I'm trying to modify a bit the MirageOS http-fetch example (https://github.com/mirage/mirage-skeleton) that can be found inside mirage-skeleton but I'm having some problems understanding why I can't move some of the function executed inside the config.ml file to my unikernel.ml file. The original config.ml file follows (I'll copy just the interesting part) :
[...]
let client =
foreign "Unikernel.Client" ## console #-> resolver #-> conduit #-> job
let () =
add_to_ocamlfind_libraries ["mirage-http"];
add_to_opam_packages ["mirage-http"];
let sv4 = stack default_console in
let res_dns = resolver_dns sv4 in
let conduit = conduit_direct sv4 in
let job = [ client $ default_console $ res_dns $ conduit ] in
register "http-fetch" job
What I'm trying to do is move these two lines :
let res_dns = resolver_dns sv4 in
let conduit = conduit_direct sv4 in
into my unikernel.ml start method. Basically I want to pass to my module just the stack and let it create a dns resolver and a conduit. My start function follows:
let start c s =
C.log_s c (sprintf "Resolving in 1s using DNS server %s" ns) >>= fun () ->
OS.Time.sleep 1.0 >>= fun () ->
let res_dns = resolver_dns s in
let conduit = conduit_direct s in
http_fetch c res_dns conduit >>= fun (data) ->
Lwt.return(dump_to_db data);
Right now I'm getting this error at http_fetch parameters submission:
Error: This expression has type Mirage.resolver Mirage.impl
but an expression was expected of type Resolver_lwt.t
What I'm asking here is mostly a conceptual question because I'm clearly missing something. I'm not an expert in OCaml/MirageOS but this controversial behaviour of type mismatch is hard to understand considering that I'm just calling the same function from a different file.
config.ml is used to generate main.ml. You can copy the generated code from there if you want.
Related
Just began with Reason and OCaml today. I've started with the https://github.com/esy-ocaml/hello-reason sample. I want to make a HTTP API call so I've installed ocaml-cohttp with: esy add #opam/cohttp-lwt.
Now I want to use that library (or any that you may have as a suggestion) within the hello-reason getting started sample.
I can't find reference documentation on how to import it. I've tried:
open cohttp-lwt
Can I use OCaml libraries within in Reason code files?
Yes, the only difference is syntax. The client tutorial can be translated directly, and automatically into this:
open Lwt;
open Cohttp;
open Cohttp_lwt_unix;
let body =
Client.get(Uri.of_string("https://www.reddit.com/"))
>>= (
((resp, body)) => {
let code = resp |> Response.status |> Code.code_of_status;
Printf.printf("Response code: %d\n", code);
Printf.printf(
"Headers: %s\n",
resp |> Response.headers |> Header.to_string,
);
body
|> Cohttp_lwt.Body.to_string
>|= (
body => {
Printf.printf("Body of length: %d\n", String.length(body));
body;
}
);
}
);
let () = {
let body = Lwt_main.run(body);
print_endline("Received body\n" ++ body);
};
Edit: hello-reason uses ocaml-dune, so you also have to add cohttp-lwt-unix to the libraries stanza in the project's dune file, as shown in the client tutorial here.
This is a follow up to this question:
How to synchronously execute an Lwt thread
I am trying to run the following piece of code:
open Lwt
open Cohttp_lwt_unix
let server_content2 x =
"in server content x" |> print_endline ;
Client.get (Uri.of_string ("http://localhost:8080/"^x)) >>= fun (_, body) ->
(Cohttp_lwt.Body.to_string body) >|= fun sc -> sc
;;
let reyolo () =
List.init 10 (fun i -> server_content2 (string_of_int i) ) ;;
let par () =
let yolo = reyolo () in
"in par" |> print_endline;
Parmap.pariter
~ncores:4
(fun p -> "before run" |> print_endline ; "content:"^(Lwt_main.run p) |> print_endline ; "after run" |> print_endline )
(Parmap.L yolo);;
par ()
I expected this to perform 10 remote connections.
What I get is in par function Lwt_main.run seems to stuck before doing an actual remote call.
I doubt it might be of any significance but the server that suppose to respond is made in python and looks like this:
import subprocess
from bottle import run, post, request, response, get, route
#route('/<path>',method = 'GET')
def process(path):
print(path)
return "yolo"
run(host='localhost', port=8080, debug=True)
The issue is that the calls to server_content2, which start the requests, occur in the parent process. The code then tries to finish them in the child processes spawned by Parmap. Lwt breaks here: it cannot, in general, keep track of I/Os across a fork.
If you store either thunks or arguments in the list yolo, and delay the calls to server_content2 so that they are done in the child processes, the requests should work. To do that, make sure the calls happen in the callback of Parmap.pariter.
I'm trying to test Nancy modules with F# as described here, the thing is I can't see how to pass the second parameter in F#.
Here's what I have so far:
let should_return_status_ok_for_get() =
let bootstrapper = new DefaultNancyBootstrapper()
let browser = new Browser(bootstrapper, fun req -> req.Accept(new Responses.Negotiation.MediaRange("application/json")))
let result = browser.Get("/Menu", fun req -> req.HttpRequest())
Assert.AreEqual (HttpStatusCode.OK, result.StatusCode)
result
in the example, I should be able to instantiate a Browser object to test a specific Module:
var browser = new Browser(with => with.Module(new MySimpleModule()));
But I get a compile time error in F# when I try:
let browser = new Browser(fun req -> req.Module(new MenuModule()))
EDIT Error: No overloads match for method 'Browser'
Are there any examples of this in F#?
Also, is this the best way to go about this in F#?
This is how I run Nancy tests in F#:
I create a new bootstrapper in my test project by deriving from the DefaultNancyBootstrapper. I use this bootstrapper to register my mocks:
type Bootstrapper() =
inherit DefaultNancyBootstrapper()
override this.ConfigureApplicationContainer(container : TinyIoCContainer) =
base.ConfigureApplicationContainer(container)
container.Register<IMyClass, MyMockClass>() |> ignore
Then I write a simple test method to execute a GET request like so:
[<TestFixture>]
type ``Health Check Tests`` () =
[<Test>]
member test.``Given the service is healthy the health check endpoint returns a HTTP 200 response with status message "Everything is OK"`` () =
let bootstrapper = new Bootstrapper()
let browser = new Browser(bootstrapper)
let result = browser.Get("/healthcheck")
let healthCheckResponse = JsonSerializer.deserialize<HealthCheckResponse> <| result.Body.AsString()
result.StatusCode |> should equal HttpStatusCode.OK
healthCheckResponse.Message |> should equal "Everything is OK"
Let me know if this helps!
Using the MailboxProcessor in F#, what is the preferred way to communicate between them? - Wrapping the agents into objects like:
type ProcessAgent(saveAgent:SaveAgent) = ...
type SaveAgent() = ...
let saveAgent = new SaveAgent()
let processAgent = new ProcessAgent(mySaveAgent)
or what about:
type ProcessAgent(cont:string -> unit) = ...
type SaveAgent() = ...
let saveAgent = new SaveAgent()
let processAgent = new ProcessAgent(fun z -> saveAgent.Add z)
or maybe even something like:
type ProcessAgent() = ...
type SaveAgent() = ...
let saveAgent = new SaveAgent()
let processAgent = new ProcessAgent()
processAgent.Process item (fun z -> saveAgent.Add z)
Also is there ever any reason to wrap a normal function, that's is not maintaining some kind of state, into an agent?
The key thing about encapsulating the agents in classes is that it lets you break the direct dependencies between them. So, you can create the individual agents and then connect them into a bigger "agent network" just by registering event handlers, calling methods, etc.
An agent can essentially expose three kinds of members:
Actions are members of type 'T -> unit. They send some message to the agent without waiting for any reply from the agent. This is essentially wrapping a call to agent.Post.
Blocking actions are members of type 'T -> Async<'R>. This is useful when you're sending some message to the agent, but then want to wait for a response (or confirmation that the action was processed). These do not block the logical thread (they are asynchronous) but they block the execution of the caller. This is essentially wrapping a call to agent.PostAndAsyncReply.
Notifications are members of type IEvent<'T> or IObservable<'T> representing some sort of notification reported from the agent - e.g. when the agent finishes doing some work and wants to notify the caller (or other agents).
In your example, the processing agent is doing some work (asynchronously) and then returns the result, so I think it makes sense to use "Blocking action". The operation of the saving agent is just an "Action", because it does not return anything. To demonstrate the last case, I'll add "flushed" notification, which gets called when the saving agent saves all queued items to the actual storage:
// Two-way communication processing a string
type ProcessMessage =
PM of string * AsyncReplyChannel<string>
type ProcessAgent() =
let agent = MailboxProcessor.Start(fun inbox -> async {
while true do
let! (PM(s, repl)) = inbox.Receive()
repl.Reply("Echo: " + s) })
// Takes input, processes it and asynchronously returns the result
member x.Process(input) =
agent.PostAndAsyncReply(fun ch -> PM(input, ch))
type SaveAgent() =
let flushed = Event<_>()
let agent = (* ... *)
// Action to be called to save a new processed value
member x.Add(res) =
agent.Post(res)
// Notification triggered when the cache is flushed
member x.Flushed = flushed.Publish
Then you can create both agents and connect them in various ways using the members:
let proc = ProcessAgent()
let save = SaveAgent()
// Process an item and then save the result
async {
let! r = proc.Process("Hi")
save.Save(r) }
// Listen to flushed notifications
save.Flushed |> Event.add (fun () ->
printfn "flushed..." )
You don't need to create a class for your agents. Why not just write a function that returns your MailboxProcessor?
let MakeSaveAgent() =
MailboxProcessor<SaveMessageType>.Start(fun inbox ->
(* etc... *))
let MakeProcessAgent (saveAgent: MailboxProcessor<SaveMessageType>) =
MailboxProcessor<ProcessMessageType>.Start(fun inbox ->
(* etc... you can send messages to saveAgent here *))
For your final question: no, not really, that would be adding unnecessary complication when a simple function returning Async<_> would suffice.
I want to create a service who generates its HTML according to the parameter given and a map. Given the parameter, the service search in the map for the html, and a function to launch on client side.
type sample =
(string (* little text *)*
Html5_types.html Eliom_content.Html5.elt (* html page *) *
(unit -> unit)(* Demonstration function *))
Given that the function is to be launched on client side, I insert it in the map as a client value :
{client{
let demo_function = ignore (Ojquery.add_html
(Ojquery.jQ "li") "<p id='test1'>new paragraph</p>") }}
let get_samples () =
let samples_map = Samples.empty in
let samples_map = Samples.add "add_html"
("text",
(Eliom_tools.F.html
(** html stuff **)
),
{unit->unit{demo_function}}) samples_map in
samples_map
And then I register the service like this :
let sample_service =
Eliom_service.service
~path:["examples"]
~get_params:Eliom_parameter.(string "entry")
()
let () =
Examples_app.register
~service:sample_service
(fun (entry) () ->
try
(let entry = Samples.find entry samples_map in
let html = ((function (name, html, func) -> html) entry) in
let func = ((function (name, html, func) -> func) entry) in
ignore {unit{%func ()}};
Lwt.return (html))
with Not_found -> Lwt.return (not_found)
)
The rest of the code is pretty much only the result of a classic eliom-distillery, with the inclusion of the ojquery package for the client function used.
The compilation phase goes smoothly, but when I try to launch the server, I get the following error message :
ocsigenserver: main: Fatal - Error in configuration file: Error while parsing configuration file: Eliom: while loading local/lib/examples/examples.cma: Failure("That function cannot be called here because it needs information about the request or the site.")
My first guess was that it is due to the fact that I store client values outside of a service, but is there any way to store this kind of values on the server?
I tried to wrap them in regular functions :
let demo_serv_func () = {unit{demo_client_func ()}}
But the problem remained...
I found the issue. The problem was not because I stored client functions, but because I used Eliom_tools.F.html outside of a service.
It happens that Eliom_tools needs the context of the service to function, and since I was storing it outside of the service, it could not work.
I solved the issue by using Eliom_tools inside the service, and storing the body of the HTML page in the map.