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

Comparing JSON-XS/XS.pm (file contents):
Revision 1.86 by root, Wed Mar 19 03:17:38 2008 UTC vs.
Revision 1.143 by root, Fri Oct 25 20:02:54 2013 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.
+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
 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.
+oriented 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;
-use strict;
+use common::sense;
-our $VERSION = '2.01';
+our $VERSION = 2.34;
 our @ISA = qw(Exporter);
-our @EXPORT = qw(encode_json decode_json to_json from_json);
+our @EXPORT = qw(encode_json decode_json);
-sub to_json($) {
-   require Carp;
-   Carp::croak ("JSON::XS::to_json has been renamed to encode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
-}
-sub from_json($) {
-   require Carp;
-   Carp::croak ("JSON::XS::from_json has been renamed to decode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
-}
 use Exporter;
 use XSLoader;
 =head1 FUNCTIONAL INTERFACE
 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 $scalar
 Returns true if the passed scalar represents either JSON::XS::true or
 JSON::XS::false, two constants that act like C<1> and C<0>, respectively
 If you didn't know about that flag, just the better, pretend it doesn't
 exist.
 =item 4. A "Unicode String" is simply a string where each character can be
-validly interpreted as a Unicode codepoint.
+validly interpreted as a Unicode code point.
 If you have UTF-8 encoded data, it is no longer a Unicode string, but a
 Unicode string encoded in UTF-8, giving you a binary string.
 =item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
 If C<$enable> is false, then the C<encode> method will not escape Unicode
 characters unless required by the JSON syntax or other flags. This results
 in a faster and more compact format.
+See also the section I<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.
   JSON::XS->new->ascii (1)->encode ([chr 0x10401])
 will not be affected in any way by this flag, as C<decode> by default
 expects Unicode, which is a strict superset of latin1.
 If C<$enable> is false, then the C<encode> method will not escape Unicode
 characters unless required by the JSON syntax or other flags.
+See also the section I<ENCODING/CODESET FLAG NOTES> later in this
+document.
 The main use for this flag is efficiently encoding binary data as JSON
 text, as most octets will not be escaped, resulting in a smaller encoded
 size. The disadvantage is that the resulting JSON text is encoded
 in latin1 (and must correctly be treated as such when storing and
 If C<$enable> is false, then the C<encode> method will return the JSON
 string as a (non-encoded) Unicode string, while C<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 I<ENCODING/CODESET FLAG NOTES> later in this
+document.
 Example, output UTF-16BE-encoded JSON:
   use Encode;
   $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
 If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
 by sorting their keys. This is adding a comparatively high overhead.
 If C<$enable> is false, then the C<encode> method will output key-value
 pairs in the order Perl stores them (which will likely change between runs
-of the same script).
+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.
 =item $json = $json->allow_nonref ([$enable])
 =item $enabled = $json->get_allow_nonref
 If C<$enable> is true (or missing), then the C<encode> method can convert a
 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)
-Converts the given Perl data structure (a simple scalar or a reference
+Converts the given Perl value or data structure to its JSON
-to a hash or array) to its JSON representation. Simple scalars will be
+representation. Croaks on error.
-converted into JSON string or number sequences, while references to arrays
-become JSON arrays and references to hashes become JSON objects. Undefined
-Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
-nor C<false> values will be generated.
 =item $perl_scalar = $json->decode ($json_text)
 The opposite of C<encode>: expects a JSON text and tries to parse it,
 returning the resulting simple scalar or reference. Croaks on error.
-JSON numbers and strings become simple Perl scalars. JSON arrays become
-Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
-C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
 =item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
 This works like the C<decode> method, but instead of raising an exception
 when there is trailing garbage after the first JSON object, it will
 silently stop parsing there and return the number of characters consumed
 so far.
 This is useful if your JSON texts are not delimited by an outer protocol
-(which is not the brightest thing to do in the first place) and you need
-to know where the JSON text ends.
+and you need to know where the JSON text ends.
    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 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. 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 erroneous 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.
+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
+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
+occurred 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
 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 (in
 which case you lose roundtripping ability, as the JSON number will be
-re-encoded toa JSON string).
+re-encoded to a JSON string).
 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 least 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
 =over 4
 =item hash references
-Perl hash references become JSON objects. As there is no inherent ordering
+Perl hash references become JSON objects. As there is no inherent
-in hash keys (or JSON objects), they will usually be encoded in a
+ordering in hash keys (or JSON objects), they will usually be encoded
-pseudo-random order that can change between runs of the same program but
+in a pseudo-random order. JSON::XS can optionally sort the hash keys
-stays generally the same within a single run of a program. JSON::XS can
+(determined by the I<canonical> flag), so the same datastructure will
-optionally sort the hash keys (determined by the I<canonical> flag), so
+serialise to the same JSON text (given same settings and version of
-the same datastructure will serialise to the same JSON text (given same
+JSON::XS), but this incurs a runtime overhead and is only rarely useful,
-settings and version of JSON::XS), but this incurs a runtime overhead
+e.g. when you want to compare some JSON text against another for equality.
-and is only rarely useful, e.g. when you want to compare some JSON text
-against another for equality.
 =item array references
 Perl array references become JSON arrays.
 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.
    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 choice is yours.
 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
+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
 The interested reader might have seen a number of flags that signify
 encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
 some confusion on what these do, so here is a short comparison:
-C<utf8> controls wether the JSON text created by C<encode> (and expected
+C<utf8> controls whether the JSON text created by C<encode> (and expected
 by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
-control wether C<encode> escapes character values outside their respective
+control whether C<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
 C<encode> and C<decode>, that is, texts encoded with any combination of
 =item C<utf8> flag disabled
 When C<utf8> is disabled (the default), then C<encode>/C<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
+characters are decoded as-is, no changes 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
 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> (see for example Douglas Crockford's
+F<json2.js> parser).
-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.
+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.:
-Undocumented/buggy Unicode handling.
+   # 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;
-No round-tripping.
+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.
-Has problems handling many Perl values (e.g. regex results and other magic
+Another problem is that some javascript implementations reserve
-values will make it croak).
+some property names for their own purposes (which probably makes
+them non-ECMAscript-compliant). For example, Iceweasel reserves the
+C<__proto__> property name for its own purposes.
-Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>
+If that is a problem, you could parse try to filter the resulting JSON
-which is not a valid JSON text.
+output for these property strings, e.g.:
-Unmaintained (maintainer unresponsive for many months, bugs are not
+   $json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
-getting fixed).
-=item JSON::Syck 0.21
+This works because C<__proto__> is not valid outside of strings, so every
+occurrence of C<"__proto__"\s*:> must be a string used as property name.
-Very buggy (often crashes).
+If you know of other incompatibilities, please let me know.
-Very inflexible (no human-readable format supported, format pretty much
-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
-escapes are not working properly, you need to set ImplicitUnicode to
-I<different> values on en- and decoding to get symmetric behaviour).
-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.
-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
-hysteria(*) and very far from the truth. In general, there is no way to
+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
-configure JSON::XS to output a data structure as valid YAML that works for
+JSON::XS to output a data structure as valid YAML> that works in all
-all cases.
+cases.
 If you really must use JSON::XS to generate YAML, you should use this
 algorithm (subject to change in future versions):
    my $to_yaml = JSON::XS->new->utf8->space_after (1);
    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 codepoints with values outside the Unicode BMP (basic
+and that you do not have characters with codepoint values outside the
-multilingual page). YAML also does not allow C<\/> sequences in strings
+Unicode BMP (basic multilingual page). YAML also does not allow C<\/>
-(which JSON::XS does not I<currently> generate).
+sequences in strings (which JSON::XS does not I<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
 =over 4
 =item (*)
-This is spread actively by the YAML team, however. For many years now they
+I have been pressured multiple times by Brian Ingerson (one of the
-claim YAML were a superset of JSON, even when proven otherwise.
+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)I<complete
+and worthless idiot>(unquote).
-Even the author of this manpage was at some point accused of providing
+In my opinion, instead of pressuring and insulting people who actually
-"incorrect" information, despite the evidence presented (claims ranged
+clarify issues with YAML and the wrong statements of some of its
-from "your documentation contains inaccurate and negative statements about
+proponents, I would kindly suggest reading the JSON spec (which is not
-YAML" (the only negative comment is this footnote, and it didn't exist
+that difficult or long) and finally make YAML compatible to it, and
-back then; the question on which claims were inaccurate was never answered
+educating users about the changes, instead of spreading lies about the
-etc.) to "the YAML spec is not up-to-date" (the *real* and supposedly
+real compatibility for many I<years> and trying to silence people who
-JSON-compatible spec is apparently not currently publicly available)
+point out that it isn't true.
-to actual requests to replace this section by *incorrect* information,
-suppressing information about the real problem).
-So whenever you are told that YAML was a superset of JSON, first check
+Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, even
-wether it is really true (it might be when you check it, but it certainly
+though the incompatibilities have been documented (and are known to Brian)
-was not true when this was written). I would much prefer if the YAML team
+for many years and the spec makes explicit claims that YAML is a superset
-would spent their time on actually making JSON compatibility a truth
+of JSON. It would be so easy to fix, but apparently, bullying people and
-(JSON, after all, has a very small and simple specification) instead of
+corrupting userdata is so much easier.
-trying to lobby/force people into reporting untruths.
 =back
 =head2 SPEED
 It seems that JSON::XS is surprisingly fast, as shown in the following
 tables. They have been generated with the help of the C<eg/bench> program
 in the JSON::XS distribution, to make it easy to compare on your own
 system.
-First comes a comparison between various modules using a very short
+First comes a comparison between various modules using
-single-line JSON string:
+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,
+   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 (http://nanoref.com/yahooapis/mgPdGg):
+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
 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 I<much> faster, cheaper, better).
+process simulations - use fork, it's I<much> faster, cheaper, better).
 (It might actually work, but you have been warned).
+=head1 THE PERILS OF SETLOCALE
+Sometimes people avoid the Perl locale support and directly call the
+system's setlocale function with C<LC_ALL>.
+This breaks both perl and modules such as JSON::XS, as stringification of
+numbers no longer works correctly (e.g. C<$x = 0.1; print "$x"+1> might
+print C<1>, and JSON::XS might output illegal JSON as JSON::XS relies on
+perl to stringify numbers).
+The solution is simple: don't call C<setlocale>, or use it for only those
+categories you need, such as C<LC_MESSAGES> or C<LC_CTYPE>.
+If you need C<LC_NUMERIC>, you should enable it only around the code that
+actually needs it (avoiding stringification of numbers), and restore it
+afterwards.
 =head1 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
+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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Revision 1.143 by root, Fri Oct 25 20:02:54 2013 UTC