/*
 *  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.tomcat.util.net;

import java.io.IOException;
import java.nio.BufferUnderflowException;
import java.nio.ByteBuffer;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.List;

import org.apache.juli.logging.Log;
import org.apache.juli.logging.LogFactory;
import org.apache.tomcat.util.http.parser.HttpParser;
import org.apache.tomcat.util.net.openssl.ciphers.Cipher;
import org.apache.tomcat.util.res.StringManager;

This class extracts the SNI host name and ALPN protocols from a TLS
client-hello message.
/**
 * This class extracts the SNI host name and ALPN protocols from a TLS
 * client-hello message.
 */
public class TLSClientHelloExtractor {

    private static final Log log = LogFactory.getLog(TLSClientHelloExtractor.class);
    private static final StringManager sm = StringManager.getManager(TLSClientHelloExtractor.class);

    private final ExtractorResult result;
    private final List<Cipher> clientRequestedCiphers;
    private final String sniValue;
    private final List<String> clientRequestedApplicationProtocols;

    private static final int TLS_RECORD_HEADER_LEN = 5;

    private static final int TLS_EXTENSION_SERVER_NAME = 0;
    private static final int TLS_EXTENSION_ALPN = 16;

    public static byte[] USE_TLS_RESPONSE = ("HTTP/1.1 400 \r\n" +
            "Content-Type: text/plain;charset=UTF-8\r\n" +
            "Connection: close\r\n" +
            "\r\n" +
            "Bad Request\r\n" +
            "This combination of host and port requires TLS.\r\n").getBytes(StandardCharsets.UTF_8);


    
Creates the instance of the parser and processes the provided buffer. The
buffer position and limit will be modified during the execution of this
method but they will be returned to the original values before the method
exits.
Params:
netInBuffer – The buffer containing the TLS data to process
Throws:
IOException – If the client hello message is malformed/**
     * Creates the instance of the parser and processes the provided buffer. The
     * buffer position and limit will be modified during the execution of this
     * method but they will be returned to the original values before the method
     * exits.
     *
     * @param netInBuffer The buffer containing the TLS data to process
     * @throws IOException If the client hello message is malformed
     */
    public TLSClientHelloExtractor(ByteBuffer netInBuffer) throws IOException {
        // Buffer is in write mode at this point. Record the current position so
        // the buffer state can be restored at the end of this method.
        int pos = netInBuffer.position();
        int limit = netInBuffer.limit();
        ExtractorResult result = ExtractorResult.NOT_PRESENT;
        List<Cipher> clientRequestedCiphers = new ArrayList<>();
        List<String> clientRequestedApplicationProtocols = new ArrayList<>();
        String sniValue = null;
        try {
            // Switch to read mode.
            netInBuffer.flip();

            // A complete TLS record header is required before we can figure out
            // how many bytes there are in the record.
            if (!isAvailable(netInBuffer, TLS_RECORD_HEADER_LEN)) {
                result = handleIncompleteRead(netInBuffer);
                return;
            }

            if (!isTLSHandshake(netInBuffer)) {
                // Is the client trying to use clear text HTTP?
                if (isHttp(netInBuffer)) {
                    result = ExtractorResult.NON_SECURE;
                }
                return;
            }

            if (!isAllRecordAvailable(netInBuffer)) {
                result = handleIncompleteRead(netInBuffer);
                return;
            }

            if (!isClientHello(netInBuffer)) {
                return;
            }

            if (!isAllClientHelloAvailable(netInBuffer)) {
                // Client hello didn't fit into single TLS record.
                // Treat this as not present.
                log.warn(sm.getString("sniExtractor.clientHelloTooBig"));
                return;
            }

            // Protocol Version
            skipBytes(netInBuffer, 2);
            // Random
            skipBytes(netInBuffer, 32);
            // Session ID (single byte for length)
            skipBytes(netInBuffer, (netInBuffer.get() & 0xFF));

            // Cipher Suites
            // (2 bytes for length, each cipher ID is 2 bytes)
            int cipherCount = netInBuffer.getChar() / 2;
            for (int i = 0; i < cipherCount; i++) {
                int cipherId = netInBuffer.getChar();
                clientRequestedCiphers.add(Cipher.valueOf(cipherId));
            }

            // Compression methods (single byte for length)
            skipBytes(netInBuffer, (netInBuffer.get() & 0xFF));

            if (!netInBuffer.hasRemaining()) {
                // No more data means no extensions present
                return;
            }

            // Extension length
            skipBytes(netInBuffer, 2);
            // Read the extensions until we run out of data or find the data
            // we need
            while (netInBuffer.hasRemaining() &&
                    (sniValue == null || clientRequestedApplicationProtocols.size() == 0)) {
                // Extension type is two byte
                char extensionType = netInBuffer.getChar();
                // Extension size is another two bytes
                char extensionDataSize = netInBuffer.getChar();
                switch (extensionType) {
                case TLS_EXTENSION_SERVER_NAME: {
                    sniValue = readSniExtension(netInBuffer);
                    break;
                }
                case TLS_EXTENSION_ALPN:
                    readAlpnExtension(netInBuffer, clientRequestedApplicationProtocols);
                    break;
                default: {
                    skipBytes(netInBuffer, extensionDataSize);
                }
                }
            }
            result = ExtractorResult.COMPLETE;
        } catch (BufferUnderflowException | IllegalArgumentException e) {
            throw new IOException(sm.getString("sniExtractor.clientHelloInvalid"), e);
        } finally {
            this.result = result;
            this.clientRequestedCiphers = clientRequestedCiphers;
            this.clientRequestedApplicationProtocols = clientRequestedApplicationProtocols;
            this.sniValue = sniValue;
            // Whatever happens, return the buffer to its original state
            netInBuffer.limit(limit);
            netInBuffer.position(pos);
        }
    }


    public ExtractorResult getResult() {
        return result;
    }


    public String getSNIValue() {
        if (result == ExtractorResult.COMPLETE) {
            return sniValue;
        } else {
            throw new IllegalStateException();
        }
    }


    public List<Cipher> getClientRequestedCiphers() {
        if (result == ExtractorResult.COMPLETE || result == ExtractorResult.NOT_PRESENT) {
            return clientRequestedCiphers;
        } else {
            throw new IllegalStateException();
        }
    }


    public List<String> getClientRequestedApplicationProtocols() {
        if (result == ExtractorResult.COMPLETE || result == ExtractorResult.NOT_PRESENT) {
            return clientRequestedApplicationProtocols;
        } else {
            throw new IllegalStateException();
        }
    }


    private static ExtractorResult handleIncompleteRead(ByteBuffer bb) {
        if (bb.limit() == bb.capacity()) {
            // Buffer not big enough
            return ExtractorResult.UNDERFLOW;
        } else {
            // Need to read more data into buffer
            return ExtractorResult.NEED_READ;
        }
    }


    private static boolean isAvailable(ByteBuffer bb, int size) {
        if (bb.remaining() < size) {
            bb.position(bb.limit());
            return false;
        }
        return true;
    }


    private static boolean isTLSHandshake(ByteBuffer bb) {
        // For a TLS client hello the first byte must be 22 - handshake
        if (bb.get() != 22) {
            return false;
        }
        // Next two bytes are major/minor version. We need at least 3.1.
        byte b2 = bb.get();
        byte b3 = bb.get();
        if (b2 < 3 || b2 == 3 && b3 == 0) {
            return false;
        }
        return true;
    }


    private static boolean isHttp(ByteBuffer bb) {
        // Based on code in Http11InputBuffer
        // Note: The actual request is not important. This code only checks that
        //       the buffer contains a correctly formatted HTTP request line.
        //       The method, target and protocol are not validated.
        byte chr = 0;
        bb.position(0);

        // Skip blank lines
        do {
            if (!bb.hasRemaining()) {
                return false;
            }
            chr = bb.get();
        } while (chr == '\r' || chr == '\n');

        // Read the method
        do {
            if (!HttpParser.isToken(chr) || !bb.hasRemaining()) {
                return false;
            }
            chr = bb.get();
        } while (chr != ' ' && chr != '\t');

        // Whitespace between method and target
        while (chr == ' ' || chr == '\t') {
            if (!bb.hasRemaining()) {
                return false;
            }
            chr = bb.get();
        }

        // Read the target
        while (chr != ' ' && chr != '\t') {
            if (HttpParser.isNotRequestTarget(chr) || !bb.hasRemaining()) {
                return false;
            }
            chr = bb.get();
        }

        // Whitespace between target and protocol
        while (chr == ' ' || chr == '\t') {
            if (!bb.hasRemaining()) {
                return false;
            }
            chr = bb.get();
        }

        // Read protocol
        do {
            if (!HttpParser.isHttpProtocol(chr) || !bb.hasRemaining()) {
                return false;
            }
            chr = bb.get();

        } while (chr != '\r' && chr != '\n');

        return true;
    }


    private static boolean isAllRecordAvailable(ByteBuffer bb) {
        // Next two bytes (unsigned) are the size of the record. We need all of
        // it.
        int size = bb.getChar();
        return isAvailable(bb, size);
    }


    private static boolean isClientHello(ByteBuffer bb) {
        // Client hello is handshake type 1
        if (bb.get() == 1) {
            return true;
        }
        return false;
    }


    private static boolean isAllClientHelloAvailable(ByteBuffer bb) {
        // Next three bytes (unsigned) are the size of the client hello. We need
        // all of it.
        int size = ((bb.get() & 0xFF) << 16) + ((bb.get() & 0xFF) << 8) + (bb.get() & 0xFF);
        return isAvailable(bb, size);
    }


    private static void skipBytes(ByteBuffer bb, int size) {
        bb.position(bb.position() + size);
    }


    private static String readSniExtension(ByteBuffer bb) {
        // First 2 bytes are size of server name list (only expecting one)
        // Next byte is type (0 for hostname)
        skipBytes(bb, 3);
        // Next 2 bytes are length of host name
        char serverNameSize = bb.getChar();
        byte[] serverNameBytes = new byte[serverNameSize];
        bb.get(serverNameBytes);
        return new String(serverNameBytes, StandardCharsets.UTF_8);
    }


    private static void readAlpnExtension(ByteBuffer bb, List<String> protocolNames) {
        // First 2 bytes are size of the protocol list
        char toRead = bb.getChar();
        byte[] inputBuffer = new byte[255];
        while (toRead > 0) {
            // Each list entry has one byte for length followed by a string of
            // that length
            int len = bb.get() & 0xFF;
            bb.get(inputBuffer, 0, len);
            protocolNames.add(new String(inputBuffer, 0, len, StandardCharsets.UTF_8));
            toRead--;
            toRead -= len;
        }
    }


    public enum ExtractorResult {
        COMPLETE,
        NOT_PRESENT,
        UNDERFLOW,
        NEED_READ,
        NON_SECURE
    }
}