Fuse in BoxLite demo

fuse_in_boxlite.py

#!/usr/bin/env python3  # Shebang for direct execution
import asyncio  # Async runtime for SimpleBox
import boxlite  # BoxLite Python SDK
import textwrap  # Embed the guest-side FUSE script as a string

# Minimal FUSE filesystem served inside the box (as a multi-line string)
FUSE_SCRIPT = textwrap.dedent(r"""
    #!/usr/bin/env python3  # Guest-side shebang
    import os, sys, time, stat  # Stdlib imports inside guest
    from mfusepy import FUSE, Operations  # FUSE bindings inside guest

    class Hello(Operations):  # Minimal FUSE filesystem implementation
        use_ns = True  # Use nanosecond timestamps to avoid utimens float deprecation
        def readdir(self, path, fh):  # List directory entries
            return [".", "..", "hello.txt"]  # Root contains one file
        def getattr(self, path, fh=None):  # Return metadata for paths
            now = time.time()  # Current timestamp for attributes
            if path == "/":  # Root directory attributes
                return dict(st_mode=stat.S_IFDIR | 0o755, st_nlink=2,
                            st_ctime=now, st_mtime=now, st_atime=now)  # Dir attrs
            return dict(st_mode=stat.S_IFREG | 0o444, st_nlink=1, st_size=12,
                        st_ctime=now, st_mtime=now, st_atime=now)  # File attrs
        def read(self, path, size, offset, fh):  # Provide file contents
            return b"hello world\n"[offset:offset+size]  # Slice static bytes

    if __name__ == "__main__":  # Guest entrypoint
        mountpoint = sys.argv[1]  # Mount target from argv
        os.makedirs(mountpoint, exist_ok=True)  # Ensure mount dir exists
        os.environ.setdefault("FUSE_LIBRARY_PATH", "/usr/lib/libfuse3.so.4")  # Point to libfuse3
        FUSE(Hello(), mountpoint, foreground=True)  # Run FUSE in foreground
""")  # End of guest script string

async def main():  # Host-side async entrypoint
    async with boxlite.SimpleBox(image="alpine:latest") as box:  # Start Alpine box
        async def run(label, *cmd):  # Helper: run a command and print outputs
            res = await box.exec(*cmd)  # Execute inside the box
            print(f"[{label}] exit={res.exit_code}")  # Show exit code
            if res.stdout:  # If stdout exists
                print(f"[{label}] stdout:\n{res.stdout.rstrip()}\n")  # Print stdout
            if res.stderr:  # If stderr exists
                print(f"[{label}] stderr:\n{res.stderr.rstrip()}\n")  # Print stderr
            return res  # Return ExecResult

        await run("apk", "apk", "add", "--no-cache",  # Install FUSE and Python
                 "fuse", "fuse3", "fuse3-libs", "python3", "py3-pip")  # Packages list

        await run("mknod", "sh", "-c", "test -e /dev/fuse || mknod /dev/fuse c 10 229")  # Ensure /dev/fuse

        await run("pip", "pip3", "install", "--no-cache-dir",  # Install mfusepy
                 "--break-system-packages", "mfusepy==3.1.0")  # Version pin

        await run("write", "sh", "-c", f"cat > /tmp/hello_fuse.py <<'PY'\n{FUSE_SCRIPT}\nPY")  # Write guest script

        await run("chmod", "chmod", "+x", "/tmp/hello_fuse.py")  # Make script executable

        await run("mkdir", "mkdir", "-p", "/tmp/mnt")  # Create mountpoint

        pid = (await run("start", "sh", "-c",  # Launch FUSE server in background
            "python3 /tmp/hello_fuse.py /tmp/mnt >/tmp/fuse.log 2>&1 & echo $!"
        )).stdout.strip()  # Capture PID

        await run("cat", "cat", "/tmp/mnt/hello.txt")  # Read from FUSE FS

        await run("fusermount", "fusermount3", "-u", "/tmp/mnt")  # Unmount

        await run("kill", "kill", pid)  # Stop server process

        await run("log", "cat", "/tmp/fuse.log")  # Show server log

        print(f"[info] FUSE server PID was {pid}")  # Final info line

if __name__ == "__main__":  # Script entrypoint
    asyncio.run(main())  # Run async main