libidav/davqlexec.c

/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 *
 * Copyright 2018 Olaf Wintermann. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *   1. Redistributions of source code must retain the above copyright
 *      notice, this list of conditions and the following disclaimer.
 *
 *   2. Redistributions in binary form must reproduce the above copyright
 *      notice, this list of conditions and the following disclaimer in the
 *      documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <inttypes.h>

#include <ucx/utils.h>
#include <ucx/map.h>
#include "davqlexec.h"
#include "utils.h"
#include "methods.h"
#include "session.h"
#include "resource.h"

DavQLArgList* dav_ql_get_args(DavQLStatement *st, va_list ap) {
    DavQLArgList *args = malloc(sizeof(DavQLArgList));
    if(!args) {
        return NULL;
    }
    args->first = NULL;
    
    DavQLArg *cur = NULL;
    UCX_FOREACH(elm, st->args) {
        intptr_t type = (intptr_t)elm->data;
        DavQLArg *arg = calloc(1, sizeof(DavQLArg));
        if(!arg) {
            dav_ql_free_arglist(args);
            return NULL;
        }
        arg->type = type;
        switch(type) {
            case 'd': {
                arg->value.d = va_arg(ap, int);
                break;
            }
            case 'u': {
                arg->value.u = va_arg(ap, unsigned int);
                break;
            }
            case 's': {
                arg->value.s = va_arg(ap, char*);
                break;
            }
            case 't': {
                arg->value.t = va_arg(ap, time_t);
                break;
            }
            default: {
                free(arg);
                dav_ql_free_arglist(args);
                return NULL;
            }
        }
        if(cur) {
            cur->next = arg;
        } else {
            args->first = arg;
        }
        cur = arg;
    }
    args->current = args->first;
    return args;
}

void dav_ql_free_arglist(DavQLArgList *args) {
    DavQLArg *arg = args->first;
    while(arg) {
        DavQLArg *next = arg->next;
        free(arg);
        arg = next;
    }
    free(args);
}

static DavQLArg* arglist_get(DavQLArgList *args) {
    DavQLArg *a = args->current;
    if(a) {
        args->current = a->next;
    }
    return a;
}

int dav_ql_getarg_int(DavQLArgList *args) {
    DavQLArg *a = arglist_get(args);
    if(a && a->type == 'd') {
        return a->value.d;
    }
    return 0;
}

unsigned int dav_ql_getarg_uint(DavQLArgList *args) {
    DavQLArg *a = arglist_get(args);
    if(a && a->type == 'u') {
        return a->value.u;
    }
    return 0;
}

char* dav_ql_getarg_str(DavQLArgList *args) {
    DavQLArg *a = arglist_get(args);
    if(a && a->type == 's') {
        return a->value.s;
    }
    return "";
}

time_t dav_ql_getarg_time(DavQLArgList *args) {
    DavQLArg *a = arglist_get(args);
    if(a && a->type == 't') {
        return a->value.t;
    }
    return 0;
}


DavResult dav_statement_exec(DavSession *sn, DavQLStatement *st, ...) {
    va_list ap;
    va_start(ap, st);
    DavResult result = dav_statement_execv(sn, st, ap);
    va_end(ap);
    return result;
}

DavResult dav_statement_execv(DavSession *sn, DavQLStatement *st, va_list ap) {
    DavResult result;
    result.result = NULL;
    result.status = 1;
    
    // make sure the statement was successfully parsed
    if(st->type == DAVQL_ERROR) {
        return result;
    }
    
    if(st->type == DAVQL_SELECT) {
        return dav_exec_select(sn, st, ap);
    } else {
        // TODO
    }
    
    return result;
}

sstr_t dav_format_string(UcxAllocator *a, sstr_t fstr, DavQLArgList *ap, davqlerror_t *error) {
    UcxBuffer *buf = ucx_buffer_new(NULL, 128, UCX_BUFFER_AUTOEXTEND);
    
    int placeholder = 0;
    for(int i=0;i<fstr.length;i++) {
        char c = fstr.ptr[i];
        if(placeholder) {
            if(c == '%') {
                // no placeholder, %% transposes to %
                ucx_buffer_putc(buf, c);
            } else {
                // detect placeholder type and insert arg
                int err = 0;
                switch(c) {
                    case 's': {
                        char *arg = dav_ql_getarg_str(ap);
                        ucx_buffer_puts(buf, arg);
                        break;
                    }
                    case 'd': {
                        int arg = dav_ql_getarg_int(ap);
                        ucx_bprintf(buf, "%d", arg);
                        break;
                    }
                    case 'u': {
                        unsigned int arg = dav_ql_getarg_uint(ap);
                        ucx_bprintf(buf, "%u", arg);
                        break;
                    }
                    case 't': {
                        // time arguments not supported for strings
                        err = 1;
                        break;
                    }
                    default: {
                        *error = DAVQL_UNKNOWN_FORMATCHAR;
                        err = 1;
                    }
                }
                if(err) {
                    ucx_buffer_free(buf);
                    sstr_t n;
                    n.ptr = NULL;
                    n.length = 0;
                    return n;
                }
            }
            placeholder = 0;
        } else {
            if(c == '%') {
                placeholder = 1;
            } else {
                ucx_buffer_putc(buf, c);
            }
        }
    }
    *error = DAVQL_OK;
    
    sstr_t ret = sstrdup_a(a, sstrn(buf->space, buf->size));
    ucx_buffer_free(buf);
    return ret;
}

static int fl_add_properties(DavSession *sn, UcxMempool *mp, UcxMap *map, DavQLExpression *expression) {
    if(!expression) {
        return 0;
    }
    
    if(expression->type == DAVQL_IDENTIFIER) {
        DavProperty *property = ucx_mempool_malloc(mp, sizeof(DavProperty));

        char *name;
        DavNamespace *ns = dav_get_property_namespace(
                sn->context,
                sstrdup_a(mp->allocator, expression->srctext).ptr,
                &name);
        if(!ns) {
            return -1;
        }
        
        property->ns = ns;
        property->name = name;
        property->value = NULL;
        
        ucx_map_sstr_put(map, expression->srctext, property);
    }
    
    if(expression->left) {
        if(fl_add_properties(sn, mp, map, expression->left)) {
            return -1;
        }
    }
    if(expression->right) {
        if(fl_add_properties(sn, mp, map, expression->right)) {
            return -1;
        }
    }
    
    return 0;
}

static UcxBuffer* fieldlist2propfindrequest(DavSession *sn, UcxMempool *mp, UcxList *fields, int *isallprop) {
    UcxMap *properties = ucx_map_new(32);
    *isallprop = 0;
    
    UCX_FOREACH(elm, fields) {
        DavQLField *field = elm->data;
        if(!sstrcmp(field->name, S("*"))) {
            ucx_map_free(properties);
            *isallprop = 1;
            return create_allprop_propfind_request();
        } else if(!sstrcmp(field->name, S("-"))) {
            ucx_map_free(properties);
            return create_propfind_request(sn, NULL, "propfind", 0);
        } else {
            if(fl_add_properties(sn, mp, properties, field->expr)) {
                // TODO: set error
                ucx_map_free(properties);
                return NULL;
            }
        }
    }
    
    UcxMapIterator i = ucx_map_iterator(properties);
    UcxKey key;
    DavProperty *value;
    UcxList *list = NULL;
    UCX_MAP_FOREACH(key, value, i) {
        list = ucx_list_append(list, value);
    }
    
    UcxBuffer *reqbuf = create_propfind_request(sn, list, "propfind", 0);
    ucx_list_free(list);
    ucx_map_free(properties);
    return reqbuf;
}

static int reset_properties(DavSession *sn, DavResult *result, DavResource *res, UcxList *fields) {
    UcxMap *new_properties = ucx_map_new_a(sn->mp->allocator, 32);
    DavResourceData *data = (DavResourceData*)res->data;
    
    // add basic properties
    void *value;
    
    sstr_t cl_keystr = dav_property_key("DAV:", "getcontentlength");
    UcxKey cl_key = ucx_key(cl_keystr.ptr, cl_keystr.length);
    value = ucx_map_get(data->properties, cl_key);
    if(value) {
        ucx_map_put(new_properties, cl_key, value);
    }
    
    sstr_t cd_keystr = dav_property_key("DAV:", "creationdate");
    UcxKey cd_key = ucx_key(cd_keystr.ptr, cd_keystr.length);
    value = ucx_map_get(data->properties, cd_key);
    if(value) {
        ucx_map_put(new_properties, cd_key, value);
    }
    
    sstr_t lm_keystr = dav_property_key("DAV:", "getlastmodified");
    UcxKey lm_key = ucx_key(lm_keystr.ptr, lm_keystr.length);
    value = ucx_map_get(data->properties, lm_key);
    if(value) {
        ucx_map_put(new_properties, lm_key, value);
    }
    
    sstr_t ct_keystr = dav_property_key("DAV:", "getcontenttype");
    UcxKey ct_key = ucx_key(ct_keystr.ptr, ct_keystr.length);
    value = ucx_map_get(data->properties, ct_key);
    if(value) {
        ucx_map_put(new_properties, ct_key, value);
    }
    
    sstr_t rt_keystr = dav_property_key("DAV:", "resourcetype");
    UcxKey rt_key = ucx_key(rt_keystr.ptr, rt_keystr.length);
    value = ucx_map_get(data->properties, rt_key);
    if(value) {
        ucx_map_put(new_properties, rt_key, value);
    }
    
    sstr_t cn_keystr = dav_property_key(DAV_NS, "crypto-name");
    UcxKey cn_key = ucx_key(cn_keystr.ptr, cn_keystr.length);
    value = ucx_map_get(data->properties, cn_key);
    if(value) {
        ucx_map_put(new_properties, cn_key, value);
    }
    
    sstr_t ck_keystr = dav_property_key(DAV_NS, "crypto-key");
    UcxKey ck_key = ucx_key(ck_keystr.ptr, ck_keystr.length);
    value = ucx_map_get(data->properties, ck_key);
    if(value) {
        ucx_map_put(new_properties, ck_key, value);
    }
    
    sstr_t ch_keystr = dav_property_key(DAV_NS, "crypto-hash");
    UcxKey ch_key = ucx_key(ch_keystr.ptr, ch_keystr.length);
    value = ucx_map_get(data->properties, ch_key);
    if(value) {
        ucx_map_put(new_properties, ch_key, value);
    }
    
    // add properties from field list
    UCX_FOREACH(elm, fields) {
        DavCompiledField *field = elm->data;
        DavQLStackObj field_result;
        if(!dav_exec_expr(field->code, res, &field_result)) {
            sstr_t str;
            str.ptr = NULL;
            str.length = 0;
            DavXmlNode *node = NULL;
            if(field_result.type == 0) {
                str = ucx_asprintf(
                        sn->mp->allocator,
                        "%d",
                        field_result.data.integer);
            } else if(field_result.type == 1) {
                if(field_result.data.string) {
                    str = sstrdup_a(sn->mp->allocator, sstrn(
                            field_result.data.string,
                            field_result.length));
                }
            } else if(field_result.type == 2) {
                node = dav_copy_node(field_result.data.node);
            } else {
                // unknown type
                // TODO: error
                resource_free_properties(sn, new_properties);
                return -1;
            }
            if(str.ptr) {
                node = dav_session_malloc(sn, sizeof(DavXmlNode));
                memset(node, 0, sizeof(DavXmlNode));
                node->type = DAV_XML_TEXT;
                node->content = str.ptr;
                node->contentlength = str.length;
            }
            if(node) {
                sstr_t key = dav_property_key(field->ns, field->name);
                
                DavNamespace *namespace = dav_session_malloc(sn, sizeof(DavNamespace));
                namespace->prefix = NULL;
                namespace->name = dav_session_strdup(sn, field->ns);

                DavProperty *prop = dav_session_malloc(sn, sizeof(DavProperty));
                prop->name = dav_session_strdup(sn, field->name);
                prop->ns = namespace;
                prop->value = node;
                
                ucx_map_sstr_put(new_properties, key, prop);
                free(key.ptr);
            }
        } else {
            // TODO: error
            resource_free_properties(sn, new_properties);
            return -1;
        }
    }
    
    ucx_map_remove(data->properties, cl_key);
    ucx_map_remove(data->properties, cd_key);
    ucx_map_remove(data->properties, lm_key);
    ucx_map_remove(data->properties, ct_key);
    ucx_map_remove(data->properties, rt_key);
    ucx_map_remove(data->properties, cn_key);
    ucx_map_remove(data->properties, ck_key);
    ucx_map_remove(data->properties, ch_key);
    
    resource_free_properties(sn, data->properties);
    data->properties = new_properties;
    
    free(cl_keystr.ptr);
    free(cd_keystr.ptr);
    free(lm_keystr.ptr);
    free(ct_keystr.ptr);
    free(rt_keystr.ptr);
    free(cn_keystr.ptr);
    free(ck_keystr.ptr);
    free(ch_keystr.ptr);
    
    return 0;
}

/*
 * execute a davql select statement
 */
DavResult dav_exec_select(DavSession *sn, DavQLStatement *st, va_list ap) {
    UcxMempool *mp = ucx_mempool_new(128);
    DavResult result;
    result.result = NULL;
    result.status = 1;
    
    DavQLArgList *args = dav_ql_get_args(st, ap);
    if(!args) {
        return result;
    }
    ucx_mempool_reg_destr(mp, args, (ucx_destructor)dav_ql_free_arglist);
    
    int isallprop;
    UcxBuffer *rqbuf = fieldlist2propfindrequest(sn, mp, st->fields, &isallprop);
    if(!rqbuf) {
        ucx_mempool_destroy(mp);
        return result;
    }
    ucx_mempool_reg_destr(mp, rqbuf, (ucx_destructor)ucx_buffer_free);
    
    // compile field list
    UcxList *cfieldlist = NULL;
    UCX_FOREACH(elm, st->fields) {
        DavQLField *field = elm->data;
        if(sstrcmp(field->name, S("*")) && sstrcmp(field->name, S("-"))) {
            // compile field expression
            UcxBuffer *code = dav_compile_expr(
                    sn->context,
                    mp->allocator,
                    field->expr,
                    args);
            if(!code) {
                // TODO: set error string
                return result;
            }
            ucx_mempool_reg_destr(mp, code, (ucx_destructor)ucx_buffer_free);
            DavCompiledField *cfield = ucx_mempool_malloc(
                    mp,
                    sizeof(DavCompiledField));
            
            char *ns;
            char *name;
            dav_get_property_namespace_str(
                sn->context,
                sstrdup_a(mp->allocator, field->name).ptr,
                &ns,
                &name);
            if(!ns || !name) {
                // TODO: set error string
                return result;
            }
            cfield->ns = ns;
            cfield->name = name;
            cfield->code = code;
            cfieldlist = ucx_list_append_a(mp->allocator, cfieldlist, cfield);
        } 
    }
    
    // get path string
    davqlerror_t error;
    sstr_t path = dav_format_string(mp->allocator, st->path, args, &error);
    if(error) {
        // TODO: cleanup
        ucx_mempool_destroy(mp);
        return result;
    }
    
    int depth = st->depth == DAV_DEPTH_PLACEHOLDER ?
            dav_ql_getarg_int(args) : st->depth;
    
    UcxBuffer *where = dav_compile_expr(sn->context, mp->allocator, st->where, args);
    if(st->where && !where) {
        // TODO: cleanup
        ucx_mempool_destroy(mp);
        return result;
    }
    if(where) {
        ucx_mempool_reg_destr(mp, where, (ucx_destructor)ucx_buffer_free);
    }
    
    // compile order criterion
    UcxList *ordercr = NULL;
    UCX_FOREACH(elm, st->orderby) {
        DavQLOrderCriterion *oc = elm->data;
        DavQLExpression *column = oc->column;
        //printf("%.*s %s\n", column->srctext.length, column->srctext.ptr, oc->descending ? "desc" : "asc");
        if(column->type == DAVQL_IDENTIFIER) {
            // TODO: remove code duplication (add_cmd)
            davqlresprop_t resprop;
            sstr_t propertyname = sstrchr(column->srctext, ':');
            if(propertyname.length > 0) {
                char *ns;
                char *name;
                dav_get_property_namespace_str(
                        sn->context,
                        sstrdup_a(mp->allocator, column->srctext).ptr,
                        &ns,
                        &name);
                if(ns && name) {
                    DavOrderCriterion *cr = ucx_mempool_malloc(mp, sizeof(DavOrderCriterion));
                    cr->type = 1;
                    sstr_t keystr = dav_property_key_a(mp->allocator, ns, name);
                    cr->column.property = ucx_key(keystr.ptr, keystr.length);
                    cr->descending = oc->descending;
                    ordercr = ucx_list_append_a(mp->allocator, ordercr, cr);
                } else {
                    // error
                    // TODO: cleanup
                    ucx_mempool_destroy(mp);
                    return result;
                }
            } else if(dav_identifier2resprop(column->srctext, &resprop)) {
                DavOrderCriterion *cr = ucx_mempool_malloc(mp, sizeof(DavOrderCriterion));
                cr->type = 0;
                cr->column.resprop = resprop;
                cr->descending = oc->descending;
                ordercr = ucx_list_append_a(mp->allocator, ordercr, cr);
            } else {
                // error
                // TODO: cleanup
                ucx_mempool_destroy(mp);
                return result;
            }
            
        } else if(column->type == DAVQL_NUMBER) {
            // TODO: implement
            fprintf(stderr, "order by number not supported\n");
            return result;
        } else {
            // something is broken
            // TODO: cleanup
            ucx_mempool_destroy(mp);
            return result;
        }
    }
    
    DavResource *selroot = dav_resource_new(sn, path.ptr);
    
    UcxList *stack = NULL; // stack with DavResource* elements
    // initialize the stack with the requested resource
    DavQLRes *res = ucx_mempool_malloc(mp, sizeof(DavQLRes));
    res->resource = selroot;
    res->depth = 0;
    stack = ucx_list_prepend(stack, res);
    
    // reuseable response buffer
    UcxBuffer *rpbuf = ucx_buffer_new(NULL, 4096, UCX_BUFFER_AUTOEXTEND);
    if(!rpbuf) {
        // TODO: cleanup
        ucx_mempool_destroy(mp);
        return result;
    }
    ucx_mempool_reg_destr(mp, rpbuf, (ucx_destructor)ucx_buffer_free);
    
    result.result = selroot;
    result.status = 0;
    
    // do a propfind request for each resource on the stack
    while(stack) {
        DavQLRes *sr = stack->data; // get first element from the stack
        stack = ucx_list_remove(stack, stack); // remove first element
        DavResource *root = sr->resource;
        
        util_set_url(sn, dav_resource_get_href(sr->resource));
        CURLcode ret = do_propfind_request(sn, rqbuf, rpbuf);
        long http_status = 0;
        curl_easy_getinfo(sn->handle, CURLINFO_RESPONSE_CODE, &http_status);
        //printf("rpbuf: %s %s\n%.*s\n\n", sr->resource->path, sr->resource->href, rpbuf->pos, rpbuf->space);
        
        if(ret == CURLE_OK && http_status == 207) {
            // in case of an redirect we have to adjust resource->href
            dav_set_effective_href(sn, root);
            
            // propfind request successful, now parse the response
            char *url = "http://url/";
            PropfindParser *parser = create_propfind_parser(rpbuf, url);
            // TODO: test if parser is null
            ResponseTag response;
            int r;
            while((r = get_propfind_response(parser, &response)) != 0) {
                if(r == -1) {
                    // error
                    result.status = -1;
                    // TODO: free resources
                    cleanup_response(&response);
                    break;
                }
                
                // the propfind multistatus response contains responses
                // for the requested resource and all childs
                // determine if the response is a child or not
                if(hrefeq(sn, root->href, response.href)) {
                    // response is the currently requested resource
                    // and not a child
                    
                    // add properties
                    add_properties(root, &response);
                    cleanup_response(&response);
                    
                    if(root == selroot) {                     
                        // The current root is the root of the select query.
                        // In this case we have to check the where clause.
                        // If root is not selroot, the where clause was
                        // already checked for the resource before it was
                        // added to the stack.
                        DavQLStackObj where_result;
                        if(!dav_exec_expr(where, root, &where_result)) {                           
                            if(where_result.data.integer != 0) { 
                                if(!reset_properties(sn, &result, root, cfieldlist)) {
                                    continue;
                                }
                                result.status = -1;
                            }
                        }
                        result.result = NULL;
                        result.status = -1;
                        dav_resource_free_all(selroot);
                        ucx_list_free(stack);
                        break;
                    }
                } else {
                    DavResource *child = response2resource(
                            sn,
                            &response,
                            root->path);
                    cleanup_response(&response);
                    // check where clause
                    DavQLStackObj where_result;
                    if(!dav_exec_expr(where, child, &where_result)) {
                        if(where_result.data.integer != 0) {
                            if(!reset_properties(sn, &result, child, cfieldlist)) {
                                //resource_add_child(root, child);
                                resource_add_ordered_child(root, child, ordercr);
                                if(child->iscollection &&
                                    (depth < 0 || depth > sr->depth+1))
                                {
                                    DavQLRes *rs = ucx_mempool_malloc(
                                            mp,
                                            sizeof(DavQLRes));
                                    rs->resource = child;
                                    rs->depth = sr->depth + 1;
                                    stack = ucx_list_prepend(stack, rs);
                                }
                            } else {
                                dav_resource_free(child);
                            }
                        } else {
                            dav_resource_free(child);
                        }
                    }
                }    
            }
            destroy_propfind_parser(parser);
        } else  {
            dav_session_set_error(sn, ret, http_status);
            result.result = NULL;
            result.status = -1;
            dav_resource_free_all(selroot);
            break;
        }
        
        // reset response buffer
        ucx_buffer_seek(rpbuf, SEEK_SET, 0);
    }
    
    ucx_mempool_destroy(mp);
    return result;
}

static int count_func_args(DavQLExpression *expr) {
    int count = 0;
    DavQLExpression *arg = expr->right;
    while(arg) {
        count++;
        if(arg->op == DAVQL_ARGLIST) {
            arg = arg->right;
        } else {
            break;
        }
    }
    return count;
}

int dav_identifier2resprop(sstr_t src, davqlresprop_t *prop) {
    if(!sstrcmp(src, S("name"))) {
        *prop = DAVQL_RES_NAME;
    } else if(!sstrcmp(src, S("path"))) {
        *prop = DAVQL_RES_PATH;
    } else if(!sstrcmp(src, S("href"))) {
        *prop = DAVQL_RES_HREF;
    } else if(!sstrcmp(src, S("contentlength"))) {
        *prop = DAVQL_RES_CONTENTLENGTH;
    } else if(!sstrcmp(src, S("contenttype"))) {
        *prop = DAVQL_RES_CONTENTTYPE;
    } else if(!sstrcmp(src, S("creationdate"))) {
        *prop = DAVQL_RES_CREATIONDATE;
    } else if(!sstrcmp(src, S("lastmodified"))) {
        *prop = DAVQL_RES_LASTMODIFIED;
    } else if(!sstrcmp(src, S("iscollection"))) {
        *prop = DAVQL_RES_ISCOLLECTION;
    } else {
        return 0;
    }
    return 1;
}

static int add_cmd(DavContext *ctx, UcxAllocator *a, UcxBuffer *bcode, DavQLExpression *expr, DavQLArgList *ap) {
    if(!expr) {
        return 0;
    }
     
    int numcmd = 1;
    DavQLCmd cmd;
    memset(&cmd, 0, sizeof(DavQLCmd));
    davqlerror_t error;
    
    sstr_t src = expr->srctext;
    switch(expr->type) {
        default: break;
        case DAVQL_NUMBER: {   
            cmd.type = DAVQL_CMD_INT;
            if(src.ptr[0] == '%') {
                cmd.data.integer = dav_ql_getarg_int(ap);
            } else if(util_strtoint(src.ptr, &cmd.data.integer)) {
                ucx_buffer_write(&cmd, sizeof(cmd), 1, bcode);
            } else {
                // error
                return -1;
            }
            
            break;
        }
        case DAVQL_STRING: {
            cmd.type = DAVQL_CMD_STRING;
            cmd.data.string = dav_format_string(a, src, ap, &error);
            ucx_buffer_write(&cmd, sizeof(cmd), 1, bcode);
            break;
        }
        case DAVQL_TIMESTAMP: {
            if(src.ptr[0] == '%') {
                cmd.type = DAVQL_CMD_TIMESTAMP;
                cmd.data.timestamp = dav_ql_getarg_time(ap);
                ucx_buffer_write(&cmd, sizeof(cmd), 1, bcode);
            } else {
                // error
                return -1;
            }
            break;
        }
        case DAVQL_IDENTIFIER: {
            sstr_t propertyname = sstrchr(src, ':');
            cmd.type = DAVQL_CMD_RES_IDENTIFIER;
            if(propertyname.length > 0) {
                cmd.type = DAVQL_CMD_PROP_IDENTIFIER;
                char *ns;
                char *name;
                dav_get_property_namespace_str(
                        ctx,
                        sstrdup_a(a, src).ptr,
                        &ns,
                        &name);
                if(ns && name) {
                    cmd.data.property.ns = ns;
                    cmd.data.property.name = name;
                } else {
                    // error
                    return -1;
                }
            } else if(!dav_identifier2resprop(src, &cmd.data.resprop)) {
                if(!sstrcmp(src, S("true"))) {
                    cmd.type = DAVQL_CMD_INT;
                    cmd.data.integer = 1;
                } else if(!sstrcmp(src, S("false"))) {
                    cmd.type = DAVQL_CMD_INT;
                    cmd.data.integer = 0;
                } else {
                    // error, unknown identifier
                    return -1;
                }
            }
            ucx_buffer_write(&cmd, sizeof(cmd), 1, bcode);
            break;
        }
        case DAVQL_UNARY: {
            numcmd += add_cmd(ctx, a, bcode, expr->left, ap);
            switch(expr->op) {
                case DAVQL_ADD: {
                    // noop
                    numcmd = 0;
                    break;
                }
                case DAVQL_SUB: {
                    cmd.type = DAVQL_CMD_OP_UNARY_SUB;
                    ucx_buffer_write(&cmd, sizeof(cmd), 1, bcode);
                    break;
                }
                case DAVQL_NEG: {
                    cmd.type = DAVQL_CMD_OP_UNARY_NEG;
                    ucx_buffer_write(&cmd, sizeof(cmd), 1, bcode);
                    break;
                }
                default: break;
            }
            break;
        }
        case DAVQL_BINARY: {
            numcmd += add_cmd(ctx, a, bcode, expr->left, ap);
            numcmd += add_cmd(ctx, a, bcode, expr->right, ap);
            switch(expr->op) {
                case DAVQL_ADD: {
                    cmd.type = DAVQL_CMD_OP_BINARY_ADD;
                    break;
                }
                case DAVQL_SUB: {
                    cmd.type = DAVQL_CMD_OP_BINARY_SUB;
                    break;
                }
                case DAVQL_MUL: {
                    cmd.type = DAVQL_CMD_OP_BINARY_MUL;
                    break;
                }
                case DAVQL_DIV: {
                    cmd.type = DAVQL_CMD_OP_BINARY_DIV;
                    break;
                }
                case DAVQL_AND: {
                    cmd.type = DAVQL_CMD_OP_BINARY_AND;
                    break;
                }
                case DAVQL_OR: {
                    cmd.type = DAVQL_CMD_OP_BINARY_OR;
                    break;
                }
                case DAVQL_XOR: {
                    cmd.type = DAVQL_CMD_OP_BINARY_XOR;
                    break;
                }
                default: break;
            }
            ucx_buffer_write(&cmd, sizeof(cmd), 1, bcode);
            break;
        }
        case DAVQL_LOGICAL: {
            if(expr->left && expr->right && expr->op != DAVQL_LOR) {
                numcmd += add_cmd(ctx, a, bcode, expr->left, ap);
                numcmd += add_cmd(ctx, a, bcode, expr->right, ap);
            }
            
            switch(expr->op) {
                case DAVQL_NOT: {
                    numcmd += add_cmd(ctx, a, bcode, expr->left, ap);
                    cmd.type = DAVQL_CMD_OP_LOGICAL_NOT;
                    ucx_buffer_write(&cmd, sizeof(cmd), 1, bcode);
                    break;
                }
                case DAVQL_LAND: {
                    cmd.type = DAVQL_CMD_OP_LOGICAL_AND;
                    ucx_buffer_write(&cmd, sizeof(cmd), 1, bcode);
                    break;
                }
                case DAVQL_LOR: {
                    int nleft = add_cmd(ctx, a, bcode, expr->left, ap);
                    
                    cmd.type = DAVQL_CMD_OP_LOGICAL_OR_L;
                    DavQLCmd *or_l = (DavQLCmd*)(bcode->space + bcode->pos);
                    ucx_buffer_write(&cmd, sizeof(cmd), 1, bcode);
                    
                    int nright = add_cmd(ctx, a, bcode, expr->right, ap);
                    or_l->data.integer = nright + 1;
                    
                    cmd.type = DAVQL_CMD_OP_LOGICAL_OR;
                    cmd.data.integer = 0;
                    ucx_buffer_write(&cmd, sizeof(cmd), 1, bcode);
                    
                    numcmd += nleft + nright;
                    break;
                }
                case DAVQL_LXOR: {
                    cmd.type = DAVQL_CMD_OP_LOGICAL_XOR;
                    ucx_buffer_write(&cmd, sizeof(cmd), 1, bcode);
                    break;
                }
                case DAVQL_EQ: {
                    cmd.type = DAVQL_CMD_OP_EQ;
                    ucx_buffer_write(&cmd, sizeof(cmd), 1, bcode);
                    break;
                }
                case DAVQL_NEQ: {
                    cmd.type = DAVQL_CMD_OP_NEQ;
                    ucx_buffer_write(&cmd, sizeof(cmd), 1, bcode);
                    break;
                }
                case DAVQL_LT: {
                    cmd.type = DAVQL_CMD_OP_LT;
                    ucx_buffer_write(&cmd, sizeof(cmd), 1, bcode);
                    break;
                }
                case DAVQL_GT: {
                    cmd.type = DAVQL_CMD_OP_GT;
                    ucx_buffer_write(&cmd, sizeof(cmd), 1, bcode);
                    break;
                }
                case DAVQL_LE: {
                    cmd.type = DAVQL_CMD_OP_LE;
                    ucx_buffer_write(&cmd, sizeof(cmd), 1, bcode);
                    break;
                }
                case DAVQL_GE: {
                    cmd.type = DAVQL_CMD_OP_GE;
                    ucx_buffer_write(&cmd, sizeof(cmd), 1, bcode);
                    break;
                }
                case DAVQL_LIKE: {
                    cmd.type = DAVQL_CMD_OP_LIKE;
                    ucx_buffer_write(&cmd, sizeof(cmd), 1, bcode);
                    break;
                }
                case DAVQL_UNLIKE: {
                    cmd.type = DAVQL_CMD_OP_UNLIKE;
                    ucx_buffer_write(&cmd, sizeof(cmd), 1, bcode);
                    break;
                }
                default: break;
            }
            break;
        }
        case DAVQL_FUNCCALL: {
            switch(expr->op) {
                case DAVQL_CALL: {
                    int nright = add_cmd(ctx, a, bcode, expr->right, ap);
                    // TODO: count args
                    DavQLExpression *funcid = expr->left;
                    if(!funcid && funcid->type != DAVQL_IDENTIFIER) {
                        // fail
                        return -1;
                    }
                    
                    // numargs
                    cmd.type = DAVQL_CMD_INT;
                    cmd.data.integer = count_func_args(expr);
                    ucx_buffer_write(&cmd, sizeof(cmd), 1, bcode);
                    
                    // TODO: resolve function name
                    cmd.type = DAVQL_CMD_CALL;
                    cmd.data.func = NULL;
                    ucx_buffer_write(&cmd, sizeof(cmd), 1, bcode);
                    
                    numcmd = 2;
                    numcmd += nright;
                    break;
                }
                case DAVQL_ARGLIST: {
                    numcmd = 0;
                    numcmd += add_cmd(ctx, a, bcode, expr->left, ap);
                    numcmd += add_cmd(ctx, a, bcode, expr->right, ap);
                    break;
                }
                default: break;
            }
            break;
        }
    }
    return numcmd;
}

UcxBuffer* dav_compile_expr(DavContext *ctx, UcxAllocator *a, DavQLExpression *lexpr, DavQLArgList  *ap) {
    UcxBuffer *bcode = ucx_buffer_new(NULL, 512, UCX_BUFFER_AUTOEXTEND);
    if(!bcode) {
        return NULL;
    }
    
    if(add_cmd(ctx, a, bcode, lexpr, ap) <= 0) {
        ucx_buffer_free(bcode);
        return NULL;
    }
    
    return bcode;
}

static int cmd_str_cmp(DavQLStackObj obj1, DavQLStackObj obj2, davqlcmdtype_t cmd) {
    sstr_t s1 = obj1.type == 1 ?
        sstrn(obj1.data.string, obj1.length) :
        ucx_sprintf("%" PRId64, obj1.data.integer);
    sstr_t s2 = obj1.type == 1 ?
        sstrn(obj2.data.string, obj2.length) :
        ucx_sprintf("%" PRId64, obj2.data.integer);
    
    int res = 0;
    switch(cmd) {
        case DAVQL_CMD_OP_EQ: {
            res = sstrcmp(s1, s2) == 0;
            break;
        }
        case DAVQL_CMD_OP_NEQ: {
            res = sstrcmp(s1, s2) != 0;
            break;
        }
        case DAVQL_CMD_OP_LT: {
            res = sstrcmp(s1, s2) < 0;
            break;
        }
        case DAVQL_CMD_OP_GT: {
            res = sstrcmp(s1, s2) > 0;
            break;
        }
        case DAVQL_CMD_OP_LE: {
            res  = sstrcmp(s1, s2) <= 0;
            break;
        }
        case DAVQL_CMD_OP_GE: {
            res = sstrcmp(s1, s2) >= 0;
            break;
        }
        default: break;
    }
    
    if(obj1.type == 0) {
        free(s1.ptr);
    }
    if(obj2.type == 0) {
        free(s2.ptr);
    }
    
    return res;
}

int dav_exec_expr(UcxBuffer *bcode, DavResource *res, DavQLStackObj *result) {
    if(!bcode) {
        result->type = 0;
        result->length = 0;
        result->data.integer = 1;
        return 0;
    }
    
    size_t count = bcode->pos / sizeof(DavQLCmd);
    DavQLCmd *cmds = (DavQLCmd*)bcode->space;
    
    // create execution stack
    size_t stsize = 64;
    size_t stpos = 0;
    DavQLStackObj *stack = calloc(stsize, sizeof(DavQLStackObj));
#define DAVQL_PUSH(obj) \
        if(stpos == stsize) { \
            stsize += 64; \
            DavQLStackObj *stack_newptr; \
            stack_newptr = realloc(stack, stsize * sizeof(DavQLStackObj)); \
            if(stack_newptr) { \
                stack = stack_newptr; \
            } else { \
                free(stack); \
                return -1; \
            }\
        } \
        stack[stpos++] = obj;
#define DAVQL_PUSH_INT(intval) \
        { \
            DavQLStackObj intobj; \
            intobj.type = 0; \
            intobj.length = 0; \
            intobj.data.integer = intval; \
            DAVQL_PUSH(intobj); \
        }
#define DAVQL_POP() stack[--stpos]
    
    DavQLStackObj obj;
    int ret = 0;
    for(size_t i=0;i<count;i++) {
        DavQLCmd cmd = cmds[i];
        switch(cmd.type) {
            case DAVQL_CMD_INT: {
                //printf("int %lld\n", cmd.data.integer);
                obj.type = 0;
                obj.length = 0;
                obj.data.integer = cmd.data.integer;
                DAVQL_PUSH(obj);
                break;
            }
            case DAVQL_CMD_STRING: {
                //printf("string \"%.*s\"\n", cmd.data.string.length, cmd.data.string.ptr);
                obj.type = 1;
                obj.length = cmd.data.string.length;
                obj.data.string = cmd.data.string.ptr;
                DAVQL_PUSH(obj);
                break;
            }
            case DAVQL_CMD_TIMESTAMP: {
                //printf("timestamp %d\n", cmd.data.timestamp);
                obj.type = 0;
                obj.length = 0;
                obj.data.integer = (int64_t)cmd.data.timestamp;
                DAVQL_PUSH(obj);
                break;
            }
            case DAVQL_CMD_RES_IDENTIFIER: {
                //char *rid[8] = {"name", "path", "href", "contentlength", "contenttype", "creationdate", "lastmodified", "iscollection"};
                //printf("resprop %s\n", rid[cmd.data.resprop]);
                switch(cmd.data.resprop) {
                    case DAVQL_RES_NAME: {
                        obj.type = 1;
                        obj.length = strlen(res->name);
                        obj.data.string = res->name;
                        break;
                    }
                    case DAVQL_RES_PATH: {
                        obj.type = 1;
                        obj.length = strlen(res->path);
                        obj.data.string = res->path;
                        break;
                    }
                    case DAVQL_RES_HREF: {
                        obj.type = 1;
                        obj.length = strlen(res->href);
                        obj.data.string = res->href;
                        break;
                    }
                    case DAVQL_RES_CONTENTLENGTH: {
                        obj.type = 0;
                        obj.length = 0;
                        obj.data.integer = res->contentlength;
                        break;
                    }
                    case DAVQL_RES_CONTENTTYPE: {
                        obj.type = 1;
                        obj.length = strlen(res->contenttype);
                        obj.data.string = res->contenttype;
                        break;
                    }
                    case DAVQL_RES_CREATIONDATE: {
                        obj.type = 0;
                        obj.length = 0;
                        obj.data.integer = res->creationdate;
                        break;
                    }
                    case DAVQL_RES_LASTMODIFIED: {
                        obj.type = 0;
                        obj.length = 0;
                        obj.data.integer = res->lastmodified;
                        break;
                    }
                    case DAVQL_RES_ISCOLLECTION: {
                        obj.type = 0;
                        obj.length = 0;
                        obj.data.integer = res->iscollection;
                        break;
                    }
                }
                DAVQL_PUSH(obj);
                break;
            }
            case DAVQL_CMD_PROP_IDENTIFIER: {
                //printf("property %s:%s\n", cmd.data.property.ns, cmd.data.property.name);
                //char *value = dav_get_string_property_ns(res, cmd.data.property.ns, cmd.data.property.name);
                DavXmlNode *value = dav_get_property_ns(res, cmd.data.property.ns, cmd.data.property.name);
                if(dav_xml_isstring(value)) {
                    obj.type = 1;
                    obj.length = (uint32_t)value->contentlength;
                    obj.data.string = value->content;
                } else {
                    obj.type = 2;
                    obj.length = 0;
                    obj.data.node = value;
                }
                DAVQL_PUSH(obj);
                break;
            }
            //case DAVQL_CMD_OP_UNARY_ADD: {
            //    printf("uadd\n");
            //    break;
            //}
            case DAVQL_CMD_OP_UNARY_SUB: {
                //printf("usub\n");
                obj = DAVQL_POP();
                if(obj.type == 0) {
                    obj.data.integer = -obj.data.integer;
                    DAVQL_PUSH(obj);
                } else {
                    ret = -1;
                    i = count; // end loop
                }
                break;
            }
            case DAVQL_CMD_OP_UNARY_NEG: {
                //printf("uneg\n");
                obj = DAVQL_POP();
                if(obj.type == 0) {
                    obj.data.integer = obj.data.integer == 0 ? 1 : 0;
                    DAVQL_PUSH(obj);
                } else {
                    ret = -1;
                    i = count; // end loop
                }
                break;
            }
            case DAVQL_CMD_OP_BINARY_ADD: {
                //printf("add\n");
                DavQLStackObj obj2 = DAVQL_POP();
                DavQLStackObj obj1 = DAVQL_POP();
                if(obj1.type == 0 && obj2.type == 0) {
                    DAVQL_PUSH_INT(obj1.data.integer + obj2.data.integer);
                } else {
                    // TODO: string concat
                }
                break;
            }
            case DAVQL_CMD_OP_BINARY_SUB: {
                //printf("sub\n");
                DavQLStackObj obj2 = DAVQL_POP();
                DavQLStackObj obj1 = DAVQL_POP();
                if(obj1.type == 0 && obj2.type == 0) {
                    DAVQL_PUSH_INT(obj1.data.integer - obj2.data.integer);
                } else {
                    // error
                    ret = -1;
                    i = count; // end loop
                }
                break;
            }
            case DAVQL_CMD_OP_BINARY_MUL: {
                //printf("mul\n");
                DavQLStackObj obj2 = DAVQL_POP();
                DavQLStackObj obj1 = DAVQL_POP();
                if(obj1.type == 0 && obj2.type == 0) {
                    DAVQL_PUSH_INT(obj1.data.integer * obj2.data.integer);
                } else {
                    // error
                    ret = -1;
                    i = count; // end loop
                }
                break;
            }
            case DAVQL_CMD_OP_BINARY_DIV: {
                //printf("div\n");
                DavQLStackObj obj2 = DAVQL_POP();
                DavQLStackObj obj1 = DAVQL_POP();
                if(obj1.type == 0 && obj2.type == 0) {
                    DAVQL_PUSH_INT(obj1.data.integer / obj2.data.integer);
                } else {
                    // error
                    ret = -1;
                    i = count; // end loop
                }
                break;
            }
            case DAVQL_CMD_OP_BINARY_AND: {
                //printf("and\n");
                DavQLStackObj obj2 = DAVQL_POP();
                DavQLStackObj obj1 = DAVQL_POP();
                if(obj1.type == 0 && obj2.type == 0) {
                    DAVQL_PUSH_INT(obj1.data.integer & obj2.data.integer);
                } else {
                    // error
                    ret = -1;
                    i = count; // end loop
                }
                break;
            }
            case DAVQL_CMD_OP_BINARY_OR: {
                //printf("or\n");
                DavQLStackObj obj2 = DAVQL_POP();
                DavQLStackObj obj1 = DAVQL_POP();
                if(obj1.type == 0 && obj2.type == 0) {
                    DAVQL_PUSH_INT(obj1.data.integer | obj2.data.integer);
                } else {
                    // error
                    ret = -1;
                    i = count; // end loop
                }
                break;
            }
            case DAVQL_CMD_OP_BINARY_XOR: {
                //printf("xor\n");
                DavQLStackObj obj2 = DAVQL_POP();
                DavQLStackObj obj1 = DAVQL_POP();
                if(obj1.type == 0 && obj2.type == 0) {
                    DAVQL_PUSH_INT(obj1.data.integer ^ obj2.data.integer);
                } else {
                    // error
                    ret = -1;
                    i = count; // end loop
                }
                break;
            }
            case DAVQL_CMD_OP_LOGICAL_NOT: {
                //printf("not\n");
                break;
            }
            case DAVQL_CMD_OP_LOGICAL_AND: {
                //printf("land\n");
                DavQLStackObj obj2 = DAVQL_POP();
                DavQLStackObj obj1 = DAVQL_POP();
                int v1 = obj1.type == 0 ? (int)obj1.data.integer : (obj1.data.string ? 1 : 0);
                int v2 = obj2.type == 0 ? (int)obj2.data.integer : (obj2.data.string ? 1 : 0);
                DAVQL_PUSH_INT(v1 && v2);
                break;
            }
            case DAVQL_CMD_OP_LOGICAL_OR_L: {
                //printf("or_l %d\n", cmd.data.integer);
                DavQLStackObj obj1 = stack[stpos];
                if((obj1.type == 0 && obj1.data.integer) || (obj1.type == 1 && obj1.data.string)) {
                    stpos--;
                    DAVQL_PUSH_INT(1);
                    i += cmd.data.integer; // jump, skip right subtree of 'or'
                }
                break;
            }
            case DAVQL_CMD_OP_LOGICAL_OR: {
                //printf("or\n");
                DavQLStackObj obj2 = DAVQL_POP();
                DavQLStackObj obj1 = DAVQL_POP();
                int v1 = obj1.type == 0 ? (int)obj1.data.integer : (obj1.data.string ? 1 : 0);
                int v2 = obj2.type == 0 ? (int)obj2.data.integer : (obj2.data.string ? 1 : 0);
                DAVQL_PUSH_INT(v1 || v2);
                break;
            }
            case DAVQL_CMD_OP_LOGICAL_XOR: {
                //printf("lxor\n");
                DavQLStackObj obj2 = DAVQL_POP();
                DavQLStackObj obj1 = DAVQL_POP();
                int v1 = obj1.type == 0 ? (int)obj1.data.integer : (obj1.data.string ? 1 : 0);
                int v2 = obj2.type == 0 ? (int)obj2.data.integer : (obj2.data.string ? 1 : 0);
                DAVQL_PUSH_INT(!v1 != !v2);
                break;
            }
            case DAVQL_CMD_OP_EQ: {
                //printf("eq\n");
                DavQLStackObj obj2 = DAVQL_POP();
                DavQLStackObj obj1 = DAVQL_POP();
                if(obj1.type == 0 && obj2.type == 0) {
                    DAVQL_PUSH_INT(obj1.data.integer == obj2.data.integer);
                } else {
                    DAVQL_PUSH_INT(cmd_str_cmp(obj1, obj2, cmd.type));
                }
                break;
            }
            case DAVQL_CMD_OP_NEQ: {
                //printf("neq\n");
                DavQLStackObj obj2 = DAVQL_POP();
                DavQLStackObj obj1 = DAVQL_POP();
                if(obj1.type == 0 && obj2.type == 0) {
                    DAVQL_PUSH_INT(obj1.data.integer != obj2.data.integer);
                } else {
                    DAVQL_PUSH_INT(cmd_str_cmp(obj1, obj2, cmd.type));
                }
                break;
            }
            case DAVQL_CMD_OP_LT: {
                //printf("lt\n");
                DavQLStackObj obj2 = DAVQL_POP();
                DavQLStackObj obj1 = DAVQL_POP();
                if(obj1.type == 0 && obj2.type == 0) {
                    DAVQL_PUSH_INT(obj1.data.integer < obj2.data.integer);
                } else {
                    DAVQL_PUSH_INT(cmd_str_cmp(obj1, obj2, cmd.type));
                }
                break;
            }
            case DAVQL_CMD_OP_GT: {
                //printf("gt\n");
                DavQLStackObj obj2 = DAVQL_POP();
                DavQLStackObj obj1 = DAVQL_POP();
                if(obj1.type == 0 && obj2.type == 0) {
                    DAVQL_PUSH_INT(obj1.data.integer > obj2.data.integer);
                } else {
                    DAVQL_PUSH_INT(cmd_str_cmp(obj1, obj2, cmd.type));
                }
                break;
            }
            case DAVQL_CMD_OP_LE: {
                //printf("le\n");
                DavQLStackObj obj2 = DAVQL_POP();
                DavQLStackObj obj1 = DAVQL_POP();
                if(obj1.type == 0 && obj2.type == 0) {
                    DAVQL_PUSH_INT(obj1.data.integer <= obj2.data.integer);
                } else {
                    DAVQL_PUSH_INT(cmd_str_cmp(obj1, obj2, cmd.type));
                }
                break;
            }
            case DAVQL_CMD_OP_GE: {
                //printf("ge\n");
                DavQLStackObj obj2 = DAVQL_POP();
                DavQLStackObj obj1 = DAVQL_POP();
                if(obj1.type == 0 && obj2.type == 0) {
                    DAVQL_PUSH_INT(obj1.data.integer >= obj2.data.integer);
                } else {
                    DAVQL_PUSH_INT(cmd_str_cmp(obj1, obj2, cmd.type));
                }
                break;
            }
            case DAVQL_CMD_OP_LIKE: {
                //printf("like\n");
                break;
            }
            case DAVQL_CMD_OP_UNLIKE: {
                //printf("unlike\n");
                break;
            }
            case DAVQL_CMD_CALL: {
                //printf("call %x\n", cmd.data.func);
                break;
            }
        }
    }
    
    if(stpos == 1) {
        *result = stack[0];
    } else {
        ret = -1;
    }
    free(stack);
    
    return ret;
}