Get value from HTTP POST request body

How can I remove the new line in the JSON (therefore in the payload)?

can you try string trim without chars?

If chars is not specified then white space is removed (spaces, tabs, newlines, and carriage returns).

string trim

http://wiki.tcl.tk/10174

 configuration

[root@ve11b:Active:In Sync] config  tmsh list ltm rule qux
ltm rule qux {
    proc key2value {l k} {
  foreach elm [split $l ,] {
    set kv [split $elm :]
    if { $k eq [string trim [lindex $kv 0]] } {
      return [string trim [lindex $kv 1]]
    }
  }
}
when HTTP_REQUEST {
  HTTP::collect [HTTP::header Content-Length]
}
when HTTP_REQUEST_DATA {
  set payload [HTTP::payload]
  log local0. "payload=$payload "
  log local0. "username=[call key2value [lindex $payload 0] \"username\"]"
  log local0. "password=[call key2value [lindex $payload 0] \"password\"]"
  HTTP::release
}
}

 client

[root@centos1 ~] curl -X POST -H "Content-type: application/json" -d $'{ "username" : "abc",\n"password" : "def" }' http://172.28.24.10
curl: (52) Empty reply from server

 /var/log/ltm

[root@ve11b:Active:In Sync] config  tail -f /var/log/ltm
Feb 20 09:58:13 ve11b info tmm[14140]: Rule /Common/qux : payload={ "username" : "abc", "password" : "def" }
Feb 20 09:58:13 ve11b info tmm[14140]: Rule /Common/qux : username="abc"
Feb 20 09:58:13 ve11b info tmm[14140]: Rule /Common/qux : password="def"