ReadContentInputStream.java

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/*
 * Sleuth Kit Data Model
 *
 * Copyright 2011-2018 Basis Technology Corp.
 * Contact: carrier <at> sleuthkit <dot> org
 *
 * Licensed 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.sleuthkit.datamodel;

import java.io.IOException;
import java.io.InputStream;

public final class ReadContentInputStream extends InputStream {

        private long currentOffset;
        private final long contentSize;
        private final Content content;

        public ReadContentInputStream(Content content) {
                this.content = content;
                this.currentOffset = 0;
                this.contentSize = content.getSize();
        }

        @Override
        public int read() throws ReadContentInputStreamException {
                byte[] buff = new byte[1];
                return (read(buff) != -1) ? buff[0] : -1;
        }

        @Override
        public int read(byte[] b) throws ReadContentInputStreamException {
                return read(b, 0, b.length);
        }

        @Override
        public int read(byte[] b, int off, int len) throws ReadContentInputStreamException {

                final int buffLen = b.length;
                //must return 0 for zero-length arrays
                if (buffLen == 0 || len == 0) {
                        return 0;
                }

                //would get an error from TSK if we try to read an empty file
                if (contentSize == 0) {
                        return -1;
                }

                // check off.  Must be in bounds of buffer
                if (off < 0 || off >= buffLen) {
                        return -1;
                }

                //eof, no data remains to be read
                if (currentOffset >= contentSize) {
                        return -1;
                }

                // Is the file big enough for the full request?
                int lenToRead = (int) Math.min(contentSize - currentOffset, len);

                // is the buffer big enough?
                lenToRead = Math.min(lenToRead, buffLen - off);

                byte[] retBuf;
                if (off == 0) {
                        //write directly to user buffer
                        retBuf = b;
                } else {
                        //write to a temp buffer, then copy to user buffer
                        retBuf = new byte[lenToRead];
                }
                try {
                        final int lenRead = content.read(retBuf, currentOffset, lenToRead);

                        if (lenRead == 0 || lenRead == -1) {
                                //error or no more bytes to read, report EOF
                                return -1;
                        } else {
                                currentOffset += lenRead;

                                //if read into user-specified offset, copy back from temp buffer to user
                                if (off != 0) {
                                        System.arraycopy(retBuf, 0, b, off, lenRead);
                                }

                                return lenRead;
                        }
                } catch (TskCoreException ex) {
                        throw new ReadContentInputStreamException(String.format("Error reading file '%s' (id=%d) at offset %d.", content.getName(), content.getId(), currentOffset), ex);
                }

        }

        @Override
        public int available() throws IOException {
                long len = contentSize - currentOffset;
                if (len < 0) {
                        return 0;
                }
                return (int) len;
        }

        @Override
        public long skip(long n) throws IOException {
                //more efficient skip() implementation than superclass
                //as it does not involve reads
                long toSkip = Math.min(n, contentSize - currentOffset);  //allow to skip to EOF
                currentOffset += toSkip;
                return toSkip;
                //0 1 2 3 4 5      len: 6
        }

        @Override
        public void close() throws IOException {
                super.close();
                //nothing to be done currently, file handles are closed when content is gc'ed
        }

        @Override
        public boolean markSupported() {
                return false;
        }


        public long getLength() {
                return contentSize;
        }

        public long getCurPosition() {
                return currentOffset;
        }

        public long seek(long newPosition) {
                if (newPosition < 0) {
                        throw new IllegalArgumentException("Illegal negative new position in the stream");
                }

                currentOffset = Math.min(newPosition, contentSize);
                return currentOffset;

        }

        public final static class ReadContentInputStreamException extends IOException {

                private static final long serialVersionUID = 1L;

                public ReadContentInputStreamException(String message) {
                        super(message);
                }

                public ReadContentInputStreamException(String message, Throwable cause) {
                        super(message, cause);
                }
        }
}