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

Comparing JSON-XS/XS.pm (file contents):
Revision 1.91 by root, Thu Mar 20 02:11:21 2008 UTC vs.
Revision 1.116 by root, Tue Feb 17 23:41:20 2009 UTC

+=head1 NAME
+JSON::XS - JSON serialising/deserialising, done correctly and fast
 =encoding utf-8
-=head1 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)
 =head1 SYNOPSIS
 primary goal is to be I<correct> and its secondary goal is to be
 I<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
+overridden) with no overhead due to emulation (by inheriting 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.
 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
 This module knows how to handle Unicode, documents how and when it does
 so, and even documents what "correct" means.
 =item * round-trip integrity
-When you serialise a perl data structure using only datatypes supported
+When you serialise a perl data structure using only data types 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). There minor I<are> exceptions to this, read the MAPPING
 section below to learn about those.
 Compared to other JSON modules and other serialisers such as Storable,
 this module usually compares favourably in terms of speed, too.
 =item * simple to use
-This module has both a simple functional interface as well as an objetc
+This module has both a simple functional interface as well as an object
 oriented interface interface.
 =item * 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
+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 want to read that
 stuff). Or you can combine those features in whatever way you like.
 =back
 =cut
 package JSON::XS;
+no warnings;
 use strict;
-our $VERSION = '2.1';
+our $VERSION = '2.232';
 our @ISA = qw(Exporter);
 our @EXPORT = qw(encode_json decode_json to_json from_json);
 sub to_json($) {
 This function call is functionally identical to:
    $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
-except being faster.
+Except being faster.
 =item $perl_scalar = decode_json $json_text
 The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries
 to parse that as an UTF-8 encoded JSON text, returning the resulting
 This function call is functionally identical to:
    $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
-except being faster.
+Except being faster.
 =item $is_boolean = JSON::XS::is_bool $scalar
 Returns true if the passed scalar represents either JSON::XS::true or
 JSON::XS::false, two constants that act like C<1> and C<0>, respectively
 If you didn't know about that flag, just the better, pretend it doesn't
 exist.
 =item 4. A "Unicode String" is simply a string where each character can be
-validly interpreted as a Unicode codepoint.
+validly interpreted as a Unicode code point.
 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.
 =item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
 Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>,
 resulting in an invalid JSON text:
    JSON::XS->new->allow_nonref->encode ("Hello, World!")
    => "Hello, World!"
+=item $json = $json->allow_unknown ([$enable])
+=item $enabled = $json->get_allow_unknown
+If C<$enable> is true (or missing), then C<encode> will I<not> throw an
+exception when it encounters values it cannot represent in JSON (for
+example, filehandles) but instead will encode a JSON C<null> value. Note
+that blessed objects are not included here and are handled separately by
+c<allow_nonref>.
+If C<$enable> is false (the default), then C<encode> will throw an
+exception when it encounters anything it cannot encode as JSON.
+This option does not affect C<decode> in any way, and it is recommended to
+leave it off unless you know your communications partner.
 =item $json = $json->allow_blessed ([$enable])
 =item $enabled = $json->get_allow_blessed
 =item $json = $json->max_depth ([$maximum_nesting_depth])
 =item $max_depth = $json->get_max_depth
 Sets the maximum nesting level (default C<512>) accepted while encoding
-or decoding. If the JSON text or Perl data structure has an equal or
+or decoding. If a higher nesting level is detected in JSON text or a Perl
-higher nesting level then this limit, then the encoder and decoder will
+data structure, then the encoder and decoder will stop and croak at that
-stop and croak at that point.
+point.
 Nesting level is defined by number of hash- or arrayrefs that the encoder
 needs to traverse to reach a given point or the number of C<{> or C<[>
 characters without their matching closing parenthesis crossed to reach a
 given character in a string.
 Setting the maximum depth to one disallows any nesting, so that ensures
 that the object is only a single hash/object or array.
-The argument to C<max_depth> will be rounded up to the next highest power
-of two. If no argument is given, the highest possible setting will be
+If no argument is given, the highest possible setting will be used, which
-used, which is rarely useful.
+is rarely useful.
+Note that nesting is implemented by recursion in C. The default value has
+been chosen to be as large as typical operating systems allow without
+crashing.
 See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
 =item $json = $json->max_size ([$maximum_string_size])
 =item $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 C<0>, meaning no limit. When C<decode>
-is called on a string longer then this number of characters it will not
+is called on a string that is longer then this many bytes, it will not
 attempt to decode the string but throw an exception. This setting has no
 effect on C<encode> (yet).
-The argument to C<max_size> will be rounded up to the next B<highest>
+If no argument is given, the limit check will be deactivated (same as when
-power of two (so may be more than requested). If no argument is given, the
+C<0> is specified).
-limit check will be deactivated (same as when C<0> is specified).
 See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
 =item $json_text = $json->encode ($perl_scalar)
    JSON::XS->new->decode_prefix ("[1] the tail")
    => ([], 3)
 =back
+=head1 INCREMENTAL PARSING
+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 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
+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 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 methods implement this incremental parser.
+=over 4
+=item [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).
+If C<$string> is given, then this string is appended to the already
+existing JSON fragment stored in the C<$json> object.
+After that, if the function is called in void context, it will simply
+return without doing anything further. This can be used to add more text
+in as many chunks as you want.
+If the method is called in scalar context, then it will try to extract
+exactly I<one> JSON object. If that is successful, it will return this
+object, otherwise it will return C<undef>. If there is a parse error,
+this method will croak just as C<decode> would do (one can then use
+C<incr_skip> to skip the errornous part). This is the most common way of
+using the method.
+And finally, in list context, it will try to extract as many objects
+from the stream as it can find and return them, or the empty list
+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.
+=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
+all other circumstances you must not call this function (I mean it.
+although in simple tests it might actually work, it I<will> fail under
+real world conditions). As a special exception, you can also call this
+method before having parsed anything.
+This function is useful in two cases: a) finding the trailing text after a
+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 parsed text from the input buffer so far. This is useful after
+C<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 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 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
+=head2 LIMITATIONS
+All options that affect decoding are supported, except
+C<allow_nonref>. The reason for this is that it cannot be made to
+work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate
+them back to back and still decode them perfectly. This does not hold true
+for JSON numbers, however.
+For example, is the string C<1> a single JSON number, or is it simply the
+start of C<12>? Or is C<12> a single JSON number, or the concatenation
+of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
+takes the conservative route and disallows this case.
+=head2 EXAMPLES
+Some examples will make all this clearer. First, a simple example that
+works similarly to C<decode_prefix>: We want to decode the JSON object at
+the start of a string and identify the portion after the JSON object:
+   my $text = "[1,2,3] hello";
+   my $json = new JSON::XS;
+   my $obj = $json->incr_parse ($text)
+      or die "expected JSON object or array at beginning of string";
+   my $tail = $json->incr_text;
+   # $tail now contains " hello"
+Easy, isn't it?
+Now for a more complicated example: Imagine a hypothetical protocol where
+you read some requests from a TCP stream, and each request is a JSON
+array, without any separation between them (in fact, it is often useful to
+use newlines as "separators", as these get interpreted as whitespace at
+the start of the JSON text, which makes it possible to test said protocol
+with C<telnet>...).
+Here is how you'd do it (it is trivial to write this in an event-based
+manner):
+   my $json = new JSON::XS;
+   # read some data from the socket
+   while (sysread $socket, my $buf, 4096) {
+      # split and decode as many requests as possible
+      for my $request ($json->incr_parse ($buf)) {
+         # act on the $request
+      }
+   }
+Another complicated example: Assume you have a string with JSON objects
+or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
+[3]>). To parse them, we have to skip the commas between the JSON texts,
+and here is where the lvalue-ness of C<incr_text> comes in useful:
+   my $text = "[1],[2], [3]";
+   my $json = new JSON::XS;
+   # void context, so no parsing done
+   $json->incr_parse ($text);
+   # now extract as many objects as possible. note the
+   # use of scalar context so incr_text can be called.
+   while (my $obj = $json->incr_parse) {
+      # do something with $obj
+      # now skip the optional comma
+      $json->incr_text =~ s/^ \s* , //x;
+   }
+Now lets go for a very complex example: Assume that you have a gigantic
+JSON array-of-objects, many gigabytes in size, and you want to parse it,
+but you cannot load it into memory fully (this has actually happened in
+the real world :).
+Well, you lost, you have to implement your own JSON parser. But JSON::XS
+can still help you: You implement a (very simple) array parser and let
+JSON decode the array elements, which are all full JSON objects on their
+own (this wouldn't work if the array elements could be JSON numbers, for
+example):
+   my $json = new JSON::XS;
+   # open the monster
+   open my $fh, "<bigfile.json"
+      or die "bigfile: $!";
+   # first parse the initial "["
+   for (;;) {
+      sysread $fh, my $buf, 65536
+         or die "read error: $!";
+      $json->incr_parse ($buf); # void context, so no parsing
+      # Exit the loop once we found and removed(!) the initial "[".
+      # In essence, we are (ab-)using the $json object as a simple scalar
+      # we append data to.
+      last if $json->incr_text =~ s/^ \s* \[ //x;
+   }
+   # now we have the skipped the initial "[", so continue
+   # parsing all the elements.
+   for (;;) {
+      # in this loop we read data until we got a single JSON object
+      for (;;) {
+         if (my $obj = $json->incr_parse) {
+            # do something with $obj
+            last;
+         }
+         # add more data
+         sysread $fh, my $buf, 65536
+            or die "read error: $!";
+         $json->incr_parse ($buf); # void context, so no parsing
+      }
+      # in this loop we read data until we either found and parsed the
+      # separating "," between elements, or the final "]"
+      for (;;) {
+         # first skip whitespace
+         $json->incr_text =~ s/^\s*//;
+         # if we find "]", we are done
+         if ($json->incr_text =~ s/^\]//) {
+            print "finished.\n";
+            exit;
+         }
+         # if we find ",", we can continue with the next element
+         if ($json->incr_text =~ s/^,//) {
+            last;
+         }
+         # if we find anything else, we have a parse error!
+         if (length $json->incr_text) {
+            die "parse error near ", $json->incr_text;
+         }
+         # else add more data
+         sysread $fh, my $buf, 65536
+            or die "read error: $!";
+         $json->incr_parse ($buf); # void context, so no parsing
+      }
+This is a complex example, but most of the complexity comes from the fact
+that we are trying to be correct (bear with me if I am wrong, I never ran
+the above example :).
 =head1 MAPPING
 This section describes how JSON::XS maps Perl values to JSON values and
 Other unblessed references are generally not allowed and will cause an
 exception to be thrown, except for references to the integers C<0> and
 C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
 also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
-   encode_json [\0,JSON::XS::true]      # yields [false,true]
+   encode_json [\0, JSON::XS::true]      # yields [false,true]
 =item JSON::XS::true, JSON::XS::false
 These special values become JSON true and JSON false values,
 respectively. You can also use C<\1> and C<\0> directly if you want.
 proper subset of most 8-bit and multibyte encodings in use in the world.
 =back
-=head1 COMPARISON
+=head2 JSON and ECMAscript
-As already mentioned, this module was created because none of the existing
+JSON syntax is based on how literals are represented in javascript (the
-JSON modules could be made to work correctly. First I will describe the
+not-standardised predecessor of ECMAscript) which is presumably why it is
-problems (or pleasures) I encountered with various existing JSON modules,
+called "JavaScript Object Notation".
-followed by some benchmark values. JSON::XS was designed not to suffer
-from any of these problems or limitations.
-=over 4
+However, JSON is not a subset (and also not a superset of course) of
+ECMAscript (the standard) or javascript (whatever browsers actually
+implement).
-=item JSON 2.xx
+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:
-A marvellous piece of engineering, this module either uses JSON::XS
+One of the problems is that U+2028 and U+2029 are valid characters inside
-directly when available (so will be 100% compatible with it, including
+JSON strings, but are not allowed in ECMAscript string literals, so the
-speed), or it uses JSON::PP, which is basically JSON::XS translated to
+following Perl fragment will not output something that can be guaranteed
-Pure Perl, which should be 100% compatible with JSON::XS, just a bit
+to be parsable by javascript's C<eval>:
-slower.
-You cannot really lose by using this module, especially as it tries very
+   use JSON::XS;
-hard to work even with ancient Perl versions, while JSON::XS does not.
-=item JSON 1.07
+   print encode_json [chr 0x2028];
-Slow (but very portable, as it is written in pure Perl).
+The right fix for this is to use a proper JSON parser in your javascript
+programs, and not rely on C<eval>.
-Undocumented/buggy Unicode handling (how JSON handles Unicode values is
+If this is not an option, you can, as a stop-gap measure, simply encode to
-undocumented. One can get far by feeding it Unicode strings and doing
+ASCII-only JSON:
-en-/decoding oneself, but Unicode escapes are not working properly).
-No round-tripping (strings get clobbered if they look like numbers, e.g.
+   use JSON::XS;
-the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
-decode into the number 2.
-=item JSON::PC 0.01
+   print JSON::XS->new->ascii->encode ([chr 0x2028]);
-Very fast.
+And if you are concerned about the size of the resulting JSON text, you
+can run some regexes to only escape U+2028 and U+2029:
-Undocumented/buggy Unicode handling.
+   use JSON::XS;
-No round-tripping.
+   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;
-Has problems handling many Perl values (e.g. regex results and other magic
+This works because U+2028/U+2029 are not allowed outside of strings and
-values will make it croak).
+are not used for syntax, so replacing them unconditionally just works.
-Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>
+Note, however, that fixing the broken JSON parser is better than working
-which is not a valid JSON text.
+around it in every other generator. The above regexes should work well in
+other languages, as long as they operate on UTF-8. It is equally valid to
+replace all occurences of U+2028/2029 directly by their \\u-escaped forms
+in unicode texts, so they can simply be used to fix any parsers relying on
+C<eval> by first applying the regexes on the encoded texts.
-Unmaintained (maintainer unresponsive for many months, bugs are not
+Note also that the above only works for U+2028 and U+2029 and thus
-getting fixed).
+only for fully ECMAscript-compliant parsers. Many existing javascript
+implementations misparse other characters as well. Best rely on a good
+JSON parser, such as Douglas Crockfords F<json2.js>, which escapes the
+above and many more problematic characters properly before passing them
+into C<eval>.
-=item JSON::Syck 0.21
+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.
-Very buggy (often crashes).
+If that is a problem, you could parse try to filter the resulting JSON
+output for these property strings, e.g.:
-Very inflexible (no human-readable format supported, format pretty much
+   $json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
-undocumented. I need at least a format for easy reading by humans and a
-single-line compact format for use in a protocol, and preferably a way to
-generate ASCII-only JSON texts).
-Completely broken (and confusingly documented) Unicode handling (Unicode
+This works because C<__proto__> is not valid outside of strings, so every
-escapes are not working properly, you need to set ImplicitUnicode to
+occurence of C<"__proto__"\s*:> must be a string used as property name.
-I<different> values on en- and decoding to get symmetric behaviour).
-No round-tripping (simple cases work, but this depends on whether the scalar
+If you know of other incompatibilities, please let me know.
-value was used in a numeric context or not).
-Dumping hashes may skip hash values depending on iterator state.
-Unmaintained (maintainer unresponsive for many months, bugs are not
-getting fixed).
-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 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 extra unnecessary work and
-the transaction will still not succeed).
-=item JSON::DWIW 0.04
-Very fast. Very natural. Very nice.
-Undocumented Unicode handling (but the best of the pack. Unicode escapes
-still don't get parsed properly).
-Very inflexible.
-No round-tripping.
-Does not generate valid JSON texts (key strings are often unquoted, empty keys
-result in nothing being output)
-Does not check input for validity.
-=back
 =head2 JSON and YAML
 You often hear that JSON is a subset of YAML. This is, however, a mass
 First comes a comparison between various modules using
 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"], \
+   {"method": "handleMessage", "params": ["user1",
-   "id": null, "array":[1,11,234,-5,1e5,1e7, true,  false]}
+   "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
+   true,  false]}
 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:
 =head1 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. It is
+not mean it's bug-free, only that I think its design is bug-free. If you
-still relatively early in its development. If you keep reporting bugs they
+keep reporting bugs they will be fixed swiftly, though.
-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.
 =cut
    "--"     => sub { $_[0] = ${$_[0]} - 1 },
    fallback => 1;
 1;
+=head1 SEE ALSO
+The F<json_xs> command line utility for quick experiments.
 =head1 AUTHOR
  Marc Lehmann <schmorp@schmorp.de>
  http://home.schmorp.de/

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Comparing JSON-XS/XS.pm (file contents): Revision 1.91 by root, Thu Mar 20 02:11:21 2008 UTC vs. Revision 1.116 by root, Tue Feb 17 23:41:20 2009 UTC

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Comparing JSON-XS/XS.pm (file contents):
Revision 1.91 by root, Thu Mar 20 02:11:21 2008 UTC vs.
Revision 1.116 by root, Tue Feb 17 23:41:20 2009 UTC