sschroe / libnodelay

A small wrapper library that adds the TCP_NODELAY option for all sockets.

libnodelay

A small wrapper library to force TCP_NODELAY on all new sockets. It is intended for use with LD_PRELOAD on Linux and wraps the socket and setsockopt calls to enforce TCP_NODELAY being set for all TCP sockets.

Compiling

To compile libnodelay simply run make inside the repository. This will build libnodelay.so for your host system.

Additionally the make targets 32 and 64 are available to specifically build the library for either 32bit or 64bit. The binary file in this case will be either libnodelay32.so or libnodelay64.so depending on the chosen target.

Usage

To use libnodelay add it to the LD_PRELOAD environment variable. The suggested way is to simply export it and run your application afterwards.

export LD_PRELOAD=/path/to/libnodelay/libnodelay.so
./application

You may also add the 32bit and 64bit library in parallel which comes in handy when dealing with a mix of 32bit and 64bit executables such as when using wine.

export LD_PRELOAD=/path/to/libnodelay/libnodelay32.so:/path/to/libnodelay/libnodelay64.so
./application

In this case you may see errors such as the following. These can be safely ignored and are merely an information that for example the 32bit library could not be used for an 64bit application. However in that case the 64bit library will have been loaded instead.

ERROR: ld.so: object '/path/to/libnodelay/libnodelay64.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS64): ignored.
ERROR: ld.so: object '/path/to/libnodelay/libnodelay32.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS32): ignored.

Testing

A small test executable is provided and can be compiled with make test. When run this executable will print whether TCP_NODELAY is set or not after creating a TCP socket.

Example:

./test
TCP_NODELAY is NOT set.

LD_PRELOAD=./libnodelay.so ./test
TCP_NODELAY is set.

Contributing

You are welcome to contribute to this project, simply open a pull request with your changes and they will be considered.

License

This project is licensed under the GPL-3.0-or-later License, see the COPYING file for details

libnodelay's Issues

`symbol lookup error: ./libnodelay.so: undefined symbol: dlsym` on Debian 11

Compiling and testing the library as described in the Readme.md gives me the error in title.
Example:

> ./test                                                                                                                                                                                             
TCP_NODELAY is NOT set.    

>  LD_PRELOAD=./libnodelay.so ./test                                                                                                                                                                                                                                                      
./test: symbol lookup error: ./libnodelay.so: undefined symbol: dlsym 

I might or might not fix this myself this afternoon