From 496433cdd2f108b483e4762776dfe1305c466eee Mon Sep 17 00:00:00 2001
From: Adam Chlipala <adam@chlipala.net>
Date: Sat, 18 Dec 2010 10:56:31 -0500
Subject: postBody type

---
 doc/manual.tex | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

(limited to 'doc/manual.tex')

diff --git a/doc/manual.tex b/doc/manual.tex
index 58fbc84d..a8d799d8 100644
--- a/doc/manual.tex
+++ b/doc/manual.tex
@@ -2077,6 +2077,8 @@ $$\begin{array}{rrcll}
 
 A web application is built from a series of modules, with one module, the last one appearing in the \texttt{.urp} file, designated as the main module.  The signature of the main module determines the URL entry points to the application.  Such an entry point should have type $\mt{t1} \to \ldots \to \mt{tn} \to \mt{transaction} \; \mt{page}$, for any integer $n \geq 0$, where $\mt{page}$ is a type synonym for top-level HTML pages, defined in $\mt{Basis}$.  If such a function is at the top level of main module $M$, with $n = 0$, it will be accessible at URI \texttt{/M/f}, and so on for more deeply-nested functions, as described in Section \ref{tag} below.  Arguments to an entry-point function are deserialized from the part of the URI following \texttt{f}.
 
+Normal links are accessible via HTTP \texttt{GET}, which the relevant standard says should never cause side effects.  To export a page which may cause side effects, accessible only via HTTP \texttt{POST}, include one argument of the page handler of type $\mt{Basis.postBody}$.  When the handler is called, this argument will receive a value that can be deconstructed into a MIME type (with $\mt{Basis.postType}$) and payload (with $\mt{Basis.postData}$).  This kind of handler will only work with \texttt{POST} payloads of MIME types besides those associated with HTML forms; for these, use Ur/Web's built-in support, as described below.
+
 When the standalone web server receives a request for a known page, it calls the function for that page, ``running'' the resulting transaction to produce the page to return to the client.  Pages link to other pages with the \texttt{link} attribute of the \texttt{a} HTML tag.  A link has type $\mt{transaction} \; \mt{page}$, and the semantics of a link are that this transaction should be run to compute the result page, when the link is followed.  Link targets are assigned URL names in the same way as top-level entry points.
 
 HTML forms are handled in a similar way.  The $\mt{action}$ attribute of a $\mt{submit}$ form tag takes a value of type $\$\mt{use} \to \mt{transaction} \; \mt{page}$, where $\mt{use}$ is a kind-$\{\mt{Type}\}$ record of the form fields used by this action handler.  Action handlers are assigned URL patterns in the same way as above.
@@ -2087,7 +2089,7 @@ Ur/Web programs generally mix server- and client-side code in a fairly transpare
 
 \medskip
 
-The HTTP standard suggests that GET requests only be used in ways that generate no side effects.  Side effecting operations should use POST requests instead.  The Ur/Web compiler enforces this rule strictly, via a simple conservative program analysis.  Any page that may have a side effect must be accessed through a form, all of which use POST requests.  A page is judged to have a side effect if its code depends syntactically on any of the side-effecting, server-side FFI functions.  Links, forms, and most client-side event handlers are not followed during this syntactic traversal, but \texttt{<body onload=\{...\}>} handlers \emph{are} examined, since they run right away and could just as well be considered parts of main page handlers.
+The HTTP standard suggests that GET requests only be used in ways that generate no side effects.  Side effecting operations should use POST requests instead.  The Ur/Web compiler enforces this rule strictly, via a simple conservative program analysis.  Any page that may have a side effect must be accessed through a form, all of which use POST requests, or via a direct call to a page handler with some argument of type $\mt{Basis.postBody}$.  A page is judged to have a side effect if its code depends syntactically on any of the side-effecting, server-side FFI functions.  Links, forms, and most client-side event handlers are not followed during this syntactic traversal, but \texttt{<body onload=\{...\}>} handlers \emph{are} examined, since they run right away and could just as well be considered parts of main page handlers.
 
 Ur/Web includes a kind of automatic protection against cross site request forgery attacks.  Whenever any page execution can have side effects and can also read at least one cookie value, all cookie values must be signed cryptographically, to ensure that the user has come to the current page by submitting a form on a real page generated by the proper server.  Signing and signature checking are inserted automatically by the compiler.  This prevents attacks like phishing schemes where users are directed to counterfeit pages with forms that submit to your application, where a user's cookies might be submitted without his knowledge, causing some undesired side effect.
 
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