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// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc.  All rights reserved.
// http://code.google.com/p/protobuf/
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
//     * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

package com.google.protobuf;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.io.IOException;

/**
 * A class which represents an arbitrary set of fields of some message type.
 * This is used to implement {@link DynamicMessage}, and also to represent
 * extensions in {@link GeneratedMessage}.  This class is package-private,
 * since outside users should probably be using {@link DynamicMessage}.
 *
 * @author kenton@google.com Kenton Varda
 */
final class FieldSet<FieldDescriptorType extends
      FieldSet.FieldDescriptorLite<FieldDescriptorType>> {
  /**
   * Interface for a FieldDescriptor or lite extension descriptor.  This
   * prevents FieldSet from depending on {@link Descriptors.FieldDescriptor}.
   */
  public interface FieldDescriptorLite<T extends FieldDescriptorLite<T>>
      extends Comparable<T> {
    int getNumber();
    WireFormat.FieldType getLiteType();
    WireFormat.JavaType getLiteJavaType();
    boolean isRepeated();
    boolean isPacked();
    Internal.EnumLiteMap<?> getEnumType();

    // If getLiteJavaType() == MESSAGE, this merges a message object of the
    // type into a builder of the type.  Returns {@code to}.
    MessageLite.Builder internalMergeFrom(
        MessageLite.Builder to, MessageLite from);
  }

  private final SmallSortedMap<FieldDescriptorType, Object> fields;
  private boolean isImmutable;

  /** Construct a new FieldSet. */
  private FieldSet() {
    this.fields = SmallSortedMap.newFieldMap(16);
  }

  /**
   * Construct an empty FieldSet.  This is only used to initialize
   * DEFAULT_INSTANCE.
   */
  private FieldSet(final boolean dummy) {
    this.fields = SmallSortedMap.newFieldMap(0);
    makeImmutable();
  }

  /** Construct a new FieldSet. */
  public static <T extends FieldSet.FieldDescriptorLite<T>>
      FieldSet<T> newFieldSet() {
    return new FieldSet<T>();
  }

  /** Get an immutable empty FieldSet. */
  @SuppressWarnings("unchecked")
  public static <T extends FieldSet.FieldDescriptorLite<T>>
      FieldSet<T> emptySet() {
    return DEFAULT_INSTANCE;
  }
  @SuppressWarnings("unchecked")
  private static final FieldSet DEFAULT_INSTANCE = new FieldSet(true);

  /** Make this FieldSet immutable from this point forward. */
  @SuppressWarnings("unchecked")
  public void makeImmutable() {
    if (isImmutable) {
      return;
    }
    fields.makeImmutable();
    isImmutable = true;
  }

  /**
   * Retuns whether the FieldSet is immutable. This is true if it is the
   * {@link #emptySet} or if {@link #makeImmutable} were called.
   *
   * @return whether the FieldSet is immutable.
   */
  public boolean isImmutable() {
    return isImmutable;
  }

  /**
   * Clones the FieldSet. The returned FieldSet will be mutable even if the
   * original FieldSet was immutable.
   *
   * @return the newly cloned FieldSet
   */
  @Override
  public FieldSet<FieldDescriptorType> clone() {
    // We can't just call fields.clone because List objects in the map
    // should not be shared.
    FieldSet<FieldDescriptorType> clone = FieldSet.newFieldSet();
    for (int i = 0; i < fields.getNumArrayEntries(); i++) {
      Map.Entry<FieldDescriptorType, Object> entry = fields.getArrayEntryAt(i);
      FieldDescriptorType descriptor = entry.getKey();
      clone.setField(descriptor, entry.getValue());
    }
    for (Map.Entry<FieldDescriptorType, Object> entry :
             fields.getOverflowEntries()) {
      FieldDescriptorType descriptor = entry.getKey();
      clone.setField(descriptor, entry.getValue());
    }
    return clone;
  }

  // =================================================================

  /** See {@link Message.Builder#clear()}. */
  public void clear() {
    fields.clear();
  }

  /**
   * Get a simple map containing all the fields.
   */
  public Map<FieldDescriptorType, Object> getAllFields() {
    return fields.isImmutable() ? fields : Collections.unmodifiableMap(fields);
  }

  /**
   * Get an iterator to the field map. This iterator should not be leaked out
   * of the protobuf library as it is not protected from mutation when
   * fields is not immutable.
   */
  public Iterator<Map.Entry<FieldDescriptorType, Object>> iterator() {
    return fields.entrySet().iterator();
  }

  /**
   * Useful for implementing
   * {@link Message#hasField(Descriptors.FieldDescriptor)}.
   */
  public boolean hasField(final FieldDescriptorType descriptor) {
    if (descriptor.isRepeated()) {
      throw new IllegalArgumentException(
        "hasField() can only be called on non-repeated fields.");
    }

    return fields.get(descriptor) != null;
  }

  /**
   * Useful for implementing
   * {@link Message#getField(Descriptors.FieldDescriptor)}.  This method
   * returns {@code null} if the field is not set; in this case it is up
   * to the caller to fetch the field's default value.
   */
  public Object getField(final FieldDescriptorType descriptor) {
    return fields.get(descriptor);
  }

  /**
   * Useful for implementing
   * {@link Message.Builder#setField(Descriptors.FieldDescriptor,Object)}.
   */
  @SuppressWarnings("unchecked")
  public void setField(final FieldDescriptorType descriptor,
                       Object value) {
    if (descriptor.isRepeated()) {
      if (!(value instanceof List)) {
        throw new IllegalArgumentException(
          "Wrong object type used with protocol message reflection.");
      }

      // Wrap the contents in a new list so that the caller cannot change
      // the list's contents after setting it.
      final List newList = new ArrayList();
      newList.addAll((List)value);
      for (final Object element : newList) {
        verifyType(descriptor.getLiteType(), element);
      }
      value = newList;
    } else {
      verifyType(descriptor.getLiteType(), value);
    }

    fields.put(descriptor, value);
  }

  /**
   * Useful for implementing
   * {@link Message.Builder#clearField(Descriptors.FieldDescriptor)}.
   */
  public void clearField(final FieldDescriptorType descriptor) {
    fields.remove(descriptor);
  }

  /**
   * Useful for implementing
   * {@link Message#getRepeatedFieldCount(Descriptors.FieldDescriptor)}.
   */
  public int getRepeatedFieldCount(final FieldDescriptorType descriptor) {
    if (!descriptor.isRepeated()) {
      throw new IllegalArgumentException(
        "getRepeatedField() can only be called on repeated fields.");
    }

    final Object value = fields.get(descriptor);
    if (value == null) {
      return 0;
    } else {
      return ((List<?>) value).size();
    }
  }

  /**
   * Useful for implementing
   * {@link Message#getRepeatedField(Descriptors.FieldDescriptor,int)}.
   */
  public Object getRepeatedField(final FieldDescriptorType descriptor,
                                 final int index) {
    if (!descriptor.isRepeated()) {
      throw new IllegalArgumentException(
        "getRepeatedField() can only be called on repeated fields.");
    }

    final Object value = fields.get(descriptor);

    if (value == null) {
      throw new IndexOutOfBoundsException();
    } else {
      return ((List<?>) value).get(index);
    }
  }

  /**
   * Useful for implementing
   * {@link Message.Builder#setRepeatedField(Descriptors.FieldDescriptor,int,Object)}.
   */
  @SuppressWarnings("unchecked")
  public void setRepeatedField(final FieldDescriptorType descriptor,
                               final int index,
                               final Object value) {
    if (!descriptor.isRepeated()) {
      throw new IllegalArgumentException(
        "getRepeatedField() can only be called on repeated fields.");
    }

    final Object list = fields.get(descriptor);
    if (list == null) {
      throw new IndexOutOfBoundsException();
    }

    verifyType(descriptor.getLiteType(), value);
    ((List) list).set(index, value);
  }

  /**
   * Useful for implementing
   * {@link Message.Builder#addRepeatedField(Descriptors.FieldDescriptor,Object)}.
   */
  @SuppressWarnings("unchecked")
  public void addRepeatedField(final FieldDescriptorType descriptor,
                               final Object value) {
    if (!descriptor.isRepeated()) {
      throw new IllegalArgumentException(
        "addRepeatedField() can only be called on repeated fields.");
    }

    verifyType(descriptor.getLiteType(), value);

    final Object existingValue = fields.get(descriptor);
    List list;
    if (existingValue == null) {
      list = new ArrayList();
      fields.put(descriptor, list);
    } else {
      list = (List) existingValue;
    }

    list.add(value);
  }

  /**
   * Verifies that the given object is of the correct type to be a valid
   * value for the given field.  (For repeated fields, this checks if the
   * object is the right type to be one element of the field.)
   *
   * @throws IllegalArgumentException The value is not of the right type.
   */
  private static void verifyType(final WireFormat.FieldType type,
                                 final Object value) {
    if (value == null) {
      throw new NullPointerException();
    }

    boolean isValid = false;
    switch (type.getJavaType()) {
      case INT:          isValid = value instanceof Integer   ; break;
      case LONG:         isValid = value instanceof Long      ; break;
      case FLOAT:        isValid = value instanceof Float     ; break;
      case DOUBLE:       isValid = value instanceof Double    ; break;
      case BOOLEAN:      isValid = value instanceof Boolean   ; break;
      case STRING:       isValid = value instanceof String    ; break;
      case BYTE_STRING:  isValid = value instanceof ByteString; break;
      case ENUM:
        // TODO(kenton):  Caller must do type checking here, I guess.
        isValid = value instanceof Internal.EnumLite;
        break;
      case MESSAGE:
        // TODO(kenton):  Caller must do type checking here, I guess.
        isValid = value instanceof MessageLite;
        break;
    }

    if (!isValid) {
      // TODO(kenton):  When chaining calls to setField(), it can be hard to
      //   tell from the stack trace which exact call failed, since the whole
      //   chain is considered one line of code.  It would be nice to print
      //   more information here, e.g. naming the field.  We used to do that.
      //   But we can't now that FieldSet doesn't use descriptors.  Maybe this
      //   isn't a big deal, though, since it would only really apply when using
      //   reflection and generally people don't chain reflection setters.
      throw new IllegalArgumentException(
        "Wrong object type used with protocol message reflection.");
    }
  }

  // =================================================================
  // Parsing and serialization

  /**
   * See {@link Message#isInitialized()}.  Note:  Since {@code FieldSet}
   * itself does not have any way of knowing about required fields that
   * aren't actually present in the set, it is up to the caller to check
   * that all required fields are present.
   */
  public boolean isInitialized() {
    for (int i = 0; i < fields.getNumArrayEntries(); i++) {
      if (!isInitialized(fields.getArrayEntryAt(i))) {
        return false;
      }
    }
    for (final Map.Entry<FieldDescriptorType, Object> entry :
             fields.getOverflowEntries()) {
      if (!isInitialized(entry)) {
        return false;
      }
    }
    return true;
  }

  @SuppressWarnings("unchecked")
  private boolean isInitialized(
      final Map.Entry<FieldDescriptorType, Object> entry) {
    final FieldDescriptorType descriptor = entry.getKey();
    if (descriptor.getLiteJavaType() == WireFormat.JavaType.MESSAGE) {
      if (descriptor.isRepeated()) {
        for (final MessageLite element:
                 (List<MessageLite>) entry.getValue()) {
          if (!element.isInitialized()) {
            return false;
          }
        }
      } else {
        if (!((MessageLite) entry.getValue()).isInitialized()) {
          return false;
        }
      }
    }
    return true;
  }

  /**
   * Given a field type, return the wire type.
   *
   * @returns One of the {@code WIRETYPE_} constants defined in
   *          {@link WireFormat}.
   */
  static int getWireFormatForFieldType(final WireFormat.FieldType type,
                                       boolean isPacked) {
    if (isPacked) {
      return WireFormat.WIRETYPE_LENGTH_DELIMITED;
    } else {
      return type.getWireType();
    }
  }

  /**
   * Like {@link #mergeFrom(Message)}, but merges from another {@link FieldSet}.
   */
  public void mergeFrom(final FieldSet<FieldDescriptorType> other) {
    for (int i = 0; i < other.fields.getNumArrayEntries(); i++) {
      mergeFromField(other.fields.getArrayEntryAt(i));
    }
    for (final Map.Entry<FieldDescriptorType, Object> entry :
             other.fields.getOverflowEntries()) {
      mergeFromField(entry);
    }
  }

  @SuppressWarnings("unchecked")
  private void mergeFromField(
      final Map.Entry<FieldDescriptorType, Object> entry) {
    final FieldDescriptorType descriptor = entry.getKey();
    final Object otherValue = entry.getValue();

    if (descriptor.isRepeated()) {
      Object value = fields.get(descriptor);
      if (value == null) {
        // Our list is empty, but we still need to make a defensive copy of
        // the other list since we don't know if the other FieldSet is still
        // mutable.
        fields.put(descriptor, new ArrayList((List) otherValue));
      } else {
        // Concatenate the lists.
        ((List) value).addAll((List) otherValue);
      }
    } else if (descriptor.getLiteJavaType() == WireFormat.JavaType.MESSAGE) {
      Object value = fields.get(descriptor);
      if (value == null) {
        fields.put(descriptor, otherValue);
      } else {
        // Merge the messages.
        fields.put(
            descriptor,
            descriptor.internalMergeFrom(
                ((MessageLite) value).toBuilder(), (MessageLite) otherValue)
            .build());
      }

    } else {
      fields.put(descriptor, otherValue);
    }
  }

  // TODO(kenton):  Move static parsing and serialization methods into some
  //   other class.  Probably WireFormat.

  /**
   * Read a field of any primitive type from a CodedInputStream.  Enums,
   * groups, and embedded messages are not handled by this method.
   *
   * @param input The stream from which to read.
   * @param type Declared type of the field.
   * @return An object representing the field's value, of the exact
   *         type which would be returned by
   *         {@link Message#getField(Descriptors.FieldDescriptor)} for
   *         this field.
   */
  public static Object readPrimitiveField(
      CodedInputStream input,
      final WireFormat.FieldType type) throws IOException {
    switch (type) {
      case DOUBLE  : return input.readDouble  ();
      case FLOAT   : return input.readFloat   ();
      case INT64   : return input.readInt64   ();
      case UINT64  : return input.readUInt64  ();
      case INT32   : return input.readInt32   ();
      case FIXED64 : return input.readFixed64 ();
      case FIXED32 : return input.readFixed32 ();
      case BOOL    : return input.readBool    ();
      case STRING  : return input.readString  ();
      case BYTES   : return input.readBytes   ();
      case UINT32  : return input.readUInt32  ();
      case SFIXED32: return input.readSFixed32();
      case SFIXED64: return input.readSFixed64();
      case SINT32  : return input.readSInt32  ();
      case SINT64  : return input.readSInt64  ();

      case GROUP:
        throw new IllegalArgumentException(
          "readPrimitiveField() cannot handle nested groups.");
      case MESSAGE:
        throw new IllegalArgumentException(
          "readPrimitiveField() cannot handle embedded messages.");
      case ENUM:
        // We don't handle enums because we don't know what to do if the
        // value is not recognized.
        throw new IllegalArgumentException(
          "readPrimitiveField() cannot handle enums.");
    }

    throw new RuntimeException(
      "There is no way to get here, but the compiler thinks otherwise.");
  }

  /** See {@link Message#writeTo(CodedOutputStream)}. */
  public void writeTo(final CodedOutputStream output)
                      throws IOException {
    for (int i = 0; i < fields.getNumArrayEntries(); i++) {
      final Map.Entry<FieldDescriptorType, Object> entry =
          fields.getArrayEntryAt(i);
      writeField(entry.getKey(), entry.getValue(), output);
    }
    for (final Map.Entry<FieldDescriptorType, Object> entry :
         fields.getOverflowEntries()) {
      writeField(entry.getKey(), entry.getValue(), output);
    }
  }

  /**
   * Like {@link #writeTo} but uses MessageSet wire format.
   */
  public void writeMessageSetTo(final CodedOutputStream output)
                                throws IOException {
    for (int i = 0; i < fields.getNumArrayEntries(); i++) {
      writeMessageSetTo(fields.getArrayEntryAt(i), output);
    }
    for (final Map.Entry<FieldDescriptorType, Object> entry :
             fields.getOverflowEntries()) {
      writeMessageSetTo(entry, output);
    }
  }

  private void writeMessageSetTo(
      final Map.Entry<FieldDescriptorType, Object> entry,
      final CodedOutputStream output) throws IOException {
    final FieldDescriptorType descriptor = entry.getKey();
    if (descriptor.getLiteJavaType() == WireFormat.JavaType.MESSAGE &&
        !descriptor.isRepeated() && !descriptor.isPacked()) {
      output.writeMessageSetExtension(entry.getKey().getNumber(),
                                      (MessageLite) entry.getValue());
    } else {
      writeField(descriptor, entry.getValue(), output);
    }
  }

  /**
   * Write a single tag-value pair to the stream.
   *
   * @param output The output stream.
   * @param type   The field's type.
   * @param number The field's number.
   * @param value  Object representing the field's value.  Must be of the exact
   *               type which would be returned by
   *               {@link Message#getField(Descriptors.FieldDescriptor)} for
   *               this field.
   */
  private static void writeElement(final CodedOutputStream output,
                                   final WireFormat.FieldType type,
                                   final int number,
                                   final Object value) throws IOException {
    // Special case for groups, which need a start and end tag; other fields
    // can just use writeTag() and writeFieldNoTag().
    if (type == WireFormat.FieldType.GROUP) {
      output.writeGroup(number, (MessageLite) value);
    } else {
      output.writeTag(number, getWireFormatForFieldType(type, false));
      writeElementNoTag(output, type, value);
    }
  }

  /**
   * Write a field of arbitrary type, without its tag, to the stream.
   *
   * @param output The output stream.
   * @param type The field's type.
   * @param value  Object representing the field's value.  Must be of the exact
   *               type which would be returned by
   *               {@link Message#getField(Descriptors.FieldDescriptor)} for
   *               this field.
   */
  private static void writeElementNoTag(
      final CodedOutputStream output,
      final WireFormat.FieldType type,
      final Object value) throws IOException {
    switch (type) {
      case DOUBLE  : output.writeDoubleNoTag  ((Double     ) value); break;
      case FLOAT   : output.writeFloatNoTag   ((Float      ) value); break;
      case INT64   : output.writeInt64NoTag   ((Long       ) value); break;
      case UINT64  : output.writeUInt64NoTag  ((Long       ) value); break;
      case INT32   : output.writeInt32NoTag   ((Integer    ) value); break;
      case FIXED64 : output.writeFixed64NoTag ((Long       ) value); break;
      case FIXED32 : output.writeFixed32NoTag ((Integer    ) value); break;
      case BOOL    : output.writeBoolNoTag    ((Boolean    ) value); break;
      case STRING  : output.writeStringNoTag  ((String     ) value); break;
      case GROUP   : output.writeGroupNoTag   ((MessageLite) value); break;
      case MESSAGE : output.writeMessageNoTag ((MessageLite) value); break;
      case BYTES   : output.writeBytesNoTag   ((ByteString ) value); break;
      case UINT32  : output.writeUInt32NoTag  ((Integer    ) value); break;
      case SFIXED32: output.writeSFixed32NoTag((Integer    ) value); break;
      case SFIXED64: output.writeSFixed64NoTag((Long       ) value); break;
      case SINT32  : output.writeSInt32NoTag  ((Integer    ) value); break;
      case SINT64  : output.writeSInt64NoTag  ((Long       ) value); break;

      case ENUM:
        output.writeEnumNoTag(((Internal.EnumLite) value).getNumber());
        break;
    }
  }

  /** Write a single field. */
  public static void writeField(final FieldDescriptorLite<?> descriptor,
                                final Object value,
                                final CodedOutputStream output)
                                throws IOException {
    WireFormat.FieldType type = descriptor.getLiteType();
    int number = descriptor.getNumber();
    if (descriptor.isRepeated()) {
      final List<?> valueList = (List<?>)value;
      if (descriptor.isPacked()) {
        output.writeTag(number, WireFormat.WIRETYPE_LENGTH_DELIMITED);
        // Compute the total data size so the length can be written.
        int dataSize = 0;
        for (final Object element : valueList) {
          dataSize += computeElementSizeNoTag(type, element);
        }
        output.writeRawVarint32(dataSize);
        // Write the data itself, without any tags.
        for (final Object element : valueList) {
          writeElementNoTag(output, type, element);
        }
      } else {
        for (final Object element : valueList) {
          writeElement(output, type, number, element);
        }
      }
    } else {
      writeElement(output, type, number, value);
    }
  }

  /**
   * See {@link Message#getSerializedSize()}.  It's up to the caller to cache
   * the resulting size if desired.
   */
  public int getSerializedSize() {
    int size = 0;
    for (int i = 0; i < fields.getNumArrayEntries(); i++) {
      final Map.Entry<FieldDescriptorType, Object> entry =
          fields.getArrayEntryAt(i);
      size += computeFieldSize(entry.getKey(), entry.getValue());
    }
    for (final Map.Entry<FieldDescriptorType, Object> entry :
         fields.getOverflowEntries()) {
      size += computeFieldSize(entry.getKey(), entry.getValue());
    }
    return size;
  }

  /**
   * Like {@link #getSerializedSize} but uses MessageSet wire format.
   */
  public int getMessageSetSerializedSize() {
    int size = 0;
    for (int i = 0; i < fields.getNumArrayEntries(); i++) {
      size += getMessageSetSerializedSize(fields.getArrayEntryAt(i));
    }
    for (final Map.Entry<FieldDescriptorType, Object> entry :
             fields.getOverflowEntries()) {
      size += getMessageSetSerializedSize(entry);
    }
    return size;
  }

  private int getMessageSetSerializedSize(
      final Map.Entry<FieldDescriptorType, Object> entry) {
    final FieldDescriptorType descriptor = entry.getKey();
    if (descriptor.getLiteJavaType() == WireFormat.JavaType.MESSAGE &&
        !descriptor.isRepeated() && !descriptor.isPacked()) {
      return CodedOutputStream.computeMessageSetExtensionSize(
          entry.getKey().getNumber(), (MessageLite) entry.getValue());
    } else {
      return computeFieldSize(descriptor, entry.getValue());
    }
  }

  /**
   * Compute the number of bytes that would be needed to encode a
   * single tag/value pair of arbitrary type.
   *
   * @param type   The field's type.
   * @param number The field's number.
   * @param value  Object representing the field's value.  Must be of the exact
   *               type which would be returned by
   *               {@link Message#getField(Descriptors.FieldDescriptor)} for
   *               this field.
   */
  private static int computeElementSize(
      final WireFormat.FieldType type,
      final int number, final Object value) {
    int tagSize = CodedOutputStream.computeTagSize(number);
    if (type == WireFormat.FieldType.GROUP) {
      tagSize *= 2;
    }
    return tagSize + computeElementSizeNoTag(type, value);
  }

  /**
   * Compute the number of bytes that would be needed to encode a
   * particular value of arbitrary type, excluding tag.
   *
   * @param type   The field's type.
   * @param value  Object representing the field's value.  Must be of the exact
   *               type which would be returned by
   *               {@link Message#getField(Descriptors.FieldDescriptor)} for
   *               this field.
   */
  private static int computeElementSizeNoTag(
      final WireFormat.FieldType type, final Object value) {
    switch (type) {
      // Note:  Minor violation of 80-char limit rule here because this would
      //   actually be harder to read if we wrapped the lines.
      case DOUBLE  : return CodedOutputStream.computeDoubleSizeNoTag  ((Double     )value);
      case FLOAT   : return CodedOutputStream.computeFloatSizeNoTag   ((Float      )value);
      case INT64   : return CodedOutputStream.computeInt64SizeNoTag   ((Long       )value);
      case UINT64  : return CodedOutputStream.computeUInt64SizeNoTag  ((Long       )value);
      case INT32   : return CodedOutputStream.computeInt32SizeNoTag   ((Integer    )value);
      case FIXED64 : return CodedOutputStream.computeFixed64SizeNoTag ((Long       )value);
      case FIXED32 : return CodedOutputStream.computeFixed32SizeNoTag ((Integer    )value);
      case BOOL    : return CodedOutputStream.computeBoolSizeNoTag    ((Boolean    )value);
      case STRING  : return CodedOutputStream.computeStringSizeNoTag  ((String     )value);
      case GROUP   : return CodedOutputStream.computeGroupSizeNoTag   ((MessageLite)value);
      case MESSAGE : return CodedOutputStream.computeMessageSizeNoTag ((MessageLite)value);
      case BYTES   : return CodedOutputStream.computeBytesSizeNoTag   ((ByteString )value);
      case UINT32  : return CodedOutputStream.computeUInt32SizeNoTag  ((Integer    )value);
      case SFIXED32: return CodedOutputStream.computeSFixed32SizeNoTag((Integer    )value);
      case SFIXED64: return CodedOutputStream.computeSFixed64SizeNoTag((Long       )value);
      case SINT32  : return CodedOutputStream.computeSInt32SizeNoTag  ((Integer    )value);
      case SINT64  : return CodedOutputStream.computeSInt64SizeNoTag  ((Long       )value);

      case ENUM:
        return CodedOutputStream.computeEnumSizeNoTag(
            ((Internal.EnumLite) value).getNumber());
    }

    throw new RuntimeException(
      "There is no way to get here, but the compiler thinks otherwise.");
  }

  /**
   * Compute the number of bytes needed to encode a particular field.
   */
  public static int computeFieldSize(final FieldDescriptorLite<?> descriptor,
                                     final Object value) {
    WireFormat.FieldType type = descriptor.getLiteType();
    int number = descriptor.getNumber();
    if (descriptor.isRepeated()) {
      if (descriptor.isPacked()) {
        int dataSize = 0;
        for (final Object element : (List<?>)value) {
          dataSize += computeElementSizeNoTag(type, element);
        }
        return dataSize +
            CodedOutputStream.computeTagSize(number) +
            CodedOutputStream.computeRawVarint32Size(dataSize);
      } else {
        int size = 0;
        for (final Object element : (List<?>)value) {
          size += computeElementSize(type, number, element);
        }
        return size;
      }
    } else {
      return computeElementSize(type, number, value);
    }
  }
}