"Uuencode is a set of algorithms for converting files into a series of 7-bit ASCII characters that can be transmitted over the Internet. Originally, uuencode stood for Unix-to-Unix encode, but it has since become a universal protocol used to transfer files between different platforms such as Unix, Windows, and Macintosh. Uuencoding is especially popular for sending e-mail attachments. Nearly all e-mail applications support uuencoding for sending attachments and uudecoding for receiving attachments."
You can learn much more or here. However, UUencoding has a few problems. Most important, no RFC describes the algorithm UUencoding and UUdecoding use to convert binaries. Consequently, various software's implementations of UUencoding can differ (as we learned when trying to open message sent from Outlook in Thunderbird). Generally, it's quite an oldtimer and nowadays should be replaced with Base64 encoding in most cases.
As I couldn't find any implementation of this encoding for.NET (at least none that actually worked for the attachments I had to deal with) I did quick research and found nice C implementation in KDE sources. Below you will find my port of this code. Most significant change is that I used Streams instead of byte arrays (the algorithm is forward only and doesn't need to load all the data to memory) and removed the part in UUDecode dealing with Unix 'begin'/'end' tags as these were already removed from the attachments I had to handle.
public static class Codecs { static readonly byte[] UUEncMap = new byte[] { 0x60, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28, 0x29, 0x2A, 0x2B, 0x2C, 0x2D, 0x2E, 0x2F, 0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3A, 0x3B, 0x3C, 0x3D, 0x3E, 0x3F, 0x40, 0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4A, 0x4B, 0x4C, 0x4D, 0x4E, 0x4F, 0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5A, 0x5B, 0x5C, 0x5D, 0x5E, 0x5F };
static readonly byte[] UUDecMap = new byte[] { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1A, 0x1B, 0x1C, 0x1D, 0x1E, 0x1F, 0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28, 0x29, 0x2A, 0x2B, 0x2C, 0x2D, 0x2E, 0x2F, 0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3A, 0x3B, 0x3C, 0x3D, 0x3E, 0x3F, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 };
public static void UUDecode(System.IO.Stream input, System.IO.Stream output) { if (input == null) throw new ArgumentNullException("input");
if (output == null) throw new ArgumentNullException("output");
long len = input.Length; if (len == 0) return;
long didx = 0; int nextByte = input.ReadByte; while (nextByte >= 0) { // get line length (in number of encoded octets) int line_len = UUDecMap[nextByte];
// ascii printable to 0-63 and 4-byte to 3-byte conversion long end = didx + line_len; byte A, B, C, D; if (end > 2) { while (didx < end - 2) { A = UUDecMap[input.ReadByte]; B = UUDecMap[input.ReadByte]; C = UUDecMap[input.ReadByte]; D = UUDecMap[input.ReadByte];
output.WriteByte((byte)(((A << 2) & 255) | ((B >> 4) & 3))); output.WriteByte((byte)(((B << 4) & 255) | ((C >> 2) & 15))); output.WriteByte((byte)(((C << 6) & 255) | (D & 63))); didx += 3; } }
if (didx < end) { A = UUDecMap[input.ReadByte]; B = UUDecMap[input.ReadByte]; output.WriteByte((byte)(((A << 2) & 255) | ((B >> 4) & 3))); didx++; }
if (didx < end) { B = UUDecMap[input.ReadByte]; C = UUDecMap[input.ReadByte]; output.WriteByte((byte)(((B << 4) & 255) | ((C >> 2) & 15))); didx++; }
// skip padding do { nextByte = input.ReadByte; } while (nextByte >= 0 && nextByte!= '\n' && nextByte!= '\r');
// skip end of line do { nextByte = input.ReadByte; } while (nextByte >= 0 && (nextByte == '\n' || nextByte == '\r')); } }
public static void UUEncode(System.IO.Stream input, System.IO.Stream output) { if (input == null) throw new ArgumentNullException("input");
if (output == null) throw new ArgumentNullException("output");
long len = input.Length; if (len == 0) return;
int sidx = 0; int line_len = 45; byte[] nl = Encoding.ASCII.GetBytes(Environment.NewLine);
byte A, B, C; // split into lines, adding line-length and line terminator while (sidx + line_len < len) { // line length output.WriteByte(UUEncMap[line_len]);
// 3-byte to 4-byte conversion + 0-63 to ascii printable conversion for (int end = sidx+line_len; sidx < end; sidx += 3) { A = (byte)input.ReadByte; B = (byte)input.ReadByte; C = (byte)input.ReadByte;
output.WriteByte(UUEncMap[(A >> 2) & 63]); output.WriteByte(UUEncMap[(B >> 4) & 15 | (A << 4) & 63]); output.WriteByte(UUEncMap[(C >> 6) & 3 | (B << 2) & 63]); output.WriteByte(UUEncMap[C & 63]); }
// line terminator for (int idx = 0; idx < nl.Length; idx++) output.WriteByte(nl[idx]); }
// line length output.WriteByte(UUEncMap[len-sidx]);
// 3-byte to 4-byte conversion + 0-63 to ascii printable conversion while (sidx + 2 < len) { A = (byte)input.ReadByte; B = (byte)input.ReadByte; C = (byte)input.ReadByte;
output.WriteByte(UUEncMap[(A >> 2) & 63]); output.WriteByte(UUEncMap[(B >> 4) & 15 | (A << 4) & 63]); output.WriteByte(UUEncMap[(C >> 6) & 3 | (B << 2) & 63]); output.WriteByte(UUEncMap[C & 63]); sidx += 3; }
if (sidx < len-1) { A = (byte)input.ReadByte; B = (byte)input.ReadByte;
output.WriteByte(UUEncMap[(A >> 2) & 63]); output.WriteByte(UUEncMap[(B >> 4) & 15 | (A << 4) & 63]); output.WriteByte(UUEncMap[(B << 2) & 63]); output.WriteByte(UUEncMap[0]); } else if (sidx < len) { A = (byte)input.ReadByte;
output.WriteByte(UUEncMap[(A >> 2) & 63]); output.WriteByte(UUEncMap[(A << 4) & 63]); output.WriteByte(UUEncMap[0]); output.WriteByte(UUEncMap[0]); }
// line terminator for (int idx = 0; idx < nl.Length; idx++) output.WriteByte(nl[idx]); } }