Jon is a text data transfer format similar to JSON encoding is simply:
JON =: lr_z_ =: 3 : '5!:5 <''y'''
rest of code:
cocurrent 'jon'
safe1 =: '''_0123456789+*-<>|;,#ijL{()a[]'
safe2 =: 'u:';'x:';'}.';'}:';'" ';'":';'! ';'$ ';'= ';'^ ';'^.'
issafe1d =: safe1 e.~ {. &>
issafe2d =: safe2 e.~ 2&{. each
isSafe =: */@:(issafe2d +. issafe1d)@:;:
doSafe =: 0 0&$`".@.isSafe
doSafed =: 3 : 0
o =. doSafe y
if. o = i.0 0 do. w=. ;: y
o =. 'terms not safe1' ; (] #~ -.@:issafe1d) w
o , 'terms not safe2' ; (] #~ -.@:issafe2d) w return. end.
o
)
the verbs ending in d are not necessary, but are there for debugging when an
expression doesn't unencode (JOFF)
JOFF =: doSafe_z_ =: doSafe_jon_
The advantage of this data format compared to JSON, is that it can be much more
concise, and for J, orders of magnitude faster than encoding or decoding JSON.
Also, J's library for JSON is limited in what it can validly parse. JON can
encode/decode any valid J noun no matter how deeply nested. For short nouns,
it can be more space efficient than 3!:1 encoding. JON also encodes binary
data (0 1 255 {a.) along side text data
lr (i.10);( 5 * i.10);(2| i.10);(10 2 $ 3 4);' '
(i.10);(5*i.10);0 1 0 1 0 1 0 1 0 1;(10 2$3 4 3 4 3 4 3 4 3 4 3 4 3 4 3 4 3 4 3
4);15$' '
doSafe lr (i.10);( 5 * i.10);(2| i.10);(2 2 $ 3 4);' '
┌───────────────────┬───────────────────────────┬───────────────────┬───┬───────────────┐
│0 1 2 3 4 5 6 7 8 9│0 5 10 15 20 25 30 35 40 45│0 1 0 1 0 1 0 1 0 1│3 4│
│
│ │ │ │3 4│
│
└───────────────────┴───────────────────────────┴───────────────────┴───┴───────────────┘
doSafe '(i.10);( 5 * i.10);(2| i.10)'
┌───────────────────┬───────────────────────────┬───────────────────┐
│0 1 2 3 4 5 6 7 8 9│0 5 10 15 20 25 30 35 40 45│0 1 0 1 0 1 0 1 0 1│
└───────────────────┴───────────────────────────┴───────────────────┘
Although its intended to reverse the output of lr, doSafe can process a subset
of J, and so instead of using lr, it's possible to craft expressions that are
shorter than what lr produces. doSafe is also useful as a server/sandbox
execution environment, and sending/receiving records and lists as single line
statements.
doSafe lr ; , 2{"1 ] 1 (5!:7) < 'doSafed_jon_'
o=.doSafe yif.o=i.0 0do.w=.;:yo=.'terms not safe1';(]#~-.@:issafe1d)wo,'terms
not safe2';(]#~-.@:issafe2d)wreturn.end.o
The way doSafe works is that first an expression is put through ;: . There is
a list of safe 1 character prefixes which includes ' and numbers, and a few J
verb families. i in this list, whitelists both i. and i:. There is also a
separate whitelist of 2 character prefixes, that can whitelist '" ' and '":'
without ".. '= ' without =. or =: This means that only quoted text (as data)
can be run.
The number of whitelisted content could be expanded. 'NB.' could be allowed by
creating a safe3 list. Many ommitted conjunctions and verbs don't need to be.
By adding some defined verbs inside the jon locale, those could also be
whitelisted. For instance the verbs v0,v1...v9 could all be "local variables"
set by calling a0...a9.
with current implementation, this is not allowed ('/' not whitelisted)
doSafe '(+/ % #) 1 2 3 '
but
doSafe '(+: + #) 1 2 3 '
5 7 9
multiline processing is also possible:
doSafe lr '3213', LF , '222'
3213
222
doSafe ;. _2 doSafe lr '3213', LF , '10+20' ,LF NB. if you expected
multiline expressions
3213 30
doSafe ;. _2 doSafe lr '3213', LF , '+\20' ,LF,'23423',LF
3213
0 NB. not allowed in one of the lines
23423
My big question though is have I overlooked any potential unsafe code that
could be run with doSafe?
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