问题
I am trying to create an app where user can upload a text file, and gets the altered text back.
I am using React as FE and ASP.NET Core for BE and Azure storage for the database storage.
This is how my HomeController looks like. I created a separate "UploadToBlob" method, to post the data
public class HomeController : Controller
{
private readonly IConfiguration _configuration;
public HomeController(IConfiguration Configuration)
{
_configuration = Configuration;
}
public IActionResult Index()
{
return View();
}
[HttpPost("UploadFiles")]
//OPTION B: Uncomment to set a specified upload file limit
[RequestSizeLimit(40000000)]
public async Task<IActionResult> Post(List<IFormFile> files)
{
var uploadSuccess = false;
string uploadedUri = null;
foreach (var formFile in files)
{
if (formFile.Length <= 0)
{
continue;
}
// read directly from stream for blob upload
using (var stream = formFile.OpenReadStream())
{
// Open the file and upload its data
(uploadSuccess, uploadedUri) = await UploadToBlob(formFile.FileName, null, stream);
}
}
if (uploadSuccess)
{
//return the data to the view, which is react display text component.
return View("DisplayText");
}
else
{
//create an error component to show there was some error while uploading
return View("UploadError");
}
}
private async Task<(bool uploadSuccess, string uploadedUri)> UploadToBlob(string fileName, object p, Stream stream)
{
if (stream is null)
{
try
{
string connectionString = Environment.GetEnvironmentVariable("AZURE_STORAGE_CONNECTION_STRING");
// Create a BlobServiceClient object which will be used to create a container client
BlobServiceClient blobServiceClient = new BlobServiceClient(connectionString);
//Create a unique name for the container
string containerName = "textdata" + Guid.NewGuid().ToString();
// Create the container and return a container client object
BlobContainerClient containerClient = await blobServiceClient.CreateBlobContainerAsync(containerName);
string localPath = "./data/";
string textFileName = "textdata" + Guid.NewGuid().ToString() + ".txt";
string localFilePath = Path.Combine(localPath, textFileName);
// Get a reference to a blob
BlobClient blobClient = containerClient.GetBlobClient(textFileName);
Console.WriteLine("Uploading to Blob storage as blob:\n\t {0}\n", blobClient.Uri);
FileStream uploadFileStream = File.OpenRead(localFilePath);
await blobClient.UploadAsync(uploadFileStream, true);
uploadFileStream.Close();
}
catch (StorageException)
{
return (false, null);
}
finally
{
// Clean up resources, e.g. blob container
//if (blobClient != null)
//{
// await blobClient.DeleteIfExistsAsync();
//}
}
}
else
{
return (false, null);
}
}
}
but the console throws errors, saying "'ControllerBase.File(byte[], string)' is a method, which is not valid in the given context (CS0119)"
And because of this error, another error follows "'HomeController.UploadToBlob(string, object, Stream)': not all code paths return a value (CS0161)"
my questions are
- Is it a better idea to create a separate method like I did?
- how can I resolve the issue regarding the "File" being valid inside of the UploadToBlob method?
- If I want to add the file type validation, where should it happen? t.ex. only text file is alid
- If I want to read the text string from the uploaded text file, where should I call the
string contents = blob.DownloadTextAsync().Result;
return contents;
- How can I pass down the "contents" to my react component? something like this?
useEffect(() => {
fetch('Home')
.then(response => response.json())
.then(data => {
setForcasts(data)
})
}, [])
Thanks for helping this super newbie with ASP.NET Core!
回答1:
1) It is ok to put uploading into separate method, it could also be put into a separate class for handling blob operations
2) File is the name of one of the controllers methods, if you want to reference the File class from System.IO namespace, you need to fully qualify the name
FileStream uploadFileStream = System.IO.File.OpenRead(localFilePath);
To the other compile error, you need to return something from the UploadToBlob method, now it does not return anything from the try block
3) File type validation can be put into the controller action method
4) it depends on what you plan to do with the text and how are you going to use it. Would it be a new action of the controller (a new API endpoint)?
5) you could create a new API endpoint for downloading files
UPDATE:
For word replacement you could use a similar method:
private Stream FindMostFrequentWordAndReplaceIt(Stream inputStream)
{
using (var sr = new StreamReader(inputStream, Encoding.UTF8)) // what is the encoding of the text?
{
var allText = sr.ReadToEnd(); // read all text into memory
// TODO: Find most frequent word in allText
// replace the word allText.Replace(oldValue, newValue, stringComparison)
var resultText = allText.Replace(...);
var result = new MemoryStream();
using (var sw = new StreamWriter(result))
{
sw.Write(resultText);
}
result.Position = 0;
return result;
}
}
it would be used in your Post method this way:
using (var stream = formFile.OpenReadStream())
{
var streamWithReplacement = FindMostFrequentWordAndReplaceIt(stream);
// Upload the replaced text:
(uploadSuccess, uploadedUri) = await UploadToBlob(formFile.FileName, null, streamWithReplacement);
}
来源：https://stackoverflow.com/questions/60927331/controllerbase-filebyte-string-is-a-method-which-is-not-valid-in-the-giv