Skin fix code (fixing Steves) for Minecraft 1.7.10 and below (requires MCP)

SkinMapper.java

classpackage net.minecraft.src;

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.HashMap;
import java.util.Map;

/**
 * Skin mapper class
 * 
 * This class is responsible for mapping Minecraft username to a 
 * skin URL. Basically this class can be used to fix Minecraft 1.7.10
 * and below issue with players all turning into Steves.
 * 
 * This class uses Mojang and Crafatar's APIs in order to make skins 
 * ~~great~~ work again. Mojang's API is used for obtaining UUID from 
 * username, and Crafatar is used to link the actual skin. Why it's 
 * using Crafatar? Because Crafatar stores skins in Steve format thus 
 * the code to convert from 64x64 to 64x32 isn't needed.
 * 
 * Feel free to use it anyway you want to.
 * 
 * @author McHorse
 * @license MIT
 */
class SkinMapper
{
    /**
     * Cache which maps player usernames to UUIDs
     */
    public final static Map<String, String> USERNAME_TO_UUID = new HashMap<String, String>();

    /**
     * Get skin URL for given username
     */
    public static String getURL(String username)
    {
        String str = getUUID(username);

        if (str != null)
        {
            str = "https://crafatar.com/skins/" + StringUtils.stripControlCodes(str);
        }

        return str;
    }

    /**
     * Get UUID from username. This method makes a request to Mojang API
     */
    public static String getUUID(String username)
    {
        String str = USERNAME_TO_UUID.get(username);

        if (str == null)
        {
            str = getPlayerUUID(username);
            USERNAME_TO_UUID.put(username, str);
        }

        return str;
    }

    private static String getPlayerUUID(String username)
    {
        String json = request(username);

        if (json != null)
        {
            String uuid = json.substring("{\"id\":\"".length());
            int index = uuid.indexOf("\"");

            if (index != -1)
            {
                uuid = uuid.substring(0, index);

                if (uuid.length() == 32)
                {
                    return uuid;
                }
            }
        }

        return null;
    }

    /**
     * Request 
     */
    private static String request(String username)
    {
        HttpURLConnection connection = null;

        try
        {
            URL url = new URL("https://api.mojang.com/users/profiles/minecraft/" + username);
            
            connection = (HttpURLConnection) url.openConnection();
            connection.setRequestMethod("GET");
            connection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
            connection.setRequestProperty("Content-Language", "en-US");

            connection.setUseCaches(false);
            connection.setDoOutput(true);

            InputStream is = connection.getInputStream();
            BufferedReader rd = new BufferedReader(new InputStreamReader(is));
            
            StringBuilder response = new StringBuilder();
            String line;

            while ((line = rd.readLine()) != null)
            {
                response.append(line);
                response.append('\r');
            }

            rd.close();
            return response.toString();
        }
        catch (Exception e)
        {
            e.printStackTrace();
            return null;
        }
        finally
        {
            if (connection != null)
            {
                connection.disconnect();
            }
        }
    }
}

/**
 * And in order to actually fix the issue with skins, you need to 
 * replace the line into EntityPlayerSP's and EntityPlayerOtherMP's
 * which starts with this.skinUrl = ... with:
 * 
 * this.skinUrl = SkinMapper.getURL(par3Session.username);
 * 
 * par3Session.username may vary depending on the class. It's either 
 * that or par2Str (in EntityPlayerOtherMP).
 */