op-batcher: prevent over-assessment of DA type (ethereum-optimism#12115)

* test: assert that default config doesn't change prematurely

* test: use a better system to ensure we are not over assessing

* return io.EOF from getReadyChannel

when the current channel has no tx data

also improve godoc

op-batcher/batcher/channel_manager.go

@@ -193,7 +193,11 @@ func (s *channelManager) TxData(l1Head eth.BlockID) (txData, error) {
 }
 
 // getReadyChannel returns the next channel ready to submit data, or an error.
-// It adds blocks from the block queue to the current channel and generates frames for it.
+// It will create a new channel if necessary.
+// If there is no data ready to send, it adds blocks from the block queue
+// to the current channel and generates frames for it.
+// Always returns nil and the io.EOF sentinel error when
+// there is no channel with txData
 func (s *channelManager) getReadyChannel(l1Head eth.BlockID) (*channel, error) {
  var firstWithTxData *channel
  for _, ch := range s.channelQueue {
@@ -239,7 +243,11 @@ func (s *channelManager) getReadyChannel(l1Head eth.BlockID) (*channel, error) {
  return nil, err
  }
 
- return s.currentChannel, nil
+ if s.currentChannel.HasTxData() {
+ return s.currentChannel, nil
+ }
+
+ return nil, io.EOF
 }
 
 // ensureChannelWithSpace ensures currentChannel is populated with a channel that has

op-batcher/batcher/channel_manager_test.go

@@ -491,9 +491,11 @@ func TestChannelManager_ChannelCreation(t *testing.T) {
 type FakeDynamicEthChannelConfig struct {
  DynamicEthChannelConfig
  chooseBlobs bool
+ assessments int
 }
 
 func (f *FakeDynamicEthChannelConfig) ChannelConfig() ChannelConfig {
+ f.assessments++
  if f.chooseBlobs {
  return f.blobConfig
  }
@@ -537,13 +539,21 @@ func TestChannelManager_TxData(t *testing.T) {
  name string
  chooseBlobsWhenChannelCreated bool
  chooseBlobsWhenChannelSubmitted bool
+
+ // * One when the channelManager was created
+ // * One when the channel is about to be submitted
+ // * Potentially one more if the replacement channel is about to be submitted,
+ // this only happens when going from calldata->blobs because
+ // the channel is no longer ready to send until more data
+ // is added.
+ numExpectedAssessments int
  }
 
  tt := []TestCase{
- {"blobs->blobs", true, true},
- {"calldata->calldata", false, false},
- {"blobs->calldata", true, false},
- {"calldata->blobs", false, true},
+ {"blobs->blobs", true, true, 2},
+ {"calldata->calldata", false, false, 2},
+ {"blobs->calldata", true, false, 2},
+ {"calldata->blobs", false, true, 3},
  }
 
  for _, tc := range tt {
@@ -590,6 +600,7 @@ func TestChannelManager_TxData(t *testing.T) {
  }
  }
 
+ require.Equal(t, tc.numExpectedAssessments, cfg.assessments)
  require.Equal(t, tc.chooseBlobsWhenChannelSubmitted, data.asBlob)
  require.Equal(t, tc.chooseBlobsWhenChannelSubmitted, m.defaultCfg.UseBlobs)
  })