--- JSON-XS/README 2007/12/05 10:59:27 1.22 +++ JSON-XS/README 2008/03/19 22:31:00 1.23 @@ -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 @@ -23,8 +22,8 @@ # 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; + + use JSON; # and do the same things, except that you have a pure-perl fallback now. @@ -53,31 +52,39 @@ 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. + + * simple to use - * reasonably versatile output formats - You can choose between the most compact guaranteed single-line + 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 @@ -127,12 +134,12 @@ 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. @@ -187,6 +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. @@ -208,6 +218,9 @@ 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 @@ -236,6 +249,9 @@ 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; @@ -320,7 +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 @@ -335,7 +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 @@ -620,20 +638,20 @@ 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", @@ -678,15 +696,17 @@ 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 @@ -715,7 +735,103 @@ $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. + 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 @@ -724,6 +840,17 @@ 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). @@ -797,10 +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): @@ -808,16 +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 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 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 @@ -826,7 +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]} @@ -855,7 +1006,7 @@ 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 | -----------|------------|------------| @@ -902,20 +1053,24 @@ 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 + as major browser developers care only for features, not about getting security right). THREADS