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

Comparing JSON-XS/README (file contents):
Revision 1.38 by root, Tue Oct 29 00:36:18 2013 UTC vs.
Revision 1.43 by root, Thu Nov 15 23:07:55 2018 UTC

 DESCRIPTION
     This module converts Perl data structures to JSON and vice versa. Its
     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 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.
-    As this is the n-th-something JSON module on CPAN, what was the reason
-    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 MAPPING, below, on how JSON::XS maps perl values to JSON values and
     vice versa.
   FEATURES
            $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
         Except being faster.
     $perl_scalar = decode_json $json_text
-        The opposite of "encode_json": expects an UTF-8 (binary) string and
+        The opposite of "encode_json": expects a UTF-8 (binary) string and
-        tries to parse that as an UTF-8 encoded JSON text, returning the
+        tries to parse that as a 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)
     The object oriented interface lets you configure your own encoding or
     decoding style, within the limits of supported formats.
     $json = new JSON::XS
         Creates a new JSON::XS object that can be used to de/encode JSON
-        strings. All boolean flags described below are by default
+        strings. All boolean flags described below are by default *disabled*
-        *disabled*.
+        (with the exception of "allow_nonref", which defaults to *enabled*
+        since version 4.0).
         The mutators for flags all return the JSON object again and thus
         calls can be chained:
            my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
     $json = $json->utf8 ([$enable])
     $enabled = $json->get_utf8
         If $enable is true (or missing), then the "encode" method will
         encode the JSON result into UTF-8, as required by many protocols,
-        while the "decode" method expects to be handled an UTF-8-encoded
+        while the "decode" method expects to be handed a 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. In future versions, enabling this option might
         enable autodetection of the UTF-16 and UTF-32 encoding families, as
         described in RFC4627.
     $json = $json->relaxed ([$enable])
     $enabled = $json->get_relaxed
         If $enable is true (or missing), then "decode" will accept some
         extensions to normal JSON syntax (see below). "encode" will not be
-        affected in anyway. *Be aware that this option makes you accept
+        affected in any way. *Be aware that this option makes you accept
         invalid JSON texts as if they were valid!*. I suggest only to use
         this option to parse application-specific files written by humans
         (configuration files, resource files etc.)
         If $enable is false (the default), then "decode" will only accept
               [
                  1, # this comment not allowed in JSON
                     # neither this one...
               ]
+        *   literal ASCII TAB characters in strings
+            Literal ASCII TAB characters are now allowed in strings (and
+            treated as "\t").
+              [
+                 "Hello\tWorld",
+                 "Hello<TAB>World", # literal <TAB> would not normally be allowed
+              ]
     $json = $json->canonical ([$enable])
     $enabled = $json->get_canonical
         If $enable is true (or missing), then the "encode" method will
         output JSON objects by sorting their keys. This is adding a
         comparatively high overhead.
         This setting has currently no effect on tied hashes.
     $json = $json->allow_nonref ([$enable])
     $enabled = $json->get_allow_nonref
+        Unlike other boolean options, this opotion is enabled by default
+        beginning with version 4.0. See "SECURITY CONSIDERATIONS" for the
+        gory details.
         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 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
+        Example, encode a Perl scalar as JSON value without enabled
-        "allow_nonref", resulting in an invalid JSON text:
+        "allow_nonref", resulting in an error:
-           JSON::XS->new->allow_nonref->encode ("Hello, World!")
+           JSON::XS->new->allow_nonref (0)->encode ("Hello, World!")
-           => "Hello, World!"
+           => hash- or arrayref expected...
     $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
         this type of conversion.
         This setting has no effect on "decode".
     $json = $json->allow_tags ([$enable])
-    $enabled = $json->allow_tags
+    $enabled = $json->get_allow_tags
         See "OBJECT SERIALISATION" for details.
         If $enable is true (or missing), then "encode", upon encountering a
         blessed object, will check for the availability of the "FREEZE"
         method on the object's class. If found, it will be used to serialise
         If $enable is false (the default), then "encode" will not consider
         this type of conversion, and tagged JSON values will cause a parse
         error in "decode", as if tags were not part of the grammar.
+    $json->boolean_values ([$false, $true])
+    ($false, $true) = $json->get_boolean_values
+        By default, JSON booleans will be decoded as overloaded
+        $Types::Serialiser::false and $Types::Serialiser::true objects.
+        With this method you can specify your own boolean values for
+        decoding - on decode, JSON "false" will be decoded as a copy of
+        $false, and JSON "true" will be decoded as $true ("copy" here is the
+        same thing as assigning a value to another variable, i.e. "$copy =
+        $false").
+        Calling this method without any arguments will reset the booleans to
+        their default values.
+        "get_boolean_values" will return both $false and $true values, or
+        the empty list when they are set to the default.
     $json = $json->filter_json_object ([$coderef->($hashref)])
         When $coderef is specified, it will be called from "decode" each
         time it decodes a JSON object. The only argument is a reference to
-        the newly-created hash. If the code references returns a single
+        the newly-created hash. If the code reference returns a single
-        scalar (which need not be a reference), this value (i.e. a copy of
+        scalar (which need not be a reference), this value (or rather a copy
-        that scalar to avoid aliasing) is inserted into the deserialised
+        of it) is inserted into the deserialised data structure. If it
-        data structure. If it returns an empty list (NOTE: *not* "undef",
+        returns an empty list (NOTE: *not* "undef", which is a valid
-        which is a valid scalar), the original deserialised hash will be
+        scalar), the original deserialised hash will be inserted. This
-        inserted. This setting can slow down decoding considerably.
+        setting can slow down decoding considerably.
         When $coderef is omitted or undefined, any existing callback will be
         removed and "decode" will not change the deserialised hash in any
         way.
         This is useful if your JSON texts are not delimited by an outer
         protocol and you need to know where the JSON text ends.
            JSON::XS->new->decode_prefix ("[1] the tail")
-           => ([], 3)
+           => ([1], 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
         can then use "incr_skip" to skip the erroneous part). This is the
         most common way of using the method.
         And finally, in list context, it will try to extract as many objects
         from the stream as it can find and return them, or the empty list
-        otherwise. For this to work, there must be no separators between the
+        otherwise. For this to work, there must be no separators (other than
-        JSON objects or arrays, instead they must be concatenated
+        whitespace) between the JSON objects or arrays, instead they must be
-        back-to-back. If an error occurs, an exception will be raised as in
+        concatenated back-to-back. If an error occurs, an exception will be
-        the scalar context case. Note that in this case, any
+        raised as in the scalar context case. Note that in this case, any
         previously-parsed JSON texts will be lost.
         Example: Parse some JSON arrays/objects in a given string and return
         them.
         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.
+        That means you can only use this function to look at or manipulate
+        text before or after complete JSON objects, not while the parser is
+        in the middle of parsing a JSON object.
         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 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 incremental parser is a non-exact parser: it works by gathering as
-    The reason for this is that it cannot be made to work sensibly: JSON
+    much text as possible that *could* be a valid JSON text, followed by
-    objects and arrays are self-delimited, i.e. you can concatenate them
+    trying to decode it.
-    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
+    That means it sometimes needs to read more data than strictly necessary
-    start of 12? Or is 12 a single JSON number, or the concatenation of 1
+    to diagnose an invalid JSON text. For example, after parsing the
-    and 2? In neither case you can tell, and this is why JSON::XS takes the
+    following fragment, the parser *could* stop with an error, as this
-    conservative route and disallows this case.
+    fragment *cannot* be the beginning of a valid JSON text:
+       [,
+    In reality, hopwever, the parser might continue to read data until a
+    length limit is exceeded or it finds a closing bracket.
   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:
         more). These values and the paclkage/classname of the object will
         then be encoded as a tagged JSON value in the following format:
            ("classname")[FREEZE return values...]
+        e.g.:
+           ("URI")["http://www.google.com/"]
+           ("MyDate")[2013,10,29]
+           ("ImageData::JPEG")["Z3...VlCg=="]
         For example, the hypothetical "My::Object" "FREEZE" method might use
         the objects "type" and "id" members to encode the object:
            sub My::Object::FREEZE {
               my ($self, $serialiser) = @_;
         will expect your input strings to be encoded as UTF-8, that is, no
         "character" of the input string must have any value > 255, as UTF-8
         does not allow that.
         The "utf8" flag therefore switches between two modes: disabled means
-        you will get a Unicode string in Perl, enabled means you get an
+        you will get a Unicode string in Perl, enabled means you get a UTF-8
-        UTF-8 encoded octet/binary string in Perl.
+        encoded octet/binary string in Perl.
     "latin1" or "ascii" flags enabled
         With "latin1" (or "ascii") enabled, "encode" will escape characters
         with ordinal values > 255 (> 127 with "ascii") and encode the
         remaining characters as specified by the "utf8" flag.
     to see whether you are vulnerable to some common attack vectors (which
     really are browser design bugs, but it is still you who will have to
     deal with it, as major browser developers care only for features, not
     about getting security right).
+  "OLD" VS. "NEW" JSON (RFC4627 VS. RFC7159)
+    JSON originally required JSON texts to represent an array or object -
+    scalar values were explicitly not allowed. This has changed, and
+    versions of JSON::XS beginning with 4.0 reflect this by allowing scalar
+    values by default.
+    One reason why one might not want this is that this removes a
+    fundamental property of JSON texts, namely that they are self-delimited
+    and self-contained, or in other words, you could take any number of
+    "old" JSON texts and paste them together, and the result would be
+    unambiguously parseable:
+       [1,3]{"k":5}[][null] # four JSON texts, without doubt
+    By allowing scalars, this property is lost: in the following example, is
+    this one JSON text (the number 12) or two JSON texts (the numbers 1 and
+    2):
+       12    # could be 12, or 1 and 2
+    Another lost property of "old" JSON is that no lookahead is required to
+    know the end of a JSON text, i.e. the JSON text definitely ended at the
+    last "]" or "}" character, there was no need to read extra characters.
+    For example, a viable network protocol with "old" JSON was to simply
+    exchange JSON texts without delimiter. For "new" JSON, you have to use a
+    suitable delimiter (such as a newline) after every JSON text or ensure
+    you never encode/decode scalar values.
+    Most protocols do work by only transferring arrays or objects, and the
+    easiest way to avoid problems with the "new" JSON definition is to
+    explicitly disallow scalar values in your encoder and decoder:
+       $json_coder = JSON::XS->new->allow_nonref (0)
+    This is a somewhat unhappy situation, and the blame can fully be put on
+    JSON's inmventor, Douglas Crockford, who unilaterally changed the format
+    in 2006 without consulting the IETF, forcing the IETF to either fork the
+    format or go with it (as I was told, the IETF wasn't amused).
+RELATIONSHIP WITH I-JSON
+    JSON is a somewhat sloppily-defined format - it carries around obvious
+    Javascript baggage, such as not really defining number range, probably
+    because Javascript only has one type of numbers: IEEE 64 bit floats
+    ("binary64").
+    For this reaosn, RFC7493 defines "Internet JSON", which is a restricted
+    subset of JSON that is supposedly more interoperable on the internet.
+    While "JSON::XS" does not offer specific support for I-JSON, it of
+    course accepts valid I-JSON and by default implements some of the
+    limitations of I-JSON, such as parsing numbers as perl numbers, which
+    are usually a superset of binary64 numbers.
+    To generate I-JSON, follow these rules:
+    *   always generate UTF-8
+        I-JSON must be encoded in UTF-8, the default for "encode_json".
+    *   numbers should be within IEEE 754 binary64 range
+        Basically all existing perl installations use binary64 to represent
+        floating point numbers, so all you need to do is to avoid large
+        integers.
+    *   objects must not have duplicate keys
+        This is trivially done, as "JSON::XS" does not allow duplicate keys.
+    *   do not generate scalar JSON texts, use "->allow_nonref (0)"
+        I-JSON strongly requests you to only encode arrays and objects into
+        JSON.
+    *   times should be strings in ISO 8601 format
+        There are a myriad of modules on CPAN dealing with ISO 8601 - search
+        for "ISO8601" on CPAN and use one.
+    *   encode binary data as base64
+        While it's tempting to just dump binary data as a string (and let
+        "JSON::XS" do the escaping), for I-JSON, it's *recommended* to
+        encode binary data as base64.
+    There are some other considerations - read RFC7493 for the details if
+    interested.
 INTEROPERABILITY WITH OTHER MODULES
     "JSON::XS" uses the Types::Serialiser module to provide boolean
     constants. That means that the JSON true and false values will be
-    comaptible to true and false values of iother modules that do the same,
+    comaptible to true and false values of other modules that do the same,
     such as JSON::PP and CBOR::XS.
+INTEROPERABILITY WITH OTHER JSON DECODERS
+    As long as you only serialise data that can be directly expressed in
+    JSON, "JSON::XS" is incapable of generating invalid JSON output (modulo
+    bugs, but "JSON::XS" has found more bugs in the official JSON testsuite
+    (1) than the official JSON testsuite has found in "JSON::XS" (0)).
+    When you have trouble decoding JSON generated by this module using other
+    decoders, then it is very likely that you have an encoding mismatch or
+    the other decoder is broken.
+    When decoding, "JSON::XS" is strict by default and will likely catch all
+    errors. There are currently two settings that change this: "relaxed"
+    makes "JSON::XS" accept (but not generate) some non-standard extensions,
+    and "allow_tags" will allow you to encode and decode Perl objects, at
+    the cost of not outputting valid JSON anymore.
+  TAGGED VALUE SYNTAX AND STANDARD JSON EN/DECODERS
+    When you use "allow_tags" to use the extended (and also nonstandard and
+    invalid) JSON syntax for serialised objects, and you still want to
+    decode the generated When you want to serialise objects, you can run a
+    regex to replace the tagged syntax by standard JSON arrays (it only
+    works for "normal" package names without comma, newlines or single
+    colons). First, the readable Perl version:
+       # if your FREEZE methods return no values, you need this replace first:
+       $json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[\s*\]/[$1]/gx;
+       # this works for non-empty constructor arg lists:
+       $json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[/[$1,/gx;
+    And here is a less readable version that is easy to adapt to other
+    languages:
+       $json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/[$1,/g;
+    Here is an ECMAScript version (same regex):
+       json = json.replace (/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/g, "[$1,");
+    Since this syntax converts to standard JSON arrays, it might be hard to
+    distinguish serialised objects from normal arrays. You can prepend a
+    "magic number" as first array element to reduce chances of a collision:
+       $json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/["XU1peReLzT4ggEllLanBYq4G9VzliwKF",$1,/g;
+    And after decoding the JSON text, you could walk the data structure
+    looking for arrays with a first element of
+    "XU1peReLzT4ggEllLanBYq4G9VzliwKF".
+    The same approach can be used to create the tagged format with another
+    encoder. First, you create an array with the magic string as first
+    member, the classname as second, and constructor arguments last, encode
+    it as part of your JSON structure, and then:
+       $json =~ s/\[\s*"XU1peReLzT4ggEllLanBYq4G9VzliwKF"\s*,\s*("([^\\":,]+|\\.|::)*")\s*,/($1)[/g;
+    Again, this has some limitations - the magic string must not be encoded
+    with character escapes, and the constructor arguments must be non-empty.
-THREADS
+(I-)THREADS
-    This module is *not* guaranteed to be thread safe and there are no plans
+    This module is *not* guaranteed to be ithread (or MULTIPLICITY-) safe
-    to change this until Perl gets thread support (as opposed to the
+    and there are no plans to change this. Note that perl's builtin
-    horribly slow so-called "threads" which are simply slow and bloated
+    so-called threads/ithreads are officially deprecated and should not be
-    process simulations - use fork, it's *much* faster, cheaper, better).
+    used.
-    (It might actually work, but you have been warned).
 THE PERILS OF SETLOCALE
     Sometimes people avoid the Perl locale support and directly call the
     system's setlocale function with "LC_ALL".
     If you need "LC_NUMERIC", you should enable it only around the code that
     actually needs it (avoiding stringification of numbers), and restore it
     afterwards.
+SOME HISTORY
+    At the time this module was created there already were a number of JSON
+    modules available on CPAN, so what was the reason to write yet another
+    JSON module? While it seems there are many JSON modules, none of them
+    correctly handled all corner cases, and in most cases their maintainers
+    are unresponsive, gone missing, or not listening to bug reports for
+    other reasons.
+    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 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
+    it and doesn't require a C compiler when that is a problem.
+    Somewhere around version 3, this module was forked into
+    "Cpanel::JSON::XS", because its maintainer had serious trouble
+    understanding JSON and insisted on a fork with many bugs "fixed" that
+    weren't actually bugs, while spreading FUD about this module without
+    actually giving any details on his accusations. You be the judge, but in
+    my personal opinion, if you want quality, you will stay away from
+    dangerous forks like that.
 BUGS
     While the goal of this module is to be correct, that unfortunately does
     not mean it's bug-free, only that I think its design is bug-free. If you
     keep reporting bugs they will be fixed swiftly, though.

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Comparing JSON-XS/README (file contents): Revision 1.38 by root, Tue Oct 29 00:36:18 2013 UTC vs. Revision 1.43 by root, Thu Nov 15 23:07:55 2018 UTC

Diff Legend

Comparing JSON-XS/README (file contents):
Revision 1.38 by root, Tue Oct 29 00:36:18 2013 UTC vs.
Revision 1.43 by root, Thu Nov 15 23:07:55 2018 UTC