Error rewrites (#43)

* pcap: reuse Frame memory

* slog: reduce heap allocations of addresses; also prevent heap alloc of dhcp options in pcap

* dns: heapless improvement; add StackAsync buffer for more heapless operation; start thinking of errors

* errors: begin standardise errors in lneto

* errors: finish standardization of errors

* fix merge issues

* add more lneto errors to rest of package

* format errors.go

tcp/handler.go

@@ -1,7 +1,6 @@
 package tcp
 
 import (
-	"errors"
 	"io"
 	"net"
 
@@ -11,11 +10,6 @@ import (
 	"github.com/soypat/lneto/internal"
 )
 
-var (
-	errMismatchedSrcPort = errors.New("source port mismatch")
-	errMismatchedDstPort = errors.New("destination port mismatch")
-)
-
 // Handler is a low level TCP handling data structure. It implements logic
 // related to data buffering, frame sequencing and connection state handling.
 // Does NOT implement IP related logic, so no CRC calculation/validation or pseudo header logic.
@@ -56,10 +50,10 @@ func (h *Handler) State() State { return h.scb.State() }
 // If the argument buffer is nil then the respective currently set buffer will be reused.
 func (h *Handler) SetBuffers(txbuf, rxbuf []byte, packets int) error {
 	if h.bufRx.Buf == nil && (len(rxbuf) < minBufferSize || len(txbuf) < minBufferSize) {
-		return errors.New("tcp: short buffer")
+		return lneto.ErrShortBuffer
 	}
 	if !h.scb.State().IsClosed() {
-		return errors.New("tcp.Handler must be closed before setting buffers")
+		return lneto.ErrInvalidConfig
 	}
 	if rxbuf != nil {
 		h.bufRx.Buf = rxbuf
@@ -156,15 +150,15 @@ func (h *Handler) Recv(incomingPacket []byte) error {
 
 	remotePort := tfrm.SourcePort()
 	if h.remotePort != 0 && remotePort != h.remotePort {
-		return errMismatchedSrcPort
+		return lneto.ErrMismatch
 	}
 	dstPort := tfrm.DestinationPort()
 	if h.localPort != dstPort {
-		return errMismatchedDstPort
+		return lneto.ErrMismatch
 	}
 	payload := tfrm.Payload()
 	if len(payload) > h.bufRx.Free() {
-		return errors.New("rx buffer full")
+		return lneto.ErrBufferFull
 	}
 	segIncoming := tfrm.Segment(len(payload))
 	if h.scb.IncomingIsKeepalive(segIncoming) {