context: //
  // Mono.Unix/UnixMarshal.cs
  //
  // Authors:
  //   Jonathan Pryor (jonpryor@vt.edu)
  //
  // (C) 2004-2006 Jonathan Pryor
  //
  // Permission is hereby granted, free of charge, to any person obtaining
  // a copy of this software and associated documentation files (the
  // "Software"), to deal in the Software without restriction, including
  // without limitation the rights to use, copy, modify, merge, publish,
  // distribute, sublicense, and/or sell copies of the Software, and to
  // permit persons to whom the Software is furnished to do so, subject to
  // the following conditions:
  // 
  // The above copyright notice and this permission notice shall be
  // included in all copies or substantial portions of the Software.
  // 
  // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  // EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  // MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  // NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
  // LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
  // OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
  // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  //
  
  using System;
  using System.IO;
  using System.Net.Sockets;
  using System.Runtime.InteropServices;
  using System.Runtime.Serialization;
  using System.Text;
  using Mono.Unix;
  
  namespace Mono.Unix {
  
  	// Scenario:  We want to be able to translate an Error to a string.
  	//  Problem:  Thread-safety.  Strerror(3) isn't thread safe (unless
  	//            thread-local-variables are used, which is probably only 
  	//            true on Windows).
  	// Solution:  Use strerror_r().
  	//  Problem:  strerror_r() isn't portable. 
  	//            (Apparently Solaris doesn't provide it.)
  	// Solution:  Cry.  Then introduce an intermediary, ErrorMarshal.
  	//            ErrorMarshal exposes a single public delegate, Translator,
  	//            which will convert an Error to a string.  It's static
  	//            constructor first tries using strerror_r().  If it works,
  	//            great; use it in the future.  If it doesn't work, fallback to
  	//            using strerror(3).
  	//            This should be thread safe, since the check is done within the
  	//            class constructor lock.
  	//            Strerror(3) will be thread-safe from managed code, but won't
  	//            be thread-safe between managed & unmanaged code.
  	internal class ErrorMarshal
  	{
  		internal delegate string ErrorTranslator (Native.Errno errno);
  
  		internal static readonly ErrorTranslator Translate;
  
  		static ErrorMarshal ()
  		{
  			try {
  				Translate = new ErrorTranslator (strerror_r);
  				Translate (Native.Errno.ERANGE);
  			}
  			catch (EntryPointNotFoundException) {
  				Translate = new ErrorTranslator (strerror);
  			}
  		}
  
  		private static string strerror (Native.Errno errno)
  		{
  			return Native.Stdlib.strerror (errno);
  		}
  
  		private static string strerror_r (Native.Errno errno)
  		{
  			StringBuilder buf = new StringBuilder (16);
  			int r = 0;
  			do {
  				buf.Capacity *= 2;
  				r = Native.Syscall.strerror_r (errno, buf);
  			} while (r == -1 && Native.Stdlib.GetLastError() == Native.Errno.ERANGE);
  
  			if (r == -1)
  				return "** Unknown error code: " + ((int) errno) + "**";
  			return buf.ToString();
  		}
  	}
  
  	public sealed /* static */ class UnixMarshal
  	{
  		private UnixMarshal () {}
  
  		[CLSCompliant (false)]
  		public static string GetErrorDescription (Native.Errno errno)
  		{
  			return ErrorMarshal.Translate (errno);
  		}
  
  		public static IntPtr AllocHeap (long size)
  		{
  			if (size < 0)
  				throw new ArgumentOutOfRangeException ("size", "< 0");
  			return Native.Stdlib.malloc ((ulong) size);
  		}
  
  		public static IntPtr ReAllocHeap (IntPtr ptr, long size)
  		{
  			if (size < 0)
  				throw new ArgumentOutOfRangeException ("size", "< 0");
  			return Native.Stdlib.realloc (ptr, (ulong) size);
  		}
  
  		public static void FreeHeap (IntPtr ptr)
  		{
  			Native.Stdlib.free (ptr);
  		}
  
  		public static unsafe string PtrToStringUnix (IntPtr p)
  		{
  			if (p == IntPtr.Zero)
  				return null;
  
  			int len = checked ((int) Native.Stdlib.strlen (p));
  			return new string ((sbyte*) p, 0, len, UnixEncoding.Instance);
  		}
  
  		public static string PtrToString (IntPtr p)
  		{
  			if (p == IntPtr.Zero)
  				return null;
  			return PtrToString (p, UnixEncoding.Instance);
  		}
  
  		public static unsafe string PtrToString (IntPtr p, Encoding encoding)
  		{
  			if (p == IntPtr.Zero)
  				return null;
  
  			if (encoding == null)
  				throw new ArgumentNullException ("encoding");
  
  			int len = GetStringByteLength (p, encoding);
  
  			// Due to variable-length encoding schemes, GetStringByteLength() may
  			// have returned multiple "null" characters.  (For example, when
  			// encoding a string into UTF-8 there will be 4 terminating nulls.)
  			// We don't want these null's to be in the returned string, so strip
  			// them off.
  			string s = new string ((sbyte*) p, 0, len, encoding);
  			len = s.Length;
  			while (len > 0 && s [len-1] == 0)
  				--len;
  			if (len == s.Length) 
  				return s;
  			return s.Substring (0, len);
  		}
  
  		private static int GetStringByteLength (IntPtr p, Encoding encoding)
  		{
  			Type encodingType = encoding.GetType ();
  
  			int len = -1;
  
  			// Encodings that will always end with a single null byte
  			if (typeof(UTF8Encoding).IsAssignableFrom (encodingType) ||
  					typeof(UTF7Encoding).IsAssignableFrom (encodingType) ||
  					typeof(UnixEncoding).IsAssignableFrom (encodingType) ||
  					typeof(ASCIIEncoding).IsAssignableFrom (encodingType)) {
  				len = checked ((int) Native.Stdlib.strlen (p));
  			}
  			// Encodings that will always end with a 0x0000 16-bit word
  			else if (typeof(UnicodeEncoding).IsAssignableFrom (encodingType)) {
  				len = GetInt16BufferLength (p);
  			}
  			// Some non-public encoding, such as Latin1 or a DBCS charset.
  			// Look for a sequence of encoding.GetMaxByteCount() bytes that are all
  			// 0, which should be the terminating null.
  			// This is "iffy", since it may fail for variable-width encodings; for
  			// example, UTF8Encoding.GetMaxByteCount(1) = 4, so this would read 3
  			// bytes past the end of the string, possibly into garbage memory
  			// (which is why we special case UTF above).
  			else {
  				len = GetRandomBufferLength (p, encoding.GetMaxByteCount(1));
  			}
  
  			if (len == -1)
  				throw new NotSupportedException ("Unable to determine native string buffer length");
  			return len;
  		}
  
  		private static int GetInt16BufferLength (IntPtr p)
  		{
  			int len = 0;
  			while (Marshal.ReadInt16 (p, len*2) != 0)
  				checked {++len;}
  			return checked(len*2);
  		}
  
  		private static int GetInt32BufferLength (IntPtr p)
  		{
  			int len = 0;
  			while (Marshal.ReadInt32 (p, len*4) != 0)
  				checked {++len;}
  			return checked(len*4);
  		}
  
  		private static int GetRandomBufferLength (IntPtr p, int nullLength)
  		{
  			switch (nullLength) {
  				case 1: return checked ((int) Native.Stdlib.strlen (p));
  				case 2: return GetInt16BufferLength (p);
  				case 4: return GetInt32BufferLength (p);
  			}
  
  			int len = 0;
  			int num_null_seen = 0;
  
  			do {
  				byte b = Marshal.ReadByte (p, len++);
  				if (b == 0)
  					++num_null_seen;
  				else
  					num_null_seen = 0;
  			} while (num_null_seen != nullLength);
  
  			return len;
  		}
  
  		/*
  		 * Marshal a C `char **'.  ANSI C `main' requirements are assumed:
  		 *
  		 *   stringArray is an array of pointers to C strings
  		 *   stringArray has a terminating NULL string.
  		 *
  		 * For example:
  		 *   stringArray[0] = "string 1";
  		 *   stringArray[1] = "string 2";
  		 *   stringArray[2] = NULL
  		 *
  		 * The terminating NULL is required so that we know when to stop looking
  		 * for strings.
  		 */
  		public static string[] PtrToStringArray (IntPtr stringArray)
  		{
  			return PtrToStringArray (stringArray, UnixEncoding.Instance);
  		}
  
  		public static string[] PtrToStringArray (IntPtr stringArray, Encoding encoding)
  		{
  			if (stringArray == IntPtr.Zero)
  				return new string[]{};
  
  			int argc = CountStrings (stringArray);
  			return PtrToStringArray (argc, stringArray, encoding);
  		}
  
  		private static int CountStrings (IntPtr stringArray)
  		{
  			int count = 0;
  			while (Marshal.ReadIntPtr (stringArray, count*IntPtr.Size) != IntPtr.Zero)
  				++count;
  			return count;
  		}
  
  		/*
  		 * Like PtrToStringArray(IntPtr), but it allows the user to specify how
  		 * many strings to look for in the array.  As such, the requirement for a
  		 * terminating NULL element is not required.
  		 *
  		 * Usage is similar to ANSI C `main': count is argc, stringArray is argv.
  		 * stringArray[count] is NOT accessed (though ANSI C requires that 
  		 * argv[argc] = NULL, which PtrToStringArray(IntPtr) requires).
  		 */
  		public static string[] PtrToStringArray (int count, IntPtr stringArray)
  		{
  			return PtrToStringArray (count, stringArray, UnixEncoding.Instance);
  		}
  
  		public static string[] PtrToStringArray (int count, IntPtr stringArray, Encoding encoding)
  		{
  			if (count < 0)
  				throw new ArgumentOutOfRangeException ("count", "< 0");
  			if (encoding == null)
  				throw new ArgumentNullException ("encoding");
  			if (stringArray == IntPtr.Zero)
  				return new string[count];
  
  			string[] members = new string[count];
  			for (int i = 0; i < count; ++i) {
  				IntPtr s = Marshal.ReadIntPtr (stringArray, i * IntPtr.Size);
  				members[i] = PtrToString (s, encoding);
  			}
  
  			return members;
  		}
  
  		public static IntPtr StringToHeap (string s)
  		{
  			return StringToHeap (s, UnixEncoding.Instance);
  		}
  
  		public static IntPtr StringToHeap (string s, Encoding encoding)
  		{
  			return StringToHeap (s, 0, s.Length, encoding);
  		}
  
  		public static IntPtr StringToHeap (string s, int index, int count)
  		{
  			return StringToHeap (s, index, count, UnixEncoding.Instance);
  		}
  
  		public static IntPtr StringToHeap (string s, int index, int count, Encoding encoding)
  		{
  			if (s == null)
  				return IntPtr.Zero;
  
  			if (encoding == null)
  				throw new ArgumentNullException ("encoding");
  
  			int min_byte_count = encoding.GetMaxByteCount(1);
  			char[] copy = s.ToCharArray (index, count);
  			byte[] marshal = new byte [encoding.GetByteCount (copy) + min_byte_count];
  
  			int bytes_copied = encoding.GetBytes (copy, 0, copy.Length, marshal, 0);
  
  			if (bytes_copied != (marshal.Length-min_byte_count))
  				throw new NotSupportedException ("encoding.GetBytes() doesn't equal encoding.GetByteCount()!");
  
  			IntPtr mem = AllocHeap (marshal.Length);
  			if (mem == IntPtr.Zero)
  				throw new UnixIOException (Native.Errno.ENOMEM);
  
  			bool copied = false;
  			try {
  				Marshal.Copy (marshal, 0, mem, marshal.Length);
  				copied = true;
  			}
  			finally {
  				if (!copied)
  					FreeHeap (mem);
  			}
  
  			return mem;
  		}
  
  		public static bool ShouldRetrySyscall (int r)
  		{
  			if (r == -1 && Native.Stdlib.GetLastError () == Native.Errno.EINTR)
  				return true;
  			return false;
  		}
  
  		[CLSCompliant (false)]
  		public static bool ShouldRetrySyscall (int r, out Native.Errno errno)
  		{
  			errno = (Native.Errno) 0;
  			if (r == -1 && (errno = Native.Stdlib.GetLastError ()) == Native.Errno.EINTR)
  				return true;
  			return false;
  		}
  
  		// we can't permit any printf(3)-style formatting information, since that
  		// would kill the stack.  However, replacing %% is silly, and some %* are
  		// permitted (such as %m in syslog to print strerror(errno)).
  		internal static string EscapeFormatString (string message, 
  				char [] permitted)
  		{
  			if (message == null)
  				return "";
  			StringBuilder sb = new StringBuilder (message.Length);
  			for (int i = 0; i < message.Length; ++i) {
  				char c = message [i];
  				sb.Append (c);
  				if (c == '%' && (i+1) < message.Length) {
  					char n = message [i+1];
  					if (n == '%' || IsCharPresent (permitted, n))
  						sb.Append (n);
  					else
  						sb.Append ('%').Append (n);
  					++i;
  				}
  				// invalid format string: % at EOS.
  				else if (c == '%')
  					sb.Append ('%');
  			}
  			return sb.ToString ();
  		}
  
  		private static bool IsCharPresent (char[] array, char c)
  		{
  			if (array == null)
  				return false;
  
gt: 			for (int i = 0; i < array.Length; ++i)