negentropy.

- a way to handle custom messages from Relay (NEG-whatever etc)
- negentropy implementation (adapted from that other one)
- nip77 nostr negentropy extension
- QueryEvents method for RelayStore that returns a channel (makes negentropy syncing work more seamlessly)

nip77/negentropy/encoding.go

@@ -0,0 +1,126 @@
+package negentropy
+
+import (
+	"bytes"
+	"encoding/hex"
+
+	"github.com/nbd-wtf/go-nostr"
+)
+
+func (n *Negentropy) DecodeTimestampIn(reader *bytes.Reader) (nostr.Timestamp, error) {
+	t, err := decodeVarInt(reader)
+	if err != nil {
+		return 0, err
+	}
+
+	timestamp := nostr.Timestamp(t)
+	if timestamp == 0 {
+		timestamp = maxTimestamp
+	} else {
+		timestamp--
+	}
+
+	timestamp += n.lastTimestampIn
+	if timestamp < n.lastTimestampIn { // Check for overflow
+		timestamp = maxTimestamp
+	}
+	n.lastTimestampIn = timestamp
+	return timestamp, nil
+}
+
+func (n *Negentropy) DecodeBound(reader *bytes.Reader) (Bound, error) {
+	timestamp, err := n.DecodeTimestampIn(reader)
+	if err != nil {
+		return Bound{}, err
+	}
+
+	length, err := decodeVarInt(reader)
+	if err != nil {
+		return Bound{}, err
+	}
+
+	id := make([]byte, length)
+	if _, err = reader.Read(id); err != nil {
+		return Bound{}, err
+	}
+
+	return Bound{Item{timestamp, hex.EncodeToString(id)}}, nil
+}
+
+func (n *Negentropy) encodeTimestampOut(timestamp nostr.Timestamp) []byte {
+	if timestamp == maxTimestamp {
+		n.lastTimestampOut = maxTimestamp
+		return encodeVarInt(0)
+	}
+	temp := timestamp
+	timestamp -= n.lastTimestampOut
+	n.lastTimestampOut = temp
+	return encodeVarInt(int(timestamp + 1))
+}
+
+func (n *Negentropy) encodeBound(bound Bound) []byte {
+	var output []byte
+
+	t := n.encodeTimestampOut(bound.Timestamp)
+	idlen := encodeVarInt(len(bound.ID) / 2)
+	output = append(output, t...)
+	output = append(output, idlen...)
+	id, _ := hex.DecodeString(bound.Item.ID)
+
+	output = append(output, id...)
+	return output
+}
+
+func getMinimalBound(prev, curr Item) Bound {
+	if curr.Timestamp != prev.Timestamp {
+		return Bound{Item{curr.Timestamp, ""}}
+	}
+
+	sharedPrefixBytes := 0
+
+	for i := 0; i < 32; i++ {
+		if curr.ID[i:i+2] != prev.ID[i:i+2] {
+			break
+		}
+		sharedPrefixBytes++
+	}
+
+	// sharedPrefixBytes + 1 to include the first differing byte, or the entire ID if identical.
+	return Bound{Item{curr.Timestamp, curr.ID[:(sharedPrefixBytes+1)*2]}}
+}
+
+func decodeVarInt(reader *bytes.Reader) (int, error) {
+	var res int = 0
+
+	for {
+		b, err := reader.ReadByte()
+		if err != nil {
+			return 0, err
+		}
+
+		res = (res << 7) | (int(b) & 127)
+		if (b & 128) == 0 {
+			break
+		}
+	}
+
+	return res, nil
+}
+
+func encodeVarInt(n int) []byte {
+	if n == 0 {
+		return []byte{0}
+	}
+
+	var o []byte
+	for n != 0 {
+		o = append([]byte{byte(n & 0x7F)}, o...)
+		n >>= 7
+	}
+
+	for i := 0; i < len(o)-1; i++ {
+		o[i] |= 0x80
+	}
+
+	return o
+}