[ViewVC] Diff of: cvs/JSON-XS/README

Comparing JSON-XS/README (file contents):
Revision 1.4 by root, Fri Mar 23 18:33:50 2007 UTC vs.
Revision 1.12 by root, Wed Jun 6 18:17:13 2007 UTC

     JSON::XS - JSON serialising/deserialising, done correctly and fast
 SYNOPSIS
      use JSON::XS;
-     # exported functions, croak on error
+     # exported functions, they croak on error
+     # and expect/generate UTF-8
      $utf8_encoded_json_text = to_json $perl_hash_or_arrayref;
      $perl_hash_or_arrayref  = from_json $utf8_encoded_json_text;
+     # objToJson and jsonToObj aliases to to_json and from_json
+     # are exported for compatibility to the JSON module,
+     # but should not be used in new code.
-     # oo-interface
+     # OO-interface
      $coder = JSON::XS->new->ascii->pretty->allow_nonref;
      $pretty_printed_unencoded = $coder->encode ($perl_scalar);
      $perl_scalar = $coder->decode ($unicode_json_text);
     See MAPPING, below, on how JSON::XS maps perl values to JSON values and
     vice versa.
   FEATURES
-    * correct handling of unicode issues
+    * correct unicode handling
         This module knows how to handle Unicode, and even documents how and
         when it does so.
     * round-trip integrity
         When you serialise a perl data structure using only datatypes
         supported by JSON, the deserialised data structure is identical on
-        the Perl level. (e.g. the string "2.0" doesn't suddenly become "2").
+        the Perl level. (e.g. the string "2.0" doesn't suddenly become "2"
+        just because it looks like a number).
     * strict checking of JSON correctness
-        There is no guessing, no generating of illegal JSON strings by
+        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 feature).
     * fast
         Compared to other JSON modules, this module compares favourably in
         interface.
     * reasonably versatile output formats
         You can choose between the most compact guarenteed single-line
         format possible (nice for simple line-based protocols), a pure-ascii
-        format (for when your transport is not 8-bit clean), or a
+        format (for when your transport is not 8-bit clean, still supports
-        pretty-printed format (for when you want to read that stuff). Or you
+        the whole unicode range), or a pretty-printed format (for when you
-        can combine those features in whatever way you like.
+        want to read that stuff). Or you can combine those features in
+        whatever way you like.
 FUNCTIONAL INTERFACE
     The following convinience methods are provided by this module. They are
     exported by default:
-    $json_string = to_json $perl_scalar
+    $json_text = to_json $perl_scalar
         Converts the given Perl data structure (a simple scalar or a
         reference to a hash or array) to a UTF-8 encoded, binary string
         (that is, the string contains octets only). Croaks on error.
-        This function call is functionally identical to
+        This function call is functionally identical to:
-        "JSON::XS->new->utf8->encode ($perl_scalar)".
+           $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
+        except being faster.
-    $perl_scalar = from_json $json_string
+    $perl_scalar = from_json $json_text
         The opposite of "to_json": expects an UTF-8 (binary) string and
-        tries to parse that as an UTF-8 encoded JSON string, returning the
+        tries to parse that as an UTF-8 encoded JSON text, returning the
         resulting simple scalar or reference. Croaks on error.
-        This function call is functionally identical to
+        This function call is functionally identical to:
-        "JSON::XS->new->utf8->decode ($json_string)".
+           $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
+        except being faster.
 OBJECT-ORIENTED INTERFACE
     The object oriented interface lets you configure your own encoding or
     decoding style, within the limits of supported formats.
         *disabled*.
         The mutators for flags all return the JSON object again and thus
         calls can be chained:
-           my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]})
+           my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
            => {"a": [1, 2]}
     $json = $json->ascii ([$enable])
         If $enable is true (or missing), then the "encode" method will not
-        generate characters outside the code range 0..127. Any unicode
+        generate characters outside the code range 0..127 (which is ASCII).
-        characters outside that range will be escaped using either a single
+        Any unicode characters outside that range will be escaped using
-        \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
+        either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
-        as per RFC4627.
+        escape sequence, as per RFC4627. The resulting encoded JSON text can
+        be treated as a native unicode string, an ascii-encoded,
+        latin1-encoded or UTF-8 encoded string, or any other superset of
+        ASCII.
         If $enable is false, then the "encode" method will not escape
-        Unicode characters unless necessary.
+        Unicode characters unless required by the JSON syntax or other
+        flags. This results in a faster and more compact format.
+        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)
+          JSON::XS->new->ascii (1)->encode ([chr 0x10401])
-          => \ud801\udc01
+          => ["\ud801\udc01"]
+    $json = $json->latin1 ([$enable])
+        If $enable is true (or missing), then the "encode" method will
+        encode the resulting JSON text as latin1 (or iso-8859-1), escaping
+        any characters outside the code range 0..255. The resulting string
+        can be treated as a latin1-encoded JSON text or a native unicode
+        string. The "decode" method will not be affected in any way by this
+        flag, as "decode" by default expects unicode, which is a strict
+        superset of latin1.
+        If $enable is false, then the "encode" method will not escape
+        Unicode characters unless required by the JSON syntax or other
+        flags.
+        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 transfering), a rare encoding for JSON. It is
+        therefore most useful when you want to store data structures known
+        to contain binary data efficiently in files or databases, not when
+        talking to other JSON encoders/decoders.
+          JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
+          => ["\x{89}\\u0abc"]    # (perl syntax, U+abc escaped, U+89 not)
     $json = $json->utf8 ([$enable])
         If $enable is true (or missing), then the "encode" method will
-        encode the JSON string into UTF-8, as required by many protocols,
+        encode the JSON result into UTF-8, as required by many protocols,
         while the "decode" method expects to be handled an UTF-8-encoded
         string. Please note that UTF-8-encoded strings do not contain any
         characters outside the range 0..255, they are thus useful for
-        bytewise/binary I/O.
+        bytewise/binary I/O. In future versions, enabling this option might
+        enable autodetection of the UTF-16 and UTF-32 encoding families, as
+        described in RFC4627.
         If $enable is false, then the "encode" method will return the JSON
         string as a (non-encoded) unicode string, while "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.
-        Example, output UTF-16-encoded JSON:
+        Example, output UTF-16BE-encoded JSON:
+          use Encode;
+          $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
+        Example, decode UTF-32LE-encoded JSON:
+          use Encode;
+          $object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);
     $json = $json->pretty ([$enable])
         This enables (or disables) all of the "indent", "space_before" and
         "space_after" (and in the future possibly more) flags in one call to
         generate the most readable (or most compact) form possible.
         multiline format as output, putting every array member or
         object/hash key-value pair into its own line, identing them
         properly.
         If $enable is false, no newlines or indenting will be produced, and
-        the resulting JSON strings is guarenteed not to contain any
+        the resulting JSON text is guarenteed not to contain any "newlines".
-        "newlines".
-        This setting has no effect when decoding JSON strings.
+        This setting has no effect when decoding JSON texts.
     $json = $json->space_before ([$enable])
         If $enable is true (or missing), then the "encode" method will add
         an extra optional space before the ":" separating keys from values
         in JSON objects.
         If $enable is false, then the "encode" method will not add any extra
         space at those places.
-        This setting has no effect when decoding JSON strings. You will also
+        This setting has no effect when decoding JSON texts. You will also
         most likely combine this setting with "space_after".
         Example, space_before enabled, space_after and indent disabled:
            {"key" :"value"}
         pairs and array members.
         If $enable is false, then the "encode" method will not add any extra
         space at those places.
-        This setting has no effect when decoding JSON strings.
+        This setting has no effect when decoding JSON texts.
         Example, space_before and indent disabled, space_after enabled:
            {"key": "value"}
         If $enable is false, then the "encode" method will output key-value
         pairs in the order Perl stores them (which will likely change
         between runs of the same script).
         This option is useful if you want the same data structure to be
-        encoded as the same JSON string (given the same overall settings).
+        encoded as the same JSON text (given the same overall settings). If
-        If it is disabled, the same hash migh be encoded differently even if
+        it is disabled, the same hash migh 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 strings.
+        This setting has no effect when decoding JSON texts.
     $json = $json->allow_nonref ([$enable])
         If $enable is true (or missing), then the "encode" method can
         convert a non-reference into its corresponding string, number or
         null JSON value, which is an extension to RFC4627. Likewise,
         "decode" will accept those JSON values instead of croaking.
         If $enable is false, then the "encode" method will croak if it isn't
-        passed an arrayref or hashref, as JSON strings must either be an
+        passed an arrayref or hashref, as JSON texts must either be an
         object or array. Likewise, "decode" will croak if given something
         that is not a JSON object or array.
         Example, encode a Perl scalar as JSON value with enabled
         "allow_nonref", resulting in an invalid JSON text:
     $json = $json->shrink ([$enable])
         Perl usually over-allocates memory a bit when allocating space for
         strings. This flag optionally resizes strings generated by either
         "encode" or "decode" to their minimum size possible. This can save
-        memory when your JSON strings are either very very long or you have
+        memory when your JSON texts are either very very long or you have
         many short strings. It will also try to downgrade any strings to
         octet-form if possible: perl stores strings internally either in an
         encoding called UTF-X or in octet-form. The latter cannot store
-        everything but uses less space in general.
+        everything but uses less space in general (and some buggy Perl or C
+        code might even rely on that internal representation being used).
+        The actual definition of what shrink does might change in future
+        versions, but it will always try to save space at the expense of
+        time.
         If $enable is true (or missing), the string returned by "encode"
         will be shrunk-to-fit, while all strings generated by "decode" will
         also be shrunk-to-fit.
         In the future, this setting might control other things, such as
         converting strings that look like integers or floats into integers
         or floats internally (there is no difference on the Perl level),
         saving space.
+    $json = $json->max_depth ([$maximum_nesting_depth])
+        Sets the maximum nesting level (default 512) accepted while encoding
+        or decoding. If the JSON text or Perl data structure has an equal or
+        higher nesting level then this limit, then the encoder and decoder
+        will stop and croak at that 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
+        "{" or "[" 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 "max_depth" will be rounded up to the next nearest
+        power of two.
+        See SECURITY CONSIDERATIONS, below, for more info on why this is
+        useful.
-    $json_string = $json->encode ($perl_scalar)
+    $json_text = $json->encode ($perl_scalar)
         Converts the given Perl data structure (a simple scalar or a
         reference to a hash or array) to its JSON representation. Simple
         scalars will be 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. "undef")
         become JSON "null" values. Neither "true" nor "false" values will be
         generated.
-    $perl_scalar = $json->decode ($json_string)
+    $perl_scalar = $json->decode ($json_text)
-        The opposite of "encode": expects a JSON string and tries to parse
+        The opposite of "encode": expects a JSON text and tries to parse it,
-        it, returning the resulting simple scalar or reference. Croaks on
+        returning the resulting simple scalar or reference. Croaks on error.
-        error.
         JSON numbers and strings become simple Perl scalars. JSON arrays
         become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
         becomes 1, "false" becomes 0 and "null" becomes "undef".
+    ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
+        This works like the "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.
+           JSON::XS->new->decode_prefix ("[1] the tail")
+           => ([], 3)
 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
     refers to the abstract Perl language itself.
   JSON -> PERL
     object
         A JSON object becomes a reference to a hash in Perl. No ordering of
-        object keys is preserved.
+        object keys is preserved (JSON does not preserver object key
+        ordering itself).
     array
         A JSON array becomes a reference to an array in Perl.
     string
     truly typeless language, so we can only guess which JSON type is meant
     by a Perl value.
     hash references
         Perl hash references become JSON objects. As there is no inherent
-        ordering in hash keys, they will usually be encoded in a
+        ordering in hash keys (or JSON objects), they will usually be
-        pseudo-random order that can change between runs of the same program
+        encoded in a pseudo-random order that can change between runs of the
-        but stays generally the same within the single run of a program.
+        same program but stays generally the same within a single run of a
-        JSON::XS can optionally sort the hash keys (determined by the
+        program. JSON::XS can optionally sort the hash keys (determined by
-        *canonical* flag), so the same datastructure will serialise to the
+        the *canonical* flag), so the same datastructure will serialise to
-        same JSON text (given same settings and version of JSON::XS), but
+        the same JSON text (given same settings and version of JSON::XS),
-        this incurs a runtime overhead.
+        but this incurs a runtime overhead and is only rarely useful, e.g.
+        when you want to compare some JSON text against another for
+        equality.
     array references
         Perl array references become JSON arrays.
+    other references
+        Other unblessed references are generally not allowed and will cause
+        an exception to be thrown, except for references to the integers 0
+        and 1, which get turned into "false" and "true" atoms in JSON. You
+        can also use "JSON::XS::false" and "JSON::XS::true" to improve
+        readability.
+           to_json [\0,JSON::XS::true]      # yields [false,true]
     blessed objects
         Blessed objects are not allowed. JSON::XS currently tries to encode
         their underlying representation (hash- or arrayref), but this
         behaviour might change in future versions.
            $x *= 1;     # same thing, the choise is yours.
         You can not currently output JSON booleans or force the type in
         other, less obscure, ways. Tell me if you need this capability.
-    circular data structures
-        Those will be encoded until memory or stackspace runs out.
 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
         Has problems handling many Perl values (e.g. regex results and other
         magic values will make it croak).
         Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}"
-        which is not a valid JSON string.
+        which is not a valid JSON text.
         Unmaintained (maintainer unresponsive for many months, bugs are not
         getting fixed).
     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 strings).
+        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 *different* values on en- and decoding to get
         symmetric behaviour).
         Very inflexible.
         No roundtripping.
-        Does not generate valid JSON (key strings are often unquoted, empty
+        Does not generate valid JSON texts (key strings are often unquoted,
-        keys result in nothing being output)
+        empty keys result in nothing being output)
         Does not check input for validity.
   SPEED
     It seems that JSON::XS is surprisingly fast, as shown in the following
     tables. They have been generated with the help of the "eg/bench" program
     in the JSON::XS distribution, to make it easy to compare on your own
     system.
-    First is a comparison between various modules using a very simple JSON
+    First comes a comparison between various modules using a very short
+    single-line JSON string:
+       {"method": "handleMessage", "params": ["user1", "we were just talking"], \
+       "id": null, "array":[1,11,234,-5,1e5,1e7, true,  false]}
-    string, showing the number of encodes/decodes per second (JSON::XS is
+    It shows the number of encodes/decodes per second (JSON::XS uses the
-    the functional interface, while JSON::XS/2 is the OO interface with
+    functional interface, while JSON::XS/2 uses the OO interface with
-    pretty-printing and hashkey sorting enabled).
+    pretty-printing and hashkey sorting enabled). Higher is better:
        module     |     encode |     decode |
        -----------|------------|------------|
-       JSON       |      14006 |       6820 |
+       JSON       |   7645.468 |   4208.613 |
-       JSON::DWIW |     200937 |     120386 |
+       JSON::DWIW |  68534.379 |  79437.576 |
-       JSON::PC   |      85065 |     129366 |
+       JSON::PC   |  65948.176 |  78251.940 |
-       JSON::Syck |      59898 |      44232 |
+       JSON::Syck |  23379.621 |  28416.694 |
-       JSON::XS   |    1171478 |     342435 |
+       JSON::XS   | 388361.481 | 199728.762 |
-       JSON::XS/2 |     730760 |     328714 |
+       JSON::XS/2 | 218453.333 | 192399.266 |
+       JSON::XS/3 | 338250.323 | 192399.266 |
+       Storable   |  15732.573 |  28571.553 |
        -----------+------------+------------+
-    That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80
+    That is, JSON::XS is about five times faster than JSON::DWIW on
+    encoding, about three times faster on decoding, and over fourty times
-    times faster than JSON, even with pretty-printing and key sorting.
+    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 8KB, generated from Yahoo! Locals
+    Using a longer test string (roughly 18KB, generated from Yahoo! Locals
     search API (http://nanoref.com/yahooapis/mgPdGg):
        module     |     encode |     decode |
        -----------|------------|------------|
-       JSON       |        673 |         38 |
+       JSON       |    254.685 |     37.665 |
-       JSON::DWIW |       5271 |        770 |
+       JSON::DWIW |   1014.244 |   1087.678 |
-       JSON::PC   |       9901 |       2491 |
+       JSON::PC   |   3602.116 |   2307.352 |
-       JSON::Syck |       2360 |        786 |
+       JSON::Syck |    558.035 |    776.263 |
-       JSON::XS   |      37398 |       3202 |
+       JSON::XS   |   5747.196 |   3543.684 |
-       JSON::XS/2 |      13765 |       3153 |
+       JSON::XS/2 |   3968.121 |   3589.170 |
+       JSON::XS/3 |   6105.246 |   3561.134 |
+       Storable   |   4456.337 |   5320.020 |
        -----------+------------+------------+
-    Again, JSON::XS leads by far in the encoding case, while still beating
+    Again, JSON::XS leads by far.
-    every other module in the decoding case.
-RESOURCE LIMITS
+    On large strings containing lots of high unicode characters, some
-    JSON::XS does not impose any limits on the size of JSON texts or Perl
+    modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
-    values they represent - if your machine can handle it, JSON::XS will
+    result will be broken due to missing (or wrong) unicode handling. Others
-    encode or decode it. Future versions might optionally impose structure
+    refuse to decode or encode properly, so it was impossible to prepare a
-    depth and memory use resource limits.
+    fair comparison table for that case.
+SECURITY CONSIDERATIONS
+    When you are using JSON in a protocol, talking to untrusted potentially
+    hostile creatures requires relatively few measures.
+    First of all, your JSON decoder should be secure, that is, should not
+    have any buffer overflows. Obviously, this module should ensure that and
+    I am trying hard on making that true, but you never know.
+    Second, you need to avoid resource-starving attacks. That means you
+    should limit the size of JSON texts you accept, or make sure then when
+    your resources run out, thats just fine (e.g. by using a separate
+    process that can crash safely). The size of a JSON text in octets or
+    characters is usually a good indication of the size of the resources
+    required to decode it into a Perl structure.
+    Third, JSON::XS recurses using the C stack when decoding objects and
+    arrays. The C stack is a limited resource: for instance, on my amd64
+    machine with 8MB of stack size I can decode around 180k nested arrays
+    but only 14k nested JSON objects (due to perl itself recursing deeply on
+    croak to free the temporary). If that is exceeded, the program crashes.
+    to be conservative, the default nesting limit is set to 512. If your
+    process has a smaller stack, you should adjust this setting accordingly
+    with the "max_depth" method.
+    And last but least, something else could bomb you that I forgot to think
+    of. In that case, you get to keep the pieces. I am always open for
+    hints, though...
 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
-    still very young and not well-tested. If you keep reporting bugs they
+    still relatively early in its development. If you keep reporting bugs
-    will be fixed swiftly, though.
+    they will be fixed swiftly, though.
 AUTHOR
      Marc Lehmann <schmorp@schmorp.de>
      http://home.schmorp.de/

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Comparing JSON-XS/README (file contents): Revision 1.4 by root, Fri Mar 23 18:33:50 2007 UTC vs. Revision 1.12 by root, Wed Jun 6 18:17:13 2007 UTC

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Comparing JSON-XS/README (file contents):
Revision 1.4 by root, Fri Mar 23 18:33:50 2007 UTC vs.
Revision 1.12 by root, Wed Jun 6 18:17:13 2007 UTC