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mcp: fix ListTools panic and null normalization on malformed tools #1120

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Merged
guglielmo-san merged 2 commits into from
Jul 30, 2026
+15 −0
Merged

mcp: fix ListTools panic and null normalization on malformed tools #1120

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659fdb5
mcp: fix ListTools panic and null normalization on malformed tools
n0liu Jul 29, 2026
b73df06
mcp: address review feedback
n0liu Jul 30, 2026
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6 changes: 6 additions & 0 deletions mcp/streamable_headers.go
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Original file line number Diff line number Diff line change
Expand Up @@ -262,6 +262,12 @@ func filterValidTools(logger *slog.Logger, tools []*Tool) []*Tool {
logger = ensureLogger(logger)
result := make([]*Tool, 0, len(tools))
for _, tool := range tools {
// A nil tool (e.g. from a malformed "tools":[null] response) is
// invalid; exclude it instead of dereferencing it.
if tool == nil {
logger.Error("excluding nil tool from tools/list")
continue
}
if err := validateParamHeaderAnnotations(tool); err != nil {
logger.Error("excluding tool from tools/list", "tool", tool.Name, "error", err)
continue
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9 changes: 9 additions & 0 deletions mcp/streamable_headers_test.go
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Expand Up @@ -969,6 +969,15 @@ func TestFilterValidTools(t *testing.T) {
t.Errorf("filterValidTools returned [%s, %s, %s, %s], want [valid, plain, nested-valid, valid-jsonschema]",
result[0].Name, result[1].Name, result[2].Name, result[3].Name)
}

// Regression for #1119: a malformed "tools":[null] response must not panic;
// nil tools are treated as invalid and excluded.
if got := filterValidTools(nil, []*Tool{nil}); len(got) != 0 {
t.Errorf("filterValidTools([nil]) returned %d tools, want 0", len(got))
}
if got := filterValidTools(nil, []*Tool{nil, valid, nil}); len(got) != 1 || got[0].Name != "valid" {
t.Errorf("filterValidTools([nil, valid, nil]) = %d tools, want [valid]", len(got))
}
}

func TestSetStandardHeadersWithParamHeaders(t *testing.T) {
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