Added FileHash Object

src/main/java/ru/bclib/api/dataexchange/FileHash.java

@@ -0,0 +1,151 @@
+package ru.bclib.api.dataexchange;
+
+import net.minecraft.network.FriendlyByteBuf;
+import org.jetbrains.annotations.NotNull;
+import ru.bclib.BCLib;
+
+import java.io.File;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+import java.util.Arrays;
+import java.util.Objects;
+
+/**
+ * Calculates a hash based on the contents of a File.
+ * <p>
+ * A File-Hash contains the md5-sum of the File, as well as its size and byte-values from defined positions
+ * <p>
+ * You can compare instances using {@link #equals(Object)} to determine if two files are
+ * identical.
+ */
+public class FileHash {
+    /**
+     * The md5-hash of the file
+     */
+    @NotNull
+    public final byte[] md5;
+
+    /**
+     * The size (in bytes) of the input.
+     */
+    public final int size;
+
+    /**
+     * a value that is directly calculated from defined byte positions.
+     */
+    public final int value;
+
+    FileHash(byte[] md5, int size, int value) {
+        Objects.nonNull(md5);
+        this.md5 = md5;
+        this.size = size;
+        this.value = value;
+    }
+
+    @Override
+    public String toString() {
+        return String.format("%08x", size)
+            + "-"
+            + String.format("%08x", value)
+            + "-"
+            + getMd5String();
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        FileHash that = (FileHash) o;
+        return size == that.size && value == that.value && Arrays.equals(md5, that.md5);
+    }
+
+    @Override
+    public int hashCode() {
+        int result = Objects.hash(size, value);
+        result = 31 * result + Arrays.hashCode(md5);
+        return result;
+    }
+
+    /**
+     * Convert the md5-hash to a human readable string
+     * @return The converted String
+     */
+    public String getMd5String(){
+        return toHexString(md5);
+    }
+    /**
+     * Serializes the Object to a buffer
+     * @param buf The buffer to write to
+     */
+    public void writeString(FriendlyByteBuf buf) {
+        buf.writeInt(size);
+        buf.writeInt(value);
+        buf.writeByteArray(md5);
+    }
+
+    /**
+     *Deserialize a Buffer to a new {@link FileHash}-Object
+     * @param buf Thea buffer to read from
+     * @return The received String
+     */
+    public static FileHash readString(FriendlyByteBuf buf){
+        final int size = buf.readInt();
+        final int value = buf.readInt();
+        final byte[] md5 = buf.readByteArray();
+
+        return new FileHash(md5, size, value);
+    }
+
+    /**
+     * Converts a byte-array to a hex-string representation
+     * @param bytes The source array
+     * @return The resulting string, or an empty String if the input was {@code null}
+     */
+    public static String toHexString(byte[] bytes) {
+        if (bytes==null) return "";
+
+        StringBuilder sb = new StringBuilder();
+        for (byte b : bytes) {
+            sb.append(String.format("%02x", b));
+        }
+        return sb.toString();
+    }
+
+    /**
+     * Create a new {@link FileHash}.
+     * @param file The input file
+     * @return A new Instance. You can compare instances using {@link #equals(Object)} to determine if two files are
+     * identical.
+     */
+    public static FileHash createFromBinary(File file){
+        if (!file.exists()) return null;
+        final Path path = file.toPath();
+
+        int size = 0;
+        byte[] md5 = new byte[0];
+        int value = 0;
+
+        try {
+            byte[] data = Files.readAllBytes(path);
+
+            size = data.length;
+
+            value = size>0 ? (data[size/3] | (data [size/2]<<8) | (data [size/5]<<16)) : -1;
+            if (size>20) value |= data[20]<<24;
+
+            MessageDigest md = MessageDigest.getInstance("MD5");
+            md.update(data);
+            md5 = md.digest();
+
+            return new FileHash(md5, size, value);
+        } catch (IOException e) {
+            BCLib.LOGGER.error("Failed to read file: " + file);
+            return null;
+        } catch (NoSuchAlgorithmException e) {
+            BCLib.LOGGER.error("Unable to build hash for file: " + file);
+        }
+    }
+}