termlog: let click figure out stdout/stderr (#4679)

passing sys.stdout to click does not work under some circumstances.
For example, we cannot `click.echo("\u2026")` from pyinstaller binaries in a Docker container
with `file=sys.stdout`. Instead, we shall pass `err`, which somehow works.

mitmproxy/addons/dumper.py

@@ -1,7 +1,6 @@
 import itertools
 import shutil
-import sys
-from typing import Optional, TextIO, Union
+from typing import IO, Optional, Union
 
 import click
 
@@ -31,10 +30,10 @@ def colorful(line, styles):
 
 
 class Dumper:
-    def __init__(self, outfile=sys.stdout, errfile=sys.stderr):
+    def __init__(self, outfile=None, errfile=None):
         self.filter: Optional[flowfilter.TFilter] = None
-        self.outfp: TextIO = outfile
-        self.errfp: TextIO = errfile
+        self.outfp: Optional[IO] = outfile
+        self.errfp: Optional[IO] = errfile
 
     def load(self, loader):
         loader.add_option(
@@ -72,12 +71,12 @@ class Dumper:
     def echo(self, text: str, ident=None, **style):
         if ident:
             text = indent(ident, text)
-        click.secho(text, file=self.outfp, **style)
+        click.secho(text, file=self.outfp, err=False, **style)
         if self.outfp:
             self.outfp.flush()
 
     def echo_error(self, text: str, **style):
-        click.secho(text, file=self.errfp, **style)
+        click.secho(text, file=self.errfp, err=True, **style)
         if self.errfp:
             self.errfp.flush()
 

mitmproxy/addons/termlog.py

@@ -1,18 +1,14 @@
-import sys
+from typing import IO, Optional
+
 import click
 
 from mitmproxy import log
 from mitmproxy import ctx
 
-# These get over-ridden by the save execution context. Keep them around so we
-# can log directly.
-realstdout = sys.stdout
-realstderr = sys.stderr
-
 
 class TermLog:
     def __init__(self, outfile=None):
-        self.outfile = outfile
+        self.outfile: Optional[IO] = outfile
 
     def load(self, loader):
         loader.add_option(
@@ -22,15 +18,10 @@ class TermLog:
         )
 
     def add_log(self, e):
-        if log.log_tier(e.level) == log.log_tier("error"):
-            outfile = self.outfile or realstderr
-        else:
-            outfile = self.outfile or realstdout
-
         if log.log_tier(ctx.options.termlog_verbosity) >= log.log_tier(e.level):
             click.secho(
                 e.msg,
-                file=outfile,
+                file=self.outfile,
                 fg=dict(error="red", warn="yellow",
                         alert="magenta").get(e.level),
                 dim=(e.level == "debug"),