feat(fs): API for replacing os calls

[maxunt]

This PR replaces calls to os.Create and os.Rename with our own API for consistent error messaging and to prevent writing over files that already exist

• CHANGELOG.md updated with a link to the PR (not the Issue)
• Well-formatted commit messages
• Rebased/mergeable
• Tests pass
• http/swagger.yml updated (if modified Go structs or API)
• Documentation updated or issue created (provide link to issue/pr)
• Signed CLA (if not already signed)

[e-dard]

I don't think you should have updated the Python code? Other than that this looks great!

[e-dard]

What's going on with this Python code?

[e-dard]

@maxunt needs at least one more careful review.

[benbjohnson]

Minor nit but it's not clear from the name that it's writing its own name to the filename. I think it would be clearer from the caller to pass in a string for the data to write. Also, probably worth adding an error check on os.File.WriteString():

// MustCreateTempFile creates a temporary file returning the path to the file.
func MustCreateTempFile(data string) string {
	f, err := ioutil.TempFile("", "fs-test")
	if err != nil {
		panic(fmt.Sprintf("failed to create temp file: %v", err))
	} else if _, err := f.WriteString(data); err != nil {
		panic(err)
	} else if err := f.Close(); err != nil {
		panic(err)
	}
	return name
}

Another approach I've been doing more lately is making the function a helper and naming it something like CreateTempFileOrFail(). That way it only fails the test instead of the whole program execution (although temp files are unlikely to fail).

// CreateTempFileOrFail creates a temporary file returning the path to the file.
func MustCreateTempFile(t testing.TB, data string) string {
	tb.Helper()
	
	f, err := ioutil.TempFile("", "fs-test")
	if err != nil {
		tb.Fatalf("failed to create temp file: %v", err)
	} else if _, err := f.WriteString(data); err != nil {
		t.Fatal(err)
	} else if err := f.Close(); err != nil {
		t.Fatal(err)
	}
	return name
}

[tmgordeeva]

LGTM, had a small question.

[tmgordeeva]

Would it be safer to rename the existing newpath to a temporary file before renaming oldpath, and then doing the removal last?

[maxunt]

I'm not exactly sure what you are asking, but using RenameFileWithReplacement is safe if you expect and are planning for any old contents of newpath to be truncated and lost. The RenameFile func exists as a tool to ensure you do not lose any data accidentally.