forked from BigfootDev/flatbuffers
c5835b896c
Also checks for nesting of objects in vector construction. This avoids common errors in FlatBuffer construction. Change-Id: I5507c5d767684e20e94883a92448f05acefba4d6 Tested: on Linux.
546 lines
21 KiB
Java
546 lines
21 KiB
Java
/*
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* Copyright 2014 Google Inc. All rights reserved.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* 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, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.google.flatbuffers;
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import static com.google.flatbuffers.Constants.*;
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import java.util.Arrays;
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import java.nio.ByteBuffer;
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import java.nio.ByteOrder;
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import java.nio.charset.Charset;
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/**
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* Class that helps you build a FlatBuffer. See the section
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* <a href="http://google.github.io/flatbuffers/md__java_usage.html">"Use in Java"</a> in the
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* main FlatBuffers documentation.
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*/
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public class FlatBufferBuilder {
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ByteBuffer bb; // Where we construct the FlatBuffer.
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int space; // Remaining space in the ByteBuffer.
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static final Charset utf8charset = Charset.forName("UTF-8");
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int minalign = 1; // Minimum alignment encountered so far.
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int[] vtable = null; // The vtable for the current table.
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int vtable_in_use = 0; // The amount of fields we're actually using.
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boolean nested = false; // Whether we are currently serializing a table.
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boolean finished = false; // Whether the buffer is finished.
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int object_start; // Starting offset of the current struct/table.
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int[] vtables = new int[16]; // List of offsets of all vtables.
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int num_vtables = 0; // Number of entries in `vtables` in use.
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int vector_num_elems = 0; // For the current vector being built.
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boolean force_defaults = false; // False omits default values from the serialized data
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/**
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* Start with a buffer of size {@code initial_size}, then grow as required.
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*
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* @param initial_size The initial size of the internal buffer to use
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*/
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public FlatBufferBuilder(int initial_size) {
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if (initial_size <= 0) initial_size = 1;
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space = initial_size;
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bb = newByteBuffer(initial_size);
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}
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/**
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* Start with a buffer of 1KiB, then grow as required.
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*/
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public FlatBufferBuilder() {
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this(1024);
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}
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/**
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* Alternative constructor allowing reuse of {@link ByteBuffer}s. The builder
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* can still grow the buffer as necessary. User classes should make sure
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* to call {@link #dataBuffer()} to obtain the resulting encoded message
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*
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* @param existing_bb The byte buffer to reuse
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*/
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public FlatBufferBuilder(ByteBuffer existing_bb) {
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init(existing_bb);
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}
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/**
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* Alternative initializer that allows reusing this object on an existing
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* ByteBuffer. This method resets the builder's internal state, but keeps
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* objects that have been allocated for temporary storage.
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*
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* @param existing_bb The byte buffer to reuse
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* @return this
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*/
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public FlatBufferBuilder init(ByteBuffer existing_bb){
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bb = existing_bb;
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bb.clear();
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bb.order(ByteOrder.LITTLE_ENDIAN);
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minalign = 1;
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space = bb.capacity();
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vtable_in_use = 0;
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nested = false;
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finished = false;
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object_start = 0;
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num_vtables = 0;
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vector_num_elems = 0;
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return this;
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}
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static ByteBuffer newByteBuffer(int capacity) {
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ByteBuffer newbb = ByteBuffer.allocate(capacity);
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newbb.order(ByteOrder.LITTLE_ENDIAN);
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return newbb;
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}
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/**
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* Doubles the size of the backing {link ByteBuffer} and copies the old data towards the
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* end of the new buffer (since we build the buffer backwards).
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*
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* @param bb The current buffer with the existing data
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* @return A new byte buffer with the old data copied copied to it. The data is
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* located at the end of the buffer.
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*/
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static ByteBuffer growByteBuffer(ByteBuffer bb) {
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int old_buf_size = bb.capacity();
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if ((old_buf_size & 0xC0000000) != 0) // Ensure we don't grow beyond what fits in an int.
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throw new AssertionError("FlatBuffers: cannot grow buffer beyond 2 gigabytes.");
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int new_buf_size = old_buf_size << 1;
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bb.position(0);
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ByteBuffer nbb = newByteBuffer(new_buf_size);
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nbb.position(new_buf_size - old_buf_size);
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nbb.put(bb);
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return nbb;
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}
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/**
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* Offset relative to the end of the buffer.
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*
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* @return Offset relative to the end of the buffer.
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*/
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public int offset() {
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return bb.capacity() - space;
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}
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/**
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* Add zero valued bytes to prepare a new entry to be added
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*
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* @param byte_size Number of bytes to add.
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*/
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public void pad(int byte_size) {
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for (int i = 0; i < byte_size; i++) bb.put(--space, (byte)0);
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}
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/**
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* Prepare to write an element of {@code size} after {@code additional_bytes}
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* have been written, e.g. if you write a string, you need to align such
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* the int length field is aligned to {@link com.google.flatbuffers.Constants#SIZEOF_INT}, and
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* the string data follows it directly. If all you need to do is alignment, {@code additional_bytes}
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* will be 0.
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*
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* @param size This is the of the new element to write
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* @param additional_bytes The padding size
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*/
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public void prep(int size, int additional_bytes) {
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// Track the biggest thing we've ever aligned to.
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if (size > minalign) minalign = size;
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// Find the amount of alignment needed such that `size` is properly
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// aligned after `additional_bytes`
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int align_size = ((~(bb.capacity() - space + additional_bytes)) + 1) & (size - 1);
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// Reallocate the buffer if needed.
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while (space < align_size + size + additional_bytes) {
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int old_buf_size = bb.capacity();
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bb = growByteBuffer(bb);
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space += bb.capacity() - old_buf_size;
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}
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pad(align_size);
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}
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// Add a scalar to the buffer, backwards from the current location.
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// Doesn't align nor check for space.
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public void putBoolean(boolean x) { bb.put (space -= 1, (byte)(x ? 1 : 0)); }
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public void putByte (byte x) { bb.put (space -= 1, x); }
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public void putShort (short x) { bb.putShort (space -= 2, x); }
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public void putInt (int x) { bb.putInt (space -= 4, x); }
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public void putLong (long x) { bb.putLong (space -= 8, x); }
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public void putFloat (float x) { bb.putFloat (space -= 4, x); }
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public void putDouble (double x) { bb.putDouble(space -= 8, x); }
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// Adds a scalar to the buffer, properly aligned, and the buffer grown
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// if needed.
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public void addBoolean(boolean x) { prep(1, 0); putBoolean(x); }
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public void addByte (byte x) { prep(1, 0); putByte (x); }
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public void addShort (short x) { prep(2, 0); putShort (x); }
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public void addInt (int x) { prep(4, 0); putInt (x); }
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public void addLong (long x) { prep(8, 0); putLong (x); }
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public void addFloat (float x) { prep(4, 0); putFloat (x); }
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public void addDouble (double x) { prep(8, 0); putDouble (x); }
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/**
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* Adds on offset, relative to where it will be written.
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*
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* @param off The offset to add
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*/
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public void addOffset(int off) {
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prep(SIZEOF_INT, 0); // Ensure alignment is already done.
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assert off <= offset();
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off = offset() - off + SIZEOF_INT;
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putInt(off);
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}
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/**
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* Start a new array/vector of objects. Users usually will not call
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* this directly. The {@code FlatBuffers} compiler will create a start/end
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* method for vector types in generated code.
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* <p>
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* The expected sequence of calls is:
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* <ol>
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* <li>Start the array using this method.</li>
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* <li>Call {@link #addOffset(int)} {@code num_elems} number of times to set
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* the offset of each element in the array.</li>
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* <li>Call {@link #endVector()} to retrieve the offset of the array.</li>
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* </ol>
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* <p>
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* For example, to create an array of strings, do:
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* <pre>{@code
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* // Need 10 strings
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* FlatBufferBuilder builder = new FlatBufferBuilder(existingBuffer);
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* int[] offsets = new int[10];
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*
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* for (int i = 0; i < 10; i++) {
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* offsets[i] = fbb.createString(" " + i);
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* }
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*
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* // Have the strings in the buffer, but don't have a vector.
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* // Add a vector that references the newly created strings:
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* builder.startVector(4, offsets.length, 4);
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*
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* // Add each string to the newly created vector
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* // The strings are added in reverse order since the buffer
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* // is filled in back to front
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* for (int i = offsets.length - 1; i >= 0; i--) {
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* builder.addOffset(offsets[i]);
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* }
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*
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* // Finish off the vector
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* int offsetOfTheVector = fbb.endVector();
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* }</pre>
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*
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* @param elem_size The size of each element in the array
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* @param num_elems The number of elements in the array
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* @param alignment The alignment of the array
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*/
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public void startVector(int elem_size, int num_elems, int alignment) {
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notNested();
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vector_num_elems = num_elems;
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prep(SIZEOF_INT, elem_size * num_elems);
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prep(alignment, elem_size * num_elems); // Just in case alignment > int.
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nested = true;
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}
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/**
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* Finish off the creation of an array and all its elements. The array
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* must be created with {@link #startVector(int, int, int)}.
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*
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* @return The offset at which the newly created array starts.
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* @see #startVector(int, int, int)
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*/
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public int endVector() {
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if (!nested)
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throw new AssertionError("FlatBuffers: endVector called without startVector");
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nested = false;
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putInt(vector_num_elems);
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return offset();
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}
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/**
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* Encode the string {@code s} in the buffer using UTF-8.
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*
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* @param s The string to encode
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* @return The offset in the buffer where the encoded string starts
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*/
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public int createString(String s) {
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byte[] utf8 = s.getBytes(utf8charset);
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addByte((byte)0);
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startVector(1, utf8.length, 1);
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bb.position(space -= utf8.length);
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bb.put(utf8, 0, utf8.length);
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return endVector();
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}
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/**
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* Encode the string {@code s} in the buffer using UTF-8.
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*
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* @param s An already encoded UTF-8 string
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* @return The offset in the buffer where the encoded string starts
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*/
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public int createString(ByteBuffer s) {
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int length = s.remaining();
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addByte((byte)0);
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startVector(1, length, 1);
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bb.position(space -= length);
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bb.put(s);
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return endVector();
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}
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/**
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* Should not be accessing the final buffer before it is finished.
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*/
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public void finished() {
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if (!finished)
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throw new AssertionError(
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"FlatBuffers: you can only access the serialized buffer after it has been" +
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" finished by FlatBufferBuilder.finish().");
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}
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/**
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* Should not be creating any other object, string or vector
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* while an object is being constructed
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*/
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public void notNested() {
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if (nested)
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throw new AssertionError("FlatBuffers: object serialization must not be nested.");
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}
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/**
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* Structures are always stored inline, they need to be created right
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* where they're used. You'll get this assertion failure if you
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* created it elsewhere.
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*
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* @param obj The offset of the created object
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*/
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public void Nested(int obj) {
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if (obj != offset())
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throw new AssertionError("FlatBuffers: struct must be serialized inline.");
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}
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/**
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* Start encoding a new object in the buffer. Users will not usually need to
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* call this directly. The {@code FlatBuffers} compiler will generate helper methods
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* that call this method internally.
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* <p>
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* For example, using the "Monster" code found on the
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* <a href="http://google.github.io/flatbuffers/md__java_usage.html">landing page</a>. An
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* object of type {@code Monster} can be created using the following code:
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*
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* <pre>{@code
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* int testArrayOfString = Monster.createTestarrayofstringVector(fbb, new int[] {
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* fbb.createString("test1"),
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* fbb.createString("test2")
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* });
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*
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* Monster.startMonster(fbb);
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* Monster.addPos(fbb, Vec3.createVec3(fbb, 1.0f, 2.0f, 3.0f, 3.0,
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* Color.Green, (short)5, (byte)6));
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* Monster.addHp(fbb, (short)80);
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* Monster.addName(fbb, str);
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* Monster.addInventory(fbb, inv);
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* Monster.addTestType(fbb, (byte)Any.Monster);
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* Monster.addTest(fbb, mon2);
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* Monster.addTest4(fbb, test4);
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* Monster.addTestarrayofstring(fbb, testArrayOfString);
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* int mon = Monster.endMonster(fbb);
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* }</pre>
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* <p>
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* Here:
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* <ul>
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* <li>The call to {@code Monster#startMonster(FlatBufferBuilder)} will call this
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* method with the right number of fields set.</li>
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* <li>{@code Monster#endMonster(FlatBufferBuilder)} will ensure {@link #endObject()} is called.</li>
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* </ul>
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* <p>
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* It's not recommended to call this method directly. If it's called manually, you must ensure
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* to audit all calls to it whenever fields are added or removed from your schema. This is
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* automatically done by the code generated by the {@code FlatBuffers} compiler.
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*
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* @param numfields The number of fields found in this object.
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*/
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public void startObject(int numfields) {
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notNested();
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if (vtable == null || vtable.length < numfields) vtable = new int[numfields];
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vtable_in_use = numfields;
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Arrays.fill(vtable, 0, vtable_in_use, 0);
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nested = true;
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object_start = offset();
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}
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// Add a scalar to a table at `o` into its vtable, with value `x` and default `d`
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public void addBoolean(int o, boolean x, boolean d) { if(force_defaults || x != d) { addBoolean(x); slot(o); } }
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public void addByte (int o, byte x, int d) { if(force_defaults || x != d) { addByte (x); slot(o); } }
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public void addShort (int o, short x, int d) { if(force_defaults || x != d) { addShort (x); slot(o); } }
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public void addInt (int o, int x, int d) { if(force_defaults || x != d) { addInt (x); slot(o); } }
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public void addLong (int o, long x, long d) { if(force_defaults || x != d) { addLong (x); slot(o); } }
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public void addFloat (int o, float x, double d) { if(force_defaults || x != d) { addFloat (x); slot(o); } }
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public void addDouble (int o, double x, double d) { if(force_defaults || x != d) { addDouble (x); slot(o); } }
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public void addOffset (int o, int x, int d) { if(force_defaults || x != d) { addOffset (x); slot(o); } }
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// Structs are stored inline, so nothing additional is being added. `d` is always 0.
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public void addStruct(int voffset, int x, int d) {
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if(x != d) {
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Nested(x);
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slot(voffset);
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}
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}
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// Set the current vtable at `voffset` to the current location in the buffer.
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public void slot(int voffset) {
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vtable[voffset] = offset();
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}
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/**
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* Finish off writing the object that is under construction.
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*
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* @return The offset to the object inside {@link #dataBuffer()}
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* @see #startObject(int)
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*/
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public int endObject() {
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if (vtable == null || !nested)
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throw new AssertionError("FlatBuffers: endObject called without startObject");
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addInt(0);
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int vtableloc = offset();
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// Write out the current vtable.
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for (int i = vtable_in_use - 1; i >= 0 ; i--) {
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// Offset relative to the start of the table.
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short off = (short)(vtable[i] != 0 ? vtableloc - vtable[i] : 0);
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addShort(off);
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}
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final int standard_fields = 2; // The fields below:
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addShort((short)(vtableloc - object_start));
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addShort((short)((vtable_in_use + standard_fields) * SIZEOF_SHORT));
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// Search for an existing vtable that matches the current one.
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int existing_vtable = 0;
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outer_loop:
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for (int i = 0; i < num_vtables; i++) {
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int vt1 = bb.capacity() - vtables[i];
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int vt2 = space;
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short len = bb.getShort(vt1);
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if (len == bb.getShort(vt2)) {
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for (int j = SIZEOF_SHORT; j < len; j += SIZEOF_SHORT) {
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if (bb.getShort(vt1 + j) != bb.getShort(vt2 + j)) {
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continue outer_loop;
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}
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}
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existing_vtable = vtables[i];
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break outer_loop;
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}
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}
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if (existing_vtable != 0) {
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// Found a match:
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// Remove the current vtable.
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space = bb.capacity() - vtableloc;
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// Point table to existing vtable.
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bb.putInt(space, existing_vtable - vtableloc);
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} else {
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// No match:
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// Add the location of the current vtable to the list of vtables.
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if (num_vtables == vtables.length) vtables = Arrays.copyOf(vtables, num_vtables * 2);
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vtables[num_vtables++] = offset();
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// Point table to current vtable.
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bb.putInt(bb.capacity() - vtableloc, offset() - vtableloc);
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}
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nested = false;
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return vtableloc;
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}
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// This checks a required field has been set in a given table that has
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// just been constructed.
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public void required(int table, int field) {
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int table_start = bb.capacity() - table;
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int vtable_start = table_start - bb.getInt(table_start);
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boolean ok = bb.getShort(vtable_start + field) != 0;
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// If this fails, the caller will show what field needs to be set.
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if (!ok)
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throw new AssertionError("FlatBuffers: field " + field + " must be set");
|
|
}
|
|
|
|
public void finish(int root_table) {
|
|
prep(minalign, SIZEOF_INT);
|
|
addOffset(root_table);
|
|
bb.position(space);
|
|
finished = true;
|
|
}
|
|
|
|
public void finish(int root_table, String file_identifier) {
|
|
prep(minalign, SIZEOF_INT + FILE_IDENTIFIER_LENGTH);
|
|
if (file_identifier.length() != FILE_IDENTIFIER_LENGTH)
|
|
throw new AssertionError("FlatBuffers: file identifier must be length " +
|
|
FILE_IDENTIFIER_LENGTH);
|
|
for (int i = FILE_IDENTIFIER_LENGTH - 1; i >= 0; i--) {
|
|
addByte((byte)file_identifier.charAt(i));
|
|
}
|
|
finish(root_table);
|
|
}
|
|
|
|
/**
|
|
* In order to save space, fields that are set to their default value
|
|
* don't get serialized into the buffer. Forcing defaults provides a
|
|
* way to manually disable this optimization.
|
|
*
|
|
* @param forceDefaults true always serializes default values
|
|
* @return this
|
|
*/
|
|
public FlatBufferBuilder forceDefaults(boolean forceDefaults){
|
|
this.force_defaults = forceDefaults;
|
|
return this;
|
|
}
|
|
|
|
// Get the ByteBuffer representing the FlatBuffer. Only call this after you've
|
|
// called finish(). The actual data starts at the ByteBuffer's current position,
|
|
// not necessarily at 0.
|
|
public ByteBuffer dataBuffer() {
|
|
finished();
|
|
return bb;
|
|
}
|
|
|
|
/**
|
|
* The FlatBuffer data doesn't start at offset 0 in the {@link ByteBuffer}, but
|
|
* now the {@code ByteBuffer}'s position is set to that location upon {@link #finish(int)}.
|
|
*
|
|
* @return The {@link ByteBuffer#position() position} the data starts in {@link #dataBuffer()}
|
|
* @deprecated This method should not be needed anymore, but is left
|
|
* here for the moment to document this API change. It will be removed in the future.
|
|
*/
|
|
@Deprecated
|
|
private int dataStart() {
|
|
finished();
|
|
return space;
|
|
}
|
|
|
|
/**
|
|
* Utility function for copying a byte array from {@code start} to
|
|
* {@code start} + {@code length}
|
|
*
|
|
* @param start Start copying at this offset
|
|
* @param length How many bytes to copy
|
|
* @return A range copy of the {@link #dataBuffer() data buffer}
|
|
* @throws IndexOutOfBoundsException If the range of bytes is ouf of bound
|
|
*/
|
|
public byte[] sizedByteArray(int start, int length){
|
|
finished();
|
|
byte[] array = new byte[length];
|
|
bb.position(start);
|
|
bb.get(array);
|
|
return array;
|
|
}
|
|
|
|
/**
|
|
* Utility function for copying a byte array that starts at 0.
|
|
*
|
|
* @return A full copy of the {@link #dataBuffer() data buffer}
|
|
*/
|
|
public byte[] sizedByteArray() {
|
|
return sizedByteArray(space, bb.capacity() - space);
|
|
}
|
|
}
|