[Hardik K (hardikkaurani)]

Summary of Changes

1. Omit Nil Header String Values in writeStringValue:

   • In writeStringValue(key, value), if key != null && !key.isEmpty() and value == null, it previously serialized key + "\r\n" without a colon or value, creating a malformed MIME header line that violates RFC 2046 and RFC 7230/5322 syntax.
   • Now checks if (key != null && !key.isEmpty() && value == null), returning immediately so that headers with null values are cleanly omitted, matching the Kiota serialization convention across SDKs.
   • Preserves delimiter emission when key == null || key.isEmpty() and value == null ("\r\n").

2. Support additionalValuesToMerge in writeObjectValue:

   • Previously writeObjectValue validated Objects.requireNonNull(additionalValuesToMerge) but completely ignored the array without serializing any additional MultipartBody parts.
   • Now filters non-null additional values and iterates through them, verifying type (MultipartBody), invoking lifecycle callbacks (onBeforeObjectSerialization, onStartObjectSerialization, onAfterObjectSerialization), and serializing each part (consistent with FormSerializationWriter and JsonSerializationWriter).

3. Unit Tests Added in MultipartSerializationWriterTests:

   • writesStringValueWithKeyValue: verifies standard header serialization (Content-Type: text/plain).
   • writeStringValueWithNilValueOmitsHeader: verifies headers with null values are omitted.
   • writeStringValueWithEmptyKeyAndNilValueWritesDelimiter: verifies delimiter emission (\r\n).
   • writeStringValueWithEmptyKeyAndValueWritesRawLine: verifies raw line serialization.
   • writesAStructuredObjectWithAdditionalValuesToMerge: verifies merging multiple MultipartBody parts.
   • throwsOnInvalidAdditionalValuesToMerge: asserts runtime exception for non-MultipartBody instances in additional values.

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[Hardik K (hardikkaurani)]

Hi Vincent Biret (@baywet),

I've opened this PR in components/serialization/multipart to:

• Omit headers when a key is provided with a null value in writeStringValue(), preventing malformed header lines without colon/value (Header\r\n).
• Support additionalValuesToMerge in writeObjectValue() by iterating over and serializing additional MultipartBody parts with lifecycle callbacks (aligning with FormSerializationWriter and JsonSerializationWriter).

Unit tests covering header omission, additional values merging, and invalid part validation have been added, and spotlessCheck / test suites pass. Whenever convenient, could you please take a look? Thanks for your time!

[Copilot]

🟡 Changes recommended

Additional bodies are appended after the primary closing boundary, causing MIME parsers to ignore their parts instead of merging them.

3 open issues

• Serialize all multipart parts under one shared boundary · New
• Use API-compatible readAllBytes helper in Android tests · New
• Isolate additional-value validation from primary-body failure · New

_{Review effort: Balanced}

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[Hardik K (hardikkaurani)]

Hi Vincent Biret (@baywet),

I have updated the PR in commit \29b7efa0\ to address the review recommendations:

1. Shared Multipart Boundary Envelope: \writeObjectValue\ now serializes all parts from merged \MultipartBody\ instances under a single shared boundary (derived from the root body) and suppresses intermediate closing boundaries, ensuring only a single terminating delimiter (----) is emitted so parts are not treated as MIME epilogue.
2. Android Compatibility in Tests: Replaced \InputStream.readAllBytes()\ with \Compatibility.readAllBytes()\ to support Android API levels < 33.
3. Isolated Validation & Boundary-Aware Assertions: Separated \�dditionalValuesToMerge\ validation testing with explicit exception message assertions, and added boundary-aware assertions verifying the full multi-part stream and absence of secondary boundaries.

Local Gradle test suites and \spotlessCheck\ pass cleanly. Whenever convenient, please take another look. Thank you!

[Copilot]

🟡 Changes recommended

Boundary rewriting also affects string payloads, which can discard content or prematurely close the multipart message.

1 open issue

• Avoid treating multipart payloads as framing delimiters · New

3 resolved since last review

• Serialize all multipart parts under one shared boundary
• Isolate additional-value validation from primary-body failure
• Use API-compatible readAllBytes helper in Android tests

_{Review effort: Balanced}

[Hardik K (hardikkaurani)]

Resolved: Introduced an explicit FramingState state machine in MultipartSerializationWriter to track MIME framing phases (EXPECTING_FIRST_BOUNDARY, IN_HEADERS, EXPECTING_PAYLOAD, EXPECTING_DELIMITER_AFTER_PAYLOAD, EXPECTING_BOUNDARY_OR_CLOSING, and FINISHED). Boundary rewriting and intermediate closing delimiter suppression are now strictly scoped to structural framing delimiters (EXPECTING_FIRST_BOUNDARY and EXPECTING_BOUNDARY_OR_CLOSING), ensuring string payloads matching boundary or delimiter patterns are emitted untouched as message content. Added regression test preservesStringPayloadMatchingBoundaryOrClosingDelimiterWhenMerging in MultipartSerializationWriterTests.

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[Hardik K (hardikkaurani)]

Hi Vincent Biret (@baywet),

I've pushed an update in commit 720ecebb addressing the review feedback:

• Framing-Scoped Boundary Rewriting: Introduced a FramingState enum in MultipartSerializationWriter to track MIME framing transitions (EXPECTING_FIRST_BOUNDARY, IN_HEADERS, EXPECTING_PAYLOAD, EXPECTING_DELIMITER_AFTER_PAYLOAD, EXPECTING_BOUNDARY_OR_CLOSING, and FINISHED). Boundary rewriting and intermediate closing delimiter suppression are now strictly restricted to structural framing delimiters (EXPECTING_FIRST_BOUNDARY and EXPECTING_BOUNDARY_OR_CLOSING). This ensures that string payloads matching boundary or delimiter patterns (sent via writeStringValue("", payload)) are emitted untouched without triggering unintended delimiter suppression or premature stream termination.
• Regression Testing: Added preservesStringPayloadMatchingBoundaryOrClosingDelimiterWhenMerging in MultipartSerializationWriterTests to verify that string payloads matching body closing delimiters are fully preserved in both non-final and final bodies.
• All tests, spotlessCheck, and spotbugs pass cleanly.

Whenever convenient, please take another look. Thank you!