node.js亚马逊s3如何检查文件是否存在

我试图弄清楚如何在S3上执行相当于fs.exists()的操作.

我成功获取了存储桶的内容,但我无法弄清楚如何在存储桶中存在特定文件时询问S3(我不想下载整个文件列表并检查客户端,因为也有很多文件).

供参考：AWS2JS documentation on S3.GET

var s3 = require('aws2js').load('s3', appConfig.awsAccessKeyId, appConfig.awsSecretAccessKey);  
s3.setBucket(appConfig.awsBucketName);

            var folder = encodeURI('reports');
            var url = '?prefix=' + folder;

            s3.get(url,{Contents: null, Key: 'reports/emot_cat_r1180341142.png'},'xml', function (error, data) {
                console.log("Error",error);
                console.log("Data",data);
                true.should.be.true;
                done();
            });

输出

{ Name: ‘umusergen’, Prefix: ‘reports’, Marker: {}, MaxKeys:
‘1000’, IsTruncated: ‘false’, Contents: [ { Key: ‘reports/’,
LastModified: ‘2013-06-16T17:44:25.000Z’,
ETag: ‘”d41d8cd98f00b204e9800998ecf8427e”‘,
Size: ‘0’,
Owner: [Object],
StorageClass: ‘STANDARD’ },
{ Key: ‘reports/emot_cat_r1180341142.png’,
LastModified: ‘2013-06-16T23:18:59.000Z’,
ETag: ‘”0b04aa9146d36a447019b1aa94be7eb3″‘,
Size: ‘26374’,
Owner: [Object],
StorageClass: ‘STANDARD’ },
{ Key: ‘reports/polarity_r1180341142.png’,
LastModified: ‘2013-06-16T23:19:00.000Z’,
ETag: ‘”22fd521e0a5e858040082d0d47078532″‘,
Size: ‘23091’,
Owner: [Object],
StorageClass: ‘STANDARD’ },
{ Key: ‘reports/wordcloud_r1180341142.png’,
LastModified: ‘2013-06-16T23:19:07.000Z’,
ETag: ‘”9f7ee9d2fdce5f460b2c42444edd6efc”‘,
Size: ‘167164’,
Owner: [Object],
StorageClass: ‘STANDARD’ } ], ‘@’: { xmlns: { xmlns: ‘07001’ } } }

“{Contents：null,Key：'[file path / name]’}”是我尝试解释上面引用的API指令.

如您所见,它只是枚举存储桶的内容,但我需要API调用来检查特定文件是否存在.

有人可以帮忙吗？我对这一切都很陌生.

您必须使用HEAD请求以HTTP方式执行此操作.不存在的文件会触发404错误.这是一个简单的实现：

var s3 = require('aws2js').load('s3', process.env.AWS_ACCEESS_KEY_ID, process.env.AWS_SECRET_ACCESS_KEY)

s3.setBucket(process.env.AWS2JS_S3_BUCKET)

s3.head(process.argv[2], function (err, res) {
    if (err) {
        console.log(err)
        return
    }
    console.log(res)
})

出于测试目的,请使用以下命令调用它：

node s3-check.js file/path.foo

例子：

node s3-check.js foo1.png
{ 'x-amz-id-2': 'BU8rLC35oZdNLh4TkE9Y5+czR5r9hg7kl/EbhkxUF+cA94F41knI2YNs/YG1acQg',
  'x-amz-request-id': '7714B364EC1A27B2',
  date: 'Mon, 17 Jun 2013 06:42:52 GMT',
  'last-modified': 'Tue, 28 May 2013 13:18:12 GMT',
  etag: '"2830931876c37237ae98458a99e86d85"',
  'accept-ranges': 'bytes',
  'content-type': 'image/png',
  'content-length': '1165',
  server: 'AmazonS3' }

node s3-check.js foo0.png
{ [Error: API error with HTTP Code: 404]
  headers:
   { 'x-amz-request-id': '96841B9C0BC5E66D',
     'x-amz-id-2': 'ZMZH9bkrR6nhDkWK1hM+qm0dlzBOYhOZhVyT3nKlMuZgPag//5EhfBuAHZq+9ZRm',
     'content-type': 'application/xml',
     'transfer-encoding': 'chunked',
     date: 'Mon, 17 Jun 2013 06:43:53 GMT',
     server: 'AmazonS3' },
  code: 404 }