How Can I Determine a File's MIME Type Using its Signature in .NET?

<.> Use the file signature in the .NET to determine the file type of the file

In many cases, the type of MIME in accurately identifying files is very important, especially when the file extension is incorrect or does not exist. .NET provided a general solution for this.

In .NET, developers can use the

function in the URLmon.dll library. This function uses a signature solution to determine the MIME type of the file.

FindMimeFromData To achieve this technology, please follow the steps below:

Introduce the necessary naming space:

1. <code class="language-csharp"> using System.Runtime.InteropServices;</code>

Initialization buffer:

2. <code class="language-csharp"> byte[] buffer = new byte[256];</code>

Read the file data into the buffer:

3. <code class="language-csharp"> using (FileStream fs = new FileStream(filename, FileMode.Open))
    {
        if (fs.Length >= 256)
            fs.Read(buffer, 0, 256);
        else
            fs.Read(buffer, 0, (int)fs.Length);
    }</code>

Call Function to retrieve MIME type:

4. FindMimeFromData

   <code class="language-csharp"> uint mimetype;
    FindMimeFromData(0, null, buffer, 256, null, 0, out mimetype, 0);
    IntPtr mimeTypePtr = new IntPtr((int)mimetype); // 修正：将mimetype强制转换为int
    string mime = Marshal.PtrToStringUni(mimeTypePtr);
    Marshal.FreeCoTaskMem(mimeTypePtr);</code>

   Back the MIME type as a string.

5. By implementing this solution, developers can reliably determine the MIME type of the file based on the signature of the file, regardless of the file extension. This technology is very valuable in various applications, including file upload processing and content delivery.

Improvement description:

In the original code

There are potential problems, because

is the type, and the constructor accepts the new IntPtr(mimetype) type. The modified code converts to mimetype to ensure compatibility. This is especially important when dealing with .NET implementation of different platforms. UInt32

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