feat(users/Profpatsch): add shortcuttable r/7711

Initial mockup for a tool which restarts its subprocess on SIGHUP, and
stops everything on SIGTERM and SIGINT.

Change-Id: Ie5260d73c2663d1821eb6623e2bc61d16f6c92cd
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11168
Autosubmit: Profpatsch <mail@profpatsch.de>
Reviewed-by: Profpatsch <mail@profpatsch.de>
Tested-by: BuildkiteCI

1 files changed, 172 insertions, 0 deletions

diff --git a/users/Profpatsch/shortcuttable/default.nix b/users/Profpatsch/shortcuttable/default.nix
new file mode 100644
index 000000000000..13ba22040056
--- /dev/null
+++ b/users/Profpatsch/shortcuttable/default.nix
@@ -0,0 +1,172 @@
+{ depot, lib, pkgs, ... }:
+
+let
+  # run prog... and restart whenever SIGHUP is received
+  #
+  # this is useful for binding to a shortcut.
+  #
+  # Unfortunately, this requires a bunch of workarounds around the semantics of `trap`,
+  # but the general idea of bundling subprocesses with `setsid` is somewhat sound.
+  runShortcuttable =
+    depot.nix.writeExecline "run-shortcuttable" { } [
+      "importas"
+      "-i"
+      "run"
+      "XDG_RUNTIME_DIR"
+      "if"
+      [ "mkdir" "-p" "\${run}/shortcuttable/test" ]
+      "getpid"
+      "-E"
+      "controlpid"
+      savePid
+      "\${run}/shortcuttable/test/control"
+      "$controlpid"
+
+      # start the program
+      "background"
+      [
+        startSaveSID
+        "\${run}/shortcuttable/test/running-sid"
+        "$@"
+      ]
+
+      "trap"
+      [
+        "SIGHUP"
+        [
+          "if"
+          [ "echo" "got hup" ]
+          "if"
+          [
+            "if"
+            [ "echo" "killing our child processes" ]
+            "envfile"
+            "\${run}/shortcuttable/test/running-sid"
+            "importas"
+            "-ui"
+            "child_sid"
+            "pid"
+            "foreground"
+            [ "ps" "-f" "--sid" "$child_sid" ]
+            ctrlCCtrlDSid
+            "$child_sid"
+          ]
+          "if"
+          [ "echo" "restarting into" "$@" ]
+          "background"
+          [
+            startSaveSID
+            "\${run}/shortcuttable/test/running-sid"
+            "$@"
+          ]
+        ]
+        "SIGTERM"
+        [
+          (killShortcuttable { signal = "TERM"; })
+          "\${run}/shortcuttable/test/running-sid"
+          "\${run}/shortcuttable/test/exit"
+        ]
+        "SIGINT"
+        [
+          (killShortcuttable { signal = "INT"; })
+          "\${run}/shortcuttable/test/running-sid"
+          "\${run}/shortcuttable/test/exit"
+        ]
+      ]
+      depot.users.Profpatsch.execline.setsid
+      "child_sid"
+      "getpid"
+      "-E"
+      "exitpid"
+      savePid
+      "\${run}/shortcuttable/test/exit"
+      "$exitpid"
+      "sleep"
+      "infinity"
+    ];
+
+  killShortcuttable = { signal }: depot.nix.writeExecline "kill-shortcuttable" { readNArgs = 2; } [
+    "if"
+    [ "echo" "got SIG${signal}, quitting" ]
+    "if"
+    [
+      "envfile"
+      "$1"
+      "importas"
+      "-ui"
+      "child_sid"
+      "pid"
+      "foreground"
+      [ "ps" "-f" "--sid" "$child_sid" ]
+      ctrlCCtrlDSid
+      "$child_sid"
+    ]
+    "if"
+    [ "echo" "killing shortcuttable loop" ]
+    "envfile"
+    "$2"
+    "importas"
+    "-ui"
+    "trap_pid"
+    "pid"
+    "foreground"
+    [ "ps" "-fp" "$trap_pid" ]
+    "kill"
+    "--signal"
+    signal
+    "$trap_pid"
+  ];
+
+  savePid = depot.nix.writeExecline "save-pid" { readNArgs = 2; } [
+    "if"
+    [ "echo" "saving process:" ]
+    "if"
+    [ "ps" "-fp" "$2" ]
+    "if"
+    [
+      "redirfd"
+      "-w"
+      "1"
+      "$1"
+      "printf"
+      "pid = %s\n"
+      "$2"
+    ]
+    "$@"
+  ];
+
+  # try to kill process, first with SIGTERM then SIGQUIT (in case it’s a repl)
+  ctrlCCtrlDSid = depot.nix.writeExecline "ctrl-c-ctrl-d" { readNArgs = 1; } [
+    "ifelse"
+    "-n"
+    [ "kill" "--signal" "TERM" "--" "-\${1}" ]
+    [
+      "if"
+      [ "echo" "could not kill via SIGTERM, trying SIGQUIT …" ]
+      "ifelse"
+      "-n"
+      [ "kill" "--signal" "QUIT" "--" "-\${1}" ]
+      [ "echo" "SIGQUIT failed as well, keeping it running" ]
+      "$@"
+    ]
+    "$@"
+  ];
+
+  startSaveSID = depot.nix.writeExecline "start-save-sid" { readNArgs = 1; } [
+    depot.users.Profpatsch.execline.setsid
+    "child_sid"
+    "importas"
+    "-ui"
+    "child_sid"
+    "child_sid"
+    "if"
+    [ "echo" "children sid:" "$child_sid" ]
+    savePid
+    "$1"
+    "$child_sid"
+    "$@"
+  ];
+
+
+in
+runShortcuttable