Plumb is a drop-in replacement for plan9's plumb utility.
Notably different from it, are how it handles the type attribute of the plumb messages.
They will be set to a proper mimetype, instead of the simple type is text that the traditional plumber utilized.
This is considerably more powerful, as you no longer need to attempt to infer the content based on URIs, extensions, or directory structure.
Your plumber rules will have to be updated to reflect this more granular message:
## In this example, plan9front's plumber is being used; but similar rule changes would apply for plan9 regular.
type is image/png
## No longer need to match paths
#data matches '[a-zA-Z¡-�0-9_\-./@]+'
#data matches '([a-zA-Z¡-�0-9_\-./@]+)\.(jpe?g|JPE?G|gif|GIF|tiff?|TIFF?|ppm|bit|png|PNG)'
arg isfile $0
plumb to image
plumb start 9 page $file
# local html files (Your dev work, for example) can be opened in your editor
type is text/html
arg isfile $0
plumb to edit
plumb start $editor $0
# remote html files will likely be opened in your browser
type is text/html
# With the above case matching local files, we no longer need this convolution
#data matches '(https?|ftp|file|gopher|mailto|news|nntp|telnet|wais|prospero)://[a-zA-Z0-9_@\-]+([.:][a-zA-Z0-9_@\-]+)*/?[a-zA-Z0-9_?,%#~&/\-+=]+([:.][a-zA-Z0-9_?,%#~&/\-+=]+)*'
plumb to web
plumb start web $0
type is application/pdf
## No longer need to match paths
#data matches '[a-zA-Z¡-�0-9_\-./@]+'
#data matches '([a-zA-Z¡-�0-9_\-./@]+)\.(ps|PS|eps|EPS|pdf|PDF|dvi|DVI)'
arg isfile $0
plumb to postscript
plumb start 9 page $file
In practice, setting a rule for most common mimetypes will serve you well. (For example, my last implementation of plumber used a relatively small amount of mimes, after a few years' worth of plumbing in this manner. See https://github.com/halfwit/Plumber/tree/master/cfg/plumber)
If the remote mimetype is application/octet-stream, which is a fallback when it cannot infer the mimetype this client will attempt to find a content-type field in any remote URL, finally setting the type to text.
Reference for mimetype: https://mimesniff.spec.whatwg.org/
Reasonably robust list of mimetypes: https://www.freeformatter.com/mime-types-list.html