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Fix UTF-8 encoding for non-ASCII tool names in HTTP client transports

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Both HttpClientSseClientTransport and HttpClientStreamableHttpTransport
set Content-Type to 'application/json' without specifying the charset.
While Java's BodyPublishers.ofString() uses UTF-8 by default, the
missing charset in the header can cause the server to interpret the
request body using a different encoding (e.g., ISO-8859-1), corrupting
non-ASCII characters such as Chinese tool names.

Explicitly set Content-Type to 'application/json; charset=utf-8' in
POST requests on both client transports.

Fixes #260
Backport of #850

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Daniel Garnier-Moiroux <git@garnier.wf>
Signed-off-by: Daniel Garnier-Moiroux <git@garnier.wf>
This commit is contained in:
RameshReddy Adutla 2026-03-04 20:59:04 +00:00 • committed by Daniel Garnier-Moiroux
commit 9ead4d154e
2 changed files with 62 additions and 2 deletions
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2
mcp-core/src/main/java/io/modelcontextprotocol/client/transport/HttpClientSseClientTransport.java
View file

@ -463,7 +463,7 @@ public class HttpClientSseClientTransport implements McpClientTransport {
return Mono.deferContextual(ctx -> {
var builder = this.requestBuilder.copy()
.uri(requestUri)
.header(HttpHeaders.CONTENT_TYPE, "application/json")
.header(HttpHeaders.CONTENT_TYPE, "application/json; charset=utf-8")
.header(MCP_PROTOCOL_VERSION_HEADER_NAME, MCP_PROTOCOL_VERSION)
.POST(HttpRequest.BodyPublishers.ofString(body));
var transportContext = ctx.getOrDefault(McpTransportContext.KEY, McpTransportContext.EMPTY);

4
mcp-core/src/main/java/io/modelcontextprotocol/client/transport/HttpClientStreamableHttpTransport.java
View file

@ -102,6 +102,8 @@ public class HttpClientStreamableHttpTransport implements McpClientTransport {
private static final String APPLICATION_JSON = "application/json";
private static final String APPLICATION_JSON_UTF8 = "application/json; charset=utf-8";
private static final String TEXT_EVENT_STREAM = "text/event-stream";
public static int NOT_FOUND = 404;
@ -477,7 +479,7 @@ public class HttpClientStreamableHttpTransport implements McpClientTransport {
var builder = requestBuilder.uri(uri)
.header(HttpHeaders.ACCEPT, APPLICATION_JSON + ", " + TEXT_EVENT_STREAM)
.header(HttpHeaders.CONTENT_TYPE, APPLICATION_JSON)
.header(HttpHeaders.CONTENT_TYPE, APPLICATION_JSON_UTF8)
.header(HttpHeaders.CACHE_CONTROL, "no-cache")
.header(HttpHeaders.PROTOCOL_VERSION,
ctx.getOrDefault(McpAsyncClient.NEGOTIATED_PROTOCOL_VERSION,