[ViewVC] Diff of: cvs/JSON-XS/README

Comparing JSON-XS/README (file contents):
Revision 1.26 by root, Tue Jun 3 06:43:45 2008 UTC vs.
Revision 1.37 by root, Thu May 23 09:32:02 2013 UTC

      $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;
+     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
     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
         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, the deserialised data structure is identical on
+        supported by JSON and Perl, the deserialised data structure is
-        the Perl level. (e.g. the string "2.0" doesn't suddenly become "2"
+        identical on the Perl level. (e.g. the string "2.0" doesn't suddenly
-        just because it looks like a number). There minor *are* exceptions
+        become "2" just because it looks like a number). There *are* minor
-        to this, read the MAPPING section below to learn about those.
+        exceptions to this, read the MAPPING section below to learn about
+        those.
     *   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
         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
         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.
+        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
     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 (JSON::XS will only attempt to parse the JSON text
+    much more efficient (and can be implemented with a minimum of method
-    once it is sure it has enough text to get a decisive result, using a
+    calls).
-    very simple but truly incremental parser).
-    The following two methods deal with this.
+    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).
         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
         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. This is useful after
+        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 occured 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 ot repeatedly parse JSON objects and want
+        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".
         Numbers containing a fractional or exponential part will always be
         represented as numeric (floating point) values, possibly at a loss
         of precision (in which case you might lose perfect roundtripping
         ability, but the JSON number will still be re-encoded as a JSON
         number).
+        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 leats 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
         You can not currently force the type in other, less obscure, ways.
         Tell me if you need this capability (but don't forget to explain why
         it's needed :).
+        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.
 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:
         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.:
+       $json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
+    This works because "__proto__" is not valid outside of strings, so every
+    occurence of ""__proto__"\s*:" must be a string used as property name.
+    If you know of other incompatibilities, please let me know.
   JSON and 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
        my $yaml = $to_yaml->encode ($ref) . "\n";
     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 and also has different and incompatible
-    unicode handling, so you should make sure that your hash keys are
+    unicode character escape syntax, so you should make sure that your hash
-    noticeably shorter than the 1024 "stream characters" YAML allows and
+    keys are noticeably shorter than the 1024 "stream characters" YAML
-    that you do not have characters with codepoint values outside the
+    allows and that you do not have characters with codepoint values outside
-    Unicode BMP (basic multilingual page). YAML also does not allow "\/"
+    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).
         (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
     tables. They have been generated with the help of the "eg/bench" program
     in the JSON::XS distribution, to make it easy to compare on your own
     system.
     single-line JSON string (also available at
     <http://dist.schmorp.de/misc/json/short.json>).
        {"method": "handleMessage", "params": ["user1",
        "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
-       true,  false]}
+       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).
+    pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink.
-    Higher is better:
+    JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ uses
+    the from_json method). Higher is better:
-       module     |     encode |     decode |
+       module        |     encode |     decode |
-       -----------|------------|------------|
+       --------------|------------|------------|
-       JSON 1.x   |   4990.842 |   4088.813 |
+       JSON::DWIW/DS |  86302.551 | 102300.098 |
-       JSON::DWIW |  51653.990 |  71575.154 |
+       JSON::DWIW/FJ |  86302.551 |  75983.768 |
-       JSON::PC   |  65948.176 |  74631.744 |
+       JSON::PP      |  15827.562 |   6638.658 |
-       JSON::PP   |   8931.652 |   3817.168 |
+       JSON::Syck    |  63358.066 |  47662.545 |
-       JSON::Syck |  24877.248 |  27776.848 |
+       JSON::XS      | 511500.488 | 511500.488 |
-       JSON::XS   | 388361.481 | 227951.304 |
+       JSON::XS/2    | 291271.111 | 388361.481 |
-       JSON::XS/2 | 227951.304 | 218453.333 |
+       JSON::XS/3    | 361577.931 | 361577.931 |
-       JSON::XS/3 | 338250.323 | 218453.333 |
+       Storable      |  66788.280 | 265462.278 |
-       Storable   |  16500.016 | 135300.129 |
-       -----------+------------+------------+
+       --------------+------------+------------+
-    That is, JSON::XS is about five times faster than JSON::DWIW on
+    That is, JSON::XS is almost six times faster than JSON::DWIW on
-    encoding, about three times faster on decoding, and over forty times
+    encoding, about five times faster on decoding, and over thirty to
-    faster than JSON, even with pretty-printing and key sorting. It also
+    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://dist.schmorp.de/misc/json/long.json>).
-       module     |     encode |     decode |
+       module        |     encode |     decode |
-       -----------|------------|------------|
+       --------------|------------|------------|
-       JSON 1.x   |     55.260 |     34.971 |
+       JSON::DWIW/DS |   1647.927 |   2673.916 |
-       JSON::DWIW |    825.228 |   1082.513 |
+       JSON::DWIW/FJ |   1630.249 |   2596.128 |
-       JSON::PC   |   3571.444 |   2394.829 |
-       JSON::PP   |    210.987 |     32.574 |
+       JSON::PP      |    400.640 |     62.311 |
-       JSON::Syck |    552.551 |    787.544 |
+       JSON::Syck    |   1481.040 |   1524.869 |
-       JSON::XS   |   5780.463 |   4854.519 |
+       JSON::XS      |  20661.596 |   9541.183 |
-       JSON::XS/2 |   3869.998 |   4798.975 |
+       JSON::XS/2    |  10683.403 |   9416.938 |
-       JSON::XS/3 |   5862.880 |   4798.975 |
+       JSON::XS/3    |  20661.596 |   9400.054 |
-       Storable   |   4445.002 |   5235.027 |
+       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
     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
     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
-    <http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
+    <http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/>
-    you are vulnerable to some common attack vectors (which really are
+    to see whether you are vulnerable to some common attack vectors (which
-    browser design bugs, but it is still you who will have to deal with it,
+    really are browser design bugs, but it is still you who will have to
-    as major browser developers care only for features, not about getting
+    deal with it, as major browser developers care only for features, not
-    security right).
+    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, 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 correcly (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 it's bug-free, only that I think its design is bug-free. If you
     keep reporting bugs they will be fixed swiftly, though.

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Comparing JSON-XS/README (file contents): Revision 1.26 by root, Tue Jun 3 06:43:45 2008 UTC vs. Revision 1.37 by root, Thu May 23 09:32:02 2013 UTC

Diff Legend

Comparing JSON-XS/README (file contents):
Revision 1.26 by root, Tue Jun 3 06:43:45 2008 UTC vs.
Revision 1.37 by root, Thu May 23 09:32:02 2013 UTC