Re: Accessing DataSocket Server with Python
On May 28, 2015, at 6:17 PM, Dan Stromberg drsali...@gmail.com wrote: I have no idea about the protocol used by NI DataSockets, but you might be able to reverse engineer the protocol by using the official client with a sniffer. Also, be aware that TCP/IP guarantees that you get the correct data in the correct order, but it doesn't guarantee anything about the sizes of the chunks in which that data arrives. So you could send 100 bytes, 100 bytes, 100 bytes, but on the other end receive 100 bytes, 50 bytes, 75 bytes, 75 bytes. When you catenate them all together, it's still the same data though. HTH. On Wed, May 27, 2015 at 4:30 AM, Garrone, Corrado While that’s certainly possible in a routed network (and even then can be overridden with the “do not fragment” bit), it won’t happen in a LAN or self-contained instrument set-up. These days, even routed networks tend to deliver anything less than a 1500 byte packet as a single entity. With fiber backbones and high-speed LANs, it is more work for a router to fragment a packet then to simply pass it on. The days of 480 byte packets pretty much went away with dial-up modems. Bill corrado.garr...@roche.com wrote: Dear Python Team, currently I am working on a research project for my bachelor degree. A LabVIEW application is used for current and power measurements, whereas the measured data are sent to DataSocket Server, a technology by National Instruments used for data exchange between computers and applications. DataSocket is based on TCP/IP and thus requesting data from DataSocket should be similar to an internet request. I know with the socket library in Python it is possible with to establish sockets, send internet requests and communicate between clients and servers. Is there a possibility to access NI DataSocket and get measurement data with Python on the same computer where Python is installed and the codes are executed? Can you maybe send me an example code where such a connection with DataSocket is established? If you got any queries, please do not hesitate to contact me. Thank you very much for your efforts. Kind regards, Corrado Garrone DH-Student Fachrichtung Elektrotechnik / Co-op Student B.Eng. Electrical Engineering Roche Diagnostics GmbH DFGHMV8Y6164 Sandhofer Strasse 116 68305 Mannheim / Germany Phone: apprentice mailto:corrado.garr...@roche.com Roche Diagnostics GmbH Sandhofer Straße 116; D‑68305 Mannheim; Telefon +49‑621‑759‑0; Telefax +49‑621‑759‑2890 Sitz der Gesellschaft: Mannheim - Registergericht: AG Mannheim HRB 3962 - Geschäftsführung: Dr. Ursula Redeker, Sprecherin; Edgar Vieth - Aufsichtsratsvorsitzender: Dr. Severin Schwan Confidentiality Note This message is intended only for the use of the named recipient(s) and may contain confidential and/or privileged information. If you are not the intended recipient, please contact the sender and delete the message. Any unauthorized use of the information contained in this message is prohibited. -- https://mail.python.org/mailman/listinfo/python-list -- https://mail.python.org/mailman/listinfo/python-list -- https://mail.python.org/mailman/listinfo/python-list
Re: Accessing DataSocket Server with Python
On 2015-05-29, Chris Angelico ros...@gmail.com wrote: On Sat, May 30, 2015 at 2:29 AM, Grant Edwards invalid@invalid.invalid wrote: If you assume TCP read/write operations are atomic and message boundaries are preserved, your code is wrong. It will eventually fail. Period. Indeed. That said, though, if your writes are all smaller than one packet, and you perfectly alternate a write and a read, a write and a read, at both ends, then you can go a very long way without ever running into this. That's true. You probably won't see a failure until you do something like run through some sort of WAN connection (satellite and PPP links are excellent for exposing bad network code), or somebody configures a switch, router, or IP interface in a goofy (but entire valid) way, or somebody changes the app such that it writes more than 1500 bytes, or it violates the strict alternation of reads/writes. But someday, somehow, (IME) one of those always happens. And whoever has to fix it will wish bad things upon you and your descendants. I've lost count of the times I've had to fix somebody else's code that broke because they assumed TCP was a datagram service rather than a byte-stream service. -- Grant Edwards grant.b.edwardsYow! UH-OH!! I put on at GREAT HEAD-ON TRAIN gmail.comCOLLISIONS of the 50's by mistake!!! -- https://mail.python.org/mailman/listinfo/python-list
Re: Accessing DataSocket Server with Python
On 2015-05-29, William Ray Wing w...@mac.com wrote: While that’s certainly possible in a routed network (and even then can be overridden with the “do not fragment” bit), it won’t happen in a LAN or self-contained instrument set-up. You don't know that. These days, even routed networks tend to deliver anything less than a 1500 byte packet as a single entity. Doesn't matter. It can still happen in the network stack on either end. If you quickly call send() which small amounts of data, it's quite possible that the network stack will combine them into a single packet. Under some conditions this is done intentionally to reduce the overall network overhead. On the receiving end, if several small packets are received between calls to recv(), then a single call to recv() will return data from multiple packets. With fiber backbones and high-speed LANs, it is more work for a router to fragment a packet then to simply pass it on. The days of 480 byte packets pretty much went away with dial-up modems. But modern TCP/IP stacks will still combine packets to save on network overhead. If you assume TCP read/write operations are atomic and message boundaries are preserved, your code is wrong. It will eventually fail. Period. -- Grant Edwards grant.b.edwardsYow! Inside, I'm already at SOBBING! gmail.com -- https://mail.python.org/mailman/listinfo/python-list
Re: Accessing DataSocket Server with Python
On Fri, May 29, 2015 at 11:37 PM, William Ray Wing w...@mac.com wrote: On May 28, 2015, at 6:17 PM, Dan Stromberg drsali...@gmail.com wrote: I have no idea about the protocol used by NI DataSockets, but you might be able to reverse engineer the protocol by using the official client with a sniffer. Also, be aware that TCP/IP guarantees that you get the correct data in the correct order, but it doesn't guarantee anything about the sizes of the chunks in which that data arrives. So you could send 100 bytes, 100 bytes, 100 bytes, but on the other end receive 100 bytes, 50 bytes, 75 bytes, 75 bytes. When you catenate them all together, it's still the same data though. HTH. On Wed, May 27, 2015 at 4:30 AM, Garrone, Corrado While that’s certainly possible in a routed network (and even then can be overridden with the “do not fragment” bit), it won’t happen in a LAN or self-contained instrument set-up. These days, even routed networks tend to deliver anything less than a 1500 byte packet as a single entity. With fiber backbones and high-speed LANs, it is more work for a router to fragment a packet then to simply pass it on. The days of 480 byte packets pretty much went away with dial-up modems. It's uncommon to receive 100, 50, 75, 75, to be sure, but it's certainly possible for multiple writes to be gathered together into single reads; there are buffers at both ends, and if there's any delay anywhere, stuff can get combined while it's waiting. (Even stuff that had previously been sent out as multiple packets, if the data has to be re-sent, might get grouped.) So you still need to consider your protocol to be a stream, and delimit messages explicitly rather than depending on the length of a socket-read. Most of these kinds of protocols seem to have some kind of message boundary system, though, so this shouldn't be a problem. (I'm not familiar with DataSocket itself, but I've used several others that are like that. Even venerable TELNET effectively does - a message is a line of text, so it's delimited by newline.) ChrisA -- https://mail.python.org/mailman/listinfo/python-list
Re: Accessing DataSocket Server with Python
On Sat, May 30, 2015 at 2:29 AM, Grant Edwards invalid@invalid.invalid wrote: If you assume TCP read/write operations are atomic and message boundaries are preserved, your code is wrong. It will eventually fail. Period. Indeed. That said, though, if your writes are all smaller than one packet, and you perfectly alternate a write and a read, a write and a read, at both ends, then you can go a very long way without ever running into this. In that case, you could have proper parsing and buffering as a failure case, with the normal case expecting a termination mark at the end of the socket-read - something like this: write(query) data = read(as_much_as_possible) if data[-1] != \n: # Huh, stuff got split. while True: more_data = read(as_much_as_possible) data += moredata if data[-1] == \n: break cope_with_possibility_of(socket_disconnection) handle_response(data) Alternating writes and reads ensures that two messages can't be combined, and if a single message fits inside a packet, it'll usually be sent that way. But you still can't guarantee that. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
Re: Accessing DataSocket Server with Python
Chris Angelico ros...@gmail.com: Indeed. That said, though, if your writes are all smaller than one packet, and you perfectly alternate a write and a read, a write and a read, at both ends, then you can go a very long way without ever running into this. Rare errors are worse than consistent errors. TCP streams are intercepted by address translators, load balancers, proxies, protocol translators and what not. They will eagerly take advantage of the fact that TCP is a full-duplex octet stream. Also, programs could be plugged into other types of octet stream with other stream chopping characteristics. Finally, the MTU size is very unpredictable. You have all kinds of encapsulation (6to4, VPN, VLAN, tunneling etc) that make it difficult to be sure about what's a small write. What's more, you should be on the lookout for partial writes not block until they finish. Typically, it is not enough to rely on TCP's flow control but also impose a separate application-level, end-to-end flow control to avoid deadlocks on the one hand and buffer overflows on the other hand. Marko -- https://mail.python.org/mailman/listinfo/python-list
Re: Accessing DataSocket Server with Python
I have no idea about the protocol used by NI DataSockets, but you might be able to reverse engineer the protocol by using the official client with a sniffer. Also, be aware that TCP/IP guarantees that you get the correct data in the correct order, but it doesn't guarantee anything about the sizes of the chunks in which that data arrives. So you could send 100 bytes, 100 bytes, 100 bytes, but on the other end receive 100 bytes, 50 bytes, 75 bytes, 75 bytes. When you catenate them all together, it's still the same data though. HTH. On Wed, May 27, 2015 at 4:30 AM, Garrone, Corrado corrado.garr...@roche.com wrote: Dear Python Team, currently I am working on a research project for my bachelor degree. A LabVIEW application is used for current and power measurements, whereas the measured data are sent to DataSocket Server, a technology by National Instruments used for data exchange between computers and applications. DataSocket is based on TCP/IP and thus requesting data from DataSocket should be similar to an internet request. I know with the socket library in Python it is possible with to establish sockets, send internet requests and communicate between clients and servers. Is there a possibility to access NI DataSocket and get measurement data with Python on the same computer where Python is installed and the codes are executed? Can you maybe send me an example code where such a connection with DataSocket is established? If you got any queries, please do not hesitate to contact me. Thank you very much for your efforts. Kind regards, Corrado Garrone DH-Student Fachrichtung Elektrotechnik / Co-op Student B.Eng. Electrical Engineering Roche Diagnostics GmbH DFGHMV8Y6164 Sandhofer Strasse 116 68305 Mannheim / Germany Phone: apprentice mailto:corrado.garr...@roche.com Roche Diagnostics GmbH Sandhofer Straße 116; D‑68305 Mannheim; Telefon +49‑621‑759‑0; Telefax +49‑621‑759‑2890 Sitz der Gesellschaft: Mannheim - Registergericht: AG Mannheim HRB 3962 - Geschäftsführung: Dr. Ursula Redeker, Sprecherin; Edgar Vieth - Aufsichtsratsvorsitzender: Dr. Severin Schwan Confidentiality Note This message is intended only for the use of the named recipient(s) and may contain confidential and/or privileged information. If you are not the intended recipient, please contact the sender and delete the message. Any unauthorized use of the information contained in this message is prohibited. -- https://mail.python.org/mailman/listinfo/python-list -- https://mail.python.org/mailman/listinfo/python-list
Accessing DataSocket Server with Python
Dear Python Team, currently I am working on a research project for my bachelor degree. A LabVIEW application is used for current and power measurements, whereas the measured data are sent to DataSocket Server, a technology by National Instruments used for data exchange between computers and applications. DataSocket is based on TCP/IP and thus requesting data from DataSocket should be similar to an internet request. I know with the socket library in Python it is possible with to establish sockets, send internet requests and communicate between clients and servers. Is there a possibility to access NI DataSocket and get measurement data with Python on the same computer where Python is installed and the codes are executed? Can you maybe send me an example code where such a connection with DataSocket is established? If you got any queries, please do not hesitate to contact me. Thank you very much for your efforts. Kind regards, *Corrado Garrone* DH-Student Fachrichtung Elektrotechnik / Co-op Student B.Eng. Electrical Engineering Roche Diagnostics GmbH DFGHMV8Y6164 Sandhofer Strasse 116 68305 Mannheim / Germany Phone: apprentice mailto:corrado.garr...@roche.com corrado.garr...@roche.com *Roche Diagnostics GmbH* Sandhofer Straße 116; D‑68305 Mannheim; Telefon +49‑621‑759‑0; Telefax +49‑621‑759‑2890 Sitz der Gesellschaft: Mannheim - Registergericht: AG Mannheim HRB 3962 - Geschäftsführung: Dr. Ursula Redeker, Sprecherin; Edgar Vieth - Aufsichtsratsvorsitzender: Dr. Severin Schwan *Confidentiality Note* This message is intended only for the use of the named recipient(s) and may contain confidential and/or privileged information. If you are not the intended recipient, please contact the sender and delete the message. Any unauthorized use of the information contained in this message is prohibited. -- https://mail.python.org/mailman/listinfo/python-list
