Implement two new flags and a special req.http header to indicate errors

* NEWS: Document changes.
* doc/vmod-dbrw.3: Likewise.
* doc/vmod-dbrw.texi: Likewise.

* configure.ac: Version 2.4.90
* src/dbrw.h (dbrw_config): New member: match_type
* src/vmod_dbrw.c (parse_flags): Handle "eq" and "regex" flags.
(findmatch): Handle the "eq" flag.
(do_rewrite): Return error code.
(vmod_rewrite): Set the X-VMOD-DBRW-Error header on errors.

* tests/atlocal.in (at_vcl_backend): Special handling for
X-VMOD-DBRW-Error.
* tests/initdb.at: Test the 'eq' flag.
* tests/rewrite07.at: New testcase.
* tests/Makefile.am: Add new testcase.
* tests/testsuite.at: Likewise.

1 files changed, 37 insertions, 1 deletions

diff --git a/doc/vmod-dbrw.texi b/doc/vmod-dbrw.texi
index 734dadb..6a987ed 100644
--- a/doc/vmod-dbrw.texi
+++ b/doc/vmod-dbrw.texi
@@ -132,7 +132,14 @@ for substituting default values and invoking built-in functions during
 the expansion of the query. @xref{Expansions}, for a detailed
 description of these.
 
+@anchor{X-VMOD-DBRW-Error}
+@vindex X-VMOD-DBRW-Error
 Having undergone expansions, the query is sent to the database server.
+If the query returns no records or if an error occured, @code{rewrite}
+returns empty string.  In case of error, it also sets the HTTP header
+@samp{X-VMOD-DBRW-Error: 1}.  It can be used in VLC code to provide a
+special handling for such failures.
+
 The returned set of records (if non-empty) is processed depending on the
 number of fields it contains.
 
@@ -166,7 +173,7 @@ resulting value is then returned to the caller.
 @cindex flags
 @anchor{flags}
 Optional @var{flags} column is a comma-separated list of flags that
-modify regular expression handling:
+control the matching algorithm.
 
 @table @samp
 @kindex NC
@@ -183,6 +190,11 @@ Treat @var{regexp} as case-insensitive regular expression.
 @item case
 Treat @var{regexp} as case-sensitive (default).
 
+@kindex eq
+@cindex exact matching
+@item eq
+Use exact string matching.
+
 @kindex QSA
 @kindex qsappend
 @cindex query string handling
@@ -209,6 +221,12 @@ the original @var{value}.
 @item R=@var{code}
 On success, set the @samp{X-VMOD-DBRW-Status} header to @var{code},
 which must be a valid HTTP status code. 
+
+@kindex regex
+@cindex regular expression matching
+@item regex
+Use regular expression matching.  This is the default.  This flag is
+provided for completeness sake, as a counterpart of @samp{eq}.
 @end table
 
 If @var{regexp} or @var{value} is NULL, strict matching is assumed
@@ -701,6 +719,24 @@ The @code{X-VMOD-DBRW-Status} header, if set, contains the status code to be
 returned to the client (@pxref{X-VMOD-DBRW-Status}).  Notice the use
 of the @command{vmod_std} module to cast it to integer.
 
+If an error occured during the rewrite, it is recommended to not
+cache the response.  This way the next request will call rewrite again
+and eventually complete the rewriting.  This can be achieved using the
+following @code{vcl_backend_response} fragment:
+
+@example
+@group
+sub vcl_backend_response
+@{
+    if (bereq.http.X-VMOD-DBRW-Error == "1") @{
+        set beresp.uncacheable = true;
+        return (deliver);
+    @}
+@}
+@end group
+@end example
+
+
 @node Reporting Bugs
 @chapter How to Report a Bug