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RFC 7639 ALPN.
Add ConnectAlpnProvider and inject ALPN header in ConnectExec/AsyncConnectExec. Provide builder hooks for fixed list or provider-driven values.
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‎httpclient5/src/main/java/org/apache/hc/client5/http/ConnectAlpnProvider.java‎

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/*
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* ====================================================================
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* Licensed to the Apache Software Foundation (ASF) under one
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* or more contributor license agreements. See the NOTICE file
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* distributed with this work for additional information
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* regarding copyright ownership. The ASF licenses this file
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* to you under the Apache License, Version 2.0 (the
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* "License"); you may not use this file except in compliance
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* with the License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing,
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* software distributed under the License is distributed on an
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* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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* KIND, either express or implied. See the License for the
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* specific language governing permissions and limitations
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* under the License.
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* ====================================================================
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*
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* This software consists of voluntary contributions made by many
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* individuals on behalf of the Apache Software Foundation. For more
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* information on the Apache Software Foundation, please see
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* <http://www.apache.org/>.
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*
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*/
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package org.apache.hc.client5.http;
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import java.util.List;
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import org.apache.hc.core5.http.HttpHost;
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/**
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* Supplies the Application-Layer Protocol Negotiation (ALPN) protocol IDs
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* to advertise in the HTTP {@code ALPN} header on a {@code CONNECT} request
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* (RFC 7639).
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*
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* <p>If this method returns {@code null} or an empty list, the client will
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* not add the {@code ALPN} header.</p>
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*
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* <p>Implementations should be fast and side-effect free; it may be invoked
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* for each CONNECT attempt.</p>
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*
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* @since 5.6
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*/
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@FunctionalInterface
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public interface ConnectAlpnProvider {
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/**
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* Returns the ALPN protocol IDs to advertise for a tunnel to {@code target}
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* over the given {@code route}.
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*
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* @param target the origin server the tunnel will connect to (non-null)
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* @param route the planned connection route, including proxy info (non-null)
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* @return list of protocol IDs (e.g., {@code "h2"}, {@code "http/1.1"});
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* {@code null} or empty to omit the header
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*/
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List<String> getAlpnForTunnel(HttpHost target, HttpRoute route);
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}

‎httpclient5/src/main/java/org/apache/hc/client5/http/impl/AlpnHeaderSupport.java‎

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/*
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* ====================================================================
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* Licensed to the Apache Software Foundation (ASF) under one
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* or more contributor license agreements. See the NOTICE file
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* distributed with this work for additional information
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* regarding copyright ownership. The ASF licenses this file
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* to you under the Apache License, Version 2.0 (the
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* "License"); you may not use this file except in compliance
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* with the License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing,
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* software distributed under the License is distributed on an
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* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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* KIND, either express or implied. See the License for the
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* specific language governing permissions and limitations
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* under the License.
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* ====================================================================
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*
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* This software consists of voluntary contributions made by many
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* individuals on behalf of the Apache Software Foundation. For more
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* information on the Apache Software Foundation, please see
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* <http://www.apache.org/>.
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*
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*/
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package org.apache.hc.client5.http.impl;
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import java.nio.charset.StandardCharsets;
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import java.util.ArrayList;
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import java.util.Collections;
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import java.util.List;
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import org.apache.hc.core5.annotation.Contract;
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import org.apache.hc.core5.annotation.Internal;
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import org.apache.hc.core5.annotation.ThreadingBehavior;
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import org.apache.hc.core5.http.message.MessageSupport;
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import org.apache.hc.core5.http.message.ParserCursor;
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import org.apache.hc.core5.util.Args;
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/**
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* Codec for the HTTP {@code ALPN} header field (RFC 7639).
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*
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* @since 5.4
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*/
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@Contract(threading = ThreadingBehavior.IMMUTABLE)
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@Internal
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public final class AlpnHeaderSupport {
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private static final char[] HEXADECIMAL = "0123456789ABCDEF".toCharArray();
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private AlpnHeaderSupport() {
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}
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/**
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* Formats a list of raw ALPN protocol IDs into a single {@code ALPN} header value.
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*/
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public static String formatValue(final List<String> protocolIds) {
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Args.notEmpty(protocolIds, "protocolIds");
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final StringBuilder sb = new StringBuilder();
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boolean first = true;
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for (final String id : protocolIds) {
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if (!first) {
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sb.append(", ");
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}
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sb.append(encodeId(id));
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first = false;
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}
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return sb.toString();
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}
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/**
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* Parses an {@code ALPN} header value into decoded protocol IDs.
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*/
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public static List<String> parseValue(final String value) {
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if (value == null || value.isEmpty()) {
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return Collections.emptyList();
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}
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final List<String> out = new ArrayList<>();
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final ParserCursor cursor = new ParserCursor(0, value.length());
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MessageSupport.parseTokens(value, cursor, token -> {
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if (!token.isEmpty()) {
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out.add(decodeId(token));
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}
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});
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return out;
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}
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/**
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* Encodes a single raw protocol ID to canonical token form.
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*/
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public static String encodeId(final String id) {
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Args.notBlank(id, "id");
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final byte[] bytes = id.getBytes(StandardCharsets.UTF_8);
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final StringBuilder sb = new StringBuilder(bytes.length);
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for (final byte b0 : bytes) {
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final int b = b0 & 0xFF;
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if (b == '%' || !isTchar(b)) {
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appendPctEncoded(b, sb);
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} else {
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sb.append((char) b);
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}
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}
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return sb.toString();
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}
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/**
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* Decodes percent-encoded token to raw ID using UTF-8.
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* Accepts lowercase hex; malformed/incomplete sequences are left literal.
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*/
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public static String decodeId(final String token) {
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Args.notBlank(token, "token");
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final byte[] buf = new byte[token.length()];
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int bi = 0;
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for (int i = 0; i < token.length(); ) {
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final char c = token.charAt(i);
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if (c == '%' && i + 2 < token.length()) {
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final int hi = hexVal(token.charAt(i + 1));
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final int lo = hexVal(token.charAt(i + 2));
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if (hi >= 0 && lo >= 0) {
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buf[bi++] = (byte) ((hi << 4) | lo);
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i += 3;
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continue;
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}
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}
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buf[bi++] = (byte) c;
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i++;
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}
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return new String(buf, 0, bi, StandardCharsets.UTF_8);
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}
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// RFC7230 tchar minus '%' (RFC7639 requires '%' be percent-encoded)
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private static boolean isTchar(final int c) {
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if (c >= '0' && c <= '9') {
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return true;
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}
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if (c >= 'A' && c <= 'Z') {
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return true;
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}
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if (c >= 'a' && c <= 'z') {
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return true;
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}
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switch (c) {
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case '!':
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case '#':
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case '$':
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case '&':
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case '\'':
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case '*':
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case '+':
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case '-':
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case '.':
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case '^':
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case '_':
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case '`':
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case '|':
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case '~':
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return true;
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default:
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return false;
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}
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}
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private static void appendPctEncoded(final int b, final StringBuilder sb) {
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sb.append('%');
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sb.append(HEXADECIMAL[(b >>> 4) & 0x0F]);
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sb.append(HEXADECIMAL[b & 0x0F]);
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}
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private static int hexVal(final char c) {
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if (c >= '0' && c <= '9') {
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return c - '0';
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}
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if (c >= 'A' && c <= 'F') {
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return 10 + (c - 'A');
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}
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if (c >= 'a' && c <= 'f') {
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return 10 + (c - 'a');
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}
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return -1;
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}
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}

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