Two Node.FileSystem bug fixes + test cases

[dkoontz]

Summary

Fixes two bugs in the FileSystem.writeFileStream JS kernel (src/Gren/Kernel/FileSystem.js) and adds an integration test suite covering some of the FileSystem API.

Bug 1: Append mode crashes with ERR_OUT_OF_RANGE

writeFileStream encodes its mode as an integer pos: 0 = Replace, -1 = Append, n > 0 = ReplaceFrom n. The start option was computed in the kernel as:

start: pos === 0 ? undefined : pos

For Append (pos = -1) this passed start: -1 to fs.createWriteStream, which Node rejects with ERR_OUT_OF_RANGE, throwing synchronously and failing the Task before any bytes are written.

Fix (384a660): widen the guard to cover both non-offset modes:

start: pos <= 0 ? undefined : pos

Bug 2: writeFileStream using the mode ReplaceFrom leaves trailing bytes from the original file if the original file's length is greater than the written value.

ReplaceFrom n opens the file with flags: "r+" and start: n. createWriteStream writes at the offset but does not truncate, so when the new payload is shorter than the suffix it replaces, stale bytes remain:

• file "abcdef", ReplaceFrom 3 + "XY" → produced "abcXYf" instead of "abcXY".

Fix (76b572): once the stream drains, truncate the file to the prefix length plus what was written:

if (pos > 0) {
fstream.on("finish", function () {
fs.truncate(filePath, pos + fstream.bytesWritten, (_) => {});
});
}

Tests

• writeFile, appendToFile
• writeFileStream in all three modes (Replace, ReplaceFrom, Append) — the latter two directly testing the bugs above
• truncateFile (shrink and zero-pad cases)
• copyFile, remove
• readFile, readFileStream (Beginning, From, Between)

[robinheghan]

Thank you!