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fix: improve error handling in HttpClientSseClientTransport and add test #391

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Merged
merged 1 commit into from
Jul 13, 2025
Merged

fix: improve error handling in HttpClientSseClientTransport and add test #391

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8 changes: 4 additions & 4 deletions 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 @@ -424,8 +424,8 @@ public Mono<Void> sendMessage(JSONRPCMessage message) {
.flatMap(body -> sendHttpPost(messageEndpointUri, body).handle((response, sink) -> {
if (response.statusCode() != 200 && response.statusCode() != 201 && response.statusCode() != 202
&& response.statusCode() != 206) {
sink.error(new RuntimeException(
"Sending message failed with a non-OK HTTP code: " + response.statusCode()));
sink.error(new RuntimeException("Sending message failed with a non-OK HTTP code: "
+ response.statusCode() + " - " + response.body()));
}
else {
sink.next(response);
Expand Down Expand Up @@ -453,15 +453,15 @@ private Mono<String> serializeMessage(final JSONRPCMessage message) {
});
}

private Mono<HttpResponse<Void>> sendHttpPost(final String endpoint, final String body) {
private Mono<HttpResponse<String>> sendHttpPost(final String endpoint, final String body) {
final URI requestUri = Utils.resolveUri(baseUri, endpoint);
final HttpRequest request = this.requestBuilder.copy()
.uri(requestUri)
.POST(HttpRequest.BodyPublishers.ofString(body))
.build();

// TODO: why discard the body?
return Mono.fromFuture(httpClient.sendAsync(request, HttpResponse.BodyHandlers.discarding()));
return Mono.fromFuture(httpClient.sendAsync(request, HttpResponse.BodyHandlers.ofString()));
}

/**
Expand Down
10 changes: 10 additions & 0 deletions ...test/java/io/modelcontextprotocol/client/transport/HttpClientSseClientTransportTests.java
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Original file line number Diff line number Diff line change
Expand Up @@ -105,6 +105,16 @@ void cleanup() {
container.stop();
}

@Test
void testErrorOnBogusMessage() {
// bogus message
JSONRPCRequest bogusMessage = new JSONRPCRequest(null, null, "test-id", Map.of("key", "value"));

StepVerifier.create(transport.sendMessage(bogusMessage))
.verifyErrorMessage(
"Sending message failed with a non-OK HTTP code: 400 - Invalid message: {\"id\":\"test-id\",\"params\":{\"key\":\"value\"}}");
}

@Test
void testMessageProcessing() {
// Create a test message
Expand Down