Added Multihash type

Author: ianopolous

src/org/ipfs/Multihash.java

@@ -0,0 +1,76 @@
+package org.ipfs;
+
+import java.io.*;
+import java.util.*;
+
+public class Multihash {
+    enum Type {
+        sha1(0x11, 20),
+        sha2_256(0x12, 32),
+        sha2_512(0x13, 64),
+        sha3(0x14, 64),
+        blake2b(0x40, 64),
+        blake2s(0x41, 32);
+
+        public int index, length;
+
+        Type(int index, int length) {
+            this.index = index;
+            this.length = length;
+        }
+
+        private static Map<Integer, Type> lookup = new TreeMap<>();
+        static {
+            for (Type t: Type.values())
+                lookup.put(t.index, t);
+        }
+
+        public static Type lookup(int t) {
+            if (!lookup.containsKey(t))
+                throw new IllegalStateException("Unknown Multihash type: "+t);
+            return lookup.get(t);
+        }
+    }
+
+    public final Type type;
+    public final byte size;
+    public final byte[] hash;
+
+    public Multihash(Type type, byte size, byte[] hash) {
+        if ((size & 0xff) != hash.length)
+            throw new IllegalStateException("Incorrect size: " + (size&0xff) + " != "+hash.length);
+        if (hash.length != type.length)
+            throw new IllegalStateException("Incorrect hash length: " + hash.length + " != "+type.length);
+        this.type = type;
+        this.size = size;
+        this.hash = hash;
+    }
+
+    public Multihash(byte[] multihash) {
+        this(Type.lookup(multihash[0] & 0xff), multihash[1], Arrays.copyOfRange(multihash, 2, multihash.length));
+    }
+
+    public byte[] toBytes() {
+        byte[] res = new byte[hash.length+2];
+        res[0] = (byte)type.index;
+        res[1] = (byte)hash.length;
+        System.arraycopy(hash, 0, res, 2, hash.length);
+        return res;
+    }
+
+    public String toHex() {
+        StringBuilder res = new StringBuilder();
+        for (byte b: toBytes())
+            res.append(String.format("%x", b&0xff));
+        return res.toString();
+    }
+
+    public static Multihash fromHex(String hex) {
+        if (hex.length() % 2 != 0)
+            throw new IllegalStateException("Uneven number of hex digits!");
+        ByteArrayOutputStream bout = new ByteArrayOutputStream();
+        for (int i=0; i < hex.length()-1; i+= 2)
+            bout.write(Integer.valueOf(hex.substring(i, i+2), 16));
+        return new Multihash(bout.toByteArray());
+    }
+}