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Apache HttpComponents Client
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/*
 * ====================================================================
 * 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.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * .
 *
 */
package org.apache.hc.client5.http.impl;

import java.util.Iterator;
import java.util.concurrent.atomic.AtomicReference;

import org.apache.hc.core5.annotation.Internal;
import org.apache.hc.core5.http.FormattedHeader;
import org.apache.hc.core5.http.Header;
import org.apache.hc.core5.http.HttpHeaders;
import org.apache.hc.core5.http.HttpMessage;
import org.apache.hc.core5.http.HttpVersion;
import org.apache.hc.core5.http.ParseException;
import org.apache.hc.core5.http.ProtocolException;
import org.apache.hc.core5.http.ProtocolVersion;
import org.apache.hc.core5.http.ProtocolVersionParser;
import org.apache.hc.core5.http.message.ParserCursor;
import org.apache.hc.core5.http.ssl.TLS;
import org.apache.hc.core5.util.Args;
import org.apache.hc.core5.util.CharArrayBuffer;
import org.apache.hc.core5.util.Tokenizer;

/**
 * Protocol switch handler.
 *
 * @since 5.4
 */
@Internal
public final class ProtocolSwitchStrategy {

    private static final ProtocolVersionParser PROTOCOL_VERSION_PARSER = ProtocolVersionParser.INSTANCE;
    private static final Tokenizer TOKENIZER = Tokenizer.INSTANCE;
    private static final Tokenizer.Delimiter UPGRADE_TOKEN_DELIMITER = Tokenizer.delimiters(',');
    private static final Tokenizer.Delimiter LAX_PROTO_DELIMITER = Tokenizer.delimiters('/', ',');

    @FunctionalInterface
    private interface HeaderConsumer {

        void accept(CharSequence buffer, ParserCursor cursor) throws ProtocolException;

    }

    public ProtocolVersion switchProtocol(final HttpMessage response) throws ProtocolException {
        final AtomicReference tlsUpgrade = new AtomicReference<>();

        parseHeaders(response, HttpHeaders.UPGRADE, (buffer, cursor) -> {
            final ProtocolVersion protocolVersion = parseProtocolVersion(buffer, cursor);
            if (protocolVersion != null) {
                if ("TLS".equalsIgnoreCase(protocolVersion.getProtocol())) {
                    tlsUpgrade.set(protocolVersion);
                } else if (!protocolVersion.equals(HttpVersion.HTTP_1_1)) {
                    throw new ProtocolException("Unsupported protocol or HTTP version: " + protocolVersion);
                }
            }
        });

        final ProtocolVersion result = tlsUpgrade.get();
        if (result != null) {
            return result;
        } else {
            throw new ProtocolException("Invalid protocol switch response: no TLS version found");
        }
    }

    private ProtocolVersion parseProtocolVersion(final CharSequence buffer, final ParserCursor cursor) throws ProtocolException {
        TOKENIZER.skipWhiteSpace(buffer, cursor);
        final String proto = TOKENIZER.parseToken(buffer, cursor, LAX_PROTO_DELIMITER);
        if (!cursor.atEnd()) {
            final char ch = buffer.charAt(cursor.getPos());
            if (ch == '/') {
                if (proto.isEmpty()) {
                    throw new ParseException("Invalid protocol", buffer, cursor.getLowerBound(), cursor.getUpperBound(), cursor.getPos());
                }
                cursor.updatePos(cursor.getPos() + 1);
                return PROTOCOL_VERSION_PARSER.parse(proto, null, buffer, cursor, UPGRADE_TOKEN_DELIMITER);
            }
        }
        if (proto.isEmpty()) {
            return null;
        } else if (proto.equalsIgnoreCase("TLS")) {
            return TLS.V_1_2.getVersion();
        } else {
            throw new ProtocolException("Unsupported or invalid protocol: " + proto);
        }
    }


    private void parseHeaders(final HttpMessage message, final String name, final HeaderConsumer consumer)
            throws ProtocolException {
        final Iterator it = message.headerIterator(name);
        while (it.hasNext()) {
            parseHeader(it.next(), consumer);
        }
    }

    private void parseHeader(final Header header, final HeaderConsumer consumer) throws ProtocolException {
        Args.notNull(header, "Header");
        if (header instanceof FormattedHeader) {
            final CharArrayBuffer buf = ((FormattedHeader) header).getBuffer();
            final ParserCursor cursor = new ParserCursor(0, buf.length());
            cursor.updatePos(((FormattedHeader) header).getValuePos());
            parseHeaderElements(buf, cursor, consumer);
        } else {
            final String value = header.getValue();
            if (value == null) {
                return;
            }
            final ParserCursor cursor = new ParserCursor(0, value.length());
            parseHeaderElements(value, cursor, consumer);
        }
    }

    private void parseHeaderElements(final CharSequence buffer,
                                     final ParserCursor cursor,
                                     final HeaderConsumer consumer) throws ProtocolException {
        while (!cursor.atEnd()) {
            consumer.accept(buffer, cursor);
            if (!cursor.atEnd()) {
                final char ch = buffer.charAt(cursor.getPos());
                if (ch == ',') {
                    cursor.updatePos(cursor.getPos() + 1);
                }
            }
        }
    }

}