Extract value from json

[NoamRotter]

Hi,

I have a webapp which accepts a POST with JSON payload.

the JSON has only one key:value

I need to write to log the value of the key.

For example:

This is the payload of the JSON:

{      "token": "c71c56b0-7590-4785-b490-0f060c563aee"  } 

I need to write to the LTM log:

c71c56b0-7590-4785-b490-0f060c563aee

I need a simple iRule which parses the payload, find the value of "token" and writes it to the ltm log.

Can someone help please?

Noam.

[PeteWhite]

when HTTP_REQUEST { if { [HTTP::method] == "POST"} { HTTP::collect } } when HTTP_REQUEST_DATA { set token [ regexp -inline -- {"token": "(.+)"} [HTTP::payload] ] log local0.debug "Token: $token" }

Try the above - I haven't tested it out but it looks ok

[NoamRotter]

Hi Pete,

Thank you for your answer.

I tested your iRule.

When using postman to post the JSON,

the postman keeps saying "Sending Request" until I hit the cancel button

I have added 2 logs line:

when HTTP_REQUEST { if { [HTTP::method] == "POST"} { log local0. ">>> Method is POST<<<" HTTP::collect log local0. ">>> HTTP Collected<<<" } } when HTTP_REQUEST_DATA { set token [ regexp -inline -- {"token": "(.+)"} [HTTP::payload] ] log local0.debug "Token: $token" }

In the ltm log I see:

Apr 29 08:27:43 bigip1 info tmm2[18399]: Rule /Common/test-iRule <HTTP_REQUEST>: >>> Method is POST<<<

Apr 29 08:27:43 bigip1 info tmm2[18399]: Rule /Common/test-iRule <HTTP_REQUEST>: >>> HTTP Collected<<<

When I disable the HTTP::collect line

Postman sends the request and finishes. Does not keep saying "Sending request"

But, the when HTTP_REQUEST_DATA part is not executed.

I moved these lines to HTTP_REQUEST part:

set token [ regexp -inline -- {"token": "(.+)"} [HTTP::payload] ]

log local0.debug "Token: $token"

like this:

when HTTP_REQUEST { if { [HTTP::method] == "POST"} { log local0. ">>> Method is POST<<<" set token [ regexp -inline -- {"token": "(.+)"} [HTTP::payload] ] log local0.debug "Token: $token" } }

And now I get in the ltm log:

Apr 29 08:33:45 bigip1 debug tmm2[18399]: Rule /Common/test-iRule <HTTP_REQUEST>: Token: {"token": "01593317-66f9-4e8a-8467-6f4652e680e3"} 01593317-66f9-4e8a-8467-6f4652e680e3

And I expected to get:

Apr 29 08:33:45 bigip1 debug tmm2[18399]: Rule /Common/test-iRule <HTTP_REQUEST>: Token: 01593317-66f9-4e8a-8467-6f4652e680e3

Thank you for your time.

Noam.

[PeteWhite · Accepted solution]

Great! HTTP::payload must be able to retrieve it because it comes in a single packet so it doesn't need to accumulate. Note that if the payload was larger ( eg 1K ) then this might fail and you'd have to use HTTP::collect.

We can use regexp in multiple ways to retrieve the substring. Try this:

when HTTP_REQUEST { if { [HTTP::method] == "POST"} { log local0. ">>> Method is POST<<<" if { [ regexp -- {"token": "(.+)"} [HTTP::payload] a b ] } { log local0.debug "Token Found a:$a b:$b" } } }

$a should be the whole of the line, $b should be only the token part.

Take a look here for more detail on how to use regexp:

PS the other way we could have done it is this:

set token [lindex [ regexp -inline -- {"token": "(.+)"} [HTTP::payload] ] 1]

[NoamRotter]

Hi Pete,

Thank you very much,

This is working as well as the PS.

👍

[PeteWhite]

Excellent! Take the rest of the day off 🙂