json-streams is a Common Lisp library for reading and writing JSON text.
- Designed to used as a building block for more high level libraries.
- No dependencies.
- Easy to use streaming API.
- Validates input and output.
- Unambiguous mapping of datatypes between lisp and JSON.
- Streaming design, can proccess JSON text of unlimted size.
- Proper handling of Unicode.
High level interface
Streaming interface for output
(with-json-output (nil :key-encoder #'string-downcase :indent t) (with-json-object (json-output-member :first-name "John") (json-output-member :last-name "Smith") (with-json-member :is-alive (json-output-boolean t)) (json-output-member :age 25) (with-json-member :address (json-output-alist '((:street-address . "21 2nd Street") (:city . "New York") (:state . "NY") (:postal-code . "10021-3100")))) (with-json-member :phone-numbers (with-json-array (json-output-plist '(:type "home" :number "212 555-1234")) (json-output-plist '(:type "office" :number "646 555-4567")) (json-output-plist '(:type "mobile" :number "123 456-7890")))) (json-output-member :children #()) (with-json-member :spouse (json-output-null))))
Macro JSON-STREAMS:WITH-JSON-OUTPUT (&optional target &rest options) &body body
The options are explained under
MAKE-JSON-OUTPUT-STREAM. Target must be a character stream or NIL. If target is NIL output is written to a string that is returned, otherwise the values of body is returned.
The following functions and macros can only be used inside the body of
WITH-JSON-ARRAY- Use any of the other functions/macros in the body to output elements of the array.
JSON-OUTPUT-MEMBERin the body.
WITH-JSON-MEMBER- The body must contain one call to one output function/macros to output the value.
JSON-OUTPUT-MEMBER- Outputs the member value using
JSON-OUTPUT-VALUE- string, number, sequence or hash-table.
false, anything else outputs
JSON-OUTPUT-NULL- Always outputs
null. No arguments.
JSON-OUTPUT-ALIST- Outputs an assoc list as a JSON object using
JSON-OUTPUT-PLIST- Outputs a propretry list as JSON object using
Parsing and writing using an unambigious s-expression notation
The high level interface uses the following datatype mapping:
|number||integer, float or ratio|
|array||(:ARRAY ... )|
|object||(:OBJECT (key . value) ... )|
The options are explained under
Function JSON-STREAMS:JSON-PARSE source &rest options => json, position
Parses a single JSON text from source. The second value is the position where parsing stopped.
Function JSON-STREAMS:JSON-PARSE-MULTIPLE source &rest options => jsons
Parses zero or more JSON texts from source. Returns a list of JSON values.
Function JSON-STREAMS:JSON-STRINGIFY value &optional target &rest options
Stringifies value into JSON text. If target is not provided or NIL, returns a string with the JSON text. Otherwise target must be a character stream.
Function JSON-STREAMS:JSON-STRINGIFY-MULTIPLE values &optional target &rest options
Stringifies multiple json values.
The streaming interface
See parse.lisp and stringify.lisp for examples of how to use the streaming interface.
Function JSON-STREAMS:MAKE-JSON-INPUT-STREAM source &key start end close-stream multiple duplicate-key-check use-ratios max-exponent raw-strings => json-input-stream
- source - A character stream or a string. When source is a string, start and end are bounding index designators of string.
- use-ratios - Default false. When false, numbers that can not be represented as integers are returned as double-floats. Then true, these numbers are returned as ratios.
- max-exponent - Default 325. The maximum (positive and negative) exponent accepted in numbers. Setting to a high number opens up for a easy to use denial-of-service attack.
- raw-strings - Default false. When true, strings are returned as
(:STRING numbers*), where numbers represent Unicode code points. For Unicode escape sequences in strings (), no UTF-16 validation or decoding is done.
- key-encoder - Default
NIL. A function taking one argument. This used by the higher lever functions to transform the keys of objects into strings.
Function JSON-STREAMS:MAKE-JSON-OUTPUT-STREAM stream &key close-stream multiple duplicate-key-check indent escape-non-ascii => json-input-stream
- stream - A character stream.
- indent - Default false. When true, the JSON text is broken into lines and indented.
- escape-non-ascii - Default false. When true, any character outside the ASCII character set will be escaped using the syntax.
- close-stream - Default false. When true, the source stream will be closed by JSON-CLOSE.
- multiple - Default false. When true, only a single JSON text (object or array) is expected in the stream. When T, zero or more JSON texts can be read from or written to stream.
- duplicate-key-check - Default true. When true, an error will be signaled when duplicate keys are detected in an object. Setting this to false avoids the added overhead of checking for duplicate keys.
Function JSON-STREAMS:JSON-READ json-input-stream => token
Parses JSON text from the underlying stream and returns the next token.
Function JSON-STREAMS:JSON-WRITE token json-output-stream => token
Outputs JSON text to underlying stream based on the given token.
Function JSON-STREAMS:JSON-CLOSE json-stream &key abort
Closes the json-stream. Applications should always call
JSON-CLOSE when finished with a JSON stream. This ensures that all syntax errors are detected. The value of abort is forwarded to
CL:CLOSE of the underlying stream (if close-stream was true) and JSON syntax checking is suppressed.
Macro JSON-STREAMS:WITH-OPEN-JSON-STREAM (var json-stream) &body
Binds var to json-stream, executes body, and ensures that JSON-CLOSE is called on json-stream.
The possible tokens for input and output are
- A number
- A string or
:BEGIN-OBJECT is returned,
JSON-READ will alternate between returning keys and values of the object, until
:END-OBJECT is returned instead of a key. Keys are always returned as strings. Values can be anything, except
:EOF. Thus some kind of recursive or stack based algorithm is neccearry.
Handling of numbers
The syntax doesn't matter: 20, 20.0 or 2e1 are all the same number, the integer 20.
The integer range is +/- (expt 10 53). Numbers outside this range can't be represented accurately. This library will refuse to write an integer outside this range. If you need to output such large numbers, convert them to double-float or string.
At input the handling of numbers outside the integer range depends on syntax. If the number contains a decimal point or an exponent it will be returned as a double-float. Otherwise an error will be signalled. The option
:USE-RATIOS disables this check.
- Thomas Bakketun <email@example.com>
- GNU General Public Licence 3.0