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mcp: avoid "null" in structuredContent

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Avoid a typed nil in structuredContent (yet another typed nil), leading
to "null" on the wire.

Fixes #417
This commit is contained in:
Rob Findley 2025-09-04 19:58:12 +00:00 • committed by Robert Findley
commit 9d34aff732
1 changed files with 54 additions and 18 deletions
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26
mcp/server.go
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@ -267,19 +267,21 @@ func toolForErr[In, Out any](t *Tool, h ToolHandlerFor[In, Out]) (*Tool, ToolHan
outval = elemZero
}
}
outbytes, err := json.Marshal(outval)
if err != nil {
return nil, fmt.Errorf("marshaling output: %w", err)
}
res.StructuredContent = json.RawMessage(outbytes) // avoid a second marshal over the wire
if outval != nil {
outbytes, err := json.Marshal(outval)
if err != nil {
return nil, fmt.Errorf("marshaling output: %w", err)
}
res.StructuredContent = json.RawMessage(outbytes) // avoid a second marshal over the wire
// If the Content field isn't being used, return the serialized JSON in a
// TextContent block, as the spec suggests:
// https://modelcontextprotocol.io/specification/2025-06-18/server/tools#structured-content.
if res.Content == nil {
res.Content = []Content{&TextContent{
Text: string(outbytes),
}}
// If the Content field isn't being used, return the serialized JSON in a
// TextContent block, as the spec suggests:
// https://modelcontextprotocol.io/specification/2025-06-18/server/tools#structured-content.
if res.Content == nil {
res.Content = []Content{&TextContent{
Text: string(outbytes),
}}
}
}
return res, nil
} // end of handler