The snap7 asynchronous client cannot read CPU information.

[Buruxianian]

Currently, when using the asynchronous client of the unpublished snap7, it has been found that get_cpu_info differs from the synchronous client: the asynchronous client returns all empty information.

async def get_cpu_info(self) -> S7CpuInfo:
    """Get CPU information."""
    if not self.get_connected():
        raise S7ConnectionError("Not connected to PLC")

    szl = await self.read_szl(0x001C, 0)

    cpu_info = S7CpuInfo()
    data = bytes(szl.Data[: szl.Header.LengthDR])

    if len(data) >= 32:
        cpu_info.ModuleTypeName = data[0:32].rstrip(b"\x00")
    if len(data) >= 56:
        cpu_info.SerialNumber = data[32:56].rstrip(b"\x00")
    if len(data) >= 80:
        cpu_info.ASName = data[56:80].rstrip(b"\x00")
    if len(data) >= 106:
        cpu_info.Copyright = data[80:106].rstrip(b"\x00")
    if len(data) >= 130:
        cpu_info.ModuleName = data[106:130].rstrip(b"\x00")

    return cpu_info
    
    
def get_cpu_info(self) -> S7CpuInfo:
    """
    Get CPU information.

    Uses read_szl(0x001C) to get component identification data.

    Returns:
        CPU information structure
    """
    if not self.get_connected():
        raise S7ConnectionError("Not connected to PLC")

    # Read SZL 0x001C for component identification
    szl = self.read_szl(0x001C, 0)

    # Parse SZL data into S7CpuInfo structure
    cpu_info = S7CpuInfo()
    data = bytes(szl.Data[: szl.Header.LengthDR])

    # S7CpuInfo field sizes (from C structure):
    # ModuleTypeName: 32 bytes
    # SerialNumber: 24 bytes
    # ASName: 24 bytes
    # Copyright: 26 bytes
    # ModuleName: 24 bytes
    if len(data) >= 30:
        cpu_info.ASName = data[6:30].rstrip(b"\x00")
    if len(data) >= 64:
        cpu_info.ModuleName = data[40:64].rstrip(b"\x00")
    if len(data) >= 134:
        cpu_info.Copyright = data[108:134].rstrip(b"\x00")
    if len(data) >= 166:
        cpu_info.SerialNumber = data[142:166].rstrip(b"\x00")
    if len(data) >= 208:
        cpu_info.ModuleTypeName = data[176:208].rstrip(b"\x00")

    return cpu_info

[gijzelaerr]

Thanks for the clear report — you're exactly right.

PR #692 fixed the SZL 0x001C field offsets in the sync Client, but async_client.py was never touched and kept the old layout. That's why the async version returns empty fields against a real PLC.

Fix is in #702. Same offsets that work for the sync client get ported over.

While I was there I also extracted the SZL parsing into snap7/szl.py so both clients call the same helper — that way a future offset fix can only exist in one place. Same treatment for the get_block_info / list_blocks dict→struct conversions, which moved into s7protocol.py. The async tests were also too weak (hasattr(info, "ModuleTypeName") was green even with all-empty fields), so they now assert the same concrete values the sync tests do.