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/*
* Copyright (C) 2016 The Android Open Source Project
*
* 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 com.android.internal.telephony.uicc.asn1;
import com.android.internal.telephony.uicc.IccUtils;
/**
* This represents a decoder helping decode an array of bytes or a hex string into
* {@link Asn1Node}s. This class tracks the next position for decoding. This class is not
* thread-safe.
*/
public final class Asn1Decoder {
// Source byte array.
private final byte[] mSrc;
// Next position of the byte in the source array for decoding.
private int mPosition;
// Exclusive end of the range in the array for decoding.
private final int mEnd;
/** Creates a decoder on a hex string. */
public Asn1Decoder(String hex) {
this(IccUtils.hexStringToBytes(hex));
}
/** Creates a decoder on a byte array. */
public Asn1Decoder(byte[] src) {
this(src, 0, src.length);
}
/**
* Creates a decoder on a byte array slice.
*
* @throws IndexOutOfBoundsException If the range defined by {@code offset} and {@code length}
* exceeds the bounds of {@code bytes}.
*/
public Asn1Decoder(byte[] bytes, int offset, int length) {
if (offset < 0 || length < 0 || offset + length > bytes.length) {
throw new IndexOutOfBoundsException(
"Out of the bounds: bytes=["
+ bytes.length
+ "], offset="
+ offset
+ ", length="
+ length);
}
mSrc = bytes;
mPosition = offset;
mEnd = offset + length;
}
/** @return The next start position for decoding. */
public int getPosition() {
return mPosition;
}
/** Returns whether the node has a next node. */
public boolean hasNextNode() {
return mPosition < mEnd;
}
/**
* Parses the next node. If the node is a constructed node, its children will be parsed only
* when they are accessed, e.g., though {@link Asn1Node#getChildren()}.
*
* @return The next decoded {@link Asn1Node}. If success, the next decoding position will also
* be updated. If any error happens, e.g., moving over the end position, {@code null}
* will be returned and the next decoding position won't be modified.
* @throws InvalidAsn1DataException If the bytes cannot be parsed.
*/
public Asn1Node nextNode() throws InvalidAsn1DataException {
if (mPosition >= mEnd) {
throw new IllegalStateException("No bytes to parse.");
}
int offset = mPosition;
// Extracts the tag.
int tagStart = offset;
byte b = mSrc[offset++];
if ((b & 0x1F) == 0x1F) {
// High-tag-number form
while (offset < mEnd && (mSrc[offset++] & 0x80) != 0) {
// Do nothing.
}
}
if (offset >= mEnd) {
// No length bytes or the tag is too long.
throw new InvalidAsn1DataException(0, "Invalid length at position: " + offset);
}
int tag;
try {
tag = IccUtils.bytesToInt(mSrc, tagStart, offset - tagStart);
} catch (IllegalArgumentException e) {
// Cannot parse the tag as an integer.
throw new InvalidAsn1DataException(0, "Cannot parse tag at position: " + tagStart, e);
}
// Extracts the length.
int dataLen;
b = mSrc[offset++];
if ((b & 0x80) == 0) {
// Short-form length
dataLen = b;
} else {
// Long-form length
int lenLen = b & 0x7F;
if (offset + lenLen > mEnd) {
// No enough bytes for the long-form length
throw new InvalidAsn1DataException(
tag, "Cannot parse length at position: " + offset);
}
try {
dataLen = IccUtils.bytesToInt(mSrc, offset, lenLen);
} catch (IllegalArgumentException e) {
// Cannot parse the data length as an integer.
throw new InvalidAsn1DataException(
tag, "Cannot parse length at position: " + offset, e);
}
offset += lenLen;
}
if (offset + dataLen > mEnd) {
// No enough data left.
throw new InvalidAsn1DataException(
tag,
"Incomplete data at position: "
+ offset
+ ", expected bytes: "
+ dataLen
+ ", actual bytes: "
+ (mEnd - offset));
}
Asn1Node root = new Asn1Node(tag, mSrc, offset, dataLen);
mPosition = offset + dataLen;
return root;
}
}
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