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WIP Streamable HTTP #1

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28 changes: 23 additions & 5 deletions mcp/src/main/java/io/modelcontextprotocol/client/transport/FlowSseClient.java
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,8 @@
*/
package io.modelcontextprotocol.client.transport;

import static io.modelcontextprotocol.spec.McpStreamableHttpClient.*;

import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
Expand Down Expand Up @@ -120,12 +122,28 @@ public FlowSseClient(HttpClient httpClient, HttpRequest.Builder requestBuilder)
* notifications
* @throws RuntimeException if the connection fails with a non-200 status code
*/
public void subscribe(String url, SseEventHandler eventHandler) {
HttpRequest request = this.requestBuilder.uri(URI.create(url))
.header("Accept", "text/event-stream")
public void subscribe(String url, String mcpSessionId, SseEventHandler eventHandler) {
HttpRequest.Builder requestBuilder = this.requestBuilder.copy()
.uri(URI.create(url))
.header("Cache-Control", "no-cache")
.GET()
.build();
.GET();
if (mcpSessionId != null) { // Using StreamableHTTP Transport
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issue (complexity): Consider refactoring header-setting logic to build the request only twice and apply missing headers in a single loop.

// 1. Copy & set the URI/GET only once
HttpRequest.Builder rb = this.requestBuilder.copy()
    .uri(URI.create(url))
    .header("Cache-Control", "no-cache")
    .GET();

// 2. Snapshot existing header names in one build()
Set<String> existing = rb.build().headers().map().keySet();

// 3. Prepare the defaults per transport
List<Map.Entry<String,String>> defaults;
if (mcpSessionId != null) {
    defaults = List.of(
      Map.entry(ACCEPT_HEADER_NAME,      ACCEPT_HEADER_VALUE),
      Map.entry(CONTENT_TYPE_HEADER_NAME, CONTENT_TYPE_HEADER_VALUE),
      Map.entry(MCP_SESSION_ID_HEADER_NAME, mcpSessionId)
    );
} else {
    defaults = List.of(
      Map.entry(ACCEPT_HEADER_NAME, "text/event-stream")
    );
}

// 4. Apply only the missing headers
for (var hdr : defaults) {
  if (!existing.contains(hdr.getKey())) {
    rb.header(hdr.getKey(), hdr.getValue());
  }
}

// 5. Final build
HttpRequest request = rb.build();

Benefits:

  • Builds the request only twice (once for header-snapshot, once final) instead of N times.
  • Flattens nested if-blocks into a single loop over defaults.
  • Maintains identical header logic and ordering.

if (!requestBuilder.build().headers().map().containsKey(ACCEPT_HEADER_NAME)) {
requestBuilder.header(ACCEPT_HEADER_NAME, ACCEPT_HEADER_GET_VALUE);
}
if (!requestBuilder.build().headers().map().containsKey(CONTENT_TYPE_HEADER_NAME)) {
requestBuilder.header(CONTENT_TYPE_HEADER_NAME, CONTENT_TYPE_HEADER_VALUE);
}
if (!requestBuilder.build().headers().map().containsKey(MCP_SESSION_ID_HEADER_NAME)) {
requestBuilder.header(MCP_SESSION_ID_HEADER_NAME, mcpSessionId);
}
}
else { // Using HTTP+SSE Transport
if (!requestBuilder.build().headers().map().containsKey(ACCEPT_HEADER_NAME)) {
requestBuilder.header(ACCEPT_HEADER_NAME, "text/event-stream");
}
}
HttpRequest request = requestBuilder.build();

StringBuilder eventBuilder = new StringBuilder();
AtomicReference<String> currentEventId = new AtomicReference<>();
Expand Down
2 changes: 1 addition & 1 deletion mcp/src/main/java/io/modelcontextprotocol/client/transport/HttpClientSseClientTransport.java
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Original file line number Diff line number Diff line change
Expand Up @@ -342,7 +342,7 @@ public Mono<Void> connect(Function<Mono<JSONRPCMessage>, Mono<JSONRPCMessage>> h
connectionFuture.set(future);

URI clientUri = Utils.resolveUri(this.baseUri, this.sseEndpoint);
sseClient.subscribe(clientUri.toString(), new FlowSseClient.SseEventHandler() {
sseClient.subscribe(clientUri.toString(), null, new FlowSseClient.SseEventHandler() {
@Override
public void onEvent(SseEvent event) {
if (isClosing) {
Expand Down
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