Syn-C | Turbo C code to ANSI C code converter | 3D Printing library

by MrDHat C++ Version: Current License: GPL-3.0

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kandi X-RAY | Syn-C Summary

Syn-C is a C++ library typically used in Modeling, 3D Printing applications. Syn-C has no bugs, it has no vulnerabilities, it has a Strong Copyleft License and it has low support. You can download it from GitHub.

Input: Turbo C compliant code Output Generated: Equivalent ANSI C code. Lexical Analysis performed using [C-Source Scanner] XML Parser uses [PugiXML] Dependencies: + GCC-G++ + Make + [FLEX] + Java Development Kit. Authors (In alphabetical order): + Akshay Katyal | [MrDHat] + Rachit Gupta | [R4CHI7] + Sidharth Kathuria | [siddharth124] The project is incomplete and is missing a lot of function definitions in the XML files. Not suitable for production as of now. Licensed under GNU GPLv3.

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Syn-C has a low active ecosystem.

It has 6 star(s) with 3 fork(s). There are 5 watchers for this library.

It had no major release in the last 6 months.

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It has a neutral sentiment in the developer community.

The latest version of Syn-C is current.

Quality

Syn-C has no bugs reported.

Security

Syn-C has no vulnerabilities reported, and its dependent libraries have no vulnerabilities reported.

License

Syn-C is licensed under the GPL-3.0 License. This license is Strong Copyleft.

Strong Copyleft licenses enforce sharing, and you can use them when creating open source projects.

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Syn-C releases are not available. You will need to build from source code and install.

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Community Discussions

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Unusually slow TCP-connection in Linux

QUESTION

Unusually slow TCP-connection in Linux

Asked 2020-Jan-27 at 13:14

I wrote user-mode client-server c application based on Berkeley sockets that interact over some private network.
The situation is definitely strange. Occasionally the connection becomes very slow under some vague circumstances. The normal TCP data exchange in my case is about 10-25 Kbytes payload per segment, but sometimes it becomes about ~200-500 bytes per segment.

After some troubleshooting, I realized that this problem is not reproducible for other network services, thus it looks like my service is to blame. But I can't figure out, what's wrong. It worked well on 3.10 Linux kernel, but have that strange behavior on 4.4. Could it be some internal kernel changes which caused such problem?

I tried to play with Linux sysctl settings:

...

ANSWER

Answered 2020-Jan-27 at 13:14

I'm not really sure this is exactly your case, but it looks similar. Seems that it's a known problem.

Reasons

A number of circumstances can lead to such Linux kernel behavior:

Specificity of kernel connection handling in SYN-cookies context with connections having zero Window Scale (or if WS modified in some other way).
Zero Window Scale you provoked by setsockopt() with SO_RCVBUF (see tcp_select_initial_window())
Extremely small backlog

Explanation

About "slow" transmission:
The Windows Scaling option is calculated at [SYN - SYN+ACK] stage by both hosts. Roughly speaking Host A says "imply my TCP window size on N during future exchange" (SYN) then Host B says "imply my TCP window size on M during future exchange" (SYN+ACK) - here N and M could be th same. So, in a normal situation, these coefficients are stored and eventually used while data exchange.
But TCP SYN-cookies technique implies forgetfulness about [SYN - SYN+ACK] stage of connection (some stated options including WS will be lost after SYN+ACK). In that case Linux kernel re-calculates WS value when ACK arrives (if the ACK has arrived, then creating a regular connection is needed). But that second recalculation could be a bit different because setsockopt() does not affect it (for some objective reasons). Here you face with situation, when your server sends zero Window Scale option with SYN+ACK, then forgets about it, then re-spawn connection (when ACK arrives) as it was with some default Window Scale (e.g. 7) and use little window implying that client will multiply it by 128. But client doesn't forget that WS is 0 and treats little window size as real - hence it send a little portions of data - hereby your "slow" connection takes the stage.

About SYN-flood:
When you have such a little backlog an simple 3 SYN-retransmits can provoke SYN-cookies (i.e. will fill in your backlog queue). BTW do you see retransmissions in tcpdump?
From ip-sysctl.txt:

Source https://stackoverflow.com/questions/59774872

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No vulnerabilities reported

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For any new features, suggestions and bugs create an issue on GitHub. If you have any questions check and ask questions on community page Stack Overflow .

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