knitr::opts_chunk$set( collapse = TRUE, comment = "#>" ) library(log4r) # Dummy Plumber request & response. req <- list( REQUEST_METHOD = "POST", PATH_INFO = "/upload", QUERY_STRING = "", HTTP_USER_AGENT = "curl/7.58.0", REMOTE_ADDR = "124.133.52.161" ) res <- list(status = 401) # Dummy CSV-parsing stuff: filename <- "catpics_01.csv" entries <- data.frame(x = 1:4124) start <- Sys.time()
Traditionally, messages emitted from R packages or scripts are unstructured messages, like this one from the shiny package:
Listening on http://localhost:8080
A richer, more structured representation of this log message might be:
level=INFO ts=2021-10-21T20:21:01Z message="starting Shiny" host=localhost port=8080 shiny_version=1.6.0 appdir=projects/mycoolapp
This second message uses structured logging, attaching relevant metadata to a log message as standalone fields.
Structured logs have two advantages:
They tend to have more standard, predictable content, which can make reading them easier (especially if you did not write the message yourself); and
They are much, much easier for log management and aggregation systems to query -- fields can be used to aggregate logs into metrics like "how many times has X happened" and "how long does task Y take on average", and individual fields can be used to answer questions like "what happened to user Z over their last few logins".
log4r includes support for two of the most popular structured logging formats:
json_log_layout
: Emit log messages as JSON, likely the most widely-used.
logfmt_layout
: Emit log messages using the more human-friendly logfmt.
To use these formats, you can pass additional arguments to the existing logging
functions info()
, warn()
and error()
.
The most popular format for structured logging is probably JSON, which you can configure as follows:
logger <- logger(appenders = console_appender(json_log_layout()))
As an example, suppose you are logging unauthorised requests to a Plumber API. You might have a log message with fields like the following:
# Here "req" and "res" are slightly fake request & response objects. info( logger, message = "authentication failed", method = req$REQUEST_METHOD, path = req$PATH_INFO, params = sub("^\\?", "", req$QUERY_STRING), user_agent = req$HTTP_USER_AGENT, remote_addr = req$REMOTE_ADDR, status = res$status )
An alternative to JSON is the popular, more human-friendly logfmt style, which you can configure as follows:
logger <- logger(appenders = console_appender(logfmt_log_layout()))
As an example, you might have the following in a script that processes many CSV files:
info( logger, message = "processed entries", file = filename, entries = nrow(entries), elapsed = unclass(difftime(Sys.time(), start, units = "secs")) )
Any scripts or data that you put into this service are public.
Add the following code to your website.
For more information on customizing the embed code, read Embedding Snippets.