# Use middleware to log time it takes client to receive response
**URL:** https://discourse.julialang.org/t/use-middleware-to-log-time-it-takes-client-to-receive-response/91250
**Category:** Web Stack
**Tags:** question, profiling
**Created:** [December 5, 2022, 9:58am UTC](https://discourse.julialang.org/t/use-middleware-to-log-time-it-takes-client-to-receive-response/91250 "2022-12-05T09:58:48Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@yakir12](https://discourse.julialang.org/u/yakir12)
#### Post date: [December 5, 2022, 9:58am UTC](https://discourse.julialang.org/t/use-middleware-to-log-time-it-takes-client-to-receive-response/91250/1 "2022-12-05T09:58:48Z")
I’m trying to understand how to use [`HTTP.jl`’s middleware](https://juliaweb.github.io/HTTP.jl/stable/server/#HTTP.Middleware) to log the amount of time between two distinct events:
1. The server started sending the response
2. The client received it
The following MWE doesn’t accomplish this, but might serve as a good starting point:
```julia
using HTTP, Random
const times = UInt64[]
function get_durations(times)
calculating, sending = round.(diff(times) ./ 10^9, digits = 4)
@info "durations:" calculating sending
empty!(times)
end
function log_time(handler)
return function(req)
ret = handler(req)
push!(times, time_ns()) # log time to send data?
get_durations(times)
return ret
end
end
function handler(req)
push!(times, time_ns()) # log starting time
data = randstring(1_000_000)
push!(times, time_ns()) # log time to calculate data
return HTTP.Response(200, data)
end
HTTP.serve(log_time(handler))
```
Maybe this is simply impossible…?
---
### Author:  [@Jeff\_Emanuel](https://discourse.julialang.org/u/Jeff_Emanuel)
#### Post date: [December 5, 2022, 3:12pm UTC](https://discourse.julialang.org/t/use-middleware-to-log-time-it-takes-client-to-receive-response/91250/2 "2022-12-05T15:12:36Z")
> [@yakir12](#):
>
> The client received it
Generally you can’t know this during request handling. There may be intervening servers, such as reverse proxies. If you control the client, maybe have the client send back a timestamp after receiving the response.
---
### Author:  [@quinnj](https://discourse.julialang.org/u/quinnj)
#### Post date: [December 6, 2022, 5:21pm UTC](https://discourse.julialang.org/t/use-middleware-to-log-time-it-takes-client-to-receive-response/91250/3 "2022-12-06T17:21:39Z")
Yeah, I agree. We could potentially add an “eventing system” to HTTP.jl on both client and server side so you could hook into various checkpoints, but even then, you would need to even both client _and_ server to really get what you’re after here.
---
### Author:  [@yakir12](https://discourse.julialang.org/u/yakir12)
#### Post date: [December 7, 2022, 7:46am UTC](https://discourse.julialang.org/t/use-middleware-to-log-time-it-takes-client-to-receive-response/91250/4 "2022-12-07T07:46:17Z")
@christopher-dG came up with a really good suggestion, and it’s to use a modified `streamhandler` (original copied from [HTTP.jl/Handlers.jl at master · JuliaWeb/HTTP.jl · GitHub](https://github.com/JuliaWeb/HTTP.jl/blob/master/src/Handlers.jl#L53-L64)), for example:
```julia
function streamhandler_with_timings(handler)
return function(stream::HTTP.Stream)
request::HTTP.Request = stream.message
request.body = read(stream)
closeread(stream)
request.response::HTTP.Response = handler(request)
request.response.request = request
@time begin
startwrite(stream)
write(stream, request.response.body)
end # done sending
return
end
end
```
What do you think about that?
---
### Author:  [@Jeff\_Emanuel](https://discourse.julialang.org/u/Jeff_Emanuel)
#### Post date: [December 7, 2022, 6:24pm UTC](https://discourse.julialang.org/t/use-middleware-to-log-time-it-takes-client-to-receive-response/91250/5 "2022-12-07T18:24:05Z")
This doesn’t address the issue raised above. The client doesn’t necessarily receive the response when the server has finished writing. It depends on your use case and client/server configuration whether it is good enough.