Add support for HTTP 1.1 If-Modified-Since behavior.

fetch(1) accepts a new argument -i <file> that if specified will cause
the file to be downloaded only if it is more recent than the mtime of
<file>.

libfetch(3) accepts the mtime in the url structure and a flag to
indicate when this behavior is desired.

PR:		bin/87841
Submitted by:	Jukka A. Ukkonen <jau@iki.fi> (partially)
Reviewed by:	des, ru
MFC after:	3 weeks

1 files changed, 24 insertions, 1 deletions

diff --git a/lib/libfetch/fetch.3 b/lib/libfetch/fetch.3
index 81b7164..9b312b0 100644
--- a/lib/libfetch/fetch.3
+++ b/lib/libfetch/fetch.3
@@ -25,7 +25,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd December 18, 2007
+.Dd December 14, 2008
 .Dt FETCH 3
 .Os
 .Sh NAME
@@ -165,9 +165,16 @@ struct url {
     char	*doc;
     off_t	 offset;
     size_t	 length;
+    time_t	 ims_time;
 };
 .Ed
 .Pp
+The
+.Va ims_time
+field stores the time value for
+.Li If-Modified-Since
+HTTP requests.
+.Pp
 The pointer returned by
 .Fn fetchMakeURL
 or
@@ -353,6 +360,22 @@ and
 .Fn fetchPutHTTP
 will use a direct connection even if a proxy server is defined.
 .Pp
+If the
+.Ql i
+(if-modified-since) flag is specified, and
+the
+.Va ims_time
+field is set in 
+.Vt "struct url" ,
+then
+.Fn fetchXGetHTTP
+and
+.Fn fetchGetHTTP
+will send a conditional
+.Li If-Modified-Since
+HTTP header to only fetch the content if it is newer than
+.Va ims_time .
+.Pp
 Since there seems to be no good way of implementing the HTTP PUT
 method in a manner consistent with the rest of the
 .Nm fetch