js实现蓝牙分包
蓝牙分包实现方法
蓝牙数据传输中，分包处理是常见需求，尤其当数据超过MTU（Maximum Transmission Unit）限制时。以下为JavaScript实现蓝牙分包的核心方法：
数据分块处理
定义分块函数，将大数据分割为适合蓝牙传输的小包：
function chunkData(data, chunkSize) {
const chunks = [];
for (let i = 0; i < data.length; i += chunkSize) {
chunks.push(data.slice(i, i + chunkSize));
}
return chunks;
}发送分包数据
通过蓝牙特征值写入分包数据：
async function sendChunkedData(characteristic, data, chunkSize = 20) {
const chunks = chunkData(data, chunkSize);
for (const chunk of chunks) {
await characteristic.writeValue(chunk);
await new Promise(resolve => setTimeout(resolve, 50)); // 添加延迟防止丢包
}
}接收端数据重组
在接收端实现数据包重组逻辑：
let receivedChunks = [];
let expectedLength = 0;
function handleNotification(event) {
const data = event.target.value;
if (data.byteLength === 4) { // 假设前4字节为数据总长度
expectedLength = new DataView(data).getUint32(0, true);
receivedChunks = [];
} else {
receivedChunks.push(data);
if (receivedChunks.reduce((acc, chunk) => acc + chunk.byteLength, 0) >= expectedLength) {
const fullData = concatenateBuffers(receivedChunks);
processCompleteData(fullData);
}
}
}缓冲区合并工具函数
实现缓冲区合并功能：
function concatenateBuffers(buffers) {
let totalLength = buffers.reduce((acc, buffer) => acc + buffer.byteLength, 0);
let result = new Uint8Array(totalLength);
let offset = 0;
buffers.forEach(buffer => {
result.set(new Uint8Array(buffer), offset);
offset += buffer.byteLength;
});
return result.buffer;
}关键注意事项
- 蓝牙4.0/4.1的典型MTU为23字节，实际可用20字节（ATT头占3字节）
- 蓝牙5.0可协商更大的MTU（最高可达517字节）
- 添加包头信息（如序列号、总包数）可提高传输可靠性
- 实现超时重传机制处理丢包情况
- 在发送大文件前先协商MTU大小
性能优化建议
采用流式传输设计减少内存占用：
class BluetoothStream {
constructor(characteristic) {
this.characteristic = characteristic;
this.buffer = new Uint8Array(0);
}
async write(data) {
const tempBuffer = new Uint8Array(this.buffer.length + data.length);
tempBuffer.set(this.buffer);
tempBuffer.set(data, this.buffer.length);
this.buffer = tempBuffer;
while (this.buffer.length >= 20) {
const chunk = this.buffer.slice(0, 20);
await this.characteristic.writeValue(chunk);
this.buffer = this.buffer.slice(20);
}
}
}
