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Standard header name used in mcp #320

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Standard header name used in mcp #320

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ed4f8e7
Standard header name used in mcp
CrazyHZM Jun 17, 2025
2c3905a
Merge branch 'refs/heads/main' into feat/header
CrazyHZM Jun 17, 2025
df10fd4
Standard last-event-id request header name
CrazyHZM Jun 18, 2025
8a4db27
Merge branch 'refs/heads/main' into feat/header
CrazyHZM Jun 24, 2025
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15 changes: 9 additions & 6 deletions .../main/java/io/modelcontextprotocol/client/transport/WebClientStreamableHttpTransport.java
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Original file line number Diff line number Diff line change
Expand Up @@ -36,6 +36,10 @@
import reactor.util.function.Tuple2;
import reactor.util.function.Tuples;

import static io.modelcontextprotocol.spec.McpSchema.Headers.LAST_EVENT_ID;
import static io.modelcontextprotocol.spec.McpSchema.Headers.MCP_SESSION_ID;


/**
* An implementation of the Streamable HTTP protocol as defined by the
* <code>2025-03-26</code> version of the MCP specification.
Expand Down Expand Up @@ -128,7 +132,7 @@ public Mono<Void> connect(Function<Mono<McpSchema.JSONRPCMessage>, Mono<McpSchem
private DefaultMcpTransportSession createTransportSession() {
Function<String, Publisher<Void>> onClose = sessionId -> sessionId == null ? Mono.empty()
: webClient.delete().uri(this.endpoint).headers(httpHeaders -> {
httpHeaders.add("mcp-session-id", sessionId);
httpHeaders.add(MCP_SESSION_ID, sessionId);
})
.retrieve()
.toBodilessEntity()
Expand Down Expand Up @@ -187,9 +191,9 @@ private Mono<Disposable> reconnect(McpTransportStream<Disposable> stream) {
.uri(this.endpoint)
.accept(MediaType.TEXT_EVENT_STREAM)
.headers(httpHeaders -> {
transportSession.sessionId().ifPresent(id -> httpHeaders.add("mcp-session-id", id));
transportSession.sessionId().ifPresent(id -> httpHeaders.add(MCP_SESSION_ID, id));
if (stream != null) {
stream.lastId().ifPresent(id -> httpHeaders.add("last-event-id", id));
stream.lastId().ifPresent(id -> httpHeaders.add(LAST_EVENT_ID, id));
}
})
.exchangeToFlux(response -> {
Expand Down Expand Up @@ -247,12 +251,11 @@ public Mono<Void> sendMessage(McpSchema.JSONRPCMessage message) {
.uri(this.endpoint)
.accept(MediaType.TEXT_EVENT_STREAM, MediaType.APPLICATION_JSON)
.headers(httpHeaders -> {
transportSession.sessionId().ifPresent(id -> httpHeaders.add("mcp-session-id", id));
transportSession.sessionId().ifPresent(id -> httpHeaders.add(MCP_SESSION_ID, id));
})
.bodyValue(message)
.exchangeToFlux(response -> {
if (transportSession
.markInitialized(response.headers().asHttpHeaders().getFirst("mcp-session-id"))) {
if (transportSession.markInitialized(response.headers().asHttpHeaders().getFirst(MCP_SESSION_ID))) {
// Once we have a session, we try to open an async stream for
// the server to send notifications and requests out-of-band.
reconnect(null).contextWrite(sink.contextView()).subscribe();
Expand Down
22 changes: 22 additions & 0 deletions mcp/src/main/java/io/modelcontextprotocol/spec/McpSchema.java
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Expand Up @@ -141,6 +141,28 @@ public static final class ErrorCodes {

}

// ---------------------------
// JSON-RPC Protocol Headers
// ---------------------------
/**
* Standard header name used in MCP JSON-RPC request and responses.
*/
public static final class Headers {
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I feel that this belongs around something like McpHttpTransport interface rather than in the McpSpec, which is more about the JSON-RPC layer.

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The primary purpose here is to provide users with the MCP standard header name information. The MCP-Session-Id does belong to the transport category. Of course, I have omitted the last-event-id here. At present, I think defining these header names as part of the MCPSchema is the most reasonable approach because I haven't thought of any other more reasonable alternatives. These header names are indeed mentioned in the Specification. Do you have any better suggestions? @chemicL


/**
* The Model Context Protocol (MCP) session ID header name.
*/
public static final String MCP_SESSION_ID = "Mcp-Session-Id";

/**
* The Last-Event-ID HTTP request header reports an EventSource object's last
* event ID string to the server when the user agent is to reestablish the
* connection.
*/
public static final String LAST_EVENT_ID = "Last-Event-ID";

}

public sealed interface Request permits InitializeRequest, CallToolRequest, CreateMessageRequest, ElicitRequest,
CompleteRequest, GetPromptRequest {

Expand Down
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