modules/core/mod_macro.c

	mod_macro.c revision f545d156561c08020a67f9640c51454c2df4fb57
/* Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/*
  $Id$
*/

#include "httpd.h"
#include "http_config.h"
#include "http_log.h"

#include "apr.h"
#include "apr_strings.h"
#include "apr_hash.h"

/************************************************ COMPILE TIME DEBUG CONTROL */
/*
   debug:
   #define MOD_MACRO_DEBUG 1

   gdb:
   run -f ./test/conf/test??.conf
*/
/* #define MOD_MACRO_DEBUG 1 */
#undef MOD_MACRO_DEBUG

#if defined(debug)
#undef debug
#endif /* debug */

#if defined(MOD_MACRO_DEBUG)
#define debug(stmt) stmt
#else
#define debug(stmt)
#endif /* MOD_MACRO_DEBUG */

/******************************************************** MODULE DECLARATION */

module AP_MODULE_DECLARE_DATA macro_module;

/********************************************************** MACRO MANAGEMENT */

/*
  this is a macro: name, arguments, contents, location.
*/
typedef struct
{
    char *name;                    /* lower case name of the macro */
    apr_array_header_t *arguments; /* of char*, macro parameter names */
    apr_array_header_t *contents;  /* of char*, macro body */
    char *location;                /* of macro definition, for error messages */
} ap_macro_t;

/* configuration tokens.
 */
#define BEGIN_MACRO "<Macro"
#define END_MACRO   "</Macro>"
#define USE_MACRO   "Use"
#define UNDEF_MACRO "UndefMacro"

/*
  Macros are kept globally...
  They are not per-server or per-directory entities.

  I would need a hook BEFORE and AFTER configuration processing
  to initialize and close them properly, but no such thing is exported,
  although it could be available from within apache.

  I would have such a hook if in server/config.c
  The "initializer" does not seem to be called before.

  note: they are in a temp_pool, and there is a lazy initialization.

  hash type: (char *) name -> (ap_macro_t *) macro
*/
static apr_hash_t *ap_macros = NULL;

/*************************************************************** PARSE UTILS */

#define empty_string_p(p) (!(p) || *(p) == '\0')
#define trim(line) while (*(line) == ' ' || *(line) == '\t') (line)++

/*
  return configuration-parsed arguments from line as an array.
  the line is expected not to contain any '\n'?
*/
static apr_array_header_t *get_arguments(apr_pool_t * pool, const char *line)
{
    apr_array_header_t *args = apr_array_make(pool, 1, sizeof(char *));

    trim(line);
    while (*line) {
        char *arg = ap_getword_conf(pool, &line);
        char **new = apr_array_push(args);
        *new = arg;
        trim(line);
    }

    return args;
}

/*
  warn if anything non blank appears, but ignore comments...
*/
static void warn_if_non_blank(
    const char * what,
    char * ptr,
    ap_configfile_t * cfg)
{
    char * p;
    for (p=ptr; *p; p++) {
        if (*p == '#')
            break;
        if (*p != ' ' && *p != '\t') {
            ap_log_error(APLOG_MARK, APLOG_NOERRNO | APLOG_WARNING, 0, NULL,
                         "%s on line %d of %s: %s",
                         what, cfg->line_number, cfg->name, ptr);
            break;
        }
    }
}

/*
  get read lines as an array till end_token.
  counts nesting for begin_token/end_token.
  it assumes a line-per-line configuration (thru getline).
  this function could be exported.
  begin_token may be NULL.
*/
static char *get_lines_till_end_token(apr_pool_t * pool,
                                      ap_configfile_t * config_file,
                                      const char *end_token,
                                      const char *begin_token,
                                      const char *where,
                                      apr_array_header_t ** plines)
{
    apr_array_header_t *lines = apr_array_make(pool, 1, sizeof(char *));
    char line[MAX_STRING_LEN];  /* sorry, but this is expected by getline:-( */
    int macro_nesting = 1, any_nesting = 1;
    int line_number_start = config_file->line_number;

    while (!ap_cfg_getline(line, MAX_STRING_LEN, config_file)) {
        char *ptr = line;
        char *first, **new;
        /* skip comments */
        if (*line == '#')
            continue;
        first = ap_getword_conf_nc(pool, &ptr);
        if (first) {
            /* detect nesting... */
            if (!strncmp(first, "</", 2)) {
                any_nesting--;
                if (any_nesting < 0) {
                    ap_log_error(APLOG_MARK, APLOG_NOERRNO | APLOG_WARNING,
                                 0, NULL,
                                 "bad (negative) nesting on line %d of %s",
                                 config_file->line_number - line_number_start,
                                 where);
                }
            }
            else if (!strncmp(first, "<", 1)) {
                any_nesting++;
            }

            if (!strcasecmp(first, end_token)) {
                /* check for proper closing */
                char * endp = (char *) ap_strrchr_c(line, '>');

                /* this cannot happen if end_token contains '>' */
                if (endp == NULL) {
                  return "end directive missing closing '>'";
                }

                warn_if_non_blank(
                    "non blank chars found after directive closing",
                    endp+1, config_file);

                macro_nesting--;
                if (!macro_nesting) {
                    if (any_nesting) {
                        ap_log_error(APLOG_MARK,
                                     APLOG_NOERRNO | APLOG_WARNING, 0, NULL,
                                     "bad cumulated nesting (%+d) in %s",
                                     any_nesting, where);
                    }
                    *plines = lines;
                    return NULL;
                }
            }
            else if (begin_token && !strcasecmp(first, begin_token)) {
                macro_nesting++;
            }
        }
        new = apr_array_push(lines);
        *new = apr_psprintf(pool, "%s" APR_EOL_STR, line); /* put EOL back? */
    }

    return apr_psprintf(pool, "expected token not found: %s", end_token);
}

/* the @* arguments are double-quote escaped when substituted */
#define ESCAPE_ARG '@'

/* other $* and %* arguments are simply replaced without escaping */
#define ARG_PREFIX "$%@"

/*
  characters allowed in an argument?
  not used yet, because that would trigger some backward compatibility.
*/
#define ARG_CONTENT              \
    "abcdefghijklmnopqrstuvwxyz"   \
    "ABCDEFGHIJKLMNOPQRSTUVWXYZ"   \
    "0123456789_" ARG_PREFIX

/*
  returns whether it looks like an argument, i.e. prefixed by ARG_PREFIX.
*/
static int looks_like_an_argument(const char *word)
{
    return ap_strchr(ARG_PREFIX, *word) != 0;
}

/*
  generates an error on macro with two arguments of the same name.
  generates an error if a macro argument name is empty.
  generates a warning if arguments name prefixes conflict.
  generates a warning if the first char of an argument is not in ARG_PREFIX
*/
static const char *check_macro_arguments(apr_pool_t * pool,
                                         const ap_macro_t * macro)
{
    char **tab = (char **) macro->arguments->elts;
    int nelts = macro->arguments->nelts;
    int i;

    for (i = 0; i < nelts; i++) {
        size_t ltabi = strlen(tab[i]);
        int j;

        if (ltabi == 0) {
            return apr_psprintf(pool,
                                "macro '%s' (%s): empty argument #%d name",
                                macro->name, macro->location, i + 1);
        }
        else if (!looks_like_an_argument(tab[i])) {
            ap_log_error(APLOG_MARK, APLOG_NOERRNO | APLOG_WARNING, 0, NULL,
                         "macro '%s' (%s) "
                         "argument name '%s' (#%d) without expected prefix, "
                         "better prefix argument names with one of '%s'.",
                         macro->name, macro->location,
                         tab[i], i + 1, ARG_PREFIX);
        }

        for (j = i + 1; j < nelts; j++) {
            size_t ltabj = strlen(tab[j]);

            /* must not use the same argument name twice */
            if (!strcmp(tab[i], tab[j])) {
                return apr_psprintf(pool,
                                   "argument name conflict in macro '%s' (%s): "
                                    "argument '%s': #%d and #%d, "
                                    "change argument names!",
                                    macro->name, macro->location,
                                    tab[i], i + 1, j + 1);
            }

            /* warn about common prefix, but only if non empty names */
            if (ltabi && ltabj &&
                !strncmp(tab[i], tab[j], ltabi < ltabj ? ltabi : ltabj)) {
                ap_log_error(APLOG_MARK, APLOG_NOERRNO | APLOG_WARNING,
                             0, NULL,
                             "macro '%s' (%s): "
                            "argument name prefix conflict (%s #%d and %s #%d),"
                             " be careful about your macro definition!",
                             macro->name, macro->location,
                             tab[i], i + 1, tab[j], j + 1);
            }
        }
    }

    return NULL;
}

/*
  warn about empty strings in array. could be legitimate.
*/
static void check_macro_use_arguments(const char *where,
                                      const apr_array_header_t * array)
{
    char **tab = (char **) array->elts;
    int i;
    for (i = 0; i < array->nelts; i++) {
        if (empty_string_p(tab[i])) {
            ap_log_error(APLOG_MARK, APLOG_NOERRNO | APLOG_WARNING, 0, NULL,
                         "%s: empty argument #%d", where, i + 1);
        }
    }
}

/******************************************************** SUBSTITUTION UTILS */

/* could be switched to '\'' */
#define DELIM '"'
#define ESCAPE '\\'

/*
  returns the number of needed escapes for the string
*/
static int number_of_escapes(const char delim, const char *str)
{
    int nesc = 0;
    const char *s = str;
    while (*s) {
        if (*s == ESCAPE || *s == delim)
            nesc++;
        s++;
    }
    debug(fprintf(stderr, "escapes: %d ---%s---\n", nesc, str));
    return nesc;
}

/*
  replace name by replacement at the beginning of buf of bufsize.
  returns an error message or NULL.
  C is not really a nice language for processing strings.
*/
static char *substitute(char *buf,
                        const int bufsize,
                        const char *name,
                        const char *replacement, const int do_esc)
{
    int lbuf = strlen(buf),
        lname = strlen(name),
        lrepl = strlen(replacement),
        lsubs = lrepl +
        (do_esc ? (2 + number_of_escapes(DELIM, replacement)) : 0),
        shift = lsubs - lname, size = lbuf + shift, i, j;

    /* buf must starts with name */
    ap_assert(!strncmp(buf, name, lname));

    /* hmmm??? */
    if (!strcmp(name, replacement))
        return NULL;

    debug(fprintf(stderr,
                  "substitute(%s,%s,%s,%d,sh=%d,lbuf=%d,lrepl=%d,lsubs=%d)\n",
                  buf, name, replacement, do_esc, shift, lbuf, lrepl, lsubs));

    if (size >= bufsize) {
        /* could/should I reallocate? */
        return "cannot substitute, buffer size too small";
    }

    /* cannot use strcpy as strings may overlap */
    if (shift != 0) {
        memmove(buf + lname + shift, buf + lname, lbuf - lname + 1);
    }

    /* insert the replacement with escapes */
    j = 0;
    if (do_esc)
        buf[j++] = DELIM;
    for (i = 0; i < lrepl; i++, j++) {
        if (do_esc && (replacement[i] == DELIM || replacement[i] == ESCAPE))
            buf[j++] = ESCAPE;
        buf[j] = replacement[i];
    }
    if (do_esc)
        buf[j++] = DELIM;

    return NULL;
}

/*
  find first occurence of args in buf.
  in case of conflict, the LONGEST argument is kept. (could be the FIRST?).
  returns the pointer and the whichone found, or NULL.
*/
static char *next_substitution(const char *buf,
                               const apr_array_header_t * args, int *whichone)
{
    char *chosen = NULL, **tab = (char **) args->elts;
    size_t lchosen = 0;
    int i;

    for (i = 0; i < args->nelts; i++) {
        char *found = ap_strstr((char *) buf, tab[i]);
        size_t lfound = strlen(tab[i]);
        if (found && (!chosen || found < chosen ||
                      (found == chosen && lchosen < lfound))) {
            chosen = found;
            lchosen = lfound;
            *whichone = i;
        }
    }

    return chosen;
}

/*
  substitute macro arguments by replacements in buf of bufsize.
  returns an error message or NULL.
  if used is defined, returns the used macro arguments.
*/
static const char *substitute_macro_args(
    char *buf,
    int bufsize,
    const ap_macro_t * macro,
    const apr_array_header_t * replacements,
    apr_array_header_t * used)
{
    char *ptr = buf,
        **atab = (char **) macro->arguments->elts,
        **rtab = (char **) replacements->elts;
    int whichone = -1;

    if (used) {
        ap_assert(used->nalloc >= replacements->nelts);
    }
    debug(fprintf(stderr, "1# %s", buf));

    while ((ptr = next_substitution(ptr, macro->arguments, &whichone))) {
        const char *errmsg = substitute(ptr, buf - ptr + bufsize,
                                        atab[whichone], rtab[whichone],
                                        atab[whichone][0] == ESCAPE_ARG);
        if (errmsg) {
            return errmsg;
        }
        ptr += strlen(rtab[whichone]);
        if (used) {
            used->elts[whichone] = 1;
        }
    }
    debug(fprintf(stderr, "2# %s", buf));

    return NULL;
}

/*
  perform substitutions in a macro contents and
  return the result as a newly allocated array, if result is defined.
  may also return an error message.
  passes used down to substitute_macro_args.
*/
static const char *process_content(apr_pool_t * pool,
                                   const ap_macro_t * macro,
                                   const apr_array_header_t * replacements,
                                   apr_array_header_t * used,
                                   apr_array_header_t ** result)
{
    apr_array_header_t *contents = macro->contents;
    char line[MAX_STRING_LEN];
    int i;

    if (result) {
        *result = apr_array_make(pool, 1, sizeof(char *));
    }

    /* for each line of the macro body */
    for (i = 0; i < contents->nelts; i++) {
        const char *errmsg;
        /* copy the line and subtitute macro parameters */
        strncpy(line, ((char **) contents->elts)[i], MAX_STRING_LEN - 1);
        errmsg = substitute_macro_args(line, MAX_STRING_LEN,
                                       macro, replacements, used);
        if (errmsg) {
            return apr_psprintf(pool,
                               "while processing line %d of macro '%s' (%s) %s",
                                i + 1, macro->name, macro->location, errmsg);
        }
        /* append substituted line to result array */
        if (result) {
            char **new = apr_array_push(*result);
            *new = apr_pstrdup(pool, line);
        }
    }

    return NULL;
}

/*
  warn if some macro arguments are not used.
*/
static const char *check_macro_contents(apr_pool_t * pool,
                                        const ap_macro_t * macro)
{
    int nelts = macro->arguments->nelts;
    char **names = (char **) macro->arguments->elts;
    apr_array_header_t *used;
    int i;
    const char *errmsg;

    if (macro->contents->nelts == 0) {
        ap_log_error(APLOG_MARK, APLOG_NOERRNO | APLOG_WARNING, 0, NULL,
                     "macro '%s' (%s): empty contents!",
                     macro->name, macro->location);
        return NULL;            /* no need to further warnings... */
    }

    used = apr_array_make(pool, nelts, sizeof(char));

    for (i = 0; i < nelts; i++) {
        used->elts[i] = 0;
    }

    errmsg = process_content(pool, macro, macro->arguments, used, NULL);

    if (errmsg) {
        return errmsg;
    }

    for (i = 0; i < nelts; i++) {
        if (!used->elts[i]) {
            ap_log_error(APLOG_MARK, APLOG_NOERRNO | APLOG_WARNING, 0, NULL,
                         "macro '%s' (%s): argument '%s' (#%d) never used",
                         macro->name, macro->location, names[i], i + 1);
        }
    }

    return NULL;
}


/************************************************** MACRO PSEUDO CONFIG FILE */

/*
  The expanded content of the macro is to be parsed as a ap_configfile_t.
  This is used to have some kind of old fashionned C object oriented inherited
  data structure for configs.

  The following struct stores the contents.

  This structure holds pointers (next, upper) to the current "file" which was
  being processed and is interrupted by the macro expansion. At the end
  of processing the macro, the initial data structure will be put back
  in place (see function next_one) and the reading will go on from there.

  If macros are used within macros, there may be a cascade of such temporary
  arrays used to insert the expanded macro contents before resuming the real
  file processing.

  There is some hopus-pocus to deal with line_number when transiting from
  one config to the other.
*/
typedef struct
{
    int index;                    /* current element */
    int char_index;               /* current char in element */
    int length;                   /* cached length of the current line */
    apr_array_header_t *contents; /* array of char * */
    ap_configfile_t *next;        /* next config once this one is processed */
    ap_configfile_t **upper;      /* hack: where to update it if needed */
} array_contents_t;

/*
  Get next config if any.
  this may be called several times if there are continuations.
*/
static int next_one(array_contents_t * ml)
{
    if (ml->next) {
        ap_assert(ml->upper);
        *(ml->upper) = ml->next;
        return 1;
    }
    return 0;
}

/*
  returns next char if possible
  this may involve switching to enclosing config.
*/
static apr_status_t array_getch(char *ch, void *param)
{
    array_contents_t *ml = (array_contents_t *) param;
    char **tab = (char **) ml->contents->elts;

    while (ml->char_index >= ml->length) {
        if (ml->index >= ml->contents->nelts) {
            /* maybe update */
            if (ml->next && ml->next->getch && next_one(ml)) {
                apr_status_t rc = ml->next->getch(ch, ml->next->param);
                if (*ch==LF)
                    ml->next->line_number++;
                return rc;
            }
            return APR_EOF;
        }
        ml->index++;
        ml->char_index = 0;
        ml->length = ml->index >= ml->contents->nelts ?
            0 : strlen(tab[ml->index]);
    }

    *ch = tab[ml->index][ml->char_index++];
    return APR_SUCCESS;
}

/*
  returns a buf a la fgets.
  no more than a line at a time, otherwise the parsing is too much ahead...
  NULL at EOF.
*/
static apr_status_t array_getstr(void *buf, size_t bufsize, void *param)
{
    array_contents_t *ml = (array_contents_t *) param;
    char *buffer = (char *) buf;
    char next = '\0';
    size_t i = 0;
    apr_status_t rc = APR_SUCCESS;

    /* read chars from stream, stop on newline */
    while (i < bufsize - 1 && next != LF &&
           ((rc = array_getch(&next, param)) == APR_SUCCESS)) {
        buffer[i++] = next;
    }

    if (rc == APR_EOF) {
        /* maybe update to next, possibly a recursion */
        if (next_one(ml)) {
            ap_assert(ml->next->getstr);
            /* keep next line count in sync! the caller will update
               the current line_number, we need to forward to the next */
            ml->next->line_number++;
            return ml->next->getstr(buf, bufsize, ml->next->param);
        }
        /* else that is really all we can do */
        return APR_EOF;
    }

    buffer[i] = '\0';

    return APR_SUCCESS;
}

/*
  close the array stream?
*/
static apr_status_t array_close(void *param)
{
    array_contents_t *ml = (array_contents_t *) param;
    /* move index at end of stream... */
    ml->index = ml->contents->nelts;
    ml->char_index = ml->length;
    return APR_SUCCESS;
}

/*
  create an array config stream insertion "object".
  could be exported.
*/
static ap_configfile_t *make_array_config(apr_pool_t * pool,
                                          apr_array_header_t * contents,
                                          const char *where,
                                          ap_configfile_t * cfg,
                                          ap_configfile_t ** upper)
{
    array_contents_t *ls =
        (array_contents_t *) apr_palloc(pool, sizeof(array_contents_t));
    ap_assert(ls!=NULL);

    ls->index = 0;
    ls->char_index = 0;
    ls->contents = contents;
    ls->length = ls->contents->nelts < 1 ?
        0 : strlen(((char **) ls->contents->elts)[0]);
    ls->next = cfg;
    ls->upper = upper;

    return ap_pcfg_open_custom(pool, where, (void *) ls,
                               array_getch, array_getstr, array_close);
}


/********************************************************** KEYWORD HANDLING */

/*
  handles: <Macro macroname arg1 arg2 ...> any trash there is ignored...
*/
static const char *macro_section(cmd_parms * cmd,
                                 void *dummy, const char *arg)
{
    apr_pool_t *pool;
    char *endp, *name, *where;
    const char *errmsg;
    ap_macro_t *macro;

    debug(fprintf(stderr, "macro_section: arg='%s'\n", arg));

    /* lazy initialization */
    if (ap_macros == NULL)
        ap_macros = apr_hash_make(cmd->temp_pool);
    ap_assert(ap_macros != NULL);

    pool = apr_hash_pool_get(ap_macros);

    endp = (char *) ap_strrchr_c(arg, '>');

    if (endp == NULL) {
        return BEGIN_MACRO "> directive missing closing '>'";
    }

    if (endp == arg) {
        return BEGIN_MACRO " macro definition: empty name";
    }

    warn_if_non_blank("non blank chars found after " BEGIN_MACRO " closing '>'",
                      endp+1, cmd->config_file);

    /* coldly drop '>[^>]*$' out */
    *endp = '\0';

    /* get lowercase macro name */
    name = ap_getword_conf(pool, &arg);
    if (empty_string_p(name)) {
        return BEGIN_MACRO " macro definition: name not found";
    }

    ap_str_tolower(name);
    macro = apr_hash_get(ap_macros, name, APR_HASH_KEY_STRING);

    if (macro != NULL) {
        /* already defined: warn about the redefinition */
        ap_log_error(APLOG_MARK, APLOG_NOERRNO | APLOG_WARNING, 0, NULL,
                     "macro '%s' multiply defined: "
                     "%s, redefined on line %d of \"%s\"",
                     macro->name, macro->location,
                     cmd->config_file->line_number, cmd->config_file->name);
    }
    else {
        /* allocate a new macro */
        macro = (ap_macro_t *) apr_palloc(pool, sizeof(ap_macro_t));
        macro->name = name;
    }

    debug(fprintf(stderr, "macro_section: name=%s\n", name));

    /* get macro arguments */
    macro->location = apr_psprintf(pool,
                                   "defined on line %d of \"%s\"",
                                   cmd->config_file->line_number,
                                   cmd->config_file->name);
    debug(fprintf(stderr, "macro_section: location=%s\n", macro->location));

    where =
        apr_psprintf(pool, "macro '%s' (%s)", macro->name, macro->location);

    if (looks_like_an_argument(name)) {
        ap_log_error(APLOG_MARK, APLOG_NOERRNO | APLOG_WARNING, 0, NULL,
                     "%s better prefix a macro name with any of '%s'",
                     where, ARG_PREFIX);
    }

    /* get macro parameters */
    macro->arguments = get_arguments(pool, arg);

    errmsg = check_macro_arguments(cmd->temp_pool, macro);

    if (errmsg) {
        return errmsg;
    }

    errmsg = get_lines_till_end_token(pool, cmd->config_file,
                                      END_MACRO, BEGIN_MACRO,
                                      where, &macro->contents);

    if (errmsg) {
        return apr_psprintf(cmd->temp_pool,
                            "%s" APR_EOL_STR "\tcontents error: %s",
                            where, errmsg);
    }

    errmsg = check_macro_contents(cmd->temp_pool, macro);

    if (errmsg) {
        return apr_psprintf(cmd->temp_pool,
                            "%s" APR_EOL_STR "\tcontents checking error: %s",
                            where, errmsg);
    }

    /* store the new macro */
    apr_hash_set(ap_macros, name, APR_HASH_KEY_STRING, macro);

    return NULL;
}

/*
  handles: Use name value1 value2 ...
*/
static const char *use_macro(cmd_parms * cmd, void *dummy, const char *arg)
{
    char *name, *recursion, *where;
    const char *errmsg;
    ap_macro_t *macro;
    apr_array_header_t *replacements;
    apr_array_header_t *contents;

    debug(fprintf(stderr, "use_macro -%s-\n", arg));

    /* must be initialized, or no macros has been defined */
    if (ap_macros == NULL) {
        return "no macro defined before " USE_MACRO;
    }

    /* get lowercase macro name */
    name = ap_getword_conf(cmd->temp_pool, &arg);
    ap_str_tolower(name);

    if (empty_string_p(name)) {
        return "no macro name specified with " USE_MACRO;
    }

    /* get macro definition */
    macro = apr_hash_get(ap_macros, name, APR_HASH_KEY_STRING);

    if (!macro) {
        return apr_psprintf(cmd->temp_pool, "macro '%s' undefined", name);
    }

    /* recursion is detected here by looking at the config file name,
     * which may already contains "macro 'foo'". Ok, it looks like a hack,
     * but otherwise it is uneasy to keep this data available somewhere...
     * the name has just the needed visibility and liveness.
     */
    recursion =
        apr_pstrcat(cmd->temp_pool, "macro '", macro->name, "'", NULL);

    if (ap_strstr((char *) cmd->config_file->name, recursion)) {
        return apr_psprintf(cmd->temp_pool,
                            "recursive use of macro '%s' is invalid",
                            macro->name);
    }

    /* get macro arguments */
    replacements = get_arguments(cmd->temp_pool, arg);

    if (macro->arguments->nelts != replacements->nelts) {
        return apr_psprintf(cmd->temp_pool,
                            "macro '%s' (%s) used "
                            "with %d arguments instead of %d",
                            macro->name, macro->location,
                            replacements->nelts, macro->arguments->nelts);
    }

    where = apr_psprintf(cmd->temp_pool,
                         "macro '%s' (%s) used on line %d of \"%s\"",
                         macro->name, macro->location,
                         cmd->config_file->line_number,
                         cmd->config_file->name);

    check_macro_use_arguments(where, replacements);

    errmsg = process_content(cmd->temp_pool, macro, replacements,
                             NULL, &contents);

    if (errmsg) {
        return apr_psprintf(cmd->temp_pool,
                            "%s error while substituting: %s",
                            where, errmsg);
    }

    /* the current "config file" is replaced by a string array...
       at the end of processing the array, the initial config file
       will be returned there (see next_one) so as to go on. */
    cmd->config_file = make_array_config(cmd->temp_pool, contents, where,
                                         cmd->config_file, &cmd->config_file);

    return NULL;
}

static const char *undef_macro(cmd_parms * cmd, void *dummy, const char *arg)
{
    char *name;
    ap_macro_t *macro;

    /* must be initialized, or no macros has been defined */
    if (ap_macros == NULL) {
        return "no macro defined before " UNDEF_MACRO;
    }

    if (empty_string_p(arg)) {
        return "no macro name specified with " UNDEF_MACRO;
    }

    /* check that the macro is defined */
    name = apr_pstrdup(cmd->temp_pool, arg);
    ap_str_tolower(name);
    macro = apr_hash_get(ap_macros, name, APR_HASH_KEY_STRING);
    if (macro == NULL) {
        /* could be a warning? */
        return apr_psprintf(cmd->temp_pool,
                            "cannot remove undefined macro '%s'", name);
    }

    /* free macro: cannot do that */
    /* remove macro from hash table */
    apr_hash_set(ap_macros, name, APR_HASH_KEY_STRING, NULL);

    return NULL;
}

/************************************************************* EXPORT MODULE */

/*
  macro module commands.
  configuration file macro stuff
  they are processed immediatly when found, hence the EXEC_ON_READ.
*/
static const command_rec macro_cmds[] = {
    AP_INIT_RAW_ARGS(BEGIN_MACRO, macro_section, NULL, EXEC_ON_READ | OR_ALL,
                     "Beginning of a macro definition section."),
    AP_INIT_RAW_ARGS(USE_MACRO, use_macro, NULL, EXEC_ON_READ | OR_ALL,
                     "Use of a macro."),
    AP_INIT_TAKE1(UNDEF_MACRO, undef_macro, NULL, EXEC_ON_READ | OR_ALL,
                  "Remove a macro definition."),

    {NULL}
};

/*
  Module hooks are request-oriented thus it does not suit configuration
  file utils a lot. I haven't found any clean hook to apply something
  before then after configuration file processing. Also what about
  .htaccess files?

  Thus I think that server/util.c or server/config.c
  would be a better place for this stuff.
*/

AP_DECLARE_MODULE(macro) = {
    STANDARD20_MODULE_STUFF,    /* common stuff */
        NULL,                   /* create per-directory config */
        NULL,                   /* merge per-directory config structures */
        NULL,                   /* create per-server config structure */
        NULL,                   /* merge per-server config structures */
        macro_cmds,             /* configuration commands */
        NULL                    /* register hooks */
};