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Fix: Add UTF-8 charset to Content-Type header for Chinese tool names
When calling tools with Chinese names using HttpClientSseClientTransport or HttpClientStreamableHttpTransport, the JSON body was sent without explicit charset encoding. This caused Chinese characters to be corrupted on the server side because the default encoding wasn't UTF-8. This fix adds '; charset=UTF-8' to the Content-Type header in both transport classes, ensuring proper encoding of non-ASCII characters. Fixes modelcontextprotocol#260
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2 files changed

Lines changed: 2 additions & 2 deletions

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‎mcp-core/src/main/java/io/modelcontextprotocol/client/transport/HttpClientSseClientTransport.java‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -445,7 +445,7 @@ private Mono<HttpResponse<String>> sendHttpPost(final String endpoint, final Str
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return Mono.deferContextual(ctx -> {
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var builder = this.requestBuilder.copy()
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.uri(requestUri)
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.header(HttpHeaders.CONTENT_TYPE, "application/json")
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.header(HttpHeaders.CONTENT_TYPE, "application/json; charset=UTF-8")
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.header(MCP_PROTOCOL_VERSION_HEADER_NAME, MCP_PROTOCOL_VERSION)
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.POST(HttpRequest.BodyPublishers.ofString(body));
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var transportContext = ctx.getOrDefault(McpTransportContext.KEY, McpTransportContext.EMPTY);

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

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -477,7 +477,7 @@ public Mono<Void> sendMessage(McpSchema.JSONRPCMessage sentMessage) {
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var builder = requestBuilder.uri(uri)
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.header(HttpHeaders.ACCEPT, APPLICATION_JSON + ", " + TEXT_EVENT_STREAM)
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.header(HttpHeaders.CONTENT_TYPE, APPLICATION_JSON)
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.header(HttpHeaders.CONTENT_TYPE, APPLICATION_JSON + "; charset=UTF-8")
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.header(HttpHeaders.CACHE_CONTROL, "no-cache")
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.header(HttpHeaders.PROTOCOL_VERSION,
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ctx.getOrDefault(McpAsyncClient.NEGOTIATED_PROTOCOL_VERSION,

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