Merge pull request #466 from ipfs/response-headers

/routing/v1: add missing HTTP cache headers

src/routing/http-routing-v1.md

@@ -4,7 +4,7 @@ description: >
   Delegated routing is a mechanism for IPFS implementations to use for offloading
   content routing, peer routing and naming to another process/server. This specification describes
   an HTTP API for delegated routing of content, peers, and IPNS.
-date: 2023-08-31
+date: 2024-03-22
 maturity: reliable
 editors:
   - name: Gus Eggert
@@ -71,6 +71,17 @@ This API uses a standard version prefix in the path, such as `/v1/...`. If a bac
 - `404` (Not Found): must be returned if no matching records are found.
 - `422` (Unprocessable Entity): request does not conform to schema or semantic constraints.
 
+#### Response Headers
+
+- `Content-Type`: the content type of this response, which MUST be `application/json` or `application/x-ndjson` (see [streaming](#streaming)).
+- `Last-Modified`: an HTTP-date timestamp ([RFC9110, Section 5.6.7](https://www.rfc-editor.org/rfc/rfc9110#section-5.6.7)) of the resolution, allowing HTTP proxies and CDNs to support inexpensive update checks via `If-Modified-Since`
+- `Cache-Control: public, max-age={ttl}, public, stale-while-revalidate={max-ttl}, stale-if-error={max-ttl}`: meaningful cache TTL returned with the response.
+  - The `max-age` SHOULD be shorter for responses whose resolution ended in no results (e.g. 15 seconds),
+    and longer for responses that have results (e.g. 5 minutes).
+  - Implementations SHOULD include `max-ttl`, set to the maximum cache window of the underlying routing system.
+    For example, if Amino DHT results are returned, `stale-while-revalidate` SHOULD be set to `172800` (48h, which at the time of writing this specification, is the provider record expiration window).
+- `Vary: Accept`: allows intermediate caches to play nicely with the different possible content types.
+
 #### Response Body
 
 ```json
@@ -108,6 +119,17 @@ represented as a CIDv1 encoded with `libp2p-key` codec.
 - `404` (Not Found): must be returned if no matching records are found.
 - `422` (Unprocessable Entity): request does not conform to schema or semantic constraints.
 
+#### Response Headers
+
+- `Content-Type`: the content type of this response, which MUST be `application/json` or `application/x-ndjson` (see [streaming](#streaming)).
+- `Last-Modified`: an HTTP-date timestamp ([RFC9110, Section 5.6.7](https://www.rfc-editor.org/rfc/rfc9110#section-5.6.7)) of the resolution, allowing HTTP proxies and CDNs to support inexpensive update checks via `If-Modified-Since`
+- `Cache-Control: public, max-age={ttl}, public, stale-while-revalidate={max-ttl}, stale-if-error={max-ttl}`: meaningful cache TTL returned with the response.
+  - When present, `ttl` SHOULD be shorter for responses whose resolution ended in no results (e.g. 15 seconds),
+    and longer for responses that have results (e.g. 5 minutes).
+  - Implementations SHOULD include `max-ttl`, set to the maximum cache window of the underlying routing system.
+    For example, if Amino DHT results are returned, `stale-while-revalidate` SHOULD be set to `172800` (48h, which at the time of writing this specification, is the provider record expiration window).
+- `Vary: Accept`: allows intermediate caches to play nicely with the different possible content types.
+
 #### Response Body
 
 ```json
@@ -148,7 +170,12 @@ Each object in the `Peers` list is a record conforming to the [Peer Schema](#pee
 #### Response Headers
 
 - `Etag`: a globally unique opaque string used for HTTP caching. MUST be derived from the protobuf record returned in the body.
-- `Cache-Control: max-age={TTL}`: cache TTL returned with :ref[IPNS Record] that has `IpnsEntry.data[TTL] > 0`. When present, SHOULD match the TTL value from the record. When record was not found (HTTP 404) or has no TTL (value is `0`), implementation SHOULD default to `max-age=60`.
+- `Cache-Control: public, max-age={ttl}, public, stale-while-revalidate={sig-ttl}, stale-if-error={sig-ttl}`: meaningful cache TTL returned with :ref[IPNS Record]
+  - The `max-age` value in seconds SHOULD match duration from `IpnsEntry.data[TTL]`, if present and bigger than `0`. Otherwise, implementation SHOULD default to `max-age=60`.
+  - Implementations SHOULD include `sig-ttl`, set to the remaining number of seconds the returned IPNS Record is valid.
+- `Expires:`: an HTTP-date timestamp ([RFC9110, Section 5.6.7](https://www.rfc-editor.org/rfc/rfc9110#section-5.6.7)) when the validity of IPNS Record expires (if `ValidityType=0`, when signature expires)
+- `Last-Modified`: an HTTP-date timestamp of when cacheable resolution occured: allows HTTP proxies and CDNs to support inexpensive update checks via `If-Modified-Since`
+- `Vary: Accept`: allows intermediate caches to play nicely with the different possible content types.
 
 #### Response Body