[officialasishkumar]

Closes #552

What: iOS now reads the fileName capture option. When result is "tmpfile", the file is written to tmp/ReactNative/<fileName><UUID>.<ext> instead of always tmp/ReactNative/<UUID>.<ext>. Without fileName, nothing changes.

Why: fileName was Android only, so on iOS the name a share target shows (WhatsApp, Mail, etc.) could not be controlled. I gave it the same meaning as on Android, where it is the prefix passed to File.createTempFile (as #740 noted), instead of the exact-name approach from the patch in the issue:

• the unique suffix means two captures with the same fileName never overwrite each other, and releaseCapture on one cannot delete the other;
• the file stays a direct child of tmp/ReactNative, the only directory releaseCapture deletes from, so releasing these captures still works;
• the path still comes from RCTTempFilePath, so its first-use cleanup of tmp/ReactNative keeps working the same way.

Like Android, a fileName shorter than 3 characters rejects the capture. A fileName containing / or a NUL byte is rejected too (fileName must be at least 3 characters long and must not contain '/'), so it cannot point outside the directory.

How: The path logic is a private class method, +[RNViewShot tempFilePathWithExtension:fileName:error:], which the tmpfile branch calls instead of RCTTempFilePath. The XCTest target can call it without an RCTBridge, in the same way RNViewShotReleaseCaptureTests calls releaseCapture:. The README and the CaptureOptions JSDoc now describe fileName for both platforms.

Tests: New cases in RNViewShotEncodingTests.mm:

• without fileName, the result is still a bare <UUID>.png in the RCTTempFilePath directory;
• with fileName, the name starts with the prefix, ends with the extension, stays in that same directory, differs between two calls, and can be written;
• "", "ab", "../escape", "dir/name" and a name containing NUL are rejected with an error.

Verified:

• npm run format:check, npm run lint:ci, npm run type-check and npm test (104 tests) pass.
• I didn't run the XCTest target locally. I compiled the new method on its own with clang (with RCTTempFilePath/RCTErrorWithMessage stubbed to match React Native) and ran the same checks the XCTests make; they all passed. The ios CI job runs the real XCTest target.

[Copilot]

🟢 Approval recommended

No active review issues are reported for the iOS filename-prefix support change.

No open issues 🎉

What changed in this PR

Adds iOS support for the fileName capture option, addressing #552 with Android-compatible prefix semantics while preserving unique temporary filenames and existing cleanup behavior.

Changes:

• Adds an iOS temporary-path helper that validates prefixes and retains the unique suffix generated by RCTTempFilePath.
• Adds XCTest coverage for default filenames, unique prefixed filenames, writable paths, and invalid input.
• Documents fileName support and prefix behavior for both Android and iOS.

File	Description
src/​index.tsx	Updates CaptureOptions.fileName documentation for both platforms.
README.md	Describes filename prefixes, uniqueness, and validation constraints.
ios/​RNViewShot.mm	Implements validated filename prefixes for temporary captures.
example/​ios/​ViewShotExampleTests/​RNViewShotEncodingTests.mm	Tests default, prefixed, and invalid temporary filenames.

_{Review effort: Balanced}