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fix(vmcp): allow server/discover in peer health probes (PAIINFRA-399) #28

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Merged
carlos-lopez-vecino merged 1 commit into from
Oct 26, 2026
Merged

fix(vmcp): allow server/discover in peer health probes (PAIINFRA-399) #28

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6 changes: 6 additions & 0 deletions pkg/vmcp/server/peer_probe.go
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Original file line number Diff line number Diff line change
Expand Up @@ -27,8 +27,14 @@ type peerProbeKey struct{}
// peerProbeMethods are the MCP methods a peer probe may send: the handshake and
// the capability lists that the health checker's ListCapabilities runs. A probe
// never calls a tool, reads a resource or gets a prompt.
//
// server/discover is the Modern (2026-07-28) handshake. Once the peer has
// cached a backend as Modern, its health checker opens with it instead of
// initialize. Refusing it makes the peer read a 403 as an auth failure, mark
// the backend unauthenticated and open its circuit breaker.
var peerProbeMethods = map[string]bool{
"initialize": true,
"server/discover": true,
"notifications/initialized": true,
"ping": true,
"tools/list": true,
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10 changes: 10 additions & 0 deletions pkg/vmcp/server/serve_health_probe_test.go
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Expand Up @@ -30,6 +30,14 @@ func TestPeerProbeMiddleware(t *testing.T) {
listBody = `{"jsonrpc":"2.0","id":2,"method":"tools/list","params":{}}`
callBody = `{"jsonrpc":"2.0","id":3,"method":"tools/call","params":{"name":"echo"}}`
getBody = `{"jsonrpc":"2.0","id":4,"method":"prompts/get","params":{"name":"p"}}`
// The Modern (2026-07-28) health probe opens with server/discover
// instead of initialize (pkg/vmcp/client probeRevision and
// modernListCapabilities).
discoverBody = `{"jsonrpc":"2.0","id":5,"method":"server/discover","params":{"_meta":{` +
`"io.modelcontextprotocol/protocolVersion":"2026-07-28",` +
`"io.modelcontextprotocol/clientCapabilities":{},` +
`"io.modelcontextprotocol/clientInfo":{"name":"toolhive-vmcp","version":"test"}}}}`
listenBody = `{"jsonrpc":"2.0","id":6,"method":"subscriptions/listen","params":{}}`
)
tests := []struct {
name string
Expand All @@ -41,6 +49,8 @@ func TestPeerProbeMiddleware(t *testing.T) {
}{
{"probe initialize is marked", http.MethodPost, health.ProbeHeaderValue, initBody, true, true},
{"probe tools/list is marked", http.MethodPost, health.ProbeHeaderValue, listBody, true, true},
{"probe server/discover is marked", http.MethodPost, health.ProbeHeaderValue, discoverBody, true, true},
{"probe subscriptions/listen is refused", http.MethodPost, health.ProbeHeaderValue, listenBody, false, false},
{"probe tools/call is refused", http.MethodPost, health.ProbeHeaderValue, callBody, false, false},
{"probe prompts/get is refused", http.MethodPost, health.ProbeHeaderValue, getBody, false, false},
{"probe with an unparsable body is refused", http.MethodPost, health.ProbeHeaderValue, `not json`, false, false},
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