我正在使用Azure的blockBlobURL.download()下载图像，但仅接收图像的顶部。我可以从Azure blob下载到可读流的数量有限制吗？内容长度为172628，并且存在属性highWaterMark: 16384。这些有关吗？
async function compareToBaseline(imageData, blobName, metadata){
const baselineBlobName = "MacOSX10.12/chrome/initial"
const containerURL = ContainerURL.fromServiceURL(serviceURL, "baselines")
const blockBlobURL = BlockBlobURL.fromContainerURL(containerURL, baselineBlobName );
let baseLineImage = await blockBlobURL.download(aborter, 0)
baseLineImage = baseLineImage.originalResponse.readableStreamBody.read()
console.log(baseLineImage.length);
baseLineImage = new Buffer(baseLineImage, 'base64');
await fs.writeFile('./newest.png', baseLineImage, 'binary', function(err){
console.log('written');
})
}
结果仅是图像的顶部。
答案 0 :(得分：0)
对Azure存储服务的每次调用都有4 MB的限制。如果您的文件大于4 MB，则必须将其分成多个块。有关更多信息，请参见Azure Storage scalability and performance targets。
这是示例c＃代码，以1MB的块大小下载非常大的文件。它也是基于性能的。
private static void DownloadLargeFile()
{
string connectionString = "connString"; //ConfigurationSettings.AppSettings["StorageConnectionString"]; //blob connection string
#pragma warning restore CS0618 // Type or member is obsolete
#pragma warning disable CS0618 // Type or member is obsolete
string sourceContainerName = "quickstartblob"; //ConfigurationSettings.AppSettings["sourcecontainerName"]; //source blob container name
#pragma warning restore CS0618 // Type or member is obsolete
string sourceBlobFileName = "QuickStart1.txt"; //source blob name
CloudStorageAccount account = CloudStorageAccount.Parse(connectionString);
var blobClient = account.CreateCloudBlobClient();
var container = blobClient.GetContainerReference(sourceContainerName);
var file = sourceBlobFileName;
var blob = container.GetBlockBlobReference(file);
//First fetch the size of the blob. We use this to create an empty file with size = blob's size
blob.FetchAttributes();
var blobSize = blob.Properties.Length;
long blockSize = (1 * 1024 * 1024);//1 MB chunk;
blockSize = Math.Min(blobSize, blockSize);
//Create an empty file of blob size
using (FileStream fs = new FileStream(file, FileMode.Create))//Create empty file.
{
fs.SetLength(blobSize);//Set its size
}
var blobRequestOptions = new BlobRequestOptions
{
RetryPolicy = new ExponentialRetry(TimeSpan.FromSeconds(5), 3),
MaximumExecutionTime = TimeSpan.FromMinutes(60),
ServerTimeout = TimeSpan.FromMinutes(60)
};
long currentPointer = 0;
long bytesRemaining = blobSize;
do
{
var bytesToFetch = Math.Min(blockSize, bytesRemaining);
using (MemoryStream ms = new MemoryStream())
{
//Download range (by default 1 MB)
blob.DownloadRangeToStream(ms, currentPointer, bytesToFetch, null, blobRequestOptions);
ms.Position = 0;
var contents = ms.ToArray();
using (var fs = new FileStream(file, FileMode.Open))//Open that file
{
fs.Position = currentPointer;//Move the cursor to the end of file.
fs.Write(contents, 0, contents.Length);//Write the contents to the end of file.
}
currentPointer += contents.Length;//Update pointer
bytesRemaining -= contents.Length;//Update bytes to fetch
}
}
while (bytesRemaining > 0);
}
类似于以下节点js
var azure = require('azure-storage');
var fs = require('fs');
module.exports = function (context, input) {
context.done();
var accessKey = 'myaccesskey';
var storageAccount = 'mystorageaccount';
var containerName = 'mycontainer';
var blobService = azure.createBlobService(storageAccount, accessKey);
var recordName = "a_large_movie.mov";
var blobName = "standard/mov/" + recordName;
var blobSize;
var chunkSize = (1024 * 512) * 8; // I'm experimenting with this variable
var startPos = 0;
var fullPath = "D:/home/site/wwwroot/myAzureFunction/input/";
var blobProperties = blobService.getBlobProperties(containerName, blobName, null, function (error, blob) {
if (error) {
throw error;
}
else {
blobSize = blob.contentLength;
context.log('Registered length: ' + blobSize);
fullPath = fullPath + recordName;
console.log(fullPath);
doDownload();
}
}
);
function doDownload() {
var stream = fs.createWriteStream(fullPath, {flags: 'a'});
var endPos = startPos + chunkSize;
if (endPos > blobSize) {
endPos = blobSize;
context.log('Reached end of file endPos: ' + endPos);
}
context.log("Downloading " + (endPos - startPos) + " bytes starting from " + startPos + " marker.");
blobService.getBlobToStream(
containerName,
blobName,
stream,
{
"rangeStart": startPos,
"rangeEnd": endPos-1
},
function(error) {
if (error) {
throw error;
}
else if (!error) {
startPos = endPos;
if (startPos <= blobSize - 1) {
doDownload();
}
}
}
);
}
};
希望有帮助。
答案 1 :(得分：0)
此问题似乎与您的其他线程Unable to read readableStreamBody from downloaded blob类似。
这是我的功能，以帮助将baseLineImage.readableStreamBody保存到文件，如下所示。
async function streamToFs(filename, readableStream) {
const ws = fs.createWriteStream(filename);
readableStream.on("data", data => {
ws.write(data);
}).on("end", () => {
console.log('written');
});
}
并如下更改代码。
async function compareToBaseline(imageData, blobName, metadata){
const baselineBlobName = "MacOSX10.12/chrome/initial"
const containerURL = ContainerURL.fromServiceURL(serviceURL, "baselines");
const blockBlobURL = BlockBlobURL.fromContainerURL(containerURL, baselineBlobName );
let baseLineImage = await blockBlobURL.download(aborter, 0);
await streamToFs('./newest.png', baseLineImage.readableStreamBody)；
}
有效。希望对您有所帮助。
答案 2 :(得分：0)
blockBlobURL.download（）对文件大小没有限制。但是read()返回null并不意味着流中没有更多数据。您需要遵循Node.js的惯例，通过监听data或readable事件来获取所有数据。
例如，彼得·潘（Peter Pan）发布的data事件。或由Node.js官方文档发布的readable事件：
readable.on('readable', () => {
let chunk;
while (null !== (chunk = readable.read())) {
console.log(`Received ${chunk.length} bytes of data.`);
}
});
请始终在read()事件回调内调用readable。