initial commitHEADmaster

10 files changed, 433 insertions, 0 deletions

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..c4a847d
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+/result
diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..b8b8894
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,19 @@
+Copyright (c) 2026 Martin Fischer <martin@push-f.com>
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..6611111
--- /dev/null
+++ b/README.md
@@ -0,0 +1,19 @@
+# web-feed-exporter
+
+Prometheus metrics for the most recently published timestamp of web feeds
+(RSS, Atom or JSON), so your Grafana dashboard can remind you to post
+to your blog or social media.
+
+## Provided metrics
+
+The following metrics are provided. All of them have a `feed` label containing the feed name.
+
+* `webfeed_items`, how many items the feed contains
+* `webfeed_newest_published_timestamp_seconds`, Unix timestamp of the newest published item
+* `webfeed_oldest_published_timestamp_seconds`, Unix timestamp of the oldest published item (that is still in the feed)
+
+## Limitations
+
+Feeds often contain only a limited number of the most recent items.
+This exporter does not store anything so it also provides no metrics
+for how many items were published in total or in specific time frames.
diff --git a/default.nix b/default.nix
new file mode 100644
index 0000000..61416cd
--- /dev/null
+++ b/default.nix
@@ -0,0 +1,8 @@
+{ pkgs ? import <nixpkgs> {} }:
+
+pkgs.buildGoModule {
+  pname = "web-feed-exporter";
+  version = "0+git";
+  src = pkgs.lib.cleanSource ./.;
+  vendorHash = (import ./hashes.nix).vendor;
+}
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..c3d92e9
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,31 @@
+module push-f.com/web-feed-exporter
+
+go 1.25.4
+
+require (
+	github.com/alecthomas/kong v1.13.0
+	github.com/google/go-cmp v0.7.0
+	github.com/mmcdole/gofeed v1.3.0
+	github.com/prometheus/client_golang v1.23.2
+	github.com/prometheus/common v0.66.1
+)
+
+require (
+	github.com/PuerkitoBio/goquery v1.8.0 // indirect
+	github.com/andybalholm/cascadia v1.3.1 // indirect
+	github.com/beorn7/perks v1.0.1 // indirect
+	github.com/cespare/xxhash/v2 v2.3.0 // indirect
+	github.com/json-iterator/go v1.1.12 // indirect
+	github.com/kr/text v0.2.0 // indirect
+	github.com/mmcdole/goxpp v1.1.1-0.20240225020742-a0c311522b23 // indirect
+	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
+	github.com/modern-go/reflect2 v1.0.2 // indirect
+	github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 // indirect
+	github.com/prometheus/client_model v0.6.2 // indirect
+	github.com/prometheus/procfs v0.16.1 // indirect
+	go.yaml.in/yaml/v2 v2.4.2 // indirect
+	golang.org/x/net v0.43.0 // indirect
+	golang.org/x/sys v0.35.0 // indirect
+	golang.org/x/text v0.28.0 // indirect
+	google.golang.org/protobuf v1.36.8 // indirect
+)
diff --git a/go.sum b/go.sum
new file mode 100644
index 0000000..e568b51
--- /dev/null
+++ b/go.sum
@@ -0,0 +1,83 @@
+github.com/PuerkitoBio/goquery v1.8.0 h1:PJTF7AmFCFKk1N6V6jmKfrNH9tV5pNE6lZMkG0gta/U=
+github.com/PuerkitoBio/goquery v1.8.0/go.mod h1:ypIiRMtY7COPGk+I/YbZLbxsxn9g5ejnI2HSMtkjZvI=
+github.com/alecthomas/assert/v2 v2.11.0 h1:2Q9r3ki8+JYXvGsDyBXwH3LcJ+WK5D0gc5E8vS6K3D0=
+github.com/alecthomas/assert/v2 v2.11.0/go.mod h1:Bze95FyfUr7x34QZrjL+XP+0qgp/zg8yS+TtBj1WA3k=
+github.com/alecthomas/kong v1.13.0 h1:5e/7XC3ugvhP1DQBmTS+WuHtCbcv44hsohMgcvVxSrA=
+github.com/alecthomas/kong v1.13.0/go.mod h1:wrlbXem1CWqUV5Vbmss5ISYhsVPkBb1Yo7YKJghju2I=
+github.com/alecthomas/repr v0.5.2 h1:SU73FTI9D1P5UNtvseffFSGmdNci/O6RsqzeXJtP0Qs=
+github.com/alecthomas/repr v0.5.2/go.mod h1:Fr0507jx4eOXV7AlPV6AVZLYrLIuIeSOWtW57eE/O/4=
+github.com/andybalholm/cascadia v1.3.1 h1:nhxRkql1kdYCc8Snf7D5/D3spOX+dBgjA6u8x004T2c=
+github.com/andybalholm/cascadia v1.3.1/go.mod h1:R4bJ1UQfqADjvDa4P6HZHLh/3OxWWEqc0Sk8XGwHqvA=
+github.com/beorn7/perks v1.0.1 h1:VlbKKnNfV8bJzeqoa4cOKqO6bYr3WgKZxO8Z16+hsOM=
+github.com/beorn7/perks v1.0.1/go.mod h1:G2ZrVWU2WbWT9wwq4/hrbKbnv/1ERSJQ0ibhJ6rlkpw=
+github.com/cespare/xxhash/v2 v2.3.0 h1:UL815xU9SqsFlibzuggzjXhog7bL6oX9BbNZnL2UFvs=
+github.com/cespare/xxhash/v2 v2.3.0/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
+github.com/creack/pty v1.1.9/go.mod h1:oKZEueFk5CKHvIhNR5MUki03XCEU+Q6VDXinZuGJ33E=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
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+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
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+github.com/hexops/gotextdiff v1.0.3 h1:gitA9+qJrrTCsiCl7+kh75nPqQt1cx4ZkudSTLoUqJM=
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+github.com/klauspost/compress v1.18.0 h1:c/Cqfb0r+Yi+JtIEq73FWXVkRonBlf0CRNYc8Zttxdo=
+github.com/klauspost/compress v1.18.0/go.mod h1:2Pp+KzxcywXVXMr50+X0Q/Lsb43OQHYWRCY2AiWywWQ=
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diff --git a/hashes.nix b/hashes.nix
new file mode 100644
index 0000000..3ecd26a
--- /dev/null
+++ b/hashes.nix
@@ -0,0 +1,3 @@
+{
+  vendor = "sha256-xNwlFPf8yg3Rbe9MWH05XNapyA1CFhhzy4jEB1VxGGQ=";
+}
diff --git a/main.go b/main.go
new file mode 100644
index 0000000..94b040d
--- /dev/null
+++ b/main.go
@@ -0,0 +1,144 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"log/slog"
+	"math"
+	"net/http"
+	"net/url"
+	"os"
+
+	"github.com/alecthomas/kong"
+	"github.com/mmcdole/gofeed"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+)
+
+type Args struct {
+	Port  int       `help:"Port to listen on" short:"p" default:"8888" env:"PORT"`
+	Feeds StringMap `placeholder:"{\"name\": \"url\", ...}" required:"" help:"Feeds to fetch" env:"FEEDS"`
+}
+
+type StringMap map[string]string
+
+func (p *StringMap) UnmarshalJSON(data []byte) error {
+	stringMap := (*map[string]string)(p)
+	return json.Unmarshal(data, &stringMap)
+}
+
+func main() {
+	logger := slog.New(slog.NewTextHandler(os.Stderr, &slog.HandlerOptions{
+		Level: slog.LevelDebug,
+	}))
+	slog.SetDefault(logger)
+
+	var args Args
+	ctx := kong.Parse(&args, kong.Description(
+		"Prometheus metrics for the most/least recently published timestamp of web feeds (RSS, Atom or JSON).",
+	))
+
+	te, err := newExporter(args.Feeds, prometheus.DefaultRegisterer)
+	ctx.FatalIfErrorf(err)
+
+	prometheus.MustRegister(te)
+	http.Handle("/metrics", promhttp.Handler())
+
+	slog.Info("starting", "urls", args.Feeds)
+	slog.Info(fmt.Sprintf("serving metrics at http://localhost:%d/metrics", args.Port))
+	http.ListenAndServe(fmt.Sprintf(":%d", args.Port), nil)
+}
+
+type Exporter struct {
+	urls                            map[string]string
+	itemCount                       *prometheus.Desc
+	newestPublishedTimestampSeconds *prometheus.Desc
+	oldestPublishedTimestampSeconds *prometheus.Desc
+}
+
+func newExporter(feeds map[string]string, reg prometheus.Registerer) (*Exporter, error) {
+	if len(feeds) == 0 {
+		return nil, fmt.Errorf("provided feeds map is empty")
+	}
+
+	for _, urlStr := range feeds {
+		url, err := url.Parse(urlStr)
+		if err != nil {
+			return nil, err
+		}
+		if url.Scheme != "http" && url.Scheme != "https" {
+			return nil, fmt.Errorf("unsupported protocol scheme %q (only http and https are supported)", url.Scheme)
+		}
+	}
+
+	return &Exporter{
+		urls: feeds,
+		itemCount: prometheus.NewDesc(
+			"webfeed_items",
+			"How many items the feed contains",
+			[]string{"feed"},
+			nil,
+		),
+		newestPublishedTimestampSeconds: prometheus.NewDesc(
+			"webfeed_newest_published_timestamp_seconds",
+			"Unix timestamp of the newest published item",
+			[]string{"feed"},
+			nil,
+		),
+		oldestPublishedTimestampSeconds: prometheus.NewDesc(
+			"webfeed_oldest_published_timestamp_seconds",
+			"Unix timestamp of the oldest published item (that is still in the feed)",
+			[]string{"feed"},
+			nil,
+		),
+	}, nil
+}
+
+func (e *Exporter) Describe(ch chan<- *prometheus.Desc) {
+	ch <- e.itemCount
+	ch <- e.newestPublishedTimestampSeconds
+	ch <- e.oldestPublishedTimestampSeconds
+}
+
+func (e *Exporter) Collect(ch chan<- prometheus.Metric) {
+	for name, url := range e.urls {
+		e.collectFeed(name, url, ch)
+	}
+}
+
+func (e *Exporter) collectFeed(name, url string, ch chan<- prometheus.Metric) {
+	feed, err := fetchFeed(url)
+	if err != nil {
+		slog.Error("failed to fetch feed", "url", url, "error", err)
+		return
+	}
+
+	ch <- prometheus.MustNewConstMetric(e.itemCount, prometheus.GaugeValue, float64(len(feed.Items)), name)
+
+	if len(feed.Items) == 0 {
+		return
+	}
+
+	newestPublished := int64(-1)
+	oldestPublished := int64(math.MaxInt64)
+
+	for _, item := range feed.Items {
+		if item.PublishedParsed != nil {
+			if item.PublishedParsed.Unix() > int64(newestPublished) {
+				newestPublished = item.PublishedParsed.Unix()
+			}
+			if item.PublishedParsed.Unix() < int64(oldestPublished) {
+				oldestPublished = item.PublishedParsed.Unix()
+			}
+		}
+	}
+
+	ch <- prometheus.MustNewConstMetric(e.newestPublishedTimestampSeconds, prometheus.GaugeValue, float64(newestPublished), name)
+	ch <- prometheus.MustNewConstMetric(e.oldestPublishedTimestampSeconds, prometheus.GaugeValue, float64(oldestPublished), name)
+}
+
+var fetchFeed = func(url string) (*gofeed.Feed, error) {
+	fp := gofeed.NewParser()
+	fp.UserAgent = "web-feed-exporter"
+	return fp.ParseURL(url)
+}
diff --git a/main_test.go b/main_test.go
new file mode 100644
index 0000000..112798e
--- /dev/null
+++ b/main_test.go
@@ -0,0 +1,90 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"path"
+	"slices"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/google/go-cmp/cmp"
+	"github.com/mmcdole/gofeed"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/common/expfmt"
+)
+
+func TestGrepRepo(t *testing.T) {
+	reposDir := t.TempDir()
+	err := os.Mkdir(path.Join(reposDir, "project1"), 0o755)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	feedUrl1 := "http://example.com/feed1.xml"
+	feedUrl2 := "http://example.com/feed2.xml"
+
+	urls := map[string]string{"feed1": feedUrl1, "feed2": feedUrl2}
+	reg := prometheus.NewRegistry()
+	te, err := newExporter(urls, reg)
+	if err != nil {
+		t.Fatal(err)
+	}
+	reg.MustRegister(te)
+
+	latestTimes := map[string][]int64{
+		feedUrl1: {1700000000, 1900000000, 1300000000},
+		feedUrl2: {1500000000},
+	}
+
+	fetchFeed = func(url string) (*gofeed.Feed, error) {
+		items := []*gofeed.Item{}
+		for _, sec := range latestTimes[url] {
+			time := time.Unix(sec, 0)
+			items = append(items, &gofeed.Item{
+				PublishedParsed: &time,
+			})
+		}
+		return &gofeed.Feed{
+			Items: items,
+		}, nil
+	}
+
+	want := "# HELP webfeed_items How many items the feed contains\n" +
+		"# TYPE webfeed_items gauge\n" +
+		fmt.Sprintf("webfeed_items{feed=\"feed1\"} %d\n", len(latestTimes[feedUrl1])) +
+		fmt.Sprintf("webfeed_items{feed=\"feed2\"} %d\n", len(latestTimes[feedUrl2])) +
+		"# HELP webfeed_newest_published_timestamp_seconds Unix timestamp of the newest published item\n" +
+		"# TYPE webfeed_newest_published_timestamp_seconds gauge\n" +
+		fmt.Sprintf("webfeed_newest_published_timestamp_seconds{feed=\"feed1\"} %.1e\n", float64(slices.Max(latestTimes[feedUrl1]))) +
+		fmt.Sprintf("webfeed_newest_published_timestamp_seconds{feed=\"feed2\"} %.1e\n", float64(slices.Max(latestTimes[feedUrl2]))) +
+		"# HELP webfeed_oldest_published_timestamp_seconds Unix timestamp of the oldest published item (that is still in the feed)\n" +
+		"# TYPE webfeed_oldest_published_timestamp_seconds gauge\n" +
+		fmt.Sprintf("webfeed_oldest_published_timestamp_seconds{feed=\"feed1\"} %.1e\n", float64(slices.Min(latestTimes[feedUrl1]))) +
+		fmt.Sprintf("webfeed_oldest_published_timestamp_seconds{feed=\"feed2\"} %.1e\n", float64(slices.Min(latestTimes[feedUrl2])))
+
+	if diff := cmp.Diff(collectMetrics(reg), want); diff != "" {
+		t.Errorf("unexpected metrics: %v", diff)
+	}
+}
+
+func collectMetrics(reg *prometheus.Registry) string {
+	mfs, done, err := prometheus.ToTransactionalGatherer(reg).Gather()
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer done()
+
+	var buf strings.Builder
+	enc := expfmt.NewEncoder(&buf, expfmt.NewFormat(expfmt.TypeTextPlain))
+
+	for _, mf := range mfs {
+		err := enc.Encode(mf)
+		if err != nil {
+			log.Fatal(err)
+		}
+	}
+	return buf.String()
+}
diff --git a/service.nix b/service.nix
new file mode 100644
index 0000000..1942107
--- /dev/null
+++ b/service.nix
@@ -0,0 +1,35 @@
+{ config, lib, pkgs, ... }:
+
+let
+  web_feed_exporter = pkgs.callPackage ./default.nix {};
+  cfg = config.services.webFeedExporter;
+in
+{
+  options.services.webFeedExporter = {
+    enable = lib.mkEnableOption "web-feed-exporter";
+
+    port = lib.mkOption {
+      type = lib.types.int;
+    };
+
+    feeds = lib.mkOption {
+      type = lib.types.attrsOf lib.types.str;
+      description = "Map of feed names to feed URLs.";
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    systemd.services.web-feed-exporter = {
+      serviceConfig = {
+        DynamicUser = true;
+        ExecStart = "${web_feed_exporter}/bin/web-feed-exporter";
+      };
+      environment = {
+        PORT = toString cfg.port;
+        FEEDS = builtins.toJSON cfg.feeds;
+      };
+
+      wantedBy = ["multi-user.target"];
+    };
+  };
+}