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 * Copyright (c) 2015, 2020, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
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 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
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package jdk.internal.net.http;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.function.Consumer;
import java.net.http.HttpHeaders;
import java.net.http.HttpResponse;
import jdk.internal.net.http.common.Logger;
import jdk.internal.net.http.common.Utils;
import static java.lang.String.format;

Implements chunked/fixed transfer encodings of HTTP/1.1 responses.
Call pushBody() to read the body (blocking). Data and errors are provided
to given Consumers. After final buffer delivered, empty optional delivered
/**
 * Implements chunked/fixed transfer encodings of HTTP/1.1 responses.
 *
 * Call pushBody() to read the body (blocking). Data and errors are provided
 * to given Consumers. After final buffer delivered, empty optional delivered
 */
class ResponseContent {

    final HttpResponse.BodySubscriber<?> pusher;
    final long contentLength;
    final HttpHeaders headers;
    // this needs to run before we complete the body
    // so that connection can be returned to pool
    private final Runnable onFinished;
    private final String dbgTag;

    ResponseContent(HttpConnection connection,
                    long contentLength,
                    HttpHeaders h,
                    HttpResponse.BodySubscriber<?> userSubscriber,
                    Runnable onFinished)
    {
        this.pusher = userSubscriber;
        this.contentLength = contentLength;
        this.headers = h;
        this.onFinished = onFinished;
        this.dbgTag = connection.dbgString() + "/ResponseContent";
    }

    static final int LF = 10;
    static final int CR = 13;

    private boolean chunkedContent, chunkedContentInitialized;

    boolean contentChunked() throws IOException {
        if (chunkedContentInitialized) {
            return chunkedContent;
        }
        if (contentLength == -2) {
            // HTTP/1.0 content
            chunkedContentInitialized = true;
            chunkedContent = false;
            return chunkedContent;
        }
        if (contentLength == -1) {
            String tc = headers.firstValue("Transfer-Encoding")
                               .orElse("");
            if (!tc.isEmpty()) {
                if (tc.equalsIgnoreCase("chunked")) {
                    chunkedContent = true;
                } else {
                    throw new IOException("invalid content");
                }
            } else {
                chunkedContent = false;
            }
        }
        chunkedContentInitialized = true;
        return chunkedContent;
    }

    interface BodyParser extends Consumer<ByteBuffer> {
        void onSubscribe(AbstractSubscription sub);
        // A current-state message suitable for inclusion in an exception
        // detail message.
        String currentStateMessage();
    }

    // Returns a parser that will take care of parsing the received byte
    // buffers and forward them to the BodySubscriber.
    // When the parser is done, it will call onComplete.
    // If parsing was successful, the throwable parameter will be null.
    // Otherwise it will be the exception that occurred
    // Note: revisit: it might be better to use a CompletableFuture than
    //       a completion handler.
    BodyParser getBodyParser(Consumer<Throwable> onComplete)
        throws IOException {
        if (contentChunked()) {
            return new ChunkedBodyParser(onComplete);
        } else {
            return contentLength == -2
                ? new UnknownLengthBodyParser(onComplete)
                : new FixedLengthBodyParser(contentLength, onComplete);
        }
    }


    static enum ChunkState {READING_LENGTH, READING_DATA, DONE}
    static final int MAX_CHUNK_HEADER_SIZE = 2050;
    class ChunkedBodyParser implements BodyParser {
        final ByteBuffer READMORE = Utils.EMPTY_BYTEBUFFER;
        final Consumer<Throwable> onComplete;
        final Logger debug = Utils.getDebugLogger(this::dbgString, Utils.DEBUG);
        final String dbgTag = ResponseContent.this.dbgTag + "/ChunkedBodyParser";

        volatile Throwable closedExceptionally;
        volatile int partialChunklen = 0; // partially read chunk len
        volatile int chunklen = -1;  // number of bytes in chunk
        volatile int bytesremaining;  // number of bytes in chunk left to be read incl CRLF
        volatile boolean cr = false;  // tryReadChunkLength has found CR
        volatile int chunkext = 0;    // number of bytes already read in the chunk extension
        volatile int digits = 0;      // number of chunkLength bytes already read
        volatile int bytesToConsume;  // number of bytes that still need to be consumed before proceeding
        volatile ChunkState state = ChunkState.READING_LENGTH; // current state
        volatile AbstractSubscription sub;
        ChunkedBodyParser(Consumer<Throwable> onComplete) {
            this.onComplete = onComplete;
        }

        String dbgString() {
            return dbgTag;
        }

        // best effort - we're assuming UTF-8 text and breaks at character boundaries
        // for this debug output. Not called.
        private void debugBuffer(ByteBuffer b) {
            if (!debug.on()) return;
            ByteBuffer printable = b.asReadOnlyBuffer();
            byte[] bytes = new byte[printable.limit() - printable.position()];
            printable.get(bytes, 0, bytes.length);
            String msg = "============== accepted ==================\n";
            try {
                var str = new String(bytes, "UTF-8");
                msg += str;
            } catch (Exception x) {
                msg += x;
                x.printStackTrace();
            }
            msg += "\n==========================================\n";
            debug.log(msg);

        }

        @Override
        public void onSubscribe(AbstractSubscription sub) {
            if (debug.on())
                debug.log("onSubscribe: "  + pusher.getClass().getName());
            pusher.onSubscribe(this.sub = sub);
        }

        @Override
        public String currentStateMessage() {
            return format("chunked transfer encoding, state: %s", state);
        }
        @Override
        public void accept(ByteBuffer b) {
            if (closedExceptionally != null) {
                if (debug.on())
                    debug.log("already closed: " + closedExceptionally);
                return;
            }
            // debugBuffer(b);
            boolean completed = false;
            try {
                List<ByteBuffer> out = new ArrayList<>();
                do {
                    if (tryPushOneHunk(b, out))  {
                        // We're done! (true if the final chunk was parsed).
                        if (!out.isEmpty()) {
                            // push what we have and complete
                            // only reduce demand if we actually push something.
                            // we would not have come here if there was no
                            // demand.
                            boolean hasDemand = sub.demand().tryDecrement();
                            assert hasDemand;
                            pusher.onNext(Collections.unmodifiableList(out));
                            if (debug.on()) debug.log("Chunks sent");
                        }
                        if (debug.on()) debug.log("done!");
                        assert closedExceptionally == null;
                        assert state == ChunkState.DONE;
                        onFinished.run();
                        pusher.onComplete();
                        if (debug.on()) debug.log("subscriber completed");
                        completed = true;
                        onComplete.accept(closedExceptionally); // should be null
                        break;
                    }
                    // the buffer may contain several hunks, and therefore
                    // we must loop while it's not exhausted.
                } while (b.hasRemaining());

                if (!completed && !out.isEmpty()) {
                    // push what we have.
                    // only reduce demand if we actually push something.
                    // we would not have come here if there was no
                    // demand.
                    boolean hasDemand = sub.demand().tryDecrement();
                    assert hasDemand;
                    pusher.onNext(Collections.unmodifiableList(out));
                    if (debug.on()) debug.log("Chunk sent");
                }
                assert state == ChunkState.DONE || !b.hasRemaining();
            } catch(Throwable t) {
                if (debug.on())
                    debug.log("Error while processing buffer: %s", (Object)t );
                closedExceptionally = t;
                if (!completed) onComplete.accept(t);
            }
        }

        // reads and returns chunklen. Position of chunkbuf is first byte
        // of chunk on return. chunklen includes the CR LF at end of chunk
        // returns -1 if needs more bytes
        private int tryReadChunkLen(ByteBuffer chunkbuf) throws IOException {
            assert state == ChunkState.READING_LENGTH;
            while (chunkbuf.hasRemaining()) {
                if (chunkext + digits >= MAX_CHUNK_HEADER_SIZE) {
                    throw new IOException("Chunk header size too long: " + (chunkext + digits));
                }
                int c = chunkbuf.get();
                if (cr) {
                    if (c == LF) {
                        return partialChunklen;
                    } else {
                        throw new IOException("invalid chunk header");
                    }
                }
                if (c == CR) {
                    cr = true;
                    if (digits == 0 && debug.on()) {
                        debug.log("tryReadChunkLen: invalid chunk header? No digits in chunkLen?");
                    }
                } else if (cr == false && chunkext > 0) {
                    // we have seen a non digit character after the chunk length.
                    // skip anything until CR is found.
                    chunkext++;
                    if (debug.on()) {
                        debug.log("tryReadChunkLen: More extraneous character after chunk length: " + c);
                    }
                } else {
                    int digit = toDigit(c);
                    if (digit < 0) {
                        if (digits > 0) {
                            // first non-digit character after chunk length.
                            // skip anything until CR is found.
                            chunkext++;
                            if (debug.on()) {
                                debug.log("tryReadChunkLen: Extraneous character after chunk length: " + c);
                            }
                        } else {
                            // there should be at list one digit in chunk length
                            throw new IOException("Illegal character in chunk size: " + c);
                        }
                    } else {
                        digits++;
                        partialChunklen = partialChunklen * 16 + digit;
                    }
                }
            }
            return -1;
        }


        // try to consume as many bytes as specified by bytesToConsume.
        // returns the number of bytes that still need to be consumed.
        // In practice this method is only called to consume one CRLF pair
        // with bytesToConsume set to 2, so it will only return 0 (if completed),
        // 1, or 2 (if chunkbuf doesn't have the 2 chars).
        private int tryConsumeBytes(ByteBuffer chunkbuf) throws IOException {
            int n = bytesToConsume;
            if (n > 0) {
                int e = Math.min(chunkbuf.remaining(), n);

                // verifies some assertions
                // this methods is called only to consume CRLF
                if (Utils.ASSERTIONSENABLED) {
                    assert n <= 2 && e <= 2;
                    ByteBuffer tmp = chunkbuf.slice();
                    // if n == 2 assert that we will first consume CR
                    assert (n == 2 && e > 0) ? tmp.get() == CR : true;
                    // if n == 1 || n == 2 && e == 2 assert that we then consume LF
                    assert (n == 1 || e == 2) ? tmp.get() == LF : true;
                }

                chunkbuf.position(chunkbuf.position() + e);
                n -= e;
                bytesToConsume = n;
            }
            assert n >= 0;
            return n;
        }

        
Returns a ByteBuffer containing chunk of data or a "hunk" of data
(a chunk of a chunk if the chunk size is larger than our ByteBuffers).
If the given chunk does not have enough data this method return
an empty ByteBuffer (READMORE).
If we encounter the final chunk (an empty chunk) this method
returns null.
/**
         * Returns a ByteBuffer containing chunk of data or a "hunk" of data
         * (a chunk of a chunk if the chunk size is larger than our ByteBuffers).
         * If the given chunk does not have enough data this method return
         * an empty ByteBuffer (READMORE).
         * If we encounter the final chunk (an empty chunk) this method
         * returns null.
         */
        ByteBuffer tryReadOneHunk(ByteBuffer chunk) throws IOException {
            int unfulfilled = bytesremaining;
            int toconsume = bytesToConsume;
            ChunkState st = state;
            if (st == ChunkState.READING_LENGTH && chunklen == -1) {
                if (debug.on()) debug.log(() ->  "Trying to read chunk len"
                        + " (remaining in buffer:"+chunk.remaining()+")");
                int clen = chunklen = tryReadChunkLen(chunk);
                if (clen == -1) return READMORE;
                digits = chunkext = 0;
                if (debug.on()) debug.log("Got chunk len %d", clen);
                cr = false; partialChunklen = 0;
                unfulfilled = bytesremaining =  clen;
                if (clen == 0) toconsume = bytesToConsume = 2; // that was the last chunk
                else st = state = ChunkState.READING_DATA; // read the data
            }

            if (toconsume > 0) {
                if (debug.on())
                    debug.log("Trying to consume bytes: %d (remaining in buffer: %s)",
                              toconsume, chunk.remaining());
                if (tryConsumeBytes(chunk) > 0) {
                    return READMORE;
                }
            }

            toconsume = bytesToConsume;
            assert toconsume == 0;


            if (st == ChunkState.READING_LENGTH) {
                // we will come here only if chunklen was 0, after having
                // consumed the trailing CRLF
                int clen = chunklen;
                assert clen == 0;
                if (debug.on()) debug.log("No more chunks: %d", clen);
                // the DONE state is not really needed but it helps with
                // assertions...
                state = ChunkState.DONE;
                return null;
            }

            int clen = chunklen;
            assert clen > 0;
            assert st == ChunkState.READING_DATA;

            ByteBuffer returnBuffer = READMORE; // May be a hunk or a chunk
            if (unfulfilled > 0) {
                int bytesread = chunk.remaining();
                if (debug.on())
                    debug.log("Reading chunk: available %d, needed %d",
                              bytesread, unfulfilled);

                int bytes2return = Math.min(bytesread, unfulfilled);
                if (debug.on())
                    debug.log( "Returning chunk bytes: %d", bytes2return);
                returnBuffer = Utils.sliceWithLimitedCapacity(chunk, bytes2return).asReadOnlyBuffer();
                unfulfilled = bytesremaining -= bytes2return;
                if (unfulfilled == 0) bytesToConsume = 2;
            }

            assert unfulfilled >= 0;

            if (unfulfilled == 0) {
                if (debug.on())
                    debug.log("No more bytes to read - %d yet to consume.",
                              unfulfilled);
                // check whether the trailing CRLF is consumed, try to
                // consume it if not. If tryConsumeBytes needs more bytes
                // then we will come back here later - skipping the block
                // that reads data because remaining==0, and finding
                // that the two bytes are now consumed.
                if (tryConsumeBytes(chunk) == 0) {
                    // we're done for this chunk! reset all states and
                    // prepare to read the next chunk.
                    chunklen = -1;
                    partialChunklen = 0;
                    cr = false;
                    digits = chunkext = 0;
                    state = ChunkState.READING_LENGTH;
                    if (debug.on()) debug.log("Ready to read next chunk");
                }
            }
            if (returnBuffer == READMORE) {
                if (debug.on()) debug.log("Need more data");
            }
            return returnBuffer;
        }


        // Attempt to parse and push one hunk from the buffer.
        // Returns true if the final chunk was parsed.
        // Returns false if we need to push more chunks.
        private boolean tryPushOneHunk(ByteBuffer b, List<ByteBuffer> out)
                throws IOException {
            assert state != ChunkState.DONE;
            ByteBuffer b1 = tryReadOneHunk(b);
            if (b1 != null) {
                //assert b1.hasRemaining() || b1 == READMORE;
                if (b1.hasRemaining()) {
                    if (debug.on())
                        debug.log("Sending chunk to consumer (%d)", b1.remaining());
                    out.add(b1);
                }
                return false; // we haven't parsed the final chunk yet.
            } else {
                return true; // we're done! the final chunk was parsed.
            }
        }

        private int toDigit(int b) throws IOException {
            if (b >= 0x30 && b <= 0x39) {
                return b - 0x30;
            }
            if (b >= 0x41 && b <= 0x46) {
                return b - 0x41 + 10;
            }
            if (b >= 0x61 && b <= 0x66) {
                return b - 0x61 + 10;
            }
            return -1;
        }

    }

    class UnknownLengthBodyParser implements BodyParser {
        final Consumer<Throwable> onComplete;
        final Logger debug = Utils.getDebugLogger(this::dbgString, Utils.DEBUG);
        final String dbgTag = ResponseContent.this.dbgTag + "/UnknownLengthBodyParser";
        volatile Throwable closedExceptionally;
        volatile AbstractSubscription sub;
        volatile int breceived = 0;

        UnknownLengthBodyParser(Consumer<Throwable> onComplete) {
            this.onComplete = onComplete;
        }

        String dbgString() {
            return dbgTag;
        }

        @Override
        public void onSubscribe(AbstractSubscription sub) {
            if (debug.on())
                debug.log("onSubscribe: " + pusher.getClass().getName());
            pusher.onSubscribe(this.sub = sub);
        }

        @Override
        public String currentStateMessage() {
            return format("http1_0 content, bytes received: %d", breceived);
        }

        @Override
        public void accept(ByteBuffer b) {
            if (closedExceptionally != null) {
                if (debug.on())
                    debug.log("already closed: " + closedExceptionally);
                return;
            }
            boolean completed = false;
            try {
                if (debug.on())
                    debug.log("Parser got %d bytes ", b.remaining());

                if (b.hasRemaining()) {
                    // only reduce demand if we actually push something.
                    // we would not have come here if there was no
                    // demand.
                    boolean hasDemand = sub.demand().tryDecrement();
                    assert hasDemand;
                    breceived += b.remaining();
                    pusher.onNext(List.of(b.asReadOnlyBuffer()));
                }
            } catch (Throwable t) {
                if (debug.on()) debug.log("Unexpected exception", t);
                closedExceptionally = t;
                if (!completed) {
                    onComplete.accept(t);
                }
            }
        }

        
Must be called externally when connection has closed
and therefore no more bytes can be read
/**
         * Must be called externally when connection has closed
         * and therefore no more bytes can be read
         */
        public void complete() {
            // We're done! All data has been received.
            if (debug.on())
                debug.log("Parser got all expected bytes: completing");
            assert closedExceptionally == null;
            onFinished.run();
            pusher.onComplete();
            onComplete.accept(closedExceptionally); // should be null
        }
    }

    class FixedLengthBodyParser implements BodyParser {
        final long contentLength;
        final Consumer<Throwable> onComplete;
        final Logger debug = Utils.getDebugLogger(this::dbgString, Utils.DEBUG);
        final String dbgTag = ResponseContent.this.dbgTag + "/FixedLengthBodyParser";
        volatile long remaining;
        volatile Throwable closedExceptionally;
        volatile AbstractSubscription sub;
        FixedLengthBodyParser(long contentLength, Consumer<Throwable> onComplete) {
            this.contentLength = this.remaining = contentLength;
            this.onComplete = onComplete;
        }

        String dbgString() {
            return dbgTag;
        }

        @Override
        public void onSubscribe(AbstractSubscription sub) {
            if (debug.on())
                debug.log("length=" + contentLength +", onSubscribe: "
                           + pusher.getClass().getName());
            pusher.onSubscribe(this.sub = sub);
            try {
                if (contentLength == 0) {
                    onFinished.run();
                    pusher.onComplete();
                    onComplete.accept(null);
                }
            } catch (Throwable t) {
                closedExceptionally = t;
                try {
                    pusher.onError(t);
                } finally {
                    onComplete.accept(t);
                }
            }
        }

        @Override
        public String currentStateMessage() {
            return format("fixed content-length: %d, bytes received: %d",
                          contentLength, contentLength - remaining);
        }

        @Override
        public void accept(ByteBuffer b) {
            if (closedExceptionally != null) {
                if (debug.on())
                    debug.log("already closed: " + closedExceptionally);
                return;
            }
            boolean completed = false;
            try {
                long unfulfilled = remaining;
                if (debug.on())
                    debug.log("Parser got %d bytes (%d remaining / %d)",
                              b.remaining(), unfulfilled, contentLength);
                assert unfulfilled != 0 || contentLength == 0 || b.remaining() == 0;

                if (unfulfilled == 0 && contentLength > 0) return;

                if (b.hasRemaining() && unfulfilled > 0) {
                    // only reduce demand if we actually push something.
                    // we would not have come here if there was no
                    // demand.
                    boolean hasDemand = sub.demand().tryDecrement();
                    assert hasDemand;
                    int amount = (int)Math.min(b.remaining(), unfulfilled); // safe cast
                    unfulfilled = remaining -= amount;
                    ByteBuffer buffer = Utils.sliceWithLimitedCapacity(b, amount);
                    pusher.onNext(List.of(buffer.asReadOnlyBuffer()));
                }
                if (unfulfilled == 0) {
                    // We're done! All data has been received.
                    if (debug.on())
                        debug.log("Parser got all expected bytes: completing");
                    assert closedExceptionally == null;
                    onFinished.run();
                    pusher.onComplete();
                    completed = true;
                    onComplete.accept(closedExceptionally); // should be null
                } else {
                    assert b.remaining() == 0;
                }
            } catch (Throwable t) {
                if (debug.on()) debug.log("Unexpected exception", t);
                closedExceptionally = t;
                if (!completed) {
                    onComplete.accept(t);
                }
            }
        }
    }
}