[BUG] Azure Storage BlobClient doesn't properly escape filenames with certain characters

[kganjam]

Describe the bug
BlobClient doesn't properly escape filenames with certain characters such as '#'. This results in a time-consuming-to-debug exception.

Expected behavior
BlobClient constructor should automatically handle proper escaping of filenames. It took me a while to figure out a workaround. Simple Uri.EscapeUriString is insufficient, though Uri.EscapeDataString appears to work.

If this behavior is by design, then the constructor should at least throw an exception up front to warn users of invalid characters and/or the docs should be updated to explicitly state how the filename needs to be encoded.

Actual behavior (include Exception or Stack Trace)
Azure.RequestFailedException: 'Service request failed.
Status: 404 (The specified blob does not exist.)
ErrorCode: BlobNotFound

To Reproduce

// These two blobs already exists and are visible in Storage Explorer
string myDir = @"MyDir_20200410/MyDir2";
string fileNameWithSpaces = "My File Name.pdf"; 
string fileNameWithSpacesAndPound = "My File Name#.pdf"; 

var blob = new BlobClient(@"DefaultEndpointsProtocol=https;AccountName=<redacted>;AccountKey=<redacted>;EndpointSuffix=core.windows.net", "MyContainer", $"{myDir}/{fileNameWithSpaces});
 var p = blob.GetProperties(); // Works with unescaped spaces

// A workaround to escape the filename
var b = new RequestUriBuilder();
b.AppendPath(Path.GetFileName(fileNameWithSpacesAndPound));
var escapedFileName = b.Path;  

blob = new BlobClient(@"DefaultEndpointsProtocol=https;AccountName=<redacted>;AccountKey=<redacted>;EndpointSuffix=core.windows.net", "MyContainer", $"{myDir}/{escapedFileName}");
 var p = blob.GetProperties(); // Works with escaped name 

blob = new BlobClient(@"DefaultEndpointsProtocol=https;AccountName=<redacted>;AccountKey=<redacted>;EndpointSuffix=core.windows.net", "MyContainer", $"{myDir}/{fileNameWithSpacesAndPound});
 var p = blob.GetProperties(); // Throws with unescaped pound character

Environment:

• Name and version of the Library package used: Azure.Storage.Blobs 12.4.1
• Hosting platform or OS and .NET runtime version (dotnet --info output for .NET Core projects):
  .NET Core SDK (reflecting any global.json):
  Version: 3.1.201
  Commit: b1768b4ae7

Runtime Environment:
OS Name: Windows
OS Version: 10.0.18363
OS Platform: Windows
RID: win10-x64
Base Path: C:\Program Files\dotnet\sdk\3.1.201\

Host (useful for support):
Version: 3.1.3
Commit: 4a9f85e9f8

.NET Core SDKs installed:
1.1.14 [C:\Program Files\dotnet\sdk]
2.1.202 [C:\Program Files\dotnet\sdk]
2.1.500 [C:\Program Files\dotnet\sdk]
2.1.512 [C:\Program Files\dotnet\sdk]
2.1.801 [C:\Program Files\dotnet\sdk]
2.2.401 [C:\Program Files\dotnet\sdk]
3.1.201 [C:\Program Files\dotnet\sdk]

• IDE and version : [e.g. Visual Studio 16.3]

[ghost]

Thanks for the feedback! We are routing this to the appropriate team for follow-up. cc @xgithubtriage.

[seanmcc-msft]

I've put out a PR to resolve this issue.