129 lines
4.5 KiB
Swift
129 lines
4.5 KiB
Swift
import Foundation
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/// 火山引擎大模型流式 ASR 二进制帧编解码。
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///
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/// 帧结构通常为：4 字节 header + 可选 sequence + 4 字节大端 payload size + payload。
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/// 为了避免运行时依赖 gzip 实现，这里显式使用 no compression；官方协议允许客户端选择
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/// no compression，服务端会沿用客户端声明的压缩方式。
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enum VolcengineFrame {
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enum MessageType: UInt8 {
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case fullClientRequest = 0b0001
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case audioOnlyRequest = 0b0010
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case fullServerResponse = 0b1001
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case errorMessage = 0b1111
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}
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enum Flags: UInt8 {
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case none = 0b0000
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case positiveSequence = 0b0001
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case lastPacket = 0b0010
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case negativeSequence = 0b0011
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}
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enum Serialization: UInt8 {
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case none = 0b0000
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case json = 0b0001
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}
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enum CompressionMethod: UInt8 {
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case none = 0b0000
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}
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static func build(
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messageType: MessageType,
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flags: Flags,
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serialization: Serialization,
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payload: Data,
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sequence: Int32? = nil
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) -> Data {
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var frame = Data()
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frame.append(0x11)
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frame.append((messageType.rawValue << 4) | flags.rawValue)
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frame.append((serialization.rawValue << 4) | CompressionMethod.none.rawValue)
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frame.append(0x00)
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// positiveSequence / negativeSequence 必须带 4 字节大端 seq；其它 flag 不带。
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if let sequence, flags == .positiveSequence || flags == .negativeSequence {
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var seq = UInt32(bitPattern: sequence).bigEndian
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withUnsafeBytes(of: &seq) { frame.append(contentsOf: $0) }
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}
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var size = UInt32(payload.count).bigEndian
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withUnsafeBytes(of: &size) { frame.append(contentsOf: $0) }
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frame.append(payload)
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return frame
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}
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static func parse(_ data: Data) -> ParsedFrame? {
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guard data.count >= 8 else { return nil }
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let headerSize = Int(data[0] & 0x0F) * 4
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guard headerSize >= 4, data.count >= headerSize + 4 else { return nil }
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let messageTypeRaw = (data[1] >> 4) & 0x0F
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let messageType = MessageType(rawValue: messageTypeRaw)
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let flagsRaw = data[1] & 0x0F
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let compression = data[2] & 0x0F
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guard compression == CompressionMethod.none.rawValue else { return nil }
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var offset = headerSize
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var sequence: Int32?
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if hasSequence(flagsRaw) {
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guard let value = readInt32(data, at: offset) else { return nil }
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sequence = value
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offset += 4
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}
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if messageType == .errorMessage {
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guard let code = readUInt32(data, at: offset),
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let messageSize = readUInt32(data, at: offset + 4) else {
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return nil
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}
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offset += 8
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guard data.count >= offset + Int(messageSize) else { return nil }
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let payload = data.subdata(in: offset..<(offset + Int(messageSize)))
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return ParsedFrame(messageType: messageType, flags: flagsRaw, sequence: sequence, errorCode: code, payload: payload)
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}
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guard let payloadSize = readUInt32(data, at: offset) else { return nil }
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offset += 4
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guard data.count >= offset + Int(payloadSize) else { return nil }
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let payload = data.subdata(in: offset..<(offset + Int(payloadSize)))
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return ParsedFrame(messageType: messageType, flags: flagsRaw, sequence: sequence, errorCode: nil, payload: payload)
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}
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struct ParsedFrame {
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let messageType: MessageType?
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let flags: UInt8
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let sequence: Int32?
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let errorCode: UInt32?
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let payload: Data
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var isFinal: Bool {
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flags == Flags.lastPacket.rawValue
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|| flags == Flags.negativeSequence.rawValue
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|| (sequence ?? 0) < 0
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}
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}
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private static func hasSequence(_ flags: UInt8) -> Bool {
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flags == Flags.positiveSequence.rawValue || flags == Flags.negativeSequence.rawValue
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}
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private static func readUInt32(_ data: Data, at offset: Int) -> UInt32? {
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guard offset >= 0, data.count >= offset + 4 else { return nil }
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var value: UInt32 = 0
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for byte in data[offset..<(offset + 4)] {
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value = (value << 8) | UInt32(byte)
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}
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return value
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}
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private static func readInt32(_ data: Data, at offset: Int) -> Int32? {
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guard let unsigned = readUInt32(data, at: offset) else { return nil }
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return Int32(bitPattern: unsigned)
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}
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}
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