simplify outputs parsing

Author: Andrei Neagu

packages/service-library/src/servicelib/archiving_utils/_interface_7zip.py

@@ -31,7 +31,7 @@
 _FILE_COUNT_RE: Final[str] = r" (\d+)\s*files"
 _PROGRESS_PERCENT_RE: Final[str] = r" (?:100|\d?\d)% "
 _ALL_DONE_RE: Final[str] = r"Everything is Ok"
-# NOTE: the size of `chunk_to_emit` should not be too big nor too small otherwise it might skip some updates
+# NOTE: the size of `chunk_to_emit` should in theory contain everything that above regexes capture
 _DEFAULT_CHUNK_SIZE: Final[NonNegativeInt] = 20
 
 
@@ -115,45 +115,36 @@ async def _output_reader(
     output_handlers: list[Callable[[str], Awaitable[None]]] | None,
     chunk_size: NonNegativeInt = _DEFAULT_CHUNK_SIZE,
 ) -> str:
-    command_output = ""
+    # NOTE: we do not read line by line but chunk by chunk otherwise we'd miss progress updates
+    # the key is to read the smallest possible chunks of data so that the progress can be properly parsed
+    if output_handlers is None:
+        output_handlers = []
 
-    # Initialize buffer to store lookbehind window
-    lookbehind_buffer = ""
+    command_output = ""
 
-    undecodable_chunk: bytes | None = None
+    lookbehind_buffer = ""  # store the last chunk
 
     while True:
         read_chunk = await stream.read(chunk_size)
         if not read_chunk:
             # Process remaining buffer if any
-            if lookbehind_buffer and output_handlers:
+            if lookbehind_buffer:
                 await asyncio.gather(
                     *[handler(lookbehind_buffer) for handler in output_handlers]
                 )
             break
 
-        try:
-            if undecodable_chunk:
-                chunk = (undecodable_chunk + read_chunk).decode("utf-8")
-                undecodable_chunk = None
-            else:
-                chunk = read_chunk.decode("utf-8")
-        except UnicodeDecodeError:
-            undecodable_chunk = read_chunk
-            continue
+        # `errors=replace`: avoids getting stuck when can't parse utf-8
+        chunk = read_chunk.decode("utf-8", errors="replace")
 
         command_output += chunk
 
         # Combine lookbehind buffer with new chunk
         chunk_to_emit = lookbehind_buffer + chunk
-
-        if output_handlers:
-            await asyncio.gather(
-                *[handler(chunk_to_emit) for handler in output_handlers]
-            )
-
         # Keep last window_size characters for next iteration
-        lookbehind_buffer = chunk_to_emit[-chunk_size:]
+        lookbehind_buffer = chunk_to_emit[-len(chunk) :]
+
+        await asyncio.gather(*[handler(chunk_to_emit) for handler in output_handlers])
 
     return command_output
 
@@ -258,6 +249,7 @@ async def unarchive_dir(
             num_steps=1, description=IDStr(f"extracting {archive_to_extract.name}")
         )
 
+    # get archive information
     archive_info_parser = ArchiveInfoParser()
     await _run_cli_command(
         f"7z l {archive_to_extract}",
@@ -279,6 +271,7 @@ async def unarchive_dir(
             )
         )
 
+        # extract archive
         async def progress_handler(byte_progress: NonNegativeInt) -> None:
             if tqdm_progress.update(byte_progress) and log_cb:
                 with log_catch(_logger, reraise=False):