JSON RPC 2.0 Batch support + fix broken Streamable HTTP transport by RomanEmreis · Pull Request #56 · RomanEmreis/neva

RomanEmreis · 2026-03-08T15:04:09Z

Summary

Implements JSON-RPC 2.0 batch request/response support (spec §6) on both the server and client sides of
Neva, plus a complete examples/batch/ workspace demonstrating the feature.

What Changed

Core Types (`neva/src/types.rs`)

Added MessageBatch — a non-empty wrapper around Vec<MessageEnvelope> enforcing the spec's "batch must contain at least one object" rule at
construction and deserialization
Added Message::Batch(MessageBatch) variant with #[serde(untagged)] ordering: Batch is last so single-message deserialization is tried first
MessageBatch implements IntoIterator for ergonomic iteration over envelopes

Server (`neva/src/app.rs`)

Handles incoming Message::Batch by processing each request concurrently and collecting responses into a single batch reply
Maintains JSON-RPC ordering: responses are returned in the same order as requests

Client Handler (`neva/src/client/handler.rs`)

Receive loop now handles Message::Batch: iterates envelopes and dispatches each Response to its waiting channel via pending.complete(resp);
non-response envelopes in a batch (protocol violations per spec) are silently ignored for robustness
Added send_batch — registers pending slots for all requests, sends the batch atomically, and cleans up slots on send failure to prevent leaks
Added timeout() / pending() accessors needed by Client::call_batch

Client (`neva/src/client.rs` + new `neva/src/client/batch.rs`)

Client::call_batch(items: Vec<MessageEnvelope>) -> Result<Vec<Response>> — sends a batch and awaits all responses concurrently using try_join_all
(short-circuits on first error)
Client::batch() -> BatchBuilder<'_> — entry point for the fluent builder API
BatchBuilder<'a> with 9 builder methods:

Method	Description
`list_tools()`	Add a `tools/list` request
`call_tool(name, args)`	Add a `tools/call` request (sets `meta` for progress tracking)
`list_resources()`	Add a `resources/list` request
`read_resource(uri)`	Add a `resources/read` request
`list_resource_templates()`	Add a `resources/templates/list` request
`list_prompts()`	Add a `prompts/list` request
`get_prompt(name, args)`	Add a `prompts/get` request (sets `meta` for progress tracking)
`ping()`	Add a `ping` request
`notify(method, params)`	Add a notification (fire-and-forget, excluded from responses)
`send()`	Flush the batch and await all responses

Example (`examples/batch/`)

A self-contained workspace (client + server) demonstrating batch in action:

Server: exposes an add tool, a greeting prompt, and three notes resources (daily, weekly, monthly)
Client: sends one batch covering all capability types — list_tools, list_resources, list_prompts, call_tool, read_resource × 2,
get_prompt, ping — then parses and logs each response

let responses = client
    .batch()
    .list_tools()
    .list_resources()
    .list_prompts()
    .call_tool("add", [("a", 40_i32), ("b", 2_i32)])
    .read_resource("notes://daily")
    .read_resource("notes://weekly")
    .get_prompt("greeting", [("name", "Neva")])
    .ping()
    .send()
    .await?;

Other

Fixed broken Streamable HTTP server flow (response flushing regression)
Graceful error on MCP protocol version mismatch (was a panic)
OSS community files: CONTRIBUTING.md, CODE_OF_CONDUCT.md, SECURITY.md, issue/PR templates, cleaned-up .gitignore
Dependency updates (neva/Cargo.toml, neva_macros/Cargo.toml)

Test Coverage

handler.rs: batch_responses_are_distributed_individually — verifies mixed-envelope batch (Response + Request + Response) dispatches only the two
responses to their pending channels
client.rs: call_batch_returns_error_when_disconnected — verifies early error when no handler is attached
All existing tests pass (54 total, 0 failures, clippy clean)

Running the Example

# Terminal 1 — server
cargo run -p server --manifest-path examples/batch/Cargo.toml

# Terminal 2 — client
cargo run -p client --manifest-path examples/batch/Cargo.toml

… files

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neva/src/types.rs

neva/src/app.rs

RomanEmreis · 2026-03-08T16:27:16Z

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neva/src/app.rs

RomanEmreis · 2026-03-08T17:26:34Z

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neva/src/transport/http/server.rs

RomanEmreis · 2026-03-08T17:45:46Z

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neva/src/transport/http/server.rs

neva/src/client.rs

…ch processing at the client side - if one item is failing the whole batch will fail too

RomanEmreis · 2026-03-14T09:32:14Z

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neva/src/client/handler.rs

neva/src/client.rs

…ction teardown for client in case of errors

RomanEmreis · 2026-03-14T10:07:59Z

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neva/src/client/handler.rs

…ponse envelopes immediately via pending.complete, collecting non-Response envelopes into deferred. The second loop processes those requests and notifications. A slow elicitation/sampling request handler in the second pass can no longer block responses that were already received in the same batch. Comment 2 — dispatch_request now always returns Response. Unknown methods produce ErrorCode::MethodNotFound.into_response(req_id), where req_id is captured before req is moved into the match. The single-message Message::Request arm also benefits: it no longer has the else { return; } branch that was silently killing the entire receive loop on unknown method requests.

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neva/src/app.rs

…untime) (which routes every Response envelope to the pending queue), the MessageEnvelope::Response arm now checks runtime.pending_requests().pop(&resp.full_id())

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neva/src/app.rs

neva/src/client/handler.rs

RomanEmreis added 4 commits March 8, 2026 12:02

dependencies updates; simplified version bump; add oss guidelines and…

b64241a

… files

graceful error on mcp version mismatch

f872803

polished gitignore

3c9b4b2

added json rpc batch support; fixed broken streamable http flow;

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RomanEmreis self-assigned this Mar 8, 2026

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RomanEmreis commented Mar 8, 2026

Summary

What Changed

Core Types (neva/src/types.rs)

Server (neva/src/app.rs)

Client Handler (neva/src/client/handler.rs)

Client (neva/src/client.rs + new neva/src/client/batch.rs)

Example (examples/batch/)

Other

Test Coverage

Running the Example

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Core Types (`neva/src/types.rs`)

Server (`neva/src/app.rs`)

Client Handler (`neva/src/client/handler.rs`)

Client (`neva/src/client.rs` + new `neva/src/client/batch.rs`)

Example (`examples/batch/`)