libidav/utils.c

/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 *
 * Copyright 2019 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 <time.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <ctype.h>
#include <ucx/string.h>
#include <ucx/buffer.h>
#include <ucx/utils.h>
#include <libxml/tree.h>
#include <curl/curl.h>

#ifdef _WIN32
#include <conio.h>
#define getpasswordchar() getch()
#else
#include <termios.h>
#define getpasswordchar() getchar()
#endif

#include "webdav.h"
#include "utils.h"
#include "crypto.h"
#include "session.h"

/*
#include <openssl/hmac.h>
#include <openssl/evp.h>
#include <openssl/bio.h>
#include <openssl/buffer.h>
#include <openssl/rand.h>
*/

static size_t extractval(sstr_t str, char *result, char delim) {
    size_t n = 0;
    for(size_t i = 0; i < str.length ; i++) {
        if(isdigit(str.ptr[i])) {
            result[n++] = str.ptr[i];
        } else if(str.ptr[i] != delim) {
            return 0;
        }
    }
    result[n] = '\0';
    return n;
}

static time_t parse_iso8601(char *iso8601str) {

    // safety
    if(!iso8601str) {
        return 0;
    }
    
    // local vars
    struct tm tparts;
    memset(&tparts, 0, sizeof(struct tm));
    long val;
    char conv[16];
    
    // work on the trimmed string
    sstr_t date = sstrtrim(sstr(iso8601str));

    sstr_t time = sstrchr(date, 'T');
    if(time.length == 0) {
        return 0;
    }
    date.length = time.ptr - date.ptr;
    time.ptr++; time.length--;
    
    sstr_t tzinfo;
    if((tzinfo = sstrchr(time, 'Z')).length > 0 ||
        (tzinfo = sstrchr(time, '+')).length > 0 ||
        (tzinfo = sstrchr(time, '-')).length > 0) {
        
        time.length = tzinfo.ptr - time.ptr;
    }

    // parse date
    if((date.length != 8 && date.length != 10)
            || extractval(date, conv , '-') != 8) {
        return 0;
    }
    val = atol(conv);
    if(val < 19000000L) {
        return 0;
    }
    tparts.tm_mday = val % 100;
    tparts.tm_mon = (val % 10000) / 100 - 1;
    tparts.tm_year = val / 10000 - 1900;
    
    // parse time and skip possible fractional seconds
    sstr_t frac;
    if((frac = sstrchr(time, '.')).length > 0 ||
        (frac = sstrchr(time, ',')).length > 0) {
        time.length = frac.ptr - time.ptr;
    }
    if((time.length != 6 && time.length != 8)
            || extractval(time, conv , ':') != 6) {
        return 0;
    }
    val = atol(conv);
    tparts.tm_sec = val % 100;
    tparts.tm_min = (val % 10000) / 100;
    tparts.tm_hour = val / 10000;


    // parse time zone (if any)
    if(tzinfo.length == 0) {
        // local time
        tparts.tm_isdst = -1;
        return mktime(&tparts);
    } else if(!sstrcmp(tzinfo, S("Z"))) {
#ifdef __FreeBSD__
        return timegm(&tparts);
#else
        return mktime(&tparts) - timezone;
#endif
    } else if(tzinfo.ptr[0] == '+' || tzinfo.ptr[0] == '-') {
        int sign = (tzinfo.ptr[0] == '+') ? -1 : 1;

        if(tzinfo.length > 6) {
            return 0;
        } else {
            tzinfo.ptr++; tzinfo.length--;
            extractval(tzinfo, conv, ':');
            val = atol(conv);
            val = 60 * (val / 100) + (val % 100);
#ifdef __FreeBSD__
            return timegm(&tparts) + (time_t) (60 * val * sign);
#else
            return mktime(&tparts) - timezone + (time_t) (60 * val * sign);            
#endif
        }
    } else {
        return 0;
    }
}


time_t util_parse_creationdate(char *str) {
    // parse a ISO-8601 date (rfc-3339)
    // example: 2012-11-29T21:35:35Z
    if(!str) {
        return 0;
    }
    
    return parse_iso8601(str);
}

time_t util_parse_lastmodified(char *str) {
    // parse a rfc-1123 date
    // example: Thu, 29 Nov 2012 21:35:35 GMT
    if(!str) {
        return 0;
    } else {
        time_t result = curl_getdate(str, NULL);
        if(result == -1) {
            // fall back to the ISO-8601 format (e.g. Microsoft Sharepoint
            // illegally uses this format for lastmodified, but also some
            // users might want to give an ISO-8601 date)
            return util_parse_creationdate(str);
        } else {
            return result;
        }
    }
}

int util_getboolean(const char *v) {
    if(v[0] == 'T' || v[0] == 't') {
        return 1;
    }
    return 0;
}

int util_strtouint(const char *str, uint64_t *value) {
    char *end;
    errno = 0;
    uint64_t val = strtoull(str, &end, 0);
    if(errno == 0) {
        *value = val;
        return 1;
    } else {
        return 0;
    }
}

int util_strtoint(const char *str, int64_t *value) {
    char *end;
    errno = 0;
    int64_t val = strtoll(str, &end, 0);
    if(errno == 0) {
        *value = val;
        return 1;
    } else {
        return 0;
    }
}

int util_szstrtouint(const char *str, uint64_t *value) {
    char *end;
    errno = 0;
    size_t len = strlen(str);
    uint64_t val = strtoull(str, &end, 0);
    if(end == str+len) {
        *value = val;
        return 1;
    } else if(end == str+len-1) {
        uint64_t mul = 1;
        switch(end[0]) {
            case 'k':
            case 'K': mul = 1024; break;
            case 'm':
            case 'M': mul = 1024*1024; break;
            case 'g':
            case 'G': mul = 1024*1024*1024; break;
            default: return 0;
        }
        
        uint64_t result = 0;
        if(util_uint_mul(val, mul, &result)) {
            return 0;
        }
        *value = result;
        return 1;
    }
    return 0;
}

int util_uint_mul(uint64_t a, uint64_t b, uint64_t *result) {
    if(a == 0 || b == 0) {
        *result = 0;
        return 0;
    }
    uint64_t r = a * b;
    if(r / b == a) {
        *result = r;
        return 0;
    } else {
        *result = 0;
        return 1;
    }
}

char* util_url_base(char *url) {
    sstr_t u = sstr(url);
    int len = u.length;
    int slashcount = 0;
    int slmax;
    if(len > 7 && !strncasecmp(url, "http://", 7)) {
        slmax = 3;
    } else if(len > 8 && !strncasecmp(url, "https://", 8)) {
        slmax = 3;
    } else {
        slmax = 1;
    }
    char c;
    int i = 0;
    for(i=0;i<len;i++) {
        c = url[i];
        if(c == '/') {
            slashcount++;
            if(slashcount == slmax) {
                i++;
                break;
            }
        }
    } 
    sstr_t server = sstrsubsl(u, 0, i);
    server = sstrdup(server);
    return server.ptr;
}

char* util_url_path(char *url) { 
    char *path = NULL;
    size_t len = strlen(url);
    int slashcount = 0;
    int slmax;
    if(len > 7 && !strncasecmp(url, "http://", 7)) {
        slmax = 3;
    } else if(len > 8 && !strncasecmp(url, "https://", 8)) {
        slmax = 3;
    } else {
        slmax = 1;
    }
    char c;
    for(int i=0;i<len;i++) {
        c = url[i];
        if(c == '/') {
            slashcount++;
            if(slashcount == slmax) {
                path = url + i;
                break;
            }
        }
    } 
    if(!path) {
        path = url + len; // empty string
    }
    return path;
}

char* util_url_decode(DavSession *sn, char *url) {
    char *unesc = curl_easy_unescape(sn->handle, url, strlen(url), NULL);
    char *ret = strdup(unesc);
    curl_free(unesc);
    return ret;
}

static size_t util_header_callback(char *buffer, size_t size,
        size_t nitems, void *data) {
    
    sstr_t sbuffer = sstrn(buffer, size*nitems);
    
    UcxMap *map = (UcxMap*) data;
    
    // if we get a status line, clear the map and exit
    if(sstrprefix(sbuffer, S("HTTP/"))) {
        ucx_map_free_content(map, free);
        ucx_map_clear(map);
        return size*nitems;
    }
    
    // if we get the terminating CRLF, just exit
    if(!sstrcmp(sbuffer, S("\r\n"))) {
        return 2;
    }
    
    sstr_t key = sbuffer;
    sstr_t value = sstrchr(sbuffer, ':');
    
    if(value.length == 0) {
        return 0; // invalid header line
    }
    
    key.length = value.ptr - key.ptr;
    value.ptr++; value.length--;
    
    key = sstrlower(sstrtrim(key));
    value = sstrdup(sstrtrim(value));
        
    ucx_map_sstr_put(map, key, value.ptr);
    
    free(key.ptr);
    
    return sbuffer.length;
}

int util_path_isrelated(const char *path1, const char *path2) {
    scstr_t p1 = scstr(path1);
    scstr_t p2 = scstr(path2);
    
    if(p1.ptr[p1.length-1] == '/') {
        p1.length--;
    }
    if(p2.ptr[p2.length-1] == '/') {
        p2.length--;
    }
    
    if(p2.length < p1.length) {
        return 0;
    }
    
    if(!sstrcmp(p1, p2)) {
        return 1;
    }
    
    if(sstrprefix(p2, p1)) {
        if(p2.ptr[p1.length] == '/') {
            return 1;
        }
    }
    
    return 0;
}

char* util_path_normalize(const char *path) {
    size_t len = strlen(path);
    UcxBuffer *buf = ucx_buffer_new(NULL, len+1, UCX_BUFFER_AUTOEXTEND);
    
    if(path[0] == '/') {
        ucx_buffer_putc(buf, '/');
    }
    
    int add_separator = 0;
    int seg_start = 0;
    for(int i=0;i<=len;i++) {
        char c = path[i];
        if(c == '/' || c == '\0') {
            const char *seg_ptr = path+seg_start;
            int seg_len = i - seg_start;
            if(seg_ptr[0] == '/') {
                seg_ptr++;
                seg_len--;
            }
            
            if(seg_len > 0) {
                scstr_t seg = scstrn(seg_ptr, seg_len);
                if(!sstrcmp(seg, SC(".."))) {
                    for(int j=buf->pos;j>=0;j--) {
                        char t = buf->space[j];
                        if(t == '/' || j == 0) {
                            buf->pos = j;
                            buf->size = j;
                            buf->space[j] = 0;
                            add_separator = t == '/' ? 1 : 0;
                            break;
                        }
                    }
                } else if(!sstrcmp(seg, SC("."))) {
                    // ignore
                } else {
                    if(add_separator) {
                        ucx_buffer_putc(buf, '/');
                    }
                    ucx_buffer_write(seg_ptr, 1, seg_len, buf);
                    add_separator = 1;
                }
            }
            
            seg_start = i;
        }
    }
    
    ucx_buffer_putc(buf, 0);
    
    
    char *space = buf->space;
    buf->flags = 0; // disable autofree
    ucx_buffer_free(buf);
    return space;
}

char* util_create_relative_path(const char *abspath, const char *base) {
    size_t path_len = strlen(abspath);
    size_t base_len = strlen(base);
    
    if(abspath[path_len-1] == '/') {
        path_len--;
    }
    if(base[base_len-1] == '/') {
        base_len--;
    }
    // get base parent
    for(int i=base_len-1;i>=0;i--) {
        if(base[i] == '/') {
            base_len = i+1;
            break;
        }
    }
    
    size_t max = path_len > base_len ? base_len : path_len;
    
    // get prefix of abspath and base
    // this dir is the root of the link
    size_t i;
    size_t last_dir = 0;
    for(i=0;i<max;i++) {
        char c = abspath[i];
        if(c != base[i]) {
            break;
        } else if(c == '/') {
            last_dir = i;
        }
    }
    
    char *ret = NULL;
    UcxBuffer *out = NULL;
    if(last_dir+1 < base_len) {
        // base is deeper than the link root, we have to go backwards
        int dircount = 0;
        for(int i=last_dir+1;i<base_len;i++) {
            if(base[i] == '/') {
                dircount++;
            }
        }
        
        out = ucx_buffer_new(NULL, dircount*3+path_len-last_dir, UCX_BUFFER_AUTOEXTEND);
        
        for(int i=0;i<dircount;i++) {
            ucx_buffer_puts(out, "../");
        }
    } else {
        out = ucx_buffer_new(NULL, 1024, path_len - last_dir);
    }
    
    ucx_buffer_puts(out, abspath + last_dir + 1);
    ucx_buffer_putc(out, 0);
    out->flags = 0;
    ret = out->space;
    ucx_buffer_free(out);
    
    return ret;
}


void util_capture_header(CURL *handle, UcxMap* map) {
    if(map) {
        curl_easy_setopt(handle, CURLOPT_HEADERFUNCTION, util_header_callback);
        curl_easy_setopt(handle, CURLOPT_HEADERDATA, map);
    } else {
        curl_easy_setopt(handle, CURLOPT_HEADERFUNCTION, NULL);
        curl_easy_setopt(handle, CURLOPT_HEADERDATA, NULL);
    }
}

char* util_resource_name(char *url) {
    sstr_t urlstr = sstr(url);
    if(urlstr.ptr[urlstr.length-1] == '/') {
        urlstr.length--;
    }
    sstr_t resname = sstrrchr(urlstr, '/');
    if(resname.length > 1) {
        return resname.ptr+1;
    } else {
        return url;
    }
}

int util_mkdir(char *path, mode_t mode) {
#ifdef _WIN32
    return mkdir(path);
#else
    return mkdir(path, mode);
#endif
}

char* util_concat_path(const char *url_base, const char *p) {
    sstr_t base = sstr((char*)url_base);
    sstr_t path;
    if(p) {
        path = sstr((char*)p);
    } else {
        path = sstrn("", 0);
    }
    
    int add_separator = 0;
    if(base.length != 0 && base.ptr[base.length-1] == '/') {
        if(path.ptr[0] == '/') {
            base.length--;
        }
    } else {
        if(path.length == 0 || path.ptr[0] != '/') {
            add_separator = 1;
        }
    }
    
    sstr_t url;
    if(add_separator) {
        url = sstrcat(3, base, sstr("/"), path);
    } else {
        url = sstrcat(2, base, path);
    }
    
    return url.ptr;
}

char* util_get_url(DavSession *sn, const char *href) {
    scstr_t base = scstr(sn->base_url);
    scstr_t href_str = scstr(href);
    
    char *base_path = util_url_path(sn->base_url);
    base.length -= strlen(base_path);
    
    sstr_t url = sstrcat(2, base, href_str);
    return url.ptr;
}

void util_set_url(DavSession *sn, const char *href) {
    char *url = util_get_url(sn, href);
    curl_easy_setopt(sn->handle, CURLOPT_URL, url);
    free(url);
}

char* util_path_to_url(DavSession *sn, char *path) {
    char *space = malloc(256);
    UcxBuffer *url = ucx_buffer_new(space, 256, UCX_BUFFER_AUTOEXTEND);
    
    // add base url
    ucx_buffer_write(sn->base_url, 1, strlen(sn->base_url), url);
    // remove trailing slash
    ucx_buffer_seek(url, -1, SEEK_CUR);
    
    sstr_t p = sstr(path);
    ssize_t ntk = 0;
    sstr_t *tks = sstrsplit(p, S("/"), &ntk);
    
    for(int i=0;i<ntk;i++) {
        sstr_t node = tks[i];
        if(node.length > 0) {
            char *esc = curl_easy_escape(sn->handle, node.ptr, node.length);
            ucx_buffer_putc(url, '/');
            ucx_buffer_write(esc, 1, strlen(esc), url);
            curl_free(esc);
        }
        free(node.ptr);
    }
    free(tks);
    if(path[p.length-1] == '/') {
        ucx_buffer_putc(url, '/');
    }
    ucx_buffer_putc(url, 0);
    
    space = url->space;
    ucx_buffer_free(url);
    
    return space;
}

char* util_parent_path(const char *path) {
    char *name = util_resource_name((char*)path);
    size_t namelen = strlen(name);
    size_t pathlen = strlen(path);
    size_t parentlen = pathlen - namelen;
    char *parent = malloc(parentlen + 1);
    memcpy(parent, path, parentlen);
    parent[parentlen] = '\0';
    return parent;
}


char* util_xml_get_text(const xmlNode *elm) {
    xmlNode *node = elm->children;
    while(node) {
        if(node->type == XML_TEXT_NODE) {
            return (char*)node->content;
        }
        node = node->next;
    }
    return NULL;
}


char* util_base64decode(const char *in) {
    int len = 0;
    return util_base64decode_len(in, &len);
}

#define WHITESPACE 64
#define EQUALS     65
#define INVALID    66
static char b64dectable[] = {
    66,66,66,66,66,66,66,66,66,66,64,66,66,66,66,66,66,66,66,66,66,66,66,66,66,
    66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,62,66,66,66,63,52,53,
    54,55,56,57,58,59,60,61,66,66,66,65,66,66,66, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
    10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,66,66,66,66,66,66,26,27,28,
    29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,66,66,
    66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,
    66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,
    66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,
    66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,
    66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,
    66,66,66,66,66,66
};
char* util_base64decode_len(const char* in, int *outlen) {
    /* code is mostly from wikibooks */
    
    if(!in) {
        *outlen = 0;
        return NULL;
    }
    
    size_t inlen = strlen(in);
    size_t bufsize = (inlen*3) / 4;
    char *outbuf = malloc(bufsize+1);
    *outlen = -1;
    
    unsigned char *out = (unsigned char*)outbuf;
    
    const char *end = in + inlen;
    char iter = 0;
    uint32_t buf = 0;
    size_t len = 0;
    
    while (in < end) {
        unsigned char c = b64dectable[*in++];
        
        switch (c) {
            case WHITESPACE: continue; /* skip whitespace */
            case INVALID: {
                  /* invalid input */
                outbuf[0] = 0;
                return outbuf;
            }
            case EQUALS: {
                /* pad character, end of data */
                in = end;
                continue;
            }
            default: {
                buf = buf << 6 | c;
                iter++; // increment the number of iteration
                /* If the buffer is full, split it into bytes */
                if (iter == 4) {
                    if ((len += 3) > bufsize) {
                        /* buffer overflow */
                        outbuf[0] = 0;
                        return outbuf;
                    }
                    *(out++) = (buf >> 16) & 255;
                    *(out++) = (buf >> 8) & 255;
                    *(out++) = buf & 255;
                    buf = 0; iter = 0;

                }
            }
        }
    }
   
    if (iter == 3) {
        if ((len += 2) > bufsize) {
            /* buffer overflow */
            outbuf[0] = 0;
            return outbuf;
        }
        *(out++) = (buf >> 10) & 255;
        *(out++) = (buf >> 2) & 255;
    }
    else if (iter == 2) {
        if (++len > bufsize) {
            /* buffer overflow */
            outbuf[0] = 0;
            return outbuf;
        }
        *(out++) = (buf >> 4) & 255;
    }

    *outlen = len; /* modify to reflect the actual output size */
    outbuf[len] = 0;
    return outbuf;
}


static char* b64enctable = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
char* util_base64encode(const char *in, size_t len) {
    // calculate length of base64 output and create buffer
    size_t outlen = 4 * ((len + 2) / 3);
    int pad = len % 3;
    
    char *out = malloc(outlen + 1);
    out[outlen] = 0;
    size_t pos = 0;
    
    // encode blocks of 3 bytes
    size_t i;
    size_t blockend = len - pad;
    for(i=0;i<blockend;i++) {
        unsigned char b1 = in[i++];
        unsigned char b2 = in[i++];
        unsigned char b3 = in[i];
        uint32_t inb = b1 << 16 | (b2 << 8) | b3;
        out[pos++] = b64enctable[(inb >> 18) & 63];
        out[pos++] = b64enctable[(inb >> 12) & 63];
        out[pos++] = b64enctable[(inb >> 6) & 63];
        out[pos++] = b64enctable[(inb) & 63];
    }
    
    // encode last bytes
    if(pad > 0) {
        char p[3] = {0, 0, 0};
        for(int j=0;i<len;i++) {
            p[j++] = in[i];
        }
        unsigned char b1 = p[0];
        unsigned char b2 = p[1];
        unsigned char b3 = p[2];
        uint32_t inb = (b1 << 16) | (b2 << 8) | b3;
        out[pos++] = b64enctable[(inb >> 18) & 63];
        out[pos++] = b64enctable[(inb >> 12) & 63];
        out[pos++] = b64enctable[(inb >> 6) & 63];
        out[pos++] = b64enctable[(inb) & 63];
        for(int k=outlen-1;k>=outlen-(3-pad);k--) {
            out[k] = '=';
        }
    }
    
    return out;
}

char* util_encrypt_str(DavSession *sn, char *str, char *key) {
    DavKey *k = dav_context_get_key(sn->context, key);
    if(!k) {
        sn->error = DAV_ERROR;
        sstr_t err = ucx_sprintf("Key %s not found", key);
        dav_session_set_errstr(sn, err.ptr);
        free(err.ptr);
        return NULL;
    }
    
    return util_encrypt_str_k(sn, str, k);
}

char* util_encrypt_str_k(DavSession *sn, char *str, DavKey *key) {
    char *enc_str = aes_encrypt(str, strlen(str), key);
    char *ret_str = dav_session_strdup(sn, enc_str);
    free(enc_str);
    return ret_str;
}

char* util_decrypt_str(DavSession *sn, char *str, char *key) {
    DavKey *k = dav_context_get_key(sn->context, key);
    if(!k) {
        sn->error = DAV_ERROR;
        sstr_t err = ucx_sprintf("Key %s not found", key);
        dav_session_set_errstr(sn, err.ptr);
        free(err.ptr);
        return NULL;
    }
    
    return util_decrypt_str_k(sn, str, k);
}

char* util_decrypt_str_k(DavSession *sn, char *str, DavKey *key) {
    size_t len = 0;
    char *dec_str = aes_decrypt(str, &len, key);
    char *ret_str = dav_session_strdup(sn, dec_str);
    free(dec_str);
    return ret_str;
}

char* util_random_str() {
    unsigned char *str = malloc(25);
    str[24] = '\0';
    
    sstr_t t = S(
            "01234567890"
            "abcdefghijklmnopqrstuvwxyz"
            "ABCDEFGHIJKLMNOPQRSTUVWXYZ");
    const unsigned char *table = (const unsigned char*)t.ptr;
    
#ifdef DAV_USE_OPENSSL
    RAND_bytes(str, 24);
#else
    dav_rand_bytes(str, 24);
#endif
    for(int i=0;i<24;i++) {
        int c = str[i] % t.length;
        str[i] = table[c];
    }
    
    return (char*)str;
}

/*
 * gets a substring from 0 to the appearance of the token
 * tokens are separated by space
 * sets sub to the substring and returns the remaining string
 */
sstr_t util_getsubstr_until_token(sstr_t str, sstr_t token, sstr_t *sub) {  
    int i;
    int token_start = -1;
    int token_end = -1;
    for(i=0;i<=str.length;i++) {
        int c;
        if(i == str.length) {
            c = ' ';
        } else {
            c = str.ptr[i];
        }
        if(c < 33) {
            if(token_start != -1) {
                token_end = i;
                size_t len = token_end - token_start;
                sstr_t tk = sstrsubsl(str, token_start, len);
                //printf("token: {%.*s}\n", token.length, token.ptr);
                if(!sstrcmp(tk, token)) {
                    *sub = sstrtrim(sstrsubsl(str, 0, token_start));
                    break;
                }
                token_start = -1;
                token_end = -1;
            }
        } else {
            if(token_start == -1) {
                token_start = i;
            }
        }
    }
    
    if(i < str.length) {
        return sstrtrim(sstrsubs(str, i));
    } else {
        str.ptr = NULL;
        str.length = 0;
        return str;
    }
}

sstr_t util_readline(FILE *stream) {
    UcxBuffer *buf = ucx_buffer_new(NULL, 128, UCX_BUFFER_AUTOEXTEND);
    
    int c;
    while((c = fgetc(stream)) != '\n') {
        ucx_buffer_putc(buf, c);
    }
    
    sstr_t str = sstrdup(sstrtrim(sstrn(buf->space, buf->size)));
    ucx_buffer_free(buf);
    return str;
}

char* util_password_input(char *prompt) {
    fprintf(stderr, "%s", prompt);
    fflush(stderr);
    
#ifndef _WIN32
    // hide terminal input
    struct termios oflags, nflags;
    tcgetattr(fileno(stdin), &oflags);
    nflags = oflags;
    nflags.c_lflag &= ~ECHO;
    nflags.c_lflag |= ECHONL;
    if (tcsetattr(fileno(stdin), TCSANOW, &nflags) != 0) {
        perror("tcsetattr");
    }
#endif
    
    // read password input
    UcxBuffer *buf = ucx_buffer_new(NULL, 128, UCX_BUFFER_AUTOEXTEND);
    int c = 0;
    while((c = getpasswordchar()) != EOF) {
        if(c == '\n' || c == '\r') {
            break;
        }
        ucx_buffer_putc(buf, c);
    }
    ucx_buffer_putc(buf, 0);
    fflush(stdin);
    
#ifndef _WIN32
    // restore terminal settings
    if (tcsetattr(fileno(stdin), TCSANOW, &oflags) != 0) {
        perror("tcsetattr");
    }
#endif
    
    char *str = buf->space;
    free(buf); // only free the UcxBuffer struct
    return str;
}


char* util_hexstr(const unsigned char *data, size_t len) {
    size_t buflen = 2*len + 4;
    UcxBuffer *buf = ucx_buffer_new(malloc(buflen), buflen + 1, 0);
    for(int i=0;i<len;i++) {
        ucx_bprintf(buf, "%x", data[i]);
    }
    ucx_buffer_putc(buf, 0);
    char *str = buf->space;
    ucx_buffer_free(buf);
    return str;
}

void util_remove_trailing_pathseparator(char *path) {
    size_t len = strlen(path);
    if(len < 2) {
        return;
    }
    
    if(path[len-1] == '/') {
        path[len-1] = '\0';
    }
}

char* util_file_hash(const char *path) {
    FILE *in = fopen(path, "r");
    if(!in) {
        return NULL;
    }
    
    DAV_SHA_CTX *sha = dav_hash_init();
    char *buf = malloc(16384);
    
    size_t r;
    while((r = fread(buf, 1, 16384, in)) > 0) {
        dav_hash_update(sha, buf, r);
    }
    
    unsigned char hash[DAV_SHA256_DIGEST_LENGTH];
    dav_hash_final(sha, hash);
    free(buf);
    fclose(in);
    
    return util_hexstr(hash, DAV_SHA256_DIGEST_LENGTH);    
}