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feat(server): support configurable max request payload size (#646)

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## 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
This commit is contained in:
johny 2026-04-01 19:57:17 +09:00 • committed by GitHub
commit 6ce9ff81e7
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1 changed files with 73 additions and 10 deletions
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5
kotlin-sdk-server/api/kotlin-sdk-server.api
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@ -227,13 +227,14 @@ public final class io/modelcontextprotocol/kotlin/sdk/server/StreamableHttpServe
}
public final class io/modelcontextprotocol/kotlin/sdk/server/StreamableHttpServerTransport$Configuration {
public synthetic fun <init> (ZZLjava/util/List;Ljava/util/List;Lio/modelcontextprotocol/kotlin/sdk/server/EventStore;Lkotlin/time/Duration;ILkotlin/jvm/internal/DefaultConstructorMarker;)V
public synthetic fun <init> (ZZLjava/util/List;Ljava/util/List;Lio/modelcontextprotocol/kotlin/sdk/server/EventStore;Lkotlin/time/Duration;Lkotlin/jvm/internal/DefaultConstructorMarker;)V
public synthetic fun <init> (ZZLjava/util/List;Ljava/util/List;Lio/modelcontextprotocol/kotlin/sdk/server/EventStore;Lkotlin/time/Duration;JILkotlin/jvm/internal/DefaultConstructorMarker;)V
public synthetic fun <init> (ZZLjava/util/List;Ljava/util/List;Lio/modelcontextprotocol/kotlin/sdk/server/EventStore;Lkotlin/time/Duration;JLkotlin/jvm/internal/DefaultConstructorMarker;)V
public final fun getAllowedHosts ()Ljava/util/List;
public final fun getAllowedOrigins ()Ljava/util/List;
public final fun getEnableDnsRebindingProtection ()Z
public final fun getEnableJsonResponse ()Z
public final fun getEventStore ()Lio/modelcontextprotocol/kotlin/sdk/server/EventStore;
public final fun getMaxRequestBodySize ()J
public final fun getRetryInterval-FghU774 ()Lkotlin/time/Duration;
}