Martin Chang replied [1] to my musings on processing malformed Gemini requests [2], saying that double slashes in URI (Uniform Resource Indicator)s are illegal, and pointed out the ABNF (Augmented Backus-Naur Form) grammar from the URI specification [3] to back up his claim:
path = path-absolute ; begins with "/" but not "//" path-absolute = "/" [ segment-nz *( "/" segment ) ] segment-nz = 1*pchar pchar = unreserved / pct-encoded / sub-delims / ":" / "@"
But he didn't quote the segment rule:
segment = *pchar
which translated says, “0 or more pchar rules.”
So the ABNF he quoted does indeed rule out //boston/2018/07/04.2. It doesn't rule out /boston//2018/07/04.2, since by the time we hit the double slash, we're in the *( "/" segment ) part of the path-absolute rule, and segment can have 0 characters. But what he quoted only applies to relative links, what I receive is an abolute link. If you follow the ABNF from that perspective:
URI-reference = URI / relative-ref
URI = scheme ":" hier-part [ "?" query ] [ "#" fragment ]
hier-part = "//" authority path-abempty
/ path-absolute
/ path-rootless
/ path-empty
path-abempty = *( "/" segment )
; other rules omitted
not only does this allow gemini://gemini.conman.org//boston/2018/07/04.2 but gemini://gemini.conman.org///////////boston/2018/07/04.2.
I can understand why this was done—to simplify the grammar as the various path- rules generally end with *( "/" segment ) allows one to end a URI with a trailing slash or not. I don't think the intent was to allow long strings of slashes, but that's the end result of a lax grammar. Martin is also correct that multiple slashes are treated as a single slash on POSIX (Portable Operating System Interface) (basically, any Unix system), that's not the case across all operating systems. One exception I can think of AmigaOS (Operating System), where each slash represents a parent directory. This command, cd /// on AmigaOS is the same as cd ‥/‥/‥ on a POSIX system. Crazy, I know. And maybe not even relevant these days, but I thought I should mention it.