wolfscp: fix ExtractFileName for separator-less paths

[yosuke-wolfssl]

Fix recursive SCP source abort on separator-less paths

Problem

A recursive SCP source request for a bare relative name with no path separator — e.g. scp -r -f scp_rk_src — aborted immediately after sending the top-level directory message, transferring no files. The receiving side saw WS_SUCCESS but ended up with an empty destination. Absolute paths and any path containing a / worked fine.

Root cause

ExtractFileName() rejected any path with no / or \ separator:

if (separator < 0)
    return WS_BAD_ARGUMENT;

In the recursive first-request path, ScpPushDir() opened the directory successfully, but the following ExtractFileName(peerRequest, ...) returned WS_BAD_ARGUMENT (-1002) for the bare name. The failure then fell into a branch mislabeled "scp: error getting file stats, abort" — so the log pointed at GetFileStats, which was never actually reached. The same helper feeds the single-file request path, so a single-file GET of a bare filename had the same latent bug.

A path with no separator is a valid bare file/directory name (the whole string is the leaf name); the existing length math already handles the separator == -1 case, so only the early-return guard was wrong.

Changes

• src/wolfscp.c — ExtractFileName(): reject only a genuinely empty path (if (pathLen == 0)) instead of any separator-less path. No behavior change for paths containing a separator (absolute paths unchanged). Fixes both the recursive-source and single-file request paths.
• src/wolfscp.c — recursive first-request branch: split the single misleading "error getting file stats" log into per-step messages (open base directory / extract name / get file stats), so a future failure names the actual culprit. Keeps the existing fallthrough cleanup style.
• tests/unit.c — test_ScpExtractFileName: new unit test covering bare name, ./ prefix, nested, absolute, ./.., trailing separator, empty, NULL args, too-small buffer, and the exact size-check boundary. ExtractFileName stays static; the test reaches it through a new wolfSSH_TestScpExtractFileName wrapper guarded by WOLFSSH_TEST_INTERNAL.
• wolfssh/internal.h: prototype for the test wrapper inside the existing WOLFSSH_TEST_INTERNAL block, sub-guarded by WOLFSSH_SCP && !WOLFSSH_SCP_USER_CALLBACKS.

Notes

ExtractFileName was never a path-traversal guard — ../x-style paths always have separator >= 0 and passed through unchanged; only a trivial bare ./.. was incidentally rejected before. Accepting ./.. now matches real scp semantics (scp -r host:. dst); ./.. directory entries are still skipped during the recursive walk, and sink-side path confinement is separate.

Testing

• tests/unit.test → ScpExtractFileName: SUCCESS. Negative control: with the old guard restored the test FAILS (exit 1), so it genuinely catches the bug.
• ASan + UBSan unit build (-fsanitize=address,undefined, no LeakSanitizer on macOS) → clean.
• scripts/scp.test → ALL Tests Passed (single-file client path unaffected).
• End-to-end: recursive transfer of a relative source tree (big.txt, sub/s.txt, top.txt) completes byte-identical (diff -r clean) against examples/echoserver.

[Copilot]

Pull request overview

Fixes wolfSCP source-mode failures when the peer requests a bare relative name (no / or \ separators), which previously caused ExtractFileName() to return WS_BAD_ARGUMENT and abort recursive (and latent single-file) transfers.

Changes:

• Update ExtractFileName() to reject only truly empty paths, allowing separator-less leaf names.
• Improve recursive first-request error logging by reporting failures per-step (open dir / extract name / stat).
• Add internal unit coverage for ExtractFileName() via a new WOLFSSH_TEST_INTERNAL wrapper and a comprehensive unit test.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/wolfscp.c	Fixes separator-less path handling in ExtractFileName(), adds an internal test wrapper, and refines recursive-request error logs.
tests/unit.c	Adds test_ScpExtractFileName covering bare names and a broad set of edge/error cases.
wolfssh/internal.h	Declares the new internal test wrapper under appropriate SCP and test guards.

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[wolfSSL-Fenrir-bot]

Fenrir Automated Review — PR #1020

Scan targets checked: wolfssh-bugs, wolfssh-src

No new issues found in the changed files. ✅