Fix UTF-8 encoding for non-ASCII tool names in HTTP client transports#850
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Kehrlann merged 1 commit intomodelcontextprotocol:mainfrom Apr 8, 2026
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Hey @rameshreddy-adutla . Thank you for your contribution. Would you mind adding a test for this? Edit: I have added tests myself. |
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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 modelcontextprotocol#260 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>
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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>
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Summary
Fixes #260
Tool names containing non-ASCII characters (e.g., Chinese
天气预报) are corrupted when sent viaHttpClientSseClientTransportandHttpClientStreamableHttpTransportbecause theContent-Typeheader is set toapplication/jsonwithout specifying the charset.While Java's
BodyPublishers.ofString()encodes the body as UTF-8 by default, the missing charset declaration in the header can cause the server to interpret the request body using a different encoding (e.g., ISO-8859-1 per HTTP/1.1 defaults), resulting in garbled tool names like天æ°é¢Dæ¥.Changes
HttpClientSseClientTransport.java: SetContent-Type: application/json; charset=utf-8in POST requests.HttpClientStreamableHttpTransport.java: AddedAPPLICATION_JSON_UTF8constant for POST request Content-Type; keptAPPLICATION_JSONfor response content-type matching.Testing
All 680 tests pass (1 pre-existing Docker failure unrelated to this change).