src/java.base/share/classes/sun/security/util/DerInputStream.java

/*
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
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 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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 * accompanied this code).
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 * 2 along with this work; if not, write to the Free Software Foundation,
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package sun.security.util;

import java.io.InputStream;
import java.io.IOException;
import java.math.BigInteger;
import java.util.Arrays;
import java.util.Date;
import java.util.Optional;
import java.util.function.Predicate;

/**
 * A DER input stream, used for parsing ASN.1 DER-encoded data such as
 * that found in X.509 certificates.  DER is a subset of BER/1, which has
 * the advantage that it allows only a single encoding of primitive data.
 * (High level data such as dates still support many encodings.)  That is,
 * it uses the "Definite" Encoding Rules (DER) not the "Basic" ones (BER).
 *
 * <P>Note that, like BER/1, DER streams are streams of explicitly
 * tagged data values.  Accordingly, this programming interface does
 * not expose any variant of the java.io.InputStream interface, since
 * that kind of input stream holds untagged data values and using that
 * I/O model could prevent correct parsing of the DER data.
 *
 * <P>At this time, this class supports only a subset of the types of DER
 * data encodings which are defined.  That subset is sufficient for parsing
 * most X.509 certificates.
 *
 *
 * @author David Brownell
 * @author Amit Kapoor
 * @author Hemma Prafullchandra
 */
public class DerInputStream {

    // The static part
    final byte[] data;
    final int start;    // inclusive
    final int end;      // exclusive
    final boolean allowBER;

    // The moving part
    int pos;
    int mark;

    /**
     * Constructs a DerInputStream by assigning all its fields.
     *
     * No checking on arguments since all callers are internal.
     * {@code data} should never be null even if length is 0.
     */
    public DerInputStream(byte[] data, int start, int length, boolean allowBER) {
        this.data = data;
        this.start = start;
        this.end = start + length;
        this.allowBER = allowBER;
        this.pos = start;
        this.mark = start;
    }

    public DerInputStream(byte[] data) throws IOException {
        this(data, 0, data.length, true);
    }

    public DerInputStream(byte[] data, int offset, int len) throws IOException {
        this(data, offset, len, true);
    }

    /**
     * Returns the remaining unread bytes, or, all bytes if none read yet.
     */
    public byte[] toByteArray() {
        return Arrays.copyOfRange(data, pos, end);
    }

    /**
     * Reads a DerValue from this stream. After the call, the data pointer
     * is right after this DerValue so that the next call will read the
     * next DerValue.
     *
     * @return the read DerValue.
     * @throws IOException if a DerValue cannot be constructed starting from
     *      this position because of byte shortage or encoding error.
     */
    public DerValue getDerValue() throws IOException {
        DerValue result = new DerValue(
                this.data, this.pos, this.end - this.pos, this.allowBER, true);
        if (result.buffer != this.data) {
            // Indefinite length observed. Unused bytes in data are appended
            // to the end of return value by DerIndefLenConverter::convertBytes
            // and stay inside result.buffer.
            int unused = result.buffer.length - result.end;
            this.pos = this.end - unused;
        } else {
            this.pos = result.end;
        }
        return result;
    }

    // The following getXyz methods are mostly shorthands for getDerValue().getXyz().

    public int getInteger() throws IOException {
        return getDerValue().getInteger();
    }

    public BigInteger getBigInteger() throws IOException {
        return getDerValue().getBigInteger();
    }

    public BigInteger getPositiveBigInteger() throws IOException {
        return getDerValue().getPositiveBigInteger();
    }

    public int getEnumerated() throws IOException {
        return getDerValue().getEnumerated();
    }

    public byte[] getBitString() throws IOException {
        return getDerValue().getBitString();
    }

    public BitArray getUnalignedBitString() throws IOException {
        return getDerValue().getUnalignedBitString();
    }

    public byte[] getOctetString() throws IOException {
        // Not identical to DerValue::getOctetString. This method
        // does not accept constructed OCTET STRING.
        DerValue v = getDerValue();
        if (v.tag != DerValue.tag_OctetString) {
            throw new IOException("DER input not an octet string");
        }
        return v.getOctetString();
    }

    public void getNull() throws IOException {
        getDerValue().getNull();
    }

    public ObjectIdentifier getOID() throws IOException {
        return getDerValue().getOID();
    }

    public String getUTF8String() throws IOException {
        return getDerValue().getUTF8String();
    }

    public String getPrintableString() throws IOException {
        return getDerValue().getPrintableString();
    }

    public String getT61String() throws IOException {
        return getDerValue().getT61String();
    }

    public String getBMPString() throws IOException {
        return getDerValue().getBMPString();
    }

    public String getIA5String() throws IOException {
        return getDerValue().getIA5String();
    }

    public String getGeneralString() throws IOException {
        return getDerValue().getGeneralString();
    }

    public Date getTime() throws IOException {
        return getDerValue().getTime();
    }

    public Date getUTCTime() throws IOException {
        return getDerValue().getUTCTime();
    }

    public Date getGeneralizedTime() throws IOException {
        return getDerValue().getGeneralizedTime();
    }

    // Read a series of DerValue objects which is the sub-elements
    // of a SEQUENCE and SET.

    public DerValue[] getSequence(int startLen) throws IOException {
        return getDerValue().subs(DerValue.tag_Sequence, startLen);
    }

    public DerValue[] getSet(int startLen) throws IOException {
        return getDerValue().subs(DerValue.tag_Set, startLen);
    }

    public DerValue[] getSet(int startLen, boolean implicit) throws IOException {
        if (implicit) {
            return getDerValue().subs((byte) 0, startLen);
        } else {
            return getSet(startLen);
        }
    }

    public int peekByte() throws IOException {
        if (pos == end) {
            throw new IOException("At end");
        }
        return data[pos];
    }

    /**
     * Get a length from the input stream, allowing for at most 32 bits of
     * encoding to be used.  (Not the same as getting a tagged integer!)
     *
     * @return the length or -1 if indefinite length found.
     * @exception IOException on parsing error or unsupported lengths.
     */
    static int getLength(InputStream in) throws IOException {
        int lenByte = in.read();
        if (lenByte == -1) {
            throw new IOException("Short read of DER length");
        }
        if (lenByte == 0x80) {
            return -1;
        }

        int value, tmp;
        String mdName = "DerInputStream.getLength(): ";
        tmp = lenByte;
        if ((tmp & 0x080) == 0x00) { // short form, 1 byte datum
            value = tmp;
        } else {                     // long form
            tmp &= 0x07f;

            // tmp > 4 indicates more than 4Gb of data.
            if (tmp > 4) {
                throw new IOException(mdName + "lengthTag=" + tmp + ", too big.");
            }

            value = 0x0ff & in.read();
            tmp--;
            if (value == 0) {
                // DER requires length value be encoded in minimum number of bytes
                throw new IOException(mdName + "Redundant length bytes found");
            }
            while (tmp-- > 0) {
                value <<= 8;
                value += 0x0ff & in.read();
            }
            if (value < 0) {
                throw new IOException(mdName + "Invalid length bytes");
            } else if (value <= 127) {
                throw new IOException(mdName + "Should use short form for length");
            }
        }
        return value;
    }

    /*
     * Get a definite length from the input stream.
     *
     * @return the length
     * @exception IOException on parsing error or if indefinite length found.
     */
    static int getDefiniteLength(InputStream in) throws IOException {
        int len = getLength(in);
        if (len < 0) {
            throw new IOException("Indefinite length encoding not supported");
        }
        return len;
    }

    /**
     * Mark the current position in the buffer, so that
     * a later call to <code>reset</code> will return here.
     * The {@code readAheadLimit} is useless here, because
     * all data is available, and we can go to anywhere at will.
     */
    public void mark(int readAheadLimit) { mark = pos; }

    /**
     * Return to the position of the last <code>mark</code>
     * call.  A mark is implicitly set at the beginning of
     * the stream when it is created.
     */
    public void reset() { pos = mark; }

    /**
     * Returns the number of bytes available for reading.
     * This is most useful for testing whether the stream is
     * empty.
     */
    public int available() { return end - pos; }

    /**
     * Ensures there is no more data. This can be called when the last
     * expected field is parsed, and we need to make sure no unread is left.
     *
     * @throws IOException if the end is NOT reached yet
     */
    public void atEnd() throws IOException {
        if (available() != 0) {
            throw new IOException("Extra unused bytes");
        }
    }

    /**
     * Checks if the tag of the next DerValue matches the rule.
     *
     * @param rule the rule to check for the tag.
     * @return true if matches, false if not or stream is at end.
     */
    private boolean checkNextTag(Predicate<Byte> rule) {
        return available() > 0 && rule.test(data[pos]);
    }

    /**
     * Detect if the tag of the next DerValue is the specified one.
     *
     * @param tag the expected tag
     * @return true if matches, false if not or stream is at end.
     */
    private boolean checkNextTag(byte tag) {
        return checkNextTag(t -> t == tag);
    }

    /**
     * Returns the next DerValue if its tag is the given one.
     *
     * @param tag the expected tag
     * @return the next DerValue, or empty if not found or stream at end
     * @throws IOException if an I/O error happens
     */
    public Optional<DerValue> getOptional(byte tag) throws IOException {
        if (checkNextTag(tag)) {
            return Optional.of(getDerValue());
        } else {
            return Optional.empty();
        }
    }

    /**
     * Detect if the next DerValue is a context-specific value
     * tagged by {@code n}.
     *
     * @param n the expected tag
     * @return true if matches, false if not or stream is at end.
     * @throws IOException if an I/O error happens while peeking the byte
     */
    public boolean seeOptionalContextSpecific(int n) throws IOException {
        return checkNextTag(t -> (t & 0x0c0) == 0x080 && (t & 0x01f) == n);
    }

    /**
     * Returns the inner DerValue if the next DerValue is
     * an EXPLICIT context-specific value tagged by {@code n}.
     *
     * @param n the expected tag
     * @return the inner DerValue, or empty if not found or stream at end
     * @throws IOException if an I/O error happens
     */
    public Optional<DerValue> getOptionalExplicitContextSpecific(int n)
            throws IOException {
        if (seeOptionalContextSpecific(n)) {
            DerInputStream sub = getDerValue().data(); // stream inside [n]
            DerValue inner = sub.getDerValue(); // inside [n]
            sub.atEnd(); // make sure there is only one inner value
            return Optional.of(inner);
        } else {
            return Optional.empty();
        }
    }

    /**
     * Returns the restored DerValue if the next DerValue is
     * an IMPLICIT context-specific value tagged by {@code n}.
     *
     * @param n the expected tag
     * @param tag the real tag for the IMPLICIT type
     * @return the restored DerValue, or empty if not found or stream at end
     * @throws IOException if an I/O error happens
     */
    public Optional<DerValue> getOptionalImplicitContextSpecific(int n, byte tag)
            throws IOException {
        if (seeOptionalContextSpecific(n)) {
            DerValue v = getDerValue(); // [n]
            // restore tag because IMPLICIT has overwritten it
            return Optional.of(v.withTag(tag));
        } else {
            return Optional.empty();
        }
    }
}