sic — quoting-proof remote command execution

Client (sic) frames argv as netstrings and pipes it over ssh to a daemon
(sicd) that execvp's it, so no shell re-parses the arguments. exec mode by
default; opt-in sh mode for pipes/redirects/globs. Go client + daemon, Python
reference daemon, design doc, quoting-hell demo, and foreground/background
agent skills.

Renamed from the climcp prototype.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EWpfhDgYNA21tETDP9ueBE

demos/quoting-hell.py

@@ -0,0 +1,178 @@
+#!/usr/bin/env python3
+"""Demonstrate quoting hell scenarios with plain SSH and how sicd fixes them.
+
+Each scenario is run both ways:
+  A) Plain SSH — shows the breakage
+  B) sic tool    — shows the fix
+
+Usage:
+  python3 demo-quoting-hell.py <host>
+"""
+import subprocess
+import sys
+import shlex
+import tempfile
+import os
+
+HOST = sys.argv[1] if len(sys.argv) > 1 else "quotesu"
+
+SIC = os.path.expanduser("~/bin/sic")
+SSH = ["/usr/bin/ssh", "-o", "StrictHostKeyChecking=no", "-o", "ConnectTimeout=5"]
+
+
+def ssh(cmd_str):
+    """Run a command string via plain SSH."""
+    return subprocess.run(
+        SSH + [HOST, cmd_str],
+        capture_output=True, text=True, timeout=10
+    )
+
+
+def sic(*args):
+    """Run argv via sic tool (which frames netstrings for sicd)."""
+    return subprocess.run(
+        [SIC, HOST] + list(args),
+        capture_output=True, text=True, timeout=10
+    )
+
+
+def section(title):
+    print(f"\n{'='*60}")
+    print(f"  {title}")
+    print(f"{'='*60}")
+
+
+def sub(test_name):
+    print(f"\n  ▶ {test_name}")
+
+
+def result(label, r):
+    stdout = r.stdout.strip() if r.stdout else ""
+    stderr = r.stderr.strip() if r.stderr else ""
+    status = "OK" if r.returncode == 0 else f"FAIL (rc={r.returncode})"
+    print(f"    {label}: {status}")
+    for line in stdout.split("\n"):
+        if line:
+            print(f"      → {line}")
+    for line in stderr.split("\n"):
+        if line:
+            print(f"      ! {line}")
+
+
+# ── 1. Space in filename ──────────────────────────────────────────
+section("1. Space in filename — the classic")
+
+sub("SSH: ssh host touch 'my file.txt'")
+# SSH concatenates args with spaces, remote shell re-splits
+r = ssh("touch 'my file.txt'")
+r2 = ssh("ls my file.txt 2>&1; echo ---; ls 'my file.txt' 2>&1")
+result("SSH", r2)
+print("    → 'touch' sees TWO args: 'my' and 'file.txt' — two files created")
+
+# Clean up
+ssh("rm -f my file.txt 'my file.txt'")
+
+sub("rs: rs quotesu touch 'my file.txt'")
+r = sic("touch", "my file.txt")
+r2 = sic("ls", "-la", "my file.txt")
+result("rs", r2)
+print("    → 'touch' sees ONE arg: 'my file.txt' — one file created")
+sic("rm", "-f", "my file.txt")
+
+
+# ── 2. Dollar sign / variable expansion ───────────────────────────
+section("2. Dollar sign — unintended variable expansion")
+
+sub("SSH: ssh host 'echo \$HOME'")
+r = ssh("echo $HOME")
+result("SSH", r)
+print("    → Remote shell expands $HOME — leaks local values")
+
+sub("SSH escaped: ssh host 'echo \\$HOME'")
+r = ssh("echo \\$HOME")
+result("SSH escaped", r)
+
+sub("rs: rs quotesu echo '\$HOME'")
+r = sic("echo", "$HOME")
+result("rs", r)
+print("    → No shell involved — literal $HOME printed")
+
+
+# ── 3. Backticks / command substitution ──────────────────────────
+section("3. Backticks — unintended command execution")
+
+sub("SSH: ssh host 'echo `hostname`'")
+r = ssh("echo `hostname`")
+result("SSH", r)
+print("    → Backticks execute on remote — prints quotesu")
+
+sub("rs: rs quotesu echo '`hostname`'")
+r = sic("echo", "`hostname`")
+result("rs", r)
+print("    → Literal backticks — no execution")
+
+
+# ── 4. Nested quotes ─────────────────────────────────────────────
+section("4. Nested quotes — escaping hell")
+
+sub('SSH: ssh host "echo \\"hello world\\""')
+r = ssh('echo "hello world"')
+result("SSH", r)
+
+sub('rs: rs quotesu echo "hello world"')
+r = sic("echo", "hello world")
+result("rs", r)
+print("    → No nested quoting needed — just pass the string")
+
+
+# ── 5. Newlines in arguments ──────────────────────────────────────
+section("5. Newlines in arguments")
+
+sub("SSH: ssh host 'echo \"line1\\nline2\"'")
+r = ssh('echo "line1\nline2"')
+result("SSH", r)
+print("    → Newline in SSH command string is fragile")
+
+sub("rs: rs quotesu echo 'line1\\nline2'")
+r = sic("echo", "line1\nline2")
+result("rs", r)
+print("    → Newline is just a byte in a netstring field")
+
+
+# ── 6. Complex python script via ssh ─────────────────────────────
+section("6. Python one-liner — where quoting really hurts")
+
+script = """python3 -c "import sys; [print(i, repr(a)) for i,a in enumerate(sys.argv)]" -- "first arg" "second arg" "arg with $HOME" "arg with \`ls\`" "nested \\"quotes\\"" """
+
+sub("SSH: the monstrosity")
+r = ssh(script)
+result("SSH", r)
+print("    → Try to get all those quoting levels right...")
+
+sub("rs: rs quotesu python3 -c ... with clean args")
+r = sic(
+    "python3", "-c",
+    "import sys; [print(i, repr(a)) for i,a in enumerate(sys.argv)]",
+    "demo",  # sys.argv[0]
+    "first arg",
+    "second arg",
+    "arg with $HOME",
+    "arg with `ls`",
+    'nested "quotes"'
+)
+result("rs", r)
+print("    → Each argument is a separate field — no escaping needed")
+
+
+# ── Summary ──────────────────────────────────────────────────────
+section("SUMMARY")
+print("""
+  The pattern in every case:
+    SSH  → flattens argv to one string, shell re-parses → QUOTING HELL
+    rs   → sends argv as framed fields, execvp directly → NO ESCAPING
+
+  Netstrings (length:bytes,) are the key: the length tells the parser
+  exactly where each field ends, so NO delimiter needs escaping.
+  This is the same insight as git -z / find -print0 / xargs -0,
+  but generalized to arbitrary remote command execution.
+""")