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flwrap

Wraps a file with a checksum so the far end knows it arrived intact

What it does

Takes a file, compresses it, adds a header with the filename and a checksum over the contents, and produces a text block that can be sent through any digital mode as if it were typed. At the far end it verifies the checksum and writes the file back out with its original name.

Why you would want it

A file sent as text through a keyboard mode arrives as text, and there is no way to tell a clean copy from one with three characters wrong. The checksum is the whole point: it converts "it looked all right" into a yes or a no. It is the simplest of the NBEMS tools and the one to use when flamp's block-fill machinery is more than the job needs.

Before it will work

fldigi or any other mode capable of sending text. Unlike flamp it does not drive the modem itself -- you paste or send the wrapped block yourself.

How it installs

  • apt: flwrap

Known problems

There is no fill mechanism. A wrapped file with one bad character fails its checksum and the whole thing is resent; for anything large over a marginal path, flamp is the right tool instead. The compression means a corrupted block usually fails to decompress rather than producing subtly wrong output, which is the safe failure but an opaque one. Debian's Homepage field for this package points at w1hkj.com, which no longer serves the project. Corrected 2026-08-29 after re-checking: it does still resolve, and both it and www.w1hkj.com 301-redirect to kylegentz.com, which has no DNS record at all — so the chain ends nowhere. The subpaths Debian cites return 404 on the way. An earlier note here said the redirect landed on "an unrelated site"; that was read from an empty response and the accurate statement is that the target does not exist. Either way the packaged link is useless, and the live project is w1hkj.org, which is what this manifest points at.

Keeping it current

  • probe: apt policy
  • strategy: apt_upgrade

Where to get help with the software itself

The W1HKJ suite -- linuxham on groups.io.

Source: catalog/packages/flwrap.yaml