HTTP Conditional Request middleware for Fetch API.
Middleware for HTTP Conditional Requests.
It conditionally processes a HTTP request based on a precondition.
It compliant with RFC 9110, 13. Conditional Requests.
For a definition of Universal HTTP middleware, see the http-middleware project.
Middleware factory is exported by default.
To evaluate precondition, you need to provide a function to retrieve the selected representation.
The following example evaluates the If-None-Match precondition and controls
the handler.
import conditionalRequests from "https://deno.land/x/http_conditional_requests@$VERSION/mod.ts";
import { assertEquals } from "https://deno.land/std/testing/asserts.ts";
import { assertSpyCalls, spy } from "https://deno.land/std/testing/mock.ts";
const selectedRepresentation = new Response("<body>", {
headers: { etag: "<etag>" },
});
const selectRepresentation = spy(() => selectedRepresentation);
const middleware = conditionalRequests(selectRepresentation);
const conditionalRequest = new Request("<uri>", {
headers: { "if-none-match": "<etag>" },
});
const handler = spy(() => selectedRepresentation);
const response = await middleware(conditionalRequest, handler);
assertSpyCalls(handler, 0);
assertSpyCalls(selectRepresentation, 1);
assertEquals(response.status, 304);RFC 9110, 13.1. Preconditions compliant and supports the following precondition:
- If-Match
- If-None-Match
- If-Modified-Since
- If-Unmodified-Since
If multiple precondition headers are present, precondition is processed according to precedence.
Middleware will effect following:
- HTTP response status
Middleware will execute only if the following conditions are met:
- The precondition header exists
If-Match- The
ETagheader exist
- The
If-None-Match- The
ETagheader exist
- The
If-Modified-Since- The
Last-Modifiedheader exist
- The
If-Unmodified-Since- The
Last-Modifiedheader exist
- The
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