如下面发布的代码所示，对于前端部分，我调用了webservice getTIFFForSubsetAsNIRRange/，我想发送body中显示的内容，webservice被成功调用，但我无法获得body发布到它。
如下所示，在后端，我使用了req.data，但它返回undefined
请让我知道如何访问发送到后端的内容

尝试解决

let data = req.body;
res.send('Data Received: ' + JSON.stringify(data));

字符串
但它会导致一个错误：
UnhandledPromiseRejection警告：错误[ERR_HTTP_HEADERS_SENT]：将标头发送到客户端后无法设置标头

前端：

drawEvt.on('drawend', e => {
    let feature = e.feature;
    let geom = feature.getGeometry();
    let wktformat = new WKT();
    let geoJSONformat = new GeoJSON();
    let wktRepresenation = wktformat.writeGeometry(geom);
    let geoJSONRepresentation = geoJSONformat.writeGeometry(geom);
    this.wktRepresenation = wktRepresenation;
    this.geoJSONRepresentation = geoJSONRepresentation;
    console.info(debugTag, 'drawEvt.on' + 'wktRepresenation:', this.wktRepresenation);
    console.info(debugTag, 'drawEvt.on' + 'geoJSONRepresentation:', this.geoJSONRepresentation);
    const requestOptions = {
        method: 'POST',
        headers: { 'Content-Type': 'application/json' },
        body: JSON.stringify({ wktRepresenation: this.wktRepresenation }),
,
    };
            
    fetch('http://localhost:4000/getTIFFForSubsetAsNIRRange/', requestOptions)
        .then(response => response.json())
        .then(data => (this.postId = data.id));
});

型

后端

app.post('/getTIFFForSubsetAsNIRRange/', async (req, res, next) => {
    console.log(res.send(req.body))
    return 'OK'
});

app.listen(port, () => {
    console.log('listening to port', port);
});

型