feat: make devp2p `MAX_MESSAGE_SIZE` configurable

[rezzmah]

Describe the feature

Problem

MAX_MESSAGE_SIZE is hardcoded to 10MB in reth-eth-wire-types

reth/crates/net/eth-wire-types/src/message.rs

Line 29 in 56bbb3c

pub const MAX_MESSAGE_SIZE: usize = 10 * 1024 * 1024;

pub const MAX_MESSAGE_SIZE: usize = 10 * 1024 * 1024;

On custom chains with large blocks, the bodies downloader's GetBlockBodies requests produce responses that exceed this limit. The
receiving node rejects them with MessageTooBig, kills the session and results in the requester having no peers.

Our team observed this at ~2ggas / ~30k txs in a block

The downloader_request_limit in reth.toml can reduce batch size as a workaround but it doesn't work if individual blocks are larger than 10mb

LMK if it makes sense and I can make a PR

Additional context

We tested modifying the hardcoded 10mb value in place and that recovered the stalled node

[mattsse]

ah yes I think I had an old draft for this somewhere, let's do it

Our team observed this at ~2ggas / ~30k txs in a block

that's why after osaka there's now an rlp size limit on the block, ~8MB or somtheting

[DeshErBojhaa]

Can I have this one? I think I can wrap this one up by Feb 28, 2026.

[rezzmah]

Can I have this one? I think I can wrap this one up by Feb 28, 2026.

sure im cool with it. will take over nxt week if not ready. Feel free to reassign @mattsse

[DeshErBojhaa]

Hey, @mattsse , can you please assign this to me?

[DeshErBojhaa]

From my understanding, we also have a 16 MB limit on the P2P stack.

reth/crates/net/eth-wire/src/p2pstream.rs

Line 34 in 59c4e24

const MAX_PAYLOAD_SIZE: usize = 16 * 1024 * 1024;

Should I ignore this 16MB constraint and just have a CLI to override the MAX_MESSAGE_SIZE?

[mattsse]

@DeshErBojhaa I think we want both, this limit and

this one as well

reth/crates/net/eth-wire/src/ethstream.rs

Line 33 in 4cec99e

pub const MAX_MESSAGE_SIZE: usize = 10 * 1024 * 1024;