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Avoid unnecessary heap allocation when parsing frame headers. #107

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Apr 18, 2019
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Avoid unnecessary heap allocation when parsing frame headers. #107

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18 changes: 9 additions & 9 deletions Sources/NIOHTTP2/HTTP2FrameParser.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -1159,17 +1159,17 @@ fileprivate struct FrameHeader {

fileprivate extension ByteBuffer {
mutating func readFrameHeader() -> FrameHeader? {
guard self.readableBytes >= 9 else {
return nil
let saveSelf = self
guard let lenHigh = self.readInteger(as: UInt16.self),
let lenLow = self.readInteger(as: UInt8.self),
let type = self.readInteger(as: UInt8.self),
let flags = self.readInteger(as: UInt8.self),
let rawStreamID = self.readInteger(as: UInt32.self) else {
self = saveSelf
return nil
}

let lenBytes: [UInt8] = self.readBytes(length: 3)!
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I think you should keep the old code but replace

let lenBytes: [UInt8] = self.readBytes(length: 3)!

with

let lenHigh = self.readInteger(as: UInt16.self)
let lenLow = self.readInteger(as: UInt8.self)
let len = UInt32(lenHigh) << 16 | UInt32(lenLow)

let len = Int(lenBytes[0]) << 16 | Int(lenBytes[1]) << 8 | Int(lenBytes[2])
let type: UInt8 = self.readInteger()!
let flags: UInt8 = self.readInteger()!
let rawStreamID: UInt32 = self.readInteger()!

return FrameHeader(length: len, type: type, flags: FrameFlags(rawValue: flags), rawStreamID: rawStreamID)
return FrameHeader(length: Int(lenHigh) << 8 | Int(lenLow), type: type, flags: FrameFlags(rawValue: flags), rawStreamID: rawStreamID)
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aren't we overwriting 8 bits here?

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No: the UInt16 is converted to an Int and shifted left 8 bits. Then the UInt8 is converted to an Int and or'ed with it, fitting into the empty space from the previous left shift.

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@Lukasa oops, thanks, brain fart :D

}

mutating func writePayloadSize(_ size: Int, at location: Int) {
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