Repository: celery/celery

Issue:
Celery breaks libs using `sys.stdout.write()`
`LoggingProxy.write()` currently always returns `None` (because in Python2 that was the correct return type!)

From the [Python docs](https://docs.python.org/release/3.9.2/library/io.html#io.TextIOBase.write):

>`write(s)`
> Write the string s to the stream and return the number of characters written.

Therefore methods that rely on `sys.stdout.write()` expect `LoggingProxy` (which `celery` replaces `sys.stdout` with) to conform to the same `IO.write()` return type.

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  for similar or identical bug reports.
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#### Related Issues

- #928

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## Environment & Settings
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**Celery version**:
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```
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<details>
<p>

```python
p = LoggingProxy(logger, loglevel=logging.ERROR)
p.closed = False
num_chars = p.write('foo')
assert num_chars == 3
```

</p>
</details>

# Expected Behavior
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`LoggingProxy` returns the number of characters/bytes written 

# Actual Behavior
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`LoggingProxy` returns `None`



Discussion:

Resolving patch:
diff --git a/celery/utils/log.py b/celery/utils/log.py
--- a/celery/utils/log.py
+++ b/celery/utils/log.py
@@ -214,19 +214,24 @@ def handleError(self, record):
         return [wrap_handler(h) for h in self.logger.handlers]
 
     def write(self, data):
+        # type: (AnyStr) -> int
         """Write message to logging object."""
         if _in_sighandler:
-            return print(safe_str(data), file=sys.__stderr__)
+            safe_data = safe_str(data)
+            print(safe_data, file=sys.__stderr__)
+            return len(safe_data)
         if getattr(self._thread, 'recurse_protection', False):
             # Logger is logging back to this file, so stop recursing.
-            return
-        data = data.strip()
+            return 0
         if data and not self.closed:
             self._thread.recurse_protection = True
             try:
-                self.logger.log(self.loglevel, safe_str(data))
+                safe_data = safe_str(data)
+                self.logger.log(self.loglevel, safe_data)
+                return len(safe_data)
             finally:
                 self._thread.recurse_protection = False
+        return 0
 
     def writelines(self, sequence):
         # type: (Sequence[str]) -> None


Test patch:
diff --git a/t/unit/app/test_log.py b/t/unit/app/test_log.py
--- a/t/unit/app/test_log.py
+++ b/t/unit/app/test_log.py
@@ -268,8 +268,9 @@ def test_logging_proxy(self):
             p.write('foo')
             assert 'foo' not in sio.getvalue()
             p.closed = False
-            p.write('foo')
-            assert 'foo' in sio.getvalue()
+            write_res = p.write('foo ')
+            assert 'foo ' in sio.getvalue()
+            assert write_res == 4
             lines = ['baz', 'xuzzy']
             p.writelines(lines)
             for line in lines:
@@ -290,7 +291,7 @@ def test_logging_proxy_recurse_protection(self):
         p = LoggingProxy(logger, loglevel=logging.ERROR)
         p._thread.recurse_protection = True
         try:
-            assert p.write('FOOFO') is None
+            assert p.write('FOOFO') == 0
         finally:
             p._thread.recurse_protection = False