FacebookPostMethod.java :  » UnTagged » snaio » org » elephantt » javabook » client » Android Open Source

package org.elephantt.javabook.client;

import org.apache.commons.httpclient.methods.PostMethod;
import org.apache.commons.httpclient.NameValuePair;

import java.util.List;
import java.util.ArrayList;
import java.util.Collections;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

/**
 * A PostMethod that supports signing the request according to FB signature rules.
 *
 * Once the sign(String) method is called, the parameters cannot be mutated.
 */
public class FacebookPostMethod extends PostMethod {
  private boolean signed = false;

  @Override
  public boolean removeParameter(String s, String s1) throws IllegalArgumentException {
    verifyState();
    return super.removeParameter(s, s1);
  }

  @Override
  public void addParameter(String s, String s1) throws IllegalArgumentException {
    verifyState();
    super.addParameter(s, s1);
  }

  @Override
  public void addParameter(NameValuePair nameValuePair) throws IllegalArgumentException {
    verifyState();
    super.addParameter(nameValuePair);
  }

  @Override
  public void addParameters(NameValuePair[] nameValuePairs) {
    verifyState();
    super.addParameters(nameValuePairs);
  }

  @Override
  public boolean removeParameter(String s) throws IllegalArgumentException {
    verifyState();
    return super.removeParameter(s);
  }

  /**
   * Signs the POST according to FB sig rules
   */
  public void sign(String secretKey) {
    NameValuePair[] params = getParameters();
    List<String> sigParams = new ArrayList<String>(params.length);
    for (NameValuePair nvp : params) {
      sigParams.add(nvp.getName() + "=" + nvp.getValue());
    }
    addParameter("sig", generateSignature(sigParams, secretKey));
    signed = true;
  }

  /**
   * Generates a sig over the params according to FB sig rules
   * @param params
   * @return
   */
  private String generateSignature(List<String> params, String secretKey) {
    StringBuilder buffer = new StringBuilder();
    Collections.sort(params);
    for (String param: params) {
      buffer.append(param);
    }

    buffer.append(secretKey);

    StringBuilder result = new StringBuilder();

    // wtf?
    for (byte b : createDigester().digest(buffer.toString().getBytes())) {
      result.append(Integer.toHexString((b & 0xf0) >>> 4));
      result.append(Integer.toHexString(b & 0x0f));
    }

    return result.toString();
  }

  private MessageDigest createDigester() {
    try {
      return MessageDigest.getInstance("MD5");
    } catch (NoSuchAlgorithmException e) {
      throw new RuntimeException("MD5 MessageDigest algo missing");
    }
  }

  private void verifyState() {
    if (signed) throw new IllegalStateException("cannot modify parameters after parameter set is signed");
  }
}