add shell monitoring

lib/build.nix

@@ -157,6 +157,16 @@
             inherit (pkgs.lib) foldlAttrs;
             inherit works;
           };
+          # shell id is based on the services config
+          shellId = builtins.hashString "sha256" (builtins.toJSON config._buildIdes.finalServices);
+          monitor = import ./monitor.nix {
+            inherit (pkgs) writeShellScriptBin;
+            inherit shellId;
+            cli = pkgs.lib.getExe cli;
+            socat = pkgs.lib.getExe pkgs.socat;
+            # TODO make this timeout more lenient?
+            timeout = if (pkgs.lib.typeOf config.monitor == "int") then config.monitor else 20;
+          };
 
           # create the ides shell
           final =
@@ -177,14 +187,28 @@
                       ''
                     else
                       "";
+                  monitorRun =
+                    let
+                      inherit (pkgs.lib) getExe;
+                    in
+                    if config.monitor then
+                      ''
+                        systemd-run --user -q -G -u ides-${shellId}-monitor ${getExe monitor.daemon} $PWD
+                        ${getExe monitor.client} $$
+                      ''
+                    else
+                      "";
                 in
                 (shellArgs.shellHook or "")
                 + ''
                   printf '[ides]: use "ides [action] [target]" to control services. type "ides help" to find out more.\n'
+                  export IDES_CTL="/run/user/$(id -u)/ides-${shellId}.sock"
                 ''
-                + autoRun;
+                + autoRun
+                + monitorRun;
             };
         in
+        # TODO make this optionally return the shell components to allow composability with other dev shell solutions
         config._buildIdes.shellFn final;
     };
 

lib/monitor.nix

@@ -0,0 +1,125 @@
+{
+  socat,
+  writeShellScriptBin,
+  shellId,
+  cli,
+  timeout,
+  ...
+}:
+let
+  wait = builtins.toString timeout;
+in
+{
+  daemon = writeShellScriptBin "ides-monitor-${shellId}" ''
+    BASE_PATH="$1"
+    SOCKET=/run/user/$(id -u)/ides-${shellId}.sock
+
+    # if socket exists, it's already being monitored
+    if [ -e "$SOCKET" ]; then
+      exit 1
+    fi
+
+    PIDS=()
+
+    # loop on socket forever
+    while true; do
+      # wait to receive a PID
+      PID=$(timeout ${wait} ${socat} UNIX-LISTEN:"$SOCKET" -)
+      # if received and unique, add to our watch
+      if [ "$?" -eq 0 ] && ! [[ "''${PIDS[@]}" =~ $PID ]]; then
+        echo adding $PID to watch
+        PIDS+=($PID)
+        echo pids are now ''${PIDS[@]}
+      fi
+
+      # check process statuses
+      DEAD=true
+      for INDEX in "''${!PIDS[@]}"; do
+        REMOVE=false
+
+        # get pid
+        CHECK="''${PIDS[$INDEX]}"
+        echo checking $CHECK
+
+        # check status
+        ALIVE=$(kill -0 "$CHECK" 2>&1 > /dev/null)
+
+        # determine eligibility to act as a service root
+        if $ALIVE; then
+
+          CMD=$(cat /proc/$CHECK/comm)
+          case "$CMD" in
+            # if host is an editor, we don't care about pwd
+            code|codium|zed|emacs|intellij*|sublime*)
+              DEAD=false
+            ;;
+            # if it's a shell we really do
+            sh|bash|zsh|fish|nu|murex|*)
+              DIR=$(readlink /proc/$CHECK/cwd)
+              if [[ "$DIR" == "$BASE_PATH"* ]]; then
+                DEAD=false
+              else
+                REMOVE=true
+              fi
+            ;;
+          esac
+
+          echo found $CHECK alive with $CMD in $DIR
+          
+        else
+
+          echo found $CHECK dead
+
+          REMOVE=true
+
+        fi
+
+        if $REMOVE; then
+          echo removing ineligible pid $CHECK 
+          unset "PIDS[$INDEX]"
+        fi
+
+      done
+      
+      if "$DEAD"; then
+        echo no live pids, breaking
+        break
+      fi
+
+    done
+
+    # loop has broken, no valid pids left
+    echo stopping all!
+    ${cli} stop
+  '';
+
+  # FIXME if the client finds its parent is an editor process,
+  # such as `code`, should it keep walking pids until the final parent?
+  client = writeShellScriptBin "ides-notify-${shellId}" ''
+    function get-parent() {
+      ps --no-header -o ppid:1 $1
+    }
+
+    function get-command() {
+      cat /proc/$1/comm
+    }
+
+    SOCKET=/var/run/user/$(id -u)/ides-${shellId}.sock
+    # wait for socket to come up
+    while ! [ -e "$SOCKET" ]; do
+      sleep 0.5
+    done
+
+    # check if our calling shell's parent process is direnv
+    PARENT=$(get-parent $1)
+    COMM=$(get-command $PARENT)
+    TARGET="$1"
+    echo found $COMM as parent
+    if [[ "$COMM" == "direnv" ]]; then
+      # if so, skip up another parent to get the process it is exporting to
+      TARGET=$(get-parent $PARENT)
+    fi
+    # tell monitor about the devshell
+    echo "$TARGET" | ${socat} - UNIX-CONNECT:"$SOCKET"
+  '';
+}

lib/options.nix

@@ -125,6 +125,12 @@
         default = true;
       };
 
+      monitor = mkOption {
+        type = types.either types.bool types.int;
+        description = "Enable, or set timeout period for, monitoring devshell activity and automatically destroy services after (experimental).";
+        default = true;
+      };
+
       # to prevent generating docs for this option; see https://github.com/NixOS/nixpkgs/issues/293510
       _module.args = mkOption {
         internal = true;