feat(cli): Use SIGUSR2 to run sysctl commands

hathor/cli/run_node.py

@@ -14,8 +14,10 @@
 
 import os
 import sys
+import tempfile
 from argparse import SUPPRESS, ArgumentParser, Namespace
-from typing import TYPE_CHECKING, Any, Callable, Optional
+from contextlib import contextmanager
+from typing import TYPE_CHECKING, Any, Callable, Iterator, Optional
 
 from pydantic import ValidationError
 from structlog import get_logger
@@ -25,6 +27,21 @@
 
 if TYPE_CHECKING:
     from hathor.cli.run_node_args import RunNodeArgs
+    from hathor.sysctl.runner import SysctlRunner
+
+
+@contextmanager
+def temp_fifo(filename: str, tempdir: str | None) -> Iterator[str]:
+    """Context Manager for creating named pipes."""
+    os.mkfifo(filename, mode=0o666)
+    fp = open(filename, 'r')
+    try:
+        yield fp
+    finally:
+        fp.close()
+        os.unlink(filename)
+        if tempdir is not None:
+            os.rmdir(tempdir)
 
 
 class RunNode:
@@ -232,12 +249,81 @@ def register_signal_handlers(self) -> None:
         if sigusr1 is not None:
             # USR1 is available in this OS.
             signal.signal(sigusr1, self.signal_usr1_handler)
+        sigusr2 = getattr(signal, 'SIGUSR2', None)
+        if sigusr2 is not None:
+            # USR1 is available in this OS.
+            signal.signal(sigusr2, self.signal_usr2_handler)
 
     def signal_usr1_handler(self, sig: int, frame: Any) -> None:
         """Called when USR1 signal is received."""
-        self.log.warn('USR1 received. Killing all connections...')
-        if self.manager and self.manager.connections:
-            self.manager.connections.disconnect_all_peers(force=True)
+        try:
+            self.log.warn('USR1 received. Killing all connections...')
+            if self.manager and self.manager.connections:
+                self.manager.connections.disconnect_all_peers(force=True)
+        except Exception:
+            # see: https://docs.python.org/3/library/signal.html#note-on-signal-handlers-and-exceptions
+            self.log.error('prevented exception from escaping the signal handler', exc_info=True)
+
+    def signal_usr2_handler(self, sig: int, frame: Any) -> None:
+        """Called when USR2 signal is received."""
+        try:
+            self.log.warn('USR2 received.')
+            self.run_sysctl_from_signal()
+        except Exception:
+            # see: https://docs.python.org/3/library/signal.html#note-on-signal-handlers-and-exceptions
+            self.log.error('prevented exception from escaping the signal handler', exc_info=True)
+
+    def run_sysctl_from_signal(self) -> None:
+        """Block the main loop, get commands from a named pipe and execute then using sysctl."""
+        from hathor.sysctl.exception import (
+            SysctlEntryNotFound,
+            SysctlException,
+            SysctlReadOnlyEntry,
+            SysctlRunnerException,
+            SysctlWriteOnlyEntry,
+        )
+
+        runner = self.get_sysctl_runner()
+
+        if self._args.data is not None:
+            basedir = self._args.data
+            tempdir = None
+        else:
+            basedir = tempfile.mkdtemp()
+            tempdir = basedir
+
+        filename = os.path.join(basedir, f'SIGUSR2-{os.getpid()}.pipe')
+        if os.path.exists(filename):
+            self.log.warn('[USR2] Pipe already exists.', pipe=filename)
+            return
+
+        with temp_fifo(filename, tempdir) as fp:
+            self.log.warn('[USR2] Waiting for commands...', pipe=filename)
+            fp = open(filename, 'r')
+            lines = fp.readlines()
+            fp.close()
+            for cmd in lines:
+                cmd = cmd.strip()
+                self.log.warn('[USR2] Command received ', cmd=cmd)
+
+                try:
+                    output = runner.run(cmd)
+                    self.log.warn('[USR2] Output', output=output)
+                except SysctlEntryNotFound:
+                    path, _, _ = runner.get_line_parts(cmd)
+                    self.log.warn('[USR2] Error', errmsg=f'{path} not found')
+                except SysctlReadOnlyEntry:
+                    path, _, _ = runner.get_line_parts(cmd)
+                    self.log.warn('[USR2] Error', errmsg=f'cannot write to {path}')
+                except SysctlWriteOnlyEntry:
+                    path, _, _ = runner.get_line_parts(cmd)
+                    self.log.warn('[USR2] Error', errmsg=f'cannot read from {path}')
+                except SysctlException as e:
+                    self.log.warn('[USR2] Error', errmsg=str(e))
+                except ValidationError as e:
+                    self.log.warn('[USR2] Error', errmsg=str(e))
+                except SysctlRunnerException as e:
+                    self.log.warn('[USR2] Error', errmsg=str(e))
 
     def check_unsafe_arguments(self) -> None:
         unsafe_args_found = []
@@ -386,6 +472,16 @@ def __init__(self, *, argv=None):
         if self._args.sysctl:
             self.init_sysctl(self._args.sysctl, self._args.sysctl_init_file)
 
+    def get_sysctl_runner(self) -> 'SysctlRunner':
+        """Create and return a SysctlRunner."""
+        from hathor.builder.sysctl_builder import SysctlBuilder
+        from hathor.sysctl.runner import SysctlRunner
+
+        builder = SysctlBuilder(self.artifacts)
+        root = builder.build()
+        runner = SysctlRunner(root)
+        return runner
+
     def init_sysctl(self, description: str, sysctl_init_file: Optional[str] = None) -> None:
         """Initialize sysctl, listen for connections and apply settings from config file if required.
 
@@ -400,14 +496,10 @@ def init_sysctl(self, description: str, sysctl_init_file: Optional[str] = None)
         """
         from twisted.internet.endpoints import serverFromString
 
-        from hathor.builder.sysctl_builder import SysctlBuilder
         from hathor.sysctl.factory import SysctlFactory
         from hathor.sysctl.init_file_loader import SysctlInitFileLoader
-        from hathor.sysctl.runner import SysctlRunner
 
-        builder = SysctlBuilder(self.artifacts)
-        root = builder.build()
-        runner = SysctlRunner(root)
+        runner = self.get_sysctl_runner()
 
         if sysctl_init_file:
             init_file_loader = SysctlInitFileLoader(runner, sysctl_init_file)