144 lines
2.9 KiB
Go
144 lines
2.9 KiB
Go
package negentropy
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import (
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"bytes"
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"fmt"
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"fiatjaf.com/nostr"
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)
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func (n *Negentropy) readTimestamp(reader *bytes.Reader) (nostr.Timestamp, error) {
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delta, err := readVarInt(reader)
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if err != nil {
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return 0, err
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}
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if delta == 0 {
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// zeroes are infinite
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timestamp := maxTimestamp
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n.lastTimestampIn = timestamp
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return timestamp, nil
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}
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// remove 1 as we always add 1 when encoding
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delta--
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// we add the previously cached timestamp to get the current
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timestamp := n.lastTimestampIn + nostr.Timestamp(delta)
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// cache this so we can apply it to the delta next time
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n.lastTimestampIn = timestamp
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return timestamp, nil
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}
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func (n *Negentropy) readBound(reader *bytes.Reader) (Bound, error) {
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timestamp, err := n.readTimestamp(reader)
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if err != nil {
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return Bound{}, fmt.Errorf("failed to decode bound timestamp: %w", err)
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}
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length, err := readVarInt(reader)
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if err != nil {
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return Bound{}, fmt.Errorf("failed to decode bound length: %w", err)
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}
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pfb := make([]byte, length)
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if _, err := reader.Read(pfb); err != nil {
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return Bound{}, fmt.Errorf("failed to read bound id: %w", err)
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}
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return Bound{timestamp, pfb}, nil
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}
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func (n *Negentropy) writeTimestamp(w *bytes.Buffer, timestamp nostr.Timestamp) {
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if timestamp == maxTimestamp {
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// zeroes are infinite
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n.lastTimestampOut = maxTimestamp // cache this (see below)
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writeVarInt(w, 0)
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return
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}
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// we will only encode the difference between this timestamp and the previous
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delta := timestamp - n.lastTimestampOut
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// we cache this here as the next timestamp we encode will be just a delta from this
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n.lastTimestampOut = timestamp
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// add 1 to prevent zeroes from being read as infinites
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writeVarInt(w, int(delta+1))
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return
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}
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func (n *Negentropy) writeBound(w *bytes.Buffer, bound Bound) {
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n.writeTimestamp(w, bound.Timestamp)
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writeVarInt(w, len(bound.IDPrefix))
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w.Write(bound.IDPrefix)
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}
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func getMinimalBound(prev, curr Item) Bound {
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if curr.Timestamp != prev.Timestamp {
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return Bound{curr.Timestamp, nil}
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}
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sharedPrefixBytes := 0
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for i := 0; i < 31; i++ {
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if curr.ID[i] != prev.ID[i] {
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break
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}
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sharedPrefixBytes++
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}
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// sharedPrefixBytes + 1 to include the first differing byte, or the entire ID if identical.
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return Bound{curr.Timestamp, curr.ID[:(sharedPrefixBytes + 1)]}
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}
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func readVarInt(reader *bytes.Reader) (int, error) {
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var res int = 0
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for {
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b, err := reader.ReadByte()
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if err != nil {
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return 0, err
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}
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res = (res << 7) | (int(b) & 127)
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if (b & 128) == 0 {
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break
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}
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}
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return res, nil
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}
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func writeVarInt(w *bytes.Buffer, n int) {
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if n == 0 {
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w.WriteByte(0)
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return
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}
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w.Write(EncodeVarInt(n))
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}
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func EncodeVarInt(n int) []byte {
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if n == 0 {
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return []byte{0}
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}
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result := make([]byte, 8)
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idx := 7
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for n != 0 {
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result[idx] = byte(n & 0x7F)
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n >>= 7
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idx--
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}
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result = result[idx+1:]
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for i := 0; i < len(result)-1; i++ {
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result[i] |= 0x80
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}
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return result
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}
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