## Summary
Add `maxRequestBodySize` parameter to
`StreamableHttpServerTransport.Configuration`, allowing consumers to set
a custom request body size limit lower than the default 4 MB.
- Add `maxRequestBodySize: Long` property to `Configuration` with a
default of 4 MB (`4,194,304` bytes)
- Replace hardcoded `MAXIMUM_MESSAGE_SIZE` constant with the
configurable value in `parseBody()`
- Use `Long` for content-length comparison to avoid `Int` overflow on
large values
## Motivation and Context
Closes#521
The `StreamableHttpServerTransport` has a hardcoded 4 MB request body
limit. Consumers who need a lower limit currently have to manually count
the request payload size before passing it to the SDK. This change makes
the limit configurable via `Configuration`.
## How Has This Been Tested?
- Existing unit tests continue to pass (default 4 MB behavior unchanged)
- Added `POST with custom max request body size rejects oversized
payload` — verifies `PayloadTooLarge` is returned for payloads exceeding
the custom limit
- Added `POST at exactly custom max request body size is not rejected as
payload too large` — verifies payloads at exactly the limit are not
rejected by the size check
```bash
./gradlew :kotlin-sdk-server:jvmTest --tests "*.StreamableHttpServerTransportTest"
```
## Breaking Changes
None. The new parameter has a default value matching the previous
hardcoded limit.
## Types of changes
- [ ] Bug fix (non-breaking change which fixes an issue)
- [x] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)
- [ ] Documentation update
## Checklist
- [x] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [x] My code follows the repository's style guidelines
- [x] New and existing tests pass locally
- [x] I have added appropriate error handling
- [x] I have added or updated documentation as needed
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