Escaped characters in keys and values

[cmaumet]

Hi @gllmflndn! The following example (from our discussion at: incf-nidash/nidmresults-spm#40 (comment)):

>> json = containers.Map('nidm_DesignMatrix/prov:atLocation','./DesignMatrix.csv');
>> jsonwrite(json)

returns:

ans =
 {"nidm_DesignMatrix\/prov:atLocation":".\/DesignMatrix.csv"}

Is there any particular reason for the slashes to be escaped? I was hoping we could get:

{"nidm_DesignMatrix/prov:atLocation": "./DesignMatrix.csv"}

I am happy to investigate this and send a PR but I would like to make sure I understand when the escapes are needed.

Thank you in advance!

[gllmflndn]

From http://json.org/, it is my understanding that '/' should have a backslash escape. Both pass validation through JSONLint though. It seems to be a frequently discussed topic, e.g.:

• http://stackoverflow.com/questions/1580647/json-why-are-forward-slashes-escaped
• Forward slashes should not be escaped ultrajson/ultrajson#110

It's all taking place there:

• https://github.com/gllmflndn/JSONio/blob/master/jsonwrite.m#L172

[cmaumet]

Thank you @gllmflndn: I was not aware of this issue! From the thread you linked to, my understanding is that both notations are valid, and that:

 {"nidm_DesignMatrix\/prov:atLocation":".\/DesignMatrix.csv"}

is equivalent to

 {"nidm_DesignMatrix/prov:atLocation":"./DesignMatrix.csv"}

In this document "control characters" are explicitly defined as U+0000 through U+001F which does not include / (U+002F).

Do you think it would make sense to use the non-escaped version by default? Or create an option to espace only if mandatory?

[gllmflndn]

JSON specification(s) are sometimes hard to follow, see:
http://seriot.ch/parsing_json.php#1
I just checked and MATLAB's jsonencode does not escape forward slashes so, for compatibility, I will just do the same here. That will solve the issue for you: how come it is a problem for you though, given that a reader would un-escape the escaped characters?

>> jsonread(jsonwrite(struct('a','./hello')))
ans = 
  struct with fields:
    a: './hello'

[gllmflndn]

Forward slashes are not escaped any more, see 3a81c3d, and this behaviour is now compatible with jsonencode.
It would be possible to add an option as suggested in pull request #2 but implementation should instead use optregistry to minimise changes throughout the file - low priority though as I hope current version fixes the issue for you.