While creating a basic MCP server in
https://github.com/openai/codex/pull/792, I discovered a number of bugs
with the initial `mcp-types` crate that I needed to fix in order to
implement the server.
For example, I discovered that when serializing a message, `"jsonrpc":
"2.0"` was not being included.
I changed the codegen so that the field is added as:
```rust
#[serde(rename = "jsonrpc", default = "default_jsonrpc")]
pub jsonrpc: String,
```
This ensures that the field is serialized as `"2.0"`, though the field
still has to be assigned, which is tedious. I may experiment with
`Default` or something else in the future. (I also considered creating a
custom serializer, but I'm not sure it's worth the trouble.)
While here, I also added `MCP_SCHEMA_VERSION` and `JSONRPC_VERSION` as
`pub const`s for the crate.
I also discovered that MCP rejects sending `null` for optional fields,
so I had to add `#[serde(skip_serializing_if = "Option::is_none")]` on
`Option` fields.
---
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