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@jcat4 jcat4 commented May 28, 2025

Motivation and Context

Closes #3

Follow-up to #27

This adds the ability to build MCP clients with the ruby sdk. I've started with just a basic HTTP transport layer. We can add other things (i.e. streamable HTTP) later.

Per this comment, we've decided to go with a pluggable approach where:

  • You create an instance of the transport layer you want to use
  • A Client is initialized with that transport layer
  • The client receives messages (i.e. tools or call_tool)
  • The client builds a JSON-RPC request object
  • The JSON-RPC request object is passed to the transport layer's send_request method to communicate with the server
  • The transport returns a JSON-RPC response object
  • The client then parses the response and does whatever it needs to with it

For simplicity, I'm just allowing custom headers to specify auth. I didn't want to build an abstraction around different auth types prematurely. I've made authentication the responsibility of the transport layer, since that's what is responsible for communication with the server.

How Has This Been Tested?

The local gem build has been tested in 2 different internal repositories and is working as expected so far.

Breaking Changes

Just the stuff from #27

Types of changes

  • Bug fix (non-breaking change which fixes an issue)
  • New feature (non-breaking change which adds functionality)
  • Breaking change (fix or feature that would cause existing functionality to change)
  • Documentation update

Checklist

  • I have read the MCP Documentation
  • My code follows the repository's style guidelines
  • New and existing tests pass locally
  • I have added appropriate error handling
  • I have added or updated documentation as needed

Additional context

@jcat4 jcat4 marked this pull request as ready for review May 29, 2025 16:22
@jcat4 jcat4 marked this pull request as draft May 29, 2025 17:54
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jcat4 commented May 29, 2025

Decided to build in auth, going to draft to test it

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jcat4 commented May 29, 2025

Auth is tested and working

@jcat4 jcat4 marked this pull request as ready for review May 29, 2025 19:47
@topherbullock
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@jcat4 can you rebase on main and resolve conflicts? seems to be largely the model_context_protocol => mcp rename

@atesgoral atesgoral mentioned this pull request Jun 15, 2025
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Thank you for your work on this, @jcat4. We're looking forward to seeing it merged. Is there an expected timeline for this?

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jcat4 commented Jun 19, 2025

@jcat4 can you rebase on main and resolve conflicts? seems to be largely the model_context_protocol => mcp rename

Sorry, lost track of this.

I thought we wanted to go with the pluggable approach? If so, I can close this

Or I can try to rework this to be closer to what y'all envisioned!

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@jcat4 @topherbullock Now that #27 is in, could we revisit this and get a client in there? 🙏

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jcat4 commented Jul 29, 2025

@jcat4 @topherbullock Now that #27 is in, could we revisit this and get a client in there? 🙏

I'll make some time this week to knock this out

@jcat4 jcat4 marked this pull request as draft July 30, 2025 16:25
@jcat4 jcat4 force-pushed the add-basic-http-client-support branch from e72bcfa to 3a0b9b8 Compare July 30, 2025 16:30
@@ -216,7 +218,7 @@ $ ruby examples/stdio_server.rb
{"jsonrpc":"2.0","id":"2","method":"tools/list"}
```

## Configuration
### Configuration
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At the moment, this is server-specific. If we have this patch a client config too (or stop having the config scoped to just the server), we can move this somewhere else in the README

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jcat4 commented Jul 31, 2025

Unsure if we still feel strongly about going with a pluggable approach, and haven't had any feedback on that yet. Will put this as-is in for review

But please let me know if we should go somewhere else with the interface! I want us to get as close to right as possible on our first release

@jcat4 jcat4 marked this pull request as ready for review July 31, 2025 19:41
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jcat4 commented Jul 31, 2025

I've tested the new code in one of our local apps, and it's working as expected.

@jcat4 jcat4 requested review from atesgoral and juharris July 31, 2025 19:42
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jcat4 commented Jul 31, 2025

Spoke with @juharris, and we decided a pluggable approach would probably be better. The primary reason is it will allow folks to implement and pass their own custom transport layers (and open the door for other gems to add more, too!). The first step might be a bit manual (create your transport, create your client by passing your transport, send messages to your client), but we can iterate later with convenience wrappers that won't break existing code

Overall, it seems like the safer bet. What we have is functional, but maybe not flexible enough for a public gem. Will begin work on this again next week when I have time, I think I can knock something out relatively quickly

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@jcat4 Thanks for doing this!

topherbullock
topherbullock previously approved these changes Aug 26, 2025
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LGTM - one nit about call_tool's arguments. input --> arguments makes it more obvious what is being passed in to the tools/call request.

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@jcat4 can you fix up the suggestions and squash your commits pls? Thanks for pushing this through!

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koic commented Aug 27, 2025

Thank you for the client implementation. I've left some minor feedback. Since it doesn’t seem to be squashed yet, please squash your commits into one at the end.

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jcat4 commented Aug 28, 2025

Since this is a user-specific setting, I think it should be defined in the developer's ~/.gitignore rather than in the repository.

@koic My view: if we never want a file committed, the repo should enforce it so we don’t rely on each contributor’s local setup. Is there a strong reason to prefer user-level ignores here?

@jcat4 jcat4 force-pushed the add-basic-http-client-support branch from 86a173a to ff333d8 Compare August 28, 2025 15:09
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koic commented Aug 28, 2025

Because these are specific to the user's development environment (such as OS or editor) and not specific to the Ruby SDK. For more details, please refer to the discussion in the following closed PRs:
https://github.com/rails/rails/pulls?q=is%3Apr+.DS_Store+is%3Aclosed+

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jcat4 commented Aug 28, 2025

Because these are specific to the user's development environment (such as OS or editor) and not specific to the Ruby SDK. For more details, please refer to the discussion in the following closed PRs: https://github.com/rails/rails/pulls?q=is%3Apr+.DS_Store+is%3Aclosed+

Thanks for this! Hmmm... I do see that's how rails operates. If this is commonly how other open source ruby repos operate, I can make this change to be more inline.

But I do wanna say, I still personally disagree, as I think this change could avoid friction. Those 14 PRs in rails where this convo had to happen are examples of friction that could be avoided.

If you have any docs or anything on hand, would love to know more about why we want to have a platform-agnostic .gitignore!

@jcat4 jcat4 force-pushed the add-basic-http-client-support branch from 972b985 to 03c492d Compare August 28, 2025 15:24
@jcat4 jcat4 requested a review from koic August 28, 2025 15:28
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koic commented Aug 28, 2025

I'm personally convinced by the reasoning in the Rails repository, so I don't have any additional documentation beyond that. In any case, this doesn't seem to be the main focus of this PR. This point can serve as a starting place for the PR itself. I do have a bit of feedback, so I'll leave some additional comments.

@jcat4 jcat4 force-pushed the add-basic-http-client-support branch from 55e07f6 to ac13bab Compare August 28, 2025 16:45
@jcat4 jcat4 force-pushed the add-basic-http-client-support branch from e9461d9 to 91d3327 Compare August 28, 2025 16:46
@jcat4 jcat4 requested a review from koic August 28, 2025 16:46
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