Base62 coding of URLs

VAR.UrlCompressor/Base62.cs

@@ -0,0 +1,133 @@
+using System;
+using System.Text;
+
+namespace VAR.UrlCompressor
+{
+    class Base62
+    {
+        private static string Base62CodingSpace = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
+
+        private static bool ReadBit(byte[] bytes, int position, int offset)
+        {
+            if (offset < 0) { return false; }
+            int tempPos = position + offset;
+            int bytePosition = tempPos / 8;
+            int bitPosition = tempPos % 8;
+            if (bytePosition >= bytes.Length) { return false; }
+            return (bytes[bytePosition] & (0x01 << (7 - bitPosition))) > 0;
+        }
+
+        private static void WriteBit(byte[] bytes, int position, int offset, bool value)
+        {
+            if (offset < 0) { return; }
+            int tempPos = position + offset;
+            int bytePosition = tempPos / 8;
+            int bitPosition = tempPos % 8;
+            if (bytePosition >= bytes.Length) { return; }
+            if (value)
+            {
+                bytes[bytePosition] = (byte)(bytes[bytePosition] | (0x01 << (7 - bitPosition)));
+            }
+            else
+            {
+                bytes[bytePosition] = (byte)(bytes[bytePosition] & (0xffffffff - (0x1 << (7 - bitPosition))));
+            }
+        }
+        
+        public static string Encode(byte[] original)
+        {
+            StringBuilder sb = new StringBuilder();
+            
+            int bitPosition = 0;
+            int lenght = original.Length * 8;
+            while (bitPosition < lenght)
+            {
+                int pad = 0;
+                if (bitPosition + 6 > lenght)
+                {
+                    pad = lenght - (bitPosition + 6);
+                }
+                bool bit0 = ReadBit(original, bitPosition, 0 + pad);
+                bool bit1 = ReadBit(original, bitPosition, 1 + pad);
+                bool bit2 = ReadBit(original, bitPosition, 2 + pad);
+                bool bit3 = ReadBit(original, bitPosition, 3 + pad);
+                bool bit4 = ReadBit(original, bitPosition, 4 + pad);
+                bool bit5 = ReadBit(original, bitPosition, 5 + pad);
+
+                if (bit0 == true && bit1 == true && bit2 == true && bit3 == true && bit4 == true)
+                {
+                    sb.Append(Base62CodingSpace[61]);
+                    bitPosition += 5;
+                    continue;
+                }
+                if (bit0 == true && bit1 == true && bit2 == true && bit3 == true && bit4 == false)
+                {
+                    sb.Append(Base62CodingSpace[60]);
+                    bitPosition += 5;
+                    continue;
+                }
+                int charIdx = (bit0 ? 0x20 : 0) | (bit1 ? 0x10 : 0) | (bit2 ? 0x08 : 0) | (bit3 ? 0x04 : 0) | (bit4 ? 0x02 : 0) | (bit5 ? 0x01 : 0);
+                sb.Append(Base62CodingSpace[charIdx]);
+                bitPosition += 6;
+            }
+            return sb.ToString();
+        }
+
+        public static byte[] Decode(string base62)
+        {
+            byte[] bytes = new byte[base62.Length * 6 / 8];
+            int bitPosition = 0;
+            for (int i = 0; i < base62.Length; i++)
+            {
+                int charIdx = Base62CodingSpace.IndexOf(base62[i]);
+                if ((i + 1) == base62.Length)
+                {
+                    // Last symbol
+                    int rest = 8 - (bitPosition % 8);
+                    if (rest == 8) { throw new Exception("Extra symbol at end"); }
+                    if ((charIdx >> rest) > 0) { throw new Exception("Invalid ending symbol"); }
+                    int pad = 6 - rest;
+                    WriteBit(bytes, bitPosition, 0 - pad, (charIdx & 0x20) > 0);
+                    WriteBit(bytes, bitPosition, 1 - pad, (charIdx & 0x10) > 0);
+                    WriteBit(bytes, bitPosition, 2 - pad, (charIdx & 0x08) > 0);
+                    WriteBit(bytes, bitPosition, 3 - pad, (charIdx & 0x04) > 0);
+                    WriteBit(bytes, bitPosition, 4 - pad, (charIdx & 0x02) > 0);
+                    WriteBit(bytes, bitPosition, 5 - pad, (charIdx & 0x01) > 0);
+
+                    break;
+                }
+
+                if (charIdx == 60)
+                {
+                    WriteBit(bytes, bitPosition, 0, true);
+                    WriteBit(bytes, bitPosition, 1, true);
+                    WriteBit(bytes, bitPosition, 2, true);
+                    WriteBit(bytes, bitPosition, 3, true);
+                    WriteBit(bytes, bitPosition, 4, false);
+                    bitPosition += 5;
+                }
+                else if (charIdx == 61)
+                {
+                    WriteBit(bytes, bitPosition, 0, true);
+                    WriteBit(bytes, bitPosition, 1, true);
+                    WriteBit(bytes, bitPosition, 2, true);
+                    WriteBit(bytes, bitPosition, 3, true);
+                    WriteBit(bytes, bitPosition, 4, true);
+                    bitPosition += 5;
+                }
+                else
+                {
+                    WriteBit(bytes, bitPosition, 0, (charIdx & 0x20) > 0);
+                    WriteBit(bytes, bitPosition, 1, (charIdx & 0x10) > 0);
+                    WriteBit(bytes, bitPosition, 2, (charIdx & 0x08) > 0);
+                    WriteBit(bytes, bitPosition, 3, (charIdx & 0x04) > 0);
+                    WriteBit(bytes, bitPosition, 4, (charIdx & 0x02) > 0);
+                    WriteBit(bytes, bitPosition, 5, (charIdx & 0x01) > 0);
+                    bitPosition += 6;
+                }
+            }
+
+            return bytes;
+        }
+    }
+}

VAR.UrlCompressor/UrlCompressor.cs

@@ -1,8 +1,5 @@
 using System;
-using System.Collections.Generic;
-using System.Linq;
 using System.Text;
-using System.Threading.Tasks;
 
 namespace VAR.UrlCompressor
 {
@@ -10,14 +7,36 @@ namespace VAR.UrlCompressor
     {
         public static string Compress(string url)
         {
-            // FIXME: Implement this
+            // Replace protocol indicator
-            return string.Empty;
+            if (url.StartsWith("https://") || url.StartsWith("HTTPS://"))
+            {
+                url = string.Format("${0}", url.Substring("https://".Length));
+            }
+            if (url.StartsWith("http://") || url.StartsWith("HTTP://"))
+            {
+                url = string.Format("#{0}", url.Substring("http://".Length));
+            }
+
+            byte[] urlBytes = Encoding.ASCII.GetBytes(url);
+            return Base62.Encode(urlBytes);
         }
 
         public static string Decompress(string compressedUrl)
         {
-            // FIXME: Implement this
+            byte[] urlBytes = Base62.Decode(compressedUrl);
-            return string.Empty;
+            string url = Encoding.ASCII.GetString(urlBytes);
+
+            // Restore protocol indicator
+            if (url.StartsWith("#"))
+            {
+                url = string.Format("http://{0}", url.Substring(1));
+            }
+            if (url.StartsWith("$"))
+            {
+                url = string.Format("https://{0}", url.Substring(1));
+            }
+
+            return url;
         }
     }
 }

VAR.UrlCompressor/VAR.UrlCompressor.csproj

@@ -40,6 +40,7 @@
     <Reference Include="System.Xml" />
   </ItemGroup>
   <ItemGroup>
+    <Compile Include="Base62.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
     <Compile Include="UrlCompressor.cs" />
   </ItemGroup>