Fix number of lines returned with host logs' query argument (#5334)

If no cursor is specified and negative num_skip is used, we're pointing
one record back from the last one, so host logs always returned 101
lines as the default. This was also the case of the lines query argument
that used the number directly as num_skip. Instead of doing that, point
N-1 records to the back and then get N records. Handle 1 record and
invalid numbers silently to avoid the need for error handling in
unpractical edge cases.

supervisor/api/host.py

@@ -61,7 +61,7 @@
 
 IDENTIFIER = "identifier"
 BOOTID = "bootid"
-DEFAULT_RANGE = 100
+DEFAULT_LINES = 100
 
 SCHEMA_OPTIONS = vol.Schema({vol.Optional(ATTR_HOSTNAME): str})
 
@@ -226,13 +226,24 @@ async def advanced_logs_handler(
             log_formatter = LogFormatter.VERBOSE
 
         if "lines" in request.query:
-            lines = request.query.get("lines", DEFAULT_RANGE)
+            lines = request.query.get("lines", DEFAULT_LINES)
+            try:
+                lines = int(lines)
+            except ValueError:
+                # If the user passed a non-integer value, just use the default instead of error.
+                lines = DEFAULT_LINES
+            finally:
+                # We can't use the entries= Range header syntax to refer to the last 1 line,
+                # and passing 1 to the calculation below would return the 1st line of the logs
+                # instead. Since this is really an edge case that doesn't matter much, we'll just
+                # return 2 lines at minimum.
+                lines = max(2, lines)
             # entries=cursor[[:num_skip]:num_entries]
-            range_header = f"entries=:-{lines}:"
+            range_header = f"entries=:-{lines-1}:{lines}"
         elif RANGE in request.headers:
             range_header = request.headers.get(RANGE)
         else:
-            range_header = f"entries=:-{DEFAULT_RANGE}:"
+            range_header = f"entries=:-{DEFAULT_LINES-1}:{DEFAULT_LINES}"
 
         async with self.sys_host.logs.journald_logs(
             params=params, range_header=range_header, accept=LogFormat.JOURNAL

tests/api/__init__.py

@@ -6,7 +6,7 @@
 
 from supervisor.host.const import LogFormat
 
-DEFAULT_LOG_RANGE = "entries=:-100:"
+DEFAULT_LOG_RANGE = "entries=:-99:100"
 
 
 async def common_test_api_advanced_logs(

tests/api/test_host.py

@@ -14,7 +14,7 @@
 from tests.dbus_service_mocks.base import DBusServiceMock
 from tests.dbus_service_mocks.systemd import Systemd as SystemdService
 
-DEFAULT_RANGE = "entries=:-100:"
+DEFAULT_RANGE = "entries=:-99:100"
 # pylint: disable=protected-access
 
 
@@ -249,7 +249,7 @@ async def test_advaced_logs_query_parameters(
     await api_client.get("/host/logs?lines=53")
     journald_logs.assert_called_once_with(
         params={"SYSLOG_IDENTIFIER": coresys.host.logs.default_identifiers},
-        range_header="entries=:-53:",
+        range_header="entries=:-52:53",
         accept=LogFormat.JOURNAL,
     )
 
@@ -277,7 +277,7 @@ async def test_advaced_logs_query_parameters(
     )
     journald_logs.assert_called_once_with(
         params={"SYSLOG_IDENTIFIER": coresys.host.logs.default_identifiers},
-        range_header="entries=:-53:",
+        range_header="entries=:-52:53",
         accept=LogFormat.JOURNAL,
     )
     journal_logs_reader.assert_called_with(ANY, LogFormatter.VERBOSE)