The following example sends a HTTP string template to the TCP port upon the register change in the custom protocol. Once the response comes, is is copied in the response global variable which is returned to the system with the readRegister function.

get_example = [[
GET /api/register-values HTTP/1.1
Host: 127.0.0.1
X-WH-APIKEY:5D78CB6F0B0ACC526F2CB8BF65B471A2E594D309
X-WH-CONNECTIONS:  1
Accept: application/json
Content-Type: application/json
]]
response = "no data"
 
function createDevices ()
  addDevice({name = "S",  shift = 0, base = 10, xtraFields = {}})
end
 
function onScanStart ()
  -- no actions on scan start 
end
 
function readRegister (reg, device, unitId)
  return response
end
 
function writeRegister (reg, device, unitId, newValue)
 
   sendString(get_example .. "\n")        
 
   local s = read_string() 
 
   if (not s) or (#s == 0) then 
       return false 
   else 
       response = s              -- copy response to global 
       return true 
   end 
 
end
 
function read_string()
    local str = {}
 
    repeat 
        local char_ = readString(1)
        if char_ then 
            -- DEBUG("Read char = " .. char_)
            table.insert(str, char_) 
        end 
    until not char_
    local response = table.concat(str)
    DEBUG("read_string going to return " .. response)
    return response
end

When you want to dynamically change your request paramters, the above example could be further extended to this verstion:

GET_TEMPLATE = { getPath = "GET /api/registers/" , 
                 reg = 611,  -- can be modified from outside 
                 getTail =  " HTTP/1.1" .. "\r\n", 
                 acceptHeader = "Accept: application/json".."\r\n", 
                --  host = "Host: 192.168.1.110".."\r\n", 
                 host = "Host: 127.0.0.1".."\r\n", 
                 apiKey = "X-WH-APIKEY: 4025D32205ADC52E8604690FFADFB4600B8D41AA".."\r\n", 
                 endLine = "\r\n"
 
}
 
function GET_TEMPLATE : make() 
    local newRequest =   self.getPath 
                      .. self.reg 
                      .. self.getTail 
 
                      .. self.acceptHeader 
                      .. self.host 
                      .. self.apiKey 
                      .. self.endLine 
 
    return newRequest
end 
 
function createDevices ()
    addDevice{name = "CMD",  shift = 0, base = 10, xtraFields = {} };
end
 
function readRegister (reg, device, unitId)
  return status_ 
end
 
function writeRegister (reg, device, unitId, newValue)
 
    -- check for zero 
    if (newValue == 0) then 
        status_ = false 
        return true              -- no GET will be done 
    else 
        GET_TEMPLATE.reg = newValue -- change target  for request 
    end 
 
    sendString_(GET_TEMPLATE : make() )
 
    local response_ = readAll()
 
    if (#response_ > 0) then 
        DEBUG("got something ... " .. response_)
        status_ = 1 
    else 
        status_ = false 
    end 
 
    return true 
end
 
------------------ Helpers ---------------
 
-- new sendString version 
function sendString_(s)
                                                DEBUG("Going to send: " .. s)
    local sendBuf = {} 
 
    for i = 1, #s do 
        table.insert(sendBuf, s : byte(i) )
    end 
    sendBytes(sendBuf)
 
end
 
-- read everything that is in buffer 
function readAll()
    local rbuf = {}
    repeat 
            local b = readString(1)
            if b then 
                table.insert(rbuf, b)
            end 
    until (not b)
 
    return table.concat(rbuf)
end 
 
------------ Not in use ------------------  
function onScanStart ()
end