Fall back on webbrowser if xdg-open is not installed on Linux (#701)

* Fall back on webbrowser if xdg-open is not installed on Linux

* python27 friendly

* reformat

* linter

lib/streamlit/env_util.py

@@ -52,3 +52,10 @@ def is_repl():
         return True
 
     return False
+
+
+def is_executable_in_path(name):
+    """Check if executable is in OS path."""
+    from distutils.spawn import find_executable
+
+    return find_executable(name) is not None

lib/streamlit/net_util.py

@@ -51,7 +51,7 @@ def get_external_ip():
             "Did not auto detect external IP.\n"
             "Please go to %s for debugging hints.",
             # fmt: on
-            util.HELP_DOC,
+            util.HELP_DOC
         )
     else:
         _external_ip = response.strip()

lib/streamlit/util.py

@@ -57,31 +57,46 @@ def open_browser(url):
 
     """
 
-    if env_util.IS_WINDOWS:
-        # Treat Windows separately because:
-        # 1. /dev/null doesn't exist.
-        # 2. subprocess.Popen(['start', url]) doesn't actually pop up the
-        #    browser even though 'start url' works from the command prompt.
-        # Fun!
-        import webbrowser
-
-        webbrowser.open(url)
-        return
-
+    # Treat Windows separately because:
+    # 1. /dev/null doesn't exist.
+    # 2. subprocess.Popen(['start', url]) doesn't actually pop up the
+    #    browser even though 'start url' works from the command prompt.
+    # Fun!
+    # Also, use webbrowser if we are on Linux and xdg-open is not installed.
+    #
     # We don't use the webbrowser module on Linux and Mac because some browsers
     # (ahem... Chrome) always print "Opening in existing browser session" to
     # the terminal, which is spammy and annoying. So instead we start the
     # browser ourselves and send all its output to /dev/null.
 
+    if env_util.IS_WINDOWS:
+        _open_browser_with_webbrowser(url)
+        return
     if env_util.IS_LINUX_OR_BSD:
-        cmd = ["xdg-open", url]
-    elif env_util.IS_DARWIN:
-        cmd = ["open", url]
-    else:
-        raise Error('Cannot open browser in platform "%s"' % system)
+        if env_util.is_executable_in_path("xdg-open"):
+            _open_browser_with_command("xdg-open", url)
+            return
+        _open_browser_with_webbrowser(url)
+        return
+    if env_util.IS_DARWIN:
+        _open_browser_with_command("open", url)
+        return
+
+    import platform
+
+    raise Error('Cannot open browser in platform "%s"' % platform.system())
+
+
+def _open_browser_with_webbrowser(url):
+    import webbrowser
+
+    webbrowser.open(url)
+
 
+def _open_browser_with_command(command, url):
+    cmd_line = [command, url]
     with open(os.devnull, "w") as devnull:
-        subprocess.Popen(cmd, stdout=devnull, stderr=subprocess.STDOUT)
+        subprocess.Popen(cmd_line, stdout=devnull, stderr=subprocess.STDOUT)
 
 
 # TODO: Move this into errors.py? Replace with StreamlitAPIException?

lib/tests/streamlit/file_util_test.py

@@ -94,7 +94,9 @@ def test_streamlit_write_exception(self):
             self.assertEqual(str(e.value), error_msg)
 
     def test_get_project_streamlit_file_path(self):
-        expected = os.path.join(os.getcwd(), file_util.CONFIG_FOLDER_NAME, "some/random/file")
+        expected = os.path.join(
+            os.getcwd(), file_util.CONFIG_FOLDER_NAME, "some/random/file"
+        )
 
         self.assertEqual(
             expected, file_util.get_project_streamlit_file_path("some/random/file")

lib/tests/streamlit/util_test.py

@@ -15,6 +15,9 @@
 
 import random
 import unittest
+from mock import patch
+from parameterized import parameterized
+
 
 from streamlit import util
 
@@ -28,3 +31,34 @@ def test_memoization(self):
         yes_memoized_func = util.memoize(non_memoized_func)
         self.assertNotEqual(non_memoized_func(), non_memoized_func())
         self.assertEqual(yes_memoized_func(), yes_memoized_func())
+
+    @parameterized.expand(
+        [("Linux", False, True), ("Windows", True, False), ("Darwin", False, True)]
+    )
+    def test_open_browser(self, os_type, webbrowser_expect, popen_expect):
+        """Test web browser opening scenarios."""
+        from streamlit import env_util
+
+        env_util.IS_WINDOWS = os_type == "Windows"
+        env_util.IS_DARWIN = os_type == "Darwin"
+        env_util.IS_LINUX_OR_BSD = os_type == "Linux"
+
+        with patch("streamlit.env_util.is_executable_in_path", return_value=True):
+            with patch("webbrowser.open") as webbrowser_open:
+                with patch("subprocess.Popen") as subprocess_popen:
+                    util.open_browser("http://some-url")
+                    self.assertEqual(webbrowser_expect, webbrowser_open.called)
+                    self.assertEqual(popen_expect, subprocess_popen.called)
+
+    def test_open_browser_linux_no_xdg(self):
+        """Test opening the browser on Linux with no xdg installed"""
+        from streamlit import env_util
+
+        env_util.IS_LINUX_OR_BSD = True
+
+        with patch("streamlit.env_util.is_executable_in_path", return_value=False):
+            with patch("webbrowser.open") as webbrowser_open:
+                with patch("subprocess.Popen") as subprocess_popen:
+                    util.open_browser("http://some-url")
+                    self.assertEqual(True, webbrowser_open.called)
+                    self.assertEqual(False, subprocess_popen.called)