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refactor: extract tool fetch loop body for safe cleanup #319

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Merged
aojea merged 1 commit into from
Aug 31, 2026
+65 −45
Merged

refactor: extract tool fetch loop body for safe cleanup #319

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110 changes: 65 additions & 45 deletions internal/node/mcp_handlers.go
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Original file line number Diff line number Diff line change
Expand Up @@ -591,58 +591,78 @@ func (n *SamNode) fetchRemoteToolCatalogue(ctx context.Context, targetPeer peer.
connectService = api.MCPServicePrefix + connectService
}

n.preparePeerAddrs(ctx, targetPeer)
session, cleanup, err := n.ConnectMCPSession(ctx, targetPeer, connectService, nil)
if err != nil {
if errors.Is(err, ErrAuthRejected) {
// Not authorized for this service: omit it entirely rather than
// leaking its existence ("what you see is what you can do", #176).
logger.Debugf("Hiding unauthorized service %s from discovery: %v", targetService, err)
continue
}
logger.Debugf("Failed to connect MCP session for service %s: %v", targetService, err)
if serviceNameFilter == "" || connectService == serviceNameFilter {
rows = append(rows, remoteToolRow{
PeerID: targetPeer.String(),
ToolName: connectService,
Error: fmt.Sprintf("failed to connect: %v", err),
})
}
continue
if err := ctx.Err(); err != nil {
return nil, err
}

listRes, err := session.ListTools(ctx, nil)
if err == nil && listRes != nil {
for _, t := range listRes.Tools {
if t == nil {
continue
}
t.Name = connectService + "/" + t.Name
if serviceNameFilter != "" && !strings.HasPrefix(t.Name, serviceNameFilter+"/") {
continue
}
rows = append(rows, remoteToolRow{
PeerID: targetPeer.String(),
ToolName: t.Name,
Description: t.Description,
})
}
} else {
if serviceNameFilter == "" || connectService == serviceNameFilter {
rows = append(rows, remoteToolRow{
PeerID: targetPeer.String(),
ToolName: targetService,
Error: fmt.Sprintf("failed to list tools: %v", err),
})
}
}

cleanup()
rows = append(rows, n.fetchToolsForRemoteService(ctx, targetPeer, connectService, targetService, serviceNameFilter)...)

@gemini-code-assist gemini-code-assist Bot Aug 31, 2026

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medium

When fetching the remote tool catalogue, if the context is canceled or times out, the loop will continue to execute for all remaining services. This results in redundant connection attempts and generates multiple misleading error rows (e.g., 'failed to connect: context canceled'). Checking ctx.Err() at the start of each iteration allows the function to return early and cleanly when the context is no longer active.

		if err := ctx.Err(); err != nil {
			return nil, err
		}
		rows = append(rows, n.fetchToolsForRemoteService(ctx, targetPeer, connectService, targetService, serviceNameFilter)...)

}

return rows, nil
}

// fetchToolsForRemoteService opens one MCP session to a single remote service,
// lists its tools, and returns the matching rows. Per-service failures are
// encoded as error rows (or omitted for AuthRejected); the session is always
// closed when the function returns.
func (n *SamNode) fetchToolsForRemoteService(
ctx context.Context,
targetPeer peer.ID,
connectService, targetService, serviceNameFilter string,
) []remoteToolRow {
n.preparePeerAddrs(ctx, targetPeer)
session, cleanup, err := n.ConnectMCPSession(ctx, targetPeer, connectService, nil)
if err != nil {
if errors.Is(err, ErrAuthRejected) {
// Not authorized for this service: omit it entirely rather than
// leaking its existence ("what you see is what you can do", #176).
logger.Debugf("Hiding unauthorized service %s from discovery: %v", targetService, err)
return nil
}
logger.Debugf("Failed to connect MCP session for service %s: %v", targetService, err)
if serviceNameFilter == "" || connectService == serviceNameFilter {
return []remoteToolRow{{
PeerID: targetPeer.String(),
ToolName: connectService,
Error: fmt.Sprintf("failed to connect: %v", err),
}}
}
return nil
}
defer cleanup()

listRes, err := session.ListTools(ctx, nil)
if err != nil {
if serviceNameFilter == "" || connectService == serviceNameFilter {
return []remoteToolRow{{
PeerID: targetPeer.String(),
ToolName: targetService,
Error: fmt.Sprintf("failed to list tools: %v", err),
}}
}
return nil
}
if listRes == nil {
return nil
}
var rows []remoteToolRow
for _, t := range listRes.Tools {
if t == nil {
continue
}
t.Name = connectService + "/" + t.Name
if serviceNameFilter != "" && !strings.HasPrefix(t.Name, serviceNameFilter+"/") {
continue
}
rows = append(rows, remoteToolRow{
PeerID: targetPeer.String(),
ToolName: t.Name,
Description: t.Description,
})
}
return rows
}

// fanOutFetch queries each peer's tool catalogue concurrently with a
// small cap and returns the filtered rows. Per-peer failures are
// logged at debug level and skipped — best-effort mesh-wide fetch.
Expand Down
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