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

Comparing JSON-XS/README (file contents):
Revision 1.23 by root, Wed Mar 19 22:31:00 2008 UTC vs.
Revision 1.29 by root, Thu Feb 19 01:13:46 2009 UTC

     primary goal is to be *correct* and its secondary goal is to be *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
+    be 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.
   FEATURES
     *   correct Unicode handling
         This module knows how to handle Unicode, documents how and when it
         does so, and even documents what "correct" means.
     *   round-trip integrity
-        When you serialise a perl data structure using only datatypes
+        When you serialise a perl data structure using only data types
         supported by JSON, the deserialised data structure is identical on
         the Perl level. (e.g. the string "2.0" doesn't suddenly become "2"
         just because it looks like a number). There minor *are* exceptions
         to this, read the MAPPING section below to learn about those.
         too.
     *   simple to use
         This module has both a simple functional interface as well as an
-        objetc oriented interface interface.
+        object oriented interface interface.
     *   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.
         This function call is functionally identical to:
            $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
-        except being faster.
+        Except being faster.
     $perl_scalar = decode_json $json_text
         The opposite of "encode_json": expects an UTF-8 (binary) string and
         tries to parse that as an UTF-8 encoded JSON text, returning the
         resulting reference. Croaks on error.
         This function call is functionally identical to:
            $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
-        except being faster.
+        Except being faster.
     $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 1 and 0,
         respectively and are used to represent JSON "true" and "false"
         If you didn't know about that flag, just the better, pretend it
         doesn't exist.
     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.
     5. A string containing "high" (> 255) character values is *not* a UTF-8
     string.
         Example, encode a Perl scalar as JSON value with enabled
         "allow_nonref", resulting in an invalid JSON text:
            JSON::XS->new->allow_nonref->encode ("Hello, World!")
            => "Hello, World!"
+    $json = $json->allow_unknown ([$enable])
+    $enabled = $json->get_allow_unknown
+        If $enable is true (or missing), then "encode" will *not* throw an
+        exception when it encounters values it cannot represent in JSON (for
+        example, filehandles) but instead will encode a JSON "null" value.
+        Note that blessed objects are not included here and are handled
+        separately by c<allow_nonref>.
+        If $enable is false (the default), then "encode" will throw an
+        exception when it encounters anything it cannot encode as JSON.
+        This option does not affect "decode" in any way, and it is
+        recommended to leave it off unless you know your communications
+        partner.
     $json = $json->allow_blessed ([$enable])
     $enabled = $json->get_allow_blessed
         If $enable is true (or missing), then the "encode" method will not
         barf when it encounters a blessed reference. Instead, the value of
         saving space.
     $json = $json->max_depth ([$maximum_nesting_depth])
     $max_depth = $json->get_max_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
+        or decoding. If a higher nesting level is detected in JSON text or a
-        higher nesting level then this limit, then the encoder and decoder
+        Perl data structure, then the encoder and decoder will stop and
-        will stop and croak at that point.
+        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 highest
-        power of two. If no argument is given, the highest possible setting
+        If no argument is given, the highest possible setting will be used,
-        will be used, which is rarely useful.
+        which 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.
     $json = $json->max_size ([$maximum_string_size])
     $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 0, meaning no limit.
-        When "decode" is called on a string longer then this number of
+        When "decode" is called on a string that is longer then this many
-        characters it will not attempt to decode the string but throw an
+        bytes, it will not attempt to decode the string but throw an
         exception. This setting has no effect on "encode" (yet).
-        The argument to "max_size" will be rounded up to the next highest
-        power of two (so may be more than requested). If no argument is
-        given, the limit check will be deactivated (same as when 0 is
+        If no argument is given, the limit check will be deactivated (same
-        specified).
+        as when 0 is specified).
         See SECURITY CONSIDERATIONS, below, for more info on why this is
         useful.
     $json_text = $json->encode ($perl_scalar)
         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)
+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 "decode_prefix" to see if a full JSON object is available, but is
+    much more efficient (and can be implemented with a minimum of method
+    calls).
+    JSON::XS will only attempt to parse the JSON text once it is sure it has
+    enough text to get a decisive result, using a very simple but truly
+    incremental parser. This means that it sometimes won't stop as early as
+    the full parser, for example, it doesn't detect parenthese mismatches.
+    The only thing it guarantees is that it starts decoding as soon as a
+    syntactically valid JSON text has been seen. This means you need to set
+    resource limits (e.g. "max_size") to ensure the parser will stop parsing
+    in the presence if syntax errors.
+    The following methods implement this incremental parser.
+    [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 $string is given, then this string is appended to the already
+        existing JSON fragment stored in the $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 *one* JSON object. If that is successful, it will
+        return this object, otherwise it will return "undef". If there is a
+        parse error, this method will croak just as "decode" would do (one
+        can then use "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.
+    $lvalue_string = $json->incr_text
+        This method returns the currently stored JSON fragment as an lvalue,
+        that is, you can manipulate it. This *only* works when a preceding
+        call to "incr_parse" in *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 *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).
+    $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
+        "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 "incr_reset" is that only text until the parse
+        error occured is removed.
+    $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.
+  LIMITATIONS
+    All options that affect decoding are supported, except "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 1 a single JSON number, or is it simply the
+    start of 12? Or is 12 a single JSON number, or the concatenation of 1
+    and 2? In neither case you can tell, and this is why JSON::XS takes the
+    conservative route and disallows this case.
+  EXAMPLES
+    Some examples will make all this clearer. First, a simple example that
+    works similarly to "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 "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. "[1],[2],
+    [3]"). To parse them, we have to skip the commas between the JSON texts,
+    and here is where the lvalue-ness of "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 :).
 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
         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.
-           encode_json [\0,JSON::XS::true]      # yields [false,true]
+           encode_json [\0, JSON::XS::true]      # yields [false,true]
     JSON::XS::true, JSON::XS::false
         These special values become JSON true and JSON false values,
         respectively. You can also use "\1" and "\0" directly if you want.
            $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 :).
+        it's needed :).
 ENCODING/CODESET FLAG NOTES
     The interested reader might have seen a number of flags that signify
     encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
     some confusion on what these do, so here is a short comparison:
-    "utf8" controls wether the JSON text created by "encode" (and expected
+    "utf8" controls whether the JSON text created by "encode" (and expected
     by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
-    control wether "encode" escapes character values outside their
+    control whether "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
     "encode" and "decode", that is, texts encoded with any combination of
         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.
-COMPARISON
+  JSON and ECMAscript
-    As already mentioned, this module was created because none of the
+    JSON syntax is based on how literals are represented in javascript (the
-    existing JSON modules could be made to work correctly. First I will
+    not-standardised predecessor of ECMAscript) which is presumably why it
-    describe the problems (or pleasures) I encountered with various existing
+    is called "JavaScript Object Notation".
-    JSON modules, followed by some benchmark values. JSON::XS was designed
-    not to suffer from any of these problems or limitations.
-    JSON 2.xx
+    However, JSON is not a subset (and also not a superset of course) of
-        A marvellous piece of engineering, this module either uses JSON::XS
+    ECMAscript (the standard) or javascript (whatever browsers actually
-        directly when available (so will be 100% compatible with it,
+    implement).
-        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
+    If you want to use javascript's "eval" function to "parse" JSON, you
-        very hard to work even with ancient Perl versions, while JSON::XS
+    might run into parse errors for valid JSON texts, or the resulting data
-        does not.
+    structure might not be queryable:
-    JSON 1.07
+    One of the problems is that U+2028 and U+2029 are valid characters
-        Slow (but very portable, as it is written in pure Perl).
+    inside JSON strings, but are not allowed in ECMAscript string literals,
+    so the following Perl fragment will not output something that can be
+    guaranteed to be parsable by javascript's "eval":
-        Undocumented/buggy Unicode handling (how JSON handles Unicode values
+       use JSON::XS;
-        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,
+       print encode_json [chr 0x2028];
-        e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that
-        will decode into the number 2.
-    JSON::PC 0.01
+    The right fix for this is to use a proper JSON parser in your javascript
-        Very fast.
+    programs, and not rely on "eval" (see for example Douglas Crockford's
+    json2.js parser).
-        Undocumented/buggy Unicode handling.
+    If this is not an option, you can, as a stop-gap measure, simply encode
+    to ASCII-only JSON:
-        No round-tripping.
+       use JSON::XS;
-        Has problems handling many Perl values (e.g. regex results and other
+       print JSON::XS->new->ascii->encode ([chr 0x2028]);
-        magic values will make it croak).
-        Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}"
+    Note that this will enlarge the resulting JSON text quite a bit if you
-        which is not a valid JSON text.
+    have many non-ASCII characters. You might be tempted to run some regexes
+    to only escape U+2028 and U+2029, e.g.:
-        Unmaintained (maintainer unresponsive for many months, bugs are not
+       # DO NOT USE THIS!
-        getting fixed).
+       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;
-    JSON::Syck 0.21
+    Note that *this is a bad idea*: the above only works for U+2028 and
-        Very buggy (often crashes).
+    U+2029 and thus only for fully ECMAscript-compliant parsers. Many
+    existing javascript implementations, however, have issues with other
+    characters as well - using "eval" naively simply *will* cause problems.
-        Very inflexible (no human-readable format supported, format pretty
+    Another problem is that some javascript implementations reserve some
-        much undocumented. I need at least a format for easy reading by
+    property names for their own purposes (which probably makes them
-        humans and a single-line compact format for use in a protocol, and
+    non-ECMAscript-compliant). For example, Iceweasel reserves the
-        preferably a way to generate ASCII-only JSON texts).
+    "__proto__" property name for it's own purposes.
-        Completely broken (and confusingly documented) Unicode handling
+    If that is a problem, you could parse try to filter the resulting JSON
-        (Unicode escapes are not working properly, you need to set
+    output for these property strings, e.g.:
-        ImplicitUnicode to *different* values on en- and decoding to get
-        symmetric behaviour).
-        No round-tripping (simple cases work, but this depends on whether
+       $json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
-        the scalar value was used in a numeric context or not).
-        Dumping hashes may skip hash values depending on iterator state.
+    This works because "__proto__" is not valid outside of strings, so every
+    occurence of ""__proto__"\s*:" must be a string used as property name.
-        Unmaintained (maintainer unresponsive for many months, bugs are not
+    If you know of other incompatibilities, please let me know.
-        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).
-    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.
   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 (as of the time of this
     writing), so let me state it clearly: *in general, there is no way to
     First comes a comparison between various modules using a very short
     single-line JSON string (also available at
     <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:
 THREADS
     This module is *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 *much* faster, cheaper, better).
+    process simulations - use fork, it's *much* faster, cheaper, better).
     (It might actually work, but you have been warned).
 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 will be fixed swiftly, though.
+    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.
+SEE ALSO
+    The json_xs command line utility for quick experiments.
 AUTHOR
      Marc Lehmann <schmorp@schmorp.de>
      http://home.schmorp.de/

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Comparing JSON-XS/README (file contents): Revision 1.23 by root, Wed Mar 19 22:31:00 2008 UTC vs. Revision 1.29 by root, Thu Feb 19 01:13:46 2009 UTC

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Comparing JSON-XS/README (file contents):
Revision 1.23 by root, Wed Mar 19 22:31:00 2008 UTC vs.
Revision 1.29 by root, Thu Feb 19 01:13:46 2009 UTC