More detailed Last-Modified/I-M-S example for .mtime().

README.rst

@@ -459,9 +459,32 @@ encountered an error.
 
 Example::
 
-  # A VCL TIME is converted to a string as an HTTP date, and hence is
-  # suitable for the Last-Modified header.
-  set resp.http.Last-Modified = rdr.mtime();
+  # A VCL TIME is converted to a string as an HTTP date, so .mtime()
+  # is suitable for the Last-Modified header. If the If-Modified-Since
+  # request header is present and designates an earlier time than
+  # .mtime(), send a 304 Not Modified response.
+
+  import std;
+
+  sub vcl_recv {
+     # std.time() parses If-Modified-Since as a TIME. If the parse
+     # fails, fall back to now (which is almost certainly not earlier
+     # than the mtime).
+     if (std.time(req.http.If-Modified-Since, now) < rdr.mtime()) {
+	return (synth(304));
+     }
+     else {
+	return (synth(200));
+     }
+  }
+
+  sub vcl_synth {
+      set resp.http.Last-Modified = rdr.mtime();
+      if (resp.status == 200) {
+	rdr.synth();
+      }
+      return(deliver);
+  }
 
 .. _xreader.next_check():
 

src/vmod_file.vcc

@@ -421,9 +421,32 @@ encountered an error.
 
 Example::
 
-  # A VCL TIME is converted to a string as an HTTP date, and hence is
-  # suitable for the Last-Modified header.
-  set resp.http.Last-Modified = rdr.mtime();
+  # A VCL TIME is converted to a string as an HTTP date, so .mtime()
+  # is suitable for the Last-Modified header. If the If-Modified-Since
+  # request header is present and designates an earlier time than
+  # .mtime(), send a 304 Not Modified response.
+
+  import std;
+
+  sub vcl_recv {
+     # std.time() parses If-Modified-Since as a TIME. If the parse
+     # fails, fall back to now (which is almost certainly not earlier
+     # than the mtime).
+     if (std.time(req.http.If-Modified-Since, now) < rdr.mtime()) {
+	return (synth(304));
+     }
+     else {
+	return (synth(200));
+     }
+  }
+
+  sub vcl_synth {
+      set resp.http.Last-Modified = rdr.mtime();
+      if (resp.status == 200) {
+	rdr.synth();
+      }
+      return(deliver);
+  }
 
 $Method DURATION .next_check()