hashing of files

core/src/main/groovy/com/muwire/core/FileHasher.groovy

@@ -1,5 +1,11 @@
 package com.muwire.core
 
+import java.nio.MappedByteBuffer
+import java.nio.channels.FileChannel
+import java.nio.channels.FileChannel.MapMode
+import java.security.MessageDigest
+import java.security.NoSuchAlgorithmException
+
 class FileHasher {
 
 	/** max size of shared file is 128 GB */
@@ -21,4 +27,43 @@ class FileHasher {
 		
 		throw new IllegalArgumentException("File too large $size")
 	}
+	
+	final MessageDigest digest
+	
+	FileHasher() {
+		try {
+			digest = MessageDigest.getInstance("SHA-256")
+		} catch (NoSuchAlgorithmException impossible) {
+			digest = null
+			System.exit(1)
+		}
+	}
+	
+	InfoHash hashFile(File file) {
+		final long length = file.length()
+		final int size = 0x1 << getPieceSize(length)
+		int numPieces = (int) (length / size)
+		if (numPieces * size < length)
+			numPieces++
+			
+		def output = new ByteArrayOutputStream()
+		RandomAccessFile raf = new RandomAccessFile(file, "r")
+		try {
+			MappedByteBuffer buf
+			for (int i = 0; i < numPieces - 1; i++) {
+				buf = raf.getChannel().map(MapMode.READ_ONLY, size * i, size)
+				digest.update buf
+				output.write(digest.digest(), 0, 32)
+			}
+			def lastPieceLength = length - (numPieces - 1) * size
+			buf = raf.getChannel().map(MapMode.READ_ONLY, length - lastPieceLength, lastPieceLength)
+			digest.update buf
+			output.write(digest.digest(), 0, 32)
+		} finally {
+			raf.close()
+		}
+		
+		byte [] hashList = output.toByteArray()
+		InfoHash.fromHashList(hashList)
+	}
 }