/*
    * Copyright 2014 The Netty Project
    *
    * The Netty Project 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:
    *
    * https://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 io.netty.handler.codec.http2;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.buffer.ByteBufUtil;
  import io.netty.buffer.Unpooled;
  import io.netty.channel.Channel;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.channel.ChannelPromise;
  import io.netty.channel.DefaultChannelPromise;
  import io.netty.handler.ssl.ApplicationProtocolNames;
  import io.netty.util.AsciiString;
  import io.netty.util.concurrent.EventExecutor;
  
  import static io.netty.buffer.Unpooled.directBuffer;
  import static io.netty.buffer.Unpooled.unreleasableBuffer;
  import static io.netty.handler.codec.http2.Http2Error.PROTOCOL_ERROR;
  import static io.netty.handler.codec.http2.Http2Exception.connectionError;
  import static io.netty.handler.codec.http2.Http2Exception.headerListSizeError;
  import static io.netty.util.CharsetUtil.UTF_8;
  import static java.lang.Math.max;
  import static java.lang.Math.min;
  import static java.util.concurrent.TimeUnit.MILLISECONDS;
  import static java.util.concurrent.TimeUnit.SECONDS;
  
  /**
   * Constants and utility method used for encoding/decoding HTTP2 frames.
   */
  public final class Http2CodecUtil {
      public static final int CONNECTION_STREAM_ID = 0;
      public static final int HTTP_UPGRADE_STREAM_ID = 1;
      public static final CharSequence HTTP_UPGRADE_SETTINGS_HEADER = AsciiString.cached("HTTP2-Settings");
      public static final CharSequence HTTP_UPGRADE_PROTOCOL_NAME = "h2c";
      public static final CharSequence TLS_UPGRADE_PROTOCOL_NAME = ApplicationProtocolNames.HTTP_2;
  
      public static final int PING_FRAME_PAYLOAD_LENGTH = 8;
      public static final short MAX_UNSIGNED_BYTE = 0xff;
      /**
       * The maximum number of padding bytes. That is the 255 padding bytes appended to the end of a frame and the 1 byte
       * pad length field.
       */
      public static final int MAX_PADDING = 256;
      public static final long MAX_UNSIGNED_INT = 0xffffffffL;
      public static final int FRAME_HEADER_LENGTH = 9;
      public static final int SETTING_ENTRY_LENGTH = 6;
      public static final int PRIORITY_ENTRY_LENGTH = 5;
      public static final int INT_FIELD_LENGTH = 4;
      public static final short MAX_WEIGHT = 256;
      public static final short MIN_WEIGHT = 1;
  
      private static final ByteBuf CONNECTION_PREFACE =
              unreleasableBuffer(directBuffer(24).writeBytes("PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n".getBytes(UTF_8)))
                      .asReadOnly();
  
      private static final int MAX_PADDING_LENGTH_LENGTH = 1;
      public static final int DATA_FRAME_HEADER_LENGTH = FRAME_HEADER_LENGTH + MAX_PADDING_LENGTH_LENGTH;
      public static final int HEADERS_FRAME_HEADER_LENGTH =
              FRAME_HEADER_LENGTH + MAX_PADDING_LENGTH_LENGTH + INT_FIELD_LENGTH + 1;
      public static final int PRIORITY_FRAME_LENGTH = FRAME_HEADER_LENGTH + PRIORITY_ENTRY_LENGTH;
      public static final int RST_STREAM_FRAME_LENGTH = FRAME_HEADER_LENGTH + INT_FIELD_LENGTH;
      public static final int PUSH_PROMISE_FRAME_HEADER_LENGTH =
              FRAME_HEADER_LENGTH + MAX_PADDING_LENGTH_LENGTH + INT_FIELD_LENGTH;
      public static final int GO_AWAY_FRAME_HEADER_LENGTH = FRAME_HEADER_LENGTH + 2 * INT_FIELD_LENGTH;
      public static final int WINDOW_UPDATE_FRAME_LENGTH = FRAME_HEADER_LENGTH + INT_FIELD_LENGTH;
      public static final int CONTINUATION_FRAME_HEADER_LENGTH = FRAME_HEADER_LENGTH;
  
      public static final char SETTINGS_HEADER_TABLE_SIZE = 1;
      public static final char SETTINGS_ENABLE_PUSH = 2;
      public static final char SETTINGS_MAX_CONCURRENT_STREAMS = 3;
      public static final char SETTINGS_INITIAL_WINDOW_SIZE = 4;
      public static final char SETTINGS_MAX_FRAME_SIZE = 5;
      public static final char SETTINGS_MAX_HEADER_LIST_SIZE = 6;
      public static final char SETTINGS_ENABLE_CONNECT_PROTOCOL = 8;
      public static final int NUM_STANDARD_SETTINGS = 7;
  
      public static final long MAX_HEADER_TABLE_SIZE = MAX_UNSIGNED_INT;
      public static final long MAX_CONCURRENT_STREAMS = MAX_UNSIGNED_INT;
      public static final int MAX_INITIAL_WINDOW_SIZE = Integer.MAX_VALUE;
      public static final int MAX_FRAME_SIZE_LOWER_BOUND = 0x4000;
      public static final int MAX_FRAME_SIZE_UPPER_BOUND = 0xffffff;
      public static final long MAX_HEADER_LIST_SIZE = MAX_UNSIGNED_INT;
  
      public static final long MIN_HEADER_TABLE_SIZE = 0;
      public static final long MIN_CONCURRENT_STREAMS = 0;
      public static final int MIN_INITIAL_WINDOW_SIZE = 0;
     public static final long MIN_HEADER_LIST_SIZE = 0;
 
     public static final int DEFAULT_WINDOW_SIZE = 65535;
     public static final short DEFAULT_PRIORITY_WEIGHT = 16;
     public static final int DEFAULT_HEADER_TABLE_SIZE = 4096;
     /**
      * <a href="https://tools.ietf.org/html/rfc7540#section-6.5.2">The initial value of this setting is unlimited</a>.
      * However in practice we don't want to allow our peers to use unlimited memory by default. So we take advantage
      * of the <q>For any given request, a lower limit than what is advertised MAY be enforced.</q> loophole.
      */
     public static final long DEFAULT_HEADER_LIST_SIZE = 8192;
     public static final int DEFAULT_MAX_FRAME_SIZE = MAX_FRAME_SIZE_LOWER_BOUND;
     /**
      * The assumed minimum value for {@code SETTINGS_MAX_CONCURRENT_STREAMS} as
      * recommended by the <a href="https://tools.ietf.org/html/rfc7540#section-6.5.2">HTTP/2 spec</a>.
      */
     public static final int SMALLEST_MAX_CONCURRENT_STREAMS = 100;
     static final int DEFAULT_MAX_RESERVED_STREAMS = SMALLEST_MAX_CONCURRENT_STREAMS;
     static final int DEFAULT_MIN_ALLOCATION_CHUNK = 1024;
     static final int DEFAULT_MAX_SMALL_CONTINUATION_FRAME = 16;
 
     /**
      * While the RFC only specified a minimum we should still pick a default which is good enough that most people
      * no need to adjust it but still be somewhat protected. Let's use the minimum
      * defined by the <a href="https://tools.ietf.org/html/rfc7540#section-6.5.2">HTTP/2 spec</a>.
      */
     static final int DEFAULT_MAX_CONCURRENT_STREAMS = SMALLEST_MAX_CONCURRENT_STREAMS;
 
     /**
      * Calculate the threshold in bytes which should trigger a {@code GO_AWAY} if a set of headers exceeds this amount.
      * @param maxHeaderListSize
      *      <a href="https://tools.ietf.org/html/rfc7540#section-6.5.2">SETTINGS_MAX_HEADER_LIST_SIZE</a> for the local
      *      endpoint.
      * @return the threshold in bytes which should trigger a {@code GO_AWAY} if a set of headers exceeds this amount.
      */
     public static long calculateMaxHeaderListSizeGoAway(long maxHeaderListSize) {
         // This is equivalent to `maxHeaderListSize * 1.25` but we avoid floating point multiplication.
         return maxHeaderListSize + (maxHeaderListSize >>> 2);
     }
 
     public static final long DEFAULT_GRACEFUL_SHUTDOWN_TIMEOUT_MILLIS = MILLISECONDS.convert(30, SECONDS);
 
     public static final int DEFAULT_MAX_QUEUED_CONTROL_FRAMES = 10000;
 
     /**
      * Returns {@code true} if the stream is an outbound stream.
      *
      * @param server    {@code true} if the endpoint is a server, {@code false} otherwise.
      * @param streamId  the stream identifier
      */
     public static boolean isOutboundStream(boolean server, int streamId) {
         boolean even = (streamId & 1) == 0;
         return streamId > 0 && server == even;
     }
 
     /**
      * Returns true if the {@code streamId} is a valid HTTP/2 stream identifier.
      */
     public static boolean isStreamIdValid(int streamId) {
         return streamId >= 0;
     }
 
     static boolean isStreamIdValid(int streamId, boolean server) {
         return isStreamIdValid(streamId) && server == ((streamId & 1) == 0);
     }
 
     /**
      * Indicates whether or not the given value for max frame size falls within the valid range.
      */
     public static boolean isMaxFrameSizeValid(int maxFrameSize) {
         return maxFrameSize >= MAX_FRAME_SIZE_LOWER_BOUND && maxFrameSize <= MAX_FRAME_SIZE_UPPER_BOUND;
     }
 
     /**
      * Returns a buffer containing the {@link #CONNECTION_PREFACE}.
      */
     public static ByteBuf connectionPrefaceBuf() {
         // Return a duplicate so that modifications to the reader index will not affect the original buffer.
         return CONNECTION_PREFACE.retainedDuplicate();
     }
 
     /**
      * Iteratively looks through the causality chain for the given exception and returns the first
      * {@link Http2Exception} or {@code null} if none.
      */
     public static Http2Exception getEmbeddedHttp2Exception(Throwable cause) {
         while (cause != null) {
             if (cause instanceof Http2Exception) {
                 return (Http2Exception) cause;
             }
             cause = cause.getCause();
         }
         return null;
     }
 
     /**
      * Creates a buffer containing the error message from the given exception. If the cause is
      * {@code null} returns an empty buffer.
      */
     public static ByteBuf toByteBuf(ChannelHandlerContext ctx, Throwable cause) {
         if (cause == null || cause.getMessage() == null) {
             return Unpooled.EMPTY_BUFFER;
         }
 
         return ByteBufUtil.writeUtf8(ctx.alloc(), cause.getMessage());
     }
 
     /**
      * Reads a big-endian (31-bit) integer from the buffer.
      */
     public static int readUnsignedInt(ByteBuf buf) {
         return buf.readInt() & 0x7fffffff;
     }
 
     /**
      * Writes an HTTP/2 frame header to the output buffer.
      */
     public static void writeFrameHeader(ByteBuf out, int payloadLength, byte type,
             Http2Flags flags, int streamId) {
         out.ensureWritable(FRAME_HEADER_LENGTH + payloadLength);
         writeFrameHeaderInternal(out, payloadLength, type, flags, streamId);
     }
 
     /**
      * Calculate the amount of bytes that can be sent by {@code state}. The lower bound is {@code 0}.
      */
     public static int streamableBytes(StreamByteDistributor.StreamState state) {
         return max(0, (int) min(state.pendingBytes(), state.windowSize()));
     }
 
     /**
      * Results in a RST_STREAM being sent for {@code streamId} due to violating
      * <a href="https://tools.ietf.org/html/rfc7540#section-6.5.2">SETTINGS_MAX_HEADER_LIST_SIZE</a>.
      * @param streamId The stream ID that was being processed when the exceptional condition occurred.
      * @param maxHeaderListSize The max allowed size for a list of headers in bytes which was exceeded.
      * @param onDecode {@code true} if the exception was encountered during decoder. {@code false} for encode.
      * @throws Http2Exception a stream error.
      */
     public static void headerListSizeExceeded(int streamId, long maxHeaderListSize,
                                               boolean onDecode) throws Http2Exception {
         throw headerListSizeError(streamId, PROTOCOL_ERROR, onDecode, "Header size exceeded max " +
                                   "allowed size (%d)", maxHeaderListSize);
     }
 
     /**
      * Results in a GO_AWAY being sent due to violating
      * <a href="https://tools.ietf.org/html/rfc7540#section-6.5.2">SETTINGS_MAX_HEADER_LIST_SIZE</a> in an unrecoverable
      * manner.
      * @param maxHeaderListSize The max allowed size for a list of headers in bytes which was exceeded.
      * @throws Http2Exception a connection error.
      */
     public static void headerListSizeExceeded(long maxHeaderListSize) throws Http2Exception {
         throw connectionError(PROTOCOL_ERROR, "Header size exceeded max " +
                 "allowed size (%d)", maxHeaderListSize);
     }
 
     static void writeFrameHeaderInternal(ByteBuf out, int payloadLength, byte type,
             Http2Flags flags, int streamId) {
         out.writeMedium(payloadLength);
         out.writeByte(type);
         out.writeByte(flags.value());
         out.writeInt(streamId);
     }
 
     /**
      * Provides the ability to associate the outcome of multiple {@link ChannelPromise}
      * objects into a single {@link ChannelPromise} object.
      */
     static final class SimpleChannelPromiseAggregator extends DefaultChannelPromise {
         private final ChannelPromise promise;
         private int expectedCount;
         private int doneCount;
         private Throwable aggregateFailure;
         private boolean doneAllocating;
 
         SimpleChannelPromiseAggregator(ChannelPromise promise, Channel c, EventExecutor e) {
             super(c, e);
             assert promise != null && !promise.isDone();
             this.promise = promise;
         }
 
         /**
          * Allocate a new promise which will be used to aggregate the overall success of this promise aggregator.
          * @return A new promise which will be aggregated.
          * {@code null} if {@link #doneAllocatingPromises()} was previously called.
          */
         public ChannelPromise newPromise() {
             assert !doneAllocating : "Done allocating. No more promises can be allocated.";
             ++expectedCount;
             return this;
         }
 
         /**
          * Signify that no more {@link #newPromise()} allocations will be made.
          * The aggregation can not be successful until this method is called.
          * @return The promise that is the aggregation of all promises allocated with {@link #newPromise()}.
          */
         public ChannelPromise doneAllocatingPromises() {
             if (!doneAllocating) {
                 doneAllocating = true;
                 if (doneCount == expectedCount || expectedCount == 0) {
                     return setPromise();
                 }
             }
             return this;
         }
 
         @Override
         public boolean tryFailure(Throwable cause) {
             if (allowFailure()) {
                 ++doneCount;
                 setAggregateFailure(cause);
                 if (allPromisesDone()) {
                     return tryPromise();
                 }
                 // TODO: We break the interface a bit here.
                 // Multiple failure events can be processed without issue because this is an aggregation.
                 return true;
             }
             return false;
         }
 
         /**
          * Fail this object if it has not already been failed.
          * <p>
          * This method will NOT throw an {@link IllegalStateException} if called multiple times
          * because that may be expected.
          */
         @Override
         public ChannelPromise setFailure(Throwable cause) {
             if (allowFailure()) {
                 ++doneCount;
                 setAggregateFailure(cause);
                 if (allPromisesDone()) {
                     return setPromise();
                 }
             }
             return this;
         }
 
         @Override
         public ChannelPromise setSuccess(Void result) {
             if (awaitingPromises()) {
                 ++doneCount;
                 if (allPromisesDone()) {
                     setPromise();
                 }
             }
             return this;
         }
 
         @Override
         public boolean trySuccess(Void result) {
             if (awaitingPromises()) {
                 ++doneCount;
                 if (allPromisesDone()) {
                     return tryPromise();
                 }
                 // TODO: We break the interface a bit here.
                 // Multiple success events can be processed without issue because this is an aggregation.
                 return true;
             }
             return false;
         }
 
         private boolean allowFailure() {
             return awaitingPromises() || expectedCount == 0;
         }
 
         private boolean awaitingPromises() {
             return doneCount < expectedCount;
         }
 
         private boolean allPromisesDone() {
             return doneCount == expectedCount && doneAllocating;
         }
 
         private ChannelPromise setPromise() {
             if (aggregateFailure == null) {
                 promise.setSuccess();
                 return super.setSuccess(null);
             } else {
                 promise.setFailure(aggregateFailure);
                 return super.setFailure(aggregateFailure);
             }
         }
 
         private boolean tryPromise() {
             if (aggregateFailure == null) {
                 promise.trySuccess();
                 return super.trySuccess(null);
             } else {
                 promise.tryFailure(aggregateFailure);
                 return super.tryFailure(aggregateFailure);
             }
         }
 
         private void setAggregateFailure(Throwable cause) {
             if (aggregateFailure == null) {
                 aggregateFailure = cause;
             }
         }
     }
 
     public static void verifyPadding(int padding) {
         if (padding < 0 || padding > MAX_PADDING) {
             throw new IllegalArgumentException(String.format("Invalid padding '%d'. Padding must be between 0 and " +
                                                              "%d (inclusive).", padding, MAX_PADDING));
         }
     }
     private Http2CodecUtil() { }
 }