srs/trunk/src/kernel/srs_kernel_utility.cpp

/**
 * The MIT License (MIT)
 *
 * Copyright (c) 2013-2018 Winlin
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of
 * this software and associated documentation files (the "Software"), to deal in
 * the Software without restriction, including without limitation the rights to
 * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
 * the Software, and to permit persons to whom the Software is furnished to do so,
 * subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
 * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
 * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
 * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

#include <srs_kernel_utility.hpp>

// for srs-librtmp, @see https://github.com/ossrs/srs/issues/213
#ifndef _WIN32
#include <unistd.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <sys/time.h>
#endif

#include <string.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>

#include <vector>
using namespace std;

#include <srs_core_autofree.hpp>
#include <srs_kernel_log.hpp>
#include <srs_kernel_error.hpp>
#include <srs_kernel_buffer.hpp>
#include <srs_kernel_flv.hpp>

// this value must:
// equals to (SRS_SYS_CYCLE_INTERVAL*SRS_SYS_TIME_RESOLUTION_MS_TIMES)*1000
// @see SRS_SYS_TIME_RESOLUTION_MS_TIMES
#define SYS_TIME_RESOLUTION_US 300*1000

srs_error_t srs_avc_nalu_read_uev(SrsBitBuffer* stream, int32_t& v)
{
    srs_error_t err = srs_success;
    
    if (stream->empty()) {
        return srs_error_new(ERROR_AVC_NALU_UEV, "empty stream");
    }
    
    // ue(v) in 9.1 Parsing process for Exp-Golomb codes
    // ISO_IEC_14496-10-AVC-2012.pdf, page 227.
    // Syntax elements coded as ue(v), me(v), or se(v) are Exp-Golomb-coded.
    //      leadingZeroBits = -1;
    //      for( b = 0; !b; leadingZeroBits++ )
    //          b = read_bits( 1 )
    // The variable codeNum is then assigned as follows:
    //      codeNum = (2<<leadingZeroBits) - 1 + read_bits( leadingZeroBits )
    int leadingZeroBits = -1;
    for (int8_t b = 0; !b && !stream->empty(); leadingZeroBits++) {
        b = stream->read_bit();
    }
    
    if (leadingZeroBits >= 31) {
        return srs_error_new(ERROR_AVC_NALU_UEV, "%dbits overflow 31bits", leadingZeroBits);
    }
    
    v = (1 << leadingZeroBits) - 1;
    for (int i = 0; i < leadingZeroBits; i++) {
        int32_t b = stream->read_bit();
        v += b << (leadingZeroBits - 1 - i);
    }
    
    return err;
}

srs_error_t srs_avc_nalu_read_bit(SrsBitBuffer* stream, int8_t& v)
{
    srs_error_t err = srs_success;
    
    if (stream->empty()) {
        return srs_error_new(ERROR_AVC_NALU_UEV, "empty stream");
    }
    
    v = stream->read_bit();
    
    return err;
}

static int64_t _srs_system_time_us_cache = 0;
static int64_t _srs_system_time_startup_time = 0;

int64_t srs_get_system_time_ms()
{
    if (_srs_system_time_us_cache <= 0) {
        srs_update_system_time_ms();
    }
    
    return _srs_system_time_us_cache / 1000;
}

int64_t srs_get_system_startup_time_ms()
{
    if (_srs_system_time_startup_time <= 0) {
        srs_update_system_time_ms();
    }
    
    return _srs_system_time_startup_time / 1000;
}

int64_t srs_update_system_time_ms()
{
    timeval now;
    
    if (gettimeofday(&now, NULL) < 0) {
        srs_warn("gettimeofday failed, ignore");
        return -1;
    }
    
    // @see: https://github.com/ossrs/srs/issues/35
    // we must convert the tv_sec/tv_usec to int64_t.
    int64_t now_us = ((int64_t)now.tv_sec) * 1000 * 1000 + (int64_t)now.tv_usec;
    
    // for some ARM os, the starttime maybe invalid,
    // for example, on the cubieboard2, the srs_startup_time is 1262304014640,
    // while now is 1403842979210 in ms, diff is 141538964570 ms, 1638 days
    // it's impossible, and maybe the problem of startup time is invalid.
    // use date +%s to get system time is 1403844851.
    // so we use relative time.
    if (_srs_system_time_us_cache <= 0) {
        _srs_system_time_startup_time = _srs_system_time_us_cache = now_us;
        return _srs_system_time_us_cache / 1000;
    }
    
    // use relative time.
    int64_t diff = now_us - _srs_system_time_us_cache;
    diff = srs_max(0, diff);
    if (diff < 0 || diff > 1000 * SYS_TIME_RESOLUTION_US) {
        srs_warn("clock jump, history=%" PRId64 "us, now=%" PRId64 "us, diff=%" PRId64 "us", _srs_system_time_us_cache, now_us, diff);
        // @see: https://github.com/ossrs/srs/issues/109
        _srs_system_time_startup_time += diff;
    }
    
    _srs_system_time_us_cache = now_us;
    srs_info("clock updated, startup=%" PRId64 "us, now=%" PRId64 "us", _srs_system_time_startup_time, _srs_system_time_us_cache);
    
    return _srs_system_time_us_cache / 1000;
}

string srs_dns_resolve(string host, int& family)
{
    addrinfo hints;
    memset(&hints, 0, sizeof(hints));
    hints.ai_family  = family;
    
    addrinfo* r = NULL;
    SrsAutoFree(addrinfo, r);
    
    if(getaddrinfo(host.c_str(), NULL, NULL, &r)) {
        return "";
    }
    
    char saddr[64];
    char* h = (char*)saddr;
    socklen_t nbh = sizeof(saddr);
    const int r0 = getnameinfo(r->ai_addr, r->ai_addrlen, h, nbh, NULL, 0, NI_NUMERICHOST);

    if(!r0) {
       family = r->ai_family;
       return string(saddr);
    }
    return "";
}

void srs_parse_hostport(const string& hostport, string& host, int& port)
{
    const size_t pos = hostport.rfind(":");   // Look for ":" from the end, to work with IPv6.
    if (pos != std::string::npos) {
        const string p = hostport.substr(pos + 1);
        if ((pos >= 1) &&
            (hostport[0]       == '[') &&
            (hostport[pos - 1] == ']')) {
            // Handle IPv6 in RFC 2732 format, e.g. [3ffe:dead:beef::1]:1935
            host = hostport.substr(1, pos - 2);
        } else {
            // Handle IP address
            host = hostport.substr(0, pos);
        }
        port = ::atoi(p.c_str());
    } else {
        host = hostport;
    }
}

string srs_any_address4listener()
{
    int fd = socket(AF_INET6, SOCK_DGRAM, 0);
    
    // socket()
    // A -1 is returned if an error occurs, otherwise the return value is a
    // descriptor referencing the socket.
    if(fd != -1) {
        close(fd);
        return "::";
    }
    
    return "0.0.0.0";
}

void srs_parse_endpoint(string hostport, string& ip, int& port)
{
    const size_t pos = hostport.rfind(":");   // Look for ":" from the end, to work with IPv6.
    if (pos != std::string::npos) {
        if ((pos >= 1) && (hostport[0] == '[') && (hostport[pos - 1] == ']')) {
            // Handle IPv6 in RFC 2732 format, e.g. [3ffe:dead:beef::1]:1935
            ip = hostport.substr(1, pos - 2);
        } else {
            // Handle IP address
            ip = hostport.substr(0, pos);
        }
        
        const string sport = hostport.substr(pos + 1);
        port = ::atoi(sport.c_str());
    } else {
        ip   = srs_any_address4listener();
        port = ::atoi(hostport.c_str());
    }
}

string srs_int2str(int64_t value)
{
    // len(max int64_t) is 20, plus one "+-."
    char tmp[22];
    snprintf(tmp, 22, "%" PRId64, value);
    return tmp;
}

string srs_float2str(double value)
{
    // len(max int64_t) is 20, plus one "+-."
    char tmp[22];
    snprintf(tmp, 22, "%.2f", value);
    return tmp;
}

string srs_bool2switch(bool v) {
    return v? "on" : "off";
}

bool srs_is_little_endian()
{
    // convert to network(big-endian) order, if not equals,
    // the system is little-endian, so need to convert the int64
    static int little_endian_check = -1;
    
    if(little_endian_check == -1) {
        union {
            int32_t i;
            int8_t c;
        } little_check_union;
        
        little_check_union.i = 0x01;
        little_endian_check = little_check_union.c;
    }
    
    return (little_endian_check == 1);
}

string srs_string_replace(string str, string old_str, string new_str)
{
    std::string ret = str;
    
    if (old_str == new_str) {
        return ret;
    }
    
    size_t pos = 0;
    while ((pos = ret.find(old_str, pos)) != std::string::npos) {
        ret = ret.replace(pos, old_str.length(), new_str);
    }
    
    return ret;
}

string srs_string_trim_end(string str, string trim_chars)
{
    std::string ret = str;
    
    for (int i = 0; i < (int)trim_chars.length(); i++) {
        char ch = trim_chars.at(i);
        
        while (!ret.empty() && ret.at(ret.length() - 1) == ch) {
            ret.erase(ret.end() - 1);
            
            // ok, matched, should reset the search
            i = 0;
        }
    }
    
    return ret;
}

string srs_string_trim_start(string str, string trim_chars)
{
    std::string ret = str;
    
    for (int i = 0; i < (int)trim_chars.length(); i++) {
        char ch = trim_chars.at(i);
        
        while (!ret.empty() && ret.at(0) == ch) {
            ret.erase(ret.begin());
            
            // ok, matched, should reset the search
            i = 0;
        }
    }
    
    return ret;
}

string srs_string_remove(string str, string remove_chars)
{
    std::string ret = str;
    
    for (int i = 0; i < (int)remove_chars.length(); i++) {
        char ch = remove_chars.at(i);
        
        for (std::string::iterator it = ret.begin(); it != ret.end();) {
            if (ch == *it) {
                it = ret.erase(it);
                
                // ok, matched, should reset the search
                i = 0;
            } else {
                ++it;
            }
        }
    }
    
    return ret;
}

bool srs_string_ends_with(string str, string flag)
{
    const size_t pos = str.rfind(flag);
    return (pos != string::npos) && (pos == str.length() - flag.length());
}

bool srs_string_ends_with(string str, string flag0, string flag1)
{
    return srs_string_ends_with(str, flag0) || srs_string_ends_with(str, flag1);
}

bool srs_string_ends_with(string str, string flag0, string flag1, string flag2)
{
    return srs_string_ends_with(str, flag0) || srs_string_ends_with(str, flag1) || srs_string_ends_with(str, flag2);
}

bool srs_string_ends_with(string str, string flag0, string flag1, string flag2, string flag3)
{
    return srs_string_ends_with(str, flag0) || srs_string_ends_with(str, flag1) || srs_string_ends_with(str, flag2) || srs_string_ends_with(str, flag3);
}

bool srs_string_starts_with(string str, string flag)
{
    return str.find(flag) == 0;
}

bool srs_string_starts_with(string str, string flag0, string flag1)
{
    return srs_string_starts_with(str, flag0) || srs_string_starts_with(str, flag1);
}

bool srs_string_starts_with(string str, string flag0, string flag1, string flag2)
{
    return srs_string_starts_with(str, flag0, flag1) || srs_string_starts_with(str, flag2);
}

bool srs_string_starts_with(string str, string flag0, string flag1, string flag2, string flag3)
{
    return srs_string_starts_with(str, flag0, flag1, flag2) || srs_string_starts_with(str, flag3);
}

bool srs_string_contains(string str, string flag)
{
    return str.find(flag) != string::npos;
}

bool srs_string_contains(string str, string flag0, string flag1)
{
    return str.find(flag0) != string::npos || str.find(flag1) != string::npos;
}

bool srs_string_contains(string str, string flag0, string flag1, string flag2)
{
    return str.find(flag0) != string::npos || str.find(flag1) != string::npos || str.find(flag2) != string::npos;
}

vector<string> srs_string_split(string str, string flag)
{
    vector<string> arr;
    
    size_t pos;
    string s = str;
    
    while ((pos = s.find(flag)) != string::npos) {
        if (pos != 0) {
            arr.push_back(s.substr(0, pos));
        }
        s = s.substr(pos + flag.length());
    }
    
    if (!s.empty()) {
        arr.push_back(s);
    }
    
    return arr;
}

string srs_string_min_match(string str, vector<string> flags)
{
    string match;
    
    size_t min_pos = string::npos;
    for (vector<string>::iterator it = flags.begin(); it != flags.end(); ++it) {
        string flag = *it;
        
        size_t pos = str.find(flag);
        if (pos == string::npos) {
            continue;
        }
        
        if (min_pos == string::npos || pos < min_pos) {
            min_pos = pos;
            match = flag;
        }
    }
    
    return match;
}

vector<string> srs_string_split(string str, vector<string> flags)
{
    vector<string> arr;
    
    size_t pos = string::npos;
    string s = str;
    
    while (true) {
        string flag = srs_string_min_match(s, flags);
        if (flag.empty()) {
            break;
        }
        
        if ((pos = s.find(flag)) == string::npos) {
            break;
        }
        
        if (pos != 0) {
            arr.push_back(s.substr(0, pos));
        }
        s = s.substr(pos + flag.length());
    }
    
    if (!s.empty()) {
        arr.push_back(s);
    }
    
    return arr;
}

int srs_do_create_dir_recursively(string dir)
{
    int ret = ERROR_SUCCESS;
    
    // stat current dir, if exists, return error.
    if (srs_path_exists(dir)) {
        return ERROR_SYSTEM_DIR_EXISTS;
    }
    
    // create parent first.
    size_t pos;
    if ((pos = dir.rfind("/")) != std::string::npos) {
        std::string parent = dir.substr(0, pos);
        ret = srs_do_create_dir_recursively(parent);
        // return for error.
        if (ret != ERROR_SUCCESS && ret != ERROR_SYSTEM_DIR_EXISTS) {
            return ret;
        }
        // parent exists, set to ok.
        ret = ERROR_SUCCESS;
    }
    
    // create curren dir.
    // for srs-librtmp, @see https://github.com/ossrs/srs/issues/213
#ifndef _WIN32
    mode_t mode = S_IRUSR|S_IWUSR|S_IXUSR|S_IRGRP|S_IWGRP|S_IXGRP|S_IROTH|S_IXOTH;
    if (::mkdir(dir.c_str(), mode) < 0) {
#else
    if (::mkdir(dir.c_str()) < 0) {
#endif
        if (errno == EEXIST) {
            return ERROR_SYSTEM_DIR_EXISTS;
        }
        
        ret = ERROR_SYSTEM_CREATE_DIR;
        srs_error("create dir %s failed. ret=%d", dir.c_str(), ret);
        return ret;
    }
    
    srs_info("create dir %s success.", dir.c_str());
    
    return ret;
}
    
bool srs_bytes_equals(void* pa, void* pb, int size)
{
    uint8_t* a = (uint8_t*)pa;
    uint8_t* b = (uint8_t*)pb;
    
    if (!a && !b) {
        return true;
    }
    
    if (!a || !b) {
        return false;
    }
    
    for(int i = 0; i < size; i++){
        if(a[i] != b[i]){
            return false;
        }
    }
    
    return true;
}

srs_error_t srs_create_dir_recursively(string dir)
{
    int ret = srs_do_create_dir_recursively(dir);
    
    if (ret == ERROR_SYSTEM_DIR_EXISTS || ret == ERROR_SUCCESS) {
        return srs_success;
    }
    
    return srs_error_new(ret, "create dir %s", dir.c_str());
}

bool srs_path_exists(std::string path)
{
    struct stat st;
    
    // stat current dir, if exists, return error.
    if (stat(path.c_str(), &st) == 0) {
        return true;
    }
    
    return false;
}

string srs_path_dirname(string path)
{
    std::string dirname = path;
    size_t pos = string::npos;
    
    if ((pos = dirname.rfind("/")) != string::npos) {
        if (pos == 0) {
            return "/";
        }
        dirname = dirname.substr(0, pos);
    }
    
    return dirname;
}

string srs_path_basename(string path)
{
    std::string dirname = path;
    size_t pos = string::npos;
    
    if ((pos = dirname.rfind("/")) != string::npos) {
        // the basename("/") is "/"
        if (dirname.length() == 1) {
            return dirname;
        }
        dirname = dirname.substr(pos + 1);
    }
    
    return dirname;
}

string srs_path_filename(string path)
{
    std::string filename = path;
    size_t pos = string::npos;
    
    if ((pos = filename.rfind(".")) != string::npos) {
        return filename.substr(0, pos);
    }
    
    return filename;
}

string srs_path_filext(string path)
{
    size_t pos = string::npos;
    
    if ((pos = path.rfind(".")) != string::npos) {
        return path.substr(pos);
    }
    
    return "";
}

bool srs_avc_startswith_annexb(SrsBuffer* stream, int* pnb_start_code)
{
    char* bytes = stream->data() + stream->pos();
    char* p = bytes;
    
    for (;;) {
        if (!stream->require((int)(p - bytes + 3))) {
            return false;
        }
        
        // not match
        if (p[0] != (char)0x00 || p[1] != (char)0x00) {
            return false;
        }
        
        // match N[00] 00 00 01, where N>=0
        if (p[2] == (char)0x01) {
            if (pnb_start_code) {
                *pnb_start_code = (int)(p - bytes) + 3;
            }
            return true;
        }
        
        p++;
    }
    
    return false;
}

bool srs_aac_startswith_adts(SrsBuffer* stream)
{
    char* bytes = stream->data() + stream->pos();
    char* p = bytes;
    
    if (!stream->require((int)(p - bytes) + 2)) {
        return false;
    }
    
    // matched 12bits 0xFFF,
    // @remark, we must cast the 0xff to char to compare.
    if (p[0] != (char)0xff || (char)(p[1] & 0xf0) != (char)0xf0) {
        return false;
    }
    
    return true;
}
    
// @see pycrc reflect at https://github.com/winlinvip/pycrc/blob/master/pycrc/algorithms.py#L107
uint64_t __crc32_reflect(uint64_t data, int width)
{
    uint64_t res = data & 0x01;
    
    for (int i = 0; i < width - 1; i++) {
        data >>= 1;
        res = (res << 1) | (data & 0x01);
    }
    
    return res;
}
    
// @see pycrc gen_table at https://github.com/winlinvip/pycrc/blob/master/pycrc/algorithms.py#L178
void __crc32_make_table(uint32_t t[256], uint32_t poly, bool reflect_in)
{
    int width = 32; // 32bits checksum.
    uint64_t msb_mask = (uint32_t)(0x01 << (width - 1));
    uint64_t mask = (uint32_t)(((msb_mask - 1) << 1) | 1);
    
    int tbl_idx_width = 8; // table index size.
    int tbl_width = 0x01 << tbl_idx_width; // table size: 256
    
    for (int i = 0; i < tbl_width; i++) {
        uint64_t reg = uint64_t(i);
        
        if (reflect_in) {
            reg = __crc32_reflect(reg, tbl_idx_width);
        }
        
        reg = reg << (width - tbl_idx_width);
        for (int j = 0; j < tbl_idx_width; j++) {
            if ((reg&msb_mask) != 0) {
                reg = (reg << 1) ^ poly;
            } else {
                reg = reg << 1;
            }
        }
        
        if (reflect_in) {
            reg = __crc32_reflect(reg, width);
        }
        
        t[i] = (uint32_t)(reg & mask);
    }
}
 
// @see pycrc table_driven at https://github.com/winlinvip/pycrc/blob/master/pycrc/algorithms.py#L207
uint32_t __crc32_table_driven(uint32_t* t, const void* buf, int size, uint32_t previous, bool reflect_in, uint32_t xor_in, bool reflect_out, uint32_t xor_out)
{
    int width = 32; // 32bits checksum.
    uint64_t msb_mask = (uint32_t)(0x01 << (width - 1));
    uint64_t mask = (uint32_t)(((msb_mask - 1) << 1) | 1);
    
    int tbl_idx_width = 8; // table index size.
    
    uint8_t* p = (uint8_t*)buf;
    uint64_t reg = 0;
    
    if (!reflect_in) {
        reg = xor_in;
        
        for (int i = 0; i < size; i++) {
            uint8_t tblidx = (uint8_t)((reg >> (width - tbl_idx_width)) ^ p[i]);
            reg = t[tblidx] ^ (reg << tbl_idx_width);
        }
    } else {
        reg = previous ^ __crc32_reflect(xor_in, width);
        
        for (int i = 0; i < size; i++) {
            uint8_t tblidx = (uint8_t)(reg ^ p[i]);
            reg = t[tblidx] ^ (reg >> tbl_idx_width);
        }
        
        reg = __crc32_reflect(reg, width);
    }
    
    if (reflect_out) {
        reg = __crc32_reflect(reg, width);
    }
    
    reg ^= xor_out;
    return (uint32_t)(reg & mask);
}
    
// @see pycrc https://github.com/winlinvip/pycrc/blob/master/pycrc/algorithms.py#L207
// IEEETable is the table for the IEEE polynomial.
static uint32_t __crc32_IEEE_table[256];
static bool __crc32_IEEE_table_initialized = false;

// @see pycrc https://github.com/winlinvip/pycrc/blob/master/pycrc/models.py#L220
//      crc32('123456789') = 0xcbf43926
// where it's defined as model:
//      'name':         'crc-32',
//      'width':         32,
//      'poly':          0x4c11db7,
//      'reflect_in':    True,
//      'xor_in':        0xffffffff,
//      'reflect_out':   True,
//      'xor_out':       0xffffffff,
//      'check':         0xcbf43926,
uint32_t srs_crc32_ieee(const void* buf, int size, uint32_t previous)
{
    // @see golang IEEE of hash/crc32/crc32.go
    // IEEE is by far and away the most common CRC-32 polynomial.
    // Used by ethernet (IEEE 802.3), v.42, fddi, gzip, zip, png, ...
    // @remark The poly of CRC32 IEEE is 0x04C11DB7, its reverse is 0xEDB88320,
    //      please read https://en.wikipedia.org/wiki/Cyclic_redundancy_check
    uint32_t poly = 0x04C11DB7;
    
    bool reflect_in = true;
    uint32_t xor_in = 0xffffffff;
    bool reflect_out = true;
    uint32_t xor_out = 0xffffffff;
    
    if (!__crc32_IEEE_table_initialized) {
        __crc32_make_table(__crc32_IEEE_table, poly, reflect_in);
        __crc32_IEEE_table_initialized = true;
    }
    
    return __crc32_table_driven(__crc32_IEEE_table, buf, size, previous, reflect_in, xor_in, reflect_out, xor_out);
}
    
// @see pycrc https://github.com/winlinvip/pycrc/blob/master/pycrc/algorithms.py#L238
// IEEETable is the table for the MPEG polynomial.
static uint32_t __crc32_MPEG_table[256];
static bool __crc32_MPEG_table_initialized = false;

// @see pycrc https://github.com/winlinvip/pycrc/blob/master/pycrc/models.py#L238
//      crc32('123456789') = 0x0376e6e7
// where it's defined as model:
//      'name':         'crc-32',
//      'width':         32,
//      'poly':          0x4c11db7,
//      'reflect_in':    False,
//      'xor_in':        0xffffffff,
//      'reflect_out':   False,
//      'xor_out':       0x0,
//      'check':         0x0376e6e7,
uint32_t srs_crc32_mpegts(const void* buf, int size)
{
    // @see golang IEEE of hash/crc32/crc32.go
    // IEEE is by far and away the most common CRC-32 polynomial.
    // Used by ethernet (IEEE 802.3), v.42, fddi, gzip, zip, png, ...
    // @remark The poly of CRC32 IEEE is 0x04C11DB7, its reverse is 0xEDB88320,
    //      please read https://en.wikipedia.org/wiki/Cyclic_redundancy_check
    uint32_t poly = 0x04C11DB7;
    
    bool reflect_in = false;
    uint32_t xor_in = 0xffffffff;
    bool reflect_out = false;
    uint32_t xor_out = 0x0;
    
    if (!__crc32_MPEG_table_initialized) {
        __crc32_make_table(__crc32_MPEG_table, poly, reflect_in);
        __crc32_MPEG_table_initialized = true;
    }
    
    return __crc32_table_driven(__crc32_MPEG_table, buf, size, 0x00, reflect_in, xor_in, reflect_out, xor_out);
}

/*
 * Copyright (c) 2006 Ryan Martell. (rdm4@martellventures.com)
 *
 * This file is part of FFmpeg.
 *
 * FFmpeg is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * FFmpeg is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with FFmpeg; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */
#ifndef UINT_MAX
#define UINT_MAX 0xffffffff
#endif
    
#ifndef AV_RB32
#   define AV_RB32(x)                                \
    (((uint32_t)((const uint8_t*)(x))[0] << 24) |    \
    (((const uint8_t*)(x))[1] << 16) |    \
    (((const uint8_t*)(x))[2] <<  8) |    \
    ((const uint8_t*)(x))[3])
#endif
    
#ifndef AV_WL32
#   define AV_WL32(p, darg) do {                \
    unsigned d = (darg);                    \
    ((uint8_t*)(p))[0] = (d);               \
    ((uint8_t*)(p))[1] = (d)>>8;            \
    ((uint8_t*)(p))[2] = (d)>>16;           \
    ((uint8_t*)(p))[3] = (d)>>24;           \
} while(0)
#endif
    
#   define AV_WN(s, p, v) AV_WL##s(p, v)
    
#   if    defined(AV_WN32) && !defined(AV_WL32)
#       define AV_WL32(p, v) AV_WN32(p, v)
#   elif !defined(AV_WN32) &&  defined(AV_WL32)
#       define AV_WN32(p, v) AV_WL32(p, v)
#   endif
    
#ifndef AV_WN32
    #   define AV_WN32(p, v) AV_WN(32, p, v)
#endif
    
#define AV_BSWAP16C(x) (((x) << 8 & 0xff00)  | ((x) >> 8 & 0x00ff))
#define AV_BSWAP32C(x) (AV_BSWAP16C(x) << 16 | AV_BSWAP16C((x) >> 16))
    
#ifndef av_bswap32
static const uint32_t av_bswap32(uint32_t x)
{
    return AV_BSWAP32C(x);
}
#endif
    
#define av_be2ne32(x) av_bswap32(x)
/**
 * @file
 * @brief Base64 encode/decode
 * @author Ryan Martell <rdm4@martellventures.com> (with lots of Michael)
 */

/* ---------------- private code */
static const uint8_t map2[256] =
{
    0xfe, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff,
    
    0x3e, 0xff, 0xff, 0xff, 0x3f, 0x34, 0x35, 0x36,
    0x37, 0x38, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0xff,
    0xff, 0xff, 0xfe, 0xff, 0xff, 0xff, 0x00, 0x01,
    0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09,
    0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f, 0x10, 0x11,
    0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x1a, 0x1b,
    0x1c, 0x1d, 0x1e, 0x1f, 0x20, 0x21, 0x22, 0x23,
    0x24, 0x25, 0x26, 0x27, 0x28, 0x29, 0x2a, 0x2b,
    0x2c, 0x2d, 0x2e, 0x2f, 0x30, 0x31, 0x32, 0x33,
    
    0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
};
    
#define BASE64_DEC_STEP(i) do { \
    bits = map2[in[i]]; \
    if (bits & 0x80) \
        goto out ## i; \
    v = i ? (v << 6) + bits : bits; \
} while(0)
    
int srs_av_base64_decode(uint8_t* out, const char* in_str, int out_size)
{
    uint8_t *dst = out;
    uint8_t *end = out + out_size;
    // no sign extension
    const uint8_t *in = (const uint8_t*)in_str;
    unsigned bits = 0xff;
    unsigned v = 0;
    
    while (end - dst > 3) {
        BASE64_DEC_STEP(0);
        BASE64_DEC_STEP(1);
        BASE64_DEC_STEP(2);
        BASE64_DEC_STEP(3);
        // Using AV_WB32 directly confuses compiler
        v = av_be2ne32(v << 8);
        AV_WN32(dst, v);
        dst += 3;
        in += 4;
    }
    if (end - dst) {
        BASE64_DEC_STEP(0);
        BASE64_DEC_STEP(1);
        BASE64_DEC_STEP(2);
        BASE64_DEC_STEP(3);
        *dst++ = v >> 16;
        if (end - dst)
            *dst++ = v >> 8;
        if (end - dst)
            *dst++ = v;
        in += 4;
    }
    while (1) {
        BASE64_DEC_STEP(0);
        in++;
        BASE64_DEC_STEP(0);
        in++;
        BASE64_DEC_STEP(0);
        in++;
        BASE64_DEC_STEP(0);
        in++;
    }
    
out3:
    *dst++ = v >> 10;
    v <<= 2;
out2:
    *dst++ = v >> 4;
out1:
out0:
    return bits & 1 ? -1 : (int)(dst - out);
}

/*****************************************************************************
 * b64_encode: Stolen from VLC's http.c.
 * Simplified by Michael.
 * Fixed edge cases and made it work from data (vs. strings) by Ryan.
 *****************************************************************************/
char* srs_av_base64_encode(char* out, int out_size, const uint8_t* in, int in_size)
{
    static const char b64[] =
    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
    char *ret, *dst;
    unsigned i_bits = 0;
    int i_shift = 0;
    int bytes_remaining = in_size;
    
    if (in_size >= (int)(UINT_MAX / 4) ||
        out_size < SRS_AV_BASE64_SIZE(in_size))
        return NULL;
    ret = dst = out;
    while (bytes_remaining > 3) {
        i_bits = AV_RB32(in);
        in += 3; bytes_remaining -= 3;
        *dst++ = b64[ i_bits>>26        ];
        *dst++ = b64[(i_bits>>20) & 0x3F];
        *dst++ = b64[(i_bits>>14) & 0x3F];
        *dst++ = b64[(i_bits>>8 ) & 0x3F];
    }
    i_bits = 0;
    while (bytes_remaining) {
        i_bits = (i_bits << 8) + *in++;
        bytes_remaining--;
        i_shift += 8;
    }
    while (i_shift > 0) {
        *dst++ = b64[(i_bits << 6 >> i_shift) & 0x3f];
        i_shift -= 6;
    }
    while ((dst - ret) & 3)
        *dst++ = '=';
    *dst = '\0';
    
    return ret;
}

#define SPACE_CHARS " \t\r\n"

int av_toupper(int c)
{
    if (c >= 'a' && c <= 'z') {
        c ^= 0x20;
    }
    return c;
}

int ff_hex_to_data(uint8_t* data, const char* p)
{
    int c, len, v;
    
    len = 0;
    v = 1;
    for (;;) {
        p += strspn(p, SPACE_CHARS);
        if (*p == '\0')
            break;
        c = av_toupper((unsigned char) *p++);
        if (c >= '0' && c <= '9')
            c = c - '0';
        else if (c >= 'A' && c <= 'F')
            c = c - 'A' + 10;
        else
            break;
        v = (v << 4) | c;
        if (v & 0x100) {
            if (data)
                data[len] = v;
            len++;
            v = 1;
        }
    }
    return len;
}

int srs_chunk_header_c0(int perfer_cid, uint32_t timestamp, int32_t payload_length, int8_t message_type, int32_t stream_id, char* cache, int nb_cache)
{
    // to directly set the field.
    char* pp = NULL;
    
    // generate the header.
    char* p = cache;
    
    // no header.
    if (nb_cache < SRS_CONSTS_RTMP_MAX_FMT0_HEADER_SIZE) {
        return 0;
    }
    
    // write new chunk stream header, fmt is 0
    *p++ = 0x00 | (perfer_cid & 0x3F);
    
    // chunk message header, 11 bytes
    // timestamp, 3bytes, big-endian
    if (timestamp < RTMP_EXTENDED_TIMESTAMP) {
        pp = (char*)&timestamp;
        *p++ = pp[2];
        *p++ = pp[1];
        *p++ = pp[0];
    } else {
        *p++ = 0xFF;
        *p++ = 0xFF;
        *p++ = 0xFF;
    }
    
    // message_length, 3bytes, big-endian
    pp = (char*)&payload_length;
    *p++ = pp[2];
    *p++ = pp[1];
    *p++ = pp[0];
    
    // message_type, 1bytes
    *p++ = message_type;
    
    // stream_id, 4bytes, little-endian
    pp = (char*)&stream_id;
    *p++ = pp[0];
    *p++ = pp[1];
    *p++ = pp[2];
    *p++ = pp[3];
    
    // for c0
    // chunk extended timestamp header, 0 or 4 bytes, big-endian
    //
    // for c3:
    // chunk extended timestamp header, 0 or 4 bytes, big-endian
    // 6.1.3. Extended Timestamp
    // This field is transmitted only when the normal time stamp in the
    // chunk message header is set to 0x00ffffff. If normal time stamp is
    // set to any value less than 0x00ffffff, this field MUST NOT be
    // present. This field MUST NOT be present if the timestamp field is not
    // present. Type 3 chunks MUST NOT have this field.
    // adobe changed for Type3 chunk:
    //        FMLE always sendout the extended-timestamp,
    //        must send the extended-timestamp to FMS,
    //        must send the extended-timestamp to flash-player.
    // @see: ngx_rtmp_prepare_message
    // @see: http://blog.csdn.net/win_lin/article/details/13363699
    // TODO: FIXME: extract to outer.
    if (timestamp >= RTMP_EXTENDED_TIMESTAMP) {
        pp = (char*)&timestamp;
        *p++ = pp[3];
        *p++ = pp[2];
        *p++ = pp[1];
        *p++ = pp[0];
    }
    
    // always has header
    return (int)(p - cache);
}

int srs_chunk_header_c3(int perfer_cid, uint32_t timestamp, char* cache, int nb_cache)
{
    // to directly set the field.
    char* pp = NULL;
    
    // generate the header.
    char* p = cache;
    
    // no header.
    if (nb_cache < SRS_CONSTS_RTMP_MAX_FMT3_HEADER_SIZE) {
        return 0;
    }
    
    // write no message header chunk stream, fmt is 3
    // @remark, if perfer_cid > 0x3F, that is, use 2B/3B chunk header,
    // SRS will rollback to 1B chunk header.
    *p++ = 0xC0 | (perfer_cid & 0x3F);
    
    // for c0
    // chunk extended timestamp header, 0 or 4 bytes, big-endian
    //
    // for c3:
    // chunk extended timestamp header, 0 or 4 bytes, big-endian
    // 6.1.3. Extended Timestamp
    // This field is transmitted only when the normal time stamp in the
    // chunk message header is set to 0x00ffffff. If normal time stamp is
    // set to any value less than 0x00ffffff, this field MUST NOT be
    // present. This field MUST NOT be present if the timestamp field is not
    // present. Type 3 chunks MUST NOT have this field.
    // adobe changed for Type3 chunk:
    //        FMLE always sendout the extended-timestamp,
    //        must send the extended-timestamp to FMS,
    //        must send the extended-timestamp to flash-player.
    // @see: ngx_rtmp_prepare_message
    // @see: http://blog.csdn.net/win_lin/article/details/13363699
    // TODO: FIXME: extract to outer.
    if (timestamp >= RTMP_EXTENDED_TIMESTAMP) {
        pp = (char*)&timestamp;
        *p++ = pp[3];
        *p++ = pp[2];
        *p++ = pp[1];
        *p++ = pp[0];
    }
    
    // always has header
    return (int)(p - cache);
}