问题描述
我想从azure blob存储中获取图像并将其发送到客户端，而不将其保存在本地。我能够从Blob存储中获取图像并将其保存到本地文件，但是在不将其保存到本地的情况下却很难将其发送到客户端。请在下面找到代码
const containerClient = blobServiceClient.getContainerClient(containerName);
const blockBlobClient = containerClient.getBlobClient(blobName);
const downloadBlockBlobResponse = await blockBlobClient.download(0);
console.log('\nDownloaded blob content...');
let f = await streamToString(downloadBlockBlobResponse.readableStreamBody)
reply.type('image/jpg').send(f)
streamToString函数如下
async function streamToString(readableStream) {
return new Promise((resolve,reject) => {
const chunks = [];
readableStream.on("data",(data) => {
chunks.push(data.toString());
});
readableStream.on("end",() => {
resolve(chunks.join(""));
});
readableStream.on("error",reject);
});
}
运行此代码时，我在浏览器中出现空白屏幕
解决方法
如果要从天蓝色的blob存储中获取图像并将其发送到客户端而不在本地保存，则节点服务器向客户端发送SAS token到客户端，客户端将直接从Azure存储中获取该图像我认为是更好的解决方案。这也减轻了节点服务器的压力：可以生成SAS令牌并将其发送到客户端，无需从存储读取数据。
尝试下面的代码来生成SAS令牌：
var azure = require('azure-storage');
var connString = "your storage connection string";
var container ="your container name";
var blobName = "your image name"
var blobService = azure.createBlobService(connString);
// Create a SAS token that expires in an hour
// Set start time to five minutes ago to avoid clock skew.
var startDate = new Date();
startDate.setMinutes(startDate.getMinutes() - 5);
var expiryDate = new Date(startDate);
expiryDate.setMinutes(startDate.getMinutes() + 60);
var sharedAccessPolicy = {
AccessPolicy: {
Permissions: [azure.BlobUtilities.SharedAccessPermissions.READ],//grent read permission only
Start: startDate,Expiry: expiryDate
}
};
var sasToken = blobService.generateSharedAccessSignature(container,blobName,sharedAccessPolicy);
var response = {};
response.image = blobService.getUrl(container,sasToken);
res.send(response);
结果：
客户端可以使用此图像URL直接从存储中访问该图像：
尝试将imageURL转换为base64图像内容，以便您可以直接基于图像内容保存/显示图像：
<html>
<body>
<img id="displayImg">
</body>
<script>
var nodeResult = {"image":"https://stantest1016.blob.core.windows.net/stantest/test.jpeg?st=2020-10-26T04%3A53%3A51Z&se=2020-10-26T05%3A53%3A51Z&sp=r&sv=2018-03-28&sr=b&sig=ZjY3LYbgvMn%2BSr4dAEUoqidVRT4YyH1FcW1DeKlpjYo%3D"}
function getImageData(nodeResult){
var xhr = new XMLHttpRequest();
xhr.onreadystatechange = function() {
if (this.readyState == 4 && this.status == 200) {
var reader = new FileReader();
reader.readAsDataURL(this.response);
reader.onload = function() {
document.getElementById('displayImg').src = reader.result;
}
};
};
xhr.open('GET',nodeResult.image);
xhr.responseType = 'blob';
xhr.send();
}
getImageData(nodeResult);
</script>
</html>
结果：
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