receive-from

Arguments: sock size &key buffer extract

This generic function is used to read from a datagram socket. You must specify a size bigger than the size of the message you expect (usually the rest of the datagram will be thrown away if it doesn't all fit).

If the buffer argument is given then it should be a Lisp vector of some raw type (like (unsigned-byte 8) but definitely not t) of at least size bytes that will be used to read in the datagram. If buffer is not given then a fresh buffer will be created (of the type appropriate to the format of the socket).

The buffer argument may be a character vector. In this case receive-from will create a temporary buffer of type (unsigned-byte 8) into which to read the octets and then octets-to-string will be used to convert those octets to characters. If you want to save the creation of this temporary array for each call to receive-from you should pass an (unsigned-byte 8) array in as the buffer. When using an 8-bit character Lisp (e.g., alisp8 or mlisp8-- see Allegro CL Executables: alisp, alisp8, mlisp, mlisp8, allegro, allegro-ansi in startup.htm), no temporary buffer is created and no conversion occurs.

If extract is unspecified or nil then the first value returned is the buffer used to read the data. If extract is true then the first value returned is a subsequence of the buffer, that subsequence being that part of the buffer that contains the data just read.

The second value returned is the number of bytes read by receive-from.

In the case of an :internet socket, the third value returned is the 32-bit internet address or the IPv6 address of the sender of the data and the fourth value is the port number.

In the case of a :file socket, the third (and last) value returned is the filename of the sender's socket (or "" if there is no filename).

See socket.htm for general information on sockets in Allegro CL.

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Created 2010.1.21.