# MultipartStream.java

    /*
     * Licensed to the Apache Software Foundation (ASF) under one or more
     * contributor license agreements.  See the NOTICE file distributed with
     * this work for additional information regarding copyright ownership.
     * The ASF licenses this file to You under the Apache License, Version 2.0
     * (the "License"); you may not use this file except in compliance with
     * the License.  You may obtain a copy of the License at
     *
     *      http://www.apache.org/licenses/LICENSE-2.0
     *
     * Unless required by applicable law or agreed to in writing, software
     * distributed under the License is distributed on an "AS IS" BASIS,
     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     * See the License for the specific language governing permissions and
     * limitations under the License.
     */
    package org.apache.commons.fileupload;

    import java.io.ByteArrayOutputStream;
    import java.io.IOException;
    import java.io.InputStream;
    import java.io.OutputStream;
    import java.io.UnsupportedEncodingException;

    import org.apache.commons.fileupload.FileUploadBase.FileUploadIOException;
    import org.apache.commons.fileupload.FileUploadBase.SizeLimitExceededException;
    import org.apache.commons.fileupload.util.Closeable;
    import org.apache.commons.fileupload.util.Streams;

    /**
     * Low level API for processing file uploads.
     *
     * <p>
     * This class can be used to process data streams conforming to MIME 'multipart' format as defined in <a href="http://www.ietf.org/rfc/rfc1867.txt">RFC
     * 1867</a>. Arbitrarily large amounts of data in the stream can be processed under constant memory usage.
     * </p>
     *
     * <p>
     * The format of the stream is defined in the following way:
     * </p>
     *
     * <pre>{@code
     *   multipart-body := preamble 1*encapsulation close-delimiter epilogue
     *   encapsulation := delimiter body CRLF
     *   delimiter := "--" boundary CRLF
     *   close-delimiter := "--" boundary "--"
     *   preamble := &lt;ignore&gt;
     *   epilogue := &lt;ignore&gt;
     *   body := header-part CRLF body-part
     *   header-part := 1*header CRLF
     *   header := header-name ":" header-value
     *   header-name := &lt;printable ASCII characters except ":"&gt;
     *   header-value := &lt;any ASCII characters except CR &amp; LF&gt;
     *   body-data := &lt;arbitrary data&gt;
     * }</pre>
     *
     * <p>
     * Note that body-data can contain another mulipart entity. There is limited support for single pass processing of such nested streams. The nested stream is
     * <strong>required</strong> to have a boundary token of the same length as the parent stream (see {@link #setBoundary(byte[])}).
     * </p>
     *
     * <p>
     * Here is an example of usage of this class.
     * </p>
     *
     * <pre>{@code
     * try {
     *     MultipartStream multipartStream = new MultipartStream(input, boundary);
     *     boolean nextPart = multipartStream.skipPreamble();
     *     OutputStream output;
     *     while (nextPart) {
     *         String header = multipartStream.readHeaders();
     *         // process headers
     *         // create some output stream
     *         multipartStream.readBodyData(output);
     *         nextPart = multipartStream.readBoundary();
     *     }
     * } catch (MultipartStream.MalformedStreamException e) {
     *     // the stream failed to follow required syntax
     * } catch (IOException e) {
     *     // a read or write error occurred
     * }
     * }</pre>
     */
    public class MultipartStream {

        /**
         * Thrown upon attempt of setting an invalid boundary token.
         */
        public static class IllegalBoundaryException extends IOException {

            /**
             * The UID to use when serializing this instance.
             */
            private static final long serialVersionUID = -161533165102632918L;

            /**
             * Constructs an {@code IllegalBoundaryException} with no
             * detail message.
             */
            public IllegalBoundaryException() {
            }

            /**
             * Constructs an {@code IllegalBoundaryException} with
             * the specified detail message.
             *
             * @param message The detail message.
             */
            public IllegalBoundaryException(final String message) {
                super(message);
            }

        }

        /**
         * An {@link InputStream} for reading an items contents.
         */
        public class ItemInputStream extends InputStream implements Closeable {

            /**
             * Offset when converting negative bytes to integers.
             */
            private static final int BYTE_POSITIVE_OFFSET = 256;

            /**
             * The number of bytes, which have been read so far.
             */
            private long total;

            /**
             * The number of bytes, which must be hold, because
             * they might be a part of the boundary.
             */
            private int pad;

            /**
             * The current offset in the buffer.
             */
            private int pos;

            /**
             * Whether the stream is already closed.
             */
            private boolean closed;

            /**
             * Creates a new instance.
             */
            ItemInputStream() {
                findSeparator();
            }

            /**
             * Returns the number of bytes, which are currently
             * available, without blocking.
             *
             * @throws IOException An I/O error occurs.
             * @return Number of bytes in the buffer.
             */
            @Override
            public int available() throws IOException {
                if (pos == -1) {
                    return tail - head - pad;
                }
                return pos - head;
            }

            /**
             * Closes the input stream.
             *
             * @throws IOException An I/O error occurred.
             */
            @Override
            public void close() throws IOException {
                close(false);
            }

            /**
             * Closes the input stream.
             *
             * @param closeUnderlying Whether to close the underlying stream (hard close)
             * @throws IOException An I/O error occurred.
             */
            public void close(final boolean closeUnderlying) throws IOException {
                if (closed) {
                    return;
                }
                if (closeUnderlying) {
                    closed = true;
                    input.close();
                } else {
                    for (;;) {
                        int available = available();
                        if (available == 0) {
                            available = makeAvailable();
                            if (available == 0) {
                                break;
                            }
                        }
                        if (skip(available) != available) {
                            // TODO log or throw?
                        }
                    }
                }
                closed = true;
            }

            /**
             * Called for finding the separator.
             */
            private void findSeparator() {
                pos = MultipartStream.this.findSeparator();
                if (pos == -1) {
                    if (tail - head > keepRegion) {
                        pad = keepRegion;
                    } else {
                        pad = tail - head;
                    }
                }
            }

            /**
             * Returns the number of bytes, which have been read
             * by the stream.
             *
             * @return Number of bytes, which have been read so far.
             */
            public long getBytesRead() {
                return total;
            }

            /**
             * Returns, whether the stream is closed.
             *
             * @return True, if the stream is closed, otherwise false.
             */
            @Override
            public boolean isClosed() {
                return closed;
            }

            /**
             * Attempts to read more data.
             *
             * @return Number of available bytes
             * @throws IOException An I/O error occurred.
             */
            private int makeAvailable() throws IOException {
                if (pos != -1) {
                    return 0;
                }

                // Move the data to the beginning of the buffer.
                total += tail - head - pad;
                System.arraycopy(buffer, tail - pad, buffer, 0, pad);

                // Refill buffer with new data.
                head = 0;
                tail = pad;

                for (;;) {
                    final int bytesRead = input.read(buffer, tail, bufSize - tail);
                    if (bytesRead == -1) {
                        // The last pad amount is left in the buffer.
                        // Boundary can't be in there so signal an error
                        // condition.
                        final String msg = "Stream ended unexpectedly";
                        throw new MalformedStreamException(msg);
                    }
                    if (notifier != null) {
                        notifier.noteBytesRead(bytesRead);
                    }
                    tail += bytesRead;

                    findSeparator();
                    final int av = available();

                    if (av > 0 || pos != -1) {
                        return av;
                    }
                }
            }

            /**
             * Returns the next byte in the stream.
             *
             * @return The next byte in the stream, as a non-negative
             *   integer, or -1 for EOF.
             * @throws IOException An I/O error occurred.
             */
            @Override
            public int read() throws IOException {
                if (closed) {
                    throw new FileItemStream.ItemSkippedException();
                }
                if (available() == 0 && makeAvailable() == 0) {
                    return -1;
                }
                ++total;
                final int b = buffer[head++];
                if (b >= 0) {
                    return b;
                }
                return b + BYTE_POSITIVE_OFFSET;
            }

            /**
             * Reads bytes into the given buffer.
             *
             * @param b The destination buffer, where to write to.
             * @param off Offset of the first byte in the buffer.
             * @param len Maximum number of bytes to read.
             * @return Number of bytes, which have been actually read,
             *   or -1 for EOF.
             * @throws IOException An I/O error occurred.
             */
            @Override
            public int read(final byte[] b, final int off, final int len) throws IOException {
                if (closed) {
                    throw new FileItemStream.ItemSkippedException();
                }
                if (len == 0) {
                    return 0;
                }
                int res = available();
                if (res == 0) {
                    res = makeAvailable();
                    if (res == 0) {
                        return -1;
                    }
                }
                res = Math.min(res, len);
                System.arraycopy(buffer, head, b, off, res);
                head += res;
                total += res;
                return res;
            }

            /**
             * Skips the given number of bytes.
             *
             * @param bytes Number of bytes to skip.
             * @return The number of bytes, which have actually been
             *   skipped.
             * @throws IOException An I/O error occurred.
             */
            @Override
            public long skip(final long bytes) throws IOException {
                if (closed) {
                    throw new FileItemStream.ItemSkippedException();
                }
                int av = available();
                if (av == 0) {
                    av = makeAvailable();
                    if (av == 0) {
                        return 0;
                    }
                }
                final long res = Math.min(av, bytes);
                head += res;
                return res;
            }

        }

        /**
         * Thrown to indicate that the input stream fails to follow the
         * required syntax.
         */
        public static class MalformedStreamException extends IOException {

            /**
             * The UID to use when serializing this instance.
             */
            private static final long serialVersionUID = 6466926458059796677L;

            /**
             * Constructs a {@code MalformedStreamException} with no
             * detail message.
             */
            public MalformedStreamException() {
            }

            /**
             * Constructs an {@code MalformedStreamException} with
             * the specified detail message.
             *
             * @param message The detail message.
             */
            public MalformedStreamException(final String message) {
                super(message);
            }

        }

        /**
         * Internal class, which is used to invoke the
         * {@link ProgressListener}.
         */
        public static class ProgressNotifier {

            /**
             * The listener to invoke.
             */
            private final ProgressListener listener;

            /**
             * Number of expected bytes, if known, or -1.
             */
            private final long contentLength;

            /**
             * Number of bytes, which have been read so far.
             */
            private long bytesRead;

            /**
             * Number of items, which have been read so far.
             */
            private int items;

            /**
             * Creates a new instance with the given listener
             * and content length.
             *
             * @param listener The listener to invoke.
             * @param contentLength The expected content length.
             */
            ProgressNotifier(final ProgressListener listener, final long contentLength) {
                this.listener = listener;
                this.contentLength = contentLength;
            }

            /**
             * Called to indicate that bytes have been read.
             *
             * @param count Number of bytes, which have been read.
             */
            void noteBytesRead(final int count) {
                /* Indicates, that the given number of bytes have been read from
                 * the input stream.
                 */
                bytesRead += count;
                notifyListener();
            }

            /**
             * Called to indicate, that a new file item has been detected.
             */
            void noteItem() {
                ++items;
                notifyListener();
            }

            /**
             * Called for notifying the listener.
             */
            private void notifyListener() {
                if (listener != null) {
                    listener.update(bytesRead, contentLength, items);
                }
            }

        }

        /**
         * The Carriage Return ASCII character value.
         */
        public static final byte CR = 0x0D;

        /**
         * The Line Feed ASCII character value.
         */
        public static final byte LF = 0x0A;

        /**
         * The dash (-) ASCII character value.
         */
        public static final byte DASH = 0x2D;

        /**
         * The maximum length of {@code header-part} that will be
         * processed (10 kilobytes = 10240 bytes.).
         *
         * @deprecated Unused. Replaced by {@link #getPartHeaderSizeMax()}.
         */
        @Deprecated
        public static final int HEADER_PART_SIZE_MAX = 10240;

        /**
         * The default length of the buffer used for processing a request.
         */
        protected static final int DEFAULT_BUFSIZE = 4096;

        /**
         * A byte sequence that marks the end of {@code header-part}
         * ({@code CRLFCRLF}).
         */
        protected static final byte[] HEADER_SEPARATOR = {CR, LF, CR, LF};

        /**
         * A byte sequence that follows a delimiter that will be
         * followed by an encapsulation ({@code CRLF}).
         */
        protected static final byte[] FIELD_SEPARATOR = {CR, LF};

        /**
         * A byte sequence that follows a delimiter of the last
         * encapsulation in the stream ({@code --}).
         */
        protected static final byte[] STREAM_TERMINATOR = {DASH, DASH};

        /**
         * A byte sequence that precedes a boundary ({@code CRLF--}).
         */
        protected static final byte[] BOUNDARY_PREFIX = {CR, LF, DASH, DASH};

        /**
         * Compares {@code count} first bytes in the arrays
         * {@code a} and {@code b}.
         *
         * @param a     The first array to compare.
         * @param b     The second array to compare.
         * @param count How many bytes should be compared.
         * @return {@code true} if {@code count} first bytes in arrays
         *         {@code a} and {@code b} are equal.
         */
        public static boolean arrayequals(final byte[] a,
                final byte[] b,
                final int count) {
            for (int i = 0; i < count; i++) {
                if (a[i] != b[i]) {
                    return false;
                }
            }
            return true;
        }

        /**
         * The input stream from which data is read.
         */
        private final InputStream input;

        /**
         * The length of the boundary token plus the leading {@code CRLF--}.
         */
        private int boundaryLength;

        /**
         * The amount of data, in bytes, that must be kept in the buffer in order
         * to detect delimiters reliably.
         */
        private final int keepRegion;

        /**
         * The byte sequence that partitions the stream.
         */
        private final byte[] boundary;

        /**
         * The table for Knuth-Morris-Pratt search algorithm.
         */
        private final int[] boundaryTable;

        /**
         * The length of the buffer used for processing the request.
         */
        private final int bufSize;

        /**
         * The buffer used for processing the request.
         */
        private final byte[] buffer;

        /**
         * The index of first valid character in the buffer.
         * 0 <= head < bufSize
         */
        private int head;

        /**
         * The index of last valid character in the buffer + 1.
         * 0 <= tail <= bufSize
         */
        private int tail;

        /**
         * The content encoding to use when reading headers.
         */
        private String headerEncoding;

        /**
         * The progress notifier, if any, or null.
         */
        private final ProgressNotifier notifier;

        /**
         * The maximum permitted size of the headers provided with a single part in bytes.
         */
        private int partHeaderSizeMax = FileUploadBase.DEFAULT_PART_HEADER_SIZE_MAX;

        /**
         * Creates a new instance.
         *
         * @deprecated 1.2.1 Use {@link #MultipartStream(InputStream, byte[], int,
         * ProgressNotifier)}
         */
        @Deprecated
        public MultipartStream() {
            this(null, null, null);
        }

        /**
         * Constructs a {@code MultipartStream} with a default size buffer.
         *
         * @param input    The {@code InputStream} to serve as a data source.
         * @param boundary The token used for dividing the stream into
         *                 {@code encapsulations}.
         *
         * @deprecated 1.2.1 Use {@link #MultipartStream(InputStream, byte[], int,
         *  ProgressNotifier)}.
         */
        @Deprecated
        public MultipartStream(final InputStream input,
                final byte[] boundary) {
            this(input, boundary, DEFAULT_BUFSIZE, null);
        }

        /**
         * Constructs a {@code MultipartStream} with a custom size buffer and no progress notifier.
         *
         * <p>
         * Note that the buffer must be at least big enough to contain the boundary string, plus 4 characters for CR/LF and double dash, plus at least one byte of
         * data. Too small a buffer size setting will degrade performance.
         * </p>
         *
         * @param input    The {@code InputStream} to serve as a data source.
         * @param boundary The token used for dividing the stream into {@code encapsulations}.
         * @param bufSize  The size of the buffer to be used, in bytes.
         * @deprecated 1.2.1 Use {@link #MultipartStream(InputStream, byte[], int, ProgressNotifier)}.
         */
        @Deprecated
        public MultipartStream(final InputStream input, final byte[] boundary, final int bufSize) {
            this(input, boundary, bufSize, null);
        }

        /**
         * Constructs a {@code MultipartStream} with a custom size buffer.
         *
         * <p>
         * Note that the buffer must be at least big enough to contain the boundary string, plus 4 characters for CR/LF and double dash, plus at least one byte of
         * data. Too small a buffer size setting will degrade performance.
         * </p>
         *
         * @param input    The {@code InputStream} to serve as a data source.
         * @param boundary The token used for dividing the stream into {@code encapsulations}.
         * @param bufSize  The size of the buffer to be used, in bytes.
         * @param notifier The notifier, which is used for calling the progress listener, if any.
         *
         * @throws IllegalArgumentException If the buffer size is too small
         * @since 1.3.1
         */
        public MultipartStream(final InputStream input, final byte[] boundary, final int bufSize, final ProgressNotifier notifier) {
            if (boundary == null) {
                throw new IllegalArgumentException("boundary may not be null");
            }
            // We prepend CR/LF to the boundary to chop trailing CR/LF from
            // body-data tokens.
            this.boundaryLength = boundary.length + BOUNDARY_PREFIX.length;
            if (bufSize < this.boundaryLength + 1) {
                throw new IllegalArgumentException("The buffer size specified for the MultipartStream is too small");
            }
            this.input = input;
            this.bufSize = Math.max(bufSize, boundaryLength * 2);
            this.buffer = new byte[this.bufSize];
            this.notifier = notifier;
            this.boundary = new byte[this.boundaryLength];
            this.boundaryTable = new int[this.boundaryLength + 1];
            this.keepRegion = this.boundary.length;
            System.arraycopy(BOUNDARY_PREFIX, 0, this.boundary, 0, BOUNDARY_PREFIX.length);
            System.arraycopy(boundary, 0, this.boundary, BOUNDARY_PREFIX.length, boundary.length);
            computeBoundaryTable();
            head = 0;
            tail = 0;
        }

        /**
         * Constructs a {@code MultipartStream} with a default size buffer.
         *
         * @param input    The {@code InputStream} to serve as a data source.
         * @param boundary The token used for dividing the stream into
         *                 {@code encapsulations}.
         * @param notifier An object for calling the progress listener, if any.
         *
         *
         * @see #MultipartStream(InputStream, byte[], int, ProgressNotifier)
         */
        MultipartStream(final InputStream input, final byte[] boundary, final ProgressNotifier notifier) {
            this(input, boundary, DEFAULT_BUFSIZE, notifier);
        }

        /**
         * Compute the table used for Knuth-Morris-Pratt search algorithm.
         */
        private void computeBoundaryTable() {
            int position = 2;
            int candidate = 0;

            boundaryTable[0] = -1;
            boundaryTable[1] = 0;

            while (position <= boundaryLength) {
                if (boundary[position - 1] == boundary[candidate]) {
                    boundaryTable[position] = candidate + 1;
                    candidate++;
                    position++;
                } else if (candidate > 0) {
                    candidate = boundaryTable[candidate];
                } else {
                    boundaryTable[position] = 0;
                    position++;
                }
            }
        }

        /**
         * Reads {@code body-data} from the current {@code encapsulation} and discards it.
         *
         * <p>
         * Use this method to skip encapsulations you don't need or don't understand.
         * </p>
         *
         * @return The amount of data discarded.
         * @throws MalformedStreamException if the stream ends unexpectedly.
         * @throws IOException              if an i/o error occurs.
         */
        public int discardBodyData() throws MalformedStreamException, IOException {
            return readBodyData(null);
        }

        /**
         * Searches for a byte of specified value in the {@code buffer},
         * starting at the specified {@code position}.
         *
         * @param value The value to find.
         * @param pos   The starting position for searching.
         * @return The position of byte found, counting from beginning of the
         *         {@code buffer}, or {@code -1} if not found.
         */
        protected int findByte(final byte value,
                final int pos) {
            for (int i = pos; i < tail; i++) {
                if (buffer[i] == value) {
                    return i;
                }
            }

            return -1;
        }

        /**
         * Searches for the {@code boundary} in the {@code buffer}
         * region delimited by {@code head} and {@code tail}.
         *
         * @return The position of the boundary found, counting from the
         *         beginning of the {@code buffer}, or {@code -1} if
         *         not found.
         */
        protected int findSeparator() {

            int bufferPos = head;
            int tablePos = 0;

            while (bufferPos < tail) {
                while (tablePos >= 0 && buffer[bufferPos] != boundary[tablePos]) {
                    tablePos = boundaryTable[tablePos];
                }
                bufferPos++;
                tablePos++;
                if (tablePos == boundaryLength) {
                    return bufferPos - boundaryLength;
                }
            }
            return -1;
        }

        /**
         * Gets the character encoding used when reading the headers of an
         * individual part. When not specified, or {@code null}, the platform
         * default encoding is used.
         *
         * @return The encoding used to read part headers.
         */
        public String getHeaderEncoding() {
            return headerEncoding;
        }

        /**
         * Obtain the per part size limit for headers.
         *
         * @return The maximum size of the headers for a single part in bytes.
         *
         * @since 1.6.0
         */
        public int getPartHeaderSizeMax() {
            return partHeaderSizeMax;
        }

        /**
         * Creates a new {@link ItemInputStream}.
         * @return A new instance of {@link ItemInputStream}.
         */
        ItemInputStream newInputStream() {
            return new ItemInputStream();
        }

        /**
         * Reads {@code body-data} from the current {@code encapsulation} and writes its contents into the output {@code Stream}.
         *
         * <p>
         * Arbitrary large amounts of data can be processed by this method using a constant size buffer. (see
         * {@link #MultipartStream(InputStream,byte[],int, MultipartStream.ProgressNotifier) constructor}).
         * </p>
         *
         * @param output The {@code Stream} to write data into. May be null, in which case this method is equivalent to {@link #discardBodyData()}.
         *
         * @return the amount of data written.
         * @throws MalformedStreamException if the stream ends unexpectedly.
         * @throws IOException              if an i/o error occurs.
         */
        public int readBodyData(final OutputStream output)
                throws MalformedStreamException, IOException {
            return (int) Streams.copy(newInputStream(), output, false); // Streams.copy closes the input stream
        }

        /**
         * Skips a {@code boundary} token, and checks whether more
         * {@code encapsulations} are contained in the stream.
         *
         * @return {@code true} if there are more encapsulations in
         *         this stream; {@code false} otherwise.
         *
         * @throws FileUploadIOException if the bytes read from the stream exceeded the size limits
         * @throws MalformedStreamException if the stream ends unexpectedly or
         *                                  fails to follow required syntax.
         */
        public boolean readBoundary()
                throws FileUploadIOException, MalformedStreamException {
            final byte[] marker = new byte[2];
            final boolean nextChunk;

            head += boundaryLength;
            try {
                marker[0] = readByte();
                if (marker[0] == LF) {
                    // Work around IE5 Mac bug with input type=image.
                    // Because the boundary delimiter, not including the trailing
                    // CRLF, must not appear within any file (RFC 2046, section
                    // 5.1.1), we know the missing CR is due to a buggy browser
                    // rather than a file containing something similar to a
                    // boundary.
                    return true;
                }

                marker[1] = readByte();
                if (arrayequals(marker, STREAM_TERMINATOR, 2)) {
                    nextChunk = false;
                } else if (arrayequals(marker, FIELD_SEPARATOR, 2)) {
                    nextChunk = true;
                } else {
                    throw new MalformedStreamException(
                    "Unexpected characters follow a boundary");
                }
            } catch (final FileUploadIOException e) {
                // wraps a SizeException, re-throw as it will be unwrapped later
                throw e;
            } catch (final IOException e) {
                throw new MalformedStreamException("Stream ended unexpectedly");
            }
            return nextChunk;
        }

        /**
         * Reads a byte from the {@code buffer}, and refills it as
         * necessary.
         *
         * @return The next byte from the input stream.
         * @throws IOException if there is no more data available.
         */
        public byte readByte() throws IOException {
            // Buffer depleted ?
            if (head == tail) {
                head = 0;
                // Refill.
                tail = input.read(buffer, head, bufSize);
                if (tail == -1) {
                    // No more data available.
                    throw new IOException("No more data is available");
                }
                if (notifier != null) {
                    notifier.noteBytesRead(tail);
                }
            }
            return buffer[head++];
        }

        /**
         * Reads the {@code header-part} of the current {@code encapsulation}.
         * <p>
         * Headers are returned verbatim to the input stream, including the trailing {@code CRLF} marker. Parsing is left to the application.
         * </p>
         *
         * @return The {@code header-part} of the current encapsulation.
         * @throws FileUploadIOException    if the bytes read from the stream exceeded the size limits.
         * @throws MalformedStreamException if the stream ends unexpectedly.
         */
        public String readHeaders() throws FileUploadIOException, MalformedStreamException {
            int i = 0;
            byte b;
            // to support multi-byte characters
            final ByteArrayOutputStream baos = new ByteArrayOutputStream();
            int size = 0;
            while (i < HEADER_SEPARATOR.length) {
                try {
                    b = readByte();
                } catch (final FileUploadIOException e) {
                    // wraps a SizeException, re-throw as it will be unwrapped later
                    throw e;
                } catch (final IOException e) {
                    throw new MalformedStreamException("Stream ended unexpectedly");
                }
                size++;
                if (getPartHeaderSizeMax() != -1 && size > getPartHeaderSizeMax()) {
                    throw new FileUploadIOException(new SizeLimitExceededException(
                            String.format("Header section has more than %s bytes (maybe it is not properly terminated)", Integer.valueOf(getPartHeaderSizeMax())),
                                    size, getPartHeaderSizeMax()));
                }
                if (b == HEADER_SEPARATOR[i]) {
                    i++;
                } else {
                    i = 0;
                }
                baos.write(b);
            }
            String headers;
            if (headerEncoding != null) {
                try {
                    headers = baos.toString(headerEncoding);
                } catch (final UnsupportedEncodingException e) {
                    // Fall back to platform default if specified encoding is not
                    // supported.
                    headers = baos.toString();
                }
            } else {
                headers = baos.toString();
            }
            return headers;
        }

        /**
         * Changes the boundary token used for partitioning the stream.
         *
         * <p>
         * This method allows single pass processing of nested multipart streams.
         * </p>
         * <p>
         * The boundary token of the nested stream is {@code required} to be of the same length as the boundary token in parent stream.
         * </p>
         *
         * <p>
         * Restoring the parent stream boundary token after processing of a nested stream is left to the application.
         * </p>
         *
         * @param boundary The boundary to be used for parsing of the nested stream.
         *
         * @throws IllegalBoundaryException if the {@code boundary} has a different length than the one being currently parsed.
         */
        public void setBoundary(final byte[] boundary) throws IllegalBoundaryException {
            if (boundary.length != boundaryLength - BOUNDARY_PREFIX.length) {
                throw new IllegalBoundaryException("The length of a boundary token cannot be changed");
            }
            System.arraycopy(boundary, 0, this.boundary, BOUNDARY_PREFIX.length, boundary.length);
            computeBoundaryTable();
        }

        /**
         * Specifies the character encoding to be used when reading the headers of
         * individual parts. When not specified, or {@code null}, the platform
         * default encoding is used.
         *
         * @param encoding The encoding used to read part headers.
         */
        public void setHeaderEncoding(final String encoding) {
            headerEncoding = encoding;
        }

        /**
         * Sets the per part size limit for headers.
         *
         * @param partHeaderSizeMax The maximum size of the headers in bytes.
         *
         * @since 1.6.0
         */
        public void setPartHeaderSizeMax(final int partHeaderSizeMax) {
            this.partHeaderSizeMax = partHeaderSizeMax;
        }

        /**
         * Finds the beginning of the first {@code encapsulation}.
         *
         * @return {@code true} if an {@code encapsulation} was found in
         *         the stream.
         *
         * @throws IOException if an i/o error occurs.
         */
        public boolean skipPreamble() throws IOException {
            // First delimiter may be not preceded with a CRLF.
            System.arraycopy(boundary, 2, boundary, 0, boundary.length - 2);
            boundaryLength = boundary.length - 2;
            computeBoundaryTable();
            try {
                // Discard all data up to the delimiter.
                discardBodyData();

                // Read boundary - if succeeded, the stream contains an
                // encapsulation.
                return readBoundary();
            } catch (final MalformedStreamException e) {
                return false;
            } finally {
                // Restore delimiter.
                System.arraycopy(boundary, 0, boundary, 2, boundary.length - 2);
                boundaryLength = boundary.length;
                boundary[0] = CR;
                boundary[1] = LF;
                computeBoundaryTable();
            }
        }

    }