Merge pull request #20 from pycompression/headerbug

Fix bug that occurred when writing the header.

Author: rhpvorderman

.github/workflows/ci.yml

@@ -0,0 +1,61 @@
+name: Continous integration
+
+on:
+  pull_request:
+  push:
+    branches:
+      - develop
+      - master
+
+
+jobs:
+  lint:
+    runs-on: ubuntu-20.04
+    strategy:
+      matrix:
+        python-version:
+          - 3.6
+    steps:
+      - uses: actions/[email protected]
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v2
+      - name: Install tox
+        run: pip install tox
+      - name: Lint
+        run: tox -e lint
+  docs:
+    needs: lint
+    runs-on: ubuntu-20.04
+    steps:
+      - uses: actions/[email protected]
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v2
+      - name: Install tox
+        run: pip install tox
+      - name: Install isal
+        run: sudo apt-get install libisal-dev
+      - name: Build docs
+        run: tox -e docs
+  test:
+    runs-on: ubuntu-20.04
+    strategy:
+      matrix:
+        python-version:
+          - 3.6
+          - 3.7
+          - 3.8
+          - 3.9
+    needs: lint
+    steps:
+      - uses: actions/[email protected]
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v2
+      - name: Install tox
+        run: pip install tox
+      - name: Install isal
+        run: sudo apt-get install libisal-dev
+      - name: Run tests
+        run: tox -e py3
+      - name: Upload coverage report
+        if: ${{ matrix.python-version == 3.6 }} # Only upload coverage once
+        uses: codecov/codecov-action@v1

.travis.yml

@@ -9,6 +9,10 @@ Changelog
 
 version 0.2.0-dev
 -----------------
++ Fixed a bug where writing of the gzip header would crash if an older version
+  of Python 3.7 was used such as on Debian or Ubuntu. This is due to
+  differences between point releases because of a backported feature. The code
+  now checks if the backported feature is present.
 + Added Python 3.9 to the testing.
 + Fixed ``setup.py`` to list setuptools as a requirement.
 + Changed homepage to reflect move to pycompression organization.

CHANGELOG.rst

@@ -159,18 +159,27 @@ def flush(self, zlib_mode=isal_zlib.Z_SYNC_FLUSH):
         super().flush(zlib_mode)
 
     def _write_gzip_header(self, compresslevel=_COMPRESS_LEVEL_TRADEOFF):
-        # Determine what xfl flag is written for the compression level.
-        # Equate the fast level to gzip level 1. All the other levels are
-        # medium.
-        if sys.version_info[0] == 3 and sys.version_info[1] < 7:
-            # Correct header introduced in 3.7
-            super()._write_gzip_header()
-        else:
+        # Python 3.9 added a `compresslevel` parameter to write gzip header.
+        # This only determines the value of one extra flag. Because this change
+        # was backported to 3.7 and 3.8 in later point versions, the attributes
+        # of the function should be checked before trying to use the
+        # compresslevel parameter.
+        # The gzip header has an extra flag that can be set depending on the
+        # compression level used. This should be set when either the fastest or
+        # best method is used. ISAL level 0 is larger than gzip level 1 and
+        # much faster, so setting the flag for fastest level is appropriate.
+        # ISAL level 1,2 and 3 (best)are similar in size and fall around the
+        # gzip level 3 size. So setting no extra flag
+        # (by using COMPRESS_LEVEL_TRADEOFF) is appropriate here.
+        if ("compresslevel" in super()._write_gzip_header.__code__.co_varnames
+            and hasattr(gzip, "_COMPRESS_LEVEL_FAST")
+                and hasattr(gzip, "_COMPRESS_LEVEL_TRADEOFF")):
             if compresslevel == _COMPRESS_LEVEL_FAST:
-                compresslevel = gzip._COMPRESS_LEVEL_FAST
+                super()._write_gzip_header(gzip._COMPRESS_LEVEL_FAST)
             else:
-                compresslevel = gzip._COMPRESS_LEVEL_TRADEOFF
-            super()._write_gzip_header(compresslevel)
+                super()._write_gzip_header(gzip._COMPRESS_LEVEL_TRADEOFF)
+        else:
+            super()._write_gzip_header()
 
     def write(self, data):
         self._check_not_closed()

src/isal/igzip.py

@@ -365,10 +365,11 @@ def test_metadata(self):
                              struct.pack('<i', mtime))  # little-endian
 
             xflByte = fRead.read(1)
-            if sys.version_info[0] == 3 and sys.version_info[1] < 7:
-                self.assertEqual(xflByte, b'\x02')  # maximum compression
+            if ("compresslevel" in
+                    gzip.GzipFile._write_gzip_header.__code__.co_varnames):
+                self.assertEqual(xflByte, b'\x00')  # fast compression
             else:
-                self.assertEqual(xflByte, b'\x00')  # medium compression
+                self.assertEqual(xflByte, b'\x02')  # maximum compression
             osByte = fRead.read(1)
             self.assertEqual(osByte, b'\xff')  # OS "unknown" (OS-independent)
 
@@ -399,8 +400,9 @@ def test_compresslevel_metadata(self):
         # specifically, discussion of XFL in section 2.3.1
         cases = [
             ('fast', 0, b'\x04'),
-            ('best', 3, b'\x00'),  # Comparable to medium gzip level.
-            ('tradeoff', 2, b'\x00'),  # Dito
+            ('best', 3, b'\x00'),  # Smaller than fast, bigger than best gzip.
+            ('tradeoff', 2, b'\x00'),  # therefore medium is appropriate.
+            ('1', 1, b'\x00')
         ]
         xflOffset = 8
 

tests/test_gzip_compliance.py

@@ -25,6 +25,8 @@ commands=
 deps=flake8
      flake8-import-order
      mypy
+# Linting does not need the installed package.
+skip_install=true
 commands =
     flake8 src tests setup.py benchmark.py