/* 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.
 */

/*
 *  ap_expr_eval.c, based on ssl_expr_eval.c from mod_ssl
 */

#include "httpd.h"
#include "http_log.h"
#include "http_core.h"
#include "http_protocol.h"
#include "http_request.h"
#include "http_ssl.h"
#include "ap_provider.h"
#include "util_varbuf.h"
#include "util_expr_private.h"
#include "util_md5.h"
#include "util_varbuf.h"

#include "apr_lib.h"
#include "apr_fnmatch.h"
#include "apr_base64.h"
#include "apr_sha1.h"
#include "apr_version.h"
#include "apr_strings.h"
#include "apr_strmatch.h"
#if APR_VERSION_AT_LEAST(1,5,0)
#include "apr_escape.h"
#endif

#include <limits.h>     /* for INT_MAX */

/* we know core's module_index is 0 */
#undef APLOG_MODULE_INDEX
#define APLOG_MODULE_INDEX AP_CORE_MODULE_INDEX

APR_HOOK_STRUCT(
    APR_HOOK_LINK(expr_lookup)
)

AP_IMPLEMENT_HOOK_RUN_FIRST(int, expr_lookup, (ap_expr_lookup_parms *parms),
                            (parms), DECLINED)

#define  LOG_MARK(info)  __FILE__, __LINE__, (info)->module_index

static int ap_expr_eval_cond(ap_expr_eval_ctx_t *ctx, const ap_expr_t *node);

static const char *ap_expr_eval_string_func(ap_expr_eval_ctx_t *ctx,
                                            const ap_expr_t *info,
                                            const ap_expr_t *args);
static const char *ap_expr_eval_re_backref(ap_expr_eval_ctx_t *ctx,
                                           unsigned int n);
static const char *ap_expr_eval_var(ap_expr_eval_ctx_t *ctx,
                                    ap_expr_var_func_t *func,
                                    const void *data);

typedef struct {
    int flags;
    const ap_expr_t *subst;
} ap_expr_regctx_t;

static const char *ap_expr_regexec(const char *subject,
                                   const ap_expr_t *reg,
                                   apr_array_header_t *list,
                                   ap_expr_eval_ctx_t *ctx);

static apr_array_header_t *ap_expr_list_make(ap_expr_eval_ctx_t *ctx,
                                             const ap_expr_t *node);

/* define AP_EXPR_DEBUG to log the parse tree when parsing an expression */
#ifdef AP_EXPR_DEBUG
static void expr_dump_tree(const ap_expr_t *e, const server_rec *s,
                           int loglevel, int indent);
#endif

/*
 * To reduce counting overhead, we only count calls to
 * ap_expr_eval_word() and ap_expr_eval_cond(). The max number of
 * stack frames is larger by some factor.
 */
#define AP_EXPR_MAX_RECURSION   20
static int inc_rec(ap_expr_eval_ctx_t *ctx)
{
    if (ctx->reclvl < AP_EXPR_MAX_RECURSION) {
        ctx->reclvl++;
        return 0;
    }
    *ctx->err = "Recursion limit reached";
    /* short circuit further evaluation */
    ctx->reclvl = INT_MAX;
    return 1;
}

static const char *ap_expr_list_pstrcat(apr_pool_t *p,
                                        const apr_array_header_t *list,
                                        const char *sep)
{
    if (list->nelts <= 0) {
        return NULL;
    }
    else if (list->nelts == 1) {
        return APR_ARRAY_IDX(list, 0, const char*);
    }
    else {
        struct ap_varbuf vb;
        int n = list->nelts - 1, i;
        apr_size_t slen = strlen(sep), vlen;
        const char *val;

        ap_varbuf_init(p, &vb, 0);
        for (i = 0; i < n; ++i) {
            val = APR_ARRAY_IDX(list, i, const char*);
            vlen = strlen(val);
            ap_varbuf_strmemcat(&vb, val, vlen);
            ap_varbuf_strmemcat(&vb, sep, slen);
        }
        val = APR_ARRAY_IDX(list, n, const char*);
        ap_varbuf_strmemcat(&vb, val, strlen(val));

        return vb.buf;
    }
}

static const char *ap_expr_eval_word(ap_expr_eval_ctx_t *ctx,
                                     const ap_expr_t *node)
{
    const char *result = "";
    if (inc_rec(ctx))
        return result;
    switch (node->node_op) {
    case op_Digit:
    case op_String:
        result = node->node_arg1;
        break;
    case op_Word:
        result = ap_expr_eval_word(ctx, node->node_arg1);
        break;
    case op_Bool:
        result = ap_expr_eval_cond(ctx, node->node_arg1) ? "true" : "false";
        break;
    case op_Var:
        result = ap_expr_eval_var(ctx, (ap_expr_var_func_t *)node->node_arg1,
                                  node->node_arg2);
        break;
    case op_Concat:
        if (((ap_expr_t *)node->node_arg2)->node_op != op_Concat &&
            ((ap_expr_t *)node->node_arg1)->node_op != op_Concat) {
            const char *s1 = ap_expr_eval_word(ctx, node->node_arg1);
            const char *s2 = ap_expr_eval_word(ctx, node->node_arg2);
            if (!*s1)
                result = s2;
            else if (!*s2)
                result = s1;
            else
                result = apr_pstrcat(ctx->p, s1, s2, NULL);
        }
        else if (((ap_expr_t *)node->node_arg1)->node_op == op_Concat) {
            const ap_expr_t *nodep = node;
            int n;
            int i = 1;
            struct iovec *vec;
            do {
                nodep = nodep->node_arg1;
                i++;
            } while (nodep->node_op == op_Concat);
            vec = apr_palloc(ctx->p, i * sizeof(struct iovec));
            n = i;
            nodep = node;
            i--;
            do {
                vec[i].iov_base = (void *)ap_expr_eval_word(ctx,
                                                            nodep->node_arg2);
                vec[i].iov_len = strlen(vec[i].iov_base);
                i--;
                nodep = nodep->node_arg1;
            } while (nodep->node_op == op_Concat);
            vec[i].iov_base = (void *)ap_expr_eval_word(ctx, nodep);
            vec[i].iov_len = strlen(vec[i].iov_base);
            result = apr_pstrcatv(ctx->p, vec, n, NULL);
        }
        else {
            const ap_expr_t *nodep = node;
            int i = 1;
            struct iovec *vec;
            do {
                nodep = nodep->node_arg2;
                i++;
            } while (nodep->node_op == op_Concat);
            vec = apr_palloc(ctx->p, i * sizeof(struct iovec));
            nodep = node;
            i = 0;
            do {
                vec[i].iov_base = (void *)ap_expr_eval_word(ctx,
                                                            nodep->node_arg1);
                vec[i].iov_len = strlen(vec[i].iov_base);
                i++;
                nodep = nodep->node_arg2;
            } while (nodep->node_op == op_Concat);
            vec[i].iov_base = (void *)ap_expr_eval_word(ctx, nodep);
            vec[i].iov_len = strlen(vec[i].iov_base);
            i++;
            result = apr_pstrcatv(ctx->p, vec, i, NULL);
        }
        break;
    case op_StringFuncCall: {
        const ap_expr_t *info = node->node_arg1;
        const ap_expr_t *args = node->node_arg2;
        result = ap_expr_eval_string_func(ctx, info, args);
        break;
    }
    case op_Join: {
        const char *sep;
        apr_array_header_t *list = ap_expr_list_make(ctx, node->node_arg1);
        sep = node->node_arg2 ? ap_expr_eval_word(ctx, node->node_arg2) : "";
        result = ap_expr_list_pstrcat(ctx->p, list, sep);
        break;
    }
    case op_Sub: {
        const ap_expr_t *reg = node->node_arg2;
        const char *subject = ap_expr_eval_word(ctx, node->node_arg1);
        result = ap_expr_regexec(subject, reg, NULL, ctx);
        break;
    }
    case op_Backref: {
        const unsigned int *np = node->node_arg1;
        result = ap_expr_eval_re_backref(ctx, *np);
        break;
    }
    default:
        *ctx->err = "Internal evaluation error: Unknown word expression node";
        break;
    }
    if (!result)
        result = "";
    ctx->reclvl--;
    return result;
}

static const char *ap_expr_eval_var(ap_expr_eval_ctx_t *ctx,
                                    ap_expr_var_func_t *func,
                                    const void *data)
{
    AP_DEBUG_ASSERT(func != NULL);
    AP_DEBUG_ASSERT(data != NULL);
    return (*func)(ctx, data);
}

static const char *ap_expr_eval_re_backref(ap_expr_eval_ctx_t *ctx, unsigned int n)
{
    int len;

    if (!ctx->re_pmatch || !ctx->re_source || !*ctx->re_source
        || **ctx->re_source == '\0' || ctx->re_nmatch < n + 1)
        return "";

    len = ctx->re_pmatch[n].rm_eo - ctx->re_pmatch[n].rm_so;
    if (len == 0)
        return "";

    return apr_pstrndup(ctx->p, *ctx->re_source + ctx->re_pmatch[n].rm_so, len);
}

static const char *ap_expr_eval_string_func(ap_expr_eval_ctx_t *ctx,
                                            const ap_expr_t *info,
                                            const ap_expr_t *arg)
{
    const void *data = info->node_arg2;

    AP_DEBUG_ASSERT(info->node_op == op_StringFuncInfo);
    AP_DEBUG_ASSERT(info->node_arg1 != NULL);
    AP_DEBUG_ASSERT(data != NULL);
    if (arg->node_op == op_ListElement) {
        /* Evaluate the list elements and store them in apr_array_header. */
        ap_expr_string_list_func_t *func = (ap_expr_string_list_func_t *)info->node_arg1;
        apr_array_header_t *args = ap_expr_list_make(ctx, arg);
        return (*func)(ctx, data, args);
    }
    else {
        ap_expr_string_func_t *func = (ap_expr_string_func_t *)info->node_arg1;
        return (*func)(ctx, data, ap_expr_eval_word(ctx, arg));
    }
}

static int intstrcmp(const char *s1, const char *s2)
{
    apr_int64_t i1 = apr_atoi64(s1);
    apr_int64_t i2 = apr_atoi64(s2);

    if (i1 < i2)
        return -1;
    else if (i1 == i2)
        return 0;
    else
        return 1;
}

static const char *ap_expr_regexec(const char *subject,
                                   const ap_expr_t *reg,
                                   apr_array_header_t *list,
                                   ap_expr_eval_ctx_t *ctx)
{
    struct ap_varbuf vb;
    const char *val = subject;
    const ap_regex_t *regex = reg->node_arg1;
    const ap_expr_regctx_t *regctx = reg->node_arg2;
    ap_regmatch_t *pmatch = NULL, match0;
    apr_size_t nmatch = 0;
    const char *str = "";
    apr_size_t len = 0;
    int empty = 0, rv;

    ap_varbuf_init(ctx->p, &vb, 0);
    if (ctx->re_nmatch > 0) {
        nmatch = ctx->re_nmatch;
        pmatch = ctx->re_pmatch;
    }
    else if (regctx->subst) {
        nmatch = 1;
        pmatch = &match0;
    }
    do {
        /* If previous match was empty, we can't issue the exact same one or
         * we'd loop indefinitely.  So let's instead ask for an anchored and
         * non-empty match (i.e. something not empty at the start of the value)
         * and if nothing is found advance by one character below.
         */
        rv = ap_regexec(regex, val, nmatch, pmatch, 
                        empty ? AP_REG_ANCHORED | AP_REG_NOTEMPTY : 0);
        if (rv == 0) {
            int pos = pmatch[0].rm_so,
                end = pmatch[0].rm_eo;
            AP_DEBUG_ASSERT(pos >= 0 && pos <= end);

            if (regctx->subst) {
                *ctx->re_source = val;
                str = ap_expr_eval_word(ctx, regctx->subst);
                len = strlen(str);
            }
            if (list) {
                char *tmp = apr_palloc(ctx->p, pos + len + 1);
                memcpy(tmp, val, pos);
                memcpy(tmp + pos, str, len + 1);
                APR_ARRAY_PUSH(list, const char*) = tmp;
            }
            else {
                ap_varbuf_grow(&vb, pos + len + 1);
                ap_varbuf_strmemcat(&vb, val, pos);
                ap_varbuf_strmemcat(&vb, str, len);
                if (!(regctx->flags & AP_REG_MULTI)) {
                    /* Single substitution, preserve remaining data */
                    ap_varbuf_strmemcat(&vb, val + end, strlen(val) - end);
                    break;
                }
            }
            /* Note an empty match */
            empty = (end == 0);
            val += end;
        }
        else if (empty) {
            /* Skip this non-matching character (or full CRLF) and restart
             * another "normal" match (possibly empty) from there.
             */
            if (val[0] == '\r' && val[1] == '\n') {
                val += 2;
            }
            else {
                val++;
            }
            empty = 0;
        }
        else {
            if (list) {
                APR_ARRAY_PUSH(list, const char*) = val;
            }
            else if (vb.avail) {
                ap_varbuf_strmemcat(&vb, val, strlen(val));
            }
            else {
                return val;
            }
            break;
        }
    } while (*val);

    return vb.buf;
}

static apr_array_header_t *ap_expr_list_make(ap_expr_eval_ctx_t *ctx,
                                             const ap_expr_t *node)
{
    apr_array_header_t *list = NULL;

    if (node->node_op == op_Split) {
        const ap_expr_t *arg = node->node_arg1;
        const ap_expr_t *reg = node->node_arg2;
        const apr_array_header_t *source = ap_expr_list_make(ctx, arg);
        int i;

        list = apr_array_make(ctx->p, source->nelts, sizeof(const char*));
        for (i = 0; i < source->nelts; ++i) {
            const char *val = APR_ARRAY_IDX(source, i, const char*);
            (void)ap_expr_regexec(val, reg, list, ctx);
        }
    }
    else if (node->node_op == op_ListElement) {
        int n = 0;
        const ap_expr_t *elem;
        for (elem = node; elem; elem = elem->node_arg2) {
            AP_DEBUG_ASSERT(elem->node_op == op_ListElement);
            n++;
        }

        list = apr_array_make(ctx->p, n, sizeof(const char*));
        for (elem = node; elem; elem = elem->node_arg2) {
            APR_ARRAY_PUSH(list, const char*) =
                ap_expr_eval_word(ctx, elem->node_arg1);
        }
    }
    else if (node->node_op == op_ListFuncCall) {
        const ap_expr_t *info = node->node_arg1;
        ap_expr_list_func_t *func = info->node_arg1;

        AP_DEBUG_ASSERT(func != NULL);
        AP_DEBUG_ASSERT(info->node_op == op_ListFuncInfo);
        list = (*func)(ctx, info->node_arg2,
                       ap_expr_eval_word(ctx, node->node_arg2));
    }
    else {
        list = apr_array_make(ctx->p, 1, sizeof(const char*));
        APR_ARRAY_PUSH(list, const char*) = ap_expr_eval_word(ctx, node);
    }

    return list;
}

static int ap_expr_eval_comp(ap_expr_eval_ctx_t *ctx, const ap_expr_t *node)
{
    const ap_expr_t *e1 = node->node_arg1;
    const ap_expr_t *e2 = node->node_arg2;
    switch (node->node_op) {
    case op_EQ:
        return (intstrcmp(ap_expr_eval_word(ctx, e1), ap_expr_eval_word(ctx, e2)) == 0);
    case op_NE:
        return (intstrcmp(ap_expr_eval_word(ctx, e1), ap_expr_eval_word(ctx, e2)) != 0);
    case op_LT:
        return (intstrcmp(ap_expr_eval_word(ctx, e1), ap_expr_eval_word(ctx, e2)) <  0);
    case op_LE:
        return (intstrcmp(ap_expr_eval_word(ctx, e1), ap_expr_eval_word(ctx, e2)) <= 0);
    case op_GT:
        return (intstrcmp(ap_expr_eval_word(ctx, e1), ap_expr_eval_word(ctx, e2)) >  0);
    case op_GE:
        return (intstrcmp(ap_expr_eval_word(ctx, e1), ap_expr_eval_word(ctx, e2)) >= 0);
    case op_STR_EQ:
        return (strcmp(ap_expr_eval_word(ctx, e1), ap_expr_eval_word(ctx, e2)) == 0);
    case op_STR_NE:
        return (strcmp(ap_expr_eval_word(ctx, e1), ap_expr_eval_word(ctx, e2)) != 0);
    case op_STR_LT:
        return (strcmp(ap_expr_eval_word(ctx, e1), ap_expr_eval_word(ctx, e2)) <  0);
    case op_STR_LE:
        return (strcmp(ap_expr_eval_word(ctx, e1), ap_expr_eval_word(ctx, e2)) <= 0);
    case op_STR_GT:
        return (strcmp(ap_expr_eval_word(ctx, e1), ap_expr_eval_word(ctx, e2)) >  0);
    case op_STR_GE:
        return (strcmp(ap_expr_eval_word(ctx, e1), ap_expr_eval_word(ctx, e2)) >= 0);
    case op_IN: {
            int n;
            const char *needle, *subject;
            apr_array_header_t *haystack;
            haystack = ap_expr_list_make(ctx, e2);
            if (haystack) {
                needle = ap_expr_eval_word(ctx, e1);
                for (n = 0; n < haystack->nelts; ++n) {
                    subject = APR_ARRAY_IDX(haystack, n, const char*);
                    if (strcmp(needle, subject) == 0) {
                        return 1;
                    }
                }
            }
            return 0;
        }
    case op_REG:
    case op_NRE: {
            const char *word = ap_expr_eval_word(ctx, e1);
            const ap_regex_t *regex = e2->node_arg1;
            int result;

            /*
             * $0 ... $9 may contain stuff the user wants to keep. Therefore
             * we only set them if there are capturing parens in the regex.
             */
            if (regex->re_nsub > 0) {
                result = (0 == ap_regexec(regex, word, ctx->re_nmatch,
                                          ctx->re_pmatch, 0));
                *ctx->re_source = result ? word : NULL;
            }
            else {
                result = (0 == ap_regexec(regex, word, 0, NULL, 0));
            }

            return result ^ (node->node_op == op_NRE);
        }
    default:
        *ctx->err = "Internal evaluation error: Unknown comp expression node";
        return -1;
    }
}

/* combined string/int comparison for compatibility with ssl_expr */
static int strcmplex(const char *str1, const char *str2)
{
    apr_size_t i, n1, n2;

    if (str1 == NULL)
        return -1;
    if (str2 == NULL)
        return +1;
    n1 = strlen(str1);
    n2 = strlen(str2);
    if (n1 > n2)
        return 1;
    if (n1 < n2)
        return -1;
    for (i = 0; i < n1; i++) {
        if (str1[i] > str2[i])
            return 1;
        if (str1[i] < str2[i])
            return -1;
    }
    return 0;
}

static int ssl_expr_eval_comp(ap_expr_eval_ctx_t *ctx, const ap_expr_t *node)
{
    const ap_expr_t *e1 = node->node_arg1;
    const ap_expr_t *e2 = node->node_arg2;
    switch (node->node_op) {
    case op_EQ:
    case op_STR_EQ:
        return (strcmplex(ap_expr_eval_word(ctx, e1), ap_expr_eval_word(ctx, e2)) == 0);
    case op_NE:
    case op_STR_NE:
        return (strcmplex(ap_expr_eval_word(ctx, e1), ap_expr_eval_word(ctx, e2)) != 0);
    case op_LT:
    case op_STR_LT:
        return (strcmplex(ap_expr_eval_word(ctx, e1), ap_expr_eval_word(ctx, e2)) <  0);
    case op_LE:
    case op_STR_LE:
        return (strcmplex(ap_expr_eval_word(ctx, e1), ap_expr_eval_word(ctx, e2)) <= 0);
    case op_GT:
    case op_STR_GT:
        return (strcmplex(ap_expr_eval_word(ctx, e1), ap_expr_eval_word(ctx, e2)) >  0);
    case op_GE:
    case op_STR_GE:
        return (strcmplex(ap_expr_eval_word(ctx, e1), ap_expr_eval_word(ctx, e2)) >= 0);
    default:
        return ap_expr_eval_comp(ctx, node);
    }
}

AP_DECLARE_NONSTD(int) ap_expr_lookup_default(ap_expr_lookup_parms *parms)
{
    return ap_run_expr_lookup(parms);
}

AP_DECLARE(const char *) ap_expr_parse(apr_pool_t *pool, apr_pool_t *ptemp,
                                       ap_expr_info_t *info, const char *expr,
                                       ap_expr_lookup_fn_t *lookup_fn)
{
    ap_expr_parse_ctx_t ctx;
    int rc;

    memset(&ctx, 0, sizeof ctx);
    ctx.pool     = pool;
    ctx.ptemp    = ptemp;
    ctx.inputbuf = expr;
    ctx.inputlen = strlen(expr);
    ctx.inputptr = ctx.inputbuf;
    ctx.flags    = info->flags;
    ctx.lookup_fn   = lookup_fn ? lookup_fn : ap_expr_lookup_default;
    ctx.at_start    = 1;

    rc = ap_expr_yylex_init(&ctx.scanner);
    if (rc)
        return "ap_expr_yylex_init error";

    ap_expr_yyset_extra(&ctx, ctx.scanner);
    rc = ap_expr_yyparse(&ctx);
    ap_expr_yylex_destroy(ctx.scanner);

    /* ctx.error: the generic bison error message
     *            (XXX: usually not very useful, should be axed)
     * ctx.error2: an additional error message
     */
    if (ctx.error) {
        if (ctx.error2)
            return apr_psprintf(pool, "%s: %s", ctx.error, ctx.error2);
        else
            return ctx.error;
    }
    else if (ctx.error2) {
        return ctx.error2;
    }

    if (rc) /* XXX can this happen? */
        return "syntax error";

#ifdef AP_EXPR_DEBUG
    if (ctx.expr)
        expr_dump_tree(ctx.expr, NULL, APLOG_NOTICE, 2);
#endif

    info->root_node = ctx.expr;

    return NULL;
}

AP_DECLARE(ap_expr_info_t*) ap_expr_parse_cmd_mi(const cmd_parms *cmd,
                                                 const char *expr,
                                                 unsigned int flags,
                                                 const char **err,
                                                 ap_expr_lookup_fn_t *lookup_fn,
                                                 int module_index)
{
    ap_expr_info_t *info = apr_pcalloc(cmd->pool, sizeof(ap_expr_info_t));
    info->filename = cmd->directive->filename;
    info->line_number = cmd->directive->line_num;
    info->flags = flags;
    info->module_index = module_index;
    *err = ap_expr_parse(cmd->pool, cmd->temp_pool, info, expr, lookup_fn);

    if (*err)
        return NULL;

    return info;
}

ap_expr_t *ap_expr_make(ap_expr_node_op_e op, const void *a1, const void *a2,
                        ap_expr_parse_ctx_t *ctx)
{
    ap_expr_t *node = apr_palloc(ctx->pool, sizeof(ap_expr_t));
    node->node_op   = op;
    node->node_arg1 = a1;
    node->node_arg2 = a2;
    return node;
}

ap_expr_t *ap_expr_concat_make(const void *a1, const void *a2,
                               ap_expr_parse_ctx_t *ctx)
{
    const ap_expr_t *node;

    /* Optimize out empty string(s) concatenation */
    if ((node = a1)
            && node->node_op == op_String
            && !*(const char *)node->node_arg1) {
        return (ap_expr_t *)a2;
    }
    if ((node = a2)
            && node->node_op == op_String
            && !*(const char *)node->node_arg1) {
        return (ap_expr_t *)a1;
    }

    return ap_expr_make(op_Concat, a1, a2, ctx);
}

ap_expr_t *ap_expr_regex_make(const char *pattern, const ap_expr_t *subst,
                              const char *flags, ap_expr_parse_ctx_t *ctx)
{
    ap_expr_t *node = NULL;
    ap_expr_regctx_t *regctx;
    ap_regex_t *regex;

    regctx = apr_pcalloc(ctx->pool, sizeof *regctx);
    regctx->subst = subst;
    if (flags) {
        for (; *flags; ++flags) {
            switch (*flags) {
            case 'i':
                regctx->flags |= AP_REG_ICASE;
                break;
            case 'm':
                regctx->flags |= AP_REG_NEWLINE;
                break;
            case 's':
                regctx->flags |= AP_REG_DOTALL;
                break;
            case 'g':
                regctx->flags |= AP_REG_MULTI;
                break;
            }
        }
    }
    regex = ap_pregcomp(ctx->pool, pattern, regctx->flags);
    if (!regex) {
        return NULL;
    }

    node = apr_palloc(ctx->pool, sizeof(ap_expr_t));
    node->node_op   = op_Regex;
    node->node_arg1 = regex;
    node->node_arg2 = regctx;
    return node;
}

static ap_expr_t *ap_expr_info_make(int type, const char *name,
                                  ap_expr_parse_ctx_t *ctx,
                                  const ap_expr_t *arg)
{
    ap_expr_t *info = apr_palloc(ctx->pool, sizeof(ap_expr_t));
    ap_expr_lookup_parms parms;
    parms.type  = type;
    parms.flags = ctx->flags;
    parms.pool  = ctx->pool;
    parms.ptemp = ctx->ptemp;
    parms.name  = name;
    parms.func  = &info->node_arg1;
    parms.data  = &info->node_arg2;
    parms.err   = &ctx->error2;
    parms.arg   = NULL;
    if (arg) {
        switch(arg->node_op) {
            case op_String:
                parms.arg = arg->node_arg1;
                break;
            case op_ListElement:
                /* save the first literal/simple string argument */
                do {
                    const ap_expr_t *val = arg->node_arg1;
                    if (val && val->node_op == op_String) {
                        parms.arg = val->node_arg1;
                        break;
                    }
                    arg = arg->node_arg2;
                } while (arg != NULL);
                break;
            default:
                break;
        }
    }
    if (ctx->lookup_fn(&parms) != OK)
        return NULL;
    return info;
}

ap_expr_t *ap_expr_str_func_make(const char *name, const ap_expr_t *arg,
                               ap_expr_parse_ctx_t *ctx)
{
    ap_expr_t *info = ap_expr_info_make(AP_EXPR_FUNC_STRING, name, ctx, arg);
    if (!info)
        return NULL;

    info->node_op = op_StringFuncInfo;
    return ap_expr_make(op_StringFuncCall, info, arg, ctx);
}

ap_expr_t *ap_expr_list_func_make(const char *name, const ap_expr_t *arg,
                                ap_expr_parse_ctx_t *ctx)
{
    ap_expr_t *info = ap_expr_info_make(AP_EXPR_FUNC_LIST, name, ctx, arg);
    if (!info)
        return NULL;

    info->node_op = op_ListFuncInfo;
    return ap_expr_make(op_ListFuncCall, info, arg, ctx);
}

ap_expr_t *ap_expr_unary_op_make(const char *name, const ap_expr_t *arg,
                               ap_expr_parse_ctx_t *ctx)
{
    ap_expr_t *info = ap_expr_info_make(AP_EXPR_FUNC_OP_UNARY, name, ctx, arg);
    if (!info)
        return NULL;

    info->node_op = op_UnaryOpInfo;
    return ap_expr_make(op_UnaryOpCall, info, arg, ctx);
}

ap_expr_t *ap_expr_binary_op_make(const char *name, const ap_expr_t *arg1,
                                const ap_expr_t *arg2, ap_expr_parse_ctx_t *ctx)
{
    ap_expr_t *args;
    ap_expr_t *info = ap_expr_info_make(AP_EXPR_FUNC_OP_BINARY, name, ctx,
                                        arg2);
    if (!info)
        return NULL;

    info->node_op = op_BinaryOpInfo;
    args = ap_expr_make(op_BinaryOpArgs, arg1, arg2, ctx);
    return ap_expr_make(op_BinaryOpCall, info, args, ctx);
}


ap_expr_t *ap_expr_var_make(const char *name, ap_expr_parse_ctx_t *ctx)
{
    ap_expr_t *node = ap_expr_info_make(AP_EXPR_FUNC_VAR, name, ctx, NULL);
    if (!node)
        return NULL;

    node->node_op = op_Var;
    return node;
}

ap_expr_t *ap_expr_backref_make(int num, ap_expr_parse_ctx_t *ctx)
{
    int *n = apr_pmemdup(ctx->pool, &num, sizeof(num));
    return ap_expr_make(op_Backref, n, NULL, ctx);
}

#ifdef AP_EXPR_DEBUG

#define MARK                        APLOG_MARK,loglevel,0,s
#define DUMP_E_E(op, e1, e2)                                                \
    do { ap_log_error(MARK,"%*s%s: %pp %pp", indent, " ", op, e1, e2);      \
         if (e1) expr_dump_tree(e1, s, loglevel, indent + 2);               \
         if (e2) expr_dump_tree(e2, s, loglevel, indent + 2);               \
    } while (0)
#define DUMP_S_E(op, s1, e1)                                                    \
    do { ap_log_error(MARK,"%*s%s: '%s' %pp", indent, " ", op, (char *)s1, e1); \
         if (e1) expr_dump_tree(e1, s, loglevel, indent + 2);                   \
    } while (0)
#define DUMP_S_P(op, s1, p1)                                                \
    ap_log_error(MARK,"%*s%s: '%s' %pp", indent, " ", op, (char *)s1, p1);
#define DUMP_P_P(op, p1, p2)                                                \
    ap_log_error(MARK,"%*s%s: %pp %pp", indent, " ", op, p1, p2);
#define DUMP_S_S(op, s1, s2)                                                       \
    ap_log_error(MARK,"%*s%s: '%s' '%s'", indent, " ", op, (char *)s1, (char *)s2)
#define DUMP_P(op, p1)                                                      \
    ap_log_error(MARK,"%*s%s: %pp", indent, " ", op, p1);
#define DUMP_IP(op, p1)                                                     \
    ap_log_error(MARK,"%*s%s: %d", indent, " ", op, *(int *)p1);
#define DUMP_S(op, s1)                                                      \
    ap_log_error(MARK,"%*s%s: '%s'", indent, " ", op, (char *)s1)

#define CASE_OP(op)                  case op: name = #op ; break;

static void expr_dump_tree(const ap_expr_t *e, const server_rec *s,
                           int loglevel, int indent)
{
    switch (e->node_op) {
    /* no arg */
    case op_NOP:
    case op_True:
    case op_False:
        {
            char *name;
            switch (e->node_op) {
            CASE_OP(op_NOP);
            CASE_OP(op_True);
            CASE_OP(op_False);
            default:
                ap_assert(0);
            }
            ap_log_error(MARK, "%*s%s", indent, " ", name);
        }
        break;

    /* arg1: string, arg2: expr */
    case op_UnaryOpCall:
    case op_BinaryOpCall:
    case op_BinaryOpArgs:
        {
            char *name;
            switch (e->node_op) {
            CASE_OP(op_BinaryOpCall);
            CASE_OP(op_UnaryOpCall);
            CASE_OP(op_BinaryOpArgs);
            default:
                ap_assert(0);
            }
            DUMP_S_E(name, e->node_arg1, e->node_arg2);
        }
        break;

    /* arg1: expr, arg2: expr */
    case op_Comp:
    case op_Not:
    case op_Or:
    case op_And:
    case op_EQ:
    case op_NE:
    case op_LT:
    case op_LE:
    case op_GT:
    case op_GE:
    case op_STR_EQ:
    case op_STR_NE:
    case op_STR_LT:
    case op_STR_LE:
    case op_STR_GT:
    case op_STR_GE:
    case op_IN:
    case op_REG:
    case op_NRE:
    case op_Word:
    case op_Bool:
    case op_Sub:
    case op_Join:
    case op_Split:
    case op_Concat:
    case op_StringFuncCall:
    case op_ListFuncCall:
    case op_ListElement:
        {
            char *name;
            switch (e->node_op) {
            CASE_OP(op_Comp);
            CASE_OP(op_Not);
            CASE_OP(op_Or);
            CASE_OP(op_And);
            CASE_OP(op_EQ);
            CASE_OP(op_NE);
            CASE_OP(op_LT);
            CASE_OP(op_LE);
            CASE_OP(op_GT);
            CASE_OP(op_GE);
            CASE_OP(op_STR_EQ);
            CASE_OP(op_STR_NE);
            CASE_OP(op_STR_LT);
            CASE_OP(op_STR_LE);
            CASE_OP(op_STR_GT);
            CASE_OP(op_STR_GE);
            CASE_OP(op_IN);
            CASE_OP(op_REG);
            CASE_OP(op_NRE);
            CASE_OP(op_Word);
            CASE_OP(op_Bool);
            CASE_OP(op_Sub);
            CASE_OP(op_Join);
            CASE_OP(op_Split);
            CASE_OP(op_Concat);
            CASE_OP(op_StringFuncCall);
            CASE_OP(op_ListFuncCall);
            CASE_OP(op_ListElement);
            default:
                ap_assert(0);
            }
            DUMP_E_E(name, e->node_arg1, e->node_arg2);
        }
        break;
    /* arg1: string */
    case op_Digit:
    case op_String:
        {
            char *name;
            switch (e->node_op) {
            CASE_OP(op_Digit);
            CASE_OP(op_String);
            default:
                ap_assert(0);
            }
            DUMP_S(name, e->node_arg1);
        }
        break;
    /* arg1: pointer, arg2: pointer */
    case op_Var:
    case op_StringFuncInfo:
    case op_UnaryOpInfo:
    case op_BinaryOpInfo:
    case op_ListFuncInfo:
        {
            char *name;
            switch (e->node_op) {
            CASE_OP(op_Var);
            CASE_OP(op_StringFuncInfo);
            CASE_OP(op_UnaryOpInfo);
            CASE_OP(op_BinaryOpInfo);
            CASE_OP(op_ListFuncInfo);
            default:
                ap_assert(0);
            }
            DUMP_P_P(name, e->node_arg1, e->node_arg2);
        }
        break;
    /* arg1: pointer */
    case op_Regex:
        DUMP_P("op_Regex", e->node_arg1);
        break;
    /* arg1: pointer to int */
    case op_Backref:
        DUMP_IP("op_Backref", e->node_arg1);
        break;
    default:
        ap_log_error(MARK, "%*sERROR: INVALID OP %d", indent, " ", e->node_op);
        break;
    }
}
#endif /* AP_EXPR_DEBUG */

#define expr_eval_log(ctx, level, ...) do { \
    ap_expr_eval_ctx_t *x = (ctx); \
    if (x->r) { \
        ap_log_rerror(LOG_MARK(x->info), (level), 0, x->r, __VA_ARGS__); \
    } \
    else if (x->c) { \
        ap_log_cerror(LOG_MARK(x->info), (level), 0, x->c, __VA_ARGS__); \
    } \
    else { \
        ap_log_error(LOG_MARK(x->info), (level), 0, x->s, __VA_ARGS__); \
    } \
} while (0)

static int ap_expr_eval_unary_op(ap_expr_eval_ctx_t *ctx, const ap_expr_t *info,
                                 const ap_expr_t *arg)
{
    ap_expr_op_unary_t *op_func = (ap_expr_op_unary_t *)info->node_arg1;
    const void *data = info->node_arg2;

    AP_DEBUG_ASSERT(info->node_op == op_UnaryOpInfo);
    AP_DEBUG_ASSERT(op_func != NULL);
    AP_DEBUG_ASSERT(data != NULL);
    return (*op_func)(ctx, data, ap_expr_eval_word(ctx, arg));
}

static int ap_expr_eval_binary_op(ap_expr_eval_ctx_t *ctx,
                                  const ap_expr_t *info,
                                  const ap_expr_t *args)
{
    ap_expr_op_binary_t *op_func = (ap_expr_op_binary_t *)info->node_arg1;
    const void *data = info->node_arg2;
    const ap_expr_t *a1 = args->node_arg1;
    const ap_expr_t *a2 = args->node_arg2;

    AP_DEBUG_ASSERT(info->node_op == op_BinaryOpInfo);
    AP_DEBUG_ASSERT(args->node_op == op_BinaryOpArgs);
    AP_DEBUG_ASSERT(op_func != NULL);
    AP_DEBUG_ASSERT(data != NULL);
    return (*op_func)(ctx, data, ap_expr_eval_word(ctx, a1),
                      ap_expr_eval_word(ctx, a2));
}


static int ap_expr_eval_cond(ap_expr_eval_ctx_t *ctx, const ap_expr_t *node)
{
    const ap_expr_t *e1 = node->node_arg1;
    const ap_expr_t *e2 = node->node_arg2;
    int result = FALSE;
    if (inc_rec(ctx))
        return result;
    while (1) {
        switch (node->node_op) {
        case op_True:
            result ^= TRUE;
            goto out;
        case op_False:
            result ^= FALSE;
            goto out;
        case op_Not:
            result = !result;
            node = e1;
            break;
        case op_Or:
            do {
                if (e1->node_op == op_Not) {
                    if (!ap_expr_eval_cond(ctx, e1->node_arg1)) {
                        result ^= TRUE;
                        goto out;
                    }
                }
                else {
                    if (ap_expr_eval_cond(ctx, e1)) {
                        result ^= TRUE;
                        goto out;
                    }
                }
                node = node->node_arg2;
                e1 = node->node_arg1;
            } while (node->node_op == op_Or);
            break;
        case op_And:
            do {
                if (e1->node_op == op_Not) {
                    if (ap_expr_eval_cond(ctx, e1->node_arg1)) {
                        result ^= FALSE;
                        goto out;
                    }
                }
                else {
                    if (!ap_expr_eval_cond(ctx, e1)) {
                        result ^= FALSE;
                        goto out;
                    }
                }
                node = node->node_arg2;
                e1 = node->node_arg1;
            } while (node->node_op == op_And);
            break;
        case op_UnaryOpCall:
            result ^= ap_expr_eval_unary_op(ctx, e1, e2);
            goto out;
        case op_BinaryOpCall:
            result ^= ap_expr_eval_binary_op(ctx, e1, e2);
            goto out;
        case op_Comp:
            if (ctx->info->flags & AP_EXPR_FLAG_SSL_EXPR_COMPAT)
                result ^= ssl_expr_eval_comp(ctx, e1);
            else
                result ^= ap_expr_eval_comp(ctx, e1);
            goto out;
        default:
            *ctx->err = "Internal evaluation error: Unknown expression node";
            goto out;
        }
        e1 = node->node_arg1;
        e2 = node->node_arg2;
    }
out:
    ctx->reclvl--;
    return result;
}

AP_DECLARE(int) ap_expr_exec(request_rec *r, const ap_expr_info_t *info,
                             const char **err)
{
    return ap_expr_exec_re(r, info, 0, NULL, NULL, err);
}

AP_DECLARE(int) ap_expr_exec_ctx(ap_expr_eval_ctx_t *ctx)
{
    int rc;

    AP_DEBUG_ASSERT(ctx->p != NULL);
    AP_DEBUG_ASSERT(ctx->err != NULL);
    AP_DEBUG_ASSERT(ctx->info != NULL);
    if (ctx->re_pmatch) {
        AP_DEBUG_ASSERT(ctx->re_source != NULL);
        AP_DEBUG_ASSERT(ctx->re_nmatch > 0);
    }
    if (!ctx->s) {
        if (ctx->r) {
            ctx->s = ctx->r->server;
        }
        else if (ctx->c) {
            ctx->s = ctx->c->base_server;
        }
    }
    if (!ctx->c) {
        if (ctx->r) {
            ctx->c = ctx->r->connection;
        }
    }
    AP_DEBUG_ASSERT(ctx->s != NULL);

    ctx->reclvl = 0;
    *ctx->err = NULL;
    if (ctx->info->flags & AP_EXPR_FLAG_STRING_RESULT) {
        *ctx->result_string = ap_expr_eval_word(ctx, ctx->info->root_node);
        if (*ctx->err != NULL) {
            expr_eval_log(ctx, APLOG_ERR, APLOGNO(03298)
                          "Evaluation of string expression from %s:%d failed: %s",
                          ctx->info->filename, ctx->info->line_number, *ctx->err);
            return -1;
        } else {
            expr_eval_log(ctx, APLOG_TRACE4,
                          "Evaluation of string expression from %s:%d gave: %s",
                          ctx->info->filename, ctx->info->line_number,
                          *ctx->result_string);
            return 1;
        }
    }
    else {
        rc = ap_expr_eval_cond(ctx, ctx->info->root_node);
        if (*ctx->err != NULL) {
            expr_eval_log(ctx, APLOG_ERR, APLOGNO(03299)
                          "Evaluation of expression from %s:%d failed: %s",
                          ctx->info->filename, ctx->info->line_number, *ctx->err);
            return -1;
        } else {
            rc = rc ? 1 : 0;
            expr_eval_log(ctx, APLOG_TRACE4,
                          "Evaluation of expression from %s:%d gave: %d",
                          ctx->info->filename, ctx->info->line_number, rc);

            if (ctx->r && ctx->vary_this && *ctx->vary_this)
                apr_table_merge(ctx->r->headers_out, "Vary", *ctx->vary_this);

            return rc;
        }
    }
}

AP_DECLARE(int) ap_expr_exec_re(request_rec *r, const ap_expr_info_t *info,
                                apr_size_t nmatch, ap_regmatch_t *pmatch,
                                const char **source, const char **err)
{
    ap_expr_eval_ctx_t ctx;
    int dont_vary = (info->flags & AP_EXPR_FLAG_DONT_VARY);
    const char *tmp_source = NULL, *vary_this = NULL;
    ap_regmatch_t tmp_pmatch[AP_MAX_REG_MATCH];

    AP_DEBUG_ASSERT((info->flags & AP_EXPR_FLAG_STRING_RESULT) == 0);

    ctx.r = r;
    ctx.c = r->connection;
    ctx.s = r->server;
    ctx.p = r->pool;
    ctx.err  = err;
    ctx.info = info;
    ctx.re_nmatch = nmatch;
    ctx.re_pmatch = pmatch;
    ctx.re_source = source;
    ctx.vary_this = dont_vary ? NULL : &vary_this;
    ctx.data = NULL;

    if (!pmatch) {
        ctx.re_nmatch = AP_MAX_REG_MATCH;
        ctx.re_pmatch = tmp_pmatch;
        ctx.re_source = &tmp_source;
    }

    return ap_expr_exec_ctx(&ctx);
}

AP_DECLARE(const char *) ap_expr_str_exec_re(request_rec *r,
                                             const ap_expr_info_t *info,
                                             apr_size_t nmatch,
                                             ap_regmatch_t *pmatch,
                                             const char **source,
                                             const char **err)
{
    ap_expr_eval_ctx_t ctx;
    int dont_vary, rc;
    const char *tmp_source, *vary_this;
    ap_regmatch_t tmp_pmatch[AP_MAX_REG_MATCH];
    const char *result;

    AP_DEBUG_ASSERT(info->flags & AP_EXPR_FLAG_STRING_RESULT);

    if (info->root_node->node_op == op_String) {
        /* short-cut for constant strings */
        *err = NULL;
        return (const char *)info->root_node->node_arg1;
    }

    tmp_source = NULL;
    vary_this = NULL;

    dont_vary = (info->flags & AP_EXPR_FLAG_DONT_VARY);

    ctx.r = r;
    ctx.c = r->connection;
    ctx.s = r->server;
    ctx.p = r->pool;
    ctx.err  = err;
    ctx.info = info;
    ctx.re_nmatch = nmatch;
    ctx.re_pmatch = pmatch;
    ctx.re_source = source;
    ctx.vary_this = dont_vary ? NULL : &vary_this;
    ctx.data = NULL;
    ctx.result_string = &result;

    if (!pmatch) {
        ctx.re_nmatch = AP_MAX_REG_MATCH;
        ctx.re_pmatch = tmp_pmatch;
        ctx.re_source = &tmp_source;
    }

    rc = ap_expr_exec_ctx(&ctx);
    if (rc > 0)
        return result;
    else if (rc < 0)
        return NULL;
    else
        ap_assert(0);
    /* Not reached */
    return NULL;
}

AP_DECLARE(const char *) ap_expr_str_exec(request_rec *r,
                                          const ap_expr_info_t *info,
                                          const char **err)
{
    return ap_expr_str_exec_re(r, info, 0, NULL, NULL, err);
}


static void add_vary(ap_expr_eval_ctx_t *ctx, const char *name)
{
    if (!ctx->vary_this)
        return;

    if (*ctx->vary_this) {
        *ctx->vary_this = apr_pstrcat(ctx->p, *ctx->vary_this, ", ", name,
                                      NULL);
    }
    else {
        *ctx->vary_this = name;
    }
}

static const char *req_table_func(ap_expr_eval_ctx_t *ctx, const void *data,
                                  const char *arg)
{
    const char *name = (const char *)data;
    apr_table_t *t;
    if (!ctx->r)
        return "";

    if (name[2] == 's') {           /* resp */
        /* Try r->headers_out first, fall back on err_headers_out. */
        const char *v = apr_table_get(ctx->r->headers_out, arg);
        if (v) {
            return v;
        }
        t = ctx->r->err_headers_out;
    }
    else if (name[0] == 'n')        /* notes */
        t = ctx->r->notes;
    else if (name[3] == 'e')        /* reqenv */
        t = ctx->r->subprocess_env;
    else if (name[3] == '_')        /* req_novary */
        t = ctx->r->headers_in;
    else {                          /* req, http */
        t = ctx->r->headers_in;
        /* Skip the 'Vary: Host' header combination
         * as indicated in rfc7231 section-7.1.4
         */
        if (strcasecmp(arg, "Host")){
            add_vary(ctx, arg);
        }
    }
    return apr_table_get(t, arg);
}

static const char *env_func(ap_expr_eval_ctx_t *ctx, const void *data,
                            const char *arg)
{
    const char *res;
    /* this order is for ssl_expr compatibility */
    if (ctx->r) {
        if ((res = apr_table_get(ctx->r->notes, arg)) != NULL)
            return res;
        else if ((res = apr_table_get(ctx->r->subprocess_env, arg)) != NULL)
            return res;
    }
    return getenv(arg);
}

static const char *osenv_func(ap_expr_eval_ctx_t *ctx, const void *data,
                              const char *arg)
{
    return getenv(arg);
}

static const char *tolower_func(ap_expr_eval_ctx_t *ctx, const void *data,
                                const char *arg)
{
    char *result = apr_pstrdup(ctx->p, arg);
    ap_str_tolower(result);
    return result;
}

static const char *toupper_func(ap_expr_eval_ctx_t *ctx, const void *data,
                                const char *arg)
{
    char *result = apr_pstrdup(ctx->p, arg);
    ap_str_toupper(result);
    return result;
}

static const char *escape_func(ap_expr_eval_ctx_t *ctx, const void *data,
                               const char *arg)
{
    return ap_escape_uri(ctx->p, arg);
}

static const char *base64_func(ap_expr_eval_ctx_t *ctx, const void *data,
                               const char *arg)
{
    return ap_pbase64encode(ctx->p, (char *)arg);
}

static const char *unbase64_func(ap_expr_eval_ctx_t *ctx, const void *data,
                               const char *arg)
{
    return ap_pbase64decode(ctx->p, arg);
}

static const char *sha1_func(ap_expr_eval_ctx_t *ctx, const void *data,
                               const char *arg)
{
    apr_sha1_ctx_t context;
    apr_byte_t sha1[APR_SHA1_DIGESTSIZE];
    char *out;

    out = apr_palloc(ctx->p, APR_SHA1_DIGESTSIZE*2+1);

    apr_sha1_init(&context);
    apr_sha1_update(&context, arg, (unsigned int)strlen(arg));
    apr_sha1_final(sha1, &context);

    ap_bin2hex(sha1, APR_SHA1_DIGESTSIZE, out);

    return out;
}

static const char *md5_func(ap_expr_eval_ctx_t *ctx, const void *data,
                               const char *arg)
{
    return ap_md5(ctx->p, (const unsigned char *)arg);
}

#if APR_VERSION_AT_LEAST(1,6,0)
static const char *ldap_func(ap_expr_eval_ctx_t *ctx, const void *data,
                               const char *arg)
{
    return apr_pescape_ldap(ctx->p, arg, APR_ESCAPE_STRING, APR_ESCAPE_LDAP_ALL);
}
#endif

static const char *escapehtml_func(ap_expr_eval_ctx_t *ctx, const void *data,
                                   const char *arg)
{
    return ap_escape_html(ctx->p, arg);
}

static int replace_func_parse_arg(ap_expr_lookup_parms *parms)
{
    const char *original = parms->arg;
    const apr_strmatch_pattern *pattern;

    if (!parms->arg) {
        *parms->err = apr_psprintf(parms->ptemp, "replace() function needs an argument");
        return !OK;
    }

    pattern = apr_strmatch_precompile(parms->pool, original, 0);
    *parms->data = pattern;
    return OK;
}

static const char *replace_func(ap_expr_eval_ctx_t *ctx, const void *data,
                               const apr_array_header_t *args)
{
    char *buff, *original, *replacement;
    struct ap_varbuf vb;
    apr_size_t repl_len, orig_len;
    const char *repl;
    apr_size_t bytes;
    apr_size_t len;
    const apr_strmatch_pattern *pattern = data;
    if (args->nelts != 3) {
        *ctx->err = apr_psprintf(ctx->p, "replace() function needs "
                                 "exactly 3 arguments, got %d", args->nelts);
        return "";
    }

    buff = APR_ARRAY_IDX(args, 0, char *);
    original = APR_ARRAY_IDX(args, 1, char *);
    replacement = APR_ARRAY_IDX(args, 2, char *);
    repl_len = strlen(replacement);
    orig_len = strlen(original);
    bytes = strlen(buff);

    ap_varbuf_init(ctx->p, &vb, 0);
    vb.strlen = 0;
    
    while ((repl = apr_strmatch(pattern, buff, bytes))) {
        len = (apr_size_t) (repl - buff);
        ap_varbuf_strmemcat(&vb, buff, len);
        ap_varbuf_strmemcat(&vb, replacement, repl_len);

        len += orig_len;
        bytes -= len;
        buff += len;
    }

    return ap_varbuf_pdup(ctx->p, &vb, NULL, 0, buff, bytes, &len);
}

#define MAX_FILE_SIZE 10*1024*1024
static const char *file_func(ap_expr_eval_ctx_t *ctx, const void *data,
                             char *arg)
{
    apr_file_t *fp;
    char *buf;
    apr_off_t offset;
    apr_size_t len;
    apr_finfo_t finfo;

    if (apr_file_open(&fp, arg, APR_READ|APR_BUFFERED,
                      APR_OS_DEFAULT, ctx->p) != APR_SUCCESS) {
        *ctx->err = apr_psprintf(ctx->p, "Cannot open file %s", arg);
        return "";
    }
    apr_file_info_get(&finfo, APR_FINFO_SIZE, fp);
    if (finfo.size > MAX_FILE_SIZE) {
        *ctx->err = apr_psprintf(ctx->p, "File %s too large", arg);
        apr_file_close(fp);
        return "";
    }
    len = (apr_size_t)finfo.size;
    if (len == 0) {
        apr_file_close(fp);
        return "";
    }
    else {
        if ((buf = (char *)apr_palloc(ctx->p, sizeof(char)*(len+1))) == NULL) {
            *ctx->err = "Cannot allocate memory";
            apr_file_close(fp);
            return "";
        }
        offset = 0;
        apr_file_seek(fp, APR_SET, &offset);
        if (apr_file_read(fp, buf, &len) != APR_SUCCESS) {
            *ctx->err = apr_psprintf(ctx->p, "Cannot read from file %s", arg);
            apr_file_close(fp);
            return "";
        }
        buf[len] = '\0';
    }
    apr_file_close(fp);
    return buf;
}

static apr_status_t stat_check(ap_expr_eval_ctx_t *ctx, const void *data, const char *arg)
{
    apr_status_t rv = APR_SUCCESS;
    if (APR_SUCCESS != (rv = ap_stat_check(arg, ctx->p))) {
        *ctx->err = apr_psprintf(ctx->p, "stat of %s not allowed", arg);
    }
    return rv;
}
static const char *filesize_func(ap_expr_eval_ctx_t *ctx, const void *data,
                                  char *arg)
{
    apr_finfo_t sb;
    if (APR_SUCCESS != stat_check(ctx, data, arg)) {
        return "";
    }
    if (apr_stat(&sb, arg, APR_FINFO_MIN, ctx->p) == APR_SUCCESS
        && sb.filetype == APR_REG && sb.size > 0)
        return apr_psprintf(ctx->p, "%" APR_OFF_T_FMT, sb.size);
    else
        return "0";
}

static const char *filemod_func(ap_expr_eval_ctx_t *ctx, const void *data,
                                  char *arg)
{
    apr_finfo_t sb;
    if (APR_SUCCESS != stat_check(ctx, data, arg)) {
        return "";
    }
    if (apr_stat(&sb, arg, APR_FINFO_MIN, ctx->p) == APR_SUCCESS
        && sb.filetype == APR_REG && sb.mtime > 0)
        return apr_psprintf(ctx->p, "%" APR_OFF_T_FMT, (apr_off_t)sb.mtime);
    else
        return "0";
}


static const char *unescape_func(ap_expr_eval_ctx_t *ctx, const void *data,
                                 const char *arg)
{
    char *result = apr_pstrdup(ctx->p, arg);
    int ret = ap_unescape_url_keep2f(result, 0);
    if (ret == OK)
        return result;
    expr_eval_log(ctx, APLOG_DEBUG, APLOGNO(00538)
                  "%s %% escape in unescape('%s') at %s:%d",
                  ret == HTTP_BAD_REQUEST ? "Bad" : "Forbidden", arg,
                  ctx->info->filename, ctx->info->line_number);
    return "";
}

static int op_nz(ap_expr_eval_ctx_t *ctx, const void *data, const char *arg)
{
    const char *name = (const char *)data;
    if (name[0] == 'z')
        return (arg[0] == '\0');
    else
        return (arg[0] != '\0');
}

static int op_file_min(ap_expr_eval_ctx_t *ctx, const void *data, const char *arg)
{
    apr_finfo_t sb;
    const char *name = (const char *)data;
    if (APR_SUCCESS != stat_check(ctx, data, arg)) {
        return FALSE;
    }
    if (apr_stat(&sb, arg, APR_FINFO_MIN, ctx->p) != APR_SUCCESS)
        return FALSE;
    switch (name[0]) {
    case 'd':
        return (sb.filetype == APR_DIR);
    case 'e':
        return TRUE;
    case 'f':
        return (sb.filetype == APR_REG);
    case 's':
        return (sb.filetype == APR_REG && sb.size > 0);
    default:
        ap_assert(0);
    }
    return FALSE;
}

static int op_file_link(ap_expr_eval_ctx_t *ctx, const void *data, const char *arg)
{
#if !defined(OS2)
    apr_finfo_t sb;
    if (APR_SUCCESS != stat_check(ctx, data, arg)) {
        return FALSE;
    }
    if (apr_stat(&sb, arg, APR_FINFO_MIN | APR_FINFO_LINK, ctx->p) == APR_SUCCESS
        && sb.filetype == APR_LNK) {
        return TRUE;
    }
#endif
    return FALSE;
}

static int op_file_xbit(ap_expr_eval_ctx_t *ctx, const void *data, const char *arg)
{
    apr_finfo_t sb;
    if (APR_SUCCESS != stat_check(ctx, data, arg)) {
        return FALSE;
    }
    if (apr_stat(&sb, arg, APR_FINFO_PROT| APR_FINFO_LINK, ctx->p) == APR_SUCCESS
        && (sb.protection & (APR_UEXECUTE | APR_GEXECUTE | APR_WEXECUTE))) {
        return TRUE;
    }
    return FALSE;
}

static int op_url_subr(ap_expr_eval_ctx_t *ctx, const void *data, const char *arg)
{
    int rc = FALSE;
    request_rec  *rsub, *r = ctx->r;
    if (!r)
        return FALSE;
    /* avoid some infinite recursions */
    if (r->main && r->main->uri && r->uri && strcmp(r->main->uri, r->uri) == 0)
        return FALSE;

    rsub = ap_sub_req_lookup_uri(arg, r, NULL);
    if (rsub->status < 400) {
            rc = TRUE;
    }
    expr_eval_log(ctx, APLOG_TRACE5,
                  "Subrequest for -U %s at %s:%d gave status: %d",
                  arg, ctx->info->filename, ctx->info->line_number,
                  rsub->status);
    ap_destroy_sub_req(rsub);
    return rc;
}

static int op_file_subr(ap_expr_eval_ctx_t *ctx, const void *data, const char *arg)
{
    int rc = FALSE;
    apr_finfo_t sb;
    request_rec *rsub, *r = ctx->r;
    if (!r)
        return FALSE;
    if (APR_SUCCESS != stat_check(ctx, data, arg)) {
        return FALSE;
    }
    rsub = ap_sub_req_lookup_file(arg, r, NULL);
    if (rsub->status < 300 &&
        /* double-check that file exists since default result is 200 */
        apr_stat(&sb, rsub->filename, APR_FINFO_MIN, ctx->p) == APR_SUCCESS) {
        rc = TRUE;
    }
    expr_eval_log(ctx, APLOG_TRACE5,
                  "Subrequest for -F %s at %s:%d gave status: %d",
                  arg, ctx->info->filename, ctx->info->line_number,
                  rsub->status);
    ap_destroy_sub_req(rsub);
    return rc;
}


APR_DECLARE_OPTIONAL_FN(int, http2_is_h2, (conn_rec *));
static APR_OPTIONAL_FN_TYPE(http2_is_h2) *is_http2 = NULL;

static const char *const conn_var_names[] = {
    "HTTPS",                    /*  0 */
    "IPV6",                     /*  1 */
    "CONN_LOG_ID",              /*  2 */
    "CONN_REMOTE_ADDR",         /*  3 */
    "HTTP2",                    /*  4 */
    NULL
};

static const char *conn_var_fn(ap_expr_eval_ctx_t *ctx, const void *data)
{
    int index = ((const char **)data - conn_var_names);
    conn_rec *c = ctx->c;
    if (!c)
        return "";

    switch (index) {
    case 0:
        if (ap_ssl_conn_is_ssl(c))
            return "on";
        else
            return "off";
    case 1:
#if APR_HAVE_IPV6
        {
            apr_sockaddr_t *addr = c->client_addr;
            if (addr->family == AF_INET6
                && !IN6_IS_ADDR_V4MAPPED((struct in6_addr *)addr->ipaddr_ptr))
                return "on";
            else
                return "off";
        }
#else
        return "off";
#endif
    case 2:
        return c->log_id;
    case 3:
        return c->client_ip;
    case 4:
        if (is_http2 && is_http2(c))
            return "on";
        else
            return "off";
    default:
        ap_assert(0);
        return NULL;
    }
}

static const char *const request_var_names[] = {
    "REQUEST_METHOD",           /*  0 */
    "REQUEST_SCHEME",           /*  1 */
    "REQUEST_URI",              /*  2 */
    "REQUEST_FILENAME",         /*  3 */
    "REMOTE_HOST",              /*  4 */
    "REMOTE_IDENT",             /*  5 */
    "REMOTE_USER",              /*  6 */
    "SERVER_ADMIN",             /*  7 */
    "SERVER_NAME",              /*  8 */
    "SERVER_PORT",              /*  9 */
    "SERVER_PROTOCOL",          /* 10 */
    "SCRIPT_FILENAME",          /* 11 */
    "PATH_INFO",                /* 12 */
    "QUERY_STRING",             /* 13 */
    "IS_SUBREQ",                /* 14 */
    "DOCUMENT_ROOT",            /* 15 */
    "AUTH_TYPE",                /* 16 */
    "THE_REQUEST",              /* 17 */
    "CONTENT_TYPE",             /* 18 */
    "HANDLER",                  /* 19 */
    "REQUEST_LOG_ID",           /* 20 */
    "SCRIPT_USER",              /* 21 */
    "SCRIPT_GROUP",             /* 22 */
    "DOCUMENT_URI",             /* 23 */
    "LAST_MODIFIED",            /* 24 */
    "CONTEXT_PREFIX",           /* 25 */
    "CONTEXT_DOCUMENT_ROOT",    /* 26 */
    "REQUEST_STATUS",           /* 27 */
    "REMOTE_ADDR",              /* 28 */
    "SERVER_PROTOCOL_VERSION",  /* 29 */
    "SERVER_PROTOCOL_VERSION_MAJOR",  /* 30 */
    "SERVER_PROTOCOL_VERSION_MINOR",  /* 31 */
    "REMOTE_PORT",                    /* 32 */
    NULL
};

static const char *request_var_fn(ap_expr_eval_ctx_t *ctx, const void *data)
{
    int index = ((const char **)data - request_var_names);
    request_rec *r = ctx->r;
    if (!r)
        return "";

    switch (index) {
    case 0:
        return r->method;
    case 1:
        return ap_http_scheme(r);
    case 2:
        return r->uri;
    case 3:
        return r->filename;
    case 4:
        return ap_get_useragent_host(r, REMOTE_NAME, NULL);
    case 5:
        return ap_get_remote_logname(r);
    case 6:
        return r->user;
    case 7:
        return r->server->server_admin;
    case 8:
        return ap_get_server_name_for_url(r);
    case 9:
        return apr_psprintf(ctx->p, "%u", ap_get_server_port(r));
    case 10:
        return r->protocol;
    case 11:
        return r->filename;
    case 12:
        return r->path_info;
    case 13:
        return r->args;
    case 14:
        return (r->main != NULL ? "true" : "false");
    case 15:
        return ap_document_root(r);
    case 16:
        return r->ap_auth_type;
    case 17:
        return r->the_request;
    case 18:
        return r->content_type;
    case 19:
        return r->handler;
    case 20:
        return r->log_id;
    case 21:
        {
            char *result = "";
            if (r->finfo.valid & APR_FINFO_USER)
                apr_uid_name_get(&result, r->finfo.user, ctx->p);
            return result;
        }
    case 22:
        {
            char *result = "";
            if (r->finfo.valid & APR_FINFO_USER)
                apr_gid_name_get(&result, r->finfo.group, ctx->p);
            return result;
        }
    case 23:
        {
            const char *uri = apr_table_get(r->subprocess_env, "DOCUMENT_URI");
            return uri ? uri : r->uri;
        }
    case 24:
        {
            apr_time_exp_t tm;
            apr_time_exp_lt(&tm, r->mtime);
            return apr_psprintf(ctx->p, "%02d%02d%02d%02d%02d%02d%02d",
                                (tm.tm_year / 100) + 19, (tm.tm_year % 100),
                                tm.tm_mon+1, tm.tm_mday, tm.tm_hour, tm.tm_min,
                                tm.tm_sec);
        }
    case 25:
        return ap_context_prefix(r);
    case 26:
        return ap_context_document_root(r);
    case 27:
        return r->status ? apr_psprintf(ctx->p, "%d", r->status) : "";
    case 28:
        return r->useragent_ip;
    case 29:
        switch (r->proto_num) {
        case 1001:  return "1001";   /* 1.1 */
        case 1000:  return "1000";   /* 1.0 */
        case 9:     return "9";      /* 0.9 */
        }
        return apr_psprintf(ctx->p, "%d", r->proto_num);
    case 30:
        switch (HTTP_VERSION_MAJOR(r->proto_num)) {
        case 0:     return "0";
        case 1:     return "1";
        }
        return apr_psprintf(ctx->p, "%d", HTTP_VERSION_MAJOR(r->proto_num));
    case 31:
        switch (HTTP_VERSION_MINOR(r->proto_num)) {
        case 0:     return "0";
        case 1:     return "1";
        case 9:     return "9";
        }
        return apr_psprintf(ctx->p, "%d", HTTP_VERSION_MINOR(r->proto_num));
    case 32:
        return apr_psprintf(ctx->p, "%u", ctx->c->client_addr->port);
    default:
        ap_assert(0);
        return NULL;
    }
}

static const char *const req_header_var_names[] = {
    "HTTP_USER_AGENT",       /* 0 */
    "HTTP_PROXY_CONNECTION", /* 1 */
    "HTTP_REFERER",          /* 2 */
    "HTTP_COOKIE",           /* 3 */
    "HTTP_FORWARDED",        /* 4 */
    "HTTP_HOST",             /* 5 */
    "HTTP_ACCEPT",           /* 6 */
    NULL
};

static const char *const req_header_header_names[] = {
    "User-Agent",
    "Proxy-Connection",
    "Referer",
    "Cookie",
    "Forwarded",
    "Host",
    "Accept"
};

static const char *req_header_var_fn(ap_expr_eval_ctx_t *ctx, const void *data)
{
    const char **const varname = (const char **)data;
    int index = (varname - req_header_var_names);
    const char *name;

    AP_DEBUG_ASSERT(index < 7);
    if (!ctx->r)
        return "";

    name = req_header_header_names[index];
    /* Skip the 'Vary: Host' header combination
     * as indicated in rfc7231 section-7.1.4
     */
    if (strcasecmp(name, "Host")){
        add_vary(ctx, name);
    }
    return apr_table_get(ctx->r->headers_in, name);
}

static const char *const misc_var_names[] = {
    "TIME_YEAR",        /* 0 */
    "TIME_MON",         /* 1 */
    "TIME_DAY",         /* 2 */
    "TIME_HOUR",        /* 3 */
    "TIME_MIN",         /* 4 */
    "TIME_SEC",         /* 5 */
    "TIME_WDAY",        /* 6 */
    "TIME",             /* 7 */
    "SERVER_SOFTWARE",  /* 8 */
    "API_VERSION",      /* 9 */
    NULL
};

static const char *misc_var_fn(ap_expr_eval_ctx_t *ctx, const void *data)
{
    apr_time_exp_t tm;
    int index = ((const char **)data - misc_var_names);
    apr_time_exp_lt(&tm, apr_time_now());

    switch (index) {
    case 0:
        return apr_psprintf(ctx->p, "%02d%02d", (tm.tm_year / 100) + 19,
                            tm.tm_year % 100);
    case 1:
        return apr_psprintf(ctx->p, "%02d", tm.tm_mon+1);
    case 2:
        return apr_psprintf(ctx->p, "%02d", tm.tm_mday);
    case 3:
        return apr_psprintf(ctx->p, "%02d", tm.tm_hour);
    case 4:
        return apr_psprintf(ctx->p, "%02d", tm.tm_min);
    case 5:
        return apr_psprintf(ctx->p, "%02d", tm.tm_sec);
    case 6:
        return apr_psprintf(ctx->p, "%d", tm.tm_wday);
    case 7:
        return apr_psprintf(ctx->p, "%02d%02d%02d%02d%02d%02d%02d",
                            (tm.tm_year / 100) + 19, (tm.tm_year % 100),
                            tm.tm_mon+1, tm.tm_mday, tm.tm_hour, tm.tm_min,
                            tm.tm_sec);
    case 8:
        return ap_get_server_banner();
    case 9:
        return apr_itoa(ctx->p, MODULE_MAGIC_NUMBER_MAJOR);
    default:
        ap_assert(0);
    }

    return NULL;
}

static int subnet_parse_arg(ap_expr_lookup_parms *parms)
{
    apr_ipsubnet_t *subnet;
    const char *addr = parms->arg;
    const char *mask;
    apr_status_t ret;

    if (!parms->arg) {
        *parms->err = apr_psprintf(parms->ptemp,
                                   "-%s requires subnet/netmask as constant argument",
                                   parms->name);
        return !OK;
    }

    mask = ap_strchr_c(addr, '/');
    if (mask) {
        addr = apr_pstrmemdup(parms->ptemp, addr, mask - addr);
        mask++;
    }

    ret = apr_ipsubnet_create(&subnet, addr, mask, parms->pool);
    if (ret != APR_SUCCESS) {
        *parms->err = "parsing of subnet/netmask failed";
        return !OK;
    }

    *parms->data = subnet;
    return OK;
}

static int op_ipmatch(ap_expr_eval_ctx_t *ctx, const void *data, const char *arg1,
                const char *arg2)
{
    apr_ipsubnet_t *subnet = (apr_ipsubnet_t *)data;
    apr_sockaddr_t *saddr;

    AP_DEBUG_ASSERT(subnet != NULL);

    /* maybe log an error if this goes wrong? */
    if (apr_sockaddr_info_get(&saddr, arg1, APR_UNSPEC, 0, 0, ctx->p) != APR_SUCCESS)
        return FALSE;

    return apr_ipsubnet_test(subnet, saddr);
}

static int op_R(ap_expr_eval_ctx_t *ctx, const void *data, const char *arg1)
{
    apr_ipsubnet_t *subnet = (apr_ipsubnet_t *)data;

    AP_DEBUG_ASSERT(subnet != NULL);

    if (!ctx->r)
        return FALSE;

    return apr_ipsubnet_test(subnet, ctx->r->useragent_addr);
}

static int op_T(ap_expr_eval_ctx_t *ctx, const void *data, const char *arg)
{
    switch (arg[0]) {
    case '\0':
        return FALSE;
    case 'o':
    case 'O':
        return strcasecmp(arg, "off") == 0 ? FALSE : TRUE;
    case 'n':
    case 'N':
        return strcasecmp(arg, "no") == 0 ? FALSE : TRUE;
    case 'f':
    case 'F':
        return strcasecmp(arg, "false") == 0 ? FALSE : TRUE;
    case '0':
        return arg[1] == '\0' ? FALSE : TRUE;
    default:
        return TRUE;
    }
}

static int op_fnmatch(ap_expr_eval_ctx_t *ctx, const void *data,
                      const char *arg1, const char *arg2)
{
    return (APR_SUCCESS == apr_fnmatch(arg2, arg1, APR_FNM_PATHNAME));
}

static int op_strmatch(ap_expr_eval_ctx_t *ctx, const void *data,
                       const char *arg1, const char *arg2)
{
    return (APR_SUCCESS == apr_fnmatch(arg2, arg1, 0));
}

static int op_strcmatch(ap_expr_eval_ctx_t *ctx, const void *data,
                        const char *arg1, const char *arg2)
{
    return (APR_SUCCESS == apr_fnmatch(arg2, arg1, APR_FNM_CASE_BLIND));
}

struct expr_provider_single {
    const void *func;
    const char *name;
    ap_expr_lookup_fn_t *arg_parsing_func;
    int restricted;
};

struct expr_provider_multi {
    const void *func;
    const char *const *names;
};

static const struct expr_provider_multi var_providers[] = {
    { misc_var_fn, misc_var_names },
    { req_header_var_fn, req_header_var_names },
    { request_var_fn, request_var_names },
    { conn_var_fn, conn_var_names },
    { NULL, NULL }
};

static const struct expr_provider_single string_func_providers[] = {
    { osenv_func,           "osenv",          NULL, 0 },
    { env_func,             "env",            NULL, 0 },
    { req_table_func,       "resp",           NULL, 0 },
    { req_table_func,       "req",            NULL, 0 },
    /* 'http' as alias for 'req' for compatibility with ssl_expr */
    { req_table_func,       "http",           NULL, 0 },
    { req_table_func,       "note",           NULL, 0 },
    { req_table_func,       "reqenv",         NULL, 0 },
    { req_table_func,       "req_novary",     NULL, 0 },
    { tolower_func,         "tolower",        NULL, 0 },
    { toupper_func,         "toupper",        NULL, 0 },
    { escape_func,          "escape",         NULL, 0 },
    { unescape_func,        "unescape",       NULL, 0 },
    { file_func,            "file",           NULL, 1 },
    { filesize_func,        "filesize",       NULL, 1 },
    { filemod_func,         "filemod",        NULL, 1 },
    { base64_func,          "base64",         NULL, 0 },
    { unbase64_func,        "unbase64",       NULL, 0 },
    { sha1_func,            "sha1",           NULL, 0 },
    { md5_func,             "md5",            NULL, 0 },
#if APR_VERSION_AT_LEAST(1,6,0)
    { ldap_func,            "ldap",           NULL, 0 },
#endif
    { replace_func,         "replace",        replace_func_parse_arg, 0 },
    { escapehtml_func,      "escapehtml",     NULL, 0 },
    { NULL, NULL, NULL}
};

static const struct expr_provider_single unary_op_providers[] = {
    { op_nz,        "n", NULL,             0 },
    { op_nz,        "z", NULL,             0 },
    { op_R,         "R", subnet_parse_arg, 0 },
    { op_T,         "T", NULL,             0 },
    { op_file_min,  "d", NULL,             1 },
    { op_file_min,  "e", NULL,             1 },
    { op_file_min,  "f", NULL,             1 },
    { op_file_min,  "s", NULL,             1 },
    { op_file_link, "L", NULL,             1 },
    { op_file_link, "h", NULL,             1 },
    { op_file_xbit, "x", NULL,             1 },
    { op_file_subr, "F", NULL,             0 },
    { op_url_subr,  "U", NULL,             0 },
    { op_url_subr,  "A", NULL,             0 },
    { NULL, NULL, NULL }
};

static const struct expr_provider_single binary_op_providers[] = {
    { op_ipmatch,   "ipmatch",      subnet_parse_arg, 0 },
    { op_fnmatch,   "fnmatch",      NULL,             0 },
    { op_strmatch,  "strmatch",     NULL,             0 },
    { op_strcmatch, "strcmatch",    NULL,             0 },
    { NULL, NULL, NULL }
};

static int core_expr_lookup(ap_expr_lookup_parms *parms)
{
    switch (parms->type) {
    case AP_EXPR_FUNC_VAR: {
            const struct expr_provider_multi *prov = var_providers;
            while (prov->func) {
                const char *const *name = prov->names;
                while (*name) {
                    if (ap_cstr_casecmp(*name, parms->name) == 0) {
                        *parms->func = prov->func;
                        *parms->data = name;
                        return OK;
                    }
                    name++;
                }
                prov++;
            }
        }
        break;
    case AP_EXPR_FUNC_STRING:
    case AP_EXPR_FUNC_OP_UNARY:
    case AP_EXPR_FUNC_OP_BINARY: {
            const struct expr_provider_single *prov = NULL;
            switch (parms->type) {
            case AP_EXPR_FUNC_STRING:
                prov = string_func_providers;
                break;
            case AP_EXPR_FUNC_OP_UNARY:
                prov = unary_op_providers;
                break;
            case AP_EXPR_FUNC_OP_BINARY:
                prov = binary_op_providers;
                break;
            default:
                ap_assert(0);
            }
            while (prov && prov->func) {
                int match;
                if (parms->type == AP_EXPR_FUNC_OP_UNARY)
                    match = !strcmp(prov->name, parms->name);
                else
                    match = !ap_cstr_casecmp(prov->name, parms->name);
                if (match) {
                    if ((parms->flags & AP_EXPR_FLAG_RESTRICTED)
                        && prov->restricted) {
                        *parms->err =
                            apr_psprintf(parms->ptemp,
                                         "%s%s not available in restricted context",
                                         (parms->type == AP_EXPR_FUNC_STRING) ? "" : "-",
                                         prov->name);
                        return !OK;
                    }
                    *parms->func = prov->func;
                    if (prov->arg_parsing_func) {
                        return prov->arg_parsing_func(parms);
                    }
                    else {
                        *parms->data = prov->name;
                        return OK;
                    }
                }
                prov++;
            }
        }
        break;
    default:
        break;
    }
    return DECLINED;
}

static int expr_lookup_not_found(ap_expr_lookup_parms *parms)
{
    const char *type;
    const char *prefix = "";

    switch (parms->type) {
    case AP_EXPR_FUNC_VAR:
        type = "Variable";
        break;
    case AP_EXPR_FUNC_STRING:
        type = "Function";
        break;
    case AP_EXPR_FUNC_LIST:
        type = "List-returning function";
        break;
    case AP_EXPR_FUNC_OP_UNARY:
        type = "Unary operator";
        break;
    case AP_EXPR_FUNC_OP_BINARY:
        type = "Binary operator";
        break;
    default:
        *parms->err = "Invalid expression type in expr_lookup";
        return !OK;
    }
    if (   parms->type == AP_EXPR_FUNC_OP_UNARY
        || parms->type == AP_EXPR_FUNC_OP_BINARY) {
        prefix = "-";
    }
    *parms->err = apr_psprintf(parms->ptemp, "%s '%s%s' does not exist", type,
                               prefix, parms->name);
    return !OK;
}

static int ap_expr_post_config(apr_pool_t *pconf, apr_pool_t *plog,
                               apr_pool_t *ptemp, server_rec *s)
{
    is_http2 = APR_RETRIEVE_OPTIONAL_FN(http2_is_h2);
    return OK;
}

void ap_expr_init(apr_pool_t *p)
{
    ap_hook_expr_lookup(core_expr_lookup, NULL, NULL, APR_HOOK_MIDDLE);
    ap_hook_expr_lookup(expr_lookup_not_found, NULL, NULL, APR_HOOK_REALLY_LAST);
    ap_hook_post_config(ap_expr_post_config, NULL, NULL, APR_HOOK_MIDDLE);
}