Commit graph go-sdk/mcp
Author SHA1 Message Date
Sam Thanawalla
bb2347385e internal/mcp: add iterator methods resources and prompts
This CL streamlines the client side pagination logic by adding a generic
helper that handles pagination. This also simplifies the existing tools
iterator method.

Change-Id: If4304deda1ccd22d0c4580d76deaefc64e5dfeb9
Reviewed-on: https://go-review.googlesource.com/c/tools/+/676975
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Reviewed-by: Robert Findley <rfindley@google.com>
Auto-Submit: Sam Thanawalla <samthanawalla@google.com>
Reviewed-by: Jonathan Amsterdam <jba@google.com>
2025-06-02 07:39:08 -07:00
Rob Findley
7f8b72203a internal/mcp: clean up diagnostics from Google import
Change-Id: Icf388c48761f0ed504f45cd07e6d1662693b1e2e
Reviewed-on: https://go-review.googlesource.com/c/tools/+/677517
Reviewed-by: Alan Donovan <adonovan@google.com>
Auto-Submit: Robert Findley <rfindley@google.com>
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2025-05-30 11:09:27 -07:00
Jonathan Amsterdam
2b9c6bff50 internal/mcp: handle synthetic responses in conformance test
Modify the conformance test driver to support outgoing responses.
They are returned for incoming requests in order.

Add a test that returns a file resource, which involves the server
sending a roots/list request to the client.

Change-Id: Ie7eb69a8c99ccbf11721518cfffb21244c03e532
Reviewed-on: https://go-review.googlesource.com/c/tools/+/677475
Commit-Queue: Jonathan Amsterdam <jba@google.com>
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2025-05-30 08:16:23 -07:00
Jonathan Amsterdam
a627a4a2dd internal/mcp: add resource conformance test
This uncovered a problem in how we represent resource results:
contents is a slice, not a single value.

I tried to use a file resource, but the server->client ListRoots
call didn't work because synthetic responses aren't supported.
Left a TODO.

I enhanced the hello example so I that could use the MCP Inspector to
work with resources.

The falseSchema change fixes a potential bug where schemas are
re-used, which is disallowed.

Change-Id: I1f0198043cb6221c2a03f4f83aa0bafbc71167f4
Reviewed-on: https://go-review.googlesource.com/c/tools/+/677136
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Sam Thanawalla <samthanawalla@google.com>
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2025-05-29 11:59:43 -07:00
Jonathan Amsterdam
92a0c702cf internal/mcp: run conformance tests on 1.24 with a GOEXPERIMENT setting
Support the conformance tests on 1.24, if the user has set

    GOEXPERIMENT=synctest

The API is different, but other than that it works fine.

Change-Id: I08ffbe094b39a73cd1fc26e7dcf6f22158b2df1d
Reviewed-on: https://go-review.googlesource.com/c/tools/+/677015
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2025-05-28 17:49:57 -07:00
Sam Thanawalla
d45330dd8f internal/mcp: add iterator method for tools
Change-Id: Ibe799caf6592b2763868bdb30f474bc224aa8b00
Reviewed-on: https://go-review.googlesource.com/c/tools/+/676915
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2025-05-28 10:49:23 -07:00
Rob Findley
e2bbd8002d internal/mcp: add JSON conformance tests, and fix some bugs
Add the beginnings of some testdata-driven conformance tests that check
JSON-level compatibility of SDK messages, and fix some bugs in our JSON
message handling:

- "params" can be missing
- "_meta" should not be null
- lists of tools/prompts/resources should not be null

In order to implement this, we need to be able to know when the server
is done processing messages. In general, this is a hard problem; for
gopls we do this with a complicated system of progress reporting and
accounting. However, the new synctest package makes this trivial, as we
can call synctest.Wait to detect when the server is idle. Therefore,
this test requires 1.25 (it uses synctest.Test, added in 1.25, and so
can't run at 1.24 with GOEXPERIMENT=synctest).

Change-Id: I97fa28b56868340ece266a58e1eb3c3bf8cfe0e9
Reviewed-on: https://go-review.googlesource.com/c/tools/+/676538
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2025-05-28 10:00:05 -07:00
Sam Thanawalla
d0bc3bc890 internal/mcp: add pagination for prompts
Change-Id: Ib231427299dbfe807fb80ad8da6ba16d4a8fde03
Reviewed-on: https://go-review.googlesource.com/c/tools/+/676615
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2025-05-28 07:06:31 -07:00
Jonathan Amsterdam
7130f0f081 internal/mcp: meta and progress token
Meta is a struct that contains a map[string]any, and a ProgressToken
field.

Each Params and Result type has a Meta as a value field.

Meta marshals and unmarshals specially, so the ProgressToken field
becomes part of the map. The marshalling code is generalized in
anticipation of every Params and Result growing a map of additional
properties.

Change-Id: I6d2f34270d33501c96437f24f91ef3e51d20d955
Reviewed-on: https://go-review.googlesource.com/c/tools/+/674956
Reviewed-by: Sam Thanawalla <samthanawalla@google.com>
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2025-05-27 12:53:53 -07:00
Sam Thanawalla
dbbdf5a181 internal/mcp: add pagination for resources
Change-Id: I9f257fa09fe82e53087616859d1ad0c03f57dab6
Reviewed-on: https://go-review.googlesource.com/c/tools/+/675696
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2025-05-27 12:29:32 -07:00
cuishuang
b7d1ec0604 all: fix some function names and typos in comment
Change-Id: I8066b22cb87e09fb160de3b8ff2d8fdde6ec3dcf
Reviewed-on: https://go-review.googlesource.com/c/tools/+/675815
Reviewed-by: David Chase <drchase@google.com>
Auto-Submit: Alan Donovan <adonovan@google.com>
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2025-05-23 10:44:52 -07:00
Sam Thanawalla
8962b38ba5 internal/mcp: add pagination for tools
This CL adds paginating functionality for tools. It uses the gob encoder
for creating opaque cursors. More CLs to follow for paginating other features.

Change-Id: I1443c0213ceb6238d844a8eee9a0be52934f5cab
Reviewed-on: https://go-review.googlesource.com/c/tools/+/675055
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Jonathan Amsterdam <jba@google.com>
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2025-05-23 07:17:52 -07:00
Jonathan Amsterdam
b1780319e4 internal/mcp: future-proof prompt handling
Pass GetPromptParams as needed, in case that type ever gets additional
properties.

Change-Id: I83fa37bb2af5633a8c2bcdc47a85c3030dfe70fb
Reviewed-on: https://go-review.googlesource.com/c/tools/+/674895
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2025-05-22 15:06:03 -07:00
Jonathan Amsterdam
edda031578 internal/mcp: implement logging
Provide a ServerSession method that directly implements the spec
method.

Also provide a custom slog.Handler that writes a notification on each
log call. It uses a slog.JSONHandler to format the message as JSON, then
adds the additional fields of LoggingMessageParams.

I decided that the direct method should handle levels, since that is
in the spec, but that rate-limiting is an extra feature, so is only
provided in the slog handler.

Change-Id: I1190ca124e992e61fb633ac52ee3492c8e6d99c9
Reviewed-on: https://go-review.googlesource.com/c/tools/+/674498
Auto-Submit: Jonathan Amsterdam <jba@google.com>
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2025-05-22 15:02:13 -07:00
Jonathan Amsterdam
715e9f1935 internal/mcp: construct README with weave
Use the weave program from golang.org/x/example to weave together
the README text with buildable programs. This ensures the code in the
README compiles.

Change-Id: Ib5e10c8f808cc6d1ed4addbee784607e910ba30b
Reviewed-on: https://go-review.googlesource.com/c/tools/+/673796
Reviewed-by: Robert Findley <rfindley@google.com>
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2025-05-21 16:21:26 -07:00
Jonathan Amsterdam
ce5b6cd926 internal/mcp: add notifications
Add notification logic for intialization and list changes.

Change-Id: I1d392bb49d5995f2046c400da955a033ab2715ce
Reviewed-on: https://go-review.googlesource.com/c/tools/+/673775
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2025-05-21 16:01:46 -07:00
Rob Findley
ec8fb49c6b all: fix typos
Fix some typos found during the Google import of x/tools.

Change-Id: I8ea38d3e1bd09bedbc98ed8c8146e88e84aa051f
Reviewed-on: https://go-review.googlesource.com/c/tools/+/674975
Auto-Submit: Robert Findley <rfindley@google.com>
Reviewed-by: Hongxiang Jiang <hxjiang@golang.org>
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2025-05-21 07:52:35 -07:00
Sam Thanawalla
172901f3ac internal/mcp: keep an ordered list of feature keys
This change is necessary to support pagination which will be implemented
in subsequent CLs.

Change-Id: I8bc616a57463ea569dc7cadf1d4f06c69602ddd5
Reviewed-on: https://go-review.googlesource.com/c/tools/+/674135
Reviewed-by: Jonathan Amsterdam <jba@google.com>
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2025-05-20 13:37:12 -07:00
Rob Findley
eb76b5a6e0 internal/mcp: remove misplaced TODO comment
Remove a TODO that was in package doc position.

Change-Id: Ib98dbcd7d733fdf0059bc3ced1fd6a1008b91a26
Reviewed-on: https://go-review.googlesource.com/c/tools/+/674257
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2025-05-19 15:17:30 -07:00
Jonathan Amsterdam
74340f088d internal/mcp: generate method names
Augment the generator to create constants for all method names.

Change-Id: I858e516b1afec0aa3cf3b9852cbdfc16aec4c553
Reviewed-on: https://go-review.googlesource.com/c/tools/+/673177
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2025-05-19 11:16:06 -07:00
Jonathan Amsterdam
9bcc6c758f internal/mcp: sampling
Implement sampling (the CreateMessage method).

Change-Id: Ie44a671dd62831122b25cd7386b5bfcdece7ff60
Reviewed-on: https://go-review.googlesource.com/c/tools/+/673176
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2025-05-19 11:15:58 -07:00
Jonathan Amsterdam
bac1b78b4a internal/mcp: client middleware
Implement middleware for clients.

Make the middleware types generic so we can factor out code
from both peers.

I was able to make the request handler generic, with one weird trick
(see handleRequest).

The first three declarations of shared.go, and a few others as well,
are copied unchanged from middleware.go.

Change-Id: Ib3239d8fcfda022ddb5b554c38cff4cdbc3704c1
Reviewed-on: https://go-review.googlesource.com/c/tools/+/673635
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2025-05-19 11:15:45 -07:00
Jonathan Amsterdam
8361df724d internal/mcp: add the FileResourceHandler method
Provide secure reading of files on the local filesystem.

There are subtleties in path manipulation on Windows that I don't fully
understand, so I defer that work for now.

Change-Id: Ic11f4617dde4ac0b31ccd5b0a772bb2f56db026f
Reviewed-on: https://go-review.googlesource.com/c/tools/+/673196
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Reviewed-by: Sam Thanawalla <samthanawalla@google.com>
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2025-05-19 11:15:23 -07:00
Jonathan Amsterdam
1323fb5216 internal/mcp: dispatcher middleware
Implement the dispatcher middleware framework, allowing users to
wrap method dispatching with their own code.

The Dispatcher functions have an untyped params arg, but expect its
value to be a typed, unmarshaled XXXParams struct. That required
splitting the elegant dispatch[P, R] function into two parts, one
to do the unmarshaling and one to call the method. The nicest way
I could find to do that was to map from method names to a pair
of functions, one to unmarshal and one to call. We could also write
it as two switches on method name, which would require less machinery
but would duplicate the list of method names, already a tad fragile
because they are literal strings.

I also exported the initialize params and result, so user Dispatchers
could access them. All Params and Result types will have to be exported
for that reason.

Change-Id: Ie2c95cc17b4ef3d3d095dccdadb294e5f1590796
Reviewed-on: https://go-review.googlesource.com/c/tools/+/673515
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2025-05-16 11:24:52 -07:00
Rob Findley
7eadde0a23 internal/mcp/design: further clean-up
Do a pass through the design doc, adding a bit more clean-up and
commentary.

Additionally, update ServerTool and ServerPrompt to be consistent with
the design.

Change-Id: I1b75c4690d86fe8946d512cb36a1fc2938b3c883
Reviewed-on: https://go-review.googlesource.com/c/tools/+/672576
Reviewed-by: Jonathan Amsterdam <jba@google.com>
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2025-05-14 14:28:07 -07:00
Rob Findley
0b09f3ad5a internal/mcp: hide CancelledParams
Since cancellation is handled transparently, this type need not be
exported.

Change-Id: Id4e195b0c3bd49eca52587032a027ffa449eb9d1
Reviewed-on: https://go-review.googlesource.com/c/tools/+/672796
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2025-05-14 12:42:31 -07:00
Rob Findley
a8b98da480 internal/mcp: reinstate ClientSession
Add a logical client session type back to the SDK, to bring it closer to
the design. Also, remove 'ConnectionOptions', which is better
implemented using middleware, and reimplement logging as a
LoggingTransport middleware, which is also added to the design.

Change-Id: I908b4f837d513ffc60ae5b6171a31519cffafebc
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2025-05-14 12:41:58 -07:00
Rob Findley
dbf57af24b internal/mcp: rename LocalTransport->InMemoryTransport, and document
Update the design to mention our in-memory transport, since it is
generally useful, and update the implementation to use distinct types
for InMemoryTransport and StdIOTransport (the fact that they are both
implemented as an io.ReadWriteCloser is an implementation detail).

Change-Id: I8228ccf2092a56a730c113c4db105fb492cce112
Reviewed-on: https://go-review.googlesource.com/c/tools/+/672715
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2025-05-14 10:11:26 -07:00
Rob Findley
ac828d5a82 internal/mcp: rename ServerConnection->ServerSession
Bring the Server implementation up to date with the spec by renaming
ServerConnection to ServerSession. Also update variable names, which
were in various states of disarray from the multiple renamings of this
type.

Change-Id: I4aec883db6d0500fb91e6daa51b702614877cf8a
Reviewed-on: https://go-review.googlesource.com/c/tools/+/672655
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2025-05-14 10:10:28 -07:00
Jonathan Amsterdam
81a8ece2dd internal/mcp: resource tweaks
Get the name and signature of the handler right.

Change-Id: I743aaaee45cc07a741ab8ad16e90e1b1d5519b64
Reviewed-on: https://go-review.googlesource.com/c/tools/+/672336
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2025-05-14 08:50:33 -07:00
Jonathan Amsterdam
bbd253ee4c internal/mcp: use RawMessage for tool args
Change the type of CallToolParams.Arguments to json.RawMessage.

Change-Id: Ief16ef261b9f41566a1a16efc60a9382a8d414eb
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2025-05-14 06:23:29 -07:00
Jonathan Amsterdam
6394485a3d internal/mcp: change CallTool signature
CallTool takes a tool name, arguments, and an options struct.

Also, pass the params to ToolHandler.

Update the design doc accordingly.

Change-Id: I21b7995b607bea976ad708ebb6ac0716018f39cb
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2025-05-14 06:23:21 -07:00
Jonathan Amsterdam
4721f501df internal/mcp: change function signatures match design doc
To ensure backward compatibility, every method in the spec now takes a
*Params struct and returns a *Result struct.

CallTools is an exception: we'll change that in the next CL.

Change-Id: I58835239c67582401b8c9c2d070702d270131c08
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2025-05-14 06:23:12 -07:00
Jonathan Amsterdam
02fa1b3ea6 internal/mcp: pointerize all the things
Use pointers for the protocol's struct types, to future-proof against
them getting large.

Change-Id: I55b204080a41c8140539697ba264e502e912e613
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2025-05-14 06:22:56 -07:00
Jonathan Amsterdam
7b100d7b30 internal/mcp: document content constructors
Also, make sure that NewBlobResourceContents creates a Blob.

Change-Id: I2f0fe2ac6410d6b155deb2c8643a40bc73e25cd4
Reviewed-on: https://go-review.googlesource.com/c/tools/+/672418
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2025-05-14 06:22:48 -07:00
Jonathan Amsterdam
aedbba98ee internal/mcp: remove omitzero
To be compatible with Go 1.23, we cannot use the
encoding/json "omitzero" option. Replace with a
custom MarshalJSON method.

Change-Id: Ied615ea04fb20e2459f9ed20ef03c81edbc74961
Reviewed-on: https://go-review.googlesource.com/c/tools/+/672417
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2025-05-13 15:48:32 -07:00
Rob Findley
dac5be2c50 internal/mcp: simplify content
Now that the protocol package is merged into the mcp package, clean up
the higher level 'Content' union types, in favor of types constructors.

Change-Id: I37bedb0ff0a296eef799ba65c37ca7f94ee1dbbe
Reviewed-on: https://go-review.googlesource.com/c/tools/+/672415
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2025-05-13 15:03:25 -07:00
Rob Findley
4f6510b9ae internal/mcp: merge the protocol package into mcp
In accordance with the updated design, merge the protocol package into
the mcp package. To do so, rename protocol.Content to WireContent and
protocol.ResourceContents to WireResource.

Also, remove some stray logging in readResource.

Change-Id: I76f61ce8d67dd3ac520ef2e1959ade0a0785a480
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2025-05-13 14:43:46 -07:00
Jonathan Amsterdam
1ae23e7031 internal/mcp: implement resources
Implementation of resources.

This follows the design sketched in design/design.md, except for
Server.FileResourceHandler, which will be in a forthcoming CL.

As the spec recommends, the server verifies an incoming URI from the
client against its list of resources, to make sure the URI came from one
of them.

Some things that aren't in the design doc:
- I provide an exported function that creates a "resource not found"
  jsonrpc2.WireEror error for server authors to return.
  A wrinkle: the MCP spec defines the error code for
  "resource not found" as -32002 [1]. That code is reserved for use
  by implementations of JSON-RPC, not applications. That matters to us
  because our JSON-RPC implementation already uses that code for the
  "server closing" error. I filed a bug against MCP about it [2] and
  chose a different code for the "resource not found" error.

- As a slight convenience, I fill in some fields in the
  ReadResourceResult if the handler doesn't set them.

[1] https://modelcontextprotocol.io/specification/2025-03-26/server/resources#error-handling
[2] https://github.com/modelcontextprotocol/modelcontextprotocol/issues/509

Change-Id: I06153da982ea00748a3691ded923448a880cea2a
Reviewed-on: https://go-review.googlesource.com/c/tools/+/671363
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Reviewed-by: Robert Findley <rfindley@google.com>
2025-05-13 11:39:49 -07:00
Jonathan Amsterdam
71265ba130 internal/mcp: adjust content types
- Change the names of some content-related types to better match
  the spec. Most notably, rename Resource to EmbeddedResource,
  because the former has a different meaning in the spec.

- Use []byte intead of string where the spec says "base64-encoded data."

- Unexport EmbeddedResource.ToWire.

Change-Id: I9f65efaadadda1b3abc0e58c64a743af1a72852c
Reviewed-on: https://go-review.googlesource.com/c/tools/+/671362
Reviewed-by: Robert Findley <rfindley@google.com>
TryBot-Bypass: Jonathan Amsterdam <jba@google.com>
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2025-05-13 08:21:01 -07:00
Jonathan Amsterdam
51ea6a4a72 internal/mcp/protocol: make type name more convenient
You can now write "*" for a name in a config to use the original
name.

Also, fix a bug in dealing with initialisms.

Change-Id: I4d5d0acb1200fff6500644457ec34c5026d63f9f
Reviewed-on: https://go-review.googlesource.com/c/tools/+/671361
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Sam Thanawalla <samthanawalla@google.com>
2025-05-13 08:19:37 -07:00
Jonathan Amsterdam
5004d3e1bb internal/mcp: implement roots
Add support for roots.

Change-Id: Ia50abc88f0047238272d698f30ce615b1a8fd486
Reviewed-on: https://go-review.googlesource.com/c/tools/+/671360
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
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Reviewed-by: Robert Findley <rfindley@google.com>
2025-05-13 07:52:49 -07:00
Jonathan Amsterdam
37ae90648b internal/mcp/protocol: featureSet[T]
What the spec calls "lists" of features (tools, prompts and so on)
are actually sets. Define a common data structure we can use to
implement all of them, and use it for server tools and prompts.

Change-Id: I257d0776b87a746ff23cd49ebcc7b317f4ea65e1
Reviewed-on: https://go-review.googlesource.com/c/tools/+/671359
Reviewed-by: Robert Findley <rfindley@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
2025-05-12 11:03:35 -07:00
Rob Findley
d174d6405a internal/mcp/design: discuss generated protocol types
Discuss generated protocol types, and expand on the section on package
layout to make it clearer how they fit in to the SDK.

Change-Id: I3beaa86c2396e0cee41dcc8eac06d93c54cb96df
Reviewed-on: https://go-review.googlesource.com/c/tools/+/671016
Reviewed-by: Jonathan Amsterdam <jba@google.com>
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2025-05-08 13:02:41 -07:00
Rob Findley
e0d4191c70 internal/mcp: a new extensibility point for HTTP transports
Expose the SSEServerTransport type, so that clients can customize the
handling of sessions and endpoints by writing their own HTTP handler.
This is similar to the behavior of the typescript SDK.

Also, finish documenting transports in the design doc.

Change-Id: Ief5aa8424ba2946a9615e366969a4750f40224a8
Reviewed-on: https://go-review.googlesource.com/c/tools/+/671015
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2025-05-08 12:19:33 -07:00
Jonathan Amsterdam
5bcbf820f2 internal/mcp/protocol: spell "Id" idiomatically
Enhance the generator so that it recognizes initialisms like "Id" and
writes them in all caps, as is idiomatic for Go.

Also, fix the import path of jsonschema in the generated code.

Change-Id: Ib12e9fbd543d360035d5e324f0aefca584ac7c85
Reviewed-on: https://go-review.googlesource.com/c/tools/+/670916
Auto-Submit: Jonathan Amsterdam <jba@google.com>
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Reviewed-by: Robert Findley <rfindley@google.com>
2025-05-08 08:22:14 -07:00
Rob Findley
390d437d4f internal/mcp/design: start a full design doc, with stubs
Start writing up a formal design doc for an MCP SDK based on what we've
learned from the prototype. Include discussion of package layout,
jsonrpc2, and transport. Lay out the rest of the design sections,
leaving stub comments describing what they should cover.

Change-Id: Id0e5b408eac8c0acb5ef90a32d0d69473d8e83f0
Reviewed-on: https://go-review.googlesource.com/c/tools/+/670536
Reviewed-by: Jonathan Amsterdam <jba@google.com>
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Auto-Submit: Robert Findley <rfindley@google.com>
2025-05-07 13:50:30 -07:00
Rob Findley
347a1a0078 internal/mcp: rename ClientConnection to ServerConnection
It's too confusing that you send server requests through the Client, and
send client requests through the ClientConnection. Rename
ClientConnection to ServerConnection, so that the types on the
server side of the control diagram start with 'Server'.

Change-Id: Idfd27af464a9296a2341cd23b2075cd9d0eb6b45
Reviewed-on: https://go-review.googlesource.com/c/tools/+/670538
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Reviewed-by: Jonathan Amsterdam <jba@google.com>
2025-05-07 10:17:38 -07:00
Jonathan Amsterdam
e0e304e51e internal/mcp: rename Make* to New*
Change-Id: I8d3d2ca125b7c24dd265937c4fe910ea823ab811
Reviewed-on: https://go-review.googlesource.com/c/tools/+/670537
Reviewed-by: Robert Findley <rfindley@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
2025-05-07 09:32:55 -07:00
Jonathan Amsterdam
f8098af1c5 internal/mcp: NewClient takes Transport
Pass the client Transport to NewClient instead of Connect.
Combine the ConnectionOptions with the ClientOptions.

Change-Id: I3acd6cf6d5bf46666742f2a73e2acaef2057ea77
Reviewed-on: https://go-review.googlesource.com/c/tools/+/670215
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Robert Findley <rfindley@google.com>
2025-05-06 12:19:25 -07:00