Enhance default Http resource handling to support "conditional GET"
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Key: FELIX-407
URL: https://issues.apache.org/jira/browse/FELIX-407
Project: Felix
Issue Type: Improvement
Components: HTTP Service
Reporter: Rob Walker
Priority: Minor
Whilst creating a generic "file serving" servlet, I realised our default HTTP
resource serving in org.apache.felix.http.jetty.OsgiResourceHandler does not
actually support "conditional GET" functionalty.
A few, relatively simple, mods could be made to support this:
(1) - enhance default handler to include last modified time in responses e.g.
response.setDateHeader("Last-Modified", urlConn.lastModified());
Note however, that Sun in their JNLP servlet document a bug where "file:" URL
resources do not return last modified correctly, so an extra test is needed for
file URLs. Following is from Sun JnlpDownloadServlet:
<code>
try {
// Get last modified time
conn = resource.openConnection();
lastModified = conn.getLastModified();
} catch (Exception e) {
// do nothing
}
if (lastModified == 0) {
// Arguably a bug in the JRE will not set the lastModified for file
URLs, and
// always return 0. This is a workaround for that problem.
String filepath = context.getRealPath(path);
if (filepath != null) {
File f = new File(filepath);
if (f.exists()) {
lastModified = f.lastModified();
}
}
<code>
(2) check incoming requests for a "If-Modified-Since" header, and if present
check against the file timestamp. If server file has not change since this
time, return a 304 (SC_NOT_MODIFIED) status
Found a useful summary from which I based the above here:
(3) for extra robustness on "file" resources the above can be extended to also
use a combination of an "ETag" header e.g. made up of file timestamp + file
size & a check against the "If-None-Match" request header
http://fishbowl.pastiche.org/2002/10/21/http_conditional_get_for_rss_hackers
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