Make temporary-file directory and buffer size configurable

src/main/java/org/verapdf/cos/COSDocument.java

@@ -30,6 +30,7 @@
 import org.verapdf.io.InternalInputStream;
 import org.verapdf.io.Reader;
 import org.verapdf.io.SeekableInputStream;
+import org.verapdf.io.TempFileHandler;
 import org.verapdf.pd.PDDocument;
 import org.verapdf.pd.encryption.StandardSecurityHandler;
 import org.verapdf.tools.resource.ASFileStreamCloser;
@@ -382,7 +383,7 @@ public void saveAs(final Writer writer) {
 	public void saveTo(final OutputStream stream) {
 		File temp = null;
 		try {
-			temp = File.createTempFile("tmp_pdf_file", ".pdf");
+			temp = TempFileHandler.createTempFile("tmp_pdf_file", ".pdf");
 			Writer pdfWriter = new Writer(this, temp.getAbsolutePath(),
 					this.getPDFSource().getStreamLength());
 			pdfWriter.writeIncrementalUpdate(changedObjects, addedObjects);

src/main/java/org/verapdf/io/InternalInputStream.java

@@ -286,7 +286,7 @@ private static File createTempFile(byte[] alreadyRead, InputStream input, Intege
 		if (maxStreamSize != null && alreadyRead.length > maxStreamSize) {
 			throw new VeraPDFParserException("Maximum allowed stream size exceeded");
 		}
-		File tmpFile = File.createTempFile("tmp_pdf_file", ".pdf");
+		File tmpFile = TempFileHandler.createTempFile("tmp_pdf_file", ".pdf");
 		try (FileOutputStream output = new FileOutputStream(tmpFile)) {
 			output.write(alreadyRead);
 			int totalRead = alreadyRead.length;

src/main/java/org/verapdf/io/InternalOutputStream.java

@@ -44,7 +44,7 @@ public class InternalOutputStream implements ASOutputStream, Closeable {
 	 * @throws IOException
 	 */
 	public static InternalOutputStream getInternalOutputStream() throws IOException {
-		File tempFile = File.createTempFile("tmp_pdf_file", ".pdf");
+		File tempFile = TempFileHandler.createTempFile("tmp_pdf_file", ".pdf");
 		return new InternalOutputStream(tempFile);
 	}
 

src/main/java/org/verapdf/io/SeekableInputStream.java

@@ -50,6 +50,13 @@ public abstract class SeekableInputStream extends ASInputStream implements BaseP
      */
     private static volatile Integer maxStreamSize = null;
 
+    /**
+     * Configurable in-memory buffer threshold: input up to this size is kept in memory, larger
+     * input is spilled to a temporary file. Defaults to {@link #MAX_BUFFER_SIZE}. A larger value
+     * trades memory for fewer temporary files; a smaller value does the opposite.
+     */
+    private static volatile int maxBufferSize = MAX_BUFFER_SIZE;
+
     /**
      * Sets the hard cap in bytes for a single spilled stream. A non-positive value removes the cap.
      *
@@ -66,6 +73,22 @@ public static Integer getMaxStreamSize() {
         return maxStreamSize;
     }
 
+    /**
+     * Sets the in-memory buffer threshold in bytes. Values below 1 restore the default.
+     *
+     * @param bytes buffer threshold in bytes, or a non-positive value for the default
+     */
+    public static void setMaxBufferSize(int bytes) {
+        maxBufferSize = bytes > 0 ? bytes : MAX_BUFFER_SIZE;
+    }
+
+    /**
+     * @return the current in-memory buffer threshold in bytes
+     */
+    public static int getMaxBufferSize() {
+        return maxBufferSize;
+    }
+
     /**
      * Goes to a particular byte in stream.
      *
@@ -203,7 +226,8 @@ public static SeekableInputStream getSeekableStream(InputStream stream, Integer
         int totalRead = 0;
         byte[] buffer = new byte[0];
         byte[] temp = new byte[ASBufferedInFilter.BF_BUFFER_SIZE];
-        int maximumSize = maxStreamSize == null ? MAX_BUFFER_SIZE : Math.min(MAX_BUFFER_SIZE, maxStreamSize + 1);
+        int bufferThreshold = maxBufferSize;
+        int maximumSize = maxStreamSize == null ? bufferThreshold : Math.min(bufferThreshold, maxStreamSize + 1);
         while (totalRead < maximumSize) {
             int read = stream.read(temp);
             if (read == -1) {

src/main/java/org/verapdf/io/TempFileHandler.java

@@ -0,0 +1,112 @@
+/*
+ * This file is part of veraPDF Parser, a module of the veraPDF project.
+ * Copyright (c) 2015-2026, veraPDF Consortium <info@verapdf.org>
+ * All rights reserved.
+ *
+ * veraPDF Parser is free software: you can redistribute it and/or modify
+ * it under the terms of either:
+ *
+ * The GNU General public license GPLv3+.
+ * You should have received a copy of the GNU General Public License
+ * along with veraPDF Parser as the LICENSE.GPL file in the root of the source
+ * tree.  If not, see http://www.gnu.org/licenses/ or
+ * https://www.gnu.org/licenses/gpl-3.0.en.html.
+ *
+ * The Mozilla Public License MPLv2+.
+ * You should have received a copy of the Mozilla Public License along with
+ * veraPDF Parser as the LICENSE.MPL file in the root of the source tree.
+ * If a copy of the MPL was not distributed with this file, you can obtain one at
+ * http://mozilla.org/MPL/2.0/.
+ */
+package org.verapdf.io;
+
+import java.io.File;
+import java.io.IOException;
+
+/**
+ * Central creation point for the temporary files that the parser writes while turning non-seekable
+ * input (embedded font programs, CMaps, decoded object streams, incremental-update output) into
+ * seekable data.
+ *
+ * <p>By default this behaves exactly like {@link File#createTempFile(String, String)} and writes into
+ * the JVM temporary directory ({@code java.io.tmpdir}). A caller that needs the temporary files in a
+ * specific directory - for example one directory per worker so files stay inside an isolated working
+ * area and can be removed deterministically - can configure a target directory. Two levels are offered:
+ * a process-wide default and a per-thread override that takes precedence. Both are optional; when
+ * neither is set the historical behaviour is preserved, so this change is backward compatible.</p>
+ *
+ * <p>The per-thread override is the natural fit for a server that validates one document per worker
+ * thread: set it before parsing, {@link #clearTempDirectory() clear} it afterwards.</p>
+ */
+public final class TempFileHandler {
+
+	private static volatile File defaultTempDirectory;
+
+	private static final ThreadLocal<File> TEMP_DIRECTORY = new ThreadLocal<>();
+
+	private TempFileHandler() {
+	}
+
+	/**
+	 * Sets the process-wide default directory for parser temporary files. {@code null} restores the
+	 * JVM default ({@code java.io.tmpdir}).
+	 *
+	 * @param directory target directory, or {@code null} for the JVM default
+	 */
+	public static void setDefaultTempDirectory(File directory) {
+		defaultTempDirectory = directory;
+	}
+
+	/**
+	 * @return the process-wide default directory, or {@code null} if none is configured
+	 */
+	public static File getDefaultTempDirectory() {
+		return defaultTempDirectory;
+	}
+
+	/**
+	 * Sets the temporary-file directory for the current thread only. It takes precedence over the
+	 * process-wide default and should be cleared when the thread is done ({@link #clearTempDirectory()}).
+	 *
+	 * @param directory target directory for this thread, or {@code null} to fall back to the default
+	 */
+	public static void setTempDirectory(File directory) {
+		if (directory == null) {
+			TEMP_DIRECTORY.remove();
+		} else {
+			TEMP_DIRECTORY.set(directory);
+		}
+	}
+
+	/**
+	 * Removes the per-thread temporary-file directory, falling back to the process-wide default.
+	 */
+	public static void clearTempDirectory() {
+		TEMP_DIRECTORY.remove();
+	}
+
+	/**
+	 * @return the directory that will be used for new temporary files on the current thread: the
+	 * per-thread override if set, otherwise the process-wide default, otherwise {@code null} (JVM default)
+	 */
+	public static File getTempDirectory() {
+		File perThread = TEMP_DIRECTORY.get();
+		return perThread != null ? perThread : defaultTempDirectory;
+	}
+
+	/**
+	 * Creates a temporary file, honouring the configured directory. Equivalent to
+	 * {@link File#createTempFile(String, String)} when no directory is configured.
+	 *
+	 * @param prefix file-name prefix, as for {@link File#createTempFile(String, String, File)}
+	 * @param suffix file-name suffix, or {@code null}
+	 * @return the newly created temporary file
+	 * @throws IOException if the file could not be created
+	 */
+	public static File createTempFile(String prefix, String suffix) throws IOException {
+		File directory = getTempDirectory();
+		return directory != null
+				? File.createTempFile(prefix, suffix, directory)
+				: File.createTempFile(prefix, suffix);
+	}
+}