Publish should now work if /tmp is on different device

Fixes #141

datasette/utils.py

@@ -8,6 +8,7 @@ import shlex
 import sqlite3
 import tempfile
 import time
+import shutil
 import urllib
 
 
@@ -186,8 +187,8 @@ def temporary_docker_directory(files, name, metadata, extra_options, branch=None
             open('metadata.json', 'w').write(json.dumps(metadata_content, indent=2))
         open('Dockerfile', 'w').write(dockerfile)
         for path, filename in zip(file_paths, file_names):
-            os.link(path, os.path.join(datasette_dir, filename))
+            link_or_copy(path, os.path.join(datasette_dir, filename))
-        yield
+        yield datasette_dir
     finally:
         tmp.cleanup()
         os.chdir(saved_cwd)
@@ -241,7 +242,7 @@ def temporary_heroku_directory(files, name, metadata, extra_options, branch=None
         open('Procfile', 'w').write(procfile_cmd)
 
         for path, filename in zip(file_paths, file_names):
-            os.link(path, os.path.join(tmp.name, filename))
+            link_or_copy(path, os.path.join(tmp.name, filename))
 
         yield
 
@@ -494,3 +495,14 @@ def to_css_class(s):
     # Attach the md5 suffix
     bits = [b for b in (s, md5_suffix) if b]
     return '-'.join(bits)
+
+
+def link_or_copy(src, dst):
+    # Intended for use in populating a temp directory. We link if possible,
+    # but fall back to copying if the temp directory is on a different device
+    # https://github.com/simonw/datasette/issues/141
+    try:
+        os.link(src, dst)
+    except OSError as e:
+        print('Got OSError {} linking {} to {}'.format(e, src, dst))
+        shutil.copyfile(src, dst)

tests/test_utils.py

@@ -3,9 +3,12 @@ Tests for various datasette helper functions.
 """
 
 from datasette import utils
+import json
+import os
 import pytest
 import sqlite3
-import json
+import tempfile
+from unittest.mock import patch
 
 
 @pytest.mark.parametrize('path,expected', [
@@ -178,3 +181,40 @@ def test_is_url(url, expected):
 ])
 def test_to_css_class(s, expected):
     assert expected == utils.to_css_class(s)
+
+
+def test_temporary_docker_directory_uses_hard_link():
+    with tempfile.TemporaryDirectory() as td:
+        os.chdir(td)
+        open('hello', 'w').write('world')
+        # Default usage of this should use symlink
+        with utils.temporary_docker_directory(
+            files=['hello'],
+            name='t',
+            metadata=None,
+            extra_options=None
+        ) as temp_docker:
+            hello = os.path.join(temp_docker, 'hello')
+            assert 'world' == open(hello).read()
+            # It should be a hard link
+            assert 2 == os.stat(hello).st_nlink
+
+
+@patch('os.link')
+def test_temporary_docker_directory_uses_copy_if_hard_link_fails(mock_link):
+    # Copy instead if os.link raises OSError (normally due to different device)
+    mock_link.side_effect = OSError
+    with tempfile.TemporaryDirectory() as td:
+        os.chdir(td)
+        open('hello', 'w').write('world')
+        # Default usage of this should use symlink
+        with utils.temporary_docker_directory(
+            files=['hello'],
+            name='t',
+            metadata=None,
+            extra_options=None
+        ) as temp_docker:
+            hello = os.path.join(temp_docker, 'hello')
+            assert 'world' == open(hello).read()
+            # It should be a copy, not a hard link
+            assert 1 == os.stat(hello).st_nlink