[ViewVC] Diff of: cvs/JSON-XS/XS.pm

Comparing JSON-XS/XS.pm (file contents):
Revision 1.107 by root, Tue Jun 3 06:43:45 2008 UTC vs.
Revision 1.133 by root, Tue Aug 17 23:27:36 2010 UTC

 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.
 =head2 FEATURES
 so, and even documents what "correct" means.
 =item * round-trip integrity
 When you serialise a perl data structure using only data types supported
-by JSON, the deserialised data structure is identical on the Perl level.
+by JSON and Perl, the deserialised data structure is identical on the Perl
-(e.g. the string "2.0" doesn't suddenly become "2" just because it looks
+level. (e.g. the string "2.0" doesn't suddenly become "2" just because
-like a number). There minor I<are> exceptions to this, read the MAPPING
+it looks like a number). There I<are> minor exceptions to this, read the
-section below to learn about those.
+MAPPING section below to learn about those.
 =item * 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
 =cut
 package JSON::XS;
-use strict;
+use common::sense;
-our $VERSION = '2.21';
+our $VERSION = '2.3';
 our @ISA = qw(Exporter);
 our @EXPORT = qw(encode_json decode_json to_json from_json);
 sub to_json($) {
 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.
 =item $json = $json->allow_nonref ([$enable])
 =item $enabled = $json->get_allow_nonref
 In some cases, there is the need for incremental parsing of JSON
 texts. While this module always has to keep both JSON text and resulting
 Perl data structure in memory at one time, it does allow you to parse a
 JSON stream incrementally. It does so by accumulating text until it has
 a full JSON object, which it then can decode. This process is similar to
-using C<decode_prefix> to see if a full JSON object is available, but is
+using C<decode_prefix> to see if a full JSON object is available, but
-much more efficient (JSON::XS will only attempt to parse the JSON text
+is much more efficient (and can be implemented with a minimum of method
+calls).
+JSON::XS will only attempt to parse the JSON text once it is sure it
-once it is sure it has enough text to get a decisive result, using a very
+has enough text to get a decisive result, using a very simple but
-simple but truly incremental parser).
+truly incremental parser. This means that it sometimes won't stop as
+early as the full parser, for example, it doesn't detect parenthese
+mismatches. 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. C<max_size>) to ensure the parser will stop
+parsing in the presence if syntax errors.
-The following two methods deal with this.
+The following methods implement this incremental parser.
 =over 4
 =item [void, scalar or list context] = $json->incr_parse ([$string])
 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]");
 =item $lvalue_string = $json->incr_text
 This method returns the currently stored JSON fragment as an lvalue, that
 is, you can manipulate it. This I<only> works when a preceding call to
 C<incr_parse> in I<scalar context> successfully returned an object. Under
 JSON object or b) parsing multiple JSON objects separated by non-JSON text
 (such as commas).
 =item $json->incr_skip
-This will reset the state of the incremental parser and will remove the
+This will reset the state of the incremental parser and will remove
-parsed text from the input buffer. This is useful after C<incr_parse>
+the parsed text from the input buffer so far. This is useful after
-died, in which case the input buffer and incremental parser state is left
+C<incr_parse> died, in which case the input buffer and incremental parser
-unchanged, to skip the text parsed so far and to reset the parse state.
+state is left unchanged, to skip the text parsed so far and to reset the
+parse state.
+The difference to C<incr_reset> is that only text until the parse error
+occured is removed.
 =item $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 to
+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.
 =back
 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.
 =item true, false
 These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
 respectively. They are overloaded to act almost exactly like the numbers
 C<1> and C<0>. You can check whether a scalar is a JSON boolean by using
 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.
 =back
 =head1 ENCODING/CODESET FLAG NOTES
 proper subset of most 8-bit and multibyte encodings in use in the world.
 =back
+=head2 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 C<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 C<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 C<eval> (see for example Douglas Crockford's
+F<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 I<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 C<eval> naively simply I<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
+C<__proto__> property name for it's 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 C<__proto__> is not valid outside of strings, so every
+occurence of C<"__proto__"\s*:> must be a string used as property name.
+If you know of other incompatibilities, please let me know.
 =head2 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: I<in general, there is no way to configure
    my $yaml = $to_yaml->encode ($ref) . "\n";
 This will I<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 that
+keys are noticeably shorter than the 1024 "stream characters" YAML allows
-you do not have characters with codepoint values outside the Unicode BMP
+and that you do not have characters with codepoint values outside the
-(basic multilingual page). YAML also does not allow C<\/> sequences in
+Unicode BMP (basic multilingual page). YAML also does not allow C<\/>
-strings (which JSON::XS does not I<currently> generate, but other JSON
+sequences in strings (which JSON::XS does not I<currently> generate, but
-generators might).
+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
 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 I<years> and trying to silence people who
 point out that it isn't true.
+Addendum/2009: the YAML 1.2 spec is still incomaptible 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 and
+corrupting userdata is so much easier.
 =back
 =head2 SPEED
 a very short single-line JSON string (also available at
 L<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). Higher is better:
+shrink. 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 encoding,
+That is, JSON::XS is almost six times faster than JSON::DWIW on encoding,
-about three times faster on decoding, and over forty times faster
+about five times faster on decoding, and over thirty to seventy times
-than JSON, even with pretty-printing and key sorting. It also compares
+faster than JSON's pure perl implementation. It also compares favourably
-favourably to Storable for small amounts of data.
+to Storable for small amounts of data.
 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
 search API (L<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 fair
 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
-L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
+L<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/> to
-you are vulnerable to some common attack vectors (which really are browser
+see whether you are vulnerable to some common attack vectors (which really
-design bugs, but it is still you who will have to deal with it, as major
+are browser design bugs, but it is still you who will have to deal with
-browser developers care only for features, not about getting security
+it, as major browser developers care only for features, not about getting
-right).
+security right).
 =head1 THREADS
 This module is I<not> guaranteed to be thread safe and there are no

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Comparing JSON-XS/XS.pm (file contents): Revision 1.107 by root, Tue Jun 3 06:43:45 2008 UTC vs. Revision 1.133 by root, Tue Aug 17 23:27:36 2010 UTC

Diff Legend

Comparing JSON-XS/XS.pm (file contents):
Revision 1.107 by root, Tue Jun 3 06:43:45 2008 UTC vs.
Revision 1.133 by root, Tue Aug 17 23:27:36 2010 UTC