Accept exact-fit ScpBuffer in no-filesystem SCP send callback

[yosuke-wolfssl]

Problem

The default no-filesystem SCP send callback (wsScpSendCallback under
NO_FILESYSTEM without WOLFSSH_SCP_USER_CALLBACKS) rejected any
ScpBuffer whose bufferSz exactly equals fileSz: its capacity checks
used >=, so an exact-fit transfer — the natural sizing for this API —
aborted with WS_SCP_ABORT on the final chunk, or immediately when the
whole file fit one request. Logic error, High severity.

Fix (src/wolfscp.c)

• >= → > on the three capacity checks, so idx + ret == bufferSz
  (and idx == bufferSz in the continue state) is accepted as an exact fit
  and completed transfers fall through to the WS_EOF return.
• idx > fileSz aborts in both transfer states, so the unsigned
  fileSz - idx size math can never be used after wraparound on a
  mis-populated application context.
• NULL check on the optional status callback before invoking it in
  the continue state.

Closes f-8821 and f-8822.

Tests (tests/unit.c)

New test_ScpSendCallback_ExactFitBuffer: exact-fit single- and
multi-chunk transfers, WS_EOF after completion, oversized-file
rejection, one-past-the-boundary reject cases for each relaxed guard,
underflow shapes where the idx > fileSz check is the only rejection
path, and a NULL status callback.

CI (.github/workflows/os-check.yml)

No existing workflow defined NO_FILESYSTEM, so the changed code and its
test were compiled nowhere in CI. A build_wolfssh_no_filesystem job is
added to the os-check workflow, reusing its cached wolfSSL builds and
version matrix (master plus the two latest releases). It builds
tests/unit.test directly — the examples do not build without a
filesystem (pre-existing, unrelated) — runs it, and requires the new test
to appear and pass, failing on silent compile-out.

Verification

• CI: the NO_FILESYSTEM job ran green on this PR with
  ScpSendCallback_ExactFitBuffer: SUCCESS in the log.
• Local NO_FILESYSTEM config: unit test clean under ASan + UBSan.
• Default config: all unit tests pass; gcc-13 -Werror preflight clean
  on 6 configs.
• Negative controls: removing any single guard makes its test case fail.

[Copilot]

Pull request overview

Fixes the default NO_FILESYSTEM SCP send callback to correctly allow exact-fit ScpBuffer transfers (where bufferSz == fileSz) and hardens bounds checking to prevent underflow/overflow paths, then adds targeted unit coverage and CI to ensure the NO_FILESYSTEM build path is compiled and tested.

Changes:

• Adjusts wsScpSendCallback() capacity/idx guards to accept exact-fit buffers and reject out-of-range indices safely.
• Adds a new unit test covering exact-fit single/multi-chunk sends, boundary rejects, underflow shapes, and NULL status callback handling under NO_FILESYSTEM.
• Introduces a GitHub Actions workflow to build and run unit tests with -DNO_FILESYSTEM.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
src/wolfscp.c	Fixes exact-fit handling and strengthens bounds checks in the no-filesystem SCP send callback.
tests/unit.c	Adds a dedicated unit test for exact-fit/no-filesystem SCP send behavior and edge cases.
.github/workflows/no-filesystem-check.yml	Adds CI coverage to compile and run unit tests with NO_FILESYSTEM enabled.

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[wolfSSL-Fenrir-bot]

Fenrir Automated Review — PR #1161

Scan targets checked:wolfssh-bugs, wolfssh-src

Findings: 1
1 finding(s) posted as inline comments (see file-level comments below)

This review was generated automatically by Fenrir. Findings are non-blocking.

[wolfSSL-Fenrir-bot]

Fenrir Automated Review — PR #1161

Scan targets checked:wolfssh-bugs, wolfssh-src

No new issues found in the changed files. ✅

[ejohnstown]

One thing to fix before merge. The CI step runs ./tests/unit.test | tee unit-test.log under bash -e with no pipefail, so the pipeline's status is tee's. Any other unit test failing is swallowed, and only the grepped name gates the job. Add set -o pipefail.

[yosuke-wolfssl]

Thank you @ejohnstown, I fixed this as you suggested.