perldoc > Cpanel::JSON::XS

📛 NAME

Cpanel::JSON::XS — cPanel fork of JSON::XS, fast and correct serializing

🚀 Quick Reference

Use CaseCommandDescription
🔁 Encode Perl to JSON (UTF-8)encode_json $perl_hash_or_arrayrefConvert Perl data structure to UTF-8 JSON string
🔁 Decode JSON to Perldecode_json $utf8_encoded_json_textParse UTF-8 JSON string to Perl data structure
⚙️ Create configurable encoderCpanel::JSON::XS->new->utf8->pretty->encode($scalar)OO interface with options like pretty print
🔒 Encode with limited ASCII$json->ascii(1)->encode($data)Escape non-ASCII characters for 7-bit transport
🔍 Decode with relaxed rules$json->relaxed(1)->decode($text)Accept comments, trailing commas, single quotes
📦 Incremental parsing$json->incr_parse($chunk)Stream JSON objects from incomplete data
🔬 Check booleanCpanel::JSON::XS::is_bool($scalar)Test if scalar is a JSON boolean value

📋 SYNOPSIS

use Cpanel::JSON::XS;

# exported functions, they croak on error
# and expect/generate UTF-8

$utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
$perl_hash_or_arrayref  = decode_json $utf8_encoded_json_text;

# OO-interface

$coder = Cpanel::JSON::XS->new->ascii->pretty->allow_nonref;
$pretty_printed_unencoded = $coder->encode ($perl_scalar);
$perl_scalar = $coder->decode ($unicode_json_text);

# Note that 5.6 misses most smart utf8 and encoding functionalities
# of newer releases.

# Note that JSON::MaybeXS will automatically use Cpanel::JSON::XS
# if available, at virtually no speed overhead either, so you should
# be able to just:

use JSON::MaybeXS;

# and do the same things, except that you have a pure-perl fallback now.

Note that this module will be replaced by a new JSON::Safe module soon,
with the same API just guaranteed safe defaults.

📖 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.

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 below for the cPanel fork.

See MAPPING, below, on how Cpanel::JSON::XS maps perl values to JSON values and vice versa.

✨ FEATURES

🍴 cPanel fork

Since the original author MLEHMANN has no public bugtracker, this cPanel fork sits now on github.

src repo: https://github.com/rurban/Cpanel-JSON-XS original: http://cvs.schmorp.de/JSON-XS/

RT: https://github.com/rurban/Cpanel-JSON-XS/issues or https://rt.cpan.org/Public/Dist/Display.html?Queue=Cpanel-JSON-XS

Changes to JSON::XS

⚙️ FUNCTIONAL INTERFACE

The following convenience methods are provided by this module. They are exported by default:

⚠️ DEPRECATED FUNCTIONS

🌐 A FEW NOTES ON UNICODE AND PERL

Since this often leads to confusion, here are a few very clear words on how Unicode works in Perl, modulo bugs.

  1. Perl strings can store characters with ordinal values > 255. This enables you to store Unicode characters as single characters in a Perl string — very natural.
  2. Perl does not associate an encoding with your strings. ... until you force it to, e.g. when matching it against a regex, or printing the scalar to a file, in which case Perl either interprets your string as locale-encoded text, octets/binary, or as Unicode, depending on various settings. In no case is an encoding stored together with your data, it is use that decides encoding, not any magical meta data.
  3. The internal utf-8 flag has no meaning with regards to the encoding of your string.
  4. A "Unicode String" is simply a string where each character can be 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.
  6. Unicode noncharacters only warn, as in core. The 66 Unicode noncharacters U+FDD0..U+FDEF, and U+*FFFE, U+*FFFF just warn, see http://www.unicode.org/versions/corrigendum9.html. But illegal surrogate pairs fail to parse.
  7. Raw non-Unicode characters above U+10FFFF are disallowed. Raw non-Unicode characters outside the valid unicode range fail to parse, because "A string is a sequence of zero or more Unicode characters" RFC 7159 section 1 and "JSON text SHALL be encoded in Unicode RFC 7159 section 8.1. We use now the UTF8_DISALLOW_SUPER flag when parsing unicode.

I hope this helps :)

🧩 OBJECT-ORIENTED INTERFACE

The object oriented interface lets you configure your own encoding or decoding style, within the limits of supported formats.

📈 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 can then 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).

Cpanel::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 mismatched parentheses. 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.

⛔ 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 Cpanel::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 Cpanel::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"

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 Cpanel::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 Cpanel::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 Cpanel::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 Cpanel::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 :).

📄 BOM

Detect all unicode Byte Order Marks on decode. Which are UTF-8, UTF-16LE, UTF-16BE, UTF-32LE and UTF-32BE. The BOM encoding is set only for one specific decode call, it does not change the state of the JSON object. Warning: With perls older than 5.20 you need load the Encode module before loading a multibyte BOM, i.e. >= UTF-16. Otherwise an error is thrown. This is an implementation limitation and might get fixed later. See https://tools.ietf.org/html/rfc7159#section-8.1 "JSON text SHALL be encoded in UTF-8, UTF-16, or UTF-32." "Implementations MUST NOT add a byte order mark to the beginning of a JSON text", "implementations (...) MAY ignore the presence of a byte order mark rather than treating it as an error". See also http://www.unicode.org/faq/utf_bom.html#BOM. Beware that Cpanel::JSON::XS is currently the only JSON module which does accept and decode a BOM. The latest JSON spec https://www.greenbytes.de/tech/webdav/rfc8259.html#character.encoding forbid the usage of UTF-16 or UTF-32, the character encoding is UTF-8. Thus in subsequent updates BOM's of UTF-16 or UTF-32 will throw an error.

🗺️ MAPPING

This section describes how Cpanel::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 (what you put in comes out as something equivalent). For the more enlightened: note that in the following descriptions, lowercase perl refers to the Perl interpreter, while uppercase Perl refers to the abstract Perl language itself.

📥 JSON → PERL

📤 PERL → JSON

The mapping from Perl to JSON is slightly more difficult, as Perl is a truly typeless language, so we can only guess which JSON type is meant by a Perl value.

📦 OBJECT SERIALIZATION

As JSON cannot directly represent Perl objects, you have to choose between a pure JSON representation (without the ability to deserialize the object automatically again), and a nonstandard extension to the JSON syntax, tagged values.

📤 SERIALIZATION

What happens when "Cpanel::JSON::XS" encounters a Perl object depends on the "allow_blessed", "convert_blessed" and "allow_tags" settings, which are used in this order:

  1. 1. "allow_tags" is enabled and the object has a "FREEZE" method. In this case, "Cpanel::JSON::XS" uses the Types::Serialiser object serialization protocol to create a tagged JSON value, using a nonstandard extension to the JSON syntax. This works by invoking the "FREEZE" method on the object, with the first argument being the object to serialize, and the second argument being the constant string "JSON" to distinguish it from other serializers. The "FREEZE" method can return any number of values (i.e. zero or 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, $serializer) = @_;

      ($self->{type}, $self->{id})
   }
  2. 2. "convert_blessed" is enabled and the object has a "TO_JSON" method. In this case, the "TO_JSON" method of the object is invoked in scalar context. It must return a single scalar that can be directly encoded into JSON. This scalar replaces the object in the JSON text. For example, the following "TO_JSON" method will convert all URI objects to JSON strings when serialized. The fact that these values originally were URI objects is lost.
       sub URI::TO_JSON {
      my ($uri) = @_;
      $uri->as_string
   }
  3. 3. "convert_blessed" is enabled and the object has a stringification overload. In this case, the overloaded "" method of the object is invoked in scalar context. It must return a single scalar that can be directly encoded into JSON. This scalar replaces the object in the JSON text. For example, the following "" method will convert all URI objects to JSON strings when serialized. The fact that these values originally were URI objects is lost.
        package URI;
    use overload '""' => sub { shift->as_string };
  4. 4. "allow_blessed" is enabled. The object will be serialized as a JSON null value.
  5. 5. none of the above If none of the settings are enabled or the respective methods are missing, "Cpanel::JSON::XS" throws an exception.

📥 DESERIALIZATION

For deserialization there are only two cases to consider: either nonstandard tagging was used, in which case "allow_tags" decides, or objects cannot be automatically be deserialized, in which case you can use postprocessing or the "filter_json_object" or "filter_json_single_key_object" callbacks to get some real objects our of your JSON. This section only considers the tagged value case: I a tagged JSON object is encountered during decoding and "allow_tags" is disabled, a parse error will result (as if tagged values were not part of the grammar). If "allow_tags" is enabled, "Cpanel::JSON::XS" will look up the "THAW" method of the package/classname used during serialization (it will not attempt to load the package as a Perl module). If there is no such method, the decoding will fail with an error. Otherwise, the "THAW" method is invoked with the classname as first argument, the constant string "JSON" as second argument, and all the values from the JSON array (the values originally returned by the "FREEZE" method) as remaining arguments. The method must then return the object. While technically you can return any Perl scalar, you might have to enable the "enable_nonref" setting to make that work in all cases, so better return an actual blessed reference. As an example, let's implement a "THAW" function that regenerates the "My::Object" from the "FREEZE" example earlier:

   sub My::Object::THAW {
      my ($class, $serializer, $type, $id) = @_;

      $class->new (type => $type, id => $id)
   }

See the "SECURITY CONSIDERATIONS" section below. Allowing external json objects being deserialized to perl objects is usually a very bad idea.

🏳️ ENCODING/CODESET FLAG NOTES

The interested reader might have seen a number of flags that signify encodings or codesets — "utf8", "latin1", "binary" and "ascii". There seems to be some confusion on what these do, so here is a short comparison:

"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 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 these flag values will be correctly decoded when the same flags are used — in general, if you use different flag settings while encoding vs. when decoding you likely have a bug somewhere.

Below comes a verbose discussion of these flags. Note that a "codeset" is simply an abstract set of character-codepoint pairs, while an encoding takes those codepoint numbers and encodes them, in our case into octets. Unicode is (among other things) a codeset, UTF-8 is an encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets and encodings at the same time, which can be confusing.

🔧 JSON and ECMAscript

JSON syntax is based on how literals are represented in javascript (the not-standardized predecessor of ECMAscript) which is presumably why it is called "JavaScript Object Notation". However, JSON is not a subset (and also not a superset of course) of ECMAscript (the standard) or javascript (whatever browsers actually implement). If you want to use javascript's "eval" function to "parse" JSON, you might run into parse errors for valid JSON texts, or the resulting data structure might not be queryable:

One of the problems is that U+2028 and U+2029 are valid characters 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":

   use Cpanel::JSON::XS;

   print encode_json [chr 0x2028];

The right fix for this is to use a proper JSON parser in your javascript programs, and not rely on "eval" (see for example Douglas Crockford's json2.js parser). If this is not an option, you can, as a stop-gap measure, simply encode to ASCII-only JSON:

   use Cpanel::JSON::XS;

   print Cpanel::JSON::XS->new->ascii->encode ([chr 0x2028]);

Note that this will enlarge the resulting JSON text quite a bit if you have many non-ASCII characters. You might be tempted to run some regexes to only escape U+2028 and U+2029, e.g.:

   # DO NOT USE THIS!
   my $json = Cpanel::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;

Note that this is a bad idea: the above only works for U+2028 and 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. Another problem is that some javascript implementations reserve some property names for their own purposes (which probably makes them non-ECMAscript-compliant). For example, Iceweasel reserves the "__proto__" property name for its own purposes. If that is a problem, you could parse try to filter the resulting JSON output for these property strings, e.g.:

   $json =~ s/"__proto__"\s*:/"__proto__renamed":/g;

This works because "__proto__" is not valid outside of strings, so every occurrence of ""__proto__"\s*:" must be a string used as property name. Unicode non-characters between U+FFFD and U+10FFFF are decoded either to the recommended U+FFFD REPLACEMENT CHARACTER (see Unicode PR #121: Recommended Practice for Replacement Characters), or in the binary or relaxed mode left as is, keeping the illegal non-characters as before. Raw non-Unicode characters outside the valid unicode range fail now to parse, because "A string is a sequence of zero or more Unicode characters" RFC 7159 section 1 and "JSON text SHALL be encoded in Unicode RFC 7159 section 8.1. We use now the UTF8_DISALLOW_SUPER flag when parsing unicode. If you know of other incompatibilities, please let me know.

🔗 JSON and YAML

You often hear that JSON is a subset of YAML. in general, there is no way to configure JSON::XS to output a data structure as valid YAML that works in all cases. If you really must use Cpanel::JSON::XS to generate YAML, you should use this algorithm (subject to change in future versions):

   my $to_yaml = Cpanel::JSON::XS->new->utf8->space_after (1);
   my $yaml = $to_yaml->encode ($ref) . "\n";

This will usually generate JSON texts that also parse as valid YAML.

🏎️ 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. JSON::XS is with Data::MessagePack and Sereal one of the fastest serializers, because JSON and JSON::XS do not support backrefs (no graph structures), only trees. Storable supports backrefs, i.e. graphs. Data::MessagePack encodes its data binary (as Storable) and supports only very simple subset of JSON.

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"], "id": null, "array":[1,11,234,-5,1e5,1e7,
   1,  0]}

It shows the number of encodes/decodes per second (JSON::XS uses the functional interface, while Cpanel::JSON::XS/2 uses the OO interface with pretty-printing and hash key sorting enabled, Cpanel::JSON::XS/3 enables shrink. JSON::DWIW/DS uses the deserialize function, while JSON::DWIW::FJ uses the from_json method). Higher is better:

   module        |     encode |     decode |
   --------------|------------|------------|
   JSON::DWIW/DS |  86302.551 | 102300.098 |
   JSON::DWIW/FJ |  86302.551 |  75983.768 |
   JSON::PP      |  15827.562 |   6638.658 |
   JSON::Syck    |  63358.066 |  47662.545 |
   JSON::XS      | 511500.488 | 511500.488 |
   JSON::XS/2    | 291271.111 | 388361.481 |
   JSON::XS/3    | 361577.931 | 361577.931 |
   Storable      |  66788.280 | 265462.278 |
   --------------+------------+------------+

That is, JSON::XS is almost six times faster than JSON::DWIW on encoding, about five times faster on decoding, and over thirty to seventy times faster than JSON's pure perl implementation. 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/json/long.json).

   module        |     encode |     decode |
   --------------|------------|------------|
   JSON::DWIW/DS |   1647.927 |   2673.916 |
   JSON::DWIW/FJ |   1630.249 |   2596.128 |
   JSON::PP      |    400.640 |     62.311 |
   JSON::Syck    |   1481.040 |   1524.869 |
   JSON::XS      |  20661.596 |   9541.183 |
   JSON::XS/2    |  10683.403 |   9416.938 |
   JSON::XS/3    |  20661.596 |   9400.054 |
   Storable      |  19765.806 |  10000.725 |
   --------------+------------+------------+

Again, JSON::XS leads by far (except for Storable which non-surprisingly decodes a bit faster). On large strings containing lots of high Unicode characters, some modules (such as JSON::PC) seem to decode faster than JSON::XS, but the result will be broken due to missing (or wrong) Unicode handling. Others refuse to decode or encode properly, so it was impossible to prepare a fair comparison table for that case. For updated graphs see https://github.com/Sereal/Sereal/wiki/Sereal-Comparison-Graphs

🤝 INTEROP with JSON and JSON::XS and other JSON modules

As long as you only serialize data that can be directly expressed in JSON, "Cpanel::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)). "Cpanel::JSON::XS" is currently the only known JSON decoder which passes all http://seriot.ch/parsing_json.html tests, while being the fastest also. 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" or "allow_blessed" will allow you to encode and decode Perl objects, at the cost of being totally insecure and not outputting valid JSON anymore. JSON-XS-3.01 broke interoperability with JSON-2.90 with booleans. See JSON. Cpanel::JSON::XS needs to know the JSON and JSON::XS versions to be able work with those objects, especially when encoding a booleans like "{"is_true":true}". So you need to load these modules before. true/false overloading and boolean representations are supported. JSON::XS and JSON::PP representations are accepted and older JSON::XS accepts Cpanel::JSON::XS booleans. All JSON modules JSON, JSON, PP, JSON::XS, Cpanel::JSON::XS produce JSON::PP::Boolean objects, just Mojo and JSON::YAJL not. Mojo produces Mojo::JSON::_Bool and JSON::YAJL::Parser just an unblessed IV. Cpanel::JSON::XS accepts JSON::PP::Boolean and Mojo::JSON::_Bool objects as booleans. I cannot think of any reason to still use JSON::XS 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 serialized objects, and you still want to decode the generated serialize 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 serialized 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.

📜 RFC7159

Since this module was written, Google has written a new JSON RFC, RFC 7159 (and RFC7158). Unfortunately, this RFC breaks compatibility with both the original JSON specification on www.json.org and RFC4627. As far as I can see, you can get partial compatibility when parsing by using "->allow_nonref". However, consider the security implications of doing so. I haven't decided yet when to break compatibility with RFC4627 by default (and potentially leave applications insecure) and change the default to follow RFC7159, but application authors are well advised to call "->allow_nonref(0)" even if this is the current default, if they cannot handle non-reference values, in preparation for the day when the default will change.

🔒 SECURITY CONSIDERATIONS

JSON::XS and Cpanel::JSON::XS are not only fast. JSON is generally the most secure serializing format, because it is the only one besides Data::MessagePack, which does not deserialize objects per default. For all languages, not just perl. The binary variant BSON (MongoDB) does more but is unsafe. It is trivial for any attacker to create such serialized objects in JSON and trick perl into expanding them, thereby triggering certain methods. Watch https://www.youtube.com/watch?v=Gzx6KlqiIZE for an exploit demo for "CVE-2015-1592 SixApart MovableType Storable Perl Code Execution" for a deserializer which expands objects. Deserializing even coderefs (methods, functions) or external data would be considered the most dangerous.

Security relevant overview of serializers regarding deserializing objects by default:

                      Objects   Coderefs  External Data

    Data::Dumper      YES       YES       YES
    Storable          YES       NO (def)  NO
    Sereal            YES       NO        NO
    YAML              YES       NO        NO
    B::C              YES       YES       YES
    B::Bytecode       YES       YES       YES
    BSON              YES       YES       NO
    JSON::SL          YES       NO        YES
    JSON              NO (def)  NO        NO
    Data::MessagePack NO        NO        NO
    XML               NO        NO        YES

    Pickle            YES       YES       YES
    PHP Deserialize   YES       NO        NO

When you are using JSON in a protocol, talking to untrusted potentially hostile creatures requires relatively few measures.

📚 "OLD" VS. "NEW" JSON (RFC 4627 VS. RFC 7159)

TL;DR: Due to security concerns, Cpanel::JSON::XS will not allow scalar data in JSON texts by default — you need to create your own Cpanel::JSON::XS object and enable "allow_nonref":

   my $json = JSON::XS->new->allow_nonref;

   $text = $json->encode ($data);
   $data = $json->decode ($text);

The long version: JSON being an important and supposedly stable format, the IETF standardized it as RFC 4627 in 2006. Unfortunately the inventor of JSON Douglas Crockford unilaterally changed the definition of JSON in javascript. Rather than create a fork, the IETF decided to standardize the new syntax (apparently, so I as told, without finding it very amusing). The biggest difference between the original JSON and the new JSON is that the new JSON supports scalars (anything other than arrays and objects) at the top-level of a JSON text. While this is strictly backwards compatible to older versions, it breaks a number of protocols that relied on sending JSON back-to-back, and is a minor security concern. For example, imagine you have two banks communicating, and on one side, the JSON coder gets upgraded. Two messages, such as 10 and 1000 might then be confused to mean 101000, something that couldn't happen in the original JSON, because neither of these messages would be valid JSON. If one side accepts these messages, then an upgrade in the coder on either side could result in this becoming exploitable. This module has always allowed these messages as an optional extension, by default disabled. The security concerns are the reason why the default is still disabled, but future versions might/will likely upgrade to the newer RFC as default format, so you are advised to check your implementation and/or override the default with "->allow_nonref (0)" to ensure that future versions are safe.

🧵 THREADS

Cpanel::JSON::XS has proper ithreads support, unlike JSON::XS. If you encounter any bugs with thread support please report them. From Version 4.00 - 4.19 you couldn't encode true with threads::shared magic.

🐛 BUGS

While the goal of the Cpanel::JSON::XS module is to be correct, that unfortunately does not mean it's bug-free, only that the author thinks its design is bug-free. If you keep reporting bugs and tests they will be fixed swiftly, though. Since the JSON::XS author refuses to use a public bugtracker and prefers private emails, we use the tracker at github, so you might want to report any issues twice. Once in private to MLEHMANN to be fixed in JSON::XS and one to our the public tracker. Issues fixed by JSON::XS with a new release will also be backported to Cpanel::JSON::XS and 5.6.2, as long as cPanel relies on 5.6.2 and Cpanel::JSON::XS as our serializer of choice.

https://github.com/rurban/Cpanel-JSON-XS/issues

📜 LICENSE

This module is available under the same licences as perl, the Artistic license and the GPL.

🔗 SEE ALSO

The cpanel_json_xs command line utility for quick experiments.

JSON, JSON::XS, JSON::MaybeXS, Mojo::JSON, Mojo::JSON::MaybeXS, JSON::SL, JSON::DWIW, JSON::YAJL, JSON::Any, Test::JSON, Locale::Wolowitz, https://metacpan.org/search?q=JSON

https://tools.ietf.org/html/rfc7159

https://tools.ietf.org/html/rfc4627

👤 AUTHOR

Reini Urban <rurban AT cpan.org>

Marc Lehmann <schmorp AT schmorp.de>, http://home.schmorp.de/

🛠️ MAINTAINER

Reini Urban <rurban AT cpan.org>

Cpanel::JSON::XS □✕
📛 NAME 🚀 Quick Reference 📋 SYNOPSIS 📖 DESCRIPTION
✨ FEATURES 🍴 cPanel fork
⚙️ FUNCTIONAL INTERFACE ⚠️ DEPRECATED FUNCTIONS 🌐 A FEW NOTES ON UNICODE AND PERL 🧩 OBJECT-ORIENTED INTERFACE 📈 INCREMENTAL PARSING
⛔ LIMITATIONS 📝 EXAMPLES
📄 BOM 🗺️ MAPPING
📥 JSON → PERL 📤 PERL → JSON 📦 OBJECT SERIALIZATION
🏳️ ENCODING/CODESET FLAG NOTES
🔧 JSON and ECMAscript 🔗 JSON and YAML 🏎️ SPEED 🤝 INTEROP with JSON and JSON::XS and other JSON modules 🏷️ TAGGED VALUE SYNTAX AND STANDARD JSON EN/DECODERS
📜 RFC7159 🔒 SECURITY CONSIDERATIONS 📚 "OLD" VS. "NEW" JSON (RFC 4627 VS. RFC 7159) 🧵 THREADS 🐛 BUGS 📜 LICENSE 🔗 SEE ALSO 👤 AUTHOR 🛠️ MAINTAINER

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