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Conditional Requests#

There are built-in utilities for handling conditional requests, which serve two broad purposes:

  1. Sparing bandwidth on reading a document that has not changed, i.e. "only send if the version is different from what I already have".
  2. Preventing multiple writers from clobbering each other's changes, i.e. "only save if the version on the server matches what I saw last".

Adding support for handling conditional requests requires four steps:

  1. Import the package.
  2. (optional) Add the response definition (304 Not Modified for reads or 412 Precondition Failed for writes)
  3. Add conditional.Params to your input struct.
  4. Check if conditional params were passed and handle them. The HasConditionalParams() and PreconditionFailed(...) methods can help with this.


Implementing a conditional read might look like:

huma.Register(api, huma.Operation{
	OperationID: "get-resource",
	Method:      http.MethodGet,
	Path:        "/resource",
	Summary:     "Get a resource",
}, func(ctx context.Context, input struct {
}) (*YourOutput, error) {
	if input.HasConditionalParams() {
		// TODO: Get the ETag and last modified time from the resource.
		etag := ""
		modified := time.Time{}

		// If preconditions fail, abort the request processing. Response status
		// codes are already set for you, but you can optionally provide a body.
		// Returns an HTTP 304 not modified.
		if err := input.PreconditionFailed(etag, modified); err != nil {
			return err

		// Otherwise do the normal request processing here...
		// ...

Conditional Request Efficiency

Note that it is more efficient to construct custom DB queries to handle conditional requests, however Huma is not aware of your database. The built-in conditional utilities are designed to be generic and work with any data source, and are a quick and easy way to get started with conditional request handling.

Dive Deeper#