[3/4] Add executor-backed RMCP HTTP client by aibrahim-oai · Pull Request #18583 · openai/codex

aibrahim-oai · 2026-04-19T18:26:03Z

Why

The RMCP layer needs a Streamable HTTP client that can talk either directly over reqwest or through the executor HTTP runner without duplicating MCP session logic higher in the stack. This PR adds that client-side transport boundary so remote Streamable HTTP MCP can reuse the same RMCP flow as the local path.

What

Add a shared rmcp-client/src/streamable_http/ module with:
- transport_client.rs for the local-or-remote transport enum
- local_client.rs for the direct reqwest implementation
- remote_client.rs for the executor-backed implementation
- common.rs for the small shared Streamable HTTP helpers
Teach RmcpClient to build Streamable HTTP transports in either local or remote mode while keeping the existing OAuth ownership in RMCP.
Translate remote POST, GET, and DELETE session operations into executor http/request calls.
Preserve RMCP session expiry handling and reconnect behavior for the remote transport.
Add remote transport coverage in rmcp-client/tests/streamable_http_remote.rs and keep the shared test support in rmcp-client/tests/streamable_http_test_support.rs.

Verification

cargo check -p codex-rmcp-client
online CI

Stack

[1/4] Add executor HTTP request protocol #18581 protocol
[2/4] Implement executor HTTP request runner #18582 runner
[3/4] Add executor-backed RMCP HTTP client #18583 RMCP client
[4/4] Honor Streamable HTTP MCP placement #18584 manager wiring and local/remote coverage

aibrahim-oai · 2026-04-19T18:26:10Z

This change is part of the following stack:

[1/4] Add executor HTTP request protocol #18581
- [2/4] Implement executor HTTP request runner #18582
  - [3/4] Add executor-backed RMCP HTTP client #18583 ◀
    - [4/4] Honor Streamable HTTP MCP placement #18584

_{Change managed by git-spice.}

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chatgpt-codex-connector · 2026-04-20T15:50:43Z

+    let metadata_client = build_http_client(&default_headers)?;
+    let mut oauth_state = OAuthState::new(url.to_string(), Some(metadata_client)).await?;


Fallback to token when environment OAuth discovery is unreachable

create_environment_oauth_transport_and_runtime performs OAuth metadata discovery with a local reqwest client (OAuthState::new(...)). For environment transport, the MCP URL can be reachable only from exec-server, so this call fails before any MCP request is proxied. create_pending_transport only falls back on NoAuthorizationSupport, so network-unreachable discovery errors abort startup even with valid stored tokens.

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chatgpt-codex-connector · 2026-04-20T16:05:06Z

+/// Starts a local exec-server and connects an initialized `ExecServerClient`.
+async fn spawn_exec_server() -> anyhow::Result<ExecServerProcess> {
+    let codex_home = TempDir::new()?;
+    let mut child = Command::new(codex_utils_cargo_bin::cargo_bin("codex")?)


Resolve codex binary before spawning exec-server test

spawn_exec_server hard-fails on cargo_bin("codex")?. In a clean cargo test -p codex-rmcp-client run, that binary is not present (could not locate binary "codex"), so the new integration test fails before exercising RMCP behavior. This makes the test non-hermetic; skip when unavailable or use a harness that guarantees the binary path.

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chatgpt-codex-connector · 2026-04-22T19:46:41Z

+    backend: Arc<dyn StreamableHttpTransportBackend>,
+}
+
+#[derive(Clone)]


Remove derive attribute from impl block

Delete #[derive(Clone)] on the impl StreamableHttpTransportClient block. derive can only be applied to structs/enums/unions, so this triggers a compile-time error (E0774) and blocks building codex-rmcp-client.

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chatgpt-codex-connector · 2026-04-22T19:46:41Z

+                    map_streamable_http_error(error, StreamableHttpTransportClientError::Remote)
+                })
+        }
+        .boxed()


Import FutureExt before calling boxed on async blocks

This module calls .boxed() on async blocks, but futures::FutureExt is never imported. Without that trait in scope, method resolution fails (no method named boxed), so the new transport backend cannot compile.

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chatgpt-codex-connector · 2026-04-22T19:46:41Z

+    StreamableHttpClientTransport<AuthClient<StreamableHttpTransportClient>>,
    OAuthPersistor,
 )> {
    let http_client = build_http_client(&default_headers)?;


Define or import build_http_client in OAuth setup

create_oauth_transport_and_runtime calls build_http_client, but this function is no longer defined/imported in rmcp_client.rs after the refactor. That leaves an unresolved symbol at compile time and prevents codex-rmcp-client from building.

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…-http-client-full-ci

aibrahim-oai · 2026-04-22T19:58:18Z

@codex review

chatgpt-codex-connector · 2026-04-22T20:06:23Z

Codex Review: Didn't find any major issues. What shall we delve into next?

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chatgpt-codex-connector · 2026-04-22T21:20:56Z

+        /*http_headers*/ None,
+        /*env_http_headers*/ None,
+        OAuthCredentialsStoreMode::File,
+        exec_client,


Wrap exec client in Arc before calling remote constructor

create_remote_client passes an ExecServerClient directly to RmcpClient::new_remote_streamable_http_client, but that API requires Arc<dyn ExecutorHttpClient>. This yields E0308 during test builds, so the new remote integration tests do not compile (cargo check -p codex-rmcp-client --tests fails).

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chatgpt-codex-connector · 2026-04-22T22:26:15Z

                http_headers,
                env_http_headers,
                store_mode,
+                runtime_environment.environment().get_http_client(),


Honor experimental_environment for Streamable HTTP placement

make_rmcp_client now always injects runtime_environment.environment().get_http_client() into new_streamable_http_client, regardless of experimental_environment. If the runtime default environment is remote, servers configured as local (experimental_environment unset/local) are still routed through exec-server HTTP, which can break localhost/private-network MCP endpoints and changes documented placement behavior.

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This was referenced Apr 19, 2026

[4/4] Honor Streamable HTTP MCP placement #18584

Merged

[2/4] Implement executor HTTP request runner #18582

Merged

[1/4] Add executor HTTP request protocol #18581

Merged

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Comment thread codex-rs/rmcp-client/src/streamable_http/remote_client.rs

aibrahim-oai force-pushed the dev/remote-mcp-http-runner-full-ci branch from 1a1b28d to afcf571 Compare April 19, 2026 18:38

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aibrahim-oai changed the title ~~Add executor-backed RMCP HTTP client~~ [3/4] Add executor-backed RMCP HTTP client Apr 19, 2026

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aibrahim-oai and others added 2 commits April 22, 2026 12:38

codex: remove streamable http wrappers

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codex: use task tracker for exec-server background tasks

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Simplify streamable HTTP transport client

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Merge branch 'dev/remote-mcp-http-runner-full-ci' into dev/remote-mcp…

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…-http-client-full-ci

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Organize streamable HTTP transport modules

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Add rustls-webpki advisory exception

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Merge branch 'main' into dev/remote-mcp-http-client-full-ci

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Add executor HTTP client capability for RMCP

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Rename executor HTTP capability to HttpClient

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Align remote streamable HTTP client naming

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Trim exec naming from remote HTTP transport

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Match HTTP indirection to ExecBackend

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Split HTTP stream helpers into modules

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Flatten HTTP helper modules

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Trim HTTP-specific exec wording

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Split local and remote HTTP client implementations

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Document HTTP runtime boundaries

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Document new Streamable HTTP files

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Rename HTTP client layers for clarity

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Flatten HTTP client adapter module

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codex: fix CI failure on PR #18583

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[3/4] Add executor-backed RMCP HTTP client#18583

[3/4] Add executor-backed RMCP HTTP client#18583
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		let metadata_client = build_http_client(&default_headers)?;
		let mut oauth_state = OAuthState::new(url.to_string(), Some(metadata_client)).await?;

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