Separate LineReader functionality from WatchLog

The buffered reading of finished lines deserves its own class to make
its function clearer, rather than bundling it within the WatchLog class.

Co-Authored-By: Michał Kępień <michal@isc.org>

diff --git a/bin/tests/system/isctest/log/watchlog.py b/bin/tests/system/isctest/log/watchlog.py
index 1ae56adef22af138f11dd52384178b7ebc5f37e0..6d85e9817d1ba28ed510dae779306ad994949619 100644 (file)
--- a/bin/tests/system/isctest/log/watchlog.py
+++ b/bin/tests/system/isctest/log/watchlog.py
@@ -64,6 +64,94 @@ class LogFile:
             assert False, f"forbidden message appeared in log {self.path}: {msg}"
 
 
+class LineReader:
+    """
+    >>> import io
+
+    >>> file = io.StringIO("complete line\\n")
+    >>> line_reader = LineReader(file)
+    >>> for line in line_reader.readlines():
+    ...     print(line.strip())
+    complete line
+
+    >>> file = io.StringIO("complete line\\nand then incomplete line")
+    >>> line_reader = LineReader(file)
+    >>> for line in line_reader.readlines():
+    ...     print(line.strip())
+    complete line
+
+    >>> file = io.StringIO("complete line\\nand then another complete line\\n")
+    >>> line_reader = LineReader(file)
+    >>> for line in line_reader.readlines():
+    ...     print(line.strip())
+    complete line
+    and then another complete line
+
+    >>> file = io.StringIO()
+    >>> line_reader = LineReader(file)
+    >>> for chunk in (
+    ...     "first line\\nsecond line\\nthi",
+    ...     "rd ",
+    ...     "line\\nfour",
+    ...     "th line\\n\\nfifth line\\n"
+    ... ):
+    ...     print("=== OUTER ITERATION ===")
+    ...     pos = file.tell()
+    ...     print(chunk, end="", file=file)
+    ...     _ = file.seek(pos)
+    ...     for line in line_reader.readlines():
+    ...         print("--- inner iteration ---")
+    ...         print(line.strip() or "<blank>")
+    === OUTER ITERATION ===
+    --- inner iteration ---
+    first line
+    --- inner iteration ---
+    second line
+    === OUTER ITERATION ===
+    === OUTER ITERATION ===
+    --- inner iteration ---
+    third line
+    === OUTER ITERATION ===
+    --- inner iteration ---
+    fourth line
+    --- inner iteration ---
+    <blank>
+    --- inner iteration ---
+    fifth line
+    """
+
+    def __init__(self, stream: TextIO):
+        self._stream = stream
+        self._linebuf = ""
+
+    def readline(self) -> Optional[str]:
+        """
+        Wrapper around io.readline() function to handle unfinished lines.
+
+        If a line ends with newline character, it's returned immediately.
+        If a line doesn't end with a newline character, the read contents are
+        buffered until the next call of this function and None is returned
+        instead.
+        """
+        read = self._stream.readline()
+        if not read.endswith("\n"):
+            self._linebuf += read
+            return None
+        read = self._linebuf + read
+        self._linebuf = ""
+        return read
+
+    def readlines(self) -> Iterator[str]:
+        """
+        Wrapper around io.readline() which only returns finished lines.
+        """
+        while True:
+            line = self.readline()
+            if line is None:
+                return
+            yield line
+
+
 class WatchLog(abc.ABC):
     """
     Wait for a log message to appear in a text file.
@@ -97,44 +185,15 @@ class WatchLog(abc.ABC):
           ...
         isctest.log.watchlog.WatchLogException: timeout must be greater than 0
         """
-        self._fd = None  # type: Optional[TextIO]
+        self._fd: Optional[TextIO] = None
+        self._reader: Optional[LineReader] = None
         self._path = path
         self._wait_function_called = False
-        self._linebuf = ""
         if timeout <= 0.0:
             raise WatchLogException("timeout must be greater than 0")
         self._timeout = timeout
         self._deadline = 0.0
 
-    def _readline(self) -> Optional[str]:
-        """
-        Wrapper around io.readline() function to handle unfinished lines.
-
-        If a line ends with newline character, it's returned immediately.
-        If a line doesn't end with a newline character, the read contents are
-        buffered until the next call of this function and None is returned
-        instead.
-        """
-        if not self._fd:
-            raise WatchLogException("file to watch isn't open")
-        read = self._fd.readline()
-        if not read.endswith("\n"):
-            self._linebuf += read
-            return None
-        read = self._linebuf + read
-        self._linebuf = ""
-        return read
-
-    def _readlines(self) -> Iterator[str]:
-        """
-        Wrapper around io.readline() which only returns finished lines.
-        """
-        while True:
-            line = self._readline()
-            if line is None:
-                return
-            yield line
-
     def _setup_wait(self, patterns: OneOrMore[FlexPattern]) -> List[Pattern]:
         self._wait_function_called = True
         self._deadline = time.monotonic() + self._timeout
@@ -163,8 +222,12 @@ class WatchLog(abc.ABC):
         return patterns
 
     def _wait_for_match(self, regexes: List[Pattern]) -> Match:
+        if not self._reader:
+            raise WatchLogException(
+                "use WatchLog as context manager before calling wait_for_*() functions"
+            )
         while time.monotonic() < self._deadline:
-            for line in self._readlines():
+            for line in self._reader.readlines():
                 for regex in regexes:
                     match = regex.search(line)
                     if match:
@@ -422,6 +485,7 @@ class WatchLog(abc.ABC):
     def __enter__(self) -> Any:
         self._fd = open(self._path, encoding="utf-8")
         self._seek_on_enter()
+        self._reader = LineReader(self._fd)
         return self
 
     @abc.abstractmethod
@@ -438,8 +502,9 @@ class WatchLog(abc.ABC):
     def __exit__(self, *_: Any) -> None:
         if not self._wait_function_called:
             raise WatchLogException("wait_for_*() was not called")
-        if self._fd:
-            self._fd.close()
+        self._reader = None
+        assert self._fd
+        self._fd.close()
 
 
 class WatchLogFromStart(WatchLog):
@@ -460,5 +525,5 @@ class WatchLogFromHere(WatchLog):
     """
 
     def _seek_on_enter(self) -> None:
-        if self._fd:
-            self._fd.seek(0, os.SEEK_END)
+        assert self._fd
+        self._fd.seek(0, os.SEEK_END)