Fleshed out implementation.

PUP/BCPLString.cs

@@ -0,0 +1,89 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace IFS
+{    
+    /// <summary>
+    /// A BCPL string is one byte of length N followed by N bytes of ASCII. 
+    /// This class is a (very) simple encapsulation of that over a byte array.
+    /// </summary>
+    public class BCPLString
+    {
+        public BCPLString(string s)
+        {
+            if (s.Length > 255)
+            {
+                throw new InvalidOperationException("Max length for a BCPL string is 255 characters.");
+            }
+            
+            _string = new byte[_string.Length];
+
+            // We simply take the low 8-bits of each Unicode character and stuff it into the
+            // byte array.  This works fine for the ASCII subset of Unicode but obviously
+            // is bad for everything else.  This is unlikely to be an issue given the lack of
+            // any real internationalization support on the IFS end of things, but might be
+            // something to look at.
+            for(int i=0;i< _string.Length; i++)
+            {
+                _string[i] = (byte)s[i];
+            }
+        }
+
+        /// <summary>
+        /// Build a new BCPL string from the raw representation
+        /// </summary>
+        /// <param name="rawData"></param>
+        public BCPLString(byte[] rawData)
+        {            
+            if (rawData.Length > 256)
+            {
+                throw new InvalidOperationException("Max length for a BCPL string is 255 characters.");
+            }
+
+            // Sanity check that first byte matches length of data sent to us
+            if (rawData.Length < 1 || rawData[0] != rawData.Length - 1)
+            {
+                throw new InvalidOperationException("BCPL length data is invalid.");
+            }
+
+            _string = new byte[rawData.Length - 1];
+            Array.Copy(rawData, 1, _string, 0, rawData.Length - 1);
+        }
+
+        /// <summary>
+        /// Returns a native representation of the BCPL string
+        /// </summary>
+        /// <returns></returns>
+        public override string ToString()
+        {
+            StringBuilder sb = new StringBuilder();
+
+            // See notes in constructor re: unicode.
+            for (int i = 0; i < _string.Length; i++)
+            {
+                sb.Append((char)_string[i]);                
+            }
+
+            return sb.ToString();
+        }
+
+        /// <summary>
+        /// Returns the raw representation of the BCPL string
+        /// </summary>
+        /// <returns></returns>
+        public byte[] ToArray()
+        {
+            byte[] a = new byte[_string.Length + 1];
+
+            a[0] = (byte)_string.Length;
+            _string.CopyTo(a, 1);
+
+            return a;
+        }
+
+        private byte[] _string;
+    }
+}