Instantiating an IFormFile from a physical file

Question

I have a physical file and I want to pass it to my controller method that requires an IFormFile type (for unit testing).

I can't find any classes that instantiate the IFormFile interface which means I can't create one.

How can I convert my physical file into an IFormFile?

Answer 1

You can instantiate a FormFile. That implements IFormFile.

Example in .Net Core 3.1 (assume 'file' is physical path & file):

using var stream = new MemoryStream(File.ReadAllBytes(file).ToArray());
var formFile = new FormFile(stream, 0, stream.Length, "streamFile", file.Split(@"\").Last());

Answer 2

Let's assume you have a controller method that accepts IFormInfo

[HttpPost]
public Task<IActionResult> Upload(IFormFile file) {

    FileDetails fileDetails = null;
    using (var reader = new StreamReader(file.OpenReadStream())) {
        var fileContent = reader.ReadToEnd();
        ContentDispositionHeaderValue parsedContentDisposition = null;
        if (ContentDispositionHeaderValue.TryParse(file.ContentDisposition, out parsedContentDisposition)) {
            fileDetails = new FileDetails {
                Filename = parsedContentDisposition.FileName,
                Content = fileContent
            };
        }
    }

    return Task.FromResult((IActionResult)fileDetails);

}

Using a mocking framework like Moq. You can use a physical file to mock the IFormFile

[TestMethod]
public async Task Controller_Should_Upload_FormFile() {
    // Arrange.
    var fileMock = new Mock<IFormFile>();
    var physicalFile = new FileInfo("filePath");
    var ms = new MemoryStream();
    var writer = new StreamWriter(ms);
    writer.Write(physicalFile.OpenRead());
    writer.Flush();
    ms.Position = 0;
    var fileName = physicalFile.Name;
    //Setup mock file using info from physical file
    fileMock.Setup(_ => _.FileName).Returns(fileName);
    fileMock.Setup(_ => _.Length).Returns(ms.Length);
    fileMock.Setup(_ => _.OpenReadStream()).Returns(ms);
    fileMock.Setup(_ => _.ContentDisposition).Returns(string.Format("inline; filename={0}", fileName));
    //...setup other members as needed.

    var sut = new MyController();
    var file = fileMock.Object;

    // Act.
    var result = await sut.Upload(file);

    //Assert.
    Assert.IsInstanceOfType(result, typeof(IActionResult));
}

The arranging of the mock can be even extracted into an extension method for reuse.

public static IFormFile AsMockIFormFile(this FileInfo physicalFile) {
    var fileMock = new Mock<IFormFile>();
    var ms = new MemoryStream();
    var writer = new StreamWriter(ms);
    writer.Write(physicalFile.OpenRead());
    writer.Flush();
    ms.Position = 0;
    var fileName = physicalFile.Name;
    //Setup mock file using info from physical file
    fileMock.Setup(_ => _.FileName).Returns(fileName);
    fileMock.Setup(_ => _.Length).Returns(ms.Length);
    fileMock.Setup(m => m.OpenReadStream()).Returns(ms);
    fileMock.Setup(m => m.ContentDisposition).Returns(string.Format("inline; filename={0}", fileName));
    //...setup other members (code removed for brevity)


    return fileMock.Object;
}

and used like

var physicalFile = new FileInfo("filePath");
IFormFile formFile = physicalFile.AsMockIFormFile();