docs: add TAR format

IPIP/0000-gateway-tar-response-format.md

@@ -0,0 +1,63 @@
+# IPIP 0000: Gateway TAR Response Format
+
+- Start Date: (format: 2022-10-10)
+- Related Issues:
+  - https://github.com/ipfs/specs/pull/288
+  - https://github.com/ipfs/go-ipfs/pull/9029
+  - https://github.com/ipfs/go-ipfs/pull/9034
+
+# Summary
+
+Add TAR as a response format for the HTTP Gateway.
+
+# Motivation
+
+Currently, the HTTP Gateway only allows the download of single files, or
+CAR archives. However, CAR files are sometimes not necessary and user may
+want to download entire directories. An example use case is for the IPFS
+Web UI, where users are able to download files or directories.
+
+# Detailed design
+
+The solution is to allow the Gateway to support producing TAR archives
+by requesting them using either the `Accept` HTTP header or the `format`
+URL query.
+
+## Test fixtures
+
+Existing `curl` and `tar` tools can be used by implementers for testing.
+
+Providing static test vectors has little value here, as different TAR libraries may produce
+different byte-to-byte files  due to unspecified ordering of files and directories inside.
+
+## Design rationale
+
+The current gateway already supports different response formats via the
+`Accept` HTTP header and the `format` URL query. This RFC proposes adding
+one more supported format to that list.
+
+### User benefit
+
+Users will be able to directly download UnixFs directories from the gateway. In the Web UI,
+for example, we will be able to create a direct link to download the file, instead of using the
+API to put the whole file in memory before downloading it, saving resources and avoiding bugs.
+
+CLI users will be able to download a directory with existing tools like `curl` and `tar`.
+
+### Compatibility
+
+This RFC is backwards compatible .
+
+### Security
+
+See below.
+
+### Alternatives
+
+An alternative was considered to also support [Gzipped TAR](https://github.com/ipfs/go-ipfs/pull/9034).
+However, there is a concern that that may be a vector for DOS attacks since compression requires
+high CPU power.
+
+### Copyright
+
+Copyright and related rights waived via [CC0](https://creativecommons.org/publicdomain/zero/1.0/).

http-gateways/PATH_GATEWAY.md

@@ -174,6 +174,7 @@ For example:
 
 - [application/vnd.ipld.raw](https://www.iana.org/assignments/media-types/application/vnd.ipld.raw) – disables [IPLD codec deserialization](https://ipld.io/docs/codecs/), requests a verifiable raw [block](https://docs.ipfs.io/concepts/glossary/#block) to be returned
 - [application/vnd.ipld.car](https://www.iana.org/assignments/media-types/application/vnd.ipld.car) – disables [IPLD codec deserialization](https://ipld.io/docs/codecs/), requests a verifiable [CAR](https://docs.ipfs.io/concepts/glossary/#car) stream to be returned
+- [application/x-tar](https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/MIME_types/Common_types) – disables [IPLD codec deserialization](https://ipld.io/docs/codecs/), requests a [TAR](https://en.wikipedia.org/wiki/Tar_(computing)) archive to be returned
 <!-- TODO: https://github.com/ipfs/go-ipfs/issues/8823
 - application/vnd.ipld.dag-json OR application/json – requests IPLD Data Model representation serialized into [DAG-JSON format](https://ipld.io/docs/codecs/known/dag-json/)
 - application/vnd.ipld.dag-cbor OR application/cbor - requests IPLD Data Model representation serialized into [DAG-CBOR format](https://ipld.io/docs/codecs/known/dag-cbor/)
@@ -241,7 +242,9 @@ Optional, `format=<format>` can be used to request specific response format.
 
 This is a URL-friendly alternative to sending
 `Accept: application/vnd.ipld.<format>` header, see [`Accept`](#accept-request-header)
-for more details.
+for more details. 
+
+In case of `Accept: application/x-tar`, the `?format=` equivalent is `tar`.
 
 <!-- TODO Planned: https://github.com/ipfs/go-ipfs/issues/8769
 - `selector=<cid>`  can be used for passing a CID with [IPLD selector](https://ipld.io/specs/selectors)