/ 
JSON-Parse-0.24_02
River stage two • 33 direct dependents • 46 total dependents
/ JSON::Parse

NAME

JSON::Parse - Convert JSON into a Perl variable

SYNOPSIS

use JSON::Parse 'parse_json';
my $json = '["golden", "fleece"]';
my $perl = parse_json ($json);
# Same effect as $perl = ['golden', 'fleece'];

Convert JSON into Perl.

DESCRIPTION

JSON::Parse converts JSON into equivalent Perl. The function "parse_json" takes one argument, a string containing JSON, and returns a Perl reference. The input to parse_json must be a complete JSON structure.

The module differs from the standard JSON module by simplifying the handling of Unicode. If its input is marked as Unicode characters, the strings in its output are also marked as Unicode characters.

JSON::Parse also provides a high speed validation function, "valid_json".

JSON means "JavaScript Object Notation" and it is specified in "RFC 4627".

FUNCTIONS

parse_json

use JSON::Parse 'parse_json';
my $perl = parse_json ('{"x":1, "y":2}');

This function converts JSON into a Perl structure, either an array reference or a hash reference.

If the first argument does not contain a valid JSON text, parse_json throws a fatal error ("dies").

If the argument contains valid JSON, the return value is either a hash or an array reference. If the input JSON text is a serialized object, a hash reference is returned:

my $perl = parse_json ('{"a":1, "b":2}');
print ref $perl, "\n";
# Prints "HASH".

If the input JSON text is a serialized array, an array reference is returned:

my $perl = parse_json ('["a", "b", "c"]');
print ref $perl, "\n";
# Prints "ARRAY".

json_file_to_perl

use JSON::Parse 'json_file_to_perl';
my $p = json_file_to_perl ('filename');

This is exactly the same as "parse_json" except that it works on a file name. The file must be in UTF-8.

valid_json

use JSON::Parse 'valid_json';
if (valid_json ($json)) {
    # do something
}

Valid_json returns 1 if its argument is valid JSON and 0 if not. It also returns 0 if the input is undefined or the empty string.

This is a high-speed validator which runs between three and ten times faster than "parse_json".

validate_json

use JSON::Parse 'validate_json';
eval {
    validate_json ('["xyz"]');
};
if ($@) {
    print "Your JSON was invalid: $@\n";
}

This is the underlying function for "valid_json". It runs at the same speed, but throws an error if the JSON is wrong, rather than returning 1 or 0. This may be useful if you want the exact error message where your input started to fail.

Mapping from JSON to Perl

JSON elements are mapped to Perl as follows:

JSON numbers

JSON numbers become Perl numbers, either integers or double-precision floating point numbers.

JSON strings

JSON strings become Perl strings. The JSON escape characters such as \t for the tab character (see section 2.5 of "RFC 4627") are mapped to the equivalent ASCII character. If the input string is marked as Unicode, Unicode escape characters of the form \uXXXX (see page three of "RFC 4627") are mapped to UTF-8. If the input string is not marked as Unicode, they are left untouched.

Handling of Unicode

If the input to "parse_json" is marked as Unicode characters, the output strings will be marked as Unicode characters. If the input is not marked as Unicode characters, the output strings will not be marked as Unicode characters. Thus,

# The scalar $sasori looks like Unicode to Perl
use utf8;
my $sasori = '["蠍"]';
my $p = parse_json ($sasori);
print utf8::is_utf8 ($p->[0]);
# Prints 1.

but

# The scalar $ebi does not look like Unicode to Perl
no utf8;
my $ebi = '["海老"]';
my $p = parse_json ($ebi);
print utf8::is_utf8 ($p->[0]);
# Prints nothing.

If Perl thinks the input string is Unicode, escapes like \u0040 are converted into the equivalent UTF-8 bytes. If Perl doesn't think the input is Unicode, the escapes are passed through unchanged.

JSON arrays

JSON arrays become Perl array references. The elements of the Perl array are in the same order as they appear in the JSON.

Thus

my $p = parse_json ('["monday", "tuesday", "wednesday"]');

has the same result as a Perl declaration of the form

my $p = [ 'monday', 'tuesday', 'wednesday' ];

JSON objects

JSON objects become Perl hashes. The members of the JSON object become key and value pairs in the Perl hash. The string part of each object member becomes the key of the Perl hash. The value part of each member is mapped to the value of the Perl hash.

Thus

my $j = <<EOF;
{"monday":["blue", "black"],
 "tuesday":["grey", "heart attack"],
 "friday":"Gotta get down on Friday"}
EOF

my $p = parse_json ($j);

has the same result as a Perl declaration of the form

my $p = {
    monday => ['blue', 'black'],
    tuesday => ['grey', 'heart attack'],
    friday => 'Gotta get down on Friday',
};

null

The JSON null literal is mapped to a scalar $JSON::Parse::null containing the undefined value.

true

The JSON true literal is mapped to a scalar $JSON::Parse::true containing the value 1.

false

The JSON false literal is mapped to a scalar $JSON::Parse::false containing the value 0.

RESTRICTIONS

This module imposes the following restrictions on its input.

JSON only

JSON::Parse is a strict parser. It only parses JSON which exactly meets the criteria of "RFC 4627". That means, for example, JSON::Parse does not accept single quotes (') instead of double quotes ("), or numbers with leading zeros, like 0123.

No incremental parsing

JSON::Parse does not do incremental parsing. JSON::Parse only parses fully-formed JSON strings which include opening and closing brackets.

UTF-8 only

Although JSON may come in various encodings of Unicode, JSON::Parse only parses the UTF-8 format. If input is in a different Unicode encoding than UTF-8, convert the input before handing it to this module. For example, for the UTF-16 format,

use Encode 'decode';
my $input_utf8 = decode ('UTF-16', $input);
my $perl = parse_json ($input_utf8);

or, for a file,

open my $input, "<:encoding(UTF-16)", 'some-json-file';

This module does not attempt to do the determination of the nature of the octet stream, as described in part 3 of "RFC 4627".

DIAGNOSTICS

"valid_json" does not produce error messages. "parse_json" and "validate_json" die on encountering invalid input.

Error messages have the line number and the byte number of the input which caused the problem. If you find the error message unclear, please report that as a bug.

Parsing errors are fatal, so to continue after an error occurs, put the parsing into an eval block:

my $p;                       
eval {                       
    $p = parse_json ($j);  
};                           
if ($@) {                    
    # handle error           
}

At the moment the exact content of the diagnostics is not documented so please review the source code if you need more details on potential outputs. The name of the exception throwing function is currently "failburger", so search through the C files in the top directory of the distribution for "failburger":

cd JSON-Parse
grep "failburger" Json3-*.c

SPEED

On the author's computer, the module's speed of parsing is approximately the same or slightly faster than JSON::XS, with small variations depending on the type of input. Some special types of input, such as floating point numbers containing an exponential part, like "1e09", are about two or three times faster to parse with this module than with JSON::XS. The parsing of exponentials is done by the system's strtod function in in JSON::Parse, but JSON::XS contains its own exponential parser.

For validation, "valid_json" is faster than any other module known to the author.

There is some benchmarking code in the github repository under the directory "benchmarks" for those wishing to test these claims. The script benchmarks/bench is an adaptation of the similar script in the JSON::XS distribution.

Here is an example with "benchmarks/long.json", originally downloaded from http://dist.schmorp.de/misc/json/long.json:

Repetitions: 50 x 100 = 5000
--------------+------------+------------+
module        |      1/min |        min |
--------------|------------|------------|
JP::valid     |   9691.538 |  0.0051591 |
JSON::Parse   |   3313.665 |  0.0150890 |
JSON::XS      |   3318.751 |  0.0150659 |
--------------+------------+------------+

Here JP::valid is the running time of JSON::Parse's "valid_json". A higher number in the second column, or a smaller number in the third column, is faster.

Here is an example with "benchmarks/words-array.json":

Repetitions: 50 x 100 = 5000		 
--------------+------------+------------+
module        |      1/min |        min |
--------------|------------|------------|
JP::valid     | 169535.327 |  0.0002949 |
JSON::Parse   |  22533.061 |  0.0022190 |
JSON::XS      |  21185.493 |  0.0023601 |
--------------+------------+------------+

Here is an example with "benchmarks/exp.json", containing floating point numbers:

Repetitions: 50 x 100 = 5000
--------------+------------+------------+
module        |      1/min |        min |
--------------|------------|------------|
JP::valid     |  83352.623 |  0.0005999 |
JSON::Parse   |  30826.870 |  0.0016220 |
JSON::XS      |  13545.743 |  0.0036912 |
--------------+------------+------------+

Here is an example with "benchmarks/literals.json", containing JSON literals:

Repetitions: 50 x 100 = 5000
--------------+------------+------------+
module        |      1/min |        min |
--------------|------------|------------|
JP::valid     | 182519.756 |  0.0002739 |
JSON::Parse   |  31564.600 |  0.0015841 |
JSON::XS      |  17939.709 |  0.0027871 |
--------------+------------+------------+

Here is an example with "benchmarks/cpantesters.json", a 250K file:

Repetitions: 5 x 10 = 50
--------------+------------+------------+
module        |      1/min |        min |
--------------|------------|------------|
JP::valid     |    876.736 |  0.0057030 |
JSON::Parse   |    140.631 |  0.0355539 |
JSON::XS      |    131.866 |  0.0379171 |
--------------+------------+------------+

SEE ALSO

RFC 4627

JSON is specified in http://www.ietf.org/rfc/rfc4627.txt.

JSON, JSON::XS

These modules allow both reading and writing of JSON.

TEST RESULTS

The ActiveState test results are at http://code.activestate.com/ppm/JSON-Parse/.

EXPORTS

The module exports nothing by default. Functions "parse_json" and "valid_json" can be exported on request.

AUTHOR

Ben Bullock, <bkb@cpan.org>

LICENSE

JSON::Parse can be used, copied, modified and redistributed under the same terms as Perl itself.