LinkedIn用户头像URL参数含义咨询（含t参数）及ASP.NET Core优化

Let's break down what each parameter in that LinkedIn image URL does, then figure out how to stop those unnecessary database updates from happening.

What Do Those URL Parameters Mean? #

Looking at your example URL:

https://media.licdn.com/dms/image/A1205CPGrwDzHZS_Apr/profile-originalphoto-shrink_900_1200/0?e=1525989600&v=beta&t=PNuO2bh5rNrIJv19PN1OXOjzDWcQgKdYCl1-ZVzgPOw

Here's the breakdown of each query parameter:

• e: This is a Unix timestamp (in seconds) marking when the URL expires. Once that time passes, the URL will no longer work—LinkedIn uses this to limit how long direct image links are valid.
• v: This denotes the version of LinkedIn's media API being used. Your example uses beta, which means you're hitting their pre-release API endpoint.
• t: This is a unique signature token, not a timestamp. LinkedIn generates this for each request to validate that the image access is authorized. It changes every time you fetch the URL, even if the underlying image is exactly the same. That's why you're seeing different URLs for the same avatar.

Fixing the Unnecessary Database Updates #

Since the t (and e) parameters change on every request but don't mean the avatar itself has changed, you need a way to compare the actual avatar identity instead of the full URL. Here are a few solid approaches:

1. Extract the Stable Image ID #

The most reliable method is to pull out the unique image identifier from the URL path. In your example, that's A1205CPGrwDzHZS_Apr—this ID stays the same as long as the user doesn't upload a new avatar.

The URL path follows this pattern: /dms/image/{IMAGE_ID}/profile-originalphoto-{SIZE}/0

You can extract this ID in C# with something like:

var avatarUrl = "your-linkedin-image-url-here";
var uri = new Uri(avatarUrl);
var pathSegments = uri.Segments;
// The image ID is the 3rd segment (index 3) after trimming the trailing slash
var imageId = pathSegments[3].TrimEnd('/');

Store this imageId in your database instead of (or alongside) the full URL. When a user logs in, compare the new image ID to the stored one—only update the database if the ID differs (meaning the user actually changed their avatar).

2. Compare the Base URL (Excluding Dynamic Params) #

If you prefer to keep using the full URL, you can strip out the dynamic t and e parameters before comparing. For example, compare only the path part of the URL:

https://media.licdn.com/dms/image/A1205CPGrwDzHZS_Apr/profile-originalphoto-shrink_900_1200/0

Just note that if LinkedIn returns different image sizes (like a thumbnail vs original), the path will change too—so this works best if you're consistently fetching the same size of avatar.

3. Use LinkedIn's API to Check for Avatar Changes #

If your app has the right permissions, you can call LinkedIn's User Profile API to get metadata about the avatar, like a last-modified timestamp or a content hash. Use that metadata to determine if the avatar has actually been updated, instead of relying on the URL itself.

内容的提问来源于stack exchange，提问作者Sam