argparser fixes and add tests.

httpie/cli/argparser.py

@@ -226,44 +226,42 @@ def _process_url(self):
 
     def _setup_standard_streams(self):
         """
-        Modify `env.stdout` and `env.stdout_isatty` based on args, if needed.
-
+        Modify env.stdout and env.stdout_isatty based on args.
         """
 
         self.args.output_file_specified = bool(self.args.output_file)
+
+        # Select the default output stream.
+        target_stream = self.env.stdout
+        target_isatty = self.env.stdout_isatty
+
         if self.args.download:
-            # FIXME: Come up with a cleaner solution.
             if not self.args.output_file and not self.env.stdout_isatty:
-                # Use stdout as the download output file.
                 self.args.output_file = self.env.stdout
-            # With `--download`, we write everything that would normally go to
-            # `stdout` to `stderr` instead. Let's replace the stream so that
-            # we don't have to use many `if`s throughout the codebase.
-            # The response body will be treated separately.
-            self.env.stdout = self.env.stderr
-            self.env.stdout_isatty = self.env.stderr_isatty
+
+            target_stream = self.env.stderr
+            target_isatty = self.env.stderr_isatty
 
         elif self.args.output_file:
-            # When not `--download`ing, then `--output` simply replaces
-            # `stdout`. The file is opened for appending, which isn't what
-            # we want in this case.
             self.args.output_file.seek(0)
             try:
                 self.args.output_file.truncate()
             except OSError as e:
-                if e.errno == errno.EINVAL:
-                    # E.g. /dev/null on Linux.
-                    pass
-                else:
+                if e.errno != errno.EINVAL:
                     raise
-            self.env.stdout = self.args.output_file
-            self.env.stdout_isatty = False
+
+            target_stream = self.args.output_file
+            target_isatty = False
+
+        self.env.stdout = target_stream
+        self.env.stdout_isatty = target_isatty
 
         if self.args.quiet:
-            self.env.quiet = self.args.quiet
+            self.env.quiet = True
             self.env.stderr = self.env.devnull
             if not (self.args.output_file_specified and not self.args.download):
                 self.env.stdout = self.env.devnull
+
             self.env.apply_warnings_filter()
 
     def _process_ssl_cert(self):
@@ -419,8 +417,7 @@ def _guess_method(self):
             else:
                 self.args.method = HTTP_GET
 
-        # FIXME: False positive, e.g., "localhost" matches but is a valid URL.
-        elif not re.match('^[a-zA-Z]+$', self.args.method):
+        elif not re.match('^[a-zA-Z]+$', self.args.method) or self.args.method.lower() == 'localhost':
             # Invoked as `http URL item+'. The URL is now in `args.method`
             # and the first ITEM is now incorrectly in `args.url`.
             try:

tests/test_cli.py

@@ -315,6 +315,21 @@ def test_guess_when_method_set_but_invalid_and_item_exists(self):
             KeyValueArg(
                 key='old_item', value='b', sep='=', orig='old_item=b'),
         ]
+
+
+    def test_guess_when_method_set_but_invalid_bare_hostname(self):
+        self.parser.args = argparse.Namespace()
+        self.parser.args.method = 'localhost'
+        self.parser.args.url = 'name=example-data'
+        self.parser.args.request_items = []
+        self.parser.args.ignore_stdin = False
+        self.parser.env = MockEnvironment()
+        self.parser._guess_method()
+        assert self.parser.args.method == 'POST'
+        assert self.parser.args.url == 'localhost'
+        assert self.parser.args.request_items == [
+            KeyValueArg(key='name', value='example-data', sep='=', orig='name=example-data')
+        ]
 
 
 class TestNoOptions:

tests/test_stream.py

@@ -2,13 +2,14 @@
 
 import pytest
 import responses
-from unittest.mock import Mock
+from unittest.mock import Mock, MagicMock
 
 from httpie.compat import is_windows
 from httpie.cli.constants import PRETTY_MAP
 from httpie.output.streams import BINARY_SUPPRESSED_NOTICE
 from httpie.plugins import ConverterPlugin
 from httpie.plugins.registry import plugin_manager
+from httpie.cli.argparser import HTTPieArgumentParser
 
 from .utils import StdinBytesIO, http, MockEnvironment, DUMMY_URL
 from .fixtures import (
@@ -49,6 +50,89 @@ def test_pretty_redirected_stream(httpbin):
              httpbin + '/get', env=env)
     assert BINARY_SUPPRESSED_NOTICE.decode() in r
 
+@pytest.fixture
+def mock_env_args():
+    """
+    Provides an isolated mock instance containing 'args' and 'env' attributes
+    to safely test stream hijacking without affecting real system streams.
+    """
+    instance = MagicMock()
+
+    # Mock CLI arguments
+    instance.args.output_file = None
+    instance.args.download = False
+    instance.args.quiet = False
+
+    # Mock Environment streams
+    instance.env.stdout = MagicMock()
+    instance.env.stdout_isatty = True
+    instance.env.stderr = MagicMock()
+    instance.env.stderr_isatty = True
+    instance.env.devnull = MagicMock()
+    instance.env.quiet = False
+
+    # Mock warning filter
+    instance.env.apply_warnings_filter = MagicMock()
+
+    return instance
+
+
+def test_setup_streams_download_with_pipe(mock_env_args):
+    """
+    Test that standard streams are correctly redirected when '--download' is used
+    and stdout is piped (isatty is False).
+    Expected: output_file becomes the original stdout, and stdout is hijacked to stderr.
+    """
+    # Setup state
+    mock_env_args.args.download = True
+    mock_env_args.env.stdout_isatty = False  # Simulating piped stdout
+
+    original_stdout = mock_env_args.env.stdout
+    original_stderr = mock_env_args.env.stderr
+    original_stderr_isatty = mock_env_args.env.stderr_isatty
+
+    # Sınıf üzerinden asıl fonksiyonu çağırıyoruz
+    HTTPieArgumentParser._setup_standard_streams(mock_env_args)
+
+    # Verify stream redirection
+    assert mock_env_args.args.output_file == original_stdout, "output_file should be assigned to original stdout"
+    assert mock_env_args.env.stdout == original_stderr, "stdout should still be hijacked to stderr"
+    assert mock_env_args.env.stdout_isatty == original_stderr_isatty
+
+
+def test_setup_streams_download_without_pipe(mock_env_args):
+    """
+    Test stream behavior when '--download' is active but running in a standard TTY.
+    Expected: output_file remains untouched, but stdout is still hijacked to stderr.
+    """
+    mock_env_args.args.download = True
+    mock_env_args.env.stdout_isatty = True  # Standard TTY
+
+    original_stderr = mock_env_args.env.stderr
+
+    # Sınıf üzerinden asıl fonksiyonu çağırıyoruz
+    HTTPieArgumentParser._setup_standard_streams(mock_env_args)
+
+    assert mock_env_args.args.output_file is None, "output_file should not be modified in TTY mode"
+    assert mock_env_args.env.stdout == original_stderr, "stdout should still be hijacked to stderr"
+
+
+def test_setup_streams_output_file_resets_pointer(mock_env_args):
+    """
+    Test that standard output files (non-download) are properly truncated
+    and the file pointer is reset to 0 before appending new data.
+    """
+    mock_env_args.args.download = False
+
+    # Mock an open file object
+    mock_file = MagicMock()
+    mock_env_args.args.output_file = mock_file
+
+    # Sınıf üzerinden asıl fonksiyonu çağırıyoruz
+    HTTPieArgumentParser._setup_standard_streams(mock_env_args)
+
+    # Verify file operations
+    mock_file.seek.assert_called_once_with(0)
 
 def test_pretty_stream_ensure_full_stream_is_retrieved(httpbin):
     env = MockEnvironment(