checker: implement ShareKey to mutualise pings across targets

A ping result depends only on the set of target addresses and the probe
count, never on which domain or service the addresses belong to. Implement
sdk.ObservationSharer so the host can collect a single ICMP probe per address
set (per user) instead of re-pinging once per record: with 1.2.3.4 present in
many domains under several A records, the same address was probed dozens of
times for identical data.

The share key sorts the resolved addresses and folds in the probe count;
evaluation thresholds (warningRTT, ...) are intentionally excluded as they
only affect how the shared observation is judged. Unresolvable inputs yield
an empty key so the host falls back to per-target caching.

checker/collect.go

@@ -23,9 +23,13 @@ package checker
 
 import (
 	"context"
+	"crypto/sha256"
+	"encoding/hex"
 	"encoding/json"
 	"fmt"
 	"net"
+	"sort"
+	"strings"
 	"time"
 
 	probing "github.com/prometheus-community/pro-bing"
@@ -96,6 +100,31 @@ func (p *pingProvider) Collect(ctx context.Context, opts sdk.CheckerOptions) (an
 	return data, nil
 }
 
+// ShareKey implements sdk.ObservationSharer. A ping result depends only on the
+// set of target addresses and the probe count, never on which domain or service
+// the addresses belong to. Returning a stable key derived from those inputs lets
+// the host mutualise a single ICMP probe across every target (of the same user)
+// that points at the same address set, instead of re-pinging once per record.
+//
+// The evaluation thresholds (warningRTT, criticalRTT, …) are intentionally
+// excluded: they only affect how the shared observation is judged, not the data
+// collected. Inputs that cannot be resolved yield "" so the host falls back to
+// the default per-target caching.
+func (p *pingProvider) ShareKey(opts sdk.CheckerOptions) (string, error) {
+	addresses, err := resolveAddresses(opts)
+	if err != nil {
+		return "", nil
+	}
+
+	sorted := append([]string(nil), addresses...)
+	sort.Strings(sorted)
+
+	count := sdk.GetIntOption(opts, "count", 5)
+
+	h := sha256.Sum256(fmt.Appendf(nil, "%d|%s", count, strings.Join(sorted, ",")))
+	return "ping:" + hex.EncodeToString(h[:8]), nil
+}
+
 // resolveAddresses extracts target IP addresses from the options.
 func resolveAddresses(opts sdk.CheckerOptions) ([]string, error) {
 	// Direct addresses (from HTTP server).

checker/collect_test.go

@@ -119,3 +119,59 @@ func TestIpsFromServiceEmpty(t *testing.T) {
 		t.Errorf("expected 0 ips, got %v", ips)
 	}
 }
+
+func TestShareKeyStableRegardlessOfOrder(t *testing.T) {
+	p := &pingProvider{}
+	a, err := p.ShareKey(sdk.CheckerOptions{"addresses": []string{"1.1.1.1", "2.2.2.2"}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	b, err := p.ShareKey(sdk.CheckerOptions{"addresses": []string{"2.2.2.2", "1.1.1.1"}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if a == "" {
+		t.Fatal("expected a non-empty share key")
+	}
+	if a != b {
+		t.Errorf("share key must not depend on address order: %q != %q", a, b)
+	}
+}
+
+func TestShareKeyDiffersByAddress(t *testing.T) {
+	p := &pingProvider{}
+	a, _ := p.ShareKey(sdk.CheckerOptions{"address": "1.1.1.1"})
+	b, _ := p.ShareKey(sdk.CheckerOptions{"address": "2.2.2.2"})
+	if a == b {
+		t.Errorf("different addresses must yield different share keys, both %q", a)
+	}
+}
+
+func TestShareKeyDiffersByCount(t *testing.T) {
+	p := &pingProvider{}
+	a, _ := p.ShareKey(sdk.CheckerOptions{"address": "1.1.1.1", "count": float64(5)})
+	b, _ := p.ShareKey(sdk.CheckerOptions{"address": "1.1.1.1", "count": float64(10)})
+	if a == b {
+		t.Errorf("different probe counts must yield different share keys, both %q", a)
+	}
+}
+
+func TestShareKeyIgnoresEvaluationThresholds(t *testing.T) {
+	p := &pingProvider{}
+	a, _ := p.ShareKey(sdk.CheckerOptions{"address": "1.1.1.1", "warningRTT": float64(100)})
+	b, _ := p.ShareKey(sdk.CheckerOptions{"address": "1.1.1.1", "warningRTT": float64(250)})
+	if a != b {
+		t.Errorf("evaluation thresholds must not affect the share key: %q != %q", a, b)
+	}
+}
+
+func TestShareKeyEmptyWhenUnresolvable(t *testing.T) {
+	p := &pingProvider{}
+	sk, err := p.ShareKey(sdk.CheckerOptions{})
+	if err != nil {
+		t.Fatalf("expected no error, got %v", err)
+	}
+	if sk != "" {
+		t.Errorf("expected empty share key (per-target fallback), got %q", sk)
+	}
+}

go.mod

@@ -3,7 +3,7 @@ module git.happydns.org/checker-ping
 go 1.25.0
 
 require (
-	git.happydns.org/checker-sdk-go v1.5.0
+	git.happydns.org/checker-sdk-go v1.11.0
 	git.happydns.org/happyDomain v0.7.0
 	github.com/miekg/dns v1.1.72
 	github.com/prometheus-community/pro-bing v0.8.0

go.sum

@@ -1,5 +1,5 @@
-git.happydns.org/checker-sdk-go v1.5.0 h1:5uD5Cm6xJ+lwnhbJ09iCXGHbYS9zRh+Yh0NeBHkAPBY=
+git.happydns.org/checker-sdk-go v1.11.0 h1:+hs8OpcgvRMAoWyfqxih/Q0KYYUI1R8oFxO4RKioMLk=
-git.happydns.org/checker-sdk-go v1.5.0/go.mod h1:aNAcfYFfbhvH9kJhE0Njp5GX0dQbxdRB0rJ0KvSC5nI=
+git.happydns.org/checker-sdk-go v1.11.0/go.mod h1:aNAcfYFfbhvH9kJhE0Njp5GX0dQbxdRB0rJ0KvSC5nI=
 git.happydns.org/happyDomain v0.7.0 h1:NV82/NbcSeRm0+IUZqaK3Vu9Ovl5+vv4AigUJZMdwws=
 git.happydns.org/happyDomain v0.7.0/go.mod h1:5tgkmqFE65kK359rY49V++49wgZ0gco+Gh9X6tbL+bY=
 github.com/bytedance/gopkg v0.1.3 h1:TPBSwH8RsouGCBcMBktLt1AymVo2TVsBVCY4b6TnZ/M=