[GitHub] [lucene-solr] dweiss commented on a change in pull request #2258: LUCENE-9686: Fix read past EOF handling in DirectIODirectory

[GitBox <gi...@apache.org>]

dweiss commented on a change in pull request #2258:
URL: https://github.com/apache/lucene-solr/pull/2258#discussion_r568136570



##########
File path: lucene/misc/src/java/org/apache/lucene/misc/store/DirectIODirectory.java
##########
@@ -381,17 +377,18 @@ public long length() {
     @Override
     public byte readByte() throws IOException {
       if (!buffer.hasRemaining()) {
-        refill();
+        refill(1);
       }
+
       return buffer.get();
     }
 
-    private void refill() throws IOException {
+    private void refill(int byteToRead) throws IOException {

Review comment:
       Should it be plural (bytesToRead)?

##########
File path: lucene/misc/src/java/org/apache/lucene/misc/store/DirectIODirectory.java
##########
@@ -381,17 +377,18 @@ public long length() {
     @Override
     public byte readByte() throws IOException {
       if (!buffer.hasRemaining()) {
-        refill();
+        refill(1);
       }
+
       return buffer.get();
     }
 
-    private void refill() throws IOException {
+    private void refill(int byteToRead) throws IOException {
       filePos += buffer.capacity();
 
       // BaseDirectoryTestCase#testSeekPastEOF test for consecutive read past EOF,
       // hence throwing EOFException early to maintain buffer state (position in particular)
-      if (filePos > channel.size()) {
+      if (filePos > channel.size() || (channel.size() - filePos < byteToRead)) {

Review comment:
       I wonder if we should move the channel's position to actually point after the last byte, then throw EOFException... so that not only we indicate an EOF but also leave the channel pointing at the end. I have a scenario in my mind when somebody tries to read a bulk of bytes, hits an eof but then a single-byte read() succeeds. That would be awkward, wouldn't it? 
   
   A refill should try to read as many bytes as it can (min(channel.size() -filePos, bytesToRead)), then potentially fail if bytesToRead is still >0 and channel is at EOF. Or is my thinking flawed somewhere?




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