/*
* 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.coyote.http2;
import java.nio.ByteBuffer;
import org.apache.tomcat.util.res.StringManager;
/**
* A decoder for HPACK.
*/
public class HpackDecoder {
protected static final StringManager sm = StringManager.getManager(HpackDecoder.class);
private static final int DEFAULT_RING_BUFFER_SIZE = 10;
/**
* The object that receives the headers that are emitted from this decoder
*/
private HeaderEmitter headerEmitter;
/**
* The header table
*/
private Hpack.HeaderField[] headerTable;
/**
* The current HEAD position of the header table. We use a ring buffer type
* construct as it would be silly to actually shuffle the items around in the
* array.
*/
private int firstSlotPosition = 0;
/**
* The current table size by index (aka the number of index positions that are filled up)
*/
private int filledTableSlots = 0;
/**
* the current calculates memory size, as per the HPACK algorithm
*/
private int currentMemorySize = 0;
/**
* The maximum allowed memory size set by the container.
*/
private int maxMemorySizeHard;
/**
* The maximum memory size currently in use. May be less than the hard limit.
*/
private int maxMemorySizeSoft;
private int maxHeaderCount = Constants.DEFAULT_MAX_HEADER_COUNT;
private int maxHeaderSize = Constants.DEFAULT_MAX_HEADER_SIZE;
private volatile int headerCount = 0;
private volatile boolean countedCookie;
private volatile int headerSize = 0;
private final StringBuilder stringBuilder = new StringBuilder();
HpackDecoder(int maxMemorySize) {
this.maxMemorySizeHard = maxMemorySize;
this.maxMemorySizeSoft = maxMemorySize;
headerTable = new Hpack.HeaderField[DEFAULT_RING_BUFFER_SIZE];
}
HpackDecoder() {
this(Hpack.DEFAULT_TABLE_SIZE);
}
/**
* Decodes the provided frame data. If this method leaves data in the buffer
* then this buffer should be compacted so this data is preserved, unless
* there is no more data in which case this should be considered a protocol error.
*
* @param buffer The buffer
*
* @throws HpackException If the packed data is not valid
*/
void decode(ByteBuffer buffer) throws HpackException {
while (buffer.hasRemaining()) {
int originalPos = buffer.position();
byte b = buffer.get();
if ((b & 0b10000000) != 0) {
//if the first bit is set it is an indexed header field
buffer.position(buffer.position() - 1); //unget the byte
int index = Hpack.decodeInteger(buffer, 7); //prefix is 7
if (index == -1) {
buffer.position(originalPos);
return;
} else if(index == 0) {
throw new HpackException(
sm.getString("hpackdecoder.zeroNotValidHeaderTableIndex"));
}
handleIndex(index);
} else if ((b & 0b01000000) != 0) {
//Literal Header Field with Incremental Indexing
String headerName = readHeaderName(buffer, 6);
if (headerName == null) {
buffer.position(originalPos);
return;
}
String headerValue = readHpackString(buffer);
if (headerValue == null) {
buffer.position(originalPos);
return;
}
emitHeader(headerName, headerValue);
addEntryToHeaderTable(new Hpack.HeaderField(headerName, headerValue));
} else if ((b & 0b11110000) == 0) {
//Literal Header Field without Indexing
String headerName = readHeaderName(buffer, 4);
if (headerName == null) {
buffer.position(originalPos);
return;
}
String headerValue = readHpackString(buffer);
if (headerValue == null) {
buffer.position(originalPos);
return;
}
emitHeader(headerName, headerValue);
} else if ((b & 0b11110000) == 0b00010000) {
//Literal Header Field never indexed
String headerName = readHeaderName(buffer, 4);
if (headerName == null) {
buffer.position(originalPos);
return;
}
String headerValue = readHpackString(buffer);
if (headerValue == null) {
buffer.position(originalPos);
return;
}
emitHeader(headerName, headerValue);
} else if ((b & 0b11100000) == 0b00100000) {
//context update max table size change
if (!handleMaxMemorySizeChange(buffer, originalPos)) {
return;
}
} else {
throw new RuntimeException("Not yet implemented");
}
}
}
private boolean handleMaxMemorySizeChange(ByteBuffer buffer, int originalPos) throws HpackException {
if (headerCount != 0) {
throw new HpackException(sm.getString("hpackdecoder.tableSizeUpdateNotAtStart"));
}
buffer.position(buffer.position() - 1); //unget the byte
int size = Hpack.decodeInteger(buffer, 5);
if (size == -1) {
buffer.position(originalPos);
return false;
}
if (size > maxMemorySizeHard) {
throw new HpackException();
}
maxMemorySizeSoft = size;
if (currentMemorySize > maxMemorySizeSoft) {
int newTableSlots = filledTableSlots;
int tableLength = headerTable.length;
int newSize = currentMemorySize;
while (newSize > maxMemorySizeSoft) {
int clearIndex = firstSlotPosition;
firstSlotPosition++;
if (firstSlotPosition == tableLength) {
firstSlotPosition = 0;
}
Hpack.HeaderField oldData = headerTable[clearIndex];
headerTable[clearIndex] = null;
newSize -= oldData.size;
newTableSlots--;
}
this.filledTableSlots = newTableSlots;
currentMemorySize = newSize;
}
return true;
}
private String readHeaderName(ByteBuffer buffer, int prefixLength) throws HpackException {
buffer.position(buffer.position() - 1); //unget the byte
int index = Hpack.decodeInteger(buffer, prefixLength);
if (index == -1) {
return null;
} else if (index != 0) {
return handleIndexedHeaderName(index);
} else {
return readHpackString(buffer);
}
}
private String readHpackString(ByteBuffer buffer) throws HpackException {
if (!buffer.hasRemaining()) {
return null;
}
byte data = buffer.get(buffer.position());
int length = Hpack.decodeInteger(buffer, 7);
if (buffer.remaining() < length) {
return null;
}
boolean huffman = (data & 0b10000000) != 0;
if (huffman) {
return readHuffmanString(length, buffer);
}
for (int i = 0; i < length; ++i) {
stringBuilder.append((char) buffer.get());
}
String ret = stringBuilder.toString();
stringBuilder.setLength(0);
return ret;
}
private String readHuffmanString(int length, ByteBuffer buffer) throws HpackException {
HPackHuffman.decode(buffer, length, stringBuilder);
String ret = stringBuilder.toString();
stringBuilder.setLength(0);
return ret;
}
private String handleIndexedHeaderName(int index) throws HpackException {
if (index <= Hpack.STATIC_TABLE_LENGTH) {
return Hpack.STATIC_TABLE[index].name;
} else {
if (index >= Hpack.STATIC_TABLE_LENGTH + filledTableSlots) {
throw new HpackException();
}
int adjustedIndex = getRealIndex(index - Hpack.STATIC_TABLE_LENGTH);
Hpack.HeaderField res = headerTable[adjustedIndex];
if (res == null) {
throw new HpackException();
}
return res.name;
}
}
/**
* Handle an indexed header representation
*
* @param index The index
* @throws HpackException
*/
private void handleIndex(int index) throws HpackException {
if (index <= Hpack.STATIC_TABLE_LENGTH) {
addStaticTableEntry(index);
} else {
int adjustedIndex = getRealIndex(index - Hpack.STATIC_TABLE_LENGTH);
Hpack.HeaderField headerField = headerTable[adjustedIndex];
emitHeader(headerField.name, headerField.value);
}
}
/**
* because we use a ring buffer type construct, and don't actually shuffle
* items in the array, we need to figure out the real index to use.
* <p/>
* package private for unit tests
*
* @param index The index from the hpack
* @return the real index into the array
*/
int getRealIndex(int index) {
//the index is one based, but our table is zero based, hence -1
//also because of our ring buffer setup the indexes are reversed
//index = 1 is at position firstSlotPosition + filledSlots
return (firstSlotPosition + (filledTableSlots - index)) % headerTable.length;
}
private void addStaticTableEntry(int index) throws HpackException {
//adds an entry from the static table.
//this must be an entry with a value as far as I can determine
Hpack.HeaderField entry = Hpack.STATIC_TABLE[index];
if (entry.value == null) {
throw new HpackException();
}
emitHeader(entry.name, entry.value);
}
private void addEntryToHeaderTable(Hpack.HeaderField entry) {
if (entry.size > maxMemorySizeSoft) {
//it is to big to fit, so we just completely clear the table.
while (filledTableSlots > 0) {
headerTable[firstSlotPosition] = null;
firstSlotPosition++;
if (firstSlotPosition == headerTable.length) {
firstSlotPosition = 0;
}
filledTableSlots--;
}
currentMemorySize = 0;
return;
}
resizeIfRequired();
int newTableSlots = filledTableSlots + 1;
int tableLength = headerTable.length;
int index = (firstSlotPosition + filledTableSlots) % tableLength;
headerTable[index] = entry;
int newSize = currentMemorySize + entry.size;
while (newSize > maxMemorySizeSoft) {
int clearIndex = firstSlotPosition;
firstSlotPosition++;
if (firstSlotPosition == tableLength) {
firstSlotPosition = 0;
}
Hpack.HeaderField oldData = headerTable[clearIndex];
headerTable[clearIndex] = null;
newSize -= oldData.size;
newTableSlots--;
}
this.filledTableSlots = newTableSlots;
currentMemorySize = newSize;
}
private void resizeIfRequired() {
if(filledTableSlots == headerTable.length) {
Hpack.HeaderField[] newArray = new Hpack.HeaderField[headerTable.length + 10]; //we only grow slowly
for(int i = 0; i < headerTable.length; ++i) {
newArray[i] = headerTable[(firstSlotPosition + i) % headerTable.length];
}
firstSlotPosition = 0;
headerTable = newArray;
}
}
/**
* Interface implemented by the intended recipient of the headers.
*/
interface HeaderEmitter {
/**
* Pass a single header to the recipient.
*
* @param name Header name
* @param value Header value
* @throws HpackException If a header is received that is not compliant
* with the HTTP/2 specification
*/
void emitHeader(String name, String value) throws HpackException;
/**
* Are the headers pass to the recipient so far valid? The decoder needs
* to process all the headers to maintain state even if there is a
* problem. In addition, it is easy for the the intended recipient to
* track if the complete set of headers is valid since to do that state
* needs to be maintained between the parsing of the initial headers and
* the parsing of any trailer headers. The recipient is the best place
* to maintain that state.
*
* @throws StreamException If the headers received to date are not valid
*/
void validateHeaders() throws StreamException;
}
HeaderEmitter getHeaderEmitter() {
return headerEmitter;
}
void setHeaderEmitter(HeaderEmitter headerEmitter) {
this.headerEmitter = headerEmitter;
// Reset limit tracking
headerCount = 0;
countedCookie = false;
headerSize = 0;
}
void setMaxHeaderCount(int maxHeaderCount) {
this.maxHeaderCount = maxHeaderCount;
}
void setMaxHeaderSize(int maxHeaderSize) {
this.maxHeaderSize = maxHeaderSize;
}
private void emitHeader(String name, String value) throws HpackException {
// Header names are forced to lower case
if ("cookie".equals(name)) {
// Only count the cookie header once since HTTP/2 splits it into
// multiple headers to aid compression
if (!countedCookie) {
headerCount ++;
countedCookie = true;
}
} else {
headerCount ++;
}
// Overhead will vary. The main concern is that lots of small headers
// trigger the limiting mechanism correctly. Therefore, use an overhead
// estimate of 3 which is the worst case for small headers.
int inc = 3 + name.length() + value.length();
headerSize += inc;
if (!isHeaderCountExceeded() && !isHeaderSizeExceeded(0)) {
headerEmitter.emitHeader(name, value);
}
}
boolean isHeaderCountExceeded() {
if (maxHeaderCount < 0) {
return false;
}
return headerCount > maxHeaderCount;
}
boolean isHeaderSizeExceeded(int unreadSize) {
if (maxHeaderSize < 0) {
return false;
}
return (headerSize + unreadSize) > maxHeaderSize;
}
boolean isHeaderSwallowSizeExceeded(int unreadSize) {
if (maxHeaderSize < 0) {
return false;
}
// Swallow the same again before closing the connection.
return (headerSize + unreadSize) > (2 * maxHeaderSize);
}
//package private fields for unit tests
int getFirstSlotPosition() {
return firstSlotPosition;
}
Hpack.HeaderField[] getHeaderTable() {
return headerTable;
}
int getFilledTableSlots() {
return filledTableSlots;
}
int getCurrentMemorySize() {
return currentMemorySize;
}
int getMaxMemorySizeSoft() {
return maxMemorySizeSoft;
}
}