.NET 7.0 Isolated Worker中BlobTrigger转Stream失败问题求助

问题场景 #

在.NET 7.0的dotnet-isolated模式下，按照文档说明使用Stream处理Blob时，函数执行崩溃。

使用的NuGet包 #

<PackageReference Include="Microsoft.Azure.Functions.Worker" Version="1.20.0" />
<PackageReference Include="Microsoft.Azure.Functions.Worker.Extensions.Storage.Blobs" Version="6.2.0" /> 
<PackageReference Include="Microsoft.Azure.Functions.Worker.Sdk" Version="1.16.4" />

函数代码 #

[Function(nameof(CMImageResizer))]
public async Task Run(
    [BlobTrigger("rawimages/{name}", Connection = "StorageAccountConnectionString")] Stream myBlob,
    [BlobInput("resizedimages/{name}", Connection = "StorageAccountConnectionString")] Stream resizedImage, string name)
{
  try
   {
   _log.LogInformation("Processing image:{name} size: {myBlobLength} Bytes", name, myBlob.Length);

报错信息 #

Executing 'Functions.CMImageResizer' (Reason='New blob detected(LogsAndContainerScan): rawimages/taladro1.jpg', Id=00c22256-e65c-478c-82c3-eaca92c310b7) 
[2023-12-24T05:35:39.632Z] Trigger Details: MessageId: 2f450295-dae1-42f5-ac2e-089d5b0d2a55, DequeueCount: 1, InsertedOn: 2023-12-24T05:35:38.000+00:00, BlobCreated: 2023-12-24T04:42:41.000+00:00, BlobLastModified: 2023-12-24T05:35:28.000+00:00 
[2023-12-24T05:35:40.601Z] Function 'CMImageResizer', Invocation id '00c22256-e65c-478c-82c3-eaca92c310b7': An exception was thrown by the invocation. 
[2023-12-24T05:35:40.604Z] Result: Function 'CMImageResizer', Invocation id '00c22256-e65c-478c-82c3-eaca92c310b7': An exception was thrown by the invocation. 
[2023-12-24T05:35:40.604Z] Exception: Microsoft.Azure.Functions.Worker.FunctionInputConverterException: Error converting 1 input parameters for Function 'CMImageResizer': Cannot convert input parameter 'myBlob' to type 'System.IO.Stream' from type 'System.ReadOnlyMemory`1[[System.Byte, System.Private.CoreLib, Version=7.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]]'. Error:System.Text.Json.JsonException: 'R' is an invalid start of a value. Path: $ | LineNumber: 0 | BytePositionInLine: 0.
[2023-12-24T05:35:40.604Z] ---> System.Text.Json.JsonReaderException: 'R' is an invalid start of a value. LineNumber: 0 | BytePositionInLine: 0.
[2023-12-24T05:35:40.604Z] at System.Text.Json.ThrowHelper.ThrowJsonReaderException(Utf8JsonReader& json, ExceptionResource resource, Byte nextByte, ReadOnlySpan`1 bytes) 
[2023-12-24T05:35:40.604Z] at System.Text.Json.Utf8JsonReader.ConsumeValue(Byte marker) 
[2023-12-24T05:35:40.604Z] at System.Text.Json.Utf8JsonReader.ReadFirstToken(Byte first) 
[2023-12-24T05:35:40.604Z] at System.Text.Json.Utf8JsonReader.ReadSingleSegment() 
[2023-12-24T05:35:40.604Z] at System.Text.Json.Utf8JsonReader.Read() 
[2023-12-24T05:35:40.604Z] at System.Text.Json.Serialization.JsonConverter`1.ReadCore(Utf8JsonReader& reader, JsonSerializerOptions options, ReadStack& state)

问题原因及修复方案 #

核心问题 #

1. JSON转换器误处理二进制数据：.NET Isolated模式默认使用JSON转换器解析输入参数，Blob的二进制内容（如图片）被错误当作JSON解析，导致JsonReaderException。
2. 绑定类型错误：代码中使用BlobInput绑定目标Blob，但BlobInput是用于读取现有Blob的输入绑定，而你需要写入处理后的图片，应使用BlobOutput绑定。

修复步骤 #

方案1：使用BinaryData处理输入（推荐）

将BlobTrigger参数改为BinaryData类型，再转换为Stream使用，同时修正输出绑定类型：

[Function(nameof(CMImageResizer))]
public async Task Run(
    [BlobTrigger("rawimages/{name}", Connection = "StorageAccountConnectionString")] BinaryData myBlobData,
    [BlobOutput("resizedimages/{name}", Connection = "StorageAccountConnectionString")] Stream resizedImage, 
    string name,
    ILogger log)
{
    try
    {
        using Stream myBlob = myBlobData.ToStream();
        log.LogInformation("Processing image:{name} size: {myBlobLength} Bytes", name, myBlob.Length);
        
        // 此处添加图片缩放逻辑，处理后写入resizedImage流
        // 示例：await myBlob.CopyToAsync(resizedImage);
    }
    catch (Exception ex)
    {
        log.LogError(ex, "Failed to process image {name}", name);
        throw;
    }
}

方案2：保留Stream类型并添加BinaryData属性

如果坚持使用Stream作为输入参数，需添加[BinaryData]属性告知运行时这是二进制数据：

[Function(nameof(CMImageResizer))]
public async Task Run(
    [BlobTrigger("rawimages/{name}", Connection = "StorageAccountConnectionString")] [BinaryData] Stream myBlob,
    [BlobOutput("resizedimages/{name}", Connection = "StorageAccountConnectionString")] Stream resizedImage, 
    string name,
    ILogger log)
{
    try
    {
        log.LogInformation("Processing image:{name} size: {myBlobLength} Bytes", name, myBlob.Length);
        // 后续处理逻辑
    }
    catch (Exception ex)
    {
        log.LogError(ex, "Failed to process image {name}", name);
        throw;
    }
}

注意事项 #

• 确保Microsoft.Azure.Functions.Worker.Extensions.Storage.Blobs版本≥6.0.0，该版本开始支持Isolated模式下的二进制数据处理。
• 使用BlobOutput绑定输出流时，无需手动关闭流，函数运行时会自动处理。

内容的提问来源于stack exchange，提问作者Vodo-Siosk Baas