web3-proxy/web3_proxy/src/rpcs/one.rs

///! Rate-limited communication with a web3 provider.
use super::blockchain::{ArcBlock, BlockHashesCache, Web3ProxyBlock};
use super::provider::Web3Provider;
use super::request::{OpenRequestHandle, OpenRequestResult};
use crate::app::{flatten_handle, AnyhowJoinHandle};
use crate::config::{BlockAndRpc, Web3RpcConfig};
use crate::frontend::authorization::Authorization;
use anyhow::{anyhow, Context};
use ethers::prelude::{Bytes, Middleware, ProviderError, TxHash, H256, U64};
use ethers::types::U256;
use futures::future::try_join_all;
use futures::StreamExt;
use hdrhistogram::Histogram;
use log::{debug, error, info, trace, warn, Level};
use migration::sea_orm::DatabaseConnection;
use parking_lot::RwLock;
use redis_rate_limiter::{RedisPool, RedisRateLimitResult, RedisRateLimiter};
use serde::ser::{SerializeStruct, Serializer};
use serde::Serialize;
use serde_json::json;
use std::cmp::min;
use std::fmt;
use std::hash::{Hash, Hasher};
use std::sync::atomic::{self, AtomicU64};
use std::{cmp::Ordering, sync::Arc};
use thread_fast_rng::rand::Rng;
use thread_fast_rng::thread_fast_rng;
use tokio::sync::{broadcast, oneshot, watch, RwLock as AsyncRwLock};
use tokio::time::{sleep, sleep_until, timeout, Duration, Instant};

pub struct Web3RpcLatencies {
    /// Traack how far behind the fastest node we are
    pub new_head: Histogram<u64>,
    /// exponentially weighted moving average of how far behind the fastest node we are
    pub new_head_ewma: u32,
    /// Track how long an rpc call takes on average
    pub request: Histogram<u64>,
    /// exponentially weighted moving average of how far behind the fastest node we are
    pub request_ewma: u32,
}

impl Default for Web3RpcLatencies {
    fn default() -> Self {
        todo!("use ewma crate, not u32");
        Self {
            new_head: Histogram::new(3).unwrap(),
            new_head_ewma: 0,
            request: Histogram::new(3).unwrap(),
            request_ewma: 0,
        }
    }
}

/// An active connection to a Web3 RPC server like geth or erigon.
#[derive(Default)]
pub struct Web3Rpc {
    pub name: String,
    pub display_name: Option<String>,
    pub db_conn: Option<DatabaseConnection>,
    pub(super) ws_url: Option<String>,
    pub(super) http_url: Option<String>,
    /// Some connections use an http_client. we keep a clone for reconnecting
    pub(super) http_client: Option<reqwest::Client>,
    /// provider is in a RwLock so that we can replace it if re-connecting
    /// it is an async lock because we hold it open across awaits
    /// this provider is only used for new heads subscriptions
    /// TODO: put the provider inside an arc?
    pub(super) provider: AsyncRwLock<Option<Arc<Web3Provider>>>,
    /// keep track of hard limits
    pub(super) hard_limit_until: Option<watch::Sender<Instant>>,
    /// rate limits are stored in a central redis so that multiple proxies can share their rate limits
    /// We do not use the deferred rate limiter because going over limits would cause errors
    pub(super) hard_limit: Option<RedisRateLimiter>,
    /// used for load balancing to the least loaded server
    pub(super) soft_limit: u32,
    /// use web3 queries to find the block data limit for archive/pruned nodes
    pub(super) automatic_block_limit: bool,
    /// only use this rpc if everything else is lagging too far. this allows us to ignore fast but very low limit rpcs
    pub(super) backup: bool,
    /// TODO: have an enum for this so that "no limit" prints pretty?
    pub(super) block_data_limit: AtomicU64,
    /// Lower tiers are higher priority when sending requests
    pub(super) tier: u64,
    /// TODO: change this to a watch channel so that http providers can subscribe and take action on change.
    pub(super) head_block: RwLock<Option<Web3ProxyBlock>>,
    /// Track how fast this RPC is
    pub(super) latency: Web3RpcLatencies,
}

impl Web3Rpc {
    /// Connect to a web3 rpc
    // TODO: have this take a builder (which will have channels attached). or maybe just take the config and give the config public fields
    #[allow(clippy::too_many_arguments)]
    pub async fn spawn(
        mut config: Web3RpcConfig,
        name: String,
        chain_id: u64,
        db_conn: Option<DatabaseConnection>,
        // optional because this is only used for http providers. websocket providers don't use it
        http_client: Option<reqwest::Client>,
        // TODO: rename to http_new_head_interval_sender?
        http_interval_sender: Option<Arc<broadcast::Sender<()>>>,
        redis_pool: Option<RedisPool>,
        // TODO: think more about soft limit. watching ewma of requests is probably better. but what should the random sort be on? maybe group on tier is enough
        // soft_limit: u32,
        block_map: BlockHashesCache,
        block_sender: Option<flume::Sender<BlockAndRpc>>,
        tx_id_sender: Option<flume::Sender<(TxHash, Arc<Self>)>>,
        reconnect: bool,
    ) -> anyhow::Result<(Arc<Web3Rpc>, AnyhowJoinHandle<()>)> {
        let hard_limit = match (config.hard_limit, redis_pool) {
            (None, None) => None,
            (Some(hard_limit), Some(redis_pool)) => {
                // TODO: in process rate limiter instead? or is deffered good enough?
                let rrl = RedisRateLimiter::new(
                    "web3_proxy",
                    &format!("{}:{}", chain_id, name),
                    hard_limit,
                    60.0,
                    redis_pool,
                );

                Some(rrl)
            }
            (None, Some(_)) => None,
            (Some(_hard_limit), None) => {
                return Err(anyhow::anyhow!(
                    "no redis client pool! needed for hard limit"
                ))
            }
        };

        let tx_id_sender = if config.subscribe_txs {
            // TODO: warn if tx_id_sender is None?
            tx_id_sender
        } else {
            None
        };

        let backup = config.backup;

        let block_data_limit: AtomicU64 = config.block_data_limit.unwrap_or_default().into();
        let automatic_block_limit =
            (block_data_limit.load(atomic::Ordering::Acquire) == 0) && block_sender.is_some();

        // track hard limit until on backup servers (which might surprise us with rate limit changes)
        // and track on servers that have a configured hard limit
        let hard_limit_until = if backup || hard_limit.is_some() {
            let (sender, _) = watch::channel(Instant::now());

            Some(sender)
        } else {
            None
        };

        if config.ws_url.is_none() && config.http_url.is_none() {
            if let Some(url) = config.url {
                if url.starts_with("ws") {
                    config.ws_url = Some(url);
                } else if url.starts_with("http") {
                    config.http_url = Some(url);
                } else {
                    return Err(anyhow!("only ws or http urls are supported"));
                }
            } else {
                return Err(anyhow!(
                    "either ws_url or http_url are required. it is best to set both"
                ));
            }
        }

        let new_connection = Self {
            name,
            db_conn: db_conn.clone(),
            display_name: config.display_name,
            http_client,
            ws_url: config.ws_url,
            http_url: config.http_url,
            hard_limit,
            hard_limit_until,
            soft_limit: config.soft_limit,
            automatic_block_limit,
            backup,
            block_data_limit,
            tier: config.tier,
            ..Default::default()
        };

        let new_connection = Arc::new(new_connection);

        // subscribe to new blocks and new transactions
        // subscribing starts the connection (with retries)
        // TODO: make transaction subscription optional (just pass None for tx_id_sender)
        let handle = {
            let new_connection = new_connection.clone();
            let authorization = Arc::new(Authorization::internal(db_conn)?);
            tokio::spawn(async move {
                new_connection
                    .subscribe(
                        &authorization,
                        block_map,
                        block_sender,
                        chain_id,
                        http_interval_sender,
                        reconnect,
                        tx_id_sender,
                    )
                    .await
            })
        };

        Ok((new_connection, handle))
    }

    // TODO: would be great if rpcs exposed this. see https://github.com/ledgerwatch/erigon/issues/6391
    async fn check_block_data_limit(
        self: &Arc<Self>,
        authorization: &Arc<Authorization>,
        unlocked_provider: Option<Arc<Web3Provider>>,
    ) -> anyhow::Result<Option<u64>> {
        if !self.automatic_block_limit {
            // TODO: is this a good thing to return?
            return Ok(None);
        }

        // TODO: check eth_syncing. if it is not false, return Ok(None)

        let mut limit = None;

        // TODO: binary search between 90k and max?
        // TODO: start at 0 or 1?
        for block_data_limit in [0, 32, 64, 128, 256, 512, 1024, 90_000, u64::MAX] {
            let handle = self
                .wait_for_request_handle(authorization, None, unlocked_provider.clone())
                .await?;

            let head_block_num_future = handle.request::<Option<()>, U256>(
                "eth_blockNumber",
                &None,
                // error here are expected, so keep the level low
                Level::Debug.into(),
                unlocked_provider.clone(),
            );

            let head_block_num = timeout(Duration::from_secs(5), head_block_num_future)
                .await
                .context("timeout fetching eth_blockNumber")?
                .context("provider error")?;

            let maybe_archive_block = head_block_num.saturating_sub((block_data_limit).into());

            trace!(
                "checking maybe_archive_block on {}: {}",
                self,
                maybe_archive_block
            );

            // TODO: wait for the handle BEFORE we check the current block number. it might be delayed too!
            // TODO: what should the request be?
            let handle = self
                .wait_for_request_handle(authorization, None, unlocked_provider.clone())
                .await?;

            let archive_result: Result<Bytes, _> = handle
                .request(
                    "eth_getCode",
                    &json!((
                        "0xdead00000000000000000000000000000000beef",
                        maybe_archive_block,
                    )),
                    // error here are expected, so keep the level low
                    Level::Trace.into(),
                    unlocked_provider.clone(),
                )
                .await;

            trace!(
                "archive_result on {} for {} ({}): {:?}",
                self,
                block_data_limit,
                maybe_archive_block,
                archive_result
            );

            if archive_result.is_err() {
                break;
            }

            limit = Some(block_data_limit);
        }

        if let Some(limit) = limit {
            if limit == 0 {
                warn!("{} is unable to serve requests", self);
            }

            self.block_data_limit
                .store(limit, atomic::Ordering::Release);
        }

        info!("block data limit on {}: {:?}", self, limit);

        Ok(limit)
    }

    /// TODO: this might be too simple. different nodes can prune differently. its possible we will have a block range
    pub fn block_data_limit(&self) -> U64 {
        self.block_data_limit.load(atomic::Ordering::Acquire).into()
    }

    pub fn has_block_data(&self, needed_block_num: &U64) -> bool {
        let head_block_num = match self.head_block.read().as_ref() {
            None => return false,
            Some(x) => *x.number(),
        };

        // this rpc doesn't have that block yet. still syncing
        if needed_block_num > &head_block_num {
            return false;
        }

        // if this is a pruning node, we might not actually have the block
        let block_data_limit: U64 = self.block_data_limit();

        let oldest_block_num = head_block_num.saturating_sub(block_data_limit);

        *needed_block_num >= oldest_block_num
    }

    /// reconnect to the provider. errors are retried forever with exponential backoff with jitter.
    /// We use the "Decorrelated" jitter from <https://aws.amazon.com/blogs/architecture/exponential-backoff-and-jitter/>
    /// TODO: maybe it would be better to use "Full Jitter". The "Full Jitter" approach uses less work, but slightly more time.
    pub async fn retrying_connect(
        self: &Arc<Self>,
        block_sender: Option<&flume::Sender<BlockAndRpc>>,
        chain_id: u64,
        db_conn: Option<&DatabaseConnection>,
        delay_start: bool,
    ) -> anyhow::Result<()> {
        // there are several crates that have retry helpers, but they all seem more complex than necessary
        // TODO: move this backoff logic into a helper function so we can use it when doing database locking
        let base_ms = 500;
        let cap_ms = 30_000;
        let range_multiplier = 3;

        // sleep once before the initial retry attempt
        // TODO: now that we use this method for our initial connection, do we still want this sleep?
        let mut sleep_ms = if delay_start {
            let first_sleep_ms = min(
                cap_ms,
                thread_fast_rng().gen_range(base_ms..(base_ms * range_multiplier)),
            );
            let reconnect_in = Duration::from_millis(first_sleep_ms);

            info!("Reconnect to {} in {}ms", self, reconnect_in.as_millis());

            sleep(reconnect_in).await;

            first_sleep_ms
        } else {
            base_ms
        };

        // retry until we succeed
        while let Err(err) = self.connect(block_sender, chain_id, db_conn).await {
            // thread_rng is crytographically secure. we don't need that here
            sleep_ms = min(
                cap_ms,
                thread_fast_rng().gen_range(base_ms..(sleep_ms * range_multiplier)),
            );

            let retry_in = Duration::from_millis(sleep_ms);

            let error_level = if self.backup {
                log::Level::Debug
            } else {
                log::Level::Info
            };

            log::log!(
                error_level,
                "Failed reconnect to {}! Retry in {}ms. err={:?}",
                self,
                retry_in.as_millis(),
                err,
            );

            sleep(retry_in).await;
        }

        Ok(())
    }

    /// connect to the web3 provider
    async fn connect(
        self: &Arc<Self>,
        block_sender: Option<&flume::Sender<BlockAndRpc>>,
        chain_id: u64,
        db_conn: Option<&DatabaseConnection>,
    ) -> anyhow::Result<()> {
        if let Ok(mut unlocked_provider) = self.provider.try_write() {
            #[cfg(test)]
            if let Some(Web3Provider::Mock) = unlocked_provider.as_deref() {
                return Ok(());
            }

            *unlocked_provider = if let Some(ws_url) = self.ws_url.as_ref() {
                // set up ws client
                match &*unlocked_provider {
                    None => {
                        info!("connecting to {}", self);
                    }
                    Some(_) => {
                        debug!("reconnecting to {}", self);

                        // tell the block subscriber that this rpc doesn't have any blocks
                        if let Some(block_sender) = block_sender {
                            block_sender
                                .send_async((None, self.clone()))
                                .await
                                .context("block_sender during connect")?;
                        }

                        // reset sync status
                        let mut head_block = self.head_block.write();
                        *head_block = None;

                        // disconnect the current provider
                        // TODO: what until the block_sender's receiver finishes updating this item?
                        *unlocked_provider = None;
                    }
                }

                let p = Web3Provider::from_str(ws_url.as_str(), None)
                    .await
                    .context(format!("failed connecting to {}", ws_url))?;

                assert!(p.ws().is_some());

                Some(Arc::new(p))
            } else {
                // http client
                if let Some(url) = &self.http_url {
                    let p = Web3Provider::from_str(url, self.http_client.clone())
                        .await
                        .context(format!("failed connecting to {}", url))?;

                    assert!(p.http().is_some());

                    Some(Arc::new(p))
                } else {
                    None
                }
            };

            let authorization = Arc::new(Authorization::internal(db_conn.cloned())?);

            // check the server's chain_id here
            // TODO: some public rpcs (on bsc and fantom) do not return an id and so this ends up being an error
            // TODO: what should the timeout be? should there be a request timeout?
            // trace!("waiting on chain id for {}", self);
            let found_chain_id: Result<U64, _> = self
                .wait_for_request_handle(&authorization, None, unlocked_provider.clone())
                .await?
                .request(
                    "eth_chainId",
                    &json!(Option::None::<()>),
                    Level::Trace.into(),
                    unlocked_provider.clone(),
                )
                .await;
            // trace!("found_chain_id: {:?}", found_chain_id);

            match found_chain_id {
                Ok(found_chain_id) => {
                    // TODO: there has to be a cleaner way to do this
                    if chain_id != found_chain_id.as_u64() {
                        return Err(anyhow::anyhow!(
                            "incorrect chain id! Config has {}, but RPC has {}",
                            chain_id,
                            found_chain_id
                        )
                        .context(format!("failed @ {}", self)));
                    }
                }
                Err(e) => {
                    return Err(anyhow::Error::from(e));
                }
            }

            self.check_block_data_limit(&authorization, unlocked_provider.clone())
                .await?;

            drop(unlocked_provider);

            info!("successfully connected to {}", self);
        } else {
            if self.provider.read().await.is_none() {
                return Err(anyhow!("failed waiting for client"));
            }
        };

        Ok(())
    }

    async fn send_head_block_result(
        self: &Arc<Self>,
        new_head_block: Result<Option<ArcBlock>, ProviderError>,
        block_sender: &flume::Sender<BlockAndRpc>,
        block_map: BlockHashesCache,
    ) -> anyhow::Result<()> {
        let new_head_block = match new_head_block {
            Ok(None) => {
                {
                    let mut head_block = self.head_block.write();

                    if head_block.is_none() {
                        // we previously sent a None. return early
                        return Ok(());
                    }
                    warn!("clearing head block on {}!", self);

                    *head_block = None;
                }

                None
            }
            Ok(Some(new_head_block)) => {
                let new_head_block = Web3ProxyBlock::try_new(new_head_block).unwrap();

                let new_hash = *new_head_block.hash();

                // if we already have this block saved, set new_head_block to that arc. otherwise store this copy
                let new_head_block = block_map
                    .get_with(new_hash, async move { new_head_block })
                    .await;

                // save the block so we don't send the same one multiple times
                // also save so that archive checks can know how far back to query
                {
                    let mut head_block = self.head_block.write();

                    let _ = head_block.insert(new_head_block.clone().into());
                }

                if self.block_data_limit() == U64::zero() {
                    let authorization = Arc::new(Authorization::internal(self.db_conn.clone())?);
                    if let Err(err) = self.check_block_data_limit(&authorization, None).await {
                        warn!(
                            "failed checking block limit after {} finished syncing. {:?}",
                            self, err
                        );
                    }
                }

                Some(new_head_block)
            }
            Err(err) => {
                warn!("unable to get block from {}. err={:?}", self, err);

                {
                    let mut head_block = self.head_block.write();

                    *head_block = None;
                }

                None
            }
        };

        // send an empty block to take this server out of rotation
        block_sender
            .send_async((new_head_block, self.clone()))
            .await
            .context("block_sender")?;

        Ok(())
    }

    /// subscribe to blocks and transactions with automatic reconnects
    /// This should only exit when the program is exiting.
    /// TODO: should more of these args be on self?
    #[allow(clippy::too_many_arguments)]
    async fn subscribe(
        self: Arc<Self>,
        authorization: &Arc<Authorization>,
        block_map: BlockHashesCache,
        block_sender: Option<flume::Sender<BlockAndRpc>>,
        chain_id: u64,
        http_interval_sender: Option<Arc<broadcast::Sender<()>>>,
        reconnect: bool,
        tx_id_sender: Option<flume::Sender<(TxHash, Arc<Self>)>>,
    ) -> anyhow::Result<()> {
        loop {
            let http_interval_receiver = http_interval_sender.as_ref().map(|x| x.subscribe());

            let mut futures = vec![];

            {
                // health check
                // TODO: move this into a proper function
                let authorization = authorization.clone();
                let block_sender = block_sender.clone();
                let conn = self.clone();
                let (ready_tx, ready_rx) = oneshot::channel();
                let f = async move {
                    // initial sleep to allow for the initial connection
                    conn.retrying_connect(
                        block_sender.as_ref(),
                        chain_id,
                        authorization.db_conn.as_ref(),
                        false,
                    )
                    .await?;

                    // provider is ready
                    ready_tx.send(()).unwrap();

                    // TODO: how often?
                    // TODO: reset this timeout every time a new block is seen
                    let health_sleep_seconds = 10;

                    // wait before doing the initial health check
                    sleep(Duration::from_secs(health_sleep_seconds)).await;

                    loop {
                        // TODO: what if we just happened to have this check line up with another restart?
                        // TODO: think more about this
                        if let Some(client) = &*conn.provider.read().await {
                            // trace!("health check unlocked with error on {}", conn);
                            // returning error will trigger a reconnect
                            // also, do the health check as a way of keeping this rpc's request_ewma accurate
                            // TODO: do a query of some kind
                        }

                        sleep(Duration::from_secs(health_sleep_seconds)).await;
                    }
                };

                futures.push(flatten_handle(tokio::spawn(f)));

                // wait on the initial connection
                ready_rx.await?;
            }

            if let Some(block_sender) = &block_sender {
                let f = self.clone().subscribe_new_heads(
                    authorization.clone(),
                    http_interval_receiver,
                    block_sender.clone(),
                    block_map.clone(),
                );

                futures.push(flatten_handle(tokio::spawn(f)));
            }

            if let Some(tx_id_sender) = &tx_id_sender {
                let f = self
                    .clone()
                    .subscribe_pending_transactions(authorization.clone(), tx_id_sender.clone());

                futures.push(flatten_handle(tokio::spawn(f)));
            }

            match try_join_all(futures).await {
                Ok(_) => {
                    // futures all exited without error. break instead of restarting subscriptions
                    break;
                }
                Err(err) => {
                    if reconnect {
                        warn!("{} connection ended. err={:?}", self, err);

                        self.clone()
                            .retrying_connect(
                                block_sender.as_ref(),
                                chain_id,
                                authorization.db_conn.as_ref(),
                                true,
                            )
                            .await?;
                    } else {
                        error!("{} subscription exited. err={:?}", self, err);
                        return Err(err);
                    }
                }
            }
        }

        info!("all subscriptions on {} completed", self);

        Ok(())
    }

    /// Subscribe to new blocks.
    async fn subscribe_new_heads(
        self: Arc<Self>,
        authorization: Arc<Authorization>,
        http_interval_receiver: Option<broadcast::Receiver<()>>,
        block_sender: flume::Sender<BlockAndRpc>,
        block_map: BlockHashesCache,
    ) -> anyhow::Result<()> {
        trace!("watching new heads on {}", self);

        let unlocked_provider = self.provider.read().await;

        match unlocked_provider.as_deref() {
            Some(Web3Provider::Http(_client)) => {
                // there is a "watch_blocks" function, but a lot of public nodes do not support the necessary rpc endpoints
                // TODO: try watch_blocks and fall back to this?

                let mut http_interval_receiver = http_interval_receiver.unwrap();

                let mut last_hash = H256::zero();

                loop {
                    // TODO: what should the max_wait be?
                    match self
                        .wait_for_request_handle(&authorization, None, unlocked_provider.clone())
                        .await
                    {
                        Ok(active_request_handle) => {
                            let block: Result<Option<ArcBlock>, _> = active_request_handle
                                .request(
                                    "eth_getBlockByNumber",
                                    &json!(("latest", false)),
                                    Level::Warn.into(),
                                    None,
                                )
                                .await;

                            match block {
                                Ok(None) => {
                                    warn!("no head block on {}", self);

                                    self.send_head_block_result(
                                        Ok(None),
                                        &block_sender,
                                        block_map.clone(),
                                    )
                                    .await?;
                                }
                                Ok(Some(block)) => {
                                    // don't send repeat blocks
                                    let new_hash =
                                        block.hash.expect("blocks here should always have hashes");

                                    if new_hash != last_hash {
                                        // new hash!
                                        last_hash = new_hash;

                                        self.send_head_block_result(
                                            Ok(Some(block)),
                                            &block_sender,
                                            block_map.clone(),
                                        )
                                        .await?;
                                    }
                                }
                                Err(err) => {
                                    // we did not get a block back. something is up with the server. take it out of rotation
                                    self.send_head_block_result(
                                        Err(err),
                                        &block_sender,
                                        block_map.clone(),
                                    )
                                    .await?;
                                }
                            }
                        }
                        Err(err) => {
                            warn!("Internal error on latest block from {}. {:?}", self, err);

                            self.send_head_block_result(Ok(None), &block_sender, block_map.clone())
                                .await?;

                            // TODO: what should we do? sleep? extra time?
                        }
                    }

                    // wait for the next interval
                    // TODO: if error or rate limit, increase interval?
                    while let Err(err) = http_interval_receiver.recv().await {
                        match err {
                            broadcast::error::RecvError::Closed => {
                                // channel is closed! that's not good. bubble the error up
                                return Err(err.into());
                            }
                            broadcast::error::RecvError::Lagged(lagged) => {
                                // querying the block was delayed
                                // this can happen if tokio is very busy or waiting for requests limits took too long
                                warn!("http interval on {} lagging by {}!", self, lagged);
                            }
                        }
                    }
                }
            }
            Some(Web3Provider::Both(_, client)) | Some(Web3Provider::Ws(client)) => {
                // todo: move subscribe_blocks onto the request handle?
                let active_request_handle = self
                    .wait_for_request_handle(&authorization, None, unlocked_provider.clone())
                    .await;
                let mut stream = client.subscribe_blocks().await?;
                drop(active_request_handle);

                // query the block once since the subscription doesn't send the current block
                // there is a very small race condition here where the stream could send us a new block right now
                // but all that does is print "new block" for the same block as current block
                // TODO: how does this get wrapped in an arc? does ethers handle that?
                // TODO: do this part over http?
                let block: Result<Option<ArcBlock>, _> = self
                    .wait_for_request_handle(&authorization, None, unlocked_provider.clone())
                    .await?
                    .request(
                        "eth_getBlockByNumber",
                        &json!(("latest", false)),
                        Level::Warn.into(),
                        unlocked_provider.clone(),
                    )
                    .await;

                let mut last_hash = match &block {
                    Ok(Some(new_block)) => new_block
                        .hash
                        .expect("blocks should always have a hash here"),
                    _ => H256::zero(),
                };

                self.send_head_block_result(block, &block_sender, block_map.clone())
                    .await?;

                while let Some(new_block) = stream.next().await {
                    // TODO: check the new block's hash to be sure we don't send dupes
                    let new_hash = new_block
                        .hash
                        .expect("blocks should always have a hash here");

                    if new_hash == last_hash {
                        // some rpcs like to give us duplicates. don't waste our time on them
                        continue;
                    } else {
                        last_hash = new_hash;
                    }

                    self.send_head_block_result(
                        Ok(Some(Arc::new(new_block))),
                        &block_sender,
                        block_map.clone(),
                    )
                    .await?;
                }

                // clear the head block. this might not be needed, but it won't hurt
                self.send_head_block_result(Ok(None), &block_sender, block_map)
                    .await?;

                // TODO: is this always an error?
                // TODO: we probably don't want a warn and to return error
                warn!("new_heads subscription to {} ended", self);
                Err(anyhow::anyhow!("new_heads subscription ended"))
            }
            None => todo!("what should happen now? wait for a connection?"),
            #[cfg(test)]
            Some(Web3Provider::Mock) => unimplemented!(),
        }
    }

    /// Turn on the firehose of pending transactions
    async fn subscribe_pending_transactions(
        self: Arc<Self>,
        authorization: Arc<Authorization>,
        tx_id_sender: flume::Sender<(TxHash, Arc<Self>)>,
    ) -> anyhow::Result<()> {
        // TODO: give this a separate client. don't use new_head_client for everything. especially a firehose this big
        // TODO: timeout
        let provider = self.provider.read().await;

        trace!("watching pending transactions on {}", self);
        // TODO: does this keep the lock open for too long?
        match provider.as_deref() {
            None => {
                // TODO: wait for a provider
                return Err(anyhow!("no provider"));
            }
            Some(Web3Provider::Http(provider)) => {
                // there is a "watch_pending_transactions" function, but a lot of public nodes do not support the necessary rpc endpoints
                // TODO: maybe subscribe to self.head_block?
                // TODO: this keeps a read lock guard open on provider_state forever. is that okay for an http client?
                futures::future::pending::<()>().await;
            }
            Some(Web3Provider::Both(_, client)) | Some(Web3Provider::Ws(client)) => {
                // TODO: maybe the subscribe_pending_txs function should be on the active_request_handle
                let active_request_handle = self
                    .wait_for_request_handle(&authorization, None, provider.clone())
                    .await?;

                let mut stream = client.subscribe_pending_txs().await?;

                drop(active_request_handle);

                while let Some(pending_tx_id) = stream.next().await {
                    tx_id_sender
                        .send_async((pending_tx_id, self.clone()))
                        .await
                        .context("tx_id_sender")?;

                    // TODO: periodically check for listeners. if no one is subscribed, unsubscribe and wait for a subscription
                }

                // TODO: is this always an error?
                // TODO: we probably don't want a warn and to return error
                warn!("pending_transactions subscription ended on {}", self);
                return Err(anyhow::anyhow!("pending_transactions subscription ended"));
            }
            #[cfg(test)]
            Some(Web3Provider::Mock) => futures::future::pending::<()>().await,
        }

        Ok(())
    }

    /// be careful with this; it might wait forever!
    /// `allow_not_ready` is only for use by health checks while starting the provider
    /// TODO: don't use anyhow. use specific error type
    pub async fn wait_for_request_handle<'a>(
        self: &'a Arc<Self>,
        authorization: &'a Arc<Authorization>,
        max_wait: Option<Duration>,
        unlocked_provider: Option<Arc<Web3Provider>>,
    ) -> anyhow::Result<OpenRequestHandle> {
        let max_wait = max_wait.map(|x| Instant::now() + x);

        loop {
            match self
                .try_request_handle(authorization, unlocked_provider.clone())
                .await
            {
                Ok(OpenRequestResult::Handle(handle)) => return Ok(handle),
                Ok(OpenRequestResult::RetryAt(retry_at)) => {
                    // TODO: emit a stat?
                    let wait = retry_at.duration_since(Instant::now());

                    trace!(
                        "waiting {} millis for request handle on {}",
                        wait.as_millis(),
                        self
                    );

                    if let Some(max_wait) = max_wait {
                        if retry_at > max_wait {
                            // break now since we will wait past our maximum wait time
                            // TODO: don't use anyhow. use specific error type
                            return Err(anyhow::anyhow!("timeout waiting for request handle"));
                        }
                    }

                    sleep_until(retry_at).await;
                }
                Ok(OpenRequestResult::NotReady) => {
                    // TODO: when can this happen? log? emit a stat?
                    trace!("{} has no handle ready", self);

                    if let Some(max_wait) = max_wait {
                        let now = Instant::now();

                        if now > max_wait {
                            return Err(anyhow::anyhow!("unable to retry for request handle"));
                        }
                    }

                    // TODO: sleep how long? maybe just error?
                    // TODO: instead of an arbitrary sleep, subscribe to the head block on this
                    sleep(Duration::from_millis(10)).await;
                }
                Err(err) => return Err(err),
            }
        }
    }

    pub async fn try_request_handle(
        self: &Arc<Self>,
        authorization: &Arc<Authorization>,
        // TODO: borrow on this instead of needing to clone the Arc?
        unlocked_provider: Option<Arc<Web3Provider>>,
    ) -> anyhow::Result<OpenRequestResult> {
        // TODO: think more about this read block
        // TODO: this should *not* be new_head_client. this should be a separate object
        if unlocked_provider.is_some() || self.provider.read().await.is_some() {
            // we already have an unlocked provider. no need to lock
        } else {
            return Ok(OpenRequestResult::NotReady);
        }

        if let Some(hard_limit_until) = self.hard_limit_until.as_ref() {
            let hard_limit_ready = hard_limit_until.borrow().clone();

            let now = Instant::now();

            if now < hard_limit_ready {
                return Ok(OpenRequestResult::RetryAt(hard_limit_ready));
            }
        }

        // check rate limits
        if let Some(ratelimiter) = self.hard_limit.as_ref() {
            // TODO: how should we know if we should set expire or not?
            match ratelimiter
                .throttle()
                .await
                .context(format!("attempting to throttle {}", self))?
            {
                RedisRateLimitResult::Allowed(_) => {
                    // trace!("rate limit succeeded")
                }
                RedisRateLimitResult::RetryAt(retry_at, _) => {
                    // rate limit gave us a wait time
                    if !self.backup {
                        let when = retry_at.duration_since(Instant::now());
                        warn!(
                            "Exhausted rate limit on {}. Retry in {}ms",
                            self,
                            when.as_millis()
                        );
                    }

                    if let Some(hard_limit_until) = self.hard_limit_until.as_ref() {
                        hard_limit_until.send_replace(retry_at.clone());
                    }

                    return Ok(OpenRequestResult::RetryAt(retry_at));
                }
                RedisRateLimitResult::RetryNever => {
                    return Ok(OpenRequestResult::NotReady);
                }
            }
        };

        let handle = OpenRequestHandle::new(authorization.clone(), self.clone()).await;

        Ok(OpenRequestResult::Handle(handle))
    }
}

impl fmt::Debug for Web3Provider {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        // TODO: the default Debug takes forever to write. this is too quiet though. we at least need the url
        f.debug_struct("Web3Provider").finish_non_exhaustive()
    }
}

impl Hash for Web3Rpc {
    fn hash<H: Hasher>(&self, state: &mut H) {
        // TODO: is this enough?
        self.name.hash(state);
    }
}

impl Eq for Web3Rpc {}

impl Ord for Web3Rpc {
    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
        self.name.cmp(&other.name)
    }
}

impl PartialOrd for Web3Rpc {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        Some(self.cmp(other))
    }
}

impl PartialEq for Web3Rpc {
    fn eq(&self, other: &Self) -> bool {
        self.name == other.name
    }
}

impl Serialize for Web3Rpc {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        // 3 is the number of fields in the struct.
        let mut state = serializer.serialize_struct("Web3Rpc", 9)?;

        // the url is excluded because it likely includes private information. just show the name that we use in keys
        state.serialize_field("name", &self.name)?;
        // a longer name for display to users
        state.serialize_field("display_name", &self.display_name)?;

        state.serialize_field("backup", &self.backup)?;

        match self.block_data_limit.load(atomic::Ordering::Relaxed) {
            u64::MAX => {
                state.serialize_field("block_data_limit", &None::<()>)?;
            }
            block_data_limit => {
                state.serialize_field("block_data_limit", &block_data_limit)?;
            }
        }

        state.serialize_field("tier", &self.tier)?;

        state.serialize_field("soft_limit", &self.soft_limit)?;

        // TODO: keep this for the "popularity_contest" command? or maybe better to just use graphana?
        // state.serialize_field(
        //     "frontend_requests",
        //     &self.frontend_requests.load(atomic::Ordering::Relaxed),
        // )?;

        {
            // TODO: maybe this is too much data. serialize less?
            let head_block = &*self.head_block.read();
            state.serialize_field("head_block", head_block)?;
        }

        state.end()
    }
}

impl fmt::Debug for Web3Rpc {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        let mut f = f.debug_struct("Web3Rpc");

        f.field("name", &self.name);

        let block_data_limit = self.block_data_limit.load(atomic::Ordering::Relaxed);
        if block_data_limit == u64::MAX {
            f.field("blocks", &"all");
        } else {
            f.field("blocks", &block_data_limit);
        }

        f.finish_non_exhaustive()
    }
}

impl fmt::Display for Web3Rpc {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        // TODO: filter basic auth and api keys
        write!(f, "{}", &self.name)
    }
}

mod tests {
    #![allow(unused_imports)]
    use super::*;
    use ethers::types::{Block, U256};
    use std::time::{SystemTime, UNIX_EPOCH};

    #[test]
    fn test_archive_node_has_block_data() {
        let now = SystemTime::now()
            .duration_since(UNIX_EPOCH)
            .expect("cannot tell the time")
            .as_secs()
            .into();

        let random_block = Block {
            hash: Some(H256::random()),
            number: Some(1_000_000.into()),
            timestamp: now,
            ..Default::default()
        };

        let random_block = Arc::new(random_block);

        let head_block = Web3ProxyBlock::try_new(random_block).unwrap();
        let block_data_limit = u64::MAX;

        let x = Web3Rpc {
            name: "name".to_string(),
            ws_url: Some("ws://example.com".to_string()),
            soft_limit: 1_000,
            automatic_block_limit: false,
            backup: false,
            block_data_limit: block_data_limit.into(),
            tier: 0,
            head_block: RwLock::new(Some(head_block.clone())),
            ..Default::default()
        };

        assert!(x.has_block_data(&0.into()));
        assert!(x.has_block_data(&1.into()));
        assert!(x.has_block_data(&head_block.number()));
        assert!(!x.has_block_data(&(head_block.number() + 1)));
        assert!(!x.has_block_data(&(head_block.number() + 1000)));
    }

    #[test]
    fn test_pruned_node_has_block_data() {
        let now = SystemTime::now()
            .duration_since(UNIX_EPOCH)
            .expect("cannot tell the time")
            .as_secs()
            .into();

        let head_block: Web3ProxyBlock = Arc::new(Block {
            hash: Some(H256::random()),
            number: Some(1_000_000.into()),
            timestamp: now,
            ..Default::default()
        })
        .try_into()
        .unwrap();

        let block_data_limit = 64;

        // TODO: this is getting long. have a `impl Default`
        let x = Web3Rpc {
            name: "name".to_string(),
            soft_limit: 1_000,
            automatic_block_limit: false,
            backup: false,
            block_data_limit: block_data_limit.into(),
            tier: 0,
            head_block: RwLock::new(Some(head_block.clone())),
            ..Default::default()
        };

        assert!(!x.has_block_data(&0.into()));
        assert!(!x.has_block_data(&1.into()));
        assert!(!x.has_block_data(&(head_block.number() - block_data_limit - 1)));
        assert!(x.has_block_data(&(head_block.number() - block_data_limit)));
        assert!(x.has_block_data(&head_block.number()));
        assert!(!x.has_block_data(&(head_block.number() + 1)));
        assert!(!x.has_block_data(&(head_block.number() + 1000)));
    }

    /*
    // TODO: think about how to bring the concept of a "lagged" node back
    #[test]
    fn test_lagged_node_not_has_block_data() {
        let now: U256 = SystemTime::now()
            .duration_since(UNIX_EPOCH)
            .expect("cannot tell the time")
            .as_secs()
            .into();

        // head block is an hour old
        let head_block = Block {
            hash: Some(H256::random()),
            number: Some(1_000_000.into()),
            timestamp: now - 3600,
            ..Default::default()
        };

        let head_block = Arc::new(head_block);

        let head_block = SavedBlock::new(head_block);
        let block_data_limit = u64::MAX;

        let metrics = OpenRequestHandleMetrics::default();

        let x = Web3Rpc {
            name: "name".to_string(),
            db_conn: None,
            display_name: None,
            url: "ws://example.com".to_string(),
            http_client: None,
            active_requests: 0.into(),
            frontend_requests: 0.into(),
            internal_requests: 0.into(),
            provider_state: AsyncRwLock::new(ProviderState::None),
            hard_limit: None,
            soft_limit: 1_000,
            automatic_block_limit: false,
            backup: false,
            block_data_limit: block_data_limit.into(),
            tier: 0,
            head_block: RwLock::new(Some(head_block.clone())),
        };

        assert!(!x.has_block_data(&0.into()));
        assert!(!x.has_block_data(&1.into()));
        assert!(!x.has_block_data(&head_block.number()));
        assert!(!x.has_block_data(&(head_block.number() + 1)));
        assert!(!x.has_block_data(&(head_block.number() + 1000)));
    }
    */
}