Question

我有这个node.js应用程序（使用socket.io），将用于监视生产环境中对网络配置更改所做的更改。它监视后台打印目录中是否有新文件，然后将信息推送到Web客户端。当我尝试运行它时，出现“错误：无法读取未定义的属性'length'。”任何帮助将不胜感激。

#!/usr/bin/env node

// Runtime configuration
const SPOOLDIR = process.env['HOME'] + "/spool";        // Where to collect files
const INTERVAL = 5000;                          // How often to scan
const GRACE = 2000;                             // Minimum age of file before processing

// Dependency modules
const fs = require("fs");
const os = require("os");
const util = require("util");
const app = require('http').createServer(handler)
const io = require('socket.io')(app);

// Global variables:
// - File cache: stat structures by filename
var CACHE={};

// Mini C STDIO  printf/fprintf routines :)
//
const STDOUT=1;
const STDERR=2;
const fprintf = function(fd, fmt) {
    utilfmt_args = Array.prototype.slice.call(arguments, 1);
    var str = util.format.apply(null, utilfmt_args);
    fs.writeSync(fd, str);
}
const printf = function() {
    Array.prototype.unshift.call(arguments, STDOUT);
    fprintf.apply(null, arguments);
}


const startFileScan = function() {
    fs.readdir(SPOOLDIR, processFileResults);
}

const processFileResults = function(err, files) {
    fprintf(STDERR, "processFileResult: %d file(s) found in %s\n", files.length, SPOOLDIR);
    if (err!=undefined) {
        fprintf(STDERR, "Can't read spool directory %s: %s\n", SPOOLDIR, err.code);
        return;
    }

    // Expire any items from the cache that are no longer present
    for (var f in CACHE) {
        if (files.indexOf(f)==-1) {
//          fprintf(STDERR, "Removing file %s from cache\n", f);
            delete CACHE[f];
        }
    }

    // Check any files that are there for modifications, processing them if so
    var currentFile = undefined;
        const doStat = function(err, stats) {
        if (err) {
            fprintf(STDERR, "Error stat()ing %s: %s\n", currentFile, err.code);
        } else {
            if (currentFile!==undefined) {
//              fprintf(STDERR, "Checking file %s with mtime %s against cache\n", currentFile, stats.mtime);
                if (!(currentFile in CACHE) || !(CACHE[currentFile].getTime()==stats.mtime.getTime())) {
                    if (stats.mtime.getTime() + GRACE < Date.now()) {
//                      fprintf(STDERR, "  Updating cache for file %s with mtime %s\n", currentFile, stats.mtime);
                        CACHE[currentFile]=stats.mtime;
//                      fprintf(STDERR, "  File %s has been modified longer than %d ms ago: scheduling for processing\n", currentFile, GRACE);
                        process.nextTick(outputDiffReport, currentFile, CACHE[currentFile]);
                }
            }           
        }
        currentFile = files.pop();
        if (currentFile===undefined) {
//          fprintf(STDERR, "File scan completed: re-scheduling next scan\n");
            process.nextTick(function() { setTimeout(startFileScan, INTERVAL); });
        } else {
            fs.stat(SPOOLDIR + "/" + currentFile, doStat);                      
        }
    };
    process.nextTick(doStat);
}

// App library routines
//
    const outputDiffReport = function(filename, mtime) {
//  fprintf(STDERR, "Processing file %s\n", filename);
    var data="";
    try {
        data = fs.readFileSync(SPOOLDIR + "/" + filename, { encoding: "utf8" });
    } catch(err) {
        fprintf(STDERR, "Can't read incoming filename %s: %s\n", filename, err.code);
    }
    content = data.split(/\n/).filter(function(x) { return x.match(/^[+\-#\[]/); }).join("\n"); 
//  content = data.split(/\n/).filter(function(x) { return ! x.match(/^\s*$/); }).join("\n");   

    io.emit('update', { 'content':  content,
                        'mtime':    mtime.toISOString(),
                        'file':     filename
                    });

fs.unlink(SPOOLDIR + "/" + filename, function() {});
}


// HTTP bootstrap handler routine. Serves out the client HTML
function handler (req, res) {
  fs.readFile(__dirname + '/index.html',
  function (err, data) {
    if (err) {
      res.writeHead(500);
      return res.end('Error loading index.html');
    }
    res.writeHead(200);
    res.end(data);
  });
}

process.on('uncaughtException', function(err) {
  console.log("ERROR: ", err.message);
  process.exit(1);
});

app.listen(8080);

process.nextTick(startFileScan);

Answer 1

调用%install时，它要么会作为第一个参数出现错误，要么会成功并为您提供processFileResults作为第一个参数，并给您第二个文件。

在尝试访问null之前，您应该检查错误并进行处理。另外，从语义上检查错误是否为files也是没有意义的，因为错误只能是undefined或错误。

null

Answer 2

原来是假脱机目录的权限问题。我创建的用于运行程序的用户对该程序没有读取权限。

Node.js“无法读取未定义的属性'length'

2 个答案: