Universal socket library for Common Lisp

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Erik Enge & Erik Huelsmann, Chun Tian (binghe), Erik Enge


Chun Tian (binghe) & Hans Huebner, Chun Tian (binghe)



USOCKET - Universal socket library for Common Lisp

This is the usocket Common Lisp sockets library - a library to bring sockets access to the broadest of Common Lisp implementations as possible.

The library currently supports:

  1. Allegro CL
  2. ABCL (ArmedBear)
  3. Clasp
  4. Clozure CL
  5. Corman Lisp
  7. CMUCL
  8. ECL
  9. LispWorks (4.3 and up)
  10. Digitool MCL and RMCL (5.0 and up)
  11. Mezzano
  12. MOCL
  13. SBCL
  14. Scieneer CL
  15. Symbolics Lisp Machine (Genera)

If your favorite Common Lisp is missing from the above list, please contact and submit a request. Please include references to available sockets functions in your Lisp implementation.

The library is ASDF-enabled, meaning that you can tar up a checkout and use that to asdf-install:install the package in your system package site. (Or use your usual ASDF tricks to use the checkout directly.)

Remarks on licensing

Even though the source code has an MIT-style license attached to it, when compiling this code with some of the supported Lisp implementations you may not end up with an MIT-style binary version due to the licensing of the implementations themselves. ECL is such an example and - when it comes to be supported - so is GCL.

Non-support of :external-format

Because of its definition in the Hyperspec, there's no common external-format between Lisp implementations: every vendor has chosen a different way to solve the problem of newline translation or character set recoding.

Because there's no way to avoid platform-specific code in the application when using external-format, the purpose of a portability layer gets defeated. So, for now, usocket doesn't support external-format.

The workaround to get reasonably portable external-format support is to layer a flexi-stream (from flexi-streams) on top of a usocket stream.

API definition

  • usocket (class)

  • stream-usocket (class; usocket derivative)

  • stream-server-usocket (class; usocket derivative)

  • socket-connect (host port &key element-type) (function)

    Create an active/connected socket. host can be a vectorized IP, or a string representation of a dotted IP address, or a hostname for lookup in the DNS system.

  • socket-listen (host port &key reuseaddress backlog element-type) (function)

    Create a passive/listening socket. For possible values of host, see socket-connect.

  • socket-accept (socket &key element-type) (method)

    Create an active/connected socket. Returns (server side) a connected socket derived from a listening/passive socket.

  • socket-close (socket) (method)

    Where socket is a previously-returned socket.

  • socket (usocket slot accessor),

    Returns the internal/implementation-defined socket representation.

  • socket-stream (socket) (usocket slot accessor),

    Returns a value which satisfies the normal stream interface.

  • socket-shutdown


  • address-in-use-error
  • address-not-available-error
  • bad-file-descriptor-error
  • connection-refused-error
  • connection-aborted-error
  • connection-reset-error
  • invalid-argument-error
  • no-buffers-error
  • operation-not-supported-error
  • operation-not-permitted-error
  • protocol-not-supported-error
  • socket-type-not-supported-error
  • network-unreachable-error
  • network-down-error
  • network-reset-error
  • host-down-error
  • host-unreachable-error
  • shutdown-error
  • timeout-error
  • unkown-error

Non-fatal conditions:

  • interrupted-condition
  • unkown-condition

(for a description of the API methods and functions see

Test suite

The test suite unfortunately isn't mature enough yet to run without some manual configuration. Several elements are required which are hard to programatically detect. Please adjust the test file before running the tests, for these variables:

  • +non-existing-host+: The stringified IP address of a host on the same subnet. No physical host may be present.
  • +unused-local-port+: A port number of a port not in use on the machine the tests run on.
  • +common-lisp-net+: A vector with 4 integer elements which make up an IP address. This must be the IP "" resolves to.

Known problems

  • CMUCL error reporting wrt sockets raises only simple-errors meaning there's no way to tell different error conditions apart. All errors are mapped to unknown-error on CMUCL.

  • The ArmedBear backend doesn't do any error mapping (yet). Java defines exceptions at the wrong level (IMO), since the exception reported bears a relation to the function failing, not the actual error that occurred: for example 'Address already in use' (when creating a passive socket) is reported as a BindException with an error text of 'Address already in use'. There's no way to sanely map BindException to a meaningfull error in usocket. [This does not mean the backend should not at least map to unknown-error!]

  • When using the library with ECL, you need the C compiler installed to be able to compile and load the Foreign Function Interface. Not all ECL targets support DFFI yet, so on some targets this would be the case anyway. By depending on this technique, usocket can reuse the FFI code on all platforms (including Windows). This benefit currently outweighs the additional requirement. (hey, it's Embeddable Common Lisp, so, you probably wanted to embed it all along, right?)

Dependencies (4)

  • bordeaux-threads
  • iolib
  • rt
  • split-sequence
  • GitHub
  • Quicklisp