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fix: improve compatibility with non-compliant MCP servers (#413)

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Addresses issues with servers like Shopify that violate MCP/HTTP specs:
- Prioritize application/json in Accept headers to fix content-type issues
- Handle non-compliant notification non-empty responses
- Add status code validation and null safety improvements

Resolves #406

Signed-off-by: Christian Tzolov <christian.tzolov@broadcom.com>
This commit is contained in:
Christian Tzolov 2025-07-18 14:43:35 +02:00
commit 4937fc1ef5
1 changed files with 37 additions and 10 deletions
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21
mcp-spring/mcp-spring-webflux/src/main/java/io/modelcontextprotocol/client/transport/WebClientStreamableHttpTransport.java
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@ -30,6 +30,7 @@ import io.modelcontextprotocol.spec.McpTransportSession;
import io.modelcontextprotocol.spec.McpTransportSessionNotFoundException;
import io.modelcontextprotocol.spec.McpTransportStream;
import io.modelcontextprotocol.util.Assert;
import io.modelcontextprotocol.util.Utils;
import reactor.core.Disposable;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;
@ -244,7 +245,7 @@ public class WebClientStreamableHttpTransport implements McpClientTransport {
Disposable connection = webClient.post()
.uri(this.endpoint)
.accept(MediaType.TEXT_EVENT_STREAM, MediaType.APPLICATION_JSON)
.accept(MediaType.APPLICATION_JSON, MediaType.TEXT_EVENT_STREAM)
.headers(httpHeaders -> {
transportSession.sessionId().ifPresent(id -> httpHeaders.add("mcp-session-id", id));
})
@ -287,7 +288,7 @@ public class WebClientStreamableHttpTransport implements McpClientTransport {
logger.trace("Received response to POST for session {}", sessionRepresentation);
// communicate to caller the message was delivered
sink.success();
return responseFlux(response);
return directResponseFlux(message, response);
}
else {
logger.warn("Unknown media type {} returned for POST in session {}", contentType,
@ -384,14 +385,22 @@ public class WebClientStreamableHttpTransport implements McpClientTransport {
return transportSession.sessionId().orElse("[missing_session_id]");
}
private Flux<McpSchema.JSONRPCMessage> responseFlux(ClientResponse response) {
private Flux<McpSchema.JSONRPCMessage> directResponseFlux(McpSchema.JSONRPCMessage sentMessage,
ClientResponse response) {
return response.bodyToMono(String.class).<Iterable<McpSchema.JSONRPCMessage>>handle((responseMessage, s) -> {
try {
McpSchema.JSONRPCMessage jsonRpcResponse = McpSchema.deserializeJsonRpcMessage(objectMapper,
responseMessage);
s.next(List.of(jsonRpcResponse));
if (sentMessage instanceof McpSchema.JSONRPCNotification && Utils.hasText(responseMessage)) {
logger.warn("Notification: {} received non-compliant response: {}", sentMessage, responseMessage);
s.complete();
}
else {
McpSchema.JSONRPCMessage jsonRpcResponse = McpSchema.deserializeJsonRpcMessage(objectMapper,
responseMessage);
s.next(List.of(jsonRpcResponse));
}
}
catch (IOException e) {
// TODO: this should be a McpTransportError
s.error(e);
}
}).flatMapIterable(Function.identity());