Joseph Ferano
23b440db16
The piece between an editor and everything else. One long-lived Session, the program it belongs to launched and owned by the same process, and a socket that takes forms and installs them. What it adds over flan reload is that the session persists - a defvar added by one evaluation is part of what the next is checked against - and that it owns the build, which is what makes its layout rules describe the process actually running rather than a guess about it. The protocol is s-expressions rather than bencode, and I changed my mind about that. The case for nREPL was reusing a designed op set and not re-litigating session identity, but with the client ours too there is no CIDER to be compatible with, its eval is string-in/string-out with no slot for which form from which file, and Emacs already has read and prin1. So: one sexp per message, length framed because the payload contains newlines. No parsing code on the editor side, and on this side the parser is the language's own reader, where :op is already a keyword and Flan source is already a string literal. An nREPL front end can sit on the same Session later; it should not gate the editor. Two silent failures the daemon refuses to have. The agent socket is chosen by the daemon and forced through FLAN_AGENT_SOCKET before spawning, because a program's source has to name some path and a daemon that guessed would compile, build and deliver a module to nobody. And delivery is checked: agent/start returning 0 means a socket was bound, not that anyone connected, so a failed connect or a reply that is not ok becomes an error the editor sees. It waits for the program to bind before accepting an evaluation, since one arriving first fails for a reason that reads like a compiler bug, and it accepts with a timeout so a program that has exited takes the daemon with it instead of leaving an editor waiting on a socket nobody serves.
212 lines
8.6 KiB
OCaml
212 lines
8.6 KiB
OCaml
(** [flan dev]: one long-lived session, the program it belongs to running
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beside it, and a socket an editor talks to.
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This is the piece between an editor and everything else. What it adds over
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[flan reload] is that the session *persists*: a [defvar] added by one
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evaluation is part of the program the next one is checked against, and the
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set of names the running process was built with is the one from the build
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this daemon actually made. A CLI that rebuilds its session from source each
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time cannot have either.
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It owns the build, which is what makes its layout rules mean anything: a
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session's struct layouts and global types describe the memory of a process
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only if it is the session that compiled it. So the daemon launches the
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program rather than attaching to one. *)
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type t = {
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session : Session.t;
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child : int; (* the running program *)
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agent : string; (* where it listens for modules *)
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dir : string; (* modules are built here, one per eval *)
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mutable n : int; (* dlopen caches by path: never reuse one *)
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}
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let await ?(ms = 5000) f =
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let rec go ms =
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if f () then true
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else if ms <= 0 then false
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else begin ignore (Unix.select [] [] [] 0.005); go (ms - 5) end
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in
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go ms
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(* ── Delivery ──────────────────────────────────────────────────────── *)
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(* The agent answers "ok" when it has queued a module, and anything else is a
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refusal with a reason. Reporting that back rather than swallowing it is what
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keeps a failed delivery from looking like a successful evaluation — the
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whole class of bug this socket makes possible. *)
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let deliver t path =
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let s = Unix.socket Unix.PF_UNIX Unix.SOCK_STREAM 0 in
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Fun.protect
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~finally:(fun () -> try Unix.close s with Unix.Unix_error _ -> ())
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(fun () ->
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Unix.connect s (Unix.ADDR_UNIX t.agent);
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let msg = path ^ "\n" in
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ignore (Unix.write_substring s msg 0 (String.length msg));
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let b = Bytes.create 1024 in
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let buf = Buffer.create 64 in
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let rec drain () =
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match Unix.read s b 0 1024 with
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| 0 -> ()
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| n -> Buffer.add_subbytes buf b 0 n; drain ()
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| exception Unix.Unix_error _ -> ()
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in
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drain ();
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String.trim (Buffer.contents buf))
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let alive t =
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match Unix.waitpid [ Unix.WNOHANG ] t.child with
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| 0, _ -> true
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| _ -> false
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| exception Unix.Unix_error _ -> false
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(* ── Ops ───────────────────────────────────────────────────────────── *)
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(* Every reply is a plist with a :status, so an editor can dispatch on one key
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and never has to guess whether a missing field means failure. *)
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let ok fields =
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"(:status \"ok\"" ^ String.concat "" (List.map (fun f -> " " ^ f) fields) ^ ")"
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let error ?loc msg =
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"(:status \"error\" :message " ^ Wire.quote msg
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^ (match loc with None -> "" | Some l -> " :loc " ^ Wire.quote l)
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^ ")"
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let eval t ~code ~origin =
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if not (alive t) then error "the program exited; restart flan dev"
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else
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match Session.eval ~origin t.session code with
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| c ->
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t.n <- t.n + 1;
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let out = Filename.concat t.dir (Printf.sprintf "m%d.so" t.n) in
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(match Build.shared ~opts:{ Build.default with Build.dev = true }
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~ir:c.Session.ir ~out () with
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| timing ->
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(match deliver t out with
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| "ok" ->
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ok
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[ ":names " ^ Wire.strings c.Session.names;
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":fns " ^ Wire.strings c.Session.fns;
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Printf.sprintf ":ms %.1f"
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(timing.Build.llc_ms +. timing.Build.link_ms) ]
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| reply -> error ("the program refused the module: " ^ reply)
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| exception Unix.Unix_error (e, _, _) ->
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error
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("cannot reach the program on " ^ t.agent ^ ": "
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^ Unix.error_message e))
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| exception Failure m -> error m)
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| exception Loc.Error (l, msg) -> error ~loc:(Loc.to_string l) msg
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let describe t =
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ok
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[ ":fns "
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^ Wire.strings
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(List.map (fun (f : Tast.fn) -> f.Tast.name)
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t.session.Session.program.Tast.fns);
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":globals "
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^ Wire.strings
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(List.map (fun (g : Tast.global) -> g.Tast.gname)
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t.session.Session.program.Tast.globals);
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":alive " ^ (if alive t then "t" else "nil") ]
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let handle t req =
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match Wire.string_field req "op" with
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| Some "eval" ->
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(match Wire.string_field req "code" with
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| Some code ->
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let origin =
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match Wire.string_field req "file" with Some f -> f | None -> "<editor>"
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in
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eval t ~code ~origin
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| None -> error "eval needs :code")
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| Some "describe" -> describe t
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| Some "close" -> ok []
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| Some op -> error ("unknown op: " ^ op)
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| None -> error "no :op"
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(* ── The loop ──────────────────────────────────────────────────────── *)
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(* One connection at a time. An editor is one client, evaluations are
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sequential by nature — each one is checked against the program the last one
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left behind — and a second concurrent evaluation would be racing for the
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same session anyway. *)
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(* Returns whether the client asked to end the session. One editor per daemon,
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so [close] shuts the whole thing down rather than waiting for another
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connection nobody is going to make. *)
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let serve t fd =
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let rec go () =
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match Wire.recv fd with
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| src ->
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let op, reply =
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match Wire.parse src with
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| req -> (Wire.string_field req "op", handle t req)
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| exception Loc.Error (_, m) -> (None, error ("bad request: " ^ m))
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in
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Wire.send fd reply;
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if op = Some "close" then true else go ()
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| exception Wire.Closed -> false
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| exception Unix.Unix_error _ -> false
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in
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go ()
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let start ~file ~sock =
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let t0 = Unix.gettimeofday () in
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let session, l = Session.create ~file in
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let dir =
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Filename.concat (Filename.get_temp_dir_name ())
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(Printf.sprintf "flan-dev-%d" (Unix.getpid ()))
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in
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(try Unix.mkdir dir 0o700 with Unix.Unix_error (Unix.EEXIST, _, _) -> ());
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let exe = Filename.concat dir "program" in
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ignore
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(Build.executable ~opts:{ Build.default with Build.dev = true }
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~csrcs:l.Load.csrcs ~lflags:l.Load.lflags session.Session.host ~out:exe);
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let agent = Filename.concat dir "agent.sock" in
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(* The program's source names some socket path; the daemon is the one that
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knows where it wants to talk to it, so it overrides through the
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environment. Guessing instead would fail silently — everything compiles,
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the module is built, and nothing ever receives it. *)
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Unix.putenv "FLAN_AGENT_SOCKET" agent;
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let child = Unix.create_process exe [| exe |] Unix.stdin Unix.stdout Unix.stderr in
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(* Wait for it to bind before accepting an evaluation. One that arrives first
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would fail for a reason that reads like a compiler bug. *)
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if not (await (fun () -> Sys.file_exists agent)) then begin
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(try Unix.kill child Sys.sigterm with Unix.Unix_error _ -> ());
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failwith
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("the program never listened on " ^ agent
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^ " — does it call (agent/start ...)?")
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end;
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let t = { session; child; agent; dir; n = 0 } in
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(try Unix.unlink sock with Unix.Unix_error _ -> ());
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let ls = Unix.socket Unix.PF_UNIX Unix.SOCK_STREAM 0 in
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Unix.bind ls (Unix.ADDR_UNIX sock);
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Unix.listen ls 4;
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Printf.eprintf "flan dev: %s ready on %s (%.0fms)\n%!" file sock
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((Unix.gettimeofday () -. t0) *. 1000.);
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(* [accept] would block past the program's own exit, so it is waited on with
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a timeout and the child checked each time round: a daemon whose program
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has finished has nothing left to do, and an editor waiting on it would
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wait forever. *)
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let rec accept_loop () =
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if alive t then
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match Unix.select [ ls ] [] [] 0.2 with
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| [], _, _ -> accept_loop ()
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| _ ->
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(match Unix.accept ls with
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| fd, _ ->
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let closed = serve t fd in
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(try Unix.close fd with Unix.Unix_error _ -> ());
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if not closed then accept_loop ()
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| exception Unix.Unix_error (Unix.EINTR, _, _) -> accept_loop ())
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| exception Unix.Unix_error (Unix.EINTR, _, _) -> accept_loop ()
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in
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Fun.protect
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~finally:(fun () ->
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(try Unix.kill child Sys.sigterm with Unix.Unix_error _ -> ());
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(try Unix.close ls with Unix.Unix_error _ -> ());
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(try Unix.unlink sock with Unix.Unix_error _ -> ()))
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accept_loop
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