netcat: add --crlf to convert LF into CRLF

[gahr]

Summary

This adds the --crlf option to netcat, which triggers translation of \n characters into \r\n sequences in the input -> network direction.
The Linux version of nc also supports this functionality with --crlf and -C. The OpenBSD version uses -C to specify client certificates. Our version is too old and doesn't have it, but I avoided adding -C anyway to ease future syncs with upstream.

Test Plan

An interactive session with nginx suffices to test that --crlf allows you to trigger an HTTP Response.

[markj]

contrib/netcat/netcat.c

174

These should be alphabetically sorted.

986

Suppose there is some data after a LF. Now, if --crlf is specified, we do not write it right away. It looks like we'll poll() and immediately try again, so this is not a problem. Am I understanding correctly?

1059

1062

If the input starts with a LF, we won't add the CR, is that right?

[gahr]

contrib/netcat/netcat.c

986

Yes

1062

Yes, we do add the CR in case the line starts with a LF.

[gahr]

Address style comments

[gahr]

Updating D41489: netcat: add --crlf to convert LF into CRLF

[markj]

contrib/netcat/netcat.c

1062

Sorry, I had misread.

[delphij]

LGTM (note that since this is OS independent it's probably worth a try to upstream it and avoid divergence from OpenBSD)

[gahr]

In D41489#946335, @delphij wrote:

LGTM (note that since this is OS independent it's probably worth a try to upstream it and avoid divergence from OpenBSD)

Good idea, I'll try that!