New Features serial_config() now accepts vector arguments to register multiple custom serialization configurations. Adds ip_addr() for returning the local network IPv4 address of all network adapters, named by interface. Adds pipe_id() for returning the integer pipe ID for a resolved 'recvAio'. Adds write_stdout() which performs a non-buffered write to stdout, to avoid interleaved messages when used concurrently by different processes. Adds read_stdin() which performs a read from stdin on a background thread, relayed via an 'inproc' socket so that it may be consumed via recv() or recv_aio(). request() gains integer argument id. This may be specified to have a special payload sent asynchronously upon timeout (to communicate with the connected party). Updates listen() and dial() argument error is replaced with fail to specify the failure mode - 'warn', 'error', or 'none' to just return an 'errorValue'. Any existing usage of error = TRUE will work only until the next release. Partial matching is no longer enabled for the mode argument to send/receive functions. send_aio() without keeping a reference to the return value no longer potentially drops sends (thanks @wch, #129). pipe_notify() no longer requires any particular sequencing of closing the socket and garbage collection of the socket / 'conditionVariable' (#143). More robust interruption on non-Windows platforms when tools::SIGINT is supplied to the flag argument of pipe_notify() (thanks @LennardLux, #97). Installation from source specifying 'INCLUDE_DIR' and 'LIB_DIR' environment variables works again, correcting a regression in v1.5.2 (#104). Windows bi-arch source builds for R <= 4.1 using rtools40 and earlier work again (regression since v1.5.1) (thanks @daroczig, #107). Bundled 'libnng' 1.10.2 pre-release updated with latest patches. Package is re-licensed under the MIT license.