tex: enhance logging section

tex/part-practical.tex

@@ -275,12 +275,49 @@ package to prevent accidental imports.
 
 \n{2}{Logging}
 
-The program uses \emph{dependency injection} to share a single logger instance,
-similar applies to the database client. These are passed around as a pointer,
-so the underlying data stays the same. As a rule of thumb throughout the
+The program uses \emph{dependency injection} to share a single logger instance
+(the same technique is also used to share the database client). This logger is
+then passed around as a pointer, so that the underlying data stays the same or
+is modified concurrently for all consumers. As a rule of thumb throughout the
 application, every larger \texttt{struct} that needs to be passed around is
 passed around as a pointer.
 
+An experimental (note: not anymore in \texttt{go1.21}, it was just recently
+brought into Go's \textit{stdlib}) library for \textit{structured} logging
+\texttt{slog} was used to facilitate every logging need the program might have.
+It supports both JSON and plain-text logging, which was made configurable by
+the program. Either a configuration file value or an environment variable can
+be used to set this.
+
+There are four log levels available by default (\texttt{DEBUG}, \texttt{INFO},
+\texttt{WARNING}, \texttt{ERROR}) and the pertinent library funtions are
+parametric. The first parameter of type \texttt{string} is the main message,
+that is supplied as a \emph{value} to the \emph{key} named appropriately
+`\texttt{msg}', a feature of structured loggers which can later be used for
+filtering. Any other parameters need to be supplied in pairs, serving as key
+and value, respectively.
+
+This main \texttt{slog} interface has been extended in package
+\texttt{slogging} to also provide the formatting functionality of the
+\texttt{fmt} standard library package. This was achieved by directly embedding
+\texttt{slog.Logger} in a custom \texttt{struct} type named \texttt{Slogger}
+and implementing the additional methods on the custom type. The new type that
+embeds the original \texttt{slog.Logger} gets to keep its methods thanks to the
+composition nature of Go. Thus, common formatting directives like the one seen
+in Listing~\ref{goFmtExpression} are now supported with the custom logger, in
+addition to anything the base \texttt{slog.Logger} offers.
+
+\vspace{\parskip}
+\begin{lstlisting}[language=Go, caption={Example formatting expression supplied
+to the logger}, label=goFmtExpression, basicstyle=\linespread{0.9}\small\ttfamily,
+backgroundcolor=\color{lstbg},
+]
+slogger.Debugf("operation %q for user %q completed at %s", op, usr.ID, time.Now())
+\end{lstlisting}
+
+Furthermore, functionality was added to support changing the log level at
+runtime, which is a convenient feature in certain situations.
+
 
 \n{2}{Authentication}