Cycle every payload pattern per packet and always run both directions

frame.go

@@ -2,7 +2,6 @@ package main
 
 import (
 	"encoding/binary"
-	"fmt"
 	"hash/crc32"
 	"math/rand/v2"
 )
@@ -61,60 +60,60 @@ var patterns = []pattern{
 	}},
 }
 
-func patternIndex(name string) (int, error) {
-	for i, p := range patterns {
-		if p.name == name {
-			return i, nil
-		}
-	}
+func patternNames() []string {
 	names := make([]string, len(patterns))
 	for i, p := range patterns {
 		names[i] = p.name
 	}
-	return 0, fmt.Errorf("unknown pattern %q (have %v)", name, names)
+	return names
 }
 
+// Every pattern is laid out at full length up front with its checksum at each
+// size, so a sender picks a pattern by choosing a buffer, never by writing one.
 type frameSpec struct {
-	patIdx    int
-	ref       []byte
-	crcFor    map[int]uint32
+	refs      [][]byte
+	crcFor    []map[int]uint32
 	dstMAC    [6]byte
 	srcMAC    [6]byte
 	etherType uint16
 	sizes     []int
 	maxSize   int
+	maxPay    int
 }
 
-func newFrameSpec(patIdx int, dst, src [6]byte, etherType uint16, sizes []int) *frameSpec {
+func newFrameSpec(dst, src [6]byte, etherType uint16, sizes []int) *frameSpec {
 	maxSize := 0
 	for _, s := range sizes {
 		if s > maxSize {
 			maxSize = s
 		}
 	}
-	ref := make([]byte, maxSize-minFrame)
-	patterns[patIdx].fill(ref)
-	crcFor := make(map[int]uint32, len(sizes))
-	for _, s := range sizes {
-		crcFor[s] = crc32.Checksum(ref[:s-minFrame], crcTable)
-	}
-	return &frameSpec{
-		patIdx:    patIdx,
-		ref:       ref,
-		crcFor:    crcFor,
+	f := &frameSpec{
 		dstMAC:    dst,
 		srcMAC:    src,
 		etherType: etherType,
 		sizes:     sizes,
 		maxSize:   maxSize,
+		maxPay:    maxSize - minFrame,
 	}
+	for _, p := range patterns {
+		ref := make([]byte, f.maxPay)
+		p.fill(ref)
+		crcFor := make(map[int]uint32, len(sizes))
+		for _, s := range sizes {
+			crcFor[s] = crc32.Checksum(ref[:s-minFrame], crcTable)
+		}
+		f.refs = append(f.refs, ref)
+		f.crcFor = append(f.crcFor, crcFor)
+	}
+	return f
 }
 
-func (f *frameSpec) prefill(buf []byte) {
+func (f *frameSpec) prefill(buf []byte, patIdx int) {
 	copy(buf[0:6], f.dstMAC[:])
 	copy(buf[6:12], f.srcMAC[:])
 	binary.BigEndian.PutUint16(buf[12:14], f.etherType)
-	copy(buf[minFrame:], f.ref)
+	copy(buf[minFrame:], f.refs[patIdx])
 }
 
 func putHeader(buf []byte, patIdx int, stream uint16, seq uint64, payLen int, crc uint32) {