Handle failures when creating dummy sources (#271)

Handle failures when creating dummy sources

This makes it possible to parse a spec file on a read-only filesystem for instance. At the cost of potentially incorrectly parsed %prep in case some sources are missing.
Related to fedora-copr/copr#2839.
RELEASE NOTES BEGIN
specfile no longer tracebacks when some sources are missing and can't be emulated. In such case the spec file is parsed without them at the cost of %setup and %patch macros potentially expanding differently than with the sources present.
RELEASE NOTES END

Reviewed-by: Laura Barcziová
Reviewed-by: Nikola Forró

Author: softwarefactory-project-zuul[bot]

specfile/spec_parser.py

@@ -99,6 +99,23 @@ def _make_dummy_sources(
         Yields:
             List of paths to each created dummy source.
         """
+
+        def write_magic(path, magic):
+            # create a file with a signature matching what RPM expects for this particular
+            # file type; this affects how %setup and %patch macros are expanded
+
+            # number of bytes that RPM reads to determine the file type
+            MAGIC_LENGTH = 13
+            try:
+                if magic:
+                    path.write_bytes(magic.ljust(MAGIC_LENGTH, b"\x00"))
+                else:
+                    path.write_bytes(MAGIC_LENGTH * b"\x00")
+            except (FileNotFoundError, OSError, PermissionError):
+                logger.warning(f"Failed to create a dummy source: {path}")
+                return False
+            return True
+
         # based on rpmFileIsCompressed() in rpmio/rpmfileutil.c in RPM source
         SIGNATURES = [
             (".bz2", b"BZh"),
@@ -110,32 +127,35 @@ def _make_dummy_sources(
             (".gz", b"\x1f\x8b"),
             (".7z", b"7z\xbc\xaf\x27\x1c"),
         ]
-        # number of bytes that RPM reads to determine the file type
-        MAGIC_LENGTH = 13
         dummy_sources = []
         for source in sources:
             filename = get_filename_from_location(source)
             if not filename:
                 continue
             path = self.sourcedir / filename
-            if path.is_file():
+            if path.exists():
                 continue
-            dummy_sources.append(path)
             for ext, magic in SIGNATURES:
                 if filename.endswith(ext):
-                    path.write_bytes(magic.ljust(MAGIC_LENGTH, b"\x00"))
+                    if write_magic(path, magic):
+                        dummy_sources.append(path)
                     break
             else:
-                path.write_bytes(MAGIC_LENGTH * b"\x00")
+                if write_magic(path, None):
+                    dummy_sources.append(path)
         for source in non_empty_sources:
             filename = get_filename_from_location(source)
             if not filename:
                 continue
             path = self.sourcedir / filename
-            if path.is_file():
+            if path.exists():
                 continue
-            dummy_sources.append(path)
-            path.write_text("DUMMY")
+            try:
+                path.write_text("DUMMY")
+            except (FileNotFoundError, OSError, PermissionError):
+                logger.warning(f"Failed to create a dummy source: {path}")
+            else:
+                dummy_sources.append(path)
         try:
             yield dummy_sources
         finally:

tests/unit/test_spec_parser.py

@@ -64,3 +64,32 @@ def test_spec_parser_macros():
             "Test package\n"
         ),
     )
+
+
+def test_spec_parser_make_dummy_sources(tmp_path):
+    regular_source = "regular-source.zip"
+    non_empty_source = "non-empty-source.tar.xz"
+    existing_source = "existing-source.tar.gz"
+    sourcedir = tmp_path / "sources"
+    sourcedir.mkdir()
+    (sourcedir / existing_source).write_text("...")
+    parser = SpecParser(sourcedir)
+    with parser._make_dummy_sources(
+        {regular_source, existing_source}, {non_empty_source}
+    ) as dummy_sources:
+        assert all(s.exists() for s in dummy_sources)
+        assert sourcedir / regular_source in dummy_sources
+        assert sourcedir / non_empty_source in dummy_sources
+        assert sourcedir / existing_source not in dummy_sources
+    assert all(not s.exists() for s in dummy_sources)
+    assert (sourcedir / existing_source).exists()
+    read_only_sourcedir = tmp_path / "read-only-sources"
+    read_only_sourcedir.mkdir()
+    (read_only_sourcedir / existing_source).write_text("...")
+    read_only_sourcedir.chmod(0o555)
+    parser = SpecParser(read_only_sourcedir)
+    with parser._make_dummy_sources(
+        {regular_source, existing_source}, {non_empty_source}
+    ) as dummy_sources:
+        assert not dummy_sources
+    assert (read_only_sourcedir / existing_source).exists()