mod_negotiation.c

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{
    int i;
    accept_rec *accept_recs;
    char *charset = variant->content_charset;
    accept_rec *star = NULL;

    /* if no Accept-Charset: header, leave quality alone (will
     * remain at the default value of 1)
     */
    if (!neg->accept_charsets) {
        if (charset && *charset)
            variant->definite = 0;
        return;
    }

    accept_recs = (accept_rec *) neg->accept_charsets->elts;

    if (charset == NULL || !*charset) {
        /* Charset of variant not known */

        /* if not a text / * type, leave quality alone */
        if (!(!strncmp(variant->mime_type, "text/", 5)
              || !strcmp(variant->mime_type, INCLUDES_MAGIC_TYPE)
              || !strcmp(variant->mime_type, INCLUDES_MAGIC_TYPE3) 
              ))
            return;

        /* Don't go guessing if we are in strict header mode,
         * e.g. when running the rvsa, as any guess won't be reflected
         * in the variant list or content-location headers.
         */
        if (neg->dont_fiddle_headers)
            return;

        charset = "iso-8859-1"; /* The default charset for HTTP text types */
    }

    /*
     * Go through each of the items on the Accept-Charset header,
     * looking for a match with this variant's charset. If none
     * match, charset is unacceptable, so set quality to 0.
     */
    for (i = 0; i < neg->accept_charsets->nelts; ++i) {

        accept_rec *type = &accept_recs[i];

        if (!strcmp(type->name, charset)) {
            variant->charset_quality = type->quality;
            return;
        }
        else if (strcmp(type->name, "*") == 0) {
            star = type;
        }
    }
    /* No explicit match */
    if (star) {
        variant->charset_quality = star->quality;
        variant->definite = 0;
        return;
    }
    /* If this variant is in charset iso-8859-1, the default is 1.0 */
    if (strcmp(charset, "iso-8859-1") == 0) {
        variant->charset_quality = 1.0f;
    }
    else {
        variant->charset_quality = 0.0f;
    }
}


/* is_identity_encoding is included for back-compat, but does anyone
 * use 7bit, 8bin or binary in their var files??
 */

static int is_identity_encoding(const char *enc)
{
    return (!enc || !enc[0] || !strcmp(enc, "7bit") || !strcmp(enc, "8bit")
            || !strcmp(enc, "binary"));
}

/*
 * set_encoding_quality determines whether the encoding for a particular
 * variant is acceptable for the user-agent.
 *
 * The rules for encoding are that if the user-agent does not supply
 * any Accept-Encoding header, then all encodings are allowed but a
 * variant with no encoding should be preferred.
 * If there is an empty Accept-Encoding header, then no encodings are 
 * acceptable. If there is a non-empty Accept-Encoding header, then
 * any of the listed encodings are acceptable, as well as no encoding
 * unless the "identity" encoding is specifically excluded.
 */
static void set_encoding_quality(negotiation_state *neg, var_rec *variant)
{
    accept_rec *accept_recs;
    const char *enc = variant->content_encoding;
    accept_rec *star = NULL;
    float value_if_not_found = 0.0f;
    int i;

    if (!neg->accept_encodings) {
        /* We had no Accept-Encoding header, assume that all
         * encodings are acceptable with a low quality,
         * but we prefer no encoding if available.
         */
        if (!enc || is_identity_encoding(enc))
            variant->encoding_quality = 1.0f;
        else
            variant->encoding_quality = 0.5f;

        return;
    }

    if (!enc || is_identity_encoding(enc)) {
        enc = "identity";
        value_if_not_found = 0.0001f;
    }

    accept_recs = (accept_rec *) neg->accept_encodings->elts;

    /* Go through each of the encodings on the Accept-Encoding: header,
     * looking for a match with our encoding. x- prefixes are ignored.
     */
    if (enc[0] == 'x' && enc[1] == '-') {
        enc += 2;
    }
    for (i = 0; i < neg->accept_encodings->nelts; ++i) {

        char *name = accept_recs[i].name;

        if (name[0] == 'x' && name[1] == '-') {
            name += 2;
        }

        if (!strcmp(name, enc)) {
            variant->encoding_quality = accept_recs[i].quality;
            return;
        }

        if (strcmp(name, "*") == 0) {
            star = &accept_recs[i];
        }

    }
    /* No explicit match */
    if (star) {
        variant->encoding_quality = star->quality;
        return;
    }

    /* Encoding not found on Accept-Encoding: header, so it is
     * _not_ acceptable unless it is the identity (no encoding)
     */
    variant->encoding_quality = value_if_not_found;
}

/************************************************************* 
 * Possible results of the variant selection algorithm 
 */
enum algorithm_results {
    alg_choice = 1,              /* choose variant */
    alg_list                     /* list variants */
};

/* Below is the 'best_match' function. It returns an int, which has
 * one of the two values alg_choice or alg_list, which give the result
 * of the variant selection algorithm.  alg_list means that no best
 * variant was found by the algorithm, alg_choice means that a best
 * variant was found and should be returned.  The list/choice
 * terminology comes from TCN (rfc2295), but is used in a more generic
 * way here.  The best variant is returned in *pbest. best_match has
 * two possible algorithms for determining the best variant: the
 * RVSA/1.0 algorithm (from RFC2296), and the standard Apache
 * algorithm. These are split out into separate functions
 * (is_variant_better_rvsa() and is_variant_better()).  Selection of
 * one is through the neg->use_rvsa flag.
 *
 * The call to best_match also creates full information, including
 * language, charset, etc quality for _every_ variant. This is needed
 * for generating a correct Vary header, and can be used for the
 * Alternates header, the human-readable list responses and 406 errors.
 */

/* Firstly, the RVSA/1.0 (HTTP Remote Variant Selection Algorithm
 * v1.0) from rfc2296.  This is the algorithm that goes together with
 * transparent content negotiation (TCN).
 */
static int is_variant_better_rvsa(negotiation_state *neg, var_rec *variant,
                                  var_rec *best, float *p_bestq)
{
    float bestq = *p_bestq, q;

    /* TCN does not cover negotiation on content-encoding.  For now,
     * we ignore the encoding unless it was explicitly excluded.
     */
    if (variant->encoding_quality == 0.0f)
        return 0;
    
    q = variant->mime_type_quality *
        variant->source_quality *
        variant->charset_quality *
        variant->lang_quality;

   /* RFC 2296 calls for the result to be rounded to 5 decimal places,
    * but we don't do that because it serves no useful purpose other
    * than to ensure that a remote algorithm operates on the same
    * precision as ours.  That is silly, since what we obviously want
    * is for the algorithm to operate on the best available precision
    * regardless of who runs it.  Since the above calculation may
    * result in significant variance at 1e-12, rounding would be bogus.
    */

#ifdef NEG_DEBUG
    fprintf(stderr, "Variant: file=%s type=%s lang=%s sourceq=%1.3f "
           "mimeq=%1.3f langq=%1.3f charq=%1.3f encq=%1.3f "
           "q=%1.5f definite=%d\n",            
            (variant->file_name ? variant->file_name : ""),
            (variant->mime_type ? variant->mime_type : ""),
            (variant->content_languages
             ? ap_array_pstrcat(neg->pool, variant->content_languages, ',')
             : ""),
            variant->source_quality,
            variant->mime_type_quality,
            variant->lang_quality,
            variant->charset_quality,
            variant->encoding_quality,
            q,
            variant->definite);
#endif

    if (q <= 0.0f) {
        return 0;
    }
    if (q > bestq) {
        *p_bestq = q;
        return 1;
    }
    if (q == bestq) {
        /* If the best variant's encoding is of lesser quality than
         * this variant, then we prefer this variant
         */
        if (variant->encoding_quality > best->encoding_quality) {
            *p_bestq = q;
            return 1;
        }
    }
    return 0;
}

/* Negotiation algorithm as used by previous versions of Apache
 * (just about). 
 */

static int is_variant_better(negotiation_state *neg, var_rec *variant,
                             var_rec *best, float *p_bestq)
{
    float bestq = *p_bestq, q;
    int levcmp;

    /* For non-transparent negotiation, server can choose how
     * to handle the negotiation. We'll use the following in
     * order: content-type, language, content-type level, charset,
     * content encoding, content length.
     *
     * For each check, we have three possible outcomes:
     *   This variant is worse than current best: return 0
     *   This variant is better than the current best:
     *          assign this variant's q to *p_bestq, and return 1
     *   This variant is just as desirable as the current best:
     *          drop through to the next test.
     *
     * This code is written in this long-winded way to allow future
     * customisation, either by the addition of additional
     * checks, or to allow the order of the checks to be determined
     * by configuration options (e.g. we might prefer to check
     * language quality _before_ content type).
     */

    /* First though, eliminate this variant if it is not
     * acceptable by type, charset, encoding or language.
     */

#ifdef NEG_DEBUG
    fprintf(stderr, "Variant: file=%s type=%s lang=%s sourceq=%1.3f "
           "mimeq=%1.3f langq=%1.3f langidx=%d charq=%1.3f encq=%1.3f \n",
            (variant->file_name ? variant->file_name : ""),
            (variant->mime_type ? variant->mime_type : ""),
            (variant->content_languages
             ? ap_array_pstrcat(neg->pool, variant->content_languages, ',')
             : ""),
            variant->source_quality,
            variant->mime_type_quality,
            variant->lang_quality,
            variant->lang_index,
            variant->charset_quality,
            variant->encoding_quality);
#endif

    if (variant->encoding_quality == 0.0f ||
        variant->lang_quality == 0.0f ||
        variant->source_quality == 0.0f ||
        variant->charset_quality == 0.0f ||
        variant->mime_type_quality == 0.0f) {
        return 0;               /* don't consider unacceptables */
    }

    q = variant->mime_type_quality * variant->source_quality;
    if (q == 0.0 || q < bestq) {
        return 0;
    }
    if (q > bestq || !best) {
        *p_bestq = q;
        return 1;
    }

    /* language */
    if (variant->lang_quality < best->lang_quality) {
        return 0;
    }
    if (variant->lang_quality > best->lang_quality) {
        *p_bestq = q;
        return 1;
    }

    /* if language qualities were equal, try the LanguagePriority stuff */
    if (best->lang_index != -1 &&
        (variant->lang_index == -1 || variant->lang_index > best->lang_index)) {
        return 0;
    }
    if (variant->lang_index != -1 &&
        (best->lang_index == -1 || variant->lang_index < best->lang_index)) {
        *p_bestq = q;
        return 1;
    }

    /* content-type level (sometimes used with text/html, though we
     * support it on other types too)
     */
    levcmp = level_cmp(variant, best);
    if (levcmp == -1) {
        return 0;
    }
    if (levcmp == 1) {
        *p_bestq = q;
        return 1;
    }

    /* charset */
    if (variant->charset_quality < best->charset_quality) {
        return 0;
    }
    /* If the best variant's charset is ISO-8859-1 and this variant has
     * the same charset quality, then we prefer this variant
     */

    if (variant->charset_quality > best->charset_quality ||
        ((variant->content_charset != NULL &&
          *variant->content_charset != '\0' &&
          strcmp(variant->content_charset, "iso-8859-1") != 0) &&
         (best->content_charset == NULL ||
          *best->content_charset == '\0' ||
          strcmp(best->content_charset, "iso-8859-1") == 0))) {
        *p_bestq = q;
        return 1;
    }

    /* Prefer the highest value for encoding_quality.
     */
    if (variant->encoding_quality < best->encoding_quality) {
       return 0;
    }
    if (variant->encoding_quality > best->encoding_quality) {
       *p_bestq = q;
       return 1;
    }

    /* content length if all else equal */
    if (find_content_length(neg, variant) >= find_content_length(neg, best)) {
        return 0;
    }

    /* ok, to get here means every thing turned out equal, except
     * we have a shorter content length, so use this variant
     */
    *p_bestq = q;
    return 1;
}

static int best_match(negotiation_state *neg, var_rec **pbest)
{
    int j;
    var_rec *best = NULL;
    float bestq = 0.0f;
    enum algorithm_results algorithm_r