The `seekablepipe` program

seekablepipe turns the reading end of a pipe into a seekable file descriptor.

Interface

     writer | seekablepipe reader [ args ... ]

seekablepipe writes writer's output in a temporary file located in /tmp (the file is unlinked as soon as it is created). Then it execs into reader, reading from a file descriptor on that temporary file.
If reader is not given, it defaults to cat.