(core) Add test_replay for easily replaying data sent to the sandbox purely within python

Summary:
Run JS with a value for SANDBOX_BUFFERS_DIR, then run test_replay in python with the same value to replay just the python code.

See test_replay.py for more info.

Test Plan:
Record some data, e.g. `SANDBOX_BUFFERS_DIR=manual npm start` or `SANDBOX_BUFFERS_DIR=server ./test/testrun.sh server`.

Then run `SANDBOX_BUFFERS_DIR=server python -m unittest test_replay` from within `core/sandbox/grist` to replay the input from the JS.

Sample of the output will look like this:

```
Checking /tmp/sandbox_buffers/server/2021-06-16T15:13:59.958Z
True
Checking /tmp/sandbox_buffers/server/2021-06-16T15:16:37.170Z
True
Checking /tmp/sandbox_buffers/server/2021-06-16T15:14:22.378Z
True
```

Reviewers: paulfitz, dsagal

Reviewed By: dsagal

Differential Revision: https://phab.getgrist.com/D2866

app/server/lib/NSandbox.ts

@@ -12,6 +12,7 @@ import {ChildProcess, spawn, SpawnOptions} from 'child_process';
 import * as path from 'path';
 import {Stream, Writable} from 'stream';
 import * as _ from 'lodash';
+import * as fs from "fs";
 
 type SandboxMethod = (...args: any[]) => any;
 
@@ -33,6 +34,10 @@ type ResolveRejectPair = [(value?: any) => void, (reason?: unknown) => void];
 // Type for basic message identifiers, available as constants in sandboxUtil.
 type MsgCode = null | true | false;
 
+// Optional root folder to store binary data sent to and from the sandbox
+// See test_replay.py
+const recordBuffersRoot = process.env.RECORD_SANDBOX_BUFFERS_DIR;
+
 export class NSandbox implements ISandbox {
   /**
    * Helper function to run the nacl sandbox. It takes care of most arguments, similarly to
@@ -92,6 +97,9 @@ export class NSandbox implements ISandbox {
 
   private _throttle: Throttle | undefined;
 
+  // Create a unique subdirectory for each sandbox process so they can be replayed separately
+  private _recordBuffersDir = recordBuffersRoot ? path.resolve(recordBuffersRoot, new Date().toISOString()) : null;
+
   /*
    * Callers may listen to events from sandbox.childProc (a ChildProcess), e.g. 'close' and 'error'.
    * The sandbox listens for 'aboutToExit' event on the process, to properly shut down.
@@ -136,6 +144,11 @@ export class NSandbox implements ISandbox {
         logMeta: this._logMeta,
       });
     }
+
+    if (this._recordBuffersDir) {
+      log.rawDebug(`Recording sandbox buffers in ${this._recordBuffersDir}`, this._logMeta);
+      fs.mkdirSync(this._recordBuffersDir, {recursive: true});
+    }
   }
 
   /**
@@ -231,7 +244,11 @@ export class NSandbox implements ISandbox {
     }
     this._marshaller.marshal(msgCode);
     this._marshaller.marshal(data);
-    return this._streamToSandbox.write(this._marshaller.dumpAsBuffer());
+    const buf = this._marshaller.dumpAsBuffer();
+    if (this._recordBuffersDir) {
+      fs.appendFileSync(path.resolve(this._recordBuffersDir, "input"), buf);
+    }
+    return this._streamToSandbox.write(buf);
   }
 
 
@@ -241,6 +258,9 @@ export class NSandbox implements ISandbox {
   private _onSandboxData(data: any) {
     this._unmarshaller.parse(data, buf => {
       const value = marshal.loads(buf, { bufferToString: true });
+      if (this._recordBuffersDir) {
+        fs.appendFileSync(path.resolve(this._recordBuffersDir, "output"), buf);
+      }
       this._onSandboxMsg(value[0], value[1]);
     });
   }

sandbox/grist/main.py

@@ -13,7 +13,7 @@ import six
 
 from acl_formula import parse_acl_formula
 import actions
-import sandbox
+from sandbox import Sandbox
 import engine
 import migrations
 import schema
@@ -23,15 +23,6 @@ import objtypes
 import logger
 log = logger.Logger(__name__, logger.INFO)
 
-def export(method):
-  # Wrap each method so that it logs a message that it's being called.
-  @functools.wraps(method)
-  def wrapper(*args, **kwargs):
-    log.debug("calling %s" % method.__name__)
-    return method(*args, **kwargs)
-
-  sandbox.register(method.__name__, wrapper)
-
 def table_data_from_db(table_name, table_data_repr):
   if table_data_repr is None:
     return actions.TableData(table_name, [], {})
@@ -51,9 +42,18 @@ def _decode_db_value(value):
   else:
     return value
 
-def main():
+def run(sandbox):
   eng = engine.Engine()
 
+  def export(method):
+    # Wrap each method so that it logs a message that it's being called.
+    @functools.wraps(method)
+    def wrapper(*args, **kwargs):
+      log.debug("calling %s" % method.__name__)
+      return method(*args, **kwargs)
+
+    sandbox.register(method.__name__, wrapper)
+
   @export
   def apply_user_actions(action_reprs):
     action_group = eng.apply_user_actions([useractions.from_repr(u) for u in action_reprs])
@@ -114,5 +114,9 @@ def main():
 
   sandbox.run()
 
+def main():
+  sandbox = Sandbox.connected_to_js_pipes()
+  run(sandbox)
+
 if __name__ == "__main__":
   main()

sandbox/grist/sandbox.py

@@ -11,7 +11,6 @@ Usage:
 
 import os
 import marshal
-import signal
 import sys
 import traceback
 
@@ -36,10 +35,16 @@ class Sandbox(object):
   DATA = True
   EXC = False
 
-  def __init__(self):
+  def __init__(self, external_input, external_output):
     self._functions = {}
-    self._external_input = os.fdopen(3, "rb", 64*1024)
-    self._external_output = os.fdopen(4, "wb", 64*1024)
+    self._external_input = external_input
+    self._external_output = external_output
+
+  @classmethod
+  def connected_to_js_pipes(cls):
+    external_input = os.fdopen(3, "rb", 64 * 1024)
+    external_output = os.fdopen(4, "wb", 64 * 1024)
+    return cls(external_input, external_output)
 
   def _send_to_js(self, msgCode, msgBody):
     # (Note that marshal version 2 is the default; we specify it explicitly for clarity. The
@@ -87,14 +92,19 @@ class Sandbox(object):
     if break_on_response:
       raise Exception("Sandbox disconnected unexpectedly")
 
+default_sandbox = None
 
-sandbox = Sandbox()
+def get_default_sandbox():
+  global default_sandbox
+  if default_sandbox is None:
+    default_sandbox = Sandbox.connected_to_js_pipes()
+  return default_sandbox
 
 def call_external(name, *args):
-  return sandbox.call_external(name, *args)
+  return get_default_sandbox().call_external(name, *args)
 
 def register(func_name, func):
-  sandbox.register(func_name, func)
+  get_default_sandbox().register(func_name, func)
 
 def run():
-  sandbox.run()
+  get_default_sandbox().run()

sandbox/grist/test_replay.py

@@ -0,0 +1,91 @@
+"""
+Replay binary data sent from JS to reproduce behaviour in the sandbox.
+
+This isn't really a test and it doesn't run under normal circumstances,
+but it's convenient to run it alongside other tests to measure total coverage.
+
+This is a tool to directly run some python code of interest to make it easier to do things like:
+
+- Use a debugger within Python
+- Measure Python code coverage from JS tests
+- Rapidly iterate on Python code without having to repeatedly run the same JS
+    or write a Python test from scratch.
+
+To use this, first set the environment variable RECORD_SANDBOX_BUFFERS_DIR to a directory path,
+then run some JS code. For example you could run some tests,
+or run `npm start` and then manually interact with a document in a way that triggers
+desired behaviour in the sandbox.
+
+This will store files like $RECORD_SANDBOX_BUFFERS_DIR/<subdirectory>/(input|output)
+Each subdirectory corresponds to a single sandbox process so that replays are isolated.
+JS tests can start many instances of the sandbox and thus create many subdirectories.
+`input` contains the binary data sent from JS to Python, `output` contains the data sent back.
+Currently, the name of each subdirectory is the time it was created.
+
+Now run this test with the same value of RECORD_SANDBOX_BUFFERS_DIR. For each subdirectory,
+it will read in `input` just as it would read the pipe from JS, and send output to a file
+`new_output` in the same subdirectory. Then it will compare the data in `output` and `new_output`.
+The outputs will usually match but there are many reasons they might differ:
+
+- Functions registered in JS tests (e.g. via plugins) but not in the python unit tests.
+- File paths in tracebacks.
+- Slight differences between standard and NaCl interpreters.
+- Functions involving randomness or time.
+
+In any case the point is usually not whether or not the outputs match, but to directly run
+just the python code of interest.
+"""
+
+from __future__ import print_function
+
+import marshal
+import os
+import unittest
+
+from main import run
+from sandbox import Sandbox
+
+
+def marshal_load_all(path):
+  result = []
+  with open(path, "rb") as f:
+    while True:
+      try:
+        result.append(marshal.load(f))
+      except EOFError:
+        break
+
+  return result
+
+
+class TestReplay(unittest.TestCase):
+  maxDiff = None
+
+  def test_replay(self):
+    root = os.environ.get("RECORD_SANDBOX_BUFFERS_DIR")
+    if not root:
+      self.skipTest("RECORD_SANDBOX_BUFFERS_DIR not set")
+    for dirpath, dirnames, filenames in os.walk(root):
+      if "input" not in filenames:
+        continue
+
+      print("Checking " + dirpath)
+
+      input_path = os.path.join(dirpath, "input")
+      output_path = os.path.join(dirpath, "output")
+      new_output_path = os.path.join(dirpath, "new_output")
+      with open(input_path, "rb") as external_input:
+        with open(new_output_path, "wb") as external_output:
+          sandbox = Sandbox(external_input, external_output)
+          run(sandbox)
+
+      original_output = marshal_load_all(output_path)
+
+      # _send_to_js does two layers of marshalling,
+      # and NSandbox._onSandboxData parses one of those layers before writing,
+      # hence original_output is 'more parsed' than marshal_load_all(new_output_path)
+      new_output = [marshal.loads(b) for b in marshal_load_all(new_output_path)]
+
+      # It's usually not worth asserting a match, see comments at the top of the file
+      print("Match:", original_output == new_output)
+      # self.assertEqual(original_output, new_output)