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+/* 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.
+ */
+
+/**
+ * @file ap_expr.h
+ * @brief Expression parser
+ *
+ * @defgroup AP_EXPR Expression parser
+ * @ingroup  APACHE_CORE
+ * @{
+ */
+
+#ifndef AP_EXPR_H
+#define AP_EXPR_H
+
+#include "httpd.h"
+#include "http_config.h"
+#include "ap_regex.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/** A node in the expression parse tree */
+typedef struct ap_expr_node ap_expr_t;
+
+/** Struct describing a parsed expression */
+typedef struct {
+    /** The root of the actual expression parse tree */
+    ap_expr_t *root_node;
+    /** The filename where the expression has been defined (for logging).
+     *  May be NULL
+     */
+    const char *filename;
+    /** The line number where the expression has been defined (for logging). */
+    unsigned int line_number;
+    /** Flags relevant for the expression, see AP_EXPR_FLAG_* */
+    unsigned int flags;
+    /** The module that is used for loglevel configuration */
+    int module_index;
+} ap_expr_info_t;
+
+/** Use ssl_expr compatibility mode (changes the meaning of the comparison
+ * operators)
+ */
+#define AP_EXPR_FLAG_SSL_EXPR_COMPAT       1
+/** Don't add siginificant request headers to the Vary response header */
+#define AP_EXPR_FLAG_DONT_VARY             2
+/** Don't allow functions/vars that bypass the current request's access
+ *  restrictions or would otherwise leak confidential information.
+ *  Used by e.g. mod_include.
+ */
+#define AP_EXPR_FLAG_RESTRICTED            4
+/** Expression evaluates to a string, not to a bool */
+#define AP_EXPR_FLAG_STRING_RESULT         8
+
+
+/**
+ * Evaluate a parse tree, simple interface
+ * @param r The current request
+ * @param expr The expression to be evaluated
+ * @param err Where an error message should be stored
+ * @return > 0 if expression evaluates to true, == 0 if false, < 0 on error
+ * @note err will be set to NULL on success, or to an error message on error
+ * @note request headers used during evaluation will be added to the Vary:
+ *       response header, unless ::AP_EXPR_FLAG_DONT_VARY is set.
+ */
+AP_DECLARE(int) ap_expr_exec(request_rec *r, const ap_expr_info_t *expr,
+                             const char **err);
+
+/**
+ * Evaluate a parse tree, with access to regexp backreference
+ * @param r The current request
+ * @param expr The expression to be evaluated
+ * @param nmatch size of the regex match vector pmatch
+ * @param pmatch information about regex matches
+ * @param source the string that pmatch applies to
+ * @param err Where an error message should be stored
+ * @return > 0 if expression evaluates to true, == 0 if false, < 0 on error
+ * @note err will be set to NULL on success, or to an error message on error
+ * @note nmatch/pmatch/source can be used both to make previous matches
+ *       available to ap_expr_exec_re and to use ap_expr_exec_re's matches
+ *       later on.
+ * @note request headers used during evaluation will be added to the Vary:
+ *       response header, unless ::AP_EXPR_FLAG_DONT_VARY is set.
+ */
+AP_DECLARE(int) ap_expr_exec_re(request_rec *r, const ap_expr_info_t *expr,
+                                apr_size_t nmatch, ap_regmatch_t *pmatch,
+                                const char **source, const char **err);
+
+/** Context used during evaluation of a parse tree, created by ap_expr_exec */
+typedef struct {
+    /** the current request */
+    request_rec *r;
+    /** the current connection */
+    conn_rec *c;
+    /** the current virtual host */
+    server_rec *s;
+    /** the pool to use */
+    apr_pool_t *p;
+    /** where to store the error string */
+    const char **err;
+    /** ap_expr_info_t for the expression */
+    const ap_expr_info_t *info;
+    /** regex match information for back references */
+    ap_regmatch_t *re_pmatch;
+    /** size of the vector pointed to by re_pmatch */
+    apr_size_t re_nmatch;
+    /** the string corresponding to the re_pmatch */
+    const char **re_source;
+    /** A string where the comma separated names of headers are stored
+     * to be later added to the Vary: header. If NULL, the caller is not
+     * interested in this information.
+     */
+    const char **vary_this;
+    /** where to store the result string */
+    const char **result_string;
+    /** Arbitrary context data provided by the caller for custom functions */
+    void *data;
+    /** The current recursion level */
+    int reclvl;
+} ap_expr_eval_ctx_t;
+
+/**
+ * Evaluate a parse tree, full featured version
+ * @param ctx The evaluation context with all data filled in
+ * @return > 0 if expression evaluates to true, == 0 if false, < 0 on error
+ * @note *ctx->err will be set to NULL on success, or to an error message on
+ *       error
+ * @note request headers used during evaluation will be added to the Vary:
+ *       response header if ctx->vary_this is set.
+ */
+AP_DECLARE(int) ap_expr_exec_ctx(ap_expr_eval_ctx_t *ctx);
+
+/**
+ * Evaluate a parse tree of a string valued expression
+ * @param r The current request
+ * @param expr The expression to be evaluated
+ * @param err Where an error message should be stored
+ * @return The result string, NULL on error
+ * @note err will be set to NULL on success, or to an error message on error
+ * @note request headers used during evaluation will be added to the Vary:
+ *       response header, unless ::AP_EXPR_FLAG_DONT_VARY is set.
+ */
+AP_DECLARE(const char *) ap_expr_str_exec(request_rec *r,
+                                          const ap_expr_info_t *expr,
+                                          const char **err);
+
+/**
+ * Evaluate a parse tree of a string valued expression
+ * @param r The current request
+ * @param expr The expression to be evaluated
+ * @param nmatch size of the regex match vector pmatch
+ * @param pmatch information about regex matches
+ * @param source the string that pmatch applies to
+ * @param err Where an error message should be stored
+ * @return The result string, NULL on error
+ * @note err will be set to NULL on success, or to an error message on error
+ * @note nmatch/pmatch/source can be used both to make previous matches
+ *       available to ap_expr_exec_re and to use ap_expr_exec_re's matches
+ *       later on.
+ * @note request headers used during evaluation will be added to the Vary:
+ *       response header, unless ::AP_EXPR_FLAG_DONT_VARY is set.
+ */
+AP_DECLARE(const char *) ap_expr_str_exec_re(request_rec *r,
+                                             const ap_expr_info_t *expr,
+                                             apr_size_t nmatch,
+                                             ap_regmatch_t *pmatch,
+                                             const char **source,
+                                             const char **err);
+
+
+/**
+ * The parser can be extended with variable lookup, functions, and
+ * and operators.
+ *
+ * During parsing, the parser calls the lookup function to resolve a
+ * name into a function pointer and an opaque context for the function.
+ * If the argument to a function or operator is constant, the lookup function
+ * may also parse that argument and store the parsed data in the context.
+ *
+ * The default lookup function is the hook ::ap_expr_lookup_default which just
+ * calls ap_run_expr_lookup. Modules can use it to make functions and
+ * variables generally available.
+ *
+ * An ap_expr consumer can also provide its own custom lookup function to
+ * modify the set of variables and functions that are available. The custom
+ * lookup function can in turn call 'ap_run_expr_lookup'.
+ */
+
+/** Unary operator, takes one string argument and returns a bool value.
+ * The name must have the form '-z' (one letter only).
+ * @param ctx The evaluation context
+ * @param data An opaque context provided by the lookup hook function
+ * @param arg The (right) operand
+ * @return 0 or 1
+ */
+typedef int ap_expr_op_unary_t(ap_expr_eval_ctx_t *ctx, const void *data,
+                               const char *arg);
+
+/** Binary operator, takes two string arguments and returns a bool value.
+ * The name must have the form '-cmp' (at least two letters).
+ * @param ctx The evaluation context
+ * @param data An opaque context provided by the lookup hook function
+ * @param arg1 The left operand
+ * @param arg2 The right operand
+ * @return 0 or 1
+ */
+typedef int ap_expr_op_binary_t(ap_expr_eval_ctx_t *ctx, const void *data,
+                                const char *arg1, const char *arg2);
+
+/** String valued function, takes a string argument and returns a string
+ * @param ctx The evaluation context
+ * @param data An opaque context provided by the lookup hook function
+ * @param arg The argument
+ * @return The functions result string, may be NULL for 'empty string'
+ */
+typedef const char *(ap_expr_string_func_t)(ap_expr_eval_ctx_t *ctx,
+                                            const void *data,
+                                            const char *arg);
+
+/** List valued function, takes a string argument and returns a list of strings
+ * Can currently only be called following the builtin '-in' operator.
+ * @param ctx The evaluation context
+ * @param data An opaque context provided by the lookup hook function
+ * @param arg The argument
+ * @return The functions result list of strings, may be NULL for 'empty array'
+ */
+typedef apr_array_header_t *(ap_expr_list_func_t)(ap_expr_eval_ctx_t *ctx,
+                                                  const void *data,
+                                                  const char *arg);
+
+/** Variable lookup function, takes no argument and returns a string
+ * @param ctx The evaluation context
+ * @param data An opaque context provided by the lookup hook function
+ * @return The expanded variable
+ */
+typedef const char *(ap_expr_var_func_t)(ap_expr_eval_ctx_t *ctx,
+                                         const void *data);
+
+/** parameter struct passed to the lookup hook functions */
+typedef struct {
+    /** type of the looked up object */
+    int type;
+#define AP_EXPR_FUNC_VAR        0
+#define AP_EXPR_FUNC_STRING     1
+#define AP_EXPR_FUNC_LIST       2
+#define AP_EXPR_FUNC_OP_UNARY   3
+#define AP_EXPR_FUNC_OP_BINARY  4
+    /** name of the looked up object */
+    const char *name;
+
+    int flags;
+
+    apr_pool_t *pool;
+    apr_pool_t *ptemp;
+
+    /** where to store the function pointer */
+    const void **func;
+    /** where to store the function's context */
+    const void **data;
+    /** where to store the error message (if any) */
+    const char **err;
+
+    /** arg for pre-parsing (only if a simple string).
+     *  For binary ops, this is the right argument. */
+    const char *arg;
+} ap_expr_lookup_parms;
+
+/** Function for looking up the provider function for a variable, operator
+ *  or function in an expression.
+ *  @param parms The parameter struct, also determins where the result is
+ *               stored.
+ *  @return OK on success,
+ *          !OK on failure,
+ *          DECLINED if the requested name is not handled by this function
+ */
+typedef int (ap_expr_lookup_fn_t)(ap_expr_lookup_parms *parms);
+
+/** Default lookup function which just calls ap_run_expr_lookup().
+ *  ap_run_expr_lookup cannot be used directly because it has the wrong
+ *  calling convention under Windows.
+ */
+AP_DECLARE_NONSTD(int) ap_expr_lookup_default(ap_expr_lookup_parms *parms);
+
+AP_DECLARE_HOOK(int, expr_lookup, (ap_expr_lookup_parms *parms))
+
+/**
+ * Parse an expression into a parse tree
+ * @param pool Pool
+ * @param ptemp temp pool
+ * @param info The ap_expr_info_t struct (with values filled in)
+ * @param expr The expression string to parse
+ * @param lookup_fn The lookup function to use, NULL for default
+ * @return NULL on success, error message on error.
+ *         A pointer to the resulting parse tree will be stored in
+ *         info->root_node.
+ */
+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);
+
+/**
+ * High level interface to ap_expr_parse that also creates ap_expr_info_t and
+ * uses info from cmd_parms to fill in most of it.
+ * @param cmd The cmd_parms struct
+ * @param expr The expression string to parse
+ * @param flags The flags to use, see AP_EXPR_FLAG_*
+ * @param err Set to NULL on success, error message on error
+ * @param lookup_fn The lookup function used to lookup vars, functions, and
+ *        operators
+ * @param module_index The module_index to set for the expression
+ * @return The parsed expression
+ * @note Usually ap_expr_parse_cmd() should be used
+ */
+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);
+
+/**
+ * Convenience wrapper for ap_expr_parse_cmd_mi() that sets
+ * module_index = APLOG_MODULE_INDEX
+ */
+#define ap_expr_parse_cmd(cmd, expr, flags, err, lookup_fn) \
+        ap_expr_parse_cmd_mi(cmd, expr, flags, err, lookup_fn, APLOG_MODULE_INDEX)
+
+ /**
+  * Internal initialisation of ap_expr (for httpd internal use)
+  */
+void ap_expr_init(apr_pool_t *pool);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* AP_EXPR_H */
+/** @} */