/*
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 *
 * Licensed 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 com.facebook.thrift.protocol;

import com.facebook.thrift.TException;
import java.util.Collections;

/** Utility class with static methods for interacting with protocol data streams. */
public class TProtocolUtil {

  /** The maximum recursive depth the skip() function will traverse before throwing a TException. */
  private static int maxSkipDepth = Integer.MAX_VALUE;

  /**
   * Specifies the maximum recursive depth that the skip function will traverse before throwing a
   * TException. This is a global setting, so any call to skip in this JVM will enforce this value.
   *
   * @param depth the maximum recursive depth. A value of 2 would allow the skip function to skip a
   *     structure or collection with basic children, but it would not permit skipping a struct that
   *     had a field containing a child struct. A value of 1 would only allow skipping of simple
   *     types and empty structs/collections.
   */
  public static void setMaxSkipDepth(int depth) {
    maxSkipDepth = depth;
  }

  /**
   * Skips over the next data element from the provided input TProtocol object.
   *
   * @param prot the protocol object to read from
   * @param type the next value will be intepreted as this TType value.
   */
  public static void skip(TProtocol prot, byte type) throws TException {
    skip(prot, type, maxSkipDepth);
  }

  /**
   * Skips over the next data element from the provided input TProtocol object.
   *
   * @param prot the protocol object to read from
   * @param type the next value will be intepreted as this TType value.
   * @param maxDepth this function will only skip complex objects to this recursive depth, to
   *     prevent Java stack overflow.
   */
  public static void skip(TProtocol prot, byte type, int maxDepth) throws TException {
    if (maxDepth <= 0) {
      throw new TException("Maximum skip depth exceeded");
    }
    switch (type) {
      case TType.BOOL:
        {
          prot.readBool();
          break;
        }
      case TType.BYTE:
        {
          prot.readByte();
          break;
        }
      case TType.I16:
        {
          prot.readI16();
          break;
        }
      case TType.I32:
        {
          prot.readI32();
          break;
        }
      case TType.I64:
        {
          prot.readI64();
          break;
        }
      case TType.DOUBLE:
        {
          prot.readDouble();
          break;
        }
      case TType.FLOAT:
        {
          prot.readFloat();
          break;
        }
      case TType.STRING:
        {
          prot.skipBinary();
          break;
        }
      case TType.STRUCT:
        {
          prot.readStructBegin(
              Collections.<Integer, com.facebook.thrift.meta_data.FieldMetaData>emptyMap());
          while (true) {
            TField field = prot.readFieldBegin();
            if (field.type == TType.STOP) {
              break;
            }
            skip(prot, field.type, maxDepth - 1);
            prot.readFieldEnd();
          }
          prot.readStructEnd();
          break;
        }
      case TType.MAP:
        {
          TMap map = prot.readMapBegin();
          for (int i = 0; (map.size < 0) ? prot.peekMap() : (i < map.size); i++) {
            skip(prot, map.keyType, maxDepth - 1);
            skip(prot, map.valueType, maxDepth - 1);
          }
          prot.readMapEnd();
          break;
        }
      case TType.SET:
        {
          TSet set = prot.readSetBegin();
          for (int i = 0; (set.size < 0) ? prot.peekSet() : (i < set.size); i++) {
            skip(prot, set.elemType, maxDepth - 1);
          }
          prot.readSetEnd();
          break;
        }
      case TType.LIST:
        {
          TList list = prot.readListBegin();
          for (int i = 0; (list.size < 0) ? prot.peekList() : (i < list.size); i++) {
            skip(prot, list.elemType, maxDepth - 1);
          }
          prot.readListEnd();
          break;
        }
      default:
        {
          throw new TProtocolException(
              TProtocolException.INVALID_DATA, "Invalid type encountered during skipping: " + type);
        }
    }
  }

  /**
   * Attempt to determine the protocol used to serialize some data.
   *
   * <p>The guess is based on known specificities of supported protocols. In some cases, no guess
   * can be done, in that case we return the fallback TProtocolFactory. To be certain to correctly
   * detect the protocol, the first encoded field should have a field id < 256
   *
   * @param data The serialized data to guess the protocol for.
   * @param fallback The TProtocol to return if no guess can be made.
   * @return a Class implementing TProtocolFactory which can be used to create a deserializer.
   */
  public static TProtocolFactory guessProtocolFactory(byte[] data, TProtocolFactory fallback) {
    //
    // If the first and last bytes are opening/closing curly braces we guess the protocol as
    // being TJSONProtocol.
    // It could not be a TCompactBinary encoding for a field of type 0xb (Map)
    // with delta id 7 as the last byte for TCompactBinary is always 0.
    //

    if ('{' == data[0] && '}' == data[data.length - 1]) {
      return new TJSONProtocol.Factory();
    }

    //
    // If the last byte is not 0, then it cannot be TCompactProtocol, it must be
    // TBinaryProtocol.
    //

    if (data[data.length - 1] != 0) {
      return new TBinaryProtocol.Factory();
    }

    //
    // A first byte of value > 16 indicates TCompactProtocol was used, and the first byte
    // encodes a delta field id (id <= 15) and a field type.
    //

    if (data[0] > 0x10) {
      return new TCompactProtocol.Factory();
    }

    //
    // If the second byte is 0 then it is a field id < 256 encoded by TBinaryProtocol.
    // It cannot possibly be TCompactProtocol since a value of 0 would imply a field id
    // of 0 as the zig zag varint encoding would end.
    //

    if (data.length > 1 && 0 == data[1]) {
      return new TBinaryProtocol.Factory();
    }

    //
    // If bit 7 of the first byte of the field id is set then we have two choices:
    // 1. A field id > 63 was encoded with TCompactProtocol.
    // 2. A field id > 0x7fff (32767) was encoded with TBinaryProtocol and the last byte of the
    //    serialized data is 0.
    // Option 2 is impossible since field ids are short and thus limited to 32767.
    //

    if (data.length > 1 && (data[1] & 0x80) != 0) {
      return new TCompactProtocol.Factory();
    }

    //
    // The remaining case is either a field id <= 63 encoded as TCompactProtocol,
    // one >= 256 encoded with TBinaryProtocol with a last byte at 0, or an empty structure.
    // As we cannot really decide, we return the fallback protocol.
    //
    return fallback;
  }
}
