Add support for SSE transport, as defined by version 2024-11-05 and
2025-03-26 of the MCP spec.
In order to achieve this, the jsonrpc2 stream must be abstracted so that
we can implement it across multiple HTTP requests. This required some
refactoring of the jsonrpc2_v2 package, so that we can avoid the
Dialer/Binder interfaces and construct the Connection directly from its
constituent primitives.
Change-Id: Id627b5b5a474d92f2c613cfad904d14611e7c768
Reviewed-on: https://go-review.googlesource.com/c/tools/+/667475
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This CL contains an minimal prototype of an MCP SDK, using the
"new" jsonrpc2_v2 package (similar to x/exp/jsonrpc2).
Much is still yet to do, but this initial version addressed the
following aspects:
- Support for newline delimited JSONRPC2 framing, and message logging.
- A generated protocol package, containing type definitions to be used
in transport.
- A minimal jsonschema package to be used for both reading the MCP spec,
and for serving Tool input schemas.
- A transport abstraction, and two transport implementations: stdio, and
local (for testing).
- Client and Server types, to be configured with features and then
connected using their Connect methods, which return (respectively) a
ServerConnection and ClientConnection object.
- A minimal binding API for tools.
A catalog of things not yet done is in doc.go, but we should review this
CL eagerly, as it contains the fundamental building blocks of an
eventual SDK.
It is the intention that this package is more-or-less standalone, as it
may eventually be carved out into a separate repository. As such, its
only dependency within x/tools is jsonrpc2_v2, and the only change
required to that package is to expose a callback when the connection is
closed.
Change-Id: Ib66018961014f85a8884d56ab721d5642c98443c
Reviewed-on: https://go-review.googlesource.com/c/tools/+/667036
Reviewed-by: Jonathan Amsterdam <jba@google.com>
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Serve had a misleading name and signature: it did not actually block
on serving the connection, and never returned a non-nil error.
Updates golang/go#56281.
Change-Id: Ia6df0ba20066811b0551df3b3267dff2fffd7881
Reviewed-on: https://go-review.googlesource.com/c/tools/+/443678
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Also make (*Connection).Close safe to call from Bind.
A jsonrpc2_v2.Server has no good way to report an error from Bind.
If the Server saves the error to return from its own Wait method, that
might not ever actually happen: Wait waits for in-flight connections
to complete, but if some existing connection stays up then Wait will
not return.
If the Server goes ahead with establishing the connection and installs
its own Handler, that Handler needs to decide whether to serve the
error from Bind or something more opaque, and at that point Bind may
as well return a handler that makes that choice more precisely.
If the Server merely logs the error and closes the Connection, then
the Bind method itself may as well do that directly too.
It seems to me that the only winning move is not to play. Only Bind is
in a position to decide how to handle its errors appropriately, so it
should not return them to the Server.
Updates golang/go#56281.
Change-Id: I07dc43ddf31253ce23da21a92d2b6c0f8d4b3afe
Reviewed-on: https://go-review.googlesource.com/c/tools/+/443677
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Also implement and use the Shutdown method, which was mentioned in a
doc comment in CL 292169 but not actually present at that time.
With proper synchronization, we don't need heuristics to determine
whether an error is due to a connection or listener being closed.
We know whether we have called Close (and why), and we can assume
that if we have called Close then that is probably the reason for
any returned error.
Fixesgolang/go#56281.
Change-Id: I5e0ed7db0f736ca8df8cd8cf556b674e7a863a69
Reviewed-on: https://go-review.googlesource.com/c/tools/+/443675
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Prior to this CL, (*Server).run only filters out inactive connections
when it accepts a new connection. If existing connections complete,
their associated resources can't be garbage-collected until either the
next connection is accepted or the Listener is closed.
This change moves the open-connection accounting to an explicit hook
passed to newConnection, eliminating the need to call Wait entirely.
For golang/go#46047
Change-Id: I3732cb463fcea0c142f17f2b1510fdfd2dbc81da
Reviewed-on: https://go-review.googlesource.com/c/tools/+/388774
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This change fixes the semantics of Close to actually wait for
in-flight requests before closing the ReadWriteCloser. (Previously,
the Close method closed the ReadWriteCloser immediately, which I
suspect is what led to many of the failures observed in
golang/go#49387 and golang/go#46520.)
It achieves this by explicitly tracking the number of in-flight
requests, including requests with pending async responses, and
explicitly rejecting new Call requests (while keeping the read loop
open!) once Close has begun.
To make it easier for me to reason about the request lifetimes, I
reduced the number of long-lived goroutines from three to just one
(the Read loop), with an additional Handler goroutine that runs only
while the Handler queue is non-empty. Now, it is clearer (I hope!)
that the number of in-flight async requests strictly decreases
after Close has begun, even though the Read goroutine continues
to read requests (and, importantly, responses) and to forward
Notifications to the preempter.
For golang/go#49387
For golang/go#46520
Change-Id: Idf5960f848108a7ced78c5382099c8692e9b181e
Reviewed-on: https://go-review.googlesource.com/c/tools/+/388134
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This eliminates a race between a successful Accept call and a
concurrent Close call, which previously could have shut down the
'run' goroutine before Accept sent to the newConns channel, causing
Accept to deadlock.
In fact, it eliminates the long-running 'run' goroutine entirely
(replacing it with a time.Timer), and in the process avoids leaking
O(N) closed connections when only the very first one is long-lived.
It also eliminates a potential double-Close bug: if the run method had
called l.wrapped.Close due to an idle timeout, a subsequent call to
Close would invoke l.wrapped.Close again. The io.Closer method
explicitly documents doubled Close calls as undefined behavior, and
many Closer implementations (especially test fakes) panic or deadlock
in that case.
It also eliminates a timer leak if the Listener rapidly oscillates
between active and idle: previously the implementation used
time.After, but it now uses an explicit time.Timer which can be
stopped (and garbage-collected) when the listener becomes active.
Idleness is now tracked based on the connection's Close method rather
than Read: we have no guarantee in general that a caller will ever
actually invoke Read (if, for example, they Close the connection as
soon as it is dialed), but we can reasonably expect a caller to at
least try to ensure that Close is always called.
We now also verify, using a finalizer on a best-effort basis, that the
Close method on each connection is called. We use the finalizer to
verify the Close call — rather than to close the connection implicitly
— because closing the connection in a finalizer would delay the start
of the idle timer by an arbitrary and unbounded duration after the
last connection is actually no longer in use.
Fixesgolang/go#46047.
Fixesgolang/go#51435.
For golang/go#46520.
For golang/go#49387.
Change-Id: If173a3ed7a44aff14734b72c8340122e8d020f26
Reviewed-on: https://go-review.googlesource.com/c/tools/+/388597
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As of golang/go#50827, gopls no longer needs to build at Go 1.12. This
was the only reason to continue using xerrors in the jsonrpc2 libraries.
Remove this usage as a step toward eliminating the xerrors dependency
from x/tools.
For golang/go#52442
Change-Id: I1a0a1bbf57e6606c66b99b27439adf6f65c26a60
Reviewed-on: https://go-review.googlesource.com/c/tools/+/401155
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The lsprpc package needs to wait on the newly bound connection to
perform some tear-down, so it must be safe to call conn.Wait from Bind.
Achieve this by switching async from an init pattern to a constructor.
This means moving async fields to pointers, but since they weren't safe
to use prior to initialization anyway this feels correct.
Change-Id: I4f93980915e0b568fbf2db3cd7d062adf06e4b99
Reviewed-on: https://go-review.googlesource.com/c/tools/+/330929
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There was already handling in isClosingErr for errors from Stdin/Stdout
and TCP connections. Add handling for io.Pipe closing errors.
Change-Id: I8d171ab49a3fffe0fca9f0482f6b92d61b1fae1f
Reviewed-on: https://go-review.googlesource.com/c/tools/+/320849
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