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codex - 💡(How to fix) Fix Upgrade `rmcp` dependency to 1.4.0 to fix MCP HTTP/Cloudflare connection issues [1 comments, 2 participants]

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openai/codex#17529•Fetched 2026-04-12 13:26:58
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The Codex CLI and codex_apps currently depend on rmcp = "0.15.0". As reported in multiple issues (e.g., #16485, #12859, #13852), this older version of the RMCP client lacks support for injecting custom HTTP headers (such as User-Agent or specific Auth headers) into Streamable HTTP and WebSocket handshakes. This causes MCP connections to fail behind Cloudflare, strict corporate proxies, or services like Supabase that require specific headers or constant re-authentication.

Root Cause

The Codex CLI and codex_apps currently depend on rmcp = "0.15.0". As reported in multiple issues (e.g., #16485, #12859, #13852), this older version of the RMCP client lacks support for injecting custom HTTP headers (such as User-Agent or specific Auth headers) into Streamable HTTP and WebSocket handshakes. This causes MCP connections to fail behind Cloudflare, strict corporate proxies, or services like Supabase that require specific headers or constant re-authentication.

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Description

The Codex CLI and codex_apps currently depend on rmcp = "0.15.0". As reported in multiple issues (e.g., #16485, #12859, #13852), this older version of the RMCP client lacks support for injecting custom HTTP headers (such as User-Agent or specific Auth headers) into Streamable HTTP and WebSocket handshakes. This causes MCP connections to fail behind Cloudflare, strict corporate proxies, or services like Supabase that require specific headers or constant re-authentication.

Proposed Solution

The rmcp crate has seen significant development and the 1.4.0 release introduces critical fixes for these exact problems:

  • StreamableHttpClient trait methods (post_message, delete_session, get_stream) now accept a headers parameter.
  • Extensive stability improvements to PaginatedRequestParams and the OAuthState machine.

We strongly recommend upgrading the rmcp dependency across the workspace to ^1.4.0.

Migration Effort

We have already successfully performed this migration in our downstream fork. Upgrading requires adapting to the new #[non_exhaustive] struct builders in rmcp::model::* (such as InitializeRequestParams, CallToolResult, ServerCapabilities, Implementation) and updating the StreamableHttpClient trait signatures in codex-rmcp-client.

If the maintainers are open to this upgrade, we would be happy to submit a Pull Request with the complete rmcp 1.4.0 migration to help close the aforementioned connection and auth issues.

extent analysis

TL;DR

Upgrading the rmcp dependency to ^1.4.0 is likely to fix the issue with MCP connections failing behind certain proxies or services.

Guidance

  • Verify that the current rmcp version is indeed 0.15.0 and that upgrading to 1.4.0 is feasible in the project.
  • Review the changes introduced in rmcp version 1.4.0, particularly the StreamableHttpClient trait methods and the PaginatedRequestParams and OAuthState machine improvements.
  • Assess the migration effort required, including adapting to new struct builders in rmcp::model::* and updating StreamableHttpClient trait signatures in codex-rmcp-client.
  • Consider submitting a Pull Request with the complete rmcp 1.4.0 migration to help close the connection and auth issues.

Example

No code snippet is provided as it is not explicitly mentioned in the issue.

Notes

The migration effort may require significant changes to the codebase, and it is recommended to thoroughly review the changes introduced in rmcp version 1.4.0 before upgrading.

Recommendation

Apply the workaround by upgrading to rmcp version ^1.4.0, as it introduces critical fixes for the exact problems reported and has been successfully tested in a downstream fork.

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