FidoNet nodediff

The FidoNet nodediff format was used to distribute changes weekly to FidoNet nodelists. In order to save transfer time with the low-bandwidth dialup connections, only the lines that were added or changed since the previous nodelist were included; a nodediff processor applied the changes to produce the new nodelist.

Nodediffs used the filename NODEDIFF.nnn where nnn was the same number as the corresponding nodelist, which was the day number within the year (001-366). Compressed versions used A, Z, etc., as the first letter of the extension to note compression method: "A" for ARC, Z for ZIP, or J, L, or R for ARJ, LZH, or RAR respectively. New FidoNet nodes needed to obtain the full nodelist once upon starting, and received and applied nodediffs weekly from then on.

A nodediff processor reads the lines of the nodediff one at a time, and (as called for by the commands in the nodediff) reads also through the previous nodelist and copies them to the output file, skips them if deleted, or inserts lines from the nodediff.

Command lines in a nodediff are:

Ann (nn is replaced with a 2-digit number): Add nn lines (this was followed by the lines to add)

Cnn Copy the next nn lines unchanged from the previous nodelist

Dnn Delete the next nn lines from the previous nodelist (skip them)