address @ajsutton review

op-node/rollup/derive/channel.go

@@ -24,9 +24,9 @@ const (
 // channel may mark itself as ready for reading once all intervening frames have been added
 type Channel struct {
 	// id of the channel
-	id        ChannelID
-	openBlock eth.L1BlockRef
-	holocene  bool
+	id             ChannelID
+	openBlock      eth.L1BlockRef
+	requireInOrder bool
 
 	// estimated memory size, used to drop the channel if we have too much data
 	size uint64
@@ -47,12 +47,14 @@ type Channel struct {
 	highestL1InclusionBlock eth.L1BlockRef
 }
 
-func NewChannel(id ChannelID, openBlock eth.L1BlockRef, holocene bool) *Channel {
+// NewChannel creates a new channel with the given id and openening block. If requireInOrder is
+// true, frames must be added in order.
+func NewChannel(id ChannelID, openBlock eth.L1BlockRef, requireInOrder bool) *Channel {
 	return &Channel{
-		id:        id,
-		inputs:    make(map[uint64]Frame),
-		openBlock: openBlock,
-		holocene:  holocene,
+		id:             id,
+		inputs:         make(map[uint64]Frame),
+		openBlock:      openBlock,
+		requireInOrder: requireInOrder,
 	}
 }
 
@@ -73,7 +75,7 @@ func (ch *Channel) AddFrame(frame Frame, l1InclusionBlock eth.L1BlockRef) error
 	if ch.closed && frame.FrameNumber >= ch.endFrameNumber {
 		return fmt.Errorf("frame number (%d) is greater than or equal to end frame number (%d) of a closed channel", frame.FrameNumber, ch.endFrameNumber)
 	}
-	if ch.holocene && int(frame.FrameNumber) != len(ch.inputs) {
+	if ch.requireInOrder && int(frame.FrameNumber) != len(ch.inputs) {
 		return fmt.Errorf("frame out of order, expected %d, got %d", len(ch.inputs), frame.FrameNumber)
 	}
 

op-node/rollup/derive/channel_stage.go

@@ -2,6 +2,7 @@ package derive
 
 import (
 	"context"
+	"errors"
 	"io"
 
 	"github.com/ethereum-optimism/optimism/op-node/rollup"
@@ -66,7 +67,7 @@ func (cs *ChannelStage) NextData(ctx context.Context) ([]byte, error) {
 	// Note that if the current channel was already completed, we would have forwarded its data
 	// already. So we start by reading in frames.
 	if cs.channel != nil && cs.channel.IsReady() {
-		panic("unexpected ready channel")
+		return nil, NewCriticalError(errors.New("unexpected ready channel"))
 	}
 
 	// ingest frames until we either hit an error (probably io.EOF) or complete a channel
@@ -109,12 +110,10 @@ func (cs *ChannelStage) NextData(ctx context.Context) ([]byte, error) {
 	ch := cs.channel
 	// Note that if we exit the frame ingestion loop, we're guaranteed to have a ready channel.
 	if ch == nil || !ch.IsReady() {
-		panic("unexpected non-ready channel")
+		return nil, NewCriticalError(errors.New("unexpected non-ready channel"))
 	}
 
 	cs.resetChannel()
 	r := ch.Reader()
-	// error always nil, as we're reading from simple bytes readers
-	data, _ := io.ReadAll(r)
-	return data, nil
+	return io.ReadAll(r)
 }