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builder.lua
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422 lines (345 loc) · 11.1 KB
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local N = require("flatbuffers.numTypes")
local ba = require("flatbuffers.binaryarray")
local compat = require("flatbuffers.compat")
local string_unpack = compat.string_unpack
local m = {}
local mt = {}
-- get locals for faster access
local VOffsetT = N.VOffsetT
local UOffsetT = N.UOffsetT
local SOffsetT = N.SOffsetT
local Bool = N.Bool
local Uint8 = N.Uint8
local Uint16 = N.Uint16
local Uint32 = N.Uint32
local Uint64 = N.Uint64
local Int8 = N.Int8
local Int16 = N.Int16
local Int32 = N.Int32
local Int64 = N.Int64
local Float32 = N.Float32
local Float64 = N.Float64
local MAX_BUFFER_SIZE = 0x80000000 -- 2 GB
local VtableMetadataFields = 2
local getAlignSize = compat.GetAlignSize
local function vtableEqual(a, objectStart, b)
UOffsetT:EnforceNumber(objectStart)
if (#a * 2) ~= #b then
return false
end
for i, elem in ipairs(a) do
local x = string_unpack(VOffsetT.packFmt, b, 1 + (i - 1) * 2)
if x ~= 0 or elem ~= 0 then
local y = objectStart - elem
if x ~= y then
return false
end
end
end
return true
end
function m.New(initialSize)
assert(0 <= initialSize and initialSize < MAX_BUFFER_SIZE)
local o =
{
finished = false,
bytes = ba.New(initialSize),
nested = false,
head = initialSize,
minalign = 1,
vtables = {}
}
setmetatable(o, {__index = mt})
return o
end
-- Clears the builder and resets the state. It does not actually clear the backing binary array, it just reuses it as
-- needed. This is a performant way to use the builder for multiple constructions without the overhead of multiple
-- builder allocations.
function mt:Clear()
self.finished = false
self.nested = false
self.minalign = 1
self.currentVTable = nil
self.objectEnd = nil
self.head = self.bytes.size -- place the head at the end of the binary array
-- clear vtables instead of making a new table
local vtable = self.vtables
local vtableCount = #vtable
for i=1,vtableCount do vtable[i] = nil end
end
function mt:Output(full)
assert(self.finished, "Builder Not Finished")
if full then
return self.bytes:Slice()
else
return self.bytes:Slice(self.head)
end
end
function mt:StartObject(numFields)
assert(not self.nested)
local vtable = {}
for _=1,numFields do
table.insert(vtable, 0)
end
self.currentVTable = vtable
self.objectEnd = self:Offset()
self.nested = true
end
function mt:WriteVtable()
self:PrependSOffsetTRelative(0)
local objectOffset = self:Offset()
local exisitingVTable
local i = #self.vtables
while i >= 1 do
if self.vtables[i] == 0 then
table.remove(self.vtables,i)
end
i = i - 1
end
i = #self.vtables
while i >= 1 do
local vt2Offset = self.vtables[i]
local vt2Start = self.bytes.size - vt2Offset
local vt2lenstr = self.bytes:Slice(vt2Start, vt2Start+1)
local vt2Len = string_unpack(VOffsetT.packFmt, vt2lenstr, 1)
local metadata = VtableMetadataFields * 2
local vt2End = vt2Start + vt2Len
local vt2 = self.bytes:Slice(vt2Start+metadata,vt2End)
if vtableEqual(self.currentVTable, objectOffset, vt2) then
exisitingVTable = vt2Offset
break
end
i = i - 1
end
if not exisitingVTable then
i = #self.currentVTable
while i >= 1 do
local off = 0
local a = self.currentVTable[i]
if a and a ~= 0 then
off = objectOffset - a
end
self:PrependVOffsetT(off)
i = i - 1
end
local objectSize = objectOffset - self.objectEnd
self:PrependVOffsetT(objectSize)
local vBytes = #self.currentVTable + VtableMetadataFields
vBytes = vBytes * 2
self:PrependVOffsetT(vBytes)
local objectStart = self.bytes.size - objectOffset
self.bytes:Set(SOffsetT:Pack(self:Offset() - objectOffset),objectStart)
table.insert(self.vtables, self:Offset())
else
local objectStart = self.bytes.size - objectOffset
self.head = objectStart
self.bytes:Set(SOffsetT:Pack(exisitingVTable - objectOffset),self.head)
end
self.currentVTable = nil
return objectOffset
end
function mt:EndObject()
assert(self.nested)
self.nested = false
return self:WriteVtable()
end
local function growByteBuffer(self, desiredSize)
local s = self.bytes.size
assert(s < MAX_BUFFER_SIZE, "Flat Buffers cannot grow buffer beyond 2 gigabytes")
local newsize = s
repeat
newsize = math.min(newsize * 2, MAX_BUFFER_SIZE)
if newsize == 0 then newsize = 1 end
until newsize > desiredSize
self.bytes:Grow(newsize)
end
function mt:Head()
return self.head
end
function mt:Offset()
return self.bytes.size - self.head
end
function mt:Pad(n)
if n > 0 then
-- pads are 8-bit, so skip the bytewidth lookup
local h = self.head - n -- UInt8
self.head = h
self.bytes:Pad(n, h)
end
end
function mt:Prep(size, additionalBytes)
if size > self.minalign then
self.minalign = size
end
local h = self.head
local k = self.bytes.size - h + additionalBytes
local alignsize = getAlignSize(k, size)
local desiredSize = alignsize + size + additionalBytes
while self.head < desiredSize do
local oldBufSize = self.bytes.size
growByteBuffer(self, desiredSize)
local updatedHead = self.head + self.bytes.size - oldBufSize
self.head = updatedHead
end
self:Pad(alignsize)
end
function mt:PrependSOffsetTRelative(off)
self:Prep(4, 0)
assert(off <= self:Offset(), "Offset arithmetic error")
local off2 = self:Offset() - off + 4
self:Place(off2, SOffsetT)
end
function mt:PrependUOffsetTRelative(off)
self:Prep(4, 0)
local soffset = self:Offset()
if off <= soffset then
local off2 = soffset - off + 4
self:Place(off2, UOffsetT)
else
error("Offset arithmetic error")
end
end
function mt:StartVector(elemSize, numElements, alignment)
assert(not self.nested)
self.nested = true
local elementSize = elemSize * numElements
self:Prep(4, elementSize) -- Uint32 length
self:Prep(alignment, elementSize)
return self:Offset()
end
function mt:EndVector(vectorNumElements)
assert(self.nested)
self.nested = false
self:Place(vectorNumElements, UOffsetT)
return self:Offset()
end
function mt:CreateString(s)
assert(not self.nested)
self.nested = true
assert(type(s) == "string")
self:Prep(4, #s + 1)
self:Place(0, Uint8)
local l = #s
self.head = self.head - l
self.bytes:Set(s, self.head, self.head + l)
return self:EndVector(l)
end
function mt:CreateByteVector(x)
assert(not self.nested)
self.nested = true
local l = #x
self:Prep(4, l)
self.head = self.head - l
self.bytes:Set(x, self.head, self.head + l)
return self:EndVector(l)
end
function mt:Slot(slotnum)
assert(self.nested)
-- n.b. slot number is 0-based
self.currentVTable[slotnum + 1] = self:Offset()
end
local function finish(self, rootTable, sizePrefix, fileIdentifier)
UOffsetT:EnforceNumber(rootTable)
local hasFid = fileIdentifier ~= nil
if hasFid then
assert(#fileIdentifier == 4, "File identifier must be exactly 4 bytes")
end
local fid_byte_count = (hasFid and 4 or 0)
-- alignment:
-- root offset (4)
-- optional file id (4)
-- optional size prefix (4)
self:Prep(
self.minalign,
(sizePrefix and 4 or 0) +
4 +
fid_byte_count
)
-- root offset (points past file identifier if present)
self:PrependUOffsetTRelative(rootTable + fid_byte_count)
-- file identifier
if hasFid then
for i = 4, 1, -1 do
self:PrependByte(string.byte(fileIdentifier, i))
end
end
-- size prefix
if sizePrefix then
local size = self.bytes.size - self.head
Int32:EnforceNumber(size)
self:PrependInt32(size)
end
self.finished = true
return self.head
end
function mt:Finish(rootTable)
return finish(self, rootTable, false, nil)
end
function mt:FinishSizePrefixed(rootTable)
return finish(self, rootTable, true, nil)
end
function mt:FinishWithIdentifier(rootTable, fileIdentifier)
return finish(self, rootTable, false, fileIdentifier)
end
function mt:FinishSizePrefixedWithIdentifier(rootTable, fileIdentifier)
return finish(self, rootTable, true, fileIdentifier)
end
function mt:Prepend(flags, off)
self:Prep(flags.bytewidth, 0)
self:Place(off, flags)
end
function mt:PrependSlot(flags, o, x, d)
flags:EnforceNumbers(x,d)
-- flags:EnforceNumber(x)
-- flags:EnforceNumber(d)
if x ~= d then
self:Prepend(flags, x)
self:Slot(o)
end
end
function mt:PrependBoolSlot(...) self:PrependSlot(Bool, ...) end
function mt:PrependByteSlot(...) self:PrependSlot(Uint8, ...) end
function mt:PrependUint8Slot(...) self:PrependSlot(Uint8, ...) end
function mt:PrependUint16Slot(...) self:PrependSlot(Uint16, ...) end
function mt:PrependUint32Slot(...) self:PrependSlot(Uint32, ...) end
function mt:PrependUint64Slot(...) self:PrependSlot(Uint64, ...) end
function mt:PrependInt8Slot(...) self:PrependSlot(Int8, ...) end
function mt:PrependInt16Slot(...) self:PrependSlot(Int16, ...) end
function mt:PrependInt32Slot(...) self:PrependSlot(Int32, ...) end
function mt:PrependInt64Slot(...) self:PrependSlot(Int64, ...) end
function mt:PrependFloat32Slot(...) self:PrependSlot(Float32, ...) end
function mt:PrependFloat64Slot(...) self:PrependSlot(Float64, ...) end
function mt:PrependUOffsetTRelativeSlot(o,x,d)
if x~=d then
self:PrependUOffsetTRelative(x)
self:Slot(o)
end
end
function mt:PrependStructSlot(v,x,d)
UOffsetT:EnforceNumber(d)
if x~=d then
UOffsetT:EnforceNumber(x)
assert(x == self:Offset(), "Tried to write a Struct at an Offset that is different from the current Offset of the Builder.")
self:Slot(v)
end
end
function mt:PrependBool(x) self:Prepend(Bool, x) end
function mt:PrependByte(x) self:Prepend(Uint8, x) end
function mt:PrependUint8(x) self:Prepend(Uint8, x) end
function mt:PrependUint16(x) self:Prepend(Uint16, x) end
function mt:PrependUint32(x) self:Prepend(Uint32, x) end
function mt:PrependUint64(x) self:Prepend(Uint64, x) end
function mt:PrependInt8(x) self:Prepend(Int8, x) end
function mt:PrependInt16(x) self:Prepend(Int16, x) end
function mt:PrependInt32(x) self:Prepend(Int32, x) end
function mt:PrependInt64(x) self:Prepend(Int64, x) end
function mt:PrependFloat32(x) self:Prepend(Float32, x) end
function mt:PrependFloat64(x) self:Prepend(Float64, x) end
function mt:PrependVOffsetT(x) self:Prepend(VOffsetT, x) end
function mt:Place(x, flags)
local d = flags:EnforceNumberAndPack(x)
local h = self.head - flags.bytewidth
self.head = h
self.bytes:Set(d, h)
end
return m