NAME

sfeedrc — sfeed_update(1) configuration file

DESCRIPTION

sfeedrc is the configuration file for sfeed_update(1) and is evaluated as a shellscript.

VARIABLES

sfeedpath: can be set for the directory to store the TAB-separated feed files. The default is $HOME/.sfeed/feeds.
maxjobs: can be used to change the amount of concurrent feed() jobs. The default is 16.

FUNCTIONS

feeds()

This function is the required "main" entry-point function called from sfeed_update(1).

feed(name, feedurl, basesiteurl, encoding)

Inside the feeds() function feeds can be defined by calling the feed() function. Its arguments are:

name: Name of the feed, this is also used as the filename for the TAB-separated feed file. The feed name cannot contain the '/' character because it is a path separator, they will be replaced with '_'. Each name should be unique.
feedurl: URL to fetch the RSS/Atom data from. This is usually a HTTP or HTTPS URL.
[basesiteurl]: Base URL of the feed links. This argument allows fixing relative item links.
According to the RSS and Atom specification, feeds should always have absolute URLs, but this is not always the case in practice.
[encoding]: Feeds are converted from this encoding to UTF-8. The encoding should be a usable character-set name for the iconv(1) tool.

OVERRIDE FUNCTIONS

Because sfeed_update(1) is a shellscript each function can be overridden to change its behaviour. Notable functions are:

fetch(name, url, feedfile)

Fetch feed from URL and write the data to stdout. Its arguments are:

name: Feed name.
url: URL to fetch.
feedfile: Used feedfile (useful for comparing modification times).

By default the tool curl(1) is used.

convertencoding(name, from, to)

Convert data from stdin from one text-encoding to another and write it to stdout. Its arguments are:

name: Feed name.
from: From text-encoding.
to: To text-encoding.

By default the tool iconv(1) is used.

parse(name, feedurl, basesiteurl)

Read RSS/Atom XML data from stdin, convert and write it as sfeed(5) data to stdout. Its arguments are:

name: Feed name.
feedurl: URL of the feed.
basesiteurl: Base URL of the feed links. This argument allows to fix relative item links.

filter(name, url)

Filter sfeed(5) data from stdin and write it to stdout. Its arguments are:

name: Feed name.
url: URL of the feed.

merge(name, oldfile, newfile)

Merge sfeed(5) data of oldfile with newfile and write it to stdout. Its arguments are:

name: Feed name.
oldfile: Old file.
newfile: New file.

order(name, url)

Sort sfeed(5) data from stdin and write it to stdout. Its arguments are:

name: Feed name.
url: URL of the feed.

EXAMPLES

An example configuration file is included named sfeedrc.example and also shown below:

#sfeedpath="$HOME/.sfeed/feeds"

# list of feeds to fetch:
feeds() {
	# feed <name> <feedurl> [basesiteurl] [encoding]
	feed "codemadness" "https://www.codemadness.org/atom_content.xml"
	feed "explosm" "http://feeds.feedburner.com/Explosm"
	feed "golang github releases" "https://github.com/golang/go/releases.atom"
	feed "linux kernel" "https://www.kernel.org/feeds/kdist.xml" "https://www.kernel.org"
	feed "reddit openbsd" "https://old.reddit.com/r/openbsd/.rss"
	feed "slashdot" "http://rss.slashdot.org/Slashdot/slashdot" "http://slashdot.org"
	feed "tweakers" "http://feeds.feedburner.com/tweakers/mixed" "http://tweakers.net" "iso-8859-1"
	# get youtube Atom feed: curl -s -L 'https://www.youtube.com/user/gocoding/videos' | sfeed_web | cut -f 1
	feed "youtube golang" "https://www.youtube.com/feeds/videos.xml?channel_id=UCO3LEtymiLrgvpb59cNsb8A"
	feed "xkcd" "https://xkcd.com/atom.xml" "https://xkcd.com"
}

To change the default curl(1) options for fetching the data, the fetch() function can be overridden and added at the top of the sfeedrc file, for example:

# fetch(name, url, feedfile)
fetch() {
	# allow for 1 redirect, set User-Agent, timeout is 15 seconds.
	curl -L --max-redirs 1 -H "User-Agent: 007" -f -s -m 15 \
		"$2" 2>/dev/null
}

Caching, incremental data updates and bandwidth saving

For HTTP servers that support it some bandwidth saving can be done by changing some of the default curl options. These options can come at a cost of some privacy, because it exposes additional metadata from the previous request.

The curl ETag options (--etag-save and --etag-compare) can be used to store and send the previous ETag header value. curl version 7.73+ is recommended for it to work properly.
The curl -z option can be used to send the modification date of a local file as a HTTP If-Modified-Since request header. The server can then respond if the data is modified or not or respond with only the incremental data.
The curl --compressed option can be used to indicate the client supports decompression. Because RSS/Atom feeds are textual XML data this generally compresses very well.
The example below also sets the User-Agent to sfeed, because some CDNs block HTTP clients based on the User-Agent request header.

Example:

mkdir -p "$HOME/.sfeed/etags" "$HOME/.sfeed/lastmod"

# fetch(name, url, feedfile)
fetch() {
	basename="$(basename "$3")"
	etag="$HOME/.sfeed/etags/${basename}"
	lastmod="$HOME/.sfeed/lastmod/${basename}"
	output="${sfeedtmpdir}/feeds/${filename}.xml"

	curl \
		-f -s -m 15 \
		-L --max-redirs 0 \
		-H "User-Agent: sfeed" \
		--compressed \
		--etag-save "${etag}" --etag-compare "${etag}" \
		-R -o "${output}" \
		-z "${lastmod}" \
		"$2" 2>/dev/null || return 1

	# succesful, but no file written: assume it is OK and Not Modified.
	[ -e "${output}" ] || return 0

	# use server timestamp from curl -R to set Last-Modified.
	touch -r "${output}" "${lastmod}" 2>/dev/null
	cat "${output}" 2>/dev/null
	# use write output status, other errors are ignored here.
	fetchstatus="$?"
	rm -f "${output}" 2>/dev/null
	return "${fetchstatus}"
}

The README file has more examples.

AUTHORS

Hiltjo Posthuma <hiltjo@codemadness.org>