Fix wrong encode for bytes in HttpPart for multipart/form-data …#4345
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iscai-msft merged 1 commit intoApr 28, 2026
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…zure#4317) `bytes` in `HttpPart<bytes>` for `multipart/form-data` was incorrectly encoded as `base64` instead of `bytes`. In `addMultipartPropertiesToModelType`, the property type is replaced with the part body type via `getClientTypeWithDiagnostics`. For `bytes`, this creates the `SdkBuiltInType` through the `Scalar` path in `addEncodeInfo` with no `defaultContentType`, which unconditionally defaults to `base64`. The part's actual content type (`application/octet-stream`) was never consulted. ### Changes - **`packages/typespec-client-generator-core/src/types.ts`** — Re-apply `addEncodeInfo` after the type replacement, passing the part's default content type so the existing content-type-aware branching (`!isMediaTypeJson && !isMediaTypeXml && !isMediaTypeTextPlain → "bytes"`) takes effect. - **`packages/typespec-client-generator-core/test/types/multipart.test.ts`** — Added encode assertions to existing test and a new test for the anonymous model repro case. ```typespec op upload( @Header contentType: "multipart/form-data", @multipartBody body: { profileImage: HttpPart<bytes>; // encode is now "bytes", was "base64" }, ): NoContentResponse; ``` --------- Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com> Co-authored-by: tadelesh <1726438+tadelesh@users.noreply.github.com>
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