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

Comparing JSON-XS/XS.pm (file contents):
Revision 1.90 by root, Wed Mar 19 22:28:43 2008 UTC vs.
Revision 1.103 by root, Tue Apr 29 16:07:56 2008 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
 package JSON::XS;
 use strict;
-our $VERSION = '2.1';
+our $VERSION = '2.2';
 our @ISA = qw(Exporter);
 our @EXPORT = qw(encode_json decode_json to_json from_json);
 sub to_json($) {
 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
+[This section and the API it details is still EXPERIMENTAL]
+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 (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).
+The following two methods deal with this.
+=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. 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.
+=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
    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
 :).
 =back
 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
 as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
 8-bit-encoding, and still get the same data structure back. This is useful
 when your channel for JSON transfer is not 8-bit clean or the encoding
 might be mangled in between (e.g. in mail), and works because ASCII is a
 proper subset of most 8-bit and multibyte encodings in use in the world.
-=back
-=head1 COMPARISON
-As already mentioned, this module was created because none of the existing
-JSON modules could be made to work correctly. First I will describe the
-problems (or pleasures) I encountered with various existing JSON modules,
-followed by some benchmark values. JSON::XS was designed not to suffer
-from any of these problems or limitations.
-=over 4
-=item JSON 2.xx
-A marvellous piece of engineering, this module either uses JSON::XS
-directly when available (so will be 100% compatible with it, including
-speed), or it uses JSON::PP, which is basically JSON::XS translated to
-Pure Perl, which should be 100% compatible with JSON::XS, just a bit
-slower.
-You cannot really lose by using this module, especially as it tries very
-hard to work even with ancient Perl versions, while JSON::XS does not.
-=item JSON 1.07
-Slow (but very portable, as it is written in pure Perl).
-Undocumented/buggy Unicode handling (how JSON handles Unicode values is
-undocumented. One can get far by feeding it Unicode strings and doing
-en-/decoding oneself, but Unicode escapes are not working properly).
-No round-tripping (strings get clobbered if they look like numbers, e.g.
-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
-Very fast.
-Undocumented/buggy Unicode handling.
-No round-tripping.
-Has problems handling many Perl values (e.g. regex results and other magic
-values will make it croak).
-Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>
-which is not a valid JSON text.
-Unmaintained (maintainer unresponsive for many months, bugs are not
-getting fixed).
-=item JSON::Syck 0.21
-Very buggy (often crashes).
-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
 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 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 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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Comparing JSON-XS/XS.pm (file contents): Revision 1.90 by root, Wed Mar 19 22:28:43 2008 UTC vs. Revision 1.103 by root, Tue Apr 29 16:07:56 2008 UTC

Diff Legend

Comparing JSON-XS/XS.pm (file contents):
Revision 1.90 by root, Wed Mar 19 22:28:43 2008 UTC vs.
Revision 1.103 by root, Tue Apr 29 16:07:56 2008 UTC