid YAML. + 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): @@ -736,16 +936,38 @@ 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 noticably 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 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 "\/" + 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. SPEED It seems that JSON::XS is surprisingly fast, as shown in the following @@ -754,7 +976,8 @@ 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]} @@ -764,11 +987,9 @@ 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 | @@ -780,16 +1001,16 @@ -----------+------------+------------+ 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. 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 1.x | 55.260 | 34.971 | JSON::DWIW | 825.228 | 1082.513 | JSON::PC | 3571.444 | 2394.829 | JSON::PP | 210.987 | 32.574 | @@ -803,9 +1024,9 @@ 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. @@ -819,7 +1040,7 @@ 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 @@ -832,28 +1053,43 @@ 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 + 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 + as major browser developers care only for features, not about getting 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/