Add concurrent index parser to Fimfarchive fetcher

fimfarchive/fetchers/fimfarchive.py

@@ -23,8 +23,13 @@ Fimfarchive fetcher.
 
 
 import json
+import marshal
 from io import BufferedReader
-from typing import Any, Dict, IO, Iterator, Optional, Tuple, Union
+from multiprocessing import Pool
+from typing import (
+    cast, Any, Callable, Dict, IO, Iterator,
+    Mapping, Optional, Tuple, Union,
+)
 from zipfile import ZipFile, BadZipFile
 
 from jmespath import compile as jmes
@@ -47,6 +52,96 @@ PATH = jmes('archive.path || path')
 
 
 compress, decompress = find_compressor()
+serialize = cast(Callable[[Dict[str, Any]], bytes], marshal.dumps)
+deserialize = cast(Callable[[bytes], Dict[str, Any]], marshal.loads)
+
+
+class Index(Mapping[int, Dict[str, Any]]):
+    """
+    Mapping from story key to meta.
+    """
+
+    def close(self) -> None:
+        """
+        Closes the index, if necessary.
+        """
+
+    def load(self, source: IO[bytes]) -> Iterator[Tuple[int, bytes]]:
+        """
+        Yields index items from a byte stream.
+
+        Args:
+            source: The stream to read from.
+
+        Returns:
+            An iterable over index items.
+
+        Raises:
+            StorySourceError: If the stream is malformed.
+        """
+        reader = BufferedReader(source, BUFFER_SIZE)  # type: ignore
+
+        with Pool() as pool:
+            parts = (part for part in reader if 2 < len(part))
+            mapper = pool.imap(self.parse, parts, 1024)
+
+            for key, value in mapper:
+                if key < 0:
+                    raise StorySourceError(value.decode())
+                else:
+                    yield key, value
+
+    @staticmethod
+    def parse(pair: bytes) -> Tuple[int, bytes]:
+        """
+        Converts a JSON key-value pair to Marshal.
+
+        Args:
+            pair: JSON key-value pair.
+
+        Returns:
+            Marshal key-value pair.
+        """
+        try:
+            key, meta = pair.split(b':', 1)
+            key = key.strip(b'\n\r\t "')
+            meta = meta.strip(b'\n\r\t ,')
+        except Exception as e:
+            return -1, f"Unknown parser error: {e}".encode()
+
+        if meta[0] != 123 or meta[-1] != 125:
+            return -1, f"Malformed JSON object for {key}.".encode()
+
+        try:
+            return int(key), serialize(json.loads(meta.decode()))
+        except UnicodeDecodeError as e:
+            return -1, f"Incorrectly encoded index: {e}".encode()
+        except ValueError as e:
+            return -1, f"Malformed meta for {key}: {e}".encode()
+
+
+class MemoryIndex(Index):
+    """
+    In-memory mapping from story key to meta.
+    """
+
+    def __init__(self, stream: IO[bytes]) -> None:
+        self.data = {k: compress(v) for k, v in self.load(stream)}
+
+    def __getitem__(self, key: int) -> Dict[str, Any]:
+        return deserialize(decompress(self.data[key]))
+
+    def __contains__(self, item) -> bool:
+        return item in self.data
+
+    def __iter__(self) -> Iterator[int]:
+        return iter(self.data)
+
+    def __len__(self) -> int:
+        return len(self.data)
+
+    def close(self):
+        self.data.close()
 
 
 class FimfarchiveFetcher(Fetcher):
@@ -73,7 +168,7 @@ class FimfarchiveFetcher(Fetcher):
             StorySourceError: If no valid Fimfarchive release can be loaded.
         """
         self.archive: ZipFile
-        self.index: Dict[int, bytes]
+        self.index: Index
         self.paths: Dict[int, str]
         self.is_open: bool = False
 
@@ -102,8 +197,7 @@ class FimfarchiveFetcher(Fetcher):
 
         try:
             with self.archive.open('index.json') as fobj:
-                reader = BufferedReader(fobj, BUFFER_SIZE)  # type: ignore
-                self.index = dict(self.load_index(reader))
+                self.index = MemoryIndex(fobj)
         except KeyError as e:
             raise StorySourceError("Archive is missing the index.") from e
         except BadZipFile as e:
@@ -112,39 +206,6 @@ class FimfarchiveFetcher(Fetcher):
         self.paths = dict()
         self.is_open = True
 
-    def load_index(
-            self,
-            source: Iterator[bytes],
-            ) -> Iterator[Tuple[int, bytes]]:
-        """
-        Yields unparsed index items from a byte stream.
-
-        Args:
-            source: The stream to read from.
-
-        Returns:
-            An iterable over index items.
-
-        Raises:
-            StorySourceError: If an item is malformed.
-        """
-        for part in source:
-            if len(part) < 3:
-                continue
-
-            line = part.strip()
-            key, meta = line.split(b':', 1)
-            key = key.strip(b' "')
-            meta = meta.strip(b' ,')
-
-            if meta[0] != 123 or meta[-1] != 125:
-                raise StorySourceError(f"Malformed index meta: {key}")
-
-            try:
-                yield int(key), compress(meta)
-            except ValueError as e:
-                raise StorySourceError(f"Malformed index key: {key}") from e
-
     def __len__(self) -> int:
         """
         Returns the total number of stories in the archive.
@@ -217,22 +278,14 @@ class FimfarchiveFetcher(Fetcher):
             self.archive.close()
 
         if hasattr(self, 'index'):
-            self.index.clear()
+            self.index.close()
 
         if hasattr(self, 'paths'):
             self.paths.clear()
 
     def fetch_meta(self, key: int) -> Dict[str, Any]:
         key = self.validate(key)
-        raw = self.index[key]
-
-        try:
-            meta = json.loads(decompress(raw).decode())
-        except UnicodeDecodeError as e:
-            raise StorySourceError("Incorrectly encoded index.") from e
-        except ValueError as e:
-            raise StorySourceError(f"Malformed meta for {key}: {raw}") from e
-
+        meta = self.index[key]
         actual = meta.get('id')
 
         if key != actual: