feat: add HTTP subscription support via polling by smartprogrammer93 · Pull Request #32 · OpenZeppelin/Robust-Provider

smartprogrammer93 · 2026-01-29T14:13:00Z

Summary

Implements HTTP subscription support via polling, allowing HTTP providers to participate in block subscriptions alongside WebSocket providers.

Resolves #23

Features

HTTP polling subscriptions: Uses Alloy's watch_blocks() API with eth_newBlockFilter + eth_getFilterChanges for efficient block polling
Seamless integration: Works transparently with existing RobustSubscription API - callers use the same subscribe_blocks() and recv() interface
Automatic deduplication: Alloy's filter-based approach prevents duplicate block emissions
Failover support: HTTP providers can participate in subscription failover chains (WS → HTTP and HTTP → WS)
Configuration propagation: Poll interval, timeouts, and buffer capacity settings carry over during failover

Usage

Enable the http-subscription feature flag:

[dependencies]
robust-provider = { version = "...", features = ["http-subscription"] }

Build with HTTP subscription support:

let provider = RobustProviderBuilder::new(ws_provider)
    .fallback(http_provider)
    .allow_http_subscriptions(true)
    .poll_interval(Duration::from_secs(12))
    .subscription_timeout(Duration::from_secs(60))
    .build()
    .await?;

// Use exactly like before - HTTP polling is transparent
let mut subscription = provider.subscribe_blocks().await?;
while let Ok(block) = subscription.recv().await {
    println!("Block {}", block.number);
}

Breaking Changes

None. Feature is behind http-subscription flag and disabled by default.

Thanks to @PoulavBhowmick03 for the massive improvements to this implementation.

Closes #23

Implements OpenZeppelin#23 - Support HTTP Subscription This PR adds the ability for HTTP providers to participate in block subscriptions via polling, enabling use cases where WebSocket connections are not available (e.g., behind load balancers). ## Changes ### New Feature (behind `http-subscription` feature flag) - Add `HttpPollingSubscription` that polls `eth_getBlockByNumber(latest)` at configurable intervals - Add `SubscriptionBackend` enum to handle both WebSocket and HTTP backends - Add `poll_interval()` and `allow_http_subscriptions()` builder methods - Seamless failover between mixed WS/HTTP provider chains ### Files - `src/robust_provider/http_subscription.rs` - New HTTP polling module - `src/robust_provider/subscription.rs` - Unified backend handling - `src/robust_provider/builder.rs` - New configuration options - `src/robust_provider/provider.rs` - Updated subscribe_blocks() - `Cargo.toml` - Added `http-subscription` feature flag ## Usage ```rust let robust = RobustProviderBuilder::new(http_provider) .allow_http_subscriptions(true) .poll_interval(Duration::from_secs(12)) .build() .await?; let mut sub = robust.subscribe_blocks().await?; ``` ## Trade-offs (documented) - Latency: up to `poll_interval` delay for block detection - RPC Load: one call per `poll_interval` - Feature-gated to ensure explicit opt-in Closes OpenZeppelin#23

Add comprehensive integration tests in tests/http_subscription.rs: - test_http_subscription_basic_flow - test_http_subscription_multiple_blocks - test_http_subscription_as_stream - test_failover_from_ws_to_http - test_failover_from_http_to_ws - test_mixed_provider_chain_failover - test_http_reconnects_to_ws_primary - test_http_only_no_ws_providers - test_http_subscription_disabled_falls_back_to_ws - test_custom_poll_interval All tests gated behind #[cfg(feature = "http-subscription")]

Audit findings addressed: Unit tests (http_subscription.rs): - Improved test_http_polling_deduplication with better verification - Renamed test_http_polling_handles_drop → test_http_polling_stops_on_drop with clearer verification logic - Added test_http_subscription_error_types for all error variants - Added test_http_polling_close_method for close() functionality Integration tests (tests/http_subscription.rs) - rewritten: - Removed broken test_http_reconnects_to_ws_primary (was meaningless) - Removed flawed test_custom_poll_interval, replaced with test_poll_interval_is_respected (measures correctly) - Renamed tests for clarity on what they actually verify - Added test_http_disabled_no_ws_fails (negative test case) - Added test_all_providers_fail_returns_error (error handling) - Added test_http_subscription_survives_temporary_errors - Added test_http_polling_deduplication (integration level) - Fixed failover tests to verify behavior correctly - Removed fragile 'pre-mine to distinguish providers' hacks Test count: 73 total (19 unit + 12 http integration + 24 subscription + 18 eth)

Tests verify that RPC calls (not just subscriptions) properly: - Failover to fallback providers when primary dies - Cycle through multiple fallbacks - Return errors when all providers exhausted - Don't retry non-retryable errors (BlockNotFound) - Complete within bounded time when providers unavailable - Work correctly for various RPC methods (get_accounts, get_balance, get_block)

Fixes two bugs in HTTP subscription handling: 1. http_config now uses configured values from RobustProviderBuilder instead of defaults when a WebSocket subscription is created first. This ensures poll_interval, call_timeout, and buffer_capacity are respected when failing over to HTTP. 2. HTTP reconnection now validates the provider is reachable before claiming success. Uses a short 50ms timeout to quickly fail and not block the failover process. Also fixes test timing in test_failover_http_to_ws_on_provider_death to mine before subscription timeout instead of after. Adds two new tests: - test_poll_interval_propagated_from_builder: verifies config propagation - test_http_reconnect_validates_provider: verifies reconnect validation

Implements OpenZeppelin#23 - Support HTTP Subscription This PR adds the ability for HTTP providers to participate in block subscriptions via polling, enabling use cases where WebSocket connections are not available (e.g., behind load balancers). - Add `HttpPollingSubscription` that polls `eth_getBlockByNumber(latest)` at configurable intervals - Add `SubscriptionBackend` enum to handle both WebSocket and HTTP backends - Add `poll_interval()` and `allow_http_subscriptions()` builder methods - Seamless failover between mixed WS/HTTP provider chains - `src/robust_provider/http_subscription.rs` - New HTTP polling module - `src/robust_provider/subscription.rs` - Unified backend handling - `src/robust_provider/builder.rs` - New configuration options - `src/robust_provider/provider.rs` - Updated subscribe_blocks() - `Cargo.toml` - Added `http-subscription` feature flag ```rust let robust = RobustProviderBuilder::new(http_provider) .allow_http_subscriptions(true) .poll_interval(Duration::from_secs(12)) .build() .await?; let mut sub = robust.subscribe_blocks().await?; ``` - Latency: up to `poll_interval` delay for block detection - RPC Load: one call per `poll_interval` - Feature-gated to ensure explicit opt-in Closes OpenZeppelin#23

Add comprehensive integration tests in tests/http_subscription.rs: - test_http_subscription_basic_flow - test_http_subscription_multiple_blocks - test_http_subscription_as_stream - test_failover_from_ws_to_http - test_failover_from_http_to_ws - test_mixed_provider_chain_failover - test_http_reconnects_to_ws_primary - test_http_only_no_ws_providers - test_http_subscription_disabled_falls_back_to_ws - test_custom_poll_interval All tests gated behind #[cfg(feature = "http-subscription")]

Audit findings addressed: Unit tests (http_subscription.rs): - Improved test_http_polling_deduplication with better verification - Renamed test_http_polling_handles_drop → test_http_polling_stops_on_drop with clearer verification logic - Added test_http_subscription_error_types for all error variants - Added test_http_polling_close_method for close() functionality Integration tests (tests/http_subscription.rs) - rewritten: - Removed broken test_http_reconnects_to_ws_primary (was meaningless) - Removed flawed test_custom_poll_interval, replaced with test_poll_interval_is_respected (measures correctly) - Renamed tests for clarity on what they actually verify - Added test_http_disabled_no_ws_fails (negative test case) - Added test_all_providers_fail_returns_error (error handling) - Added test_http_subscription_survives_temporary_errors - Added test_http_polling_deduplication (integration level) - Fixed failover tests to verify behavior correctly - Removed fragile 'pre-mine to distinguish providers' hacks Test count: 73 total (19 unit + 12 http integration + 24 subscription + 18 eth)

Tests verify that RPC calls (not just subscriptions) properly: - Failover to fallback providers when primary dies - Cycle through multiple fallbacks - Return errors when all providers exhausted - Don't retry non-retryable errors (BlockNotFound) - Complete within bounded time when providers unavailable - Work correctly for various RPC methods (get_accounts, get_balance, get_block)

Fixes two bugs in HTTP subscription handling: 1. http_config now uses configured values from RobustProviderBuilder instead of defaults when a WebSocket subscription is created first. This ensures poll_interval, call_timeout, and buffer_capacity are respected when failing over to HTTP. 2. HTTP reconnection now validates the provider is reachable before claiming success. Uses a short 50ms timeout to quickly fail and not block the failover process. Also fixes test timing in test_failover_http_to_ws_on_provider_death to mine before subscription timeout instead of after. Adds two new tests: - test_poll_interval_propagated_from_builder: verifies config propagation - test_http_reconnect_validates_provider: verifies reconnect validation

0xNeshi

Thanks for the contribution!

First "shallower" review iteration, will dive deeper in the following ones

src/robust_provider/http_subscription.rs

src/robust_provider/subscription.rs

src/robust_provider/http_subscription.rs

src/robust_provider/provider.rs

0xNeshi · 2026-02-11T12:49:30Z

Also, resolve conflicts please

- Add http-subscription feature to VSCode settings for rust-analyzer - Make HTTP_RECONNECT_VALIDATION_TIMEOUT public - Fix HTTP subscription fallback: try fallback providers when primary HTTP fails - Fix buffer_capacity: use mpsc channel with configured capacity - Fix error documentation: use proper error list with stars - Remove unused imports (FutureExt, Stream)

- Add pub const DEFAULT_CALL_TIMEOUT (30 seconds) - Add pub const DEFAULT_BUFFER_CAPACITY (128) - Update rustdocs to reference the new constants - Update Default impl to use constants instead of magic numbers - Update test to use constants for consistency Addresses reviewer comment on line 105 about converting constants into actual pub const values.

0xNeshi

After all there are still some things to address

src/robust_provider/http_subscription.rs

src/robust_provider/builder.rs

src/robust_provider/http_subscription.rs

src/robust_provider/mod.rs

src/robust_provider/subscription.rs

src/robust_provider/provider.rs

src/robust_provider/http_subscription.rs

Refactor

PoulavBhowmick03 · 2026-02-27T12:22:36Z

@0xNeshi are there any further tests to be written post your PR?

0xNeshi

I think we're almost ready to merge. Running all the workflows to ensure all's fine.

Once merged, we'll create a new release @LeoPatOZ @pepebndc

src/robust_provider/subscription.rs

src/robust_provider/provider.rs

src/robust_provider/subscription.rs

0xNeshi · 2026-03-04T10:56:38Z

The failing test is flaky, will be handled as part of #59

0xNeshi · 2026-03-04T11:20:04Z

@smartprogrammer93 we'd like to get this merged for you asap, I will create a new PR addressing all of the comments. Merge that, and we merge this.

PoulavBhowmick03 · 2026-03-04T11:27:09Z

@smartprogrammer93 we'd like to get this merged for you asap, I will create a new PR addressing all of the comments. Merge that, and we merge this.

Should I address the comments you made or are you making a new PR to this?

0xNeshi · 2026-03-04T11:31:14Z

@smartprogrammer93 we'd like to get this merged for you asap, I will create a new PR addressing all of the comments. Merge that, and we merge this.

Should I address the comments you made or are you making a new PR to this?

I'm making it, will have it up in the next 10-15 mins

0xNeshi · 2026-03-04T12:00:49Z

@smartprogrammer93 smartprogrammer93#2

Feat/http subscription

0xNeshi

Glad we were able to finalize this, thanks for the good work (and patience) @smartprogrammer93

smartprogrammer93 requested review from 0xNeshi, LeoPatOZ and pepebndc as code owners January 29, 2026 14:13

smartprogrammer93 force-pushed the feat/http-subscription branch from 64ba47c to 3a73de3 Compare January 29, 2026 14:14

smartprogrammer93 marked this pull request as draft January 29, 2026 14:14

smartprogrammer93 added 4 commits January 29, 2026 17:59

smartprogrammer93 force-pushed the feat/http-subscription branch 2 times, most recently from f94c84d to b6001af Compare January 29, 2026 15:55

PoulavBhowmick03 and others added 10 commits February 3, 2026 00:10

refactor: use Alloy's watch_blocks() for HTTP polling

66cc162

fix tests, add buffer and implement is_empty method

e4d249d

refactor: use Alloy's watch_blocks() for HTTP polling

e3d7833

fix tests, add buffer and implement is_empty method

d9e14e4

fix: add http-subscription feature fields to test_provider helper

06a94ff

smartprogrammer93 force-pushed the feat/http-subscription branch from e4d249d to 06a94ff Compare February 5, 2026 17:03

smartprogrammer93 marked this pull request as ready for review February 5, 2026 17:17

0xNeshi reviewed Feb 11, 2026

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smartprogrammer93 added 4 commits February 14, 2026 20:40

Merge origin/main into pr-32

36a967b

fix: address remaining maintainer comments

ec651ad

0xNeshi mentioned this pull request Feb 26, 2026

When a Subscription Channel for a Provider is Closed, the Next Provider Should Be Tried #56

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0xNeshi reviewed Feb 26, 2026

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refactor

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0xNeshi reviewed Feb 26, 2026

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0xNeshi and others added 4 commits February 27, 2026 09:42

add test_mixed_chain_skips_http_until_ws_is_found

5eab3ee

add test-log crate

c89615c

add additional tests

4beb33d

Merge pull request #1 from 0xNeshi/feat/http-subscription

34e3deb

Refactor

0xNeshi mentioned this pull request Mar 3, 2026

Refactor smartprogrammer93/Robust-Provider#1

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Apply suggestion from @0xNeshi

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src/robust_provider/subscription.rs Show resolved Hide resolved

src/robust_provider/provider.rs Show resolved Hide resolved

0xNeshi reviewed Mar 3, 2026

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src/robust_provider/subscription.rs Show resolved Hide resolved

refactor stream creation when building SubscriptionBackend::HttpPolling

b9bbc55

0xNeshi added 2 commits March 4, 2026 12:28

explain the subscribe_blocks logic in a comment

6690229

remove mentions of require_pubsub

14d3d2a

0xNeshi added 2 commits March 4, 2026 12:44

update doc wording in builder.rs

6ce15ab

update readme to mention http subscriptions

eeef439

0xNeshi mentioned this pull request Mar 4, 2026

Feat/http subscription smartprogrammer93/Robust-Provider#2

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PoulavBhowmick03 added 2 commits March 4, 2026 19:20

Merge pull request #2 from 0xNeshi/feat/http-subscription

a6272cd

Feat/http subscription

Merge branch 'main' into feat/http-subscription

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0xNeshi approved these changes Mar 5, 2026

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0xNeshi assigned smartprogrammer93 and PoulavBhowmick03 Mar 5, 2026

0xNeshi merged commit 29276a7 into OpenZeppelin:main Mar 5, 2026
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Summary

Features

Usage

Breaking Changes

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