使用BlobContainerClient操作Azure Blob Storage遇412条件不满足错误

本地使用BlobContainerClient从Azure Blob Storage下载Blob到本地后删除的流程运行正常，但部署后报以下错误：

412 (The condition specified using HTTP conditional header(s) is not met.)

示例代码：

BlobContainerClient container = new BlobContainerClient(azureBlobSettings.Connectionstring, azureBlobSettings.Containername);

var blobList = container.GetBlobs();

foreach (var blobItem in blobList)
{
    if (blobItem.Name.Contains(".csv"))
    {
        LogInfo($"Downloading file {blobItem.Name} ...");

        var blob = container.GetBlobClient(blobItem.Name);

        var blobSplit = blob.Name.Split("/");
        var blobPath = blobSplit[0];
        var blobName = blobSplit[1];

        blob.DownloadTo($"{csvSettings.TargetPath}{blobName}");

        blob.DeleteIfExists();
    }
}

详细错误栈：

at Azure.Storage.Blobs.BlobRestClient.Download(String snapshot, String versionId, Nullable`1 timeout, String range, String leaseId, Nullable`1 rangeGetContentMD5, Nullable`1 rangeGetContentCRC64, String encryptionKey, String encryptionKeySha256, Nullable`1 encryptionAlgorithm, Nullable`1 ifModifiedSince, Nullable`1 ifUnmodifiedSince, String ifMatch, String ifNoneMatch, String ifTags,CancellationToken cancellationToken)
at Azure.Storage.Blobs.Specialized.BlobBaseClient.StartDownloadAsync(HttpRange range, BlobRequestConditions conditions, Boolean rangeGetContentHash, Int64 startOffset, Boolean async, CancellationToken cancellationToken)
at Azure.Storage.Blobs.Specialized.BlobBaseClient.DownloadStreamingInternal(HttpRange range, BlobRequestConditions conditions, Boolean rangeGetContentHash, IProgress`1 progressHandler, String operationName, Boolean async, CancellationToken cancellationToken)
at Azure.Storage.Blobs.Specialized.BlobBaseClient.DownloadStreaming(HttpRange range, BlobRequestConditions conditions, Boolean rangeGetContentHash, IProgress`1 progressHandler, CancellationToken cancellationToken)
at Azure.Storage.Blobs.PartitionedDownloader.DownloadTo(Stream destination, BlobRequestConditions conditions, CancellationToken cancellationToken)
at Azure.Storage.Blobs.Specialized.BlobBaseClient.StagedDownloadAsync(Stream destination, BlobRequestConditions conditions, IProgress`1 progressHandler, StorageTransferOptions transferOptions, Boolean async, CancellationToken cancellationToken)
at Azure.Core.Pipeline.TaskExtensions.EnsureCompleted[T](Task`1 task)   
at Azure.Storage.Blobs.Specialized.BlobBaseClient.DownloadTo(String path, BlobRequestConditions conditions, StorageTransferOptions transferOptions, CancellationToken cancellationToken)
at Azure.Storage.Blobs.Specialized.BlobBaseClient.DownloadTo(String path, CancellationToken cancellationToken)
at Azure.Storage.Blobs.Specialized.BlobBaseClient.DownloadTo(String path)

问题原因及解决办法 #

1. 并发操作冲突 #

部署后多实例同时执行逻辑，或Blob在获取列表后到下载前被修改/删除。GetBlobs()返回的是快照数据，遍历到Blob时它可能已被其他操作修改，导致下载时条件不满足。

解决：
遍历Blob时记录ETag，下载时指定匹配条件，确保下载的是列表获取时的版本：

var blob = container.GetBlobClient(blobItem.Name);
// 仅当Blob的ETag与列表中获取的一致时才下载
var conditions = new BlobRequestConditions { IfMatch = blobItem.Properties.ETag };
blob.DownloadTo($"{csvSettings.TargetPath}{blobName}", conditions);

2. Blob被其他进程锁定或修改 #

部署环境中可能有其他服务同时访问Blob，比如上传未完成、Blob被租赁锁定。

解决：

• 检查Blob是否有活跃租赁，有则先释放再操作；
• 改用Azure Event Grid监听Blob创建事件触发下载，替代定时轮询，确保Blob上传完成后再处理。

3. 分区下载的条件冲突 #

DownloadTo内部分块下载，若Blob在分块过程中被修改，后续分块请求会触发412错误。

解决：
改用DownloadContent先将Blob内容读到内存再写入本地，减少分块冲突：

var content = blob.DownloadContent();
File.WriteAllBytes($"{csvSettings.TargetPath}{blobName}", content.Value.Content);

4. 目录结构处理异常 #

代码中手动用Split("/")处理Blob名称，若Blob名称含多个斜杠或为根目录下文件，会导致数组越界，间接引发异常（错误码可能表现为412）。

解决：
用Path.GetFileName安全获取文件名：

var blobName = Path.GetFileName(blob.Name);

内容的提问来源于stack exchange，提问作者Anthony Cuartero