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Base62 coding of URLs

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This commit is contained in:
Valeriano A.R.
2017-07-09 19:17:38 +02:00
parent 837513cfcb
commit d753a9fc3c
3 changed files with 160 additions and 7 deletions
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133
VAR.UrlCompressor/Base62.cs Normal file
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@@ -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;
}
}
}

33
VAR.UrlCompressor/UrlCompressor.cs
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@@ -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
return string.Empty;
// Replace protocol indicator
if (url.StartsWith("https://") || url.StartsWith("HTTPS://"))
{
url = string.Format("${0}", url.Substring("https://".Length));
}
if (url.StartsWith("http://") || url.StartsWith("HTTP://"))
{
url = string.Format("#{0}", url.Substring("http://".Length));
}
byte[] urlBytes = Encoding.ASCII.GetBytes(url);
return Base62.Encode(urlBytes);
}
public static string Decompress(string compressedUrl)
{
// FIXME: Implement this
return string.Empty;
byte[] urlBytes = Base62.Decode(compressedUrl);
string url = Encoding.ASCII.GetString(urlBytes);
// Restore protocol indicator
if (url.StartsWith("#"))
{
url = string.Format("http://{0}", url.Substring(1));
}
if (url.StartsWith("$"))
{
url = string.Format("https://{0}", url.Substring(1));
}
return url;
}
}
}

1
VAR.UrlCompressor/VAR.UrlCompressor.csproj
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@@ -40,6 +40,7 @@
<Reference Include="System.Xml" />
</ItemGroup>
<ItemGroup>
<Compile Include="Base62.cs" />
<Compile Include="Properties\AssemblyInfo.cs" />
<Compile Include="UrlCompressor.cs" />
</ItemGroup>