parse kdb+ HTTP response type - kdb

Question

I am trying to communicate with kdb+ via HTTP. I succeeded to get the the response from the DB when I did it from the browser, but for some reason, the response is neither JSON nor anything that looks machine readable.
What I did:
Opened a port on q console (8080)
Defined a function getData that gives me the data I want.
The above steps can be presented in this .q file I created:
\p 8080
system["l db"]
getData: {[a;b] ?[table;((>=;`start;$[`long;a]);(<=;`end;$[`long;b]));0b;()]}
h:hopen `:localhost:8080:user:pass
I then typed http://localhost:8080/?getData[1;2] in the browser to get the results
Got the results as text with spaces inside <pre> tag.
The Problem
I have no I idea how to parse it to JSON. How can I solve this? is there a way to tell kdb+ to send response in JSON format?

Answer 1

The solution I found:
If you add .json before the ? in the url (i.e. http://localhost:8080/.json?getData[1;2]) the response will be in JSON.

Answer 2

It looks like, based on your code, the following may work to return data:
http://localhost:8080/?getData[a;b]
Where a and b are start and end times (or dates, this will depend on your data).
e.g.
http://localhost:8080/?getData[2021.07.23;2021.07.30]
In order to convert a KDB+ object to json you can make use of the .j.j operator.
For example you can change your code to something like:
getData:{[a;b] t:?[table;((>=;`start;$[`long;a]);(<=;`end;$[`long;b]));0b;()];.j.j t}
If you want to see what the incoming request looks like on your Q process you could add some logging to .z.ph (the default http message handler), e.g. something like:
.z.ph:{[zph;x]zph 0N!x}[.z.ph]
This will log any incoming requests out to your q process using 0N! and then run the usual .z.ph message handing code on it