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

Comparing JSON-XS/XS.pm (file contents):
Revision 1.87 by root, Wed Mar 19 13:25:26 2008 UTC vs.
Revision 1.95 by root, Tue Mar 25 16:56:09 2008 UTC

+=head1 NAME
 =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)
 package JSON::XS;
 use strict;
-our $VERSION = '2.01';
+our $VERSION = '2.1';
 our @ISA = qw(Exporter);
 our @EXPORT = qw(encode_json decode_json to_json from_json);
 sub to_json($) {
 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);
    => ([], 3)
 =back
+=head1 INCREMENTAL PARSING
+[This section 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>. 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.
+=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).
+=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
 vice versa. These mappings are designed to "do the right thing" in most
 circumstances automatically, preserving round-tripping characteristics
    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
 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
 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);
 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
 noticeably shorter than the 1024 "stream characters" YAML allows and that
-you do not have codepoints with values outside the Unicode BMP (basic
+you do not have characters with codepoint values outside the Unicode BMP
-multilingual page). YAML also does not allow C<\/> sequences in strings
+(basic multilingual page). YAML also does not allow C<\/> sequences in
-(which JSON::XS does not I<currently> generate).
+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
-wether it is really true (it might be when you check it, but it certainly
-was not true when this was written). I would much prefer if the YAML team
-would spent their time on actually making JSON compatibility a truth
-(JSON, after all, has a very small and simple specification) instead of
-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"], \
    "id": null, "array":[1,11,234,-5,1e5,1e7, true,  false]}
 It shows the number of encodes/decodes per second (JSON::XS uses
 about three times faster on decoding, and over forty times faster
 than JSON, even with pretty-printing and key sorting. It also compares
 favourably to Storable for small amounts of data.
 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
-search API (http://dist.schmorp.de/misc/yahoo.json).
+search API (L<http://dist.schmorp.de/misc/json/long.json>).
    module     |     encode |     decode |
    -----------|------------|------------|
    JSON 1.x   |     55.260 |     34.971 |
    JSON::DWIW |    825.228 |   1082.513 |
 =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. It is
 still relatively early in its development. If you keep reporting bugs they
 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.
    "--"     => 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 1.87 by root, Wed Mar 19 13:25:26 2008 UTC vs. Revision 1.95 by root, Tue Mar 25 16:56:09 2008 UTC

Diff Legend

Comparing JSON-XS/XS.pm (file contents):
Revision 1.87 by root, Wed Mar 19 13:25:26 2008 UTC vs.
Revision 1.95 by root, Tue Mar 25 16:56:09 2008 UTC