Document FEED_URI_PARAMS

docs/topics/feed-exports.rst

@@ -321,13 +321,14 @@ The following is a list of the accepted keys and the setting that is used
 as a fallback value if that key is not provided for a specific feed definition.
 
 * ``format``: the serialization format to be used for the feed.
-  See :ref:`topics-feed-format` for possible values. 
+  See :ref:`topics-feed-format` for possible values.
   Mandatory, no fallback setting
+* ``batch_item_count``: falls back to :setting:`FEED_EXPORT_BATCH_ITEM_COUNT`
 * ``encoding``: falls back to :setting:`FEED_EXPORT_ENCODING`
 * ``fields``: falls back to :setting:`FEED_EXPORT_FIELDS`
 * ``indent``: falls back to :setting:`FEED_EXPORT_INDENT`
 * ``store_empty``: falls back to :setting:`FEED_STORE_EMPTY`
-* ``batch_item_count``: falls back to :setting:`FEED_EXPORT_BATCH_ITEM_COUNT`
+* ``uri_params``: falls back to :setting:`FEED_URI_PARAMS`
 
 .. setting:: FEED_EXPORT_ENCODING
 
@@ -500,7 +501,7 @@ generated:
 * ``%(batch_time)s`` - gets replaced by a timestamp when the feed is being created
   (e.g. ``2020-03-28T14-45-08.237134``)
 
-* ``%(batch_id)d`` - gets replaced by the sequence number of the batch.
+* ``%(batch_id)d`` - gets replaced by the 1-based sequence number of the batch.
 
   Use :ref:`printf-style string formatting <python:old-string-formatting>` to
   alter the number format. For example, to make the batch ID a 5-digit
@@ -517,16 +518,74 @@ And your :command:`crawl` command line is::
 
 The command line above can generate a directory tree like::
 
-->projectname
--->dirname
---->1-filename2020-03-28T14-45-08.237134.json
---->2-filename2020-03-28T14-45-09.148903.json
---->3-filename2020-03-28T14-45-10.046092.json
+    ->projectname
+    -->dirname
+    --->1-filename2020-03-28T14-45-08.237134.json
+    --->2-filename2020-03-28T14-45-09.148903.json
+    --->3-filename2020-03-28T14-45-10.046092.json
 
 Where the first and second files contain exactly 100 items. The last one contains
 100 items or fewer.
 
 
+.. setting:: FEED_URI_PARAMS
+
+FEED_URI_PARAMS
+---------------
+
+Default: ``None``
+
+A string with the import path of a function to set the parameters to apply with
+:ref:`printf-style string formatting <python:old-string-formatting>` to the
+feed URI.
+
+The function signature should be as follows:
+
+.. function:: uri_params(params, spider)
+
+   Return a :class:`dict` of key-value pairs to apply to the feed URI using
+   :ref:`printf-style string formatting <python:old-string-formatting>`.
+
+   :param params: default key-value pairs
+
+        Specifically:
+
+        -   ``batch_id``: ID of the file batch. See
+            :setting:`FEED_EXPORT_BATCH_ITEM_COUNT`.
+
+            If :setting:`FEED_EXPORT_BATCH_ITEM_COUNT` is ``0``, ``batch_id``
+            is always ``1``.
+
+        -   ``batch_time``: UTC date and time, in ISO format with ``:``
+            replaced with ``-``.
+
+            See :setting:`FEED_EXPORT_BATCH_ITEM_COUNT`.
+
+        -   ``time``: ``batch_time``, with microseconds set to ``0``.
+   :type params: dict
+
+   :param spider: source spider of the feed items
+   :type spider: scrapy.spiders.Spider
+
+For example, to include the :attr:`name <scrapy.spiders.Spider.name>` of the
+source spider in the feed URI:
+
+#.  Define the following function somewhere in your project::
+
+        # myproject/utils.py
+        def uri_params(params, spider):
+            return {**params, 'spider_name': spider.name}
+
+#.  Point :setting:`FEED_URI_PARAMS` to that function in your settings::
+
+        # myproject/settings.py
+        FEED_URI_PARAMS = 'myproject.utils.uri_params'
+
+#.  Use ``%(spider_name)s`` in your feed URI::
+
+        scrapy crawl <spider_name> -o "%(spider_name)s.jl"
+
+
 .. _URIs: https://en.wikipedia.org/wiki/Uniform_Resource_Identifier
 .. _Amazon S3: https://aws.amazon.com/s3/
 .. _botocore: https://github.com/boto/botocore