Experimental: pass first stage parameters in argv

[moreati]

Before (line continuations added manually)

The context label (alex@kintha:<pid>) and preamble length (18191) are encoded inside the base64

ssh -o LogLevel ERROR -o Compression yes -o ServerAliveInterval 15 -o ServerAliveCountMax 3 -o BatchMode yes -o StrictHostKeyChecking yes foo \
    python -c \
    'import sys;sys.path=[p for p in sys.path if p];import binascii,os,zlib;exec(zlib.decompress(binascii.a2b_base64("eNqVkl1PwjAUhu/5Fd61i8toh0pYXCIBFBP5yIIuBheyj04aRtt0GwN/vR0zuGGM8W5P3/ec93Q9ju7aPDUEFQRqLakXNaLxhYKYyw3UrFb5HeXChEjHCGnf7Oh1kkrFFYcJTwl06iDr4NahUFAF5szfqvgl8mwbDH1ZUAZ8FtUl01tapncLcO+opIfUIHsS5pkfJERVtfNUtgPK2uKQrTkD1pnj3GAaXfDveHVuIhOfJtgRmVLOllanrCxbWqqGsB2V6hTMXxfj2XT11H+eDsaj4eremU1WrtOfz0cO8GyAwfFvnPx95+EFKaE5euVRmMCmoDfxEsAtzfg7YZafkP3dhrJs7VtX3ZvOtQa0lupSSJoRiHUweVzMEEJvDKj0kEfqilorFuUmxBEXhKknBzJQVQP7I6GBEZGQb4UkaQpjYUjiRxB3e2bvWPb1nmcdXB0UASg3RTmq5MHv7uIv98/xcXP8016Z2icQlOoP")))'

After (line continuations added manually)

The base64 blob (first stage), context label, and preamble length are seperate argv items.

ssh -o LogLevel ERROR -o Compression yes -o ServerAliveInterval 15 -o ServerAliveCountMax 3 -o BatchMode yes -o StrictHostKeyChecking yes foo \
    python -c \
    'import sys;sys.path=[p for p in sys.path if p];import binascii,os,zlib;exec(zlib.decompress(binascii.a2b_base64(sys.argv[1]),-15))' \
    pZJdS8MwGIXv+yu8GW/CSpd2F2KhF2ObTnAflGmRWUY/0hnckpK0q/PXm7IxW0URvcvDOXlP3nB8M/CEsnKWU4QNaVYNYtmFhkzIF4Rdoz6nZe4gYtqE4A/2zSZJrdpHTrZCUeQ3QTYhaEKl4RhY8min41ck7DbICVeuE3bVQVn0lSZlEcVb6nkwimTFuH3VK5XsxYz38kPxLDi4bWfXA8e6hF9n7KlUTPCV2w/PIQ6pR7j6AuV7JrUKi8flZD5b3w3uZ8PJeLS+9ufTdeAPFouxD6EH9j8T7T8lNv0D/+aBaKH9HUePxi1qC+anbwO0Y4XYUO52FIZOrUZys9cPx4YeUUlWUGSbML1dzgkhTxx0dCJSvRw2srpMWSpyynVrQMaAjaH3tmWxldJE7HJJlUKZJWmUIsYLdB7fD3F9/9SN9qTAhCqGunTZKX/4nbX62fp1Abu9wLmdDn4H \
    alex@kintha:58688 \
    18191

[moreati]

The old arrangemet was 759 bytes, as measured by preamble_size.py, latest compression tweaks and code golfing have dropped that to approx 743 bytes. The new arrangement is 773 bytes, including latest compression tweaks and golfing.

Benefits of the new arrangement are

• static first stage
  • speedup - It doesn't have to be dynamically regenerated for each context/connection.
  • transparency - the scary base64 blob can be reversed once, analysed once, subjected to much tighter filtering or allow listing
  • less magic - no 'constants' that are actually string labels replaced at runtime
  • looser coupling - between the python -c ... stage (zeroth stage) and the first stage.

[moreati]

refs #711

[moreati]

env -S ... might be of use

-S, --split-string=S
    process and split S into separate arguments; used to pass multiple arguments on shebang lines

-- https://manpages.debian.org/trixie/coreutils/env.1.en.html