On Thu, Jul 6, 2017 at 1:37 AM, Yaron Minsky <yminsky@janestreet.com> wrote:
The fact that you're ignoring the result of Pipe.iter is concerning. That function should return a deferred that becomes determined once the iteration is complete. It's hard to say without having a bit more of the program, but I suspect the bug is related to that.

y


​Ah!​ Thank-you Yaron. Is something close to this schematic looking more plausible?

let run : Command.t =
  let cmd_proc : (unit -> unit Deferred.Or_error.t) Param.t =
    let open Command.Let_syntax in
    [%map_open
       let uri = ... 
       and ... in
       fun () ->
          Async_client.post ... uri >>|
          fun (_, body) ->
            let r = Cohttp_async.Body.to_pipe body in
            Async.Pipe.iter
              r
              ~continue_on_error:true
              ~f:(fun s -> Async.return (printf "%s" s)) >>|
            fun () -> Ok ()
    ] in
  Command.async_or_error' ~summary:"..." cmd_proc

let main : Command.t =
  Command.group ~summary:"..."
  [
    "run", run
  ]

let () = Command.run ~v main


On Thu, Jul 6, 2017 at 8:23 AM, Nicolás Ojeda Bär <nicolas.ojeda.bar@lexifi.com> wrote:
Hi Shayne,

I am not very familiar with Async, but did you remember to run the scheduler (Scheduler.go () or similar) ?

Cheers,
Nicolas


On Thu, Jul 6, 2017 at 12:55 AM, Shayne Fletcher <shayne.fletcher.50@gmail.com> wrote:
Can anyone help me out with this?

In short, I'm doing a HTTP POST with a handler along the lines of:
```
fun ((resp : Cohttp_async.Response.t)
    , (body : Cohttp_async.Body.t)) : unit Or_error.t ->
     let r : string Async.Pipe.Reader.t = Cohttp_async.Body.to_pipe body in
     let _ =
      Async.Pipe.iter
        r
        ~continue_on_error:true
        ~f:(fun s -> Async.return (printf "%s" s)) in
      (Ok () : unit Or_error.t)

```

Each time I invoke the program I get, more or less output (very occasionally none) but never all of it. The response header says it's "fixed  2700816" and indeed, if I replace the code above with
```
fun ((resp : Cohttp_async.Response.t)
    , (body : Cohttp_async.Body.t)) : unit Or_error.t ->
  let r : string Async.Pipe.Reader.t = Cohttp_async.Body.to_pipe body in
  let n : int Deferred.t =
    Async.Pipe.fold
      r
      ~init:0
      ~f:(fun acc s ->
            printf "acc : %d\n" acc; Async.return (acc + String.length s)
          ) in
  let _ : unit Deferred.t = n  >>| fun n -> printf "Chars read : %d" n in
  (Ok () : unit Or_error.t)

 ```
then (for example), on the first run I might see
```
acc : 0
acc : 1118
acc : 7503
acc : 8780

```

and then on the second run I might see
```
acc : 0
acc : 1118
acc : 4949

```
but never have I seen "Chars read : 2700816".

I've tried a bunch of different things:

  - `Pipe.read_all`:
     ```
       let _ =
         Async.Pipe.read_all r >>|
         fun q -> Queue.iter q ~f:(fun s -> printf "%s" s) in
       ...

     ```
     No output.
     
  - `Pipe.drain_and_count`:
    ```
      let _ =
        Async.Pipe.drain_and_count r >>|
        fun n -> printf "Count %d\n" n in
      ...

    ```
    No output.
  
  - `Pipe.to_list`:
     ```
     let _ =
       Async.Pipe.to_list r >>|
       fun l -> printf "%s" (String.concat ~sep:"" l) in
     ...

     ```
     No output.
  
Also tried the obvious:

  - `Cohttp_async.Body.to_string`:
    ```
      let s = Cohttp_async.Body.to_string body in
      let _ = s >>| fun  s -> printf "%s" s in
      ...

    ```
    No output.

I'm new to this and obviously missing something fundamental :) Is there a kind soul out there who can give me a hint on how to proceed please?

Thanks!

--
Shayne Fletcher





--
Shayne Fletcher