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package com.qcloud.cos.internal;

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

import com.qcloud.cos.exception.CosClientException;

public class LengthCheckInputStream extends SdkFilterInputStream {
    public static final boolean INCLUDE_SKIPPED_BYTES = true;
    public static final boolean EXCLUDE_SKIPPED_BYTES = false;
    /**
     * Total number of bytes expected to be read from the underlying input stream.
     */
    private final long expectedLength;
    /**
     * True if skipped bytes are to be included as part of the data length; false otherwise.
     */
    private final boolean includeSkipped;
    /**
     * The length of the data read from the underlying input stream so far.
     */
    private long dataLength;
    private long marked; // used for mark-and-reset purposes

    /**
     * Used for diagnostic purposes. True if reset has been called since last marked; False
     * otherwise.
     */
    private boolean resetSinceLastMarked;
    private int markCount, resetCount;

    /**
     * Constructs an input stream that performs length check to ensure the number of bytes read from
     * the underlying input stream is the same as the expected total.
     * 
     * @param in the underlying input stream
     * @param expectedLength the total length of the data in bytes expected to be read from the
     *        underlying input stream; must be non-negative.
     * @param includeSkipped true if bytes skipped are to be considered as part of the data length;
     *        false otherwise. Typically, this parameter should be set to false for uploading data
     *        to COS, but set to true for receiving data from COS.
     */
    public LengthCheckInputStream(InputStream in, long expectedLength, boolean includeSkipped) {
        super(in);
        if (expectedLength < 0)
            throw new IllegalArgumentException();
        this.expectedLength = expectedLength;
        this.includeSkipped = includeSkipped;
    }

    /**
     * {@inheritDoc}
     * 
     * @throws CosClientException if the data length read has exceeded the expected total, or if
     *         the total data length is not the same as the expected total.
     */
    @Override
    public int read() throws IOException {
        final int c = super.read();
        if (c >= 0)
            dataLength++;
        checkLength(c == -1);
        return c;
    }

    /**
     * {@inheritDoc}
     * 
     * @throws CosClientException if the data length read has exceeded the expected total, or if
     *         the total data length is not the same as the expected total.
     */
    @Override
    public int read(byte[] b, int off, int len) throws IOException {
        int readLen = super.read(b, off, len);
        dataLength += readLen >= 0 ? readLen : 0;
        checkLength(readLen == -1);
        return readLen;
    }

    @Override
    public void mark(int readlimit) {
        if (markSupported()) {
            super.mark(readlimit);
            marked = dataLength;
            markCount++;
            resetSinceLastMarked = false;
        }
    }

    @Override
    public void reset() throws IOException {
        if (markSupported()) {
            super.reset();
            dataLength = marked;
            resetCount++;
            resetSinceLastMarked = true;
        } else {
            throw new IOException("mark/reset not supported");
        }
    }

    /**
     * Checks the data length read so far against the expected total.
     * 
     * @param eof true if end of stream has been encountered; false otherwise
     * 
     * @throws CosClientException if the data length read has exceeded the expected total, or if
     *         the total data length is not the same as the expected total.
     */
    private void checkLength(boolean eof) {
        if (eof) {
            if (dataLength != expectedLength) {
                throw new CosClientException(
                        "Data read has a different length than the expected: " + diagnosticInfo());
            }
        } else if (dataLength > expectedLength) {
            throw new CosClientException("More data read than expected: " + diagnosticInfo());
        }
    }

    private String diagnosticInfo() {
        return new StringBuilder().append("dataLength=").append(dataLength)
                .append("; expectedLength=").append(expectedLength).append("; includeSkipped=")
                .append(includeSkipped).append("; in.getClass()=").append(in.getClass())
                .append("; markedSupported=").append(markSupported()).append("; marked=")
                .append(marked).append("; resetSinceLastMarked=").append(resetSinceLastMarked)
                .append("; markCount=").append(markCount).append("; resetCount=").append(resetCount)
                .toString();
    }

    /**
     * {@inheritDoc}
     * 
     * @throws CosClientException if {@link #includeSkipped} is true and the data length skipped
     *         has exceeded the expected total.
     */
    @Override
    public long skip(long n) throws IOException {
        final long skipped = super.skip(n);
        if (includeSkipped && skipped > 0) {
            dataLength += skipped;
            checkLength(false);
        }
        return skipped;
    }
}