preserve empty lines in CVS log messages over pserver

Empty lines sent by the CVS server in rlog output were being stripped
by our custom cvs client implementation. Unfortunately, this resulted
in empty lines being stripped from CVS log messages, which is fixed
with this commit. The rsync access method already preserved log
messages properly, and now the pserver access method does the same.

swh/loader/cvs/cvsclient.py

@@ -271,8 +271,6 @@ class CVSClient:
                 raise CVSProtocolError("CVS server error: %s" % line)
             if line == b"ok\n":
                 break
-            elif line == b"M \n":
-                continue
             elif line[0:2] == b"M ":
                 rlog_output.write(line[2:])
             elif line[0:8] == b"MT text ":

swh/loader/cvs/rlog.py

@@ -350,7 +350,9 @@ def _parse_log_header(
                 state = 0
 
         if state == 0:
-            if line[:9] == b"RCS file:":
+            if line == "\n":
+                continue
+            elif line[:9] == b"RCS file:":
                 filename = line[10:-1]
             elif line[:5] == b"head:":
                 # head = line[6:-1]

swh/loader/cvs/tests/test_loader.py

@@ -709,3 +709,91 @@ def test_loader_cvs_pserver_split_commits_by_commitid(swh_storage, datadir, tmp_
         "skipped_content": 0,
         "snapshot": 18,
     }
+
+
+GREEK_SNAPSHOT6 = Snapshot(
+    id=hash_to_bytes("b4c9423b2711c181251deb458d4ab4a3172948ac"),
+    branches={
+        b"HEAD": SnapshotBranch(
+            target=hash_to_bytes("f317c720e1929fec0afce10e6a8cfd24ef76dfc7"),
+            target_type=TargetType.REVISION,
+        )
+    },
+)
+
+
+def test_loader_cvs_empty_lines_in_log_message(swh_storage, datadir, tmp_path):
+    """Conversion of RCS history with empty lines in a log message"""
+    archive_name = "greek-repository6"
+    extracted_name = "greek-repository"
+    archive_path = os.path.join(datadir, f"{archive_name}.tgz")
+    repo_url = prepare_repository_from_archive(archive_path, extracted_name, tmp_path)
+    repo_url += "/greek-tree"  # CVS module name
+
+    loader = CvsLoader(
+        swh_storage, repo_url, cvsroot_path=os.path.join(tmp_path, extracted_name)
+    )
+
+    assert loader.load() == {"status": "eventful"}
+
+    assert_last_visit_matches(
+        loader.storage,
+        repo_url,
+        status="full",
+        type="cvs",
+        snapshot=GREEK_SNAPSHOT6.id,
+    )
+
+    check_snapshot(GREEK_SNAPSHOT6, loader.storage)
+
+    stats = get_stats(loader.storage)
+    assert stats == {
+        "content": 9,
+        "directory": 22,
+        "origin": 1,
+        "origin_visit": 1,
+        "release": 0,
+        "revision": 8,
+        "skipped_content": 0,
+        "snapshot": 8,
+    }
+
+
+def test_loader_cvs_pserver_empty_lines_in_log_message(swh_storage, datadir, tmp_path):
+    """Conversion via pserver with empty lines in a log message"""
+    archive_name = "greek-repository6"
+    extracted_name = "greek-repository"
+    archive_path = os.path.join(datadir, f"{archive_name}.tgz")
+    repo_url = prepare_repository_from_archive(archive_path, extracted_name, tmp_path)
+    repo_url += "/greek-tree"  # CVS module name
+
+    # Ask our cvsclient to connect via the 'cvs server' command
+    repo_url = f"fake://{repo_url[7:]}"
+
+    loader = CvsLoader(
+        swh_storage, repo_url, cvsroot_path=os.path.join(tmp_path, extracted_name)
+    )
+
+    assert loader.load() == {"status": "eventful"}
+
+    assert_last_visit_matches(
+        loader.storage,
+        repo_url,
+        status="full",
+        type="cvs",
+        snapshot=GREEK_SNAPSHOT6.id,
+    )
+
+    check_snapshot(GREEK_SNAPSHOT6, loader.storage)
+
+    stats = get_stats(loader.storage)
+    assert stats == {
+        "content": 9,
+        "directory": 22,
+        "origin": 1,
+        "origin_visit": 1,
+        "release": 0,
+        "revision": 8,
+        "skipped_content": 0,
+        "snapshot": 8,
+    }