[Resolved] Where is application output? print, logging, etc. about shiny

[afparsons]

Aha! I guess stdout is directed to /dev/null?

See the "printf tracing" section available here: https://shiny.rstudio.com/articles/debugging.html

Also see this StackOverflow question: https://stackoverflow.com/questions/33912150/how-can-i-get-standard-output-written-to-a-log-file-when-a-shiny-app-is-deployed.

Since I was using the logging [GitHub] package, I added a handler to the root logger.

# logging level DEBUG
logging::basicConfig(level = 10)
    
# write logging output to the stderr file
logging::addHandler(writeToFile, logger = '', file = stderr())

However, I switched to logger [GitHub], as it appears to be more feature-rich and more-frequently maintained. The idea is the same:

# set the logger level
logger::log_threshold(INFO)

# direct the logger to write to stderr, since shiny only logs stderr
logger::log_appender(logger::appender_file(file = stderr()))

One could also just use R's base::cat(), like so:

base::cat(file = stderr(), 'my string', toString(some_variable), '\n')

...at which point one might consider writing their own little, customized shinyCat(...) function, which just wraps the above cat() and automatically sets file = stderr().

That's similar to the solution "Sebastian" proposed on StackOverflow:

if (!interactive()) sink(stderr(), type = "output")

Anyway, resolved.

[eddelbuettel]

It's also simply more of a 'run shiny from the console directly and see logs' versus 'run shiny server as a daemon and scratch your head where logs are' question that has nothing to do with Rocker, per se.

Still a frequent head-scratcher.