从base64检查文​​件类型? [英] Checking file type from base64?

问题描述

我有一个带有以下OperationContract的WCF REST服务，可将文件保存在磁盘上:

I have a WCF REST Service with the following OperationContract that saves files on the disk:

[OperationContract] [WebInvoke(UriTemplate = "FileSave", Method = "POST", RequestFormat = WebMessageFormat.Json, ResponseFormat = WebMessageFormat.Json, BodyStyle = WebMessageBodyStyle.WrappedRequest)] ResponseHandler FileSave(string fileName, string fileContent);

[OperationContract] [WebInvoke(UriTemplate = "FileSave", Method = "POST", RequestFormat = WebMessageFormat.Json, ResponseFormat = WebMessageFormat.Json, BodyStyle = WebMessageBodyStyle.WrappedRequest)] ResponseHandler FileSave(string fileName, string fileContent);

通过javascript发送文件-使用HTML File API =>二进制数据=> base-64编码的ASCII字符串(= fileContent在操作合同中已收到)

Files are sent through javascript - using HTML File API => binary data => base-64 encoded ASCII string (=fileContent is recieved in the operation contract)

我想在将文件保存到磁盘之前检查文件类型. 我知道以下解决方案: https://codereview.stackexchange.com/questions/29301/checking- mime-type-from-a-base64-string 但我不确定这是否是最好的方法.另外，我测试了上传多个txt文件，每个文件都有不同的前5个字符.

I want to check the file type before saving the file on the disk. I am aware of the following solution: https://codereview.stackexchange.com/questions/29301/checking-mime-type-from-a-base64-string but I am not sure if it is the best way to go. Also, I have tested uploading several txt files and each one has different first 5 chars.

因此，我正在寻找一个代码片段，其中应包括检查几种常见的文件类型.

So I am looking for a code snippet that would include checking for several common file types.

谢谢您的任何想法

推荐答案

在此处检查此链接:

http://codeanalyse.com/2016/10/02/extracting-file-extension-base64-string/

这将包括检查几种常见的文件类型"

This "would include checking for several common file types"

/// <summary>
/// To demonstrate extraction of file extension from base64 string.
/// </summary>
/// <param name="base64String">base64 string.</param>
/// <returns>Henceforth file extension from string.</returns>
public static string GetFileExtension(string base64String)
{
var data = base64String.Substring(0, 5);

switch (data.ToUpper())
 {
     case "IVBOR":
        return "png";
     case "/9J/4":
         return "jpg";
     case "AAAAF":
         return "mp4";
     case "JVBER":
         return "pdf";
     case "AAABA":
         return "ico";
     case "UMFYI":
         return "rar";
     case "E1XYD":
         return "rtf";
     case "U1PKC":
        return "txt";
     case "MQOWM":
     case "77U/M":
        return "srt";
     default:
        return string.Empty;
 }
}

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