From ac7e70883c18602e7fd4b525b9e6fb9ea9620a6b Mon Sep 17 00:00:00 2001
From: Keuin <keuinx@gmail.com>
Date: Wed, 20 Jan 2021 19:50:42 +0800
Subject: refactor

---
 .../incremental/identifier/Sha256Identifier.java   | 88 ++++++++++++++++++++++
 1 file changed, 88 insertions(+)
 create mode 100644 src/main/java/com/keuin/kbackupfabric/backup/incremental/identifier/Sha256Identifier.java

(limited to 'src/main/java/com/keuin/kbackupfabric/backup/incremental/identifier/Sha256Identifier.java')

diff --git a/src/main/java/com/keuin/kbackupfabric/backup/incremental/identifier/Sha256Identifier.java b/src/main/java/com/keuin/kbackupfabric/backup/incremental/identifier/Sha256Identifier.java
new file mode 100644
index 0000000..50e6aa4
--- /dev/null
+++ b/src/main/java/com/keuin/kbackupfabric/backup/incremental/identifier/Sha256Identifier.java
@@ -0,0 +1,88 @@
+package com.keuin.kbackupfabric.backup.incremental.identifier;
+
+import com.keuin.kbackupfabric.util.BytesUtil;
+
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.IOException;
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+import java.util.Objects;
+
+/**
+ * Identifier based on sha256.
+ * Immutable.
+ */
+public class Sha256Identifier extends SingleHashIdentifier {
+
+    private static final int SHA256_LENGTH = 32;
+    private static final Sha256Identifier DUMMY = new Sha256Identifier(new byte[SHA256_LENGTH]); // only for using its hash method
+    private static final FileIdentifierProvider<Sha256Identifier> factory = Sha256Identifier::fromFile;
+    private static final String marker = "S2";
+
+    public static Sha256Identifier fromFile(File file) throws IOException {
+        if (!file.isFile()) {
+            throw new IllegalArgumentException("file is not a file");
+        }
+        return new Sha256Identifier(DUMMY.hash(file));
+    }
+
+    /**
+     * Load sha-256 from a named file. Only used in StorageObjectLoader.
+     *
+     * @param fileName the file name.
+     * @return identifier.
+     */
+    static Sha256Identifier fromFileName(String fileName) {
+        if (!fileName.matches(marker + "-[0-9A-Fa-f]{32}"))
+            return null;
+        String hexString = fileName.substring(marker.length() + 1);
+        return new Sha256Identifier(BytesUtil.hexToBytes(hexString));
+    }
+
+    public static FileIdentifierProvider<Sha256Identifier> getFactory() {
+        return factory;
+    }
+
+    protected Sha256Identifier(byte[] hash) {
+        super(hash, marker);
+        Objects.requireNonNull(hash);
+        if (hash.length != SHA256_LENGTH) {
+            throw new IllegalStateException(String.format("SHA256 must be %d bytes", SHA256_LENGTH));
+        }
+    }
+
+    @Override
+    protected byte[] hash(File file) throws IOException {
+        try {
+            MessageDigest digest = MessageDigest.getInstance("SHA-256");
+
+            try (FileInputStream inputStream = new FileInputStream(file)) {
+                // This does not work. I don't know why
+//            FileChannel channel = inputStream.getChannel();
+//            ByteBuffer buffer = ByteBuffer.allocate(128);
+//            int readLength;
+//            while ((readLength = channel.read(buffer)) > 0)
+//                digest.update(buffer);
+
+                // This also works, without warnings
+                byte[] readBuffer = new byte[1024 * 1024];
+                int readLength;
+                while ((readLength = inputStream.read(readBuffer)) > 0)
+                    digest.update(readBuffer, 0, readLength);
+
+                // The below lines also works, but the IDE will complain about the while loop
+//            DigestInputStream digestInputStream = new DigestInputStream(inputStream, digest);
+//            while(digestInputStream.read() > 0)
+//                ;
+
+                return digest.digest();
+            }
+
+        } catch (NoSuchAlgorithmException ignored) {
+            // this shouldn't happen
+            return new byte[SHA256_LENGTH];
+        }
+    }
+
+}
-- 
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