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kapi.cpp
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kapi.cpp
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#include <iostream>
#include <iomanip>
#include <stdexcept>
#include <sstream>
#include <cstring>
#include <ctime>
#include <cerrno>
#include <openssl/buffer.h>
#include <openssl/sha.h>
#include <openssl/hmac.h>
#include <openssl/bio.h>
#include "kapi.hpp"
#define CURL_VERBOSE 0L //1L = enabled, 0L = disabled
//------------------------------------------------------------------------------
namespace Kraken {
//------------------------------------------------------------------------------
// helper function to compute SHA256:
static std::vector<unsigned char> sha256(const std::string& data)
{
std::vector<unsigned char> digest(SHA256_DIGEST_LENGTH);
SHA256_CTX ctx;
SHA256_Init(&ctx);
SHA256_Update(&ctx, data.c_str(), data.length());
SHA256_Final(digest.data(), &ctx);
return digest;
}
//------------------------------------------------------------------------------
// helper function to decode a base64 string to a vector of bytes:
static std::vector<unsigned char> b64_decode(const std::string& data)
{
BIO* b64 = BIO_new(BIO_f_base64());
BIO_set_flags(b64, BIO_FLAGS_BASE64_NO_NL);
BIO* bmem = BIO_new_mem_buf((void*)data.c_str(),data.length());
bmem = BIO_push(b64, bmem);
std::vector<unsigned char> output(data.length());
int decoded_size = BIO_read(bmem, output.data(), output.size());
BIO_free_all(bmem);
if (decoded_size < 0)
throw std::runtime_error("failed while decoding base64.");
return output;
}
//------------------------------------------------------------------------------
// helper function to encode a vector of bytes to a base64 string:
static std::string b64_encode(const std::vector<unsigned char>& data)
{
BIO* b64 = BIO_new(BIO_f_base64());
BIO_set_flags(b64, BIO_FLAGS_BASE64_NO_NL);
BIO* bmem = BIO_new(BIO_s_mem());
b64 = BIO_push(b64, bmem);
BIO_write(b64, data.data(), data.size());
BIO_flush(b64);
BUF_MEM* bptr = NULL;
BIO_get_mem_ptr(b64, &bptr);
std::string output(bptr->data, bptr->length);
BIO_free_all(b64);
return output;
}
//------------------------------------------------------------------------------
// helper function to hash with HMAC algorithm:
static std::vector<unsigned char>
hmac_sha512(const std::vector<unsigned char>& data,
const std::vector<unsigned char>& key)
{
unsigned int len = EVP_MAX_MD_SIZE;
std::vector<unsigned char> digest(len);
HMAC_CTX *ctx = HMAC_CTX_new();
if (ctx == NULL) {
throw std::runtime_error("cannot create HMAC_CTX");
}
HMAC_Init_ex(ctx, key.data(), key.size(), EVP_sha512(), NULL);
HMAC_Update(ctx, data.data(), data.size());
HMAC_Final(ctx, digest.data(), &len);
HMAC_CTX_free(ctx);
return digest;
}
//------------------------------------------------------------------------------
// builds a query string from KAPI::Input (a=1&b=2&...)
static std::string build_query(const KAPI::Input& input)
{
std::ostringstream oss;
KAPI::Input::const_iterator it = input.begin();
for (; it != input.end(); ++it) {
if (it != input.begin()) oss << '&'; // delimiter
oss << it->first <<'='<< it->second;
}
return oss.str();
}
//------------------------------------------------------------------------------
// helper function to create a nonce:
static std::string create_nonce()
{
std::ostringstream oss;
timeval tp;
if (gettimeofday(&tp, NULL) != 0) {
oss << "gettimeofday() failed: " << strerror(errno);
throw std::runtime_error(oss.str());
}
else {
// format output string
oss << std::setfill('0')
<< std::setw(10) << tp.tv_sec
<< std::setw(6) << tp.tv_usec;
}
return oss.str();
}
//------------------------------------------------------------------------------
// constructor with all explicit parameters
KAPI::KAPI(const std::string& key, const std::string& secret,
const std::string& url, const std::string& version)
:key_(key), secret_(secret), url_(url), version_(version)
{
init();
}
//------------------------------------------------------------------------------
// default API base URL and API version
KAPI::KAPI(const std::string& key, const std::string& secret)
:key_(key), secret_(secret), url_("https://api.kraken.com"), version_("0")
{
init();
}
//------------------------------------------------------------------------------
// constructor with empty API key and API secret
KAPI::KAPI()
:key_(""), secret_(""), url_("https://api.kraken.com"), version_("0")
{
init();
}
//------------------------------------------------------------------------------
// initializes libcurl:
void KAPI::init()
{
curl_ = curl_easy_init();
if (curl_) {
curl_easy_setopt(curl_, CURLOPT_VERBOSE, CURL_VERBOSE);
curl_easy_setopt(curl_, CURLOPT_SSL_VERIFYPEER, 1L);
curl_easy_setopt(curl_, CURLOPT_SSL_VERIFYHOST, 2L);
curl_easy_setopt(curl_, CURLOPT_USERAGENT, "Kraken C++ API Client");
curl_easy_setopt(curl_, CURLOPT_POST, 1L);
// set callback function
curl_easy_setopt(curl_, CURLOPT_WRITEFUNCTION, KAPI::write_cb);
}
else {
throw std::runtime_error("can't create curl handle");
}
}
//------------------------------------------------------------------------------
// destructor:
KAPI::~KAPI()
{
curl_easy_cleanup(curl_);
}
//------------------------------------------------------------------------------
// returns message signature generated from a URI path, a nonce
// and postdata, message signature is created as a follows:
//
// hmac_sha512(path + sha256(nonce + postdata), b64decode(secret))
//
// and the result is converted in a base64 string:
std::string KAPI::signature(const std::string& path,
const std::string& nonce,
const std::string& postdata) const
{
// add path to data to encrypt
std::vector<unsigned char> data(path.begin(), path.end());
// concatenate nonce and postdata and compute SHA256
std::vector<unsigned char> nonce_postdata = sha256(nonce + postdata);
// concatenate path and nonce_postdata (path + sha256(nonce + postdata))
data.insert(data.end(), nonce_postdata.begin(), nonce_postdata.end());
// and compute HMAC
return b64_encode( hmac_sha512(data, b64_decode(secret_)) );
}
//------------------------------------------------------------------------------
// CURL write function callback:
size_t KAPI::write_cb(char* ptr, size_t size, size_t nmemb, void* userdata)
{
std::string* response = reinterpret_cast<std::string*>(userdata);
size_t real_size = size * nmemb;
response->append(ptr, real_size);
return real_size;
}
//------------------------------------------------------------------------------
// deals with public API methods:
std::string KAPI::public_method(const std::string& method,
const KAPI::Input& input) const
{
// build method URL
std::string path = "/" + version_ + "/public/" + method;
std::string method_url = url_ + path + "?" + build_query(input);
curl_easy_setopt(curl_, CURLOPT_URL, method_url.c_str());
// reset the http header
curl_easy_setopt(curl_, CURLOPT_HTTPHEADER, NULL);
// where CURL write callback function stores the response
std::string response;
curl_easy_setopt(curl_, CURLOPT_WRITEDATA, static_cast<void*>(&response));
// Set GET method
curl_easy_setopt(curl_, CURLOPT_HTTPGET, 1L);
// perform CURL request
CURLcode result = curl_easy_perform(curl_);
if (result != CURLE_OK) {
std::ostringstream oss;
oss << "curl_easy_perform() failed: "<< curl_easy_strerror(result);
throw std::runtime_error(oss.str());
}
return response;
}
//------------------------------------------------------------------------------
// deals with private API methods:
std::string KAPI::private_method(const std::string& method,
const KAPI::Input& input) const
{
// build method URL
std::string path = "/" + version_ + "/private/" + method;
std::string method_url = url_ + path;
curl_easy_setopt(curl_, CURLOPT_URL, method_url.c_str());
// create a nonce and and postdata
std::string nonce = create_nonce();
std::string postdata = "nonce=" + nonce;
// if 'input' is not empty generate other postdata
if (!input.empty())
postdata = postdata + "&" + build_query(input);
curl_easy_setopt(curl_, CURLOPT_POSTFIELDS, postdata.c_str());
// add custom header
curl_slist* chunk = NULL;
std::string key_header = "API-Key: " + key_;
std::string sign_header = "API-Sign: " + signature(path, nonce, postdata);
chunk = curl_slist_append(chunk, key_header.c_str());
chunk = curl_slist_append(chunk, sign_header.c_str());
curl_easy_setopt(curl_, CURLOPT_HTTPHEADER, chunk);
// where CURL write callback function stores the response
std::string response;
curl_easy_setopt(curl_, CURLOPT_WRITEDATA, static_cast<void*>(&response));
// perform CURL request
CURLcode result = curl_easy_perform(curl_);
// free the custom headers
curl_slist_free_all(chunk);
// check perform result
if (result != CURLE_OK) {
std::ostringstream oss;
oss << "curl_easy_perform() failed: " << curl_easy_strerror(result);
throw std::runtime_error(oss.str());
}
return response;
}
//------------------------------------------------------------------------------
// helper function to initialize Kraken API library's resources:
void initialize()
{
CURLcode code = curl_global_init(CURL_GLOBAL_ALL);
if (code != CURLE_OK) {
std::ostringstream oss;
oss << "curl_global_init() failed: " << curl_easy_strerror(code);
throw std::runtime_error(oss.str());
}
}
//------------------------------------------------------------------------------
// helper function to terminate Kraken API library's resources:
void terminate()
{
curl_global_cleanup();
}
//------------------------------------------------------------------------------
} //namespace Kraken
//------------------------------------------------------------------------------