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How to use wrk to generate HTTP payloads

Posted on Edited on In Disqus:
There are some simple Lua scripts in the wrk repo, but sometimes we need to generate HTTP payload dynamically to test the server. This blog could help you to create your own script.

a HTTP benchmarking tool

Please refer to wrk in Github

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wrk -t12 -c400 -d30s http://127.0.0.1:8080/index.html

What if we want to make some HTTP POST requests.

Here is the Lua script in the repo, which allows the user to create an HTTP POST request.

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-- example HTTP POST script which demonstrates setting the
-- HTTP method, body, and adding a header

wrk.method = "POST"
wrk.body   = "foo=bar&baz=quux"
wrk.headers["Content-Type"] = "application/x-www-form-urlencoded"

I don’t think it’s a good example, and it seems to tell you that you could not modify other parts of the request.

Let’s see counter.lua

This is another Lua script in the repo. Well, I need to make an HTTP POST payload, but it’s for GET.

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counter = 0

request = function()
   path = "/" .. counter
   wrk.headers["X-Counter"] = counter
   counter = counter + 1
   return wrk.format(nil, path)
end

One thing is for sure: there is a request function to generate a payload, which means we can override this function to achieve the effect we want.

Deep into source code

The code below is from the src/wrk.lua:

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function wrk.init(args)

    -- other headers

    -- generate the default req payload
    local req = wrk.format()
    wrk.request = function()
        return req
    end
end

-- `wrk.format` allow user to generate the request.
function wrk.format(method, path, headers, body)
   local method  = method  or wrk.method
   local path    = path    or wrk.path
   local headers = headers or wrk.headers
   local body    = body    or wrk.body
   local s       = {}

   if not headers["Host"] then
      headers["Host"] = wrk.headers["Host"]
   end

   headers["Content-Length"] = body and string.len(body)

   s[1] = string.format("%s %s HTTP/1.1", method, path)
   for name, value in pairs(headers) do
      s[#s+1] = string.format("%s: %s", name, value)
   end

   s[#s+1] = ""
   s[#s+1] = body or ""

   return table.concat(s, "\r\n")
end

Dynamically generate the payload

Since we know how wrk builds the request payload, we can create our own request function. It’s more like a generator that creates payload dynamically.

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-- Randomly generate start and amount
request = function()
    local path = "/comments"
    local start = math.random(1, 30000)
    local amount = math.random(10, 30)
    local body = "url=xxx1"
        .. string.format("&start=%d", start)
        .. string.format("&amount=%d", amount)
        .. string.format("&parm=%d", xx)

    local headers = {}
    headers["Content-Type"] = "application/x-www-form-urlencoded"
    return wrk.format('POST', path, headers, body)
end

It’s easy to use the Lua script in wrk.

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./wrk -t4 -c2000 -d30s \
     --latency -T5s  \
     -s scripts/post.lua \
     http://127.0.0.1:8888/comments

Hope you will enjoy this small tool.