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  1. Subversion
  2. SVN-4514

HTTP Header "Cache-Control" should be omitted on HEAD URLs

    Details

    • Type: New Feature
    • Status: Resolved
    • Priority: Major
    • Resolution: Fixed
    • Affects Version/s: trunk
    • Fix Version/s: 1.10.0
    • Component/s: mod_dav_svn
    • Labels:
      None

      Description

      When accessing a Subversion repository via http:// URL using a web browser, mod_dav_svn returns a "Cache-Control: max-age=604800" header (only on files, not on directories).

      This makes the web browser cache the file content for up to a week.

      This makes a lot of sense when a fixed revision was requested, but URLs that imply HEAD, no Cache-Control should be sent. (Note that a Last-Modified header is always sent as well, which should be good enough AFAICT.)

      Example:

      ▶ wget -Sq -O /dev/null http://svn.apache.org/repos/asf/subversion/trunk/subversion/mod_dav_svn/repos.c
        HTTP/1.1 200 OK
        Date: Thu, 10 Jul 2014 15:16:28 GMT
        Server: Apache/2.2.25 (Unix) DAV/2 mod_wsgi/3.1 Python/2.7.3 SVN/1.8.1 mod_ssl/2.2.25 OpenSSL/1.0.1h
        Last-Modified: Mon, 23 Jun 2014 20:50:11 GMT
        ETag: "1604933//subversion/trunk/subversion/mod_dav_svn/repos.c"
        Cache-Control: max-age=604800
        Accept-Ranges: bytes
        Content-Length: 164114
        Vary: Accept-Encoding
        Keep-Alive: timeout=15, max=1000
        Connection: Keep-Alive
        Content-Type: text/plain; charset=ISO-8859-1
      

      (Cache-Control is sent but should not be, as no revision was requested.)

      URLs like these should still return a Cache-Control header, as they contain an explicit revision:

      http://svn.apache.org/repos/asf/subversion/trunk/subversion/mod_dav_svn/repos.c?p=1000000

      http://svn.apache.org/repos/asf/subversion/trunk/subversion/mod_dav_svn/repos.c?r=1000000

      URLs that point at directories never include a Cache-Control header. IMHO directories with explicit revisions should also have a Cache-Control header.

      The main point of this issue however: do not confuse web browsers & force users to hard-reload a file URL of HEAD to see recent modifications.

      The header is conditionally hardcoded in subversion/mod_dav_svn/repos.c around line 3050 as:

        /* As version resources don't change, encourage caching. */
        if ((resource->type == DAV_RESOURCE_TYPE_REGULAR
             && resource->versioned && !resource->collection)
            || resource->type == DAV_RESOURCE_TYPE_VERSION)
          /* Cache resource for one week (specified in seconds). */
          apr_table_setn(r->headers_out, "Cache-Control", "max-age=604800");
      

      In pseudo code, I think this should become:

        if ((...) && an_explicit_revision_number_was_passed_as_GET_param)
          apr_table_setn(r->headers_out, "Cache-Control", "max-age=604800");
      

      The GET params are 'r' and 'p'. It seems they don't accept "HEAD", so it might be enough to include the Cache-Control header iff a revision param is non-empty (not having looked through the code too closely yet).

      Original issue reported by neels

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            • Assignee:
              ivan.z Ivan Zhakov
              Reporter:
              subversion-importer Subversion Importer
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              Dates

              • Created:
                Updated:
                Resolved: