WIP trying to figure out git

documentation/git_notes.md

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+The relevant ulities for implementing a git server are:
+* git-upload-pack
+* git-recieve-pack
+* git-fetch-pack
+* git-send-pack
+
+Not all of these are installed by git packages,
+but they are very much real binaries produced by standard builds.
+
+Communication model:
+       (client)          (server)
+    git-fetch-pack => git-upload-pack   # pull
+    git-send-pack  => git-recieve-pack  # push

gn-daemon

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+#!/usr/bin/env python3
+"""
+gn-daemon: Gorillanest daemon accepting commands over SSH
+
+Commands:
+    git-upload-pack
+    git-receive-pack
+    new-repo [--migrate URL] [--pull-mirror]
+    git config remote.$1.$2 $3
+        /* NOTE: 
+         *   git actually allows adding arbitrary bullshit,
+         *   therefor the maximum number of remotes must be limited
+         *   and the fields must be on a whitelist;
+         *   a special field should be added called sync,
+         *   which determines mirror frequency
+         */
+"""
+import asyncio
+import os
+import asyncssh
+import subprocess
+import logging
+from sys import exit
+
+logging.basicConfig(level=logging.INFO)
+log = logging.getLogger("gn-daemon")
+
+HOST_KEY_PATH = "gn_host_key"   # XXX
+LISTEN_ADDR = "0.0.0.0"
+LISTEN_PORT = 2222
+
+def connection_made(conn):
+    log.info("Connection from %s", conn.get_extra_info("peername"))
+
+def connection_lost(exc):
+    if exc: log.warning("Connection error: %s", exc)
+    else: log.info("Connection closed")
+
+def validate_password(username, password):
+    return username == "anon" and password == "passwd"
+
+# Implementing AsyncSSH functionality is done though primarily polymorphism.
+#  This is the class it expects.
+#  Complete function definitions are moved out so that
+#   this class doesn't dominate the script,
+#   and its never in question what should and should not be inside it.
+class GNServer(asyncssh.SSHServer):
+    def connection_made(self, conn): connection_made(conn)
+    def connection_lost(self, exc):  connection_lost(exc)
+
+    def begin_auth(self, username):    return True
+    def password_auth_supported(self): return True
+
+    def validate_password(self, username, password):
+        return validate_password(username, password)
+# ---
+
+def ensure_host_key(path: str):
+    if os.path.exists(path): return path
+
+    log.info("Generating ephemeral host key (saved to %s)", path)
+    key = asyncssh.generate_private_key('ssh-rsa')
+    with open(path, "wb") as f: f.write(key.export_private_key())
+    os.chmod(path, 0o600)
+
+    return path
+
+async def gn_process(proc : asyncssh.SSHServerProcess):
+    cmd = proc.command
+
+    async def pump(reader, writer):
+        while True:
+            data = await reader.read(4096)
+            if not data: break
+            log.info(data)
+            writer.write(str(data))
+            await writer.drain()
+
+    sub = await asyncio.create_subprocess_exec(
+        '/bin/sh', '-c', cmd, # XXX
+        stdin=asyncio.subprocess.PIPE,
+        stdout=asyncio.subprocess.PIPE,
+        stderr=asyncio.subprocess.PIPE,
+    )
+
+    await asyncio.gather(
+        pump(proc.stdin, sub.stdin),
+        pump(sub.stdout, proc.stdout),
+        pump(sub.stderr, proc.stderr)
+    )
+
+    rc = await sub.wait()
+    proc.exit(rc)
+
+async def start_server():
+    host_key_path = ensure_host_key(HOST_KEY_PATH)
+
+    await asyncssh.create_server(
+        GNServer,
+        LISTEN_ADDR,
+        LISTEN_PORT,
+        server_host_keys=[host_key_path],
+        process_factory=gn_process,
+    )
+
+    await asyncio.Future()
+
+if __name__ == "__main__":
+    try: asyncio.run(start_server())
+    except (OSError, asyncssh.Error) as exc:
+        log.error("Error starting server: %s", exc)