How to set mod_deflate preferred compression method to deflate

Question

mod_deflate always sends gzip data when the request header Accept-Encoding is gip, deflate.

How can I tell mod_deflate to prefer to send deflate (NOT zlib) instead of gzip?

If this isn't possible...why would the develpers name the module mod_deflate when it can't deflate. Also, what is the best way, if any, for me to submit a bug report to have this fixed in future releases?

Answer 1

After looking at the source code for mod_deflate I have come to the conclusion that it is impossible to send anything other than gzip.

Now, I'm not a c programmer and I don't think I'll be able to commit any patches myself...but from the source I can see that there are a few things that need to be fixed (warning, I've never written any c...so this is all probably terribly wrong)

/* add this method */
static const char *deflate_set_preferred_method(cmd_parms *cmd, void *dummy,
                                const char *arg1)
{
    deflate_filter_config *c = ap_get_module_config(cmd->server->module_config,
                                                &deflate_module);

    if (arg2 != NULL && (!strcasecmp(arg1, "deflate") || !strcasecmp(arg1, "gzip") || !strcasecmp(arg1, "zlib") ) ) {
        c->preferred_method = apr_pstrdup(cmd->pool, arg1);
    }
    else {
        return apr_psprintf(cmd->pool, "Unknown preferred method type %s", arg1);
    }

    return NULL;
}

/* update some code to define "preferred_method" */


/* 
   Update all code that references the string "gzip" to take 
   into account "deflate", and "zlib" as well.

   This is the part I really have no clue how to do.
   lines: 539, 604, 607, 616, and 624 should be updates

   line 624 could read something like this: */

if( !strcasecmp(preferred_method,"gzip") ){
    /* add immortal gzip header */
    e = apr_bucket_immortal_create(gzip_header, sizeof gzip_header,
                                   f->c->bucket_alloc);
    APR_BRIGADE_INSERT_TAIL(ctx->bb, e);
}
else if( !strcasecmp(preferred_method, "zlib") ){
   /* do something to add the zlib headers here */
}

/* update this method */
static const command_rec deflate_filter_cmds[] = {
    AP_INIT_TAKE12("DeflateFilterNote", deflate_set_note, NULL, RSRC_CONF,
                  "Set a note to report on compression ratio"),
    AP_INIT_TAKE1("DeflateWindowSize", deflate_set_window_size, NULL,
                  RSRC_CONF, "Set the Deflate window size (1-15)"),
    AP_INIT_TAKE1("DeflateBufferSize", deflate_set_buffer_size, NULL, RSRC_CONF,
                  "Set the Deflate Buffer Size"),
    AP_INIT_TAKE1("DeflateMemLevel", deflate_set_memlevel, NULL, RSRC_CONF,
                  "Set the Deflate Memory Level (1-9)"),
    AP_INIT_TAKE1("DeflateCompressionLevel", deflate_set_compressionlevel, NULL, RSRC_CONF,
                  "Set the Deflate Compression Level (1-9)"),
    AP_INIT_TAKE1("DeflatePreferredMethod", deflate_set_preferred_method, NULL, RSRC_CONF,
                  "Set the Preferred Compression Method: deflate, gzip, or zlib (not-recommended)"),
    {NULL}
};