fix: write binary graphviz output to temp file when stdout is tty (#564)

## Summary

When using graphviz output formats like png, jpeg, pdf, etc., the output
is binary and was previously written directly to stdout. This causes
issues when stdout is a terminal (isatty), as binary data would be
spewed to the console.

This fix addresses the issue by:
- Detecting when stdout is a tty and the output is binary
- Writing to a temporary file with appropriate extension
- Printing the file path to stderr
- Opening the file with webbrowser.open()

This matches the behavior suggested in the original issue.

## Changes

- Modified `print_graphviz()` to handle tty case for binary output
- Updated `render_graphviz()` to pass output format to
`print_graphviz()`
- Added test `test_print_graphviz_binary_tty_handling` to verify the fix

## Testing

- All existing graphviz tests pass
- New test verifies the tty handling behavior

Closes #103

---------

Co-authored-by: Funan Zhou <matrix@blocksec.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: 3 people

src/pipdeptree/_render/graphviz.py

@@ -3,6 +3,8 @@
 import math
 import os
 import sys
+import tempfile
+import webbrowser
 from collections import deque
 from typing import TYPE_CHECKING
 
@@ -16,7 +18,10 @@
 
 def render_graphviz(tree: PackageDAG, *, output_format: str, reverse: bool, max_depth: float = math.inf) -> None:
     output = dump_graphviz(tree, output_format=output_format, is_reverse=reverse, max_depth=max_depth)
-    print_graphviz(output)
+    if isinstance(output, bytes):
+        print_graphviz(output, output_format=output_format)
+    else:
+        print_graphviz(output)
 
 
 def dump_graphviz(
@@ -76,13 +81,28 @@ def dump_graphviz(
         return graph.pipe()
 
 
-def print_graphviz(dump_output: str | bytes) -> None:
+def print_graphviz(dump_output: str | bytes, *, output_format: str = "dot") -> None:
     """
-    Dump the data generated by GraphViz to stdout.
+    Dump the data generated by GraphViz to stdout or open in browser/viewer.
 
     :param dump_output: The output from dump_graphviz
+    :param output_format: The output format (used to determine file extension)
 
     """
+    if isinstance(dump_output, bytes) and sys.stdout.isatty():
+        with tempfile.NamedTemporaryFile(
+            suffix=f".{output_format}",
+            delete=False,
+        ) as temp_file:
+            temp_file.write(dump_output)
+            temp_path = temp_file.name
+
+        print(f"Binary output file written to: {temp_path}", file=sys.stderr)  # noqa: T201
+        print("Opening file with default application...", file=sys.stderr)  # noqa: T201
+        if not webbrowser.open(temp_path):
+            print("Could not open file with default application. Please open it manually.", file=sys.stderr)  # noqa: T201
+        return
+
     if isinstance(dump_output, str):
         print(dump_output)  # noqa: T201
     else:

tests/render/test_graphviz.py

@@ -126,3 +126,66 @@ def test_render_dot_with_depth_zero(example_dag: PackageDAG) -> None:
     assert "a [label=" in output
     assert "g [label=" in output
     assert "->" not in output
+
+
+def test_print_graphviz_binary_tty_handling(mocker: MockerFixture, example_dag: PackageDAG) -> None:
+    """Test that binary output is written to a temp file when stdout is a tty."""
+    output = dump_graphviz(example_dag, output_format="pdf")
+    assert isinstance(output, bytes)
+
+    # Mock stdout.isatty() to return True
+    mock_stdout = mocker.patch.object(sys, "stdout")
+    mock_stdout.isatty.return_value = True
+    mock_stdout.fileno.return_value = 1
+
+    # Mock webbrowser.open to avoid actually opening a browser
+    mock_open = mocker.patch("webbrowser.open")
+
+    # Capture temp file creation
+    class MockTempFile:
+        def __init__(self, *_args: object, **_kwargs: object) -> None:
+            self._content = b""
+            self._name = "/tmp/pipdeptree_test_output.pdf"  # noqa: S108  # Mock path for testing
+            self._closed = False
+
+        def write(self, data: bytes) -> None:
+            self._content += data
+
+        @property
+        def name(self) -> str:
+            return self._name
+
+        def __enter__(self) -> "MockTempFile":  # noqa: PYI034, UP037
+            return self
+
+        def __exit__(self, *_args: object) -> None:
+            self._closed = True
+
+    mocker.patch("tempfile.NamedTemporaryFile", return_value=MockTempFile())
+
+    print_graphviz(output, output_format="pdf")
+
+    # Verify that webbrowser.open was called with the temp file path
+    mock_open.assert_called_once_with("/tmp/pipdeptree_test_output.pdf")  # noqa: S108  # Mock path for testing
+
+
+def test_print_graphviz_binary_non_tty_handling(mocker: MockerFixture, example_dag: PackageDAG) -> None:
+    """Test that binary output is written directly to stdout when stdout is not a tty."""
+    output = dump_graphviz(example_dag, output_format="pdf")
+    assert isinstance(output, bytes)
+
+    # Mock stdout.isatty() to return False (non-tty, e.g., piped output)
+    mock_stdout = mocker.patch.object(sys, "stdout")
+    mock_stdout.isatty.return_value = False
+    mock_stdout.fileno.return_value = 1
+
+    # Mock fdopen to capture binary write
+    mock_fdopen = mocker.patch("os.fdopen")
+    mock_bytestream = mocker.MagicMock()
+    mock_fdopen.return_value.__enter__.return_value = mock_bytestream
+
+    print_graphviz(output, output_format="pdf")
+
+    # Verify that binary data was written to stdout
+    mock_fdopen.assert_called_once_with(1, "wb")
+    mock_bytestream.write.assert_called_once_with(output)