Seekable

.gitignore

@@ -3,8 +3,6 @@ __pycache__/
 
 /*.egg-info
 
-/test_data/file0.txt
-/test_data/file1.bin
 /test_data/test.a
 
 /dist/

ar/substream.py

@@ -1,3 +1,4 @@
+import errno
 import io
 
 class Substream(io.RawIOBase):
@@ -8,16 +9,22 @@ def __init__(self, file: io.RawIOBase, start: int, size: int):
         self.size = size
         self.position = 0
 
-    def seek(self, offset, origin=0):
+    def seek(self, offset, origin=0) -> int:
         if origin == 0:
-            self.position = offset
+            position = offset
         elif origin == 1:
-            self.position += offset
+            position = self.position + offset
         elif origin == 2:
-            self.position = self.size + offset
+            position = self.size + offset
         else:
             raise ValueError(f"Unexpected origin: {origin}")
 
+        if position < 0 or position > self.size:
+            raise OSError(errno.EINVAL, "Invalid argument")
+
+        self.position = position
+        return self.position
+
     def seekable(self):
         return True
 

ar/tests/test_roundtrip.py

@@ -1,5 +1,6 @@
 # pylint: disable=redefined-outer-name
 import subprocess
+import tempfile
 from pathlib import Path
 
 import pytest
@@ -12,15 +13,23 @@
 
 @pytest.fixture
 def simple_archive():
-    # Create archive
-    TEST_DATA.mkdir(exist_ok=True)
-
-    (TEST_DATA / 'file0.txt').write_text('Hello')
-    (TEST_DATA / 'file1.bin').write_bytes(b'\xc3\x28')  # invalid utf-8 characters
-    (TEST_DATA / 'long_file_name_test0.txt').write_text('Hello2')
-    (TEST_DATA / 'long_file_name_test1.bin').write_bytes(b'\xc3\x28')
-    subprocess.check_call('ar r test.a file0.txt file1.bin long_file_name_test0.txt long_file_name_test1.bin'.split(), cwd=str(TEST_DATA))
-    return TEST_DATA / 'test.a'
+    archive_path = TEST_DATA / 'test.a'
+    if archive_path.exists():
+        return archive_path
+
+    archive_full_path = archive_path.resolve()
+    with tempfile.TemporaryDirectory() as tmpdir:
+        tmp_path = Path(tmpdir)
+        (tmp_path / 'file0.txt').write_text('Hello')
+        (tmp_path / 'file1.bin').write_bytes(b'\xc3\x28')  # invalid utf-8 characters
+        (tmp_path / 'long_file_name_test0.txt').write_text('Hello2')
+        (tmp_path / 'long_file_name_test1.bin').write_bytes(b'\xc3\x28')
+        subprocess.check_call(
+            ['ar', 'r', str(archive_full_path), 'file0.txt', 'file1.bin', 'long_file_name_test0.txt', 'long_file_name_test1.bin'],
+            cwd=tmpdir,
+        )
+
+    return archive_path
 
 
 def test_list(simple_archive):

ar/tests/test_seek.py

@@ -0,0 +1,77 @@
+# pylint: disable=redefined-outer-name
+import errno
+from pathlib import Path
+
+import pytest
+
+from ar import Archive
+
+
+ARCHIVE = Path('test_data/linux.a')
+
+
+def test_seekable():
+    with ARCHIVE.open('rb') as f:
+        archive = Archive(f)
+        file0 = archive.open('file0.txt', 'r')
+        assert file0.seekable()
+
+
+def test_seek_from_start():
+    with ARCHIVE.open('rb') as f:
+        archive = Archive(f)
+        file0 = archive.open('file0.txt', 'r')
+        file0.seek(2)
+        assert file0.tell() == 2
+        assert file0.read(1) == 'l'
+
+
+def test_seek_from_current():
+    with ARCHIVE.open('rb') as f:
+        archive = Archive(f)
+        file0 = archive.open('file0.txt', 'r')
+        assert file0.read(1) == 'H'
+        file0.seek(1, 1)
+        assert file0.tell() == 2
+        assert file0.read(2) == 'll'
+
+
+def test_seek_from_end():
+    with ARCHIVE.open('rb') as f:
+        archive = Archive(f)
+        file0 = archive.open('file0.txt', 'r')
+        file_size = 5
+        file0.seek(-2, 2)
+        assert file0.tell() == file_size - 2
+        assert file0.read() == 'lo'
+
+
+def test_seek_before_start_raises_oserror():
+    with ARCHIVE.open('rb') as f:
+        archive = Archive(f)
+        file0 = archive.open('file0.txt', 'r')
+        with pytest.raises(OSError) as excinfo:
+            file0.seek(-1)
+        assert excinfo.value.errno == errno.EINVAL
+        assert file0.tell() == 0
+
+
+def test_seek_beyond_end_raises_oserror():
+    with ARCHIVE.open('rb') as f:
+        archive = Archive(f)
+        file0 = archive.open('file0.txt', 'r')
+        with pytest.raises(OSError) as excinfo:
+            file0.seek(6, 0)
+        assert excinfo.value.errno == errno.EINVAL
+        assert file0.tell() == 0
+
+
+def test_seek_from_current_outside_bounds_raises_oserror():
+    with ARCHIVE.open('rb') as f:
+        archive = Archive(f)
+        file0 = archive.open('file0.txt', 'r')
+        assert file0.read(1) == 'H'
+        with pytest.raises(OSError) as excinfo:
+            file0.seek(-2, 1)
+        assert excinfo.value.errno == errno.EINVAL
+        assert file0.tell() == 1