content: package org.knowm.xchange.okcoin;
  
  import java.io.UnsupportedEncodingException;
  import java.security.MessageDigest;
  import java.security.NoSuchAlgorithmException;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.List;
  import java.util.Map;
  import javax.ws.rs.FormParam;
  import si.mazi.rescu.Params;
  import si.mazi.rescu.ParamsDigest;
  import si.mazi.rescu.RestInvocation;
  
  public class OkCoinDigest implements ParamsDigest {
  
    private static final char[] DIGITS_UPPER = {
      '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'
    };
  
    private final String apikey;
    private final String secretKey;
    private final MessageDigest md;
  
    public OkCoinDigest(String apikey, String secretKey) {
  
      this.apikey = apikey;
      this.secretKey = secretKey;
  
      try {
        md = MessageDigest.getInstance("MD5");
      } catch (NoSuchAlgorithmException e) {
        throw new RuntimeException("Problem instantiating message digest.");
      }
    }
  
    private static char[] encodeHex(byte[] data, char[] toDigits) {
  
      int l = data.length;
      char[] out = new char[l << 1];
      // two characters form the hex value.
      for (int i = 0, j = 0; i < l; i++) {
        out[j++] = toDigits[(0xF0 & data[i]) >>> 4];
        out[j++] = toDigits[0x0F & data[i]];
      }
      return out;
    }
  
    @Override
    public String digestParams(RestInvocation restInvocation) {
  
      final Params params = restInvocation.getParamsMap().get(FormParam.class);
      final Map<String, String> nameValueMap = params.asHttpHeaders();
  
      nameValueMap.remove("sign");
      nameValueMap.put("api_key", apikey);
  
      // odd requirements for buy/sell market orders
      if (nameValueMap.containsKey("type") && nameValueMap.get("type").contains("market")) {
        if (nameValueMap.get("type").equals("buy_market")) {
          nameValueMap.remove("amount");
        } else if (nameValueMap.get("type").equals("sell_market")) {
          nameValueMap.remove("price");
        }
      }
      final List<Map.Entry<String, String>> nameValueList = new ArrayList<>(nameValueMap.entrySet());
      Collections.sort(nameValueList, (e1, e2) -> e1.getKey().compareTo(e2.getKey()));
  
      final Params newParams = Params.of();
      for (int i = 0; i < nameValueList.size(); i++) {
        Map.Entry<String, String> param = nameValueList.get(i);
        newParams.add(param.getKey(), param.getValue());
      }
  
      // final String message = newParams.asQueryString() + "&secret_key=" + secretKey;
      final String message = newParams.toString() + "&secret_key=" + secretKey;
  
      try {
        md.reset();
  
        byte[] digest = md.digest(message.getBytes("US-ASCII"));
  
        return String.valueOf(encodeHex(digest, DIGITS_UPPER));
      } catch (UnsupportedEncodingException e) {
        throw new RuntimeException("Codec error", e);
      }
    }
  }
  