运行我的应用程序时出现此异常。它也发生在真正的Azure blob存储中。
我已经向Fiddler发现了导致此问题的请求：
GET http://127.0.0.1:10000/devstoreaccount1/ebb413ed-fdb5-49f2-a5ac-74faa7e2d3bf/8844c3ec-9e4b-43ec-88b2-58eddf65fc0a/perro?timeout=90 HTTP/1.1
x-ms-version: 2009-09-19
User-Agent: WA-Storage/6.0.6002.18006
x-ms-range: bytes=0-524304
If-Match: 0x8CDA190BD304DD0
x-ms-date: Wed, 23 Feb 2011 16:49:18 GMT
Authorization: SharedKey devstoreaccount1:5j3IScY9UJLN3o1ICWKwVEazO4/IDJG796sdZKqHlR4=
Host: 127.0.0.1:10000
这就是回应：
HTTP/1.1 412 The condition specified using HTTP conditional header(s) is not met.
Content-Length: 252
Content-Type: application/xml
Server: Windows-Azure-Blob/1.0 Microsoft-HTTPAPI/2.0
x-ms-request-id: fbff9d15-65c8-4f21-9088-c95e4496c62c
x-ms-version: 2009-09-19
Date: Wed, 23 Feb 2011 16:49:18 GMT
<?xml version="1.0" encoding="utf-8"?><Error><Code>ConditionNotMet</Code><Message>The condition specified using HTTP conditional header(s) is not met.
RequestId:fbff9d15-65c8-4f21-9088-c95e4496c62c
Time:2011-02-23T16:49:18.8790478Z</Message></Error>
当我使用从此行检索的Stream时会发生这种情况：
blob.OpenRead();
为什么ETAG会在读操作中介意？我怎么能避免这个问题？
每次我在blob存储上启动多个并行任务时都会发生这种情况。
如果我使用：
blob.OpenRead(new BlobRequestOptions() { AccessCondition = AccessCondition.IfMatch("*") });
我得到了这个没有内部的异常（在它有一个带有详细信息的WebException之前），或者是Fiddler中的一个失败行：
Microsoft.WindowsAzure.StorageClient.StorageClientException was unhandled
Message=The conditionals specified for this operation did not match server.
Source=mscorlib
StackTrace:
Server stack trace:
at Microsoft.WindowsAzure.StorageClient.Tasks.Task`1.get_Result()
at Microsoft.WindowsAzure.StorageClient.Tasks.Task`1.ExecuteAndWait()
at Microsoft.WindowsAzure.StorageClient.TaskImplHelper.ExecuteImpl[T](Func`2 impl)
at Microsoft.WindowsAzure.StorageClient.BlobReadStream.Read(Byte[] buffer, Int32 offset, Int32 count)
at System.IO.BinaryReader.ReadBytes(Int32 count)
at System.Runtime.Serialization.Formatters.Binary.SerializationHeaderRecord.Read(__BinaryParser input)
at System.Runtime.Serialization.Formatters.Binary.__BinaryParser.ReadSerializationHeaderRecord()
at System.Runtime.Serialization.Formatters.Binary.__BinaryParser.Run()
at System.Runtime.Serialization.Formatters.Binary.ObjectReader.Deserialize(HeaderHandler handler, __BinaryParser serParser, Boolean fCheck, Boolean isCrossAppDomain, IMethodCallMessage methodCallMessage)
at System.Runtime.Serialization.Formatters.Binary.BinaryFormatter.Deserialize(Stream serializationStream, HeaderHandler handler, Boolean fCheck, Boolean isCrossAppDomain, IMethodCallMessage methodCallMessage)
...........
提前致谢。
答案 0 :(得分：6)
Bufff ......错误解决了！
好吧，当你执行CloudBlob.OpenRead()时，客户端库正在执行两项操作：
首先，获取blob阻止列表：
GET /devstoreaccount1/etagtest/test2.txt?comp=blocklist&blocklisttype=Committed&timeout=90 HTTP/1.1
x-ms-version: 2009-09-19
User-Agent: WA-Storage/6.0.6002.18006
x-ms-date: Wed, 23 Feb 2011 22:21:01 GMT
Authorization: SharedKey devstoreaccount1:SPOBe/IUrZJvoPXnAdD/Twnppvu37+qrUbHnaBHJY24=
Host: 127.0.0.1:10000
HTTP/1.1 200 OK
Transfer-Encoding: chunked
Content-Type: application/xml
Last-Modified: Wed, 23 Feb 2011 22:20:33 GMT
ETag: 0x8CDA1BF0593B660
Server: Windows-Azure-Blob/1.0 Microsoft-HTTPAPI/2.0
x-ms-request-id: ecffddf2-137f-403c-9595-c8fc2847c9d0
x-ms-version: 2009-09-19
x-ms-blob-content-length: 4
Date: Wed, 23 Feb 2011 22:21:02 GMT
在回应中注意ETag。
其次，我想开始检索它，现在注意请求中的ETag：
GET /devstoreaccount1/etagtest/test2.txt?timeout=90 HTTP/1.1
x-ms-version: 2009-09-19
User-Agent: WA-Storage/6.0.6002.18006
x-ms-range: bytes=0-525311
If-Match: 0x8CDA1BF0593B660
x-ms-date: Wed, 23 Feb 2011 22:21:02 GMT
Authorization: SharedKey devstoreaccount1:WXzXRv5e9+p0SzlHUAd7iv7jRHXvf+27t9tO4nrhY5Q=
Host: 127.0.0.1:10000
HTTP/1.1 206 Partial Content
Content-Length: 4
Content-Type: text/plain
Content-Range: bytes 0-3/4
Last-Modified: Wed, 23 Feb 2011 22:20:33 GMT
ETag: 0x8CDA1BF0593B660
Server: Windows-Azure-Blob/1.0 Microsoft-HTTPAPI/2.0
x-ms-request-id: db1e221d-fc61-4837-a255-28b1547cb5d7
x-ms-version: 2009-09-19
x-ms-lease-status: unlocked
x-ms-blob-type: BlockBlob
Date: Wed, 23 Feb 2011 22:21:02 GMT
如果另一个WebRole在调用之间的blob中做了什么，会发生什么？ 是竞争条件。
解决方案：使用CloudBlob.DownloadToStream()，该方法只发出一个电话：
GET /devstoreaccount1/etagtestxx/test2.txt?timeout=90 HTTP/1.1
x-ms-version: 2009-09-19
User-Agent: WA-Storage/6.0.6002.18006
x-ms-date: Wed, 23 Feb 2011 22:34:02 GMT
Authorization: SharedKey devstoreaccount1:VjXIO2kbjCIP4UeiXPtxDxmFLeoYAKOqiRv4SV3bZno=
Host: 127.0.0.1:10000
HTTP/1.1 200 OK
Content-Length: 4
Content-Type: text/plain
Last-Modified: Wed, 23 Feb 2011 22:33:47 GMT
ETag: 0x8CDA1C0DEB562D0
Server: Windows-Azure-Blob/1.0 Microsoft-HTTPAPI/2.0
x-ms-request-id: 183a05bb-ea47-4811-8768-6a62195cdb64
x-ms-version: 2009-09-19
x-ms-lease-status: unlocked
x-ms-blob-type: BlockBlob
Date: Wed, 23 Feb 2011 22:34:02 GMT
明天早上我会在工作中练习，看看会发生什么。
答案 1 :(得分：1)
我想到的一件事是
中的ETagIf-Match: 0x8CDA190BD304DD0
是畸形的;有效的（强）etag总是双引号。
Dunno这是否与你的问题有关。
答案 2 :(得分：1)
您仍然可以使用OpenRead，您需要传递OperationContext实例，如下面的代码：
// cloudBlob instance of CloudPageBlob
OperationContext context = new OperationContext();
context.SendingRequest += (sender, e) => {
e.Request.Headers["if-match"] = "*";
};
using (AutoResetEvent waitHandle = new AutoResetEvent(false))
{
cloudBlob.StreamMinimumReadSizeInBytes = 16385;
var result = cloudBlob.BeginOpenRead(null, null, context,
ar => waitHandle.Set(),
null);
waitHandle.WaitOne();
using (Stream blobStream = vhd.EndOpenRead(result))
{
var k = blobStream.ReadByte();
}
}
答案 3 :(得分：0)
如果您不想使用 DownloadToStream 将 blob 数据存储在您的内存中，并且仍想使用 blob 读取，那么您可以在与参考 blob 上可用的任何 Etag 匹配的读取操作上添加访问条件，如下所示
var accessCondition = new AccessCondition();
var blobRequestOptions = new BlobRequestOptions();
var operationContext = new OperationContext();
// Added match of any ETag access condition so that it will not cause any issue due to ongoing concurrent modification on the same blob
accessCondition.IfMatchETag = "*";
var blobStream = await blobRef.OpenReadAsync(accessCondition, blobRequestOptions, operationContext);