sahilTakiar commented on a change in pull request #597: HDFS-3246: pRead
equivalent for direct read path
URL: https://github.com/apache/hadoop/pull/597#discussion_r267932621
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File path:
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/crypto/CryptoInputStream.java
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@@ -375,7 +397,70 @@ private void decrypt(long position, byte[] buffer, int
offset, int length)
returnDecryptor(decryptor);
}
}
-
+
+ /**
+ * Decrypt n bytes in buf starting at start. Output is also put into buf
+ * starting at current position. buf.position() and buf.limit() should be
+ * unchanged after decryption. It is thread-safe.
+ *
+ * <p>
+ * This method decrypts the input buf chunk-by-chunk and writes the
+ * decrypted output back into the input buf. It uses two local buffers
+ * taken from the {@link #bufferPool} to assist in this process: one is
+ * designated as the input buffer and it stores a single chunk of the
+ * given buf, the other is designated as the output buffer, which stores
+ * the output of decrypting the input buffer. Both buffers are of size
+ * {@link #bufferSize}.
+ * </p>
+ *
+ * <p>
+ * Decryption is done by using a {@link Decryptor} and the
+ * {@link #decrypt(Decryptor, ByteBuffer, ByteBuffer, byte)} method. Once
+ * the decrypted data is written into the output buffer, is is copied back
+ * into buf. Both buffers are returned back into the pool once the entire
+ * buf is decrypted.
+ * </p>
+ */
+ private void decrypt(long position, ByteBuffer buf, int n, int start)
+ throws IOException {
+ ByteBuffer localInBuffer = getBuffer();
+ ByteBuffer localOutBuffer = getBuffer();
+ final int pos = buf.position();
+ final int limit = buf.limit();
+ int len = 0;
+ Decryptor localDecryptor = null;
+ try {
+ localDecryptor = getDecryptor();
+ byte[] localIV = initIV.clone();
+ updateDecryptor(localDecryptor, position, localIV);
+ byte localPadding = getPadding(position);
+ // Set proper position for inputdata.
+ localInBuffer.position(localPadding);
+
+ while (len < n) {
+ buf.position(start + len);
+ buf.limit(start + len + Math.min(n - len, localInBuffer.remaining()));
+ localInBuffer.put(buf);
+ // Do decryption
+ try {
+ decrypt(localDecryptor, localInBuffer, localOutBuffer, localPadding);
+ buf.position(start + len);
+ buf.limit(limit);
Review comment:
Well the invariant you want to preserve is that `buf.put(inputBuf)` should
only be called with the original value of `buf.limit()` so that you don't
exceed the given limit. Using `start + len + Math.min(n - len,
localInBuffer.remaining())` as the limit could violate this if `n + start >
buf.limit()`.
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