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mcp: handle bad or missing params (#210)

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Audit all cases where params must not be null, and enforce this using
methodInfo via a new methodFlags bitfield that parameterizes method
requirements. Write extensive conformance tests catching all the
(server-side) crashes that were possible.

We should go further and validate schema against the spec, but that is
more indirect, more complicated, and potentially slower. For now we
adopt this more explicit approach.

Still TODO in a subsequent CL: verify the client side of this with
client conformance tests.

Additionally, improve some error messages that were redundant or leaked
internal implementation details.

Fixes #195
This commit is contained in:
Robert Findley 2025-07-31 10:57:59 -04:00 • committed by GitHub
commit b34ba2149d
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1 changed files with 170 additions and 52 deletions
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24
mcp/client.go
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@ -286,17 +286,21 @@ func (c *Client) AddReceivingMiddleware(middleware ...Middleware[*ClientSession]
}
// clientMethodInfos maps from the RPC method name to serverMethodInfos.
//
// The 'allowMissingParams' values are extracted from the protocol schema.
// TODO(rfindley): actually load and validate the protocol schema, rather than
// curating these method flags.
var clientMethodInfos = map[string]methodInfo{
methodComplete: newMethodInfo(sessionMethod((*ClientSession).Complete), true),
methodPing: newMethodInfo(sessionMethod((*ClientSession).ping), true),
methodListRoots: newMethodInfo(clientMethod((*Client).listRoots), true),
methodCreateMessage: newMethodInfo(clientMethod((*Client).createMessage), true),
notificationToolListChanged: newMethodInfo(clientMethod((*Client).callToolChangedHandler), false),
notificationPromptListChanged: newMethodInfo(clientMethod((*Client).callPromptChangedHandler), false),
notificationResourceListChanged: newMethodInfo(clientMethod((*Client).callResourceChangedHandler), false),
notificationResourceUpdated: newMethodInfo(clientMethod((*Client).callResourceUpdatedHandler), false),
notificationLoggingMessage: newMethodInfo(clientMethod((*Client).callLoggingHandler), false),
notificationProgress: newMethodInfo(sessionMethod((*ClientSession).callProgressNotificationHandler), false),
methodComplete: newMethodInfo(sessionMethod((*ClientSession).Complete), 0),
methodPing: newMethodInfo(sessionMethod((*ClientSession).ping), missingParamsOK),
methodListRoots: newMethodInfo(clientMethod((*Client).listRoots), missingParamsOK),
methodCreateMessage: newMethodInfo(clientMethod((*Client).createMessage), 0),
notificationToolListChanged: newMethodInfo(clientMethod((*Client).callToolChangedHandler), notification|missingParamsOK),
notificationPromptListChanged: newMethodInfo(clientMethod((*Client).callPromptChangedHandler), notification|missingParamsOK),
notificationResourceListChanged: newMethodInfo(clientMethod((*Client).callResourceChangedHandler), notification|missingParamsOK),
notificationResourceUpdated: newMethodInfo(clientMethod((*Client).callResourceUpdatedHandler), notification|missingParamsOK),
notificationLoggingMessage: newMethodInfo(clientMethod((*Client).callLoggingHandler), notification),
notificationProgress: newMethodInfo(sessionMethod((*ClientSession).callProgressNotificationHandler), notification),
}
func (cs *ClientSession) sendingMethodInfos() map[string]methodInfo {