# Class `nixio.README`

General Information.

## Tables

Errorhandling | General error handling information.
Functions | Function conventions.
Platforms | Platform information.
TLS-Crypto | Cryptography and TLS libraries.

## Tables

Errorhandling
  General error handling information.
  - Most of the functions available in this library may fail. If any error occurs the function returns nil or false, an error code (usually errno) and an additional error message text (if avaialable).
  - At the moment false is only returned when a non-blocking I/O function fails with EAGAIN, EWOULDBLOCK or WSAEWOULDBLOCK for any others nil is returned as first parameter. Therefore you can use false to write portable non-blocking I/O applications.
  - Note that the function documentation does only mention the return values in case of a successful operation.
  - You can find a table of common error numbers and other useful constants like signal numbers in nixio.const e.g. nixio.const.EINVAL, nixio.const.SIGTERM, etc. For portability there is a second error constant table nixio.const_sock for socket error codes. This might be important if you are dealing with Windows applications, on POSIX however const_sock is just an alias for const.
  - With some exceptions - which are explicitely stated in the function documentation - all blocking functions are signal-protected and will not fail with EINTR.
  - On POSIX the SIGPIPE signal will be set to ignore upon initialization. You should restore the default behaviour or set a custom signal handler in your program after loading nixio if you need this behaviour.
Functions
  Function conventions.
  In general all functions are namend and behave like their POSIX API counterparts - where applicable - applying the following rules:
  - Functions should be named like the underlying POSIX API function omitting prefixes or suffixes - especially when placed in an object-context ( lockf -> File:lock, fsync -> File:sync, dup2 -> dup, ...)
  - If you are unclear about the behaviour of a function you should consult your OS API documentation (e.g. the manpages).
  - If the name is significantly different from the POSIX-function, the underlying function(s) are stated in the documentation.
  - Parameters should reflect those of the C-API, buffer length arguments and by-reference parameters should be omitted for pratical purposes.
  - If a C function accepts a bitfield as parameter, it should be translated into lower case string flags representing the flags if the bitfield is the last parameter and also omitting prefixes or suffixes. (e.g. waitpid (pid, &s, WNOHANG | WUNTRACED) -> waitpid(pid, "nohang", "untraced"), getsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt)) -> Socket:getopt("socket", "reuseaddr"), etc.)
  - If it is not applicable to provide a string representation of the bitfield a bitfield generator helper is provided. It is named FUNCTION_flags. (open("/tmp/test", O_RDONLY | O_NONBLOCK) -> open("/tmp/test", open_flags( "rdonly", "nonblock")))
Platforms
  Platform information.
  - The minimum platform requirements are a decent POSIX 2001 support. Builds are more or less tested on Linux, Solaris and FreeBSD. Builds for Windows XP SP1 and later can be compiled with MinGW either from Windows itself or using the MinGW cross-compiler. Earlier versions of Windows are not supported.
  - In general all functions which don't have any remarks in their documentation are available on all platforms.
  - Functions with a (POSIX), (Linux) or similar prefix are only available on these specific platforms. Same appplies to parameters of functions with a similar suffix.
  - Some functions might have limitations on some platforms. This should be stated in the documentation. Please also consult your OS API documentation.
TLS-Crypto
  Cryptography and TLS libraries.
  - Currently 3 underlying cryptography libraries are supported: openssl, cyassl and axTLS. The name of the library in use is written to nixio.tls_provider
  - You should whenever possible use openssl or cyassl as axTLS has only limited support. It does not provide support for non-blocking sockets and is probably less audited than the other ones.
  - As the supported Windows versions are not suitable for embedded devices axTLS is at the moment not supported on Windows.