From 842e1c8f42703fe6e30ee64f7e3229efec964d96 Mon Sep 17 00:00:00 2001
From: Chris Schinnerl <chris@sia.tech>
Date: Wed, 31 Jan 2024 15:14:06 -0400
Subject: [PATCH] chain: add Announcement type and ForEachAnnouncement

---
 chain/announcements.go | 99 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 99 insertions(+)
 create mode 100644 chain/announcements.go

diff --git a/chain/announcements.go b/chain/announcements.go
new file mode 100644
index 0000000..ed5f662
--- /dev/null
+++ b/chain/announcements.go
@@ -0,0 +1,99 @@
+package chain
+
+import (
+	"bytes"
+
+	"go.sia.tech/core/types"
+)
+
+// AnnouncementSpecifier is the specifier used in the arbitrary data section
+// (for v1 txns) and the attestation value (for v2 txns) when a host announces
+// its net address.
+const AnnouncementSpecifier = "HostAnnouncement"
+
+type (
+	// Announcement represents a v1 or v2 host announcement after it has been
+	// validated
+	Announcement struct {
+		NetAddress string
+		PublicKey  types.PublicKey
+	}
+
+	// V1Announcement represents a host announcement in v1 as stored in the
+	// arbitrary data section of a transaction
+	V1Announcement struct {
+		Specifier  types.Specifier
+		NetAddress string
+		PublicKey  types.UnlockKey
+		Signature  types.Signature
+	}
+)
+
+// DecoderFrom decodes a signed announcement
+func (a *V1Announcement) DecodeFrom(d *types.Decoder) {
+	a.Specifier.DecodeFrom(d)
+	a.NetAddress = d.ReadString()
+	a.PublicKey.DecodeFrom(d)
+	a.Signature.DecodeFrom(d)
+}
+
+// EncodeTo encodes a signed announcement
+func (a V1Announcement) EncodeTo(e *types.Encoder) {
+	a.Specifier.EncodeTo(e)
+	e.WriteString(a.NetAddress)
+	a.PublicKey.EncodeTo(e)
+	a.Signature.EncodeTo(e)
+}
+
+// VerifySignature verifies the signature of the announcement using its public
+// key. This can only succeed if the PublicKey is a valid ed25519 public key.
+func (a V1Announcement) VerifySignature() bool {
+	buf := new(bytes.Buffer)
+	e := types.NewEncoder(buf)
+	a.Specifier.EncodeTo(e)
+	e.WriteString(a.NetAddress)
+	a.PublicKey.EncodeTo(e)
+	e.Flush()
+	annHash := types.HashBytes(buf.Bytes())
+	var pk types.PublicKey
+	copy(pk[:], a.PublicKey.Key)
+	return pk.VerifyHash(annHash, a.Signature)
+}
+
+// ForEachAnnouncement calls fn on each host announcement in a block.
+func ForEachAnnouncement(b types.Block, fn func(Announcement)) {
+	for _, txn := range b.Transactions {
+		for _, arb := range txn.ArbitraryData {
+			// decode announcement
+			var ha V1Announcement
+			dec := types.NewBufDecoder(arb)
+			ha.DecodeFrom(dec)
+			if err := dec.Err(); err != nil {
+				continue
+			} else if ha.Specifier != types.NewSpecifier(AnnouncementSpecifier) {
+				continue
+			}
+			// verify signature
+			if !ha.VerifySignature() {
+				continue
+			}
+			var pk types.PublicKey
+			copy(pk[:], ha.PublicKey.Key)
+			fn(Announcement{
+				NetAddress: ha.NetAddress,
+				PublicKey:  pk,
+			})
+		}
+	}
+	for _, txn := range b.V2Transactions() {
+		for _, att := range txn.Attestations {
+			if att.Key != AnnouncementSpecifier {
+				continue
+			}
+			fn(Announcement{
+				NetAddress: string(att.Value),
+				PublicKey:  att.PublicKey,
+			})
+		}
+	}
+}