The 428 Precondition Required is an HTTP status code that indicates a server requires specific conditions to be met before processing a request. This 428 status code was introduced to prevent “lost update” problems when multiple clients try to modify a resource simultaneously.
When you encounter a 428 HTTP response, it means the server needs the client to include certain preconditions in their request headers, typically using the If-Match or If-Unmodified-Since headers.
What Causes the 428 Precondition Required?
The 428 status typically occurs in situations where data consistency is crucial. Common causes include:
- When a client attempts to update a resource without checking if it has been modified since their last retrieval, the server enforces the precondition to prevent accidental overwrites of changes made by other users.
- In scenarios where multiple users or applications might modify the same resource concurrently, the server requires precondition headers to maintain data integrity.
- When working with critical systems where data accuracy is important, like financial transactions or inventory management, servers may enforce the 428 Precondition Required to ensure safe updates.
Example
Request:
PUT /api/products/123 HTTP/1.1
Host: example.com
Content-Type: application/json
{
"name": "Updated Product Name",
"price": 29.99
}
Response:
HTTP/1.1 428 Precondition Required
Content-Type: application/json
Date: Sat, 11 Jan 2025 12:00:00 GMT
{
"error": "428 Precondition Required",
"message": "This request requires a precondition. Please include an If-Match header with the current ETag of the resource.",
"required_header": "If-Match"
}
In this example, the server requires the client to include an If-Match header with the current ETag of the product before allowing the update.
This ensures that the client is working with the most recent version of the resource and prevents unintended overwrites of data modified by other users.
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