--- JSON-XS/README 2007/03/22 23:24:18 1.3 +++ JSON-XS/README 2007/03/23 18:33:50 1.4 @@ -4,6 +4,17 @@ SYNOPSIS use JSON::XS; + # exported functions, croak on error + + $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; + $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; + + # oo-interface + + $coder = JSON::XS->new->ascii->pretty->allow_nonref; + $pretty_printed_unencoded = $coder->encode ($perl_scalar); + $perl_scalar = $coder->decode ($unicode_json_text); + 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*. @@ -17,10 +28,13 @@ 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 handling of unicode issues - This module knows how to handle Unicode, and even documents how it - does so. + This module knows how to handle Unicode, and even documents how and + when it does so. * round-trip integrity When you serialise a perl data structure using only datatypes @@ -29,20 +43,23 @@ * strict checking of JSON correctness There is no guessing, no generating of illegal JSON strings by - default, and only JSON is accepted as input (the latter is a - security feature). + default, and only JSON is accepted as input by default (the latter + is a security feature). * fast - compared to other JSON modules, this module compares favourably. + Compared to other JSON modules, this module compares favourably in + terms of speed, too. * simple to use This module has both a simple functional interface as well as an OO interface. * reasonably versatile output formats - You can choose between the most compact format possible, a - pure-ascii format, or a pretty-printed format. Or you can combine - those features in whatever way you like. + You can choose between the most compact guarenteed single-line + format possible (nice for simple line-based protocols), a pure-ascii + format (for when your transport is not 8-bit clean), or a + pretty-printed format (for when you want to read that stuff). Or you + can combine those features in whatever way you like. FUNCTIONAL INTERFACE The following convinience methods are provided by this module. They are @@ -53,16 +70,16 @@ reference to a hash or array) to a UTF-8 encoded, binary string (that is, the string contains octets only). Croaks on error. - This function call is functionally identical to "JSON::XS->new->utf8 - (1)->encode ($perl_scalar)". + This function call is functionally identical to + "JSON::XS->new->utf8->encode ($perl_scalar)". $perl_scalar = from_json $json_string The opposite of "to_json": expects an UTF-8 (binary) string and tries to parse that as an UTF-8 encoded JSON string, returning the resulting simple scalar or reference. Croaks on error. - This function call is functionally identical to "JSON::XS->new->utf8 - (1)->decode ($json_string)". + This function call is functionally identical to + "JSON::XS->new->utf8->decode ($json_string)". OBJECT-ORIENTED INTERFACE The object oriented interface lets you configure your own encoding or @@ -79,12 +96,12 @@ my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]}) => {"a": [1, 2]} - $json = $json->ascii ($enable) - If $enable is true, then the "encode" method will not generate - characters outside the code range 0..127. Any unicode characters - outside that range will be escaped using either a single \uXXXX (BMP - characters) or a double \uHHHH\uLLLLL escape sequence, as per - RFC4627. + $json = $json->ascii ([$enable]) + If $enable is true (or missing), then the "encode" method will not + generate characters outside the code range 0..127. Any unicode + characters outside that range will be escaped using either a single + \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, + as per RFC4627. If $enable is false, then the "encode" method will not escape Unicode characters unless necessary. @@ -92,23 +109,28 @@ JSON::XS->new->ascii (1)->encode (chr 0x10401) => \ud801\udc01 - $json = $json->utf8 ($enable) - If $enable is true, then the "encode" method will encode the JSON - string into UTF-8, as required by many protocols, while the "decode" - method expects to be handled an UTF-8-encoded string. Please note - that UTF-8-encoded strings do not contain any characters outside the - range 0..255, they are thus useful for bytewise/binary I/O. + $json = $json->utf8 ([$enable]) + If $enable is true (or missing), then the "encode" method will + encode the JSON string into UTF-8, as required by many protocols, + while the "decode" method expects to be handled an UTF-8-encoded + string. Please note that UTF-8-encoded strings do not contain any + characters outside the range 0..255, they are thus useful for + bytewise/binary I/O. If $enable is false, then the "encode" method will return the JSON string as a (non-encoded) unicode string, while "decode" expects thus a unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs to be done yourself, e.g. using the Encode module. - $json = $json->pretty ($enable) + Example, output UTF-16-encoded JSON: + + $json = $json->pretty ([$enable]) This enables (or disables) all of the "indent", "space_before" and "space_after" (and in the future possibly more) flags in one call to generate the most readable (or most compact) form possible. + Example, pretty-print some simple structure: + my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]}) => { @@ -118,10 +140,11 @@ ] } - $json = $json->indent ($enable) - If $enable is true, then the "encode" method will use a multiline - format as output, putting every array member or object/hash - key-value pair into its own line, identing them properly. + $json = $json->indent ([$enable]) + If $enable is true (or missing), then the "encode" method will use a + multiline format as output, putting every array member or + object/hash key-value pair into its own line, identing them + properly. If $enable is false, no newlines or indenting will be produced, and the resulting JSON strings is guarenteed not to contain any @@ -129,10 +152,10 @@ This setting has no effect when decoding JSON strings. - $json = $json->space_before ($enable) - If $enable is true, then the "encode" method will add an extra - optional space before the ":" separating keys from values in JSON - objects. + $json = $json->space_before ([$enable]) + If $enable is true (or missing), then the "encode" method will add + an extra optional space before the ":" separating keys from values + in JSON objects. If $enable is false, then the "encode" method will not add any extra space at those places. @@ -140,10 +163,14 @@ This setting has no effect when decoding JSON strings. You will also most likely combine this setting with "space_after". - $json = $json->space_after ($enable) - If $enable is true, then the "encode" method will add an extra - optional space after the ":" separating keys from values in JSON - objects and extra whitespace after the "," separating key-value + Example, space_before enabled, space_after and indent disabled: + + {"key" :"value"} + + $json = $json->space_after ([$enable]) + If $enable is true (or missing), then the "encode" method will add + an extra optional space after the ":" separating keys from values in + JSON objects and extra whitespace after the "," separating key-value pairs and array members. If $enable is false, then the "encode" method will not add any extra @@ -151,10 +178,14 @@ This setting has no effect when decoding JSON strings. - $json = $json->canonical ($enable) - If $enable is true, then the "encode" method will output JSON - objects by sorting their keys. This is adding a comparatively high - overhead. + Example, space_before and indent disabled, space_after enabled: + + {"key": "value"} + + $json = $json->canonical ([$enable]) + 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. If $enable is false, then the "encode" method will output key-value pairs in the order Perl stores them (which will likely change @@ -168,17 +199,45 @@ This setting has no effect when decoding JSON strings. - $json = $json->allow_nonref ($enable) - If $enable is true, 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. + $json = $json->allow_nonref ([$enable]) + If $enable is true (or missing), then the "encode" method can + convert a non-reference into its corresponding string, number or + null JSON value, which is an extension to RFC4627. Likewise, + "decode" will accept those JSON values instead of croaking. If $enable is false, then the "encode" method will croak if it isn't passed an arrayref or hashref, as JSON strings must either be an object or array. Likewise, "decode" will croak if given something that is not a JSON object or array. + Example, encode a Perl scalar as JSON value with enabled + "allow_nonref", resulting in an invalid JSON text: + + JSON::XS->new->allow_nonref->encode ("Hello, World!") + => "Hello, World!" + + $json = $json->shrink ([$enable]) + Perl usually over-allocates memory a bit when allocating space for + strings. This flag optionally resizes strings generated by either + "encode" or "decode" to their minimum size possible. This can save + memory when your JSON strings are either very very long or you have + many short strings. It will also try to downgrade any strings to + octet-form if possible: perl stores strings internally either in an + encoding called UTF-X or in octet-form. The latter cannot store + everything but uses less space in general. + + If $enable is true (or missing), the string returned by "encode" + will be shrunk-to-fit, while all strings generated by "decode" will + also be shrunk-to-fit. + + If $enable is false, then the normal perl allocation algorithms are + used. If you work with your data, then this is likely to be faster. + + In the future, this setting might control other things, such as + converting strings that look like integers or floats into integers + or floats internally (there is no difference on the Perl level), + saving space. + $json_string = $json->encode ($perl_scalar) Converts the given Perl data structure (a simple scalar or a reference to a hash or array) to its JSON representation. Simple @@ -197,6 +256,107 @@ become Perl arrayrefs and JSON objects become Perl hashrefs. "true" becomes 1, "false" becomes 0 and "null" becomes "undef". +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 + (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 uppcercase *Perl* + refers to the abstract Perl language itself. + + JSON -> PERL + object + A JSON object becomes a reference to a hash in Perl. No ordering of + object keys is preserved. + + array + A JSON array becomes a reference to an array in Perl. + + string + A JSON string becomes a string scalar in Perl - Unicode codepoints + in JSON are represented by the same codepoints in the Perl string, + so no manual decoding is necessary. + + number + A JSON number becomes either an integer or numeric (floating point) + scalar in perl, depending on its range and any fractional parts. On + the Perl level, there is no difference between those as Perl handles + all the conversion details, but an integer may take slightly less + memory and might represent more values exactly than (floating point) + numbers. + + true, false + These JSON atoms become 0, 1, respectively. Information is lost in + this process. Future versions might represent those values + differently, but they will be guarenteed to act like these integers + would normally in Perl. + + null + A JSON null atom becomes "undef" in 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. + + hash references + Perl hash references become JSON objects. As there is no inherent + ordering in hash keys, they will usually be encoded in a + pseudo-random order that can change between runs of the same program + but stays generally the same within the single run of a program. + JSON::XS can optionally sort the hash keys (determined by the + *canonical* flag), so the same datastructure will serialise to the + same JSON text (given same settings and version of JSON::XS), but + this incurs a runtime overhead. + + array references + Perl array references become JSON arrays. + + blessed objects + Blessed objects are not allowed. JSON::XS currently tries to encode + their underlying representation (hash- or arrayref), but this + behaviour might change in future versions. + + simple scalars + Simple Perl scalars (any scalar that is not a reference) are the + most difficult objects to encode: JSON::XS will encode undefined + scalars as JSON null value, scalars that have last been used in a + string context before encoding as JSON strings and anything else as + number value: + + # dump as number + to_json [2] # yields [2] + to_json [-3.0e17] # yields [-3e+17] + my $value = 5; to_json [$value] # yields [5] + + # used as string, so dump as string + print $value; + to_json [$value] # yields ["5"] + + # undef becomes null + to_json [undef] # yields [null] + + You can force the type to be a string by stringifying it: + + my $x = 3.1; # some variable containing a number + "$x"; # stringified + $x .= ""; # another, more awkward way to stringify + print $x; # perl does it for you, too, quite often + + You can force the type to be a number by numifying it: + + my $x = "3"; # some variable containing a string + $x += 0; # numify it, ensuring it will be dumped as a number + $x *= 1; # same thing, the choise is yours. + + You can not currently output JSON booleans or force the type in + other, less obscure, ways. Tell me if you need this capability. + + circular data structures + Those will be encoded until memory or stackspace runs out. + COMPARISON As already mentioned, this module was created because none of the existing JSON modules could be made to work correctly. First I will @@ -316,8 +476,11 @@ Again, JSON::XS leads by far in the encoding case, while still beating every other module in the decoding case. - Last example is an almost 8MB large hash with many large binary values - (PNG files), resulting in a lot of escaping: +RESOURCE LIMITS + JSON::XS does not impose any limits on the size of JSON texts or Perl + values they represent - if your machine can handle it, JSON::XS will + encode or decode it. Future versions might optionally impose structure + depth and memory use resource limits. BUGS While the goal of this module is to be correct, that unfortunately does