I am facing issue in the IPDUM messages.
We have two IPDUM messages In the first IPDUM message the multiplexor is at the last byte(8th byte)
during testing for the IPDUM messages the fist byte is not updated as per the multiplexor value but other bytes are updated as per expectation.
Could you please let me know what could be the issue.
In the second IPDUM message the multiplexor is at the first byte but during testing multiplexor value is not getting updated.
could you let me the solution for this.
Related
Once in a while, seekbar values of ExpandedControllerActivity goes out of sync after back to back playback. The max value is 1 and current progress is 1 and this causes the thumb to be at the end irrespective of the actual playback duration. Receiver has correct duration values and sends correct values (when using chrome inspect).
Are there any recommendation to debug these issues at client end as ExpandedControllerActivity source code is obfuscated.
Similar issue tracked at https://issuetracker.google.com/issues/120069343.
In our case, this was resolved by receiver setting stream duration explicitly.
I need to transfer data over a serial port. In order to ensure integrity of the data, I want a small envelope protocol around each protobuf message. I thought about the following:
message type (1 byte)
message size (2 bytes)
protobuf message (N bytes)
(checksum; optional)
The message type will mostly be a mapping between messages defined in proto files. However, if a message gets corrupted or some bytes are lost, the message size will not be correct and all subsequent bytes cannot be interpreted anymore. One way to solve this would be the introduction of limiters between messages, but for that I need to choose something that is not used by protobuf. Is there a byte sequence that is never used by any protobuf message?
I also thought about a different way. If the master finds out that packages are corrupted, it should reset the communication to a clean start. For that I want the master to send a RESTART command to the slave. The slave should answer with an ACK and then start sending complete messages again. All bytes received between RESTART and ACK are to be discarded by the master. I want to encode ACK and RESTART as special messages. But with that approach I face the same problem: I need to find byte sequences for ACK and RESTART that are not used by any protobuf messages.
Maybe I am also taking the wrong approach - feel free to suggest other approaches to deal with lost bytes.
Is there a byte sequence that is never used by any protobuf message?
No; it is a binary serializer and can contain arbitrary binary payloads (especially in the bytes type). You cannot use sentinel values. Length prefix is fine (your "message size" header), and a checksum may be a pragmatic option. Alternatively, you could impose an artificial sentinel to follow each message (maybe a guid chosen per-connection as part of the initial handshake), and use that to double-check that everything looks correct.
One way to help recover packet synchronization after a rare problem is to use synchronization words in the beginning of the message, and use the checksum to check for valid messages.
This means that you put a constant value, e.g. 0x12345678, before your message type field. Then if a message fails checksum check, you can recover by finding the next 0x12345678 in your data.
Even though that value could sometimes occur in the middle of the message, it doesn't matter much. The checksum check will very probably catch that there isn't a real message at that position, and you can search forwards until you find the next marker.
I'm writing a small app to test out how torrent p2p works and I created a sample torrent and am seeding it from my Deluge client. From my app I'm trying to connect to Deluge and download the file.
The torrent in question is a single-file torrent (file is called A - without any extension), and its data is the ASCII string Test.
Referring to this I was able to submit the initial handshake and also get a valid response back.
Immediately afterwards Deluge is sending even more data. From the 5th byte it would seem like it is a bitfield message, but I'm not sure what to make of it. I read that torrent clients may send a mixture of Bitfield and Have messages to show which parts of the torrent they possess. (My client isn't sending any bitfield, since it is assuming not to have any part of the file in question).
If my understanding is correct, it's stating that the message size is 2: one for identifier + payload. If that's the case why is it sending so much more data, and what's that supposed to be?
Same thing happens after my app sends an interested command. Deluge responds with a 1-byte message of unchoke (but then again appends more data).
And finally when it actually submits the piece, I'm not sure what to make of the data. The first underlined byte is 84 which corresponds to the letter T, as expected, but I cannot make much more sense of the rest of the data.
Note that the link in question does not really specify how the clients should supply messages in order once the initial handshake is completed. I just assumed to send interested and request based on what seemed to make sense to me, but I might be completely off.
I don't think Deluge is sending the additional bytes you're seeing.
If you look at them, you'll notice that all of the extra bytes are bytes that already existed in the handshake message, which should have been the longest message you received so far.
I think you're reading new messages into the same buffer, without zeroing it out or anything, so you're seeing bytes from earlier messages again, following the bytes of the latest message you read.
Consider checking if the network API you're using has a way to check the number of bytes actually received, and only look at that slice of the buffer, not the entire thing.
This question suggests that the Node.js Net module doesn't handle ip-fragmentation:
Node.js how to handle packet fragmentation with net.Server
I can almost not imagine it's true, but I can't find any documentation about this (please forgive me if it shouldn't be too hard to find information about this :-) ). Is it true?
If not: thank you, that's a real day-safer to me :-).
If it is true: how to handle this problem if I don't know how large the whole datagram is?
Situation:
I have a TCP connection with an embedded system (Wiznet W5500). The MSS (Maximum Segment Size, mostly equal to MTU - 40) will be set to 536 and data packages are a variable size and may be over 4kb in size. So the data package will be send in multiple segments. Will the 'on data' event be triggered once a segment is received or only when the whole package is received?
Side question: Am I right that the data segment (about what Wiznet is talking in the explanation of the MSS register) equel is to a ip-fragment?
So if I have to send 4000byte (ie payload) and the MSS is set to 536 I will receive consecutively:
segment1: 536bytes payload
segment2: 536bytes payload
segment3: 536bytes payload
segment4: 536bytes payload
segment5: 536bytes payload
segment6: 536bytes payload
segment7: 536bytes payload
segment8: 248bytes payload
May the 'on data' event only be triggered after segment 8 an will the 'data argument' contain the whole package or may it happen that the 'on data' event will be triggered after every separately received segment?
How can I make 100% sure that I get the whole package before I continue to process it?
Solution I thought of:
First 2 byte of the data package is the byte length of the whole length, I keep concattenating received data until I have received as many bytes. If I received more than the package size, I'll assume these successive bytes are the start of a subsequent data package.
I do believe this 'solution' is somewhat tricky and I hope it's not required.
Thanks in advance! If any information is missing: I'm sorry, please feel free to ask for it :-).
I am a big fan of nodeJS, but in this case you should use python with scapy :)
http://www.secdev.org/projects/scapy/
Does anyone know what 2 parameters in the fetchMaxBytes represent?
If its represented as 1024*1024, does that mean that the consumer will fetch 1024 messages of each 1Kb? Or will it jest fetch 1Mb of messages?
I was not able to find any relevant information from the documentation except this: "The maximum bytes to include in the message set for this partition. This helps bound the size of the response."
I need this parameter to get messages one by one rather than getting a couple of messages in a single shot.
I am not familiar with node.js but I assume fetchMaxBytes corresponds to replicate.fetch.max.bytes. For this case, the value is the maximum buffer size (in bytes, ie, 1024*1024 = 1MB) for fetching messages. A buffer can contain multiple messages of arbitrary size. It basically means, wait for fetching not longer as "until a buffer got filled up".