provide "extractor" and "job" keys for logging output

This allows for stuff like "{extractor.url}" and "{extractor.category}"
in logging format strings.
Accessing 'extractor' and 'job' in any way will return "None" if those
fields aren't defined, i.e. in general logging messages.

gallery_dl/output.py

@@ -1,6 +1,6 @@
 # -*- coding: utf-8 -*-
 
-# Copyright 2015-2018 Mike Fährmann
+# Copyright 2015-2019 Mike Fährmann
 #
 # This program is free software; you can redistribute it and/or modify
 # it under the terms of the GNU General Public License version 2 as
@@ -9,9 +9,121 @@
 import os
 import sys
 import shutil
-from . import config
+import logging
+from . import config, util
 
 
+# --------------------------------------------------------------------
+# Logging
+
+LOG_FORMAT = "[{name}][{levelname}] {message}"
+LOG_FORMAT_DATE = "%Y-%m-%d %H:%M:%S"
+LOG_LEVEL = logging.INFO
+
+
+class Logger(logging.Logger):
+    """Custom logger that includes extractor and job info in log records"""
+    extractor = util.NONE
+    job = util.NONE
+
+    def makeRecord(self, name, level, fn, lno, msg, args, exc_info,
+                   func=None, extra=None, sinfo=None,
+                   factory=logging._logRecordFactory):
+        rv = factory(name, level, fn, lno, msg, args, exc_info, func, sinfo)
+        rv.extractor = self.extractor
+        rv.job = self.job
+        return rv
+
+
+def initialize_logging(loglevel):
+    """Setup basic logging functionality before configfiles have been loaded"""
+    # convert levelnames to lowercase
+    for level in (10, 20, 30, 40, 50):
+        name = logging.getLevelName(level)
+        logging.addLevelName(level, name.lower())
+
+    # register custom Logging class
+    logging.Logger.manager.setLoggerClass(Logger)
+
+    # setup basic logging to stderr
+    formatter = logging.Formatter(LOG_FORMAT, LOG_FORMAT_DATE, "{")
+    handler = logging.StreamHandler()
+    handler.setFormatter(formatter)
+    handler.setLevel(loglevel)
+    root = logging.getLogger()
+    root.setLevel(logging.NOTSET)
+    root.addHandler(handler)
+
+    return logging.getLogger("gallery-dl")
+
+
+def setup_logging_handler(key, fmt=LOG_FORMAT, lvl=LOG_LEVEL):
+    """Setup a new logging handler"""
+    opts = config.interpolate(("output", key))
+    if not opts:
+        return None
+    if not isinstance(opts, dict):
+        opts = {"path": opts}
+
+    path = opts.get("path")
+    mode = opts.get("mode", "w")
+    encoding = opts.get("encoding", "utf-8")
+    try:
+        path = util.expand_path(path)
+        handler = logging.FileHandler(path, mode, encoding)
+    except (OSError, ValueError) as exc:
+        logging.getLogger("gallery-dl").warning(
+            "%s: %s", key, exc)
+        return None
+    except TypeError as exc:
+        logging.getLogger("gallery-dl").warning(
+            "%s: missing or invalid path (%s)", key, exc)
+        return None
+
+    level = opts.get("level", lvl)
+    logfmt = opts.get("format", fmt)
+    datefmt = opts.get("format-date", LOG_FORMAT_DATE)
+    formatter = logging.Formatter(logfmt, datefmt, "{")
+    handler.setFormatter(formatter)
+    handler.setLevel(level)
+
+    return handler
+
+
+def configure_logging_handler(key, handler):
+    """Configure a logging handler"""
+    opts = config.interpolate(("output", key))
+    if not opts:
+        return
+    if isinstance(opts, str):
+        opts = {"format": opts}
+    if handler.level == LOG_LEVEL and "level" in opts:
+        handler.setLevel(opts["level"])
+    if "format" in opts or "format-date" in opts:
+        logfmt = opts.get("format", LOG_FORMAT)
+        datefmt = opts.get("format-date", LOG_FORMAT_DATE)
+        formatter = logging.Formatter(logfmt, datefmt, "{")
+        handler.setFormatter(formatter)
+
+
+# --------------------------------------------------------------------
+# Utility functions
+
+def replace_std_streams(errors="replace"):
+    """Replace standard streams and set their error handlers to 'errors'"""
+    for name in ("stdout", "stdin", "stderr"):
+        stream = getattr(sys, name)
+        setattr(sys, name, stream.__class__(
+            stream.buffer,
+            errors=errors,
+            newline=stream.newlines,
+            line_buffering=stream.line_buffering,
+        ))
+
+
+# --------------------------------------------------------------------
+# Downloader output
+
 def select():
     """Automatically select a suitable output class"""
     pdict = {