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feat: provide blanket implementations for ClientHandler and ServerHandler traits - #609

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alexhancock merged 4 commits into
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tninesling:handler-blankets
Jan 14, 2026
Merged

feat: provide blanket implementations for ClientHandler and ServerHandler traits#609
alexhancock merged 4 commits into
modelcontextprotocol:mainfrom
tninesling:handler-blankets

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Adds blanket implementations for Box<T> and Arc<T> when T implements ClientHandler or ServerHandler.

Motivation and Context

When building an MCP service, we may want to wrap it in a smart pointer before passing it into the tower service constructor. In my case, I want to spawn a background thread to do some work using some session state as requests are processed. However, introducing the Arc results in a compilation error:

use std::sync::Arc;use rmcp::ServerHandler;use rmcp::transport::StreamableHttpService;structMyService;implServerHandlerforMyService{}fnstart_server(){let my_service = Arc::new(MyService);// This gives "the trait bound `Arc<MyService>: ServerHandler` is not satisfied"let http_service = StreamableHttpService::new(move || Ok(my_service),Default::default(),Default::default(),);// ...}

How Has This Been Tested?

Added integration tests and confirmed this fixes the compilation error in my project.

Breaking Changes

I believe adding blanket implementations of this kind is typically considered a breaking change, although it should be a no-op for most users.

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

I omitted blanket implementations for &T and &mut T due to the 'static bound on the traits, and I omitted Rc<T> due to the Sync bound.

@github-actionsgithub-actionsBot added T-test Testing related changes T-core Core library changes T-handler Handler implementation changes labels Jan 7, 2026
@alexhancock

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@tninesling Nice! A good idea

I had a play with macros to see if it could dedupe some of the volume

Let me know what you think of 0b54219

It's somewhat vibecoded so let me know if it does the job and if you like it

@tninesling

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ContributorAuthor

Let me know what you think of 0b54219

Thanks for taking a look @alexhancock. As long as those tests pass, it fixes the issue I ran into. Although, the macros in that commit add a lot of indirection that make it hard to read. I agree with the direction of deduplicating the implementations though. I added some simpler macros in a493962, which are slightly more verbose, but hopefully easier to read and maintain.

alexhancock
alexhancock previously approved these changes Jan 13, 2026

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Yeah this seems like a good middleground, and cuts down on a lot of the original bloat. Thanks!

@alexhancock

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@tninesling Can you run the formatter: cargo fmt and then also make the commit messages only have valid https://www.conventionalcommits.org? Then we can merge

@tnineslingtninesling changed the title Provide blanket implementations for ClientHandler and ServerHandler traitsfeat: Provide blanket implementations for ClientHandler and ServerHandler traitsJan 13, 2026
@tnineslingtninesling changed the title feat: Provide blanket implementations for ClientHandler and ServerHandler traitsfeat: provide blanket implementations for ClientHandler and ServerHandler traitsJan 13, 2026
@alexhancock
alexhancock merged commit 81f8588 into modelcontextprotocol:mainJan 14, 2026
11 checks passed
@alexhancockalexhancock mentioned this pull request Jan 14, 2026
takumi-earth pushed a commit to earthlings-dev/rmcp that referenced this pull request Jan 27, 2026
…dler traits (modelcontextprotocol#609)
* feat!: implement ServerHandler for Box<H> and Arc<H> where H is a ServerHandler
* feat!: implement ClientHandler for Box<H> and Arc<H> where H is a ClientHandler
* test: test Box and Arc have blanket implementations for handler traits
* refactor: deduplicate blanket implementations with macros
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@tninesling@alexhancock@scutuatua-crypto
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feat: provide blanket implementations for ClientHandler and ServerHandler traits by tninesling · Pull Request #609 · modelcontextprotocol/rust-sdk · GitHub
Skip to content

feat: provide blanket implementations for ClientHandler and ServerHandler traits - #609

Merged
alexhancock merged 4 commits into
modelcontextprotocol:mainfrom
tninesling:handler-blankets
Jan 14, 2026
Merged

feat: provide blanket implementations for ClientHandler and ServerHandler traits#609
alexhancock merged 4 commits into
modelcontextprotocol:mainfrom
tninesling:handler-blankets

Conversation

@tninesling

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Adds blanket implementations for Box<T> and Arc<T> when T implements ClientHandler or ServerHandler.

Motivation and Context

When building an MCP service, we may want to wrap it in a smart pointer before passing it into the tower service constructor. In my case, I want to spawn a background thread to do some work using some session state as requests are processed. However, introducing the Arc results in a compilation error:

use std::sync::Arc;use rmcp::ServerHandler;use rmcp::transport::StreamableHttpService;structMyService;implServerHandlerforMyService{}fnstart_server(){let my_service = Arc::new(MyService);// This gives "the trait bound `Arc<MyService>: ServerHandler` is not satisfied"let http_service = StreamableHttpService::new(move || Ok(my_service),Default::default(),Default::default(),);// ...}

How Has This Been Tested?

Added integration tests and confirmed this fixes the compilation error in my project.

Breaking Changes

I believe adding blanket implementations of this kind is typically considered a breaking change, although it should be a no-op for most users.

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

I omitted blanket implementations for &T and &mut T due to the 'static bound on the traits, and I omitted Rc<T> due to the Sync bound.

@github-actionsgithub-actionsBot added T-test Testing related changes T-core Core library changes T-handler Handler implementation changes labels Jan 7, 2026
@alexhancock

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@tninesling Nice! A good idea

I had a play with macros to see if it could dedupe some of the volume

Let me know what you think of 0b54219

It's somewhat vibecoded so let me know if it does the job and if you like it

@tninesling

Copy link
Copy Markdown
ContributorAuthor

Let me know what you think of 0b54219

Thanks for taking a look @alexhancock. As long as those tests pass, it fixes the issue I ran into. Although, the macros in that commit add a lot of indirection that make it hard to read. I agree with the direction of deduplicating the implementations though. I added some simpler macros in a493962, which are slightly more verbose, but hopefully easier to read and maintain.

alexhancock
alexhancock previously approved these changes Jan 13, 2026

@alexhancockalexhancock left a comment

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Yeah this seems like a good middleground, and cuts down on a lot of the original bloat. Thanks!

@alexhancock

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@tninesling Can you run the formatter: cargo fmt and then also make the commit messages only have valid https://www.conventionalcommits.org? Then we can merge

@tnineslingtninesling changed the title Provide blanket implementations for ClientHandler and ServerHandler traitsfeat: Provide blanket implementations for ClientHandler and ServerHandler traitsJan 13, 2026
@tnineslingtninesling changed the title feat: Provide blanket implementations for ClientHandler and ServerHandler traitsfeat: provide blanket implementations for ClientHandler and ServerHandler traitsJan 13, 2026
@alexhancock
alexhancock merged commit 81f8588 into modelcontextprotocol:mainJan 14, 2026
11 checks passed
@alexhancockalexhancock mentioned this pull request Jan 14, 2026
takumi-earth pushed a commit to earthlings-dev/rmcp that referenced this pull request Jan 27, 2026
…dler traits (modelcontextprotocol#609)
* feat!: implement ServerHandler for Box<H> and Arc<H> where H is a ServerHandler
* feat!: implement ClientHandler for Box<H> and Arc<H> where H is a ClientHandler
* test: test Box and Arc have blanket implementations for handler traits
* refactor: deduplicate blanket implementations with macros
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T-coreCore library changesT-handlerHandler implementation changesT-testTesting related changes

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@tninesling@alexhancock@scutuatua-crypto
, 'i'); if (__m === '*' || __re.test(location.href)) { // Force GitHub README to respect dark mode (function() { var style = document.createElement('style'); style.textContent = ' .markdown-body { color-scheme: dark light; } .markdown-body pre { background: #161b22 !important; } .markdown-body code { background: rgba(110, 118, 129, 0.4) !important; } .markdown-body table th, .markdown-body table td { border-color: #30363d !important; } .markdown-body img { background: #0d1117; } .markdown-body blockquote { border-left-color: #8b949e; } .markdown-body hr { border-color: #30363d; } '; document.head.appendChild(style); })(); } } catch(__e) { console.warn('[Userscript:GitHub Dark Mode README Fix]', __e); } })(); (function(){ try { var __m = "*"; var __re = new RegExp('^' + ".*" + ' feat: provide blanket implementations for ClientHandler and ServerHandler traits by tninesling · Pull Request #609 · modelcontextprotocol/rust-sdk · GitHub
Skip to content

feat: provide blanket implementations for ClientHandler and ServerHandler traits - #609

Merged
alexhancock merged 4 commits into
modelcontextprotocol:mainfrom
tninesling:handler-blankets
Jan 14, 2026
Merged

feat: provide blanket implementations for ClientHandler and ServerHandler traits#609
alexhancock merged 4 commits into
modelcontextprotocol:mainfrom
tninesling:handler-blankets

Conversation

@tninesling

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Adds blanket implementations for Box<T> and Arc<T> when T implements ClientHandler or ServerHandler.

Motivation and Context

When building an MCP service, we may want to wrap it in a smart pointer before passing it into the tower service constructor. In my case, I want to spawn a background thread to do some work using some session state as requests are processed. However, introducing the Arc results in a compilation error:

use std::sync::Arc;use rmcp::ServerHandler;use rmcp::transport::StreamableHttpService;structMyService;implServerHandlerforMyService{}fnstart_server(){let my_service = Arc::new(MyService);// This gives "the trait bound `Arc<MyService>: ServerHandler` is not satisfied"let http_service = StreamableHttpService::new(move || Ok(my_service),Default::default(),Default::default(),);// ...}

How Has This Been Tested?

Added integration tests and confirmed this fixes the compilation error in my project.

Breaking Changes

I believe adding blanket implementations of this kind is typically considered a breaking change, although it should be a no-op for most users.

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

I omitted blanket implementations for &T and &mut T due to the 'static bound on the traits, and I omitted Rc<T> due to the Sync bound.

@github-actionsgithub-actionsBot added T-test Testing related changes T-core Core library changes T-handler Handler implementation changes labels Jan 7, 2026
@alexhancock

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Contributor

@tninesling Nice! A good idea

I had a play with macros to see if it could dedupe some of the volume

Let me know what you think of 0b54219

It's somewhat vibecoded so let me know if it does the job and if you like it

@tninesling

Copy link
Copy Markdown
ContributorAuthor

Let me know what you think of 0b54219

Thanks for taking a look @alexhancock. As long as those tests pass, it fixes the issue I ran into. Although, the macros in that commit add a lot of indirection that make it hard to read. I agree with the direction of deduplicating the implementations though. I added some simpler macros in a493962, which are slightly more verbose, but hopefully easier to read and maintain.

alexhancock
alexhancock previously approved these changes Jan 13, 2026

@alexhancockalexhancock left a comment

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Yeah this seems like a good middleground, and cuts down on a lot of the original bloat. Thanks!

@alexhancock

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@tninesling Can you run the formatter: cargo fmt and then also make the commit messages only have valid https://www.conventionalcommits.org? Then we can merge

@tnineslingtninesling changed the title Provide blanket implementations for ClientHandler and ServerHandler traitsfeat: Provide blanket implementations for ClientHandler and ServerHandler traitsJan 13, 2026
@tnineslingtninesling changed the title feat: Provide blanket implementations for ClientHandler and ServerHandler traitsfeat: provide blanket implementations for ClientHandler and ServerHandler traitsJan 13, 2026
@alexhancock
alexhancock merged commit 81f8588 into modelcontextprotocol:mainJan 14, 2026
11 checks passed
@alexhancockalexhancock mentioned this pull request Jan 14, 2026
takumi-earth pushed a commit to earthlings-dev/rmcp that referenced this pull request Jan 27, 2026
…dler traits (modelcontextprotocol#609)
* feat!: implement ServerHandler for Box<H> and Arc<H> where H is a ServerHandler
* feat!: implement ClientHandler for Box<H> and Arc<H> where H is a ClientHandler
* test: test Box and Arc have blanket implementations for handler traits
* refactor: deduplicate blanket implementations with macros
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Skip to content

feat: provide blanket implementations for ClientHandler and ServerHandler traits - #609

Merged
alexhancock merged 4 commits into
modelcontextprotocol:mainfrom
tninesling:handler-blankets
Jan 14, 2026
Merged

feat: provide blanket implementations for ClientHandler and ServerHandler traits#609
alexhancock merged 4 commits into
modelcontextprotocol:mainfrom
tninesling:handler-blankets

Conversation

@tninesling

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Contributor

Adds blanket implementations for Box<T> and Arc<T> when T implements ClientHandler or ServerHandler.

Motivation and Context

When building an MCP service, we may want to wrap it in a smart pointer before passing it into the tower service constructor. In my case, I want to spawn a background thread to do some work using some session state as requests are processed. However, introducing the Arc results in a compilation error:

use std::sync::Arc;use rmcp::ServerHandler;use rmcp::transport::StreamableHttpService;structMyService;implServerHandlerforMyService{}fnstart_server(){let my_service = Arc::new(MyService);// This gives "the trait bound `Arc<MyService>: ServerHandler` is not satisfied"let http_service = StreamableHttpService::new(move || Ok(my_service),Default::default(),Default::default(),);// ...}

How Has This Been Tested?

Added integration tests and confirmed this fixes the compilation error in my project.

Breaking Changes

I believe adding blanket implementations of this kind is typically considered a breaking change, although it should be a no-op for most users.

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

I omitted blanket implementations for &T and &mut T due to the 'static bound on the traits, and I omitted Rc<T> due to the Sync bound.

@github-actionsgithub-actionsBot added T-test Testing related changes T-core Core library changes T-handler Handler implementation changes labels Jan 7, 2026
@alexhancock

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@tninesling Nice! A good idea

I had a play with macros to see if it could dedupe some of the volume

Let me know what you think of 0b54219

It's somewhat vibecoded so let me know if it does the job and if you like it

@tninesling

Copy link
Copy Markdown
ContributorAuthor

Let me know what you think of 0b54219

Thanks for taking a look @alexhancock. As long as those tests pass, it fixes the issue I ran into. Although, the macros in that commit add a lot of indirection that make it hard to read. I agree with the direction of deduplicating the implementations though. I added some simpler macros in a493962, which are slightly more verbose, but hopefully easier to read and maintain.

alexhancock
alexhancock previously approved these changes Jan 13, 2026

@alexhancockalexhancock left a comment

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Yeah this seems like a good middleground, and cuts down on a lot of the original bloat. Thanks!

@alexhancock

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@tninesling Can you run the formatter: cargo fmt and then also make the commit messages only have valid https://www.conventionalcommits.org? Then we can merge

@tnineslingtninesling changed the title Provide blanket implementations for ClientHandler and ServerHandler traitsfeat: Provide blanket implementations for ClientHandler and ServerHandler traitsJan 13, 2026
@tnineslingtninesling changed the title feat: Provide blanket implementations for ClientHandler and ServerHandler traitsfeat: provide blanket implementations for ClientHandler and ServerHandler traitsJan 13, 2026
@alexhancock
alexhancock merged commit 81f8588 into modelcontextprotocol:mainJan 14, 2026
11 checks passed
@alexhancockalexhancock mentioned this pull request Jan 14, 2026
takumi-earth pushed a commit to earthlings-dev/rmcp that referenced this pull request Jan 27, 2026
…dler traits (modelcontextprotocol#609)
* feat!: implement ServerHandler for Box<H> and Arc<H> where H is a ServerHandler
* feat!: implement ClientHandler for Box<H> and Arc<H> where H is a ClientHandler
* test: test Box and Arc have blanket implementations for handler traits
* refactor: deduplicate blanket implementations with macros
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3 participants

@tninesling@alexhancock@scutuatua-crypto
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Skip to content

feat: provide blanket implementations for ClientHandler and ServerHandler traits - #609

Merged
alexhancock merged 4 commits into
modelcontextprotocol:mainfrom
tninesling:handler-blankets
Jan 14, 2026
Merged

feat: provide blanket implementations for ClientHandler and ServerHandler traits#609
alexhancock merged 4 commits into
modelcontextprotocol:mainfrom
tninesling:handler-blankets

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@tninesling

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Adds blanket implementations for Box<T> and Arc<T> when T implements ClientHandler or ServerHandler.

Motivation and Context

When building an MCP service, we may want to wrap it in a smart pointer before passing it into the tower service constructor. In my case, I want to spawn a background thread to do some work using some session state as requests are processed. However, introducing the Arc results in a compilation error:

use std::sync::Arc;use rmcp::ServerHandler;use rmcp::transport::StreamableHttpService;structMyService;implServerHandlerforMyService{}fnstart_server(){let my_service = Arc::new(MyService);// This gives "the trait bound `Arc<MyService>: ServerHandler` is not satisfied"let http_service = StreamableHttpService::new(move || Ok(my_service),Default::default(),Default::default(),);// ...}

How Has This Been Tested?

Added integration tests and confirmed this fixes the compilation error in my project.

Breaking Changes

I believe adding blanket implementations of this kind is typically considered a breaking change, although it should be a no-op for most users.

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

I omitted blanket implementations for &T and &mut T due to the 'static bound on the traits, and I omitted Rc<T> due to the Sync bound.

@github-actionsgithub-actionsBot added T-test Testing related changes T-core Core library changes T-handler Handler implementation changes labels Jan 7, 2026
@alexhancock

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Contributor

@tninesling Nice! A good idea

I had a play with macros to see if it could dedupe some of the volume

Let me know what you think of 0b54219

It's somewhat vibecoded so let me know if it does the job and if you like it

@tninesling

Copy link
Copy Markdown
ContributorAuthor

Let me know what you think of 0b54219

Thanks for taking a look @alexhancock. As long as those tests pass, it fixes the issue I ran into. Although, the macros in that commit add a lot of indirection that make it hard to read. I agree with the direction of deduplicating the implementations though. I added some simpler macros in a493962, which are slightly more verbose, but hopefully easier to read and maintain.

alexhancock
alexhancock previously approved these changes Jan 13, 2026

@alexhancockalexhancock left a comment

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Yeah this seems like a good middleground, and cuts down on a lot of the original bloat. Thanks!

@alexhancock

Copy link
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Contributor

@tninesling Can you run the formatter: cargo fmt and then also make the commit messages only have valid https://www.conventionalcommits.org? Then we can merge

@tnineslingtninesling changed the title Provide blanket implementations for ClientHandler and ServerHandler traitsfeat: Provide blanket implementations for ClientHandler and ServerHandler traitsJan 13, 2026
@tnineslingtninesling changed the title feat: Provide blanket implementations for ClientHandler and ServerHandler traitsfeat: provide blanket implementations for ClientHandler and ServerHandler traitsJan 13, 2026
@alexhancock
alexhancock merged commit 81f8588 into modelcontextprotocol:mainJan 14, 2026
11 checks passed
@alexhancockalexhancock mentioned this pull request Jan 14, 2026
takumi-earth pushed a commit to earthlings-dev/rmcp that referenced this pull request Jan 27, 2026
…dler traits (modelcontextprotocol#609)
* feat!: implement ServerHandler for Box<H> and Arc<H> where H is a ServerHandler
* feat!: implement ClientHandler for Box<H> and Arc<H> where H is a ClientHandler
* test: test Box and Arc have blanket implementations for handler traits
* refactor: deduplicate blanket implementations with macros
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@tninesling@alexhancock@scutuatua-crypto
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feat: provide blanket implementations for ClientHandler and ServerHandler traits - #609

Merged
alexhancock merged 4 commits into
modelcontextprotocol:mainfrom
tninesling:handler-blankets
Jan 14, 2026
Merged

feat: provide blanket implementations for ClientHandler and ServerHandler traits#609
alexhancock merged 4 commits into
modelcontextprotocol:mainfrom
tninesling:handler-blankets

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Adds blanket implementations for Box<T> and Arc<T> when T implements ClientHandler or ServerHandler.

Motivation and Context

When building an MCP service, we may want to wrap it in a smart pointer before passing it into the tower service constructor. In my case, I want to spawn a background thread to do some work using some session state as requests are processed. However, introducing the Arc results in a compilation error:

use std::sync::Arc;use rmcp::ServerHandler;use rmcp::transport::StreamableHttpService;structMyService;implServerHandlerforMyService{}fnstart_server(){let my_service = Arc::new(MyService);// This gives "the trait bound `Arc<MyService>: ServerHandler` is not satisfied"let http_service = StreamableHttpService::new(move || Ok(my_service),Default::default(),Default::default(),);// ...}

How Has This Been Tested?

Added integration tests and confirmed this fixes the compilation error in my project.

Breaking Changes

I believe adding blanket implementations of this kind is typically considered a breaking change, although it should be a no-op for most users.

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

I omitted blanket implementations for &T and &mut T due to the 'static bound on the traits, and I omitted Rc<T> due to the Sync bound.

@github-actionsgithub-actionsBot added T-test Testing related changes T-core Core library changes T-handler Handler implementation changes labels Jan 7, 2026
@alexhancock

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@tninesling Nice! A good idea

I had a play with macros to see if it could dedupe some of the volume

Let me know what you think of 0b54219

It's somewhat vibecoded so let me know if it does the job and if you like it

@tninesling

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Let me know what you think of 0b54219

Thanks for taking a look @alexhancock. As long as those tests pass, it fixes the issue I ran into. Although, the macros in that commit add a lot of indirection that make it hard to read. I agree with the direction of deduplicating the implementations though. I added some simpler macros in a493962, which are slightly more verbose, but hopefully easier to read and maintain.

alexhancock
alexhancock previously approved these changes Jan 13, 2026

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Yeah this seems like a good middleground, and cuts down on a lot of the original bloat. Thanks!

@alexhancock

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@tninesling Can you run the formatter: cargo fmt and then also make the commit messages only have valid https://www.conventionalcommits.org? Then we can merge

@tnineslingtninesling changed the title Provide blanket implementations for ClientHandler and ServerHandler traitsfeat: Provide blanket implementations for ClientHandler and ServerHandler traitsJan 13, 2026
@tnineslingtninesling changed the title feat: Provide blanket implementations for ClientHandler and ServerHandler traitsfeat: provide blanket implementations for ClientHandler and ServerHandler traitsJan 13, 2026
@alexhancock
alexhancock merged commit 81f8588 into modelcontextprotocol:mainJan 14, 2026
11 checks passed
@alexhancockalexhancock mentioned this pull request Jan 14, 2026
takumi-earth pushed a commit to earthlings-dev/rmcp that referenced this pull request Jan 27, 2026
…dler traits (modelcontextprotocol#609)
* feat!: implement ServerHandler for Box<H> and Arc<H> where H is a ServerHandler
* feat!: implement ClientHandler for Box<H> and Arc<H> where H is a ClientHandler
* test: test Box and Arc have blanket implementations for handler traits
* refactor: deduplicate blanket implementations with macros
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@tninesling@alexhancock@scutuatua-crypto
, 'i'); if (__m === '*' || __re.test(location.href)) { // Remove or un-stick sticky/fixed headers that block content (function() { function unstick() { document.querySelectorAll('header, nav, [role="banner"], .header, .navbar, .sticky, .fixed-top, [style*="position: fixed"], [style*="position:sticky"]').forEach(function(el) { if (el.style.position === 'fixed' || el.style.position === 'sticky' || getComputedStyle(el).position === 'fixed' || getComputedStyle(el).position === 'sticky') { el.style.position = 'static'; el.style.top = 'auto'; el.style.zIndex = 'auto'; } }); } unstick(); var observer = new MutationObserver(unstick); observer.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] }); })(); } } catch(__e) { console.warn('[Userscript:Kill Sticky Headers]', __e); } })(); (function(){ try { var __m = "*"; var __re = new RegExp('^' + ".*" + ' feat: provide blanket implementations for ClientHandler and ServerHandler traits by tninesling · Pull Request #609 · modelcontextprotocol/rust-sdk · GitHub
Skip to content

feat: provide blanket implementations for ClientHandler and ServerHandler traits - #609

Merged
alexhancock merged 4 commits into
modelcontextprotocol:mainfrom
tninesling:handler-blankets
Jan 14, 2026
Merged

feat: provide blanket implementations for ClientHandler and ServerHandler traits#609
alexhancock merged 4 commits into
modelcontextprotocol:mainfrom
tninesling:handler-blankets

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@tninesling

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Adds blanket implementations for Box<T> and Arc<T> when T implements ClientHandler or ServerHandler.

Motivation and Context

When building an MCP service, we may want to wrap it in a smart pointer before passing it into the tower service constructor. In my case, I want to spawn a background thread to do some work using some session state as requests are processed. However, introducing the Arc results in a compilation error:

use std::sync::Arc;use rmcp::ServerHandler;use rmcp::transport::StreamableHttpService;structMyService;implServerHandlerforMyService{}fnstart_server(){let my_service = Arc::new(MyService);// This gives "the trait bound `Arc<MyService>: ServerHandler` is not satisfied"let http_service = StreamableHttpService::new(move || Ok(my_service),Default::default(),Default::default(),);// ...}

How Has This Been Tested?

Added integration tests and confirmed this fixes the compilation error in my project.

Breaking Changes

I believe adding blanket implementations of this kind is typically considered a breaking change, although it should be a no-op for most users.

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

I omitted blanket implementations for &T and &mut T due to the 'static bound on the traits, and I omitted Rc<T> due to the Sync bound.

@github-actionsgithub-actionsBot added T-test Testing related changes T-core Core library changes T-handler Handler implementation changes labels Jan 7, 2026
@alexhancock

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@tninesling Nice! A good idea

I had a play with macros to see if it could dedupe some of the volume

Let me know what you think of 0b54219

It's somewhat vibecoded so let me know if it does the job and if you like it

@tninesling

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ContributorAuthor

Let me know what you think of 0b54219

Thanks for taking a look @alexhancock. As long as those tests pass, it fixes the issue I ran into. Although, the macros in that commit add a lot of indirection that make it hard to read. I agree with the direction of deduplicating the implementations though. I added some simpler macros in a493962, which are slightly more verbose, but hopefully easier to read and maintain.

alexhancock
alexhancock previously approved these changes Jan 13, 2026

@alexhancockalexhancock left a comment

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Yeah this seems like a good middleground, and cuts down on a lot of the original bloat. Thanks!

@alexhancock

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@tninesling Can you run the formatter: cargo fmt and then also make the commit messages only have valid https://www.conventionalcommits.org? Then we can merge

@tnineslingtninesling changed the title Provide blanket implementations for ClientHandler and ServerHandler traitsfeat: Provide blanket implementations for ClientHandler and ServerHandler traitsJan 13, 2026
@tnineslingtninesling changed the title feat: Provide blanket implementations for ClientHandler and ServerHandler traitsfeat: provide blanket implementations for ClientHandler and ServerHandler traitsJan 13, 2026
@alexhancock
alexhancock merged commit 81f8588 into modelcontextprotocol:mainJan 14, 2026
11 checks passed
@alexhancockalexhancock mentioned this pull request Jan 14, 2026
takumi-earth pushed a commit to earthlings-dev/rmcp that referenced this pull request Jan 27, 2026
…dler traits (modelcontextprotocol#609)
* feat!: implement ServerHandler for Box<H> and Arc<H> where H is a ServerHandler
* feat!: implement ClientHandler for Box<H> and Arc<H> where H is a ClientHandler
* test: test Box and Arc have blanket implementations for handler traits
* refactor: deduplicate blanket implementations with macros
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3 participants

@tninesling@alexhancock@scutuatua-crypto
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Skip to content

feat: provide blanket implementations for ClientHandler and ServerHandler traits - #609

Merged
alexhancock merged 4 commits into
modelcontextprotocol:mainfrom
tninesling:handler-blankets
Jan 14, 2026
Merged

feat: provide blanket implementations for ClientHandler and ServerHandler traits#609
alexhancock merged 4 commits into
modelcontextprotocol:mainfrom
tninesling:handler-blankets

Conversation

@tninesling

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Contributor

Adds blanket implementations for Box<T> and Arc<T> when T implements ClientHandler or ServerHandler.

Motivation and Context

When building an MCP service, we may want to wrap it in a smart pointer before passing it into the tower service constructor. In my case, I want to spawn a background thread to do some work using some session state as requests are processed. However, introducing the Arc results in a compilation error:

use std::sync::Arc;use rmcp::ServerHandler;use rmcp::transport::StreamableHttpService;structMyService;implServerHandlerforMyService{}fnstart_server(){let my_service = Arc::new(MyService);// This gives "the trait bound `Arc<MyService>: ServerHandler` is not satisfied"let http_service = StreamableHttpService::new(move || Ok(my_service),Default::default(),Default::default(),);// ...}

How Has This Been Tested?

Added integration tests and confirmed this fixes the compilation error in my project.

Breaking Changes

I believe adding blanket implementations of this kind is typically considered a breaking change, although it should be a no-op for most users.

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

I omitted blanket implementations for &T and &mut T due to the 'static bound on the traits, and I omitted Rc<T> due to the Sync bound.

@github-actionsgithub-actionsBot added T-test Testing related changes T-core Core library changes T-handler Handler implementation changes labels Jan 7, 2026
@alexhancock

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Contributor

@tninesling Nice! A good idea

I had a play with macros to see if it could dedupe some of the volume

Let me know what you think of 0b54219

It's somewhat vibecoded so let me know if it does the job and if you like it

@tninesling

Copy link
Copy Markdown
ContributorAuthor

Let me know what you think of 0b54219

Thanks for taking a look @alexhancock. As long as those tests pass, it fixes the issue I ran into. Although, the macros in that commit add a lot of indirection that make it hard to read. I agree with the direction of deduplicating the implementations though. I added some simpler macros in a493962, which are slightly more verbose, but hopefully easier to read and maintain.

alexhancock
alexhancock previously approved these changes Jan 13, 2026

@alexhancockalexhancock left a comment

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Yeah this seems like a good middleground, and cuts down on a lot of the original bloat. Thanks!

@alexhancock

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Contributor

@tninesling Can you run the formatter: cargo fmt and then also make the commit messages only have valid https://www.conventionalcommits.org? Then we can merge

@tnineslingtninesling changed the title Provide blanket implementations for ClientHandler and ServerHandler traitsfeat: Provide blanket implementations for ClientHandler and ServerHandler traitsJan 13, 2026
@tnineslingtninesling changed the title feat: Provide blanket implementations for ClientHandler and ServerHandler traitsfeat: provide blanket implementations for ClientHandler and ServerHandler traitsJan 13, 2026
@alexhancock
alexhancock merged commit 81f8588 into modelcontextprotocol:mainJan 14, 2026
11 checks passed
@alexhancockalexhancock mentioned this pull request Jan 14, 2026
takumi-earth pushed a commit to earthlings-dev/rmcp that referenced this pull request Jan 27, 2026
…dler traits (modelcontextprotocol#609)
* feat!: implement ServerHandler for Box<H> and Arc<H> where H is a ServerHandler
* feat!: implement ClientHandler for Box<H> and Arc<H> where H is a ClientHandler
* test: test Box and Arc have blanket implementations for handler traits
* refactor: deduplicate blanket implementations with macros
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3 participants

@tninesling@alexhancock@scutuatua-crypto