fix: exchange: allow up to 10k messages per block

Also explicitly limit how many bytes we're willing to read in one go
such that we're capable of reading a worst-case tipset (like, really,
never going to happen worst-case). Previously, this wasn't an issue.
However, we've bumped the max number of messages from 8,192 to 150,000
and need to limit allocations somewhere else.

chain/exchange/client.go

@@ -4,6 +4,7 @@ import (
 	"bufio"
 	"context"
 	"fmt"
+	"io"
 	"math/rand"
 	"time"
 
@@ -23,6 +24,10 @@ import (
 	"github.com/filecoin-project/lotus/lib/peermgr"
 )
 
+// Set the max exchange message size to 120MiB. Purely based on gas numbers, we can include ~8MiB of
+// messages per block, so I've set this to 120MiB to be _very_ safe.
+const maxExchangeMessageSize = (15 * 8) << 20
+
 // client implements exchange.Client, using the libp2p ChainExchange protocol
 // as the fetching mechanism.
 type client struct {
@@ -434,10 +439,11 @@ func (c *client) sendRequestToPeer(ctx context.Context, peer peer.ID, req *Reque
 		log.Warnw("CloseWrite err", "error", err)
 	}
 
-	// Read response.
+	// Read response, limiting the size of the response to maxExchangeMessageSize as we allow a
+	// lot of messages (10k+) but they'll mostly be quite small.
 	var res Response
 	err = cborutil.ReadCborRPC(
-		bufio.NewReader(incrt.New(stream, ReadResMinSpeed, ReadResDeadline)),
+		bufio.NewReader(io.LimitReader(incrt.New(stream, ReadResMinSpeed, ReadResDeadline), maxExchangeMessageSize)),
 		&res)
 	if err != nil {
 		c.peerTracker.logFailure(peer, build.Clock.Since(connectionStart), req.Length)

chain/exchange/protocol.go

@@ -154,6 +154,8 @@ type BSTipSet struct {
 // FIXME: The logic to decompress this structure should belong
 //
 //	to itself, not to the consumer.
+//
+// NOTE: Max messages is: BlockMessageLimit (10k) * MaxTipsetSize (15) = 150k
 type CompactedMessages struct {
 	Bls         []*types.Message
 	BlsIncludes [][]uint64