[plugin] SSH: rejig how the Dropbear process is stopped so it will be stopped when the plugin is disabled

plugins/SSH.koplugin/main.lua

@@ -99,15 +99,46 @@ function SSH:isRunning()
     return util.pathExists("/tmp/dropbear_koreader.pid")
 end
 
-function SSH:stop()
-    os.execute("cat /tmp/dropbear_koreader.pid | xargs kill")
-    UIManager:show(InfoMessage:new {
-        text = T(_("SSH server stopped.")),
-        timeout = 2,
-    })
+--- Stops the Dropbear process started by this plugin.
+--- @param force boolean If true, forces the process to stop if it doesn't exit gracefully.
+--- @return boolean Success, string|nil Error
+function SSH:stopPlugin(force)
+    if not self:isRunning() then
+        return true
+    end
 
-    if self:isRunning() then
-        os.remove("/tmp/dropbear_koreader.pid")
+    local pid_path = "/tmp/dropbear_koreader.pid"
+
+    local function readPID()
+        local f = io.open(pid_path, "r")
+        if not f then return nil end
+        local s = f:read("*l")
+        f:close()
+        return s and tonumber(s) or nil
+    end
+
+    local pid = readPID()
+
+    local function isProcAlive(p)
+        return p and util.pathExists("/proc/" .. p)
+    end
+
+    local function send(sig, p)
+        return os.execute(string.format("kill -%s %d", sig, p)) == 0
+    end
+
+    send("TERM", pid)
+    for _ = 1, 20 do
+        if not isProcAlive(pid) then break end
+        ffiutil.sleep(0.1)
+    end
+
+    if isProcAlive(pid) and force then
+        send("KILL", pid)
+        for _ = 1, 10 do
+            if not isProcAlive(pid) then break end
+            ffiutil.sleep(0.1)
+        end
     end
 
     -- Plug the hole in the Kindle's firewall
@@ -119,6 +150,33 @@ function SSH:stop()
             "iptables -D OUTPUT -p tcp --sport", self.SSH_port,
             "-m conntrack --ctstate ESTABLISHED -j ACCEPT"))
     end
+
+    if not isProcAlive(pid) then
+        os.remove(pid_path)
+        return true
+    end
+    return false, "dropbear process did not exit"
+end
+
+function SSH:stop()
+    local ok, err = self:stopPlugin(false)
+    if not ok then
+        logger.warn("SSH: graceful stop failed:", err)
+        ok, err = self:stopPlugin(true)
+        if not ok then
+            logger.err("SSH: force-stop failed:", err)
+            UIManager:show(InfoMessage:new{
+                icon = "notice-warning",
+                text = _("Failed to stop SSH server."),
+            })
+        end
+    end
+    if ok then
+        UIManager:Show(InfoMessage:new{
+            text = _("SSH server stopped."),
+            timeout = 2,
+        })
+    end
 end
 
 function SSH:onToggleSSHServer()