MIME type is a mechanism by which the server identifies file content types, and missing or incorrect configuration can cause resource loading to fail. There are two main ways to manage MIME types with specific extensions in IIS: 1. Add or modify them through the IIS manager graphical interface; 2. Configure in the web.config file. Common MIME types that need to be added manually include .webmanifest, .woff2, .svg, .mp4 and .pdf. Notes include inheritance issues, IIS version differences and browser cache impact. Proper configuration is essential to ensure that modern web resources are loading properly.

Managing MIME types for specific file extensions in IIS is mainly to ensure that the server can correctly identify and send file content to the browser. If you encounter some static resources (such as .webmanifest or .woff2) that cannot be loaded, it is likely that it is caused by missing or errors in the MIME type configuration.

What is the MIME type?

The MIME (Multipurpose Internet Mail Extensions) type is a way the server uses to tell the browser the current response content type. For example:

• .html file corresponds to text/html
• .jpg image corresponding to image/jpeg

If a file extension does not have a corresponding MIME type, IIS may not send it by default, or use application/octet-stream instead, which will cause the browser to refuse to load certain resources, especially font files or PWA-related files.

How to add or modify MIME types in IIS?

You can manage MIME types in two ways: use the IIS Manager graphical interface, or edit the web.config file directly.

Method 1: Set up through IIS Manager

1. Open IIS Manager
2. Select the site or application you want to configure
3. Double-click the MIME Type icon
4. Click "Add" in the action bar on the right
5. Enter the extension and the corresponding MIME type, such as:
   • Extension: .woff2
   • MIME type: font/woff2

Note: If you already have a MIME type with a certain extension, remember to delete it first and then add a new one, otherwise it may conflict.

Method 2: Config configuration file through web.config

If you want to configure the following project deployment, it is recommended to add the following configuration segment in web.config :

 <configuration>
  <system.webServer>
    <staticContent>
      <mimeMap fileExtension=".webmanifest" mimeType="application/manifest json" />
      <mimeMap fileExtension=".woff2" mimeType="font/woff2" />
    </staticContent>
  </system.webServer>
</configuration>

This can avoid repeated configurations on different servers and facilitate version control.

Common MIME types that need to be added manually

Some modern web technologies use file formats that are not supported by default on the old version of IIS, and common ones include:

• .webmanifest → application/manifest json
• .woff2 → font/woff2
• .svg (used as an image) → image/svg xml
• .mp4 → video/mp4
• .pdf → application/pdf

If some resources are denied loading after your application is deployed, especially fonts, PWA manifests, videos and other resources, the first reaction should be to check whether these extensions are configured with the correct MIME type.

Notes and FAQs

• Inheritance problem : If you set the MIME type at the site level, if the child application does not have its own web.config , it will inherit the parent configuration. Sometimes this can cause unexpected behavior.
• IIS version difference : The default MIME types supported by different versions of IIS are slightly different, and it is best to confirm the target environment before deployment.
• Caching problem : After changing the MIME type, the browser may still report an error because the cache is still reported. It is recommended to clear the cache or use in incognito mode to test.

Basically that's it. Although configuring MIME types seems simple, it is one of the key points that are easily overlooked during deployment.

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