You can edit this page using wiki syntax for markup.

Article contents:== chicken-cjson [[toc:]] [[http://call-cc.org/|Chicken Scheme]] bindings for the JSON parser [[https://github.com/DaveGamble/cJSON|cjson]]. It cannot read from ports and must have the entire JSON object in memory. It also does not serialize to ports as {{cjson->string}} returns a string. The {{string->json}} procedure returns the same datastrucures as {{medea}}'s, {{read-json}}, so if you're passing that strings already, {{string->json}} should be a drop-in replacement: <enscript highlight="bash"> $ printf '{"array":[1,2,3],"null":null}' | csi -R cjson -p '(string->json (read-line))' ((null . null) (array . #(1.0 2.0 3.0))) $ printf '{"array":[1,2,3],"null":null}' | csi -R medea -p '(read-json (read-line))' ((array . #(1 2 3)) (null . null)) </enscript> {{chicken-cjson}} may offer a significant performance improvement over [[http://wiki.call-cc.org/eggref/4/medea|medea]] and [[http://wiki.call-cc.org/eggref/4/json|json]], but comes at a price: all data must be availabe as a string. This means you cannot parse JSON coming in from a port directly, and that's why there is no {{read-json}} here. {{chicken-cjson}} offers an alternative API which exposes a JSON c-struct as a {{#<cjson>}} scheme record, and accompanying procedures like {{cjson-string}}. This is for performance reasons and allows you to pick apart JSON objects using lolevel C-functions, without transitioning into the Scheme data-structure. This may be faster but is a lot uglier: <enscript highlight="bash"> $ printf '{"array":[1,2,3],"null":null}' |\ csi -R cjson -p '(cjson-double (cjson-array-ref (cjson-obj-ref (string->cjson (read-line)) "array") 1))' 2.0 </enscript> Note that if you know that a number is fixnum, you can use {{cjson-int}} instead. === Repository [[https://github.com/Adellica/chicken-cjson|https://github.com/Adellica/chicken-cjson]] === Requirements None. [[https://github.com/DaveGamble/cJSON|cjson]] comes bundled. === TODO * Make {{cjson-schemify}} faster yet by avoiding the O(n) procedures {{cjson-obj-ref}} and {{cjson-array-ref}} * Update to [[https://github.com/DaveGamble/cJSON|cjson]] version [[https://github.com/DaveGamble/cJSON/releases/tag/v1.2.1|1.2.1]] * Add support for modifying {{cjson}} records like {{cJSON_AddItemToArray}} * Make {{with-cjson}} that allocates and deallocates in block, and does it fast? * Make a common JSON API for all json parsers in CHICKEN? === API <procedure> (string->cjson string)</procedure> Note that that's not {{string->json}}! Parses the string and returns a {{#<cjson>}} record which holds a c-struct representing the JSON. The returned record has a finalizer attached to it so the underlying c-struct gets freed on garbage collection. <procedure> (string->cjson* string)</procedure> Like {{string->cjson}} but does not attach a finalizer to the {{#<cjson>}} record. {{cjson-free}} must be explicitly called later on the returned value to avoid memory leaks. This is sometimes faster than attaching finalizers, particularly if there are large numbers of {{#<cjson>}} objects. <procedure> (cjson->string cjson [pretty-print?])</procedure> Convert the {{#<cjson>}} object to its JSON-representation, returned as a string. {{pretty-print?}} defaults to true. Note that this can only serialize [[https://github.com/DaveGamble/cJSON|cjson]] records, and not scheme objects. <procedure> (cjson-schemify cjson)</procedure> Convert the {{#<cjson>}} object to scheme data-structures. The data-structures are the same as [[http://wiki.call-cc.org/eggref/4/medea|medea]]'s, where {{array => vector}} and {{object => alist}}. <procedure> (string->json string)</procedure> Make scheme data-structures of the json data in {{string}} using [cjson]: <enscript highlight="scheme"> (define (string->json str) (let* ((j (string->cjson* str)) (s (cjson-schemify j))) (cjson-free j) s)) </enscript> For string inputs, this should be API-equivalent of [[http://wiki.call-cc.org/eggref/4/medea|medea]]'s {{(read-json)}}. <procedure> (cjson-type cjson)</procedure> Pick out the type of a [[https://github.com/DaveGamble/cJSON|cjson]] record. Returns a fixnum. [variable] cjson/false [variable] cjson/true [variable] cjson/null [variable] cjson/number [variable] cjson/string [variable] cjson/array [variable] cjson/object Exposes the [[https://github.com/DaveGamble/cJSON|cjson]]-type constants. <procedure> (cjson-int cjson)</procedure> <procedure> (cjson-double cjson)</procedure> <procedure> (cjson-string cjson)</procedure> <procedure> (cjson-key cjson)</procedure> "Unbox" the json value. {{cjson-type}} must match like this: <enscript highlight="scheme"> (select (cjson-type cjson) ((cjson/false) #f) ((cjson/true) #t) ((cjson/null) 'null) ((cjson/number) (cjson-double cjson)) ((csjon/string) (cjson-string cjson)) (else (error "probably a vector or object"))) [procedure] (cjson-array-size cjson) </enscript> Return the number of elements in the array. If [[https://github.com/DaveGamble/cJSON|cjson]]'s type is not an array, this is undefined bahaviour. <procedure> (cjson-array-ref cjson index)</procedure> Return the element of {{cjson}} at position {{index}}. {{index}} must be a fixnum. Undefined behaviour if {{cjson}} is not an array. <procedure> (cjson-obj-ref cjson key)</procedure> Select field {{key}} from {{cjson}}. Key must be a string. Undefined behaviour if {{cjson}} is not of type {{cjosn/object}}. === Performance The performance characteristics of JSON parsing is mysterious. It is recommended to use [[http://wiki.call-cc.org/eggref/4/medea|medea]] or [[http://wiki.call-cc.org/eggref/4/json|json]] in most usage-cases because they can parse directly off ports and they also serialize. For particular cases, however, there may be significant performace improvements in using [[https://github.com/DaveGamble/cJSON|cjson]]. Sometimes the speedup is negligible: <enscript highlight="bash"> $ (echo '[' ; for i in {0..1000} ; do echo '"str", 1, 2, 3, 4,' ; done ; echo ' 0]') > bigjson $ time csi -R medea -e '(pp (read-json))' < bigjson >/dev/null real 0m0.152s user 0m0.140s sys 0m0.013s $ time csi -R cjson -e '(pp (string->json (read-string)))' < bigjson >/dev/null real 0m0.114s user 0m0.103s sys 0m0.010s </enscript> Here, having to doing a {{read-string}} first isn't great. [[https://github.com/DaveGamble/cJSON|cjson]] may shine when you already have the JSON data as a string: <enscript highlight="bash"> $ for i in {0..100000} ; do echo '{"field" : {"id" : 1}}' ; done > jsonlines $ time csi -R medea -R ports -e '(port-for-each (lambda (line) (pp (alist-ref `field (read-json line)))) read-line)' < jsonlines > /dev/null real 0m3.997s user 0m3.933s sys 0m0.067s $ time csi -R cjson -R ports -e '(port-for-each (lambda (line) (pp (alist-ref `field (string->json line)))) read-line)' < jsonlines > /dev/null real 0m1.099s user 0m1.083s sys 0m0.017s </enscript> That's four times faster. In some cases, though, keeping the {{#<cjson>}} record and using its combersome API can pay off: <enscript highlight="bash"> $ JSON='{"field" : {"id" : "ID"} , "a":1, "b":2, "c":[1,{"x":{"y":"y"}},3],"d":{"e":[]}}' $ for i in {0..100000} ; do echo $JSON ; done > jsonlines $ for f in test*.scm ; do echo ===== $f === ; cat $f ; done ===== test-cjson.scm === (import cjson ports) (port-for-each (lambda (line) (let ((cjson (string->cjson* line))) (print (cjson-string (cjson-obj-ref (cjson-obj-ref cjson "field") "id"))) (cjson-free cjson))) read-line) ===== test-medea.scm === (import medea ports) (port-for-each (lambda (line) (print (alist-ref 'id (alist-ref 'field (read-json line))))) read-line) $ for f in test*.scm ; do echo $f ; time csi -s $f < jsonlines >/dev/null ; done test-cjson.scm real 0m0.541s user 0m0.523s sys 0m0.020s test-medea.scm real 0m13.870s user 0m13.717s sys 0m0.153s $ time jq '.field.id' < jsonlines > /dev/null real 0m0.513s user 0m0.500s sys 0m0.017s </enscript> In this particular run, {{chicken-cjson}} is 25 times faster than medea, and performas about as well as [[https://stedolan.github.io/jq/|jq]]. This speedup typically only happens where you are parsing a lot of JSON, but only a small part of that needs to go back into scheme. Also, this only works because we have one JSON object per line, effectively giving us a json-object delimiter. Description of your changes:

I would like to authenticate

Spam control

What do you get when you subtract 11 from 14?