pool: http-mover refactor file release on channel close code

Motivation:

There are a few ways in which a channel can close while transfers are
underway.  There is code in each case that handles closing all the files
currently being transferred.  This code is largely copy-n-pasted, with
some minor changes, which makes the code non-DRY.

This patch is in preparation for a subsequent patch that distinguishes
between a failed upload because the the client disconnected and a failed
upload because the connection was idle for too long.

Modification:

Handle file releasing in a single place.

Result:

No user- or admin observable changes.

Target: master
Requires-notes: no
Requires-book: no
Patch: https://rb.dcache.org/r/12471/
Acked-by: Tigran Mkrtchyan

modules/dcache/src/main/java/org/dcache/http/HttpPoolRequestHandler.java

@@ -64,6 +64,7 @@
 import static io.netty.handler.codec.http.HttpHeaders.is100ContinueExpected;
 import static io.netty.handler.codec.http.HttpResponseStatus.*;
 import static io.netty.handler.codec.http.HttpVersion.HTTP_1_1;
+import static java.util.Objects.requireNonNull;
 import static org.dcache.util.Checksums.TO_RFC3230;
 import static org.dcache.util.StringMarkup.percentEncode;
 import static org.dcache.util.StringMarkup.quotedString;
@@ -113,6 +114,28 @@ public class HttpPoolRequestHandler extends HttpRequestHandler
 
     private Optional<ChecksumType> _wantedDigest;
 
+    /**
+     * A simple data class to encapsulate the errors to return by the mover to
+     * the pool for file uploads and downloads, should transfers be aborted.
+     */
+    private static class FileReleaseErrors
+    {
+        private Optional<? extends Exception> errorForDownload = Optional.empty();
+        private Optional<? extends Exception> errorForUpload = Optional.empty();
+
+        public FileReleaseErrors downloadsSeeError(Exception e)
+        {
+            errorForDownload = Optional.of(requireNonNull(e));
+            return this;
+        }
+
+        public FileReleaseErrors uploadsSeeError(Exception e)
+        {
+            errorForUpload = Optional.of(requireNonNull(e));
+            return this;
+        }
+    }
+
     public HttpPoolRequestHandler(NettyTransferService<HttpProtocolInfo> server, int chunkSize)
     {
         _server = server;
@@ -238,35 +261,44 @@ public void channelActive(ChannelHandlerContext ctx) throws Exception
         _logger.debug("HTTP connection from {} established", ctx.channel().remoteAddress());
     }
 
-    @Override
-    public void channelInactive(ChannelHandlerContext ctx) throws Exception
+    private static FileReleaseErrors uploadsSeeError(Exception e)
+    {
+        return new FileReleaseErrors().uploadsSeeError(e);
+    }
+
+    private static FileReleaseErrors downloadsSeeError(Exception e)
+    {
+        return new FileReleaseErrors().downloadsSeeError(e);
+    }
+
+    private void releaseAllFiles(FileReleaseErrors errors)
     {
-        _logger.debug("HTTP connection from {} closed", ctx.channel().remoteAddress());
         for (NettyTransferService<HttpProtocolInfo>.NettyMoverChannel file: _files) {
-            if (file == _writeChannel) {
-                file.release(new FileCorruptedCacheException("Connection lost before end of file."));
+            Optional<? extends Exception> possibleError = file == _writeChannel
+                    ? errors.errorForUpload : errors.errorForDownload;
+            if (possibleError.isPresent()) {
+                file.release(possibleError.get());
             } else {
                 file.release();
             }
         }
         _files.clear();
     }
 
+    @Override
+    public void channelInactive(ChannelHandlerContext ctx) throws Exception
+    {
+        _logger.debug("HTTP connection from {} closed", ctx.channel().remoteAddress());
+        releaseAllFiles(uploadsSeeError(new FileCorruptedCacheException("Connection lost before end of file.")));
+    }
+
     public void exceptionCaught(ChannelHandlerContext ctx, Throwable t)
     {
         if (t instanceof ClosedChannelException) {
             _logger.info("Connection {} unexpectedly closed.", ctx.channel());
         } else if (t instanceof Exception) {
-            for (NettyTransferService<HttpProtocolInfo>.NettyMoverChannel file : _files) {
-                CacheException cause;
-                if (file == _writeChannel) {
-                    cause = new FileCorruptedCacheException("Connection lost before end of file: " + t, t);
-                } else {
-                    cause = new CacheException(t.toString(), t);
-                }
-                file.release(cause);
-            }
-            _files.clear();
+            releaseAllFiles(downloadsSeeError(new CacheException(t.toString(), t))
+                    .uploadsSeeError(new FileCorruptedCacheException("Connection lost before end of file: " + t, t)));
             ctx.close();
         } else {
             Thread me = Thread.currentThread();