node-red-nodes/storage/tail/28-tail.js

module.exports = function(RED) {
    "use strict";
    var fs = require('fs');
    var Tail = require('tail').Tail;

    function TailNode(n) {
        RED.nodes.createNode(this,n);

        this.filename = n.filename;
        this.filetype = n.filetype || "text";
        this.split = new RegExp(n.split.replace(/\\r/g,'\r').replace(/\\n/g,'\n').replace(/\\t/g,'\t') || "[\r]{0,1}\n");
        var node = this;

        var fileTail = function() {
            if (fs.existsSync(node.filename)) {
                if (node.filetype === "text") {
                    node.tail = new Tail(node.filename,{separator:node.split, flushAtEOF:true});
                }
                else {
                    node.tail = new Tail(node.filename,{separator:null, flushAtEOF:true, encoding:"binary"});
                }

                node.tail.on("line", function(data) {
                    if (data.length > 0) {
                        var msg = { topic:node.filename };
                        if (node.filetype === "text") {
                            msg.payload = data.toString();
                            node.send(msg);
                        }
                        else {
                            msg.payload = Buffer.from(data,"binary");
                            //msg.payload = data;
                            node.send(msg);
                        }
                    }
                });

                node.tail.on("error", function(err) {
                    node.error(err.toString());
                });
            }
            else {
                node.tout = setTimeout(function() { fileTail(); },10000);
                node.warn(RED._("tail.errors.filenotfound") + ": "+node.filename);
            }
        }

        fileTail();

        node.on("close", function() {
            /* istanbul ignore else */
            if (node.tail) { node.tail.unwatch(); }
            delete node.tail;
            if (node.tout) { clearTimeout(node.tout); }
        });
    }

    RED.nodes.registerType("tail",TailNode);
}