Book.getContentHash() implementation

src/org/geometerplus/android/fbreader/api/ApiServerImplementation.java

@@ -186,8 +186,7 @@ public class ApiServerImplementation extends ApiInterface.Stub implements Api, A
 	}
 
 	public String getBookHash() {
-		// TODO: implement
-		return null;
+		return myReader.Model.Book.getContentHashCode();
 	}
 
 	// page information

src/org/geometerplus/fbreader/library/Book.java

@@ -20,6 +20,10 @@
 package org.geometerplus.fbreader.library;
 
 import java.util.*;
+import java.io.InputStream;
+import java.io.IOException;
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
 
 import org.geometerplus.zlibrary.core.util.ZLMiscUtil;
 import org.geometerplus.zlibrary.core.filesystem.*;
@@ -415,6 +419,41 @@ public class Book {
 		}
 	}
 
+	public String getContentHashCode() {
+		InputStream stream = null;
+
+		try {
+			final MessageDigest hash = MessageDigest.getInstance("SHA-256");
+			stream = File.getInputStream();
+
+			final byte[] buffer = new byte[2048];
+			while (true) {
+				final int nread = stream.read(buffer);
+				if (nread == -1) {
+					break;
+				}
+				hash.update(buffer, 0, nread);
+			}
+
+			final Formatter f = new Formatter();
+			for (byte b : hash.digest()) {
+				f.format("%02X", b & 0xFF);
+			}
+			return f.toString();
+		} catch (IOException e) {
+			return null;
+		} catch (NoSuchAlgorithmException e) {
+			return null;
+		} finally {
+			if (stream != null) {
+				try {
+					stream.close();
+				} catch (IOException e) {
+				}
+			}
+		}
+	}
+
 	@Override
 	public int hashCode() {
 		return (int)myId;