Document SEVAL-HANDLER; pull in former toothless.tex.

doc/latex/httpd.tex

@@ -459,7 +459,7 @@ exported by the \ex{httpd\=basic\=handlers} structure:
 \item If the path looks like \ex{("cgi-\ob{}bin"\ob{} "calendar")},
     pass ("calendar") off to the CGI request handler.
   \item If the path looks like \ex{("seval"\ob{} \ldots)}, the tail
-    of the path is passed off to the code-uploading seval path
+    of the path is passed off to the code-uploading \ex{seval} path
     handler.
   \item Otherwise, the whole path is passed to a rooted file handler,
     who will convert it into a filename, rooted at
@@ -564,6 +564,64 @@ structure.
 \end{itemize}
 \end{desc}      
 
+\section{Scheme-Evaluating Request Handlers}
+
+The \ex{httpd-seval-handlers} structure contains a handler which
+demonstrates how to safely evaluate Scheme code uploaded from the
+client to the server.
+
+\defvar{seval-handler}{request-handler}
+\begin{desc}
+  This request handler is suitable for receiving code entered into an
+  HTML text form. The Scheme code being uploaded is being \ex{POST}ed
+  to the server (from a form).  The code should be URI-encoded in the
+  URL as \texttt{program=}$\left<\mathrm{stuff}\right>$.
+  $\mathrm{stuff}$ must be an (URI-encoded) Scheme expression which
+  the handler evaluates in a separate subprocess.  (It waits for 10
+  seconds for a result, then kills the subprocess.)  The handler then
+  prints the return values of the Scheme code.
+\end{desc}
+
+The following structures define environments that are \RnRS without
+features that could examine or effect the file system.  You can also
+use them as models of how to execute code in other protected
+environments in \scm.
+
+\subsection{The \protect{\texttt{loser}} structure}
+The \ex{loser} package exports only one procedure:
+
+\begin{defundesc}{loser}{name}{nothing}
+  Raises an error like ``Illegal call \var{name}''.
+\end{defundesc}
+
+\subsection{The \protect{\texttt{toothless}} structure}
+The \ex{toothless} structure contains everything of \RnRS except
+that following procedure cause an error if called:
+\begin{itemize}
+\item \ex{call-with-input-file}
+\item \ex{call-with-output-file}
+\item \ex{load}
+\item \ex{open-input-file}
+\item \ex{open-output-file}
+\item \ex{transcript-on}
+\item \ex{with-input-from-file}
+\item \ex{with-input-to-file}
+\item \ex{eval}
+\item \ex{interaction-environment}
+\item \ex{scheme-report-environment}
+\end{itemize}
+
+\subsection{The \protect{\texttt{toothless-eval}} structure}
+
+\begin{defundesc}{eval-safely} {expression} {any result}
+  Creates a brand-new structure, imports the \ex{toothless} structure,
+  and evaluates \semvar{expression} in it. When the evaluation is
+  done, the environment is thrown away, so \semvar{expression}'s
+  side-effects don't persist from one \ex{eval\=safely} call to the
+  next.  If \semvar{expression} raises an error exception,
+  \ex{eval-safely} returns \sharpf.
+\end{defundesc}
+
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