[ByGh00st]

Follow-up to #1302 and #1304 per @Pr0methean's direction ("Treat them as non-streamable"), fixing the fuzz_write CI failures in run 43566959380 and unblocking v9.6.0 (#1297).

Cause

When ZipWriter::new_append reopens an archive and rewrites the central directory at dir_start (#1302), any custom extra field whose central-directory representation shrinks on round-trip causes finalize() (footer_end < stream_end) to zero central_start and relocate the footer to EOF:

• 0x5455 (ExtendedTimestamp) when data.len() != 1 and (data.len() != 5 || data[0] & 1 == 0) (re-serializes as 1 or 5 bytes).
• 0xa11e (DataStreamAlignment) and 0xd935 (AndroidZipAlignment), which ExtraFields::central_extra_fields omits from the rewritten central directory.
• 0x0001 (Zip64ExtendedInfo), which replace_zip64_extra_field strips/replaces.

Changes

• Expose read-only FileOptions::extra_fields(&self) -> &[CustomExtraField] (src/write/options.rs).
• Mark FileOperation::is_streamable as false when central_extra_fields_shrink_on_reopen(options) is true (fuzz/write/src/main.rs).
• Add reopen-extended-timestamp-extra-field-shrinks.bin regression input and unit test shrinking_central_extra_fields_mark_operation_non_streamable.

/cc @Pr0methean @ychampion

---

^{Open in [code]smith · Need help on this PR? Tag @codesmith-bot with what you need.}

[amazon-q-developer]

The changes are correct and well-targeted. The root cause analysis in the PR description is accurate, and the fix is properly scoped to the fuzz harness.

src/write/options.rs: The new extra_fields(&self) -> &[CustomExtraField] accessor is a clean, minimal public API addition needed to let the fuzz harness inspect extra fields without reaching into private internals.

fuzz/write/src/main.rs: central_extra_fields_shrink_on_reopen correctly identifies all three categories of shrinking central-directory extra fields documented in the PR (alignment fields, ZIP64, and ExtendedTimestamp). The ExtendedTimestamp branch logic at line 221 (field.data.len() != 1 && (field.data.len() != 5 || field.data[0] & 1 == 0)) correctly mirrors the re-serialization behaviour of parse_central_header. All test vector cases in shrinking_central_extra_fields_mark_operation_non_streamable are consistent with the logic.

No blocking defects found. The PR is ready to merge.

---

You can now have the agent implement changes and create commits directly on your pull request's source branch. Simply comment with /q followed by your request in natural language to ask the agent to make changes.