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IPIP-328: JSON and CBOR Response Formats on HTTP Gateways
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| # IPIP-328: JSON and CBOR Response Formats on HTTP Gateways | ||
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| - Start Date: 2022-10-07 | ||
| - Related Issues: | ||
| - [ipfs/in-web-browsers/issues/182] | ||
| - [ipfs/specs/pull/328] | ||
| - [ipfs/kubo/issues/8823] | ||
| - [ipfs/kubo/pull/9335] | ||
| - [ipfs/go-ipfs/issues/7552] | ||
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| ## Summary | ||
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| Add support for the [DAG-JSON], [DAG-CBOR], JSON and CBOR response formats in | ||
| the [HTTP Gateway](../http-gateways/). | ||
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| ## Motivation | ||
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| Currently, the gateway supports requesting data in the [DAG-PB], RAW, [CAR] and | ||
| TAR formats. In addition, it allows for traversing of links encoded through CBOR | ||
| Tag 42, as long as they are intermediate links, and not the final document. | ||
| It works on both DAG-CBOR, and its JSON representation, DAG-JSON. However, it | ||
| should be possible to download deserialized versions of the final JSON/CBOR document | ||
| in raw format (not wrapped in UnixFS). | ||
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| The main functional gap in the IPFS ecosystem is the lack of support for | ||
| non-UnixFS DAGs on HTTP gateways. Users are able to create custom DAGs based on | ||
| traversable DAG-CBOR thanks to [CBOR tag 42 being reserved for CIDs][cbor-42] | ||
| and DAG-JSON documents, but they are unable to load deserialized documents from | ||
| a local gateway, which is severely decreasing the utility of non-UnixFS DAGs. | ||
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| Adding JSON and CBOR response types will also benefit UnixFS. DAG-PB has a | ||
| [logical format][dag-pb-format] which makes it possible to represent a DAG-PB | ||
| directory as a [DAG-JSON] document. This means that, if we support DAG-JSON in | ||
| the gateway, then we would support | ||
| [JSON responses for directory listings][ipfs/go-ipfs/issues/7552], which has been | ||
| requested by our users in the past. | ||
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| In addition, this functionality is already present on the current Kubo CLI. By | ||
| bringing it to the gateways, we provide users with more power when it comes | ||
| to storing and fetching CBOR and JSON in IPFS. | ||
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| ## Detailed design | ||
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| The solution is to allow the Gateway to support serializing data as [DAG-JSON], | ||
| [DAG-CBOR], JSON and CBOR by requesting them using either the `Accept` HTTP header | ||
| or the `format` URL query. In addition, if the resolved CID is of one of the | ||
| aforementioned types, the gateway should be able to resolve them instead of | ||
| failing with `node type unknown`. | ||
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| ## Test fixtures | ||
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| - [`bafybeiegxwlgmoh2cny7qlolykdf7aq7g6dlommarldrbm7c4hbckhfcke`][f-dag-pb] is a | ||
| DAG-PB directory. | ||
| - [`bafkreidmwhhm6myajxlpu7kofe3aqwf4ezxxn46cp5fko7mb6x74g4k5nm`][f-dag-pb-json] | ||
| is the aforementioned DAG-PB directory's [Logical DAG-JSON representation][dag-pb-format] that | ||
| is expected to be returned when using `?format=dag-json`. | ||
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| ## Design rationale | ||
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| The current gateway already supports different response formats via the | ||
| `Accept` HTTP header and the `format` URL query. This IPIP proposes adding | ||
| JSON and CBOR formats to that list. | ||
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| In addition, the current gateway already supports traversing through DAG-CBOR | ||
| and DAG-JSON links if they are intermediary documents. With this IPIP, we aim | ||
| to be able to download the DAG-CBOR, DAG-JSON, JSON and CBOR documents | ||
| themselves, with correct `Content-Type` headers. | ||
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| ### User benefit | ||
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| The user benefits from this change as they will now be able to retrieve | ||
| content encoded in the traversable DAG-JSON and DAG-CBOR formats. This is | ||
| something that has been [requested before][ipfs/go-ipfs/issues/7552]. | ||
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| In addition, both UX and DX are significantly improved, since every UnixFS directory can | ||
| now be inspected in a regular web browser via `?format=json`. This can remove the | ||
| need for parsing HTML with directory listing. | ||
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| ### Compatibility | ||
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| This IPIP adds new response types and does not modify existing ones, | ||
| making it a backwards-compatible change. | ||
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| ### Security | ||
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| Serializers and deserializers for the JSON and CBOR must follow the security | ||
| considerations of the original specifications, found in: | ||
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| - [RFC 8259 (JSON), Section 12][rfc8259-sec12] | ||
| - [RFC 8949 (CBOR), Section 10][rfc8949-sec10] | ||
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| DAG-JSON and DAG-CBOR follow the same security considerations as JSON and CBOR. | ||
| Note that DAG-JSON and DAG-CBOR are stricter subsets of JSON and CBOR, respectively. | ||
| Therefore they must follow their specification and error if the payload is not | ||
| strict enough: | ||
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| - [DAG-JSON Spec][dag-json-spec] | ||
| - [DAG-CBOR Spec][dag-cbor-spec] | ||
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| ### Alternatives | ||
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| #### Why four content types? | ||
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| If we do not introduce DAG-JSON, DAG-CBOR, JSON and CBOR response formats in | ||
| the gateway, the usage of IPFS is constricted to files and directories represented | ||
| by UnixFS (DAG-PB) codec. Therefore, if a user wants to store JSON and/or CBOR | ||
| in IPFS, they have to wrap it as a UnixFS file in order to be able to fetch it | ||
| through the gateway. That adds size and processing overhead. | ||
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| In addition, we could introduce only DAG-JSON and DAG-CBOR. However, not | ||
| supporting the generic variants, JSON and CBOR, would lead to poor UX. The | ||
| ability to retrieve DAG-JSON as `application/json` is an important step | ||
| for the interoperability of the HTTP Gateway with web browsers and other tools | ||
| that expect specific Content Types. Namely, `Content-Type: application/json` with | ||
| `Content-Disposition: inline` allows for JSON preview to be rendered in a web browser | ||
| and webdev tools. | ||
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| #### Why JSON/CBOR pathing is limited to full blocks? | ||
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| Finally, we considered supporting pathing within both DAG and non-DAG variants | ||
| of the JSON and CBOR codecs. Pathing within these documents could lead to responses | ||
| with extracts from the document. For example, if we have the document: | ||
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| ```json | ||
| { | ||
| "link" { | ||
| "to": { | ||
| "some": { | ||
| "cid2": <cbor tag 42 pointing at different CID> | ||
| } | ||
| } | ||
| } | ||
| } | ||
| ``` | ||
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| With CID `bafy`, and we navigate to `/ipfs/bafy/link/to`, we would be able to | ||
| retrieve an extract from the document. | ||
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| ```json | ||
| { | ||
| "some": { | ||
| "cid2": <cbor tag 42 pointing at different CID> | ||
| } | ||
| } | ||
| ``` | ||
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| However, supporting this raises questions whose answers are not clearly defined | ||
| or agreed upon yet. Right now, pathing is only supported over CID-based Links, | ||
| such as Tag 42 in CBOR. In addition, some HTTP headers regarding caching are based | ||
| on the CID, and adding extraction pathings would not be clear. Giving users the | ||
| possibility to retrieve JSON, CBOR, DAG-JSON AND DAG-CBOR documents through the | ||
| gateway is, in itself, a progress and will open the doors for new tools and explorations. | ||
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| ### Copyright | ||
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| Copyright and related rights waived via [CC0](https://creativecommons.org/publicdomain/zero/1.0/). | ||
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| [cbor-42]: https://github.com/core-wg/yang-cbor/issues/13#issuecomment-524378859 | ||
| [DAG-PB]: https://ipld.io/docs/codecs/known/dag-pb/ | ||
| [dag-pb-format]: https://ipld.io/specs/codecs/dag-pb/spec/#logical-format | ||
| [DAG-JSON]: https://ipld.io/docs/codecs/known/dag-json/ | ||
| [DAG-CBOR]: https://ipld.io/docs/codecs/known/dag-cbor/ | ||
| [CAR]: https://ipld.io/specs/transport/car/ | ||
| [ipfs/in-web-browsers/issues/182]: https://github.com/ipfs/in-web-browsers/issues/182 | ||
| [ipfs/specs/pull/328]: https://github.com/ipfs/specs/pull/328 | ||
| [ipfs/kubo/issues/8823]: https://github.com/ipfs/kubo/issues/8823 | ||
| [ipfs/kubo/pull/9335]: https://github.com/ipfs/kubo/pull/9335 | ||
| [ipfs/go-ipfs/issues/7552]: https://github.com/ipfs/go-ipfs/issues/7552 | ||
| [f-dag-pb]: https://dweb.link/ipfs/bafybeiegxwlgmoh2cny7qlolykdf7aq7g6dlommarldrbm7c4hbckhfcke | ||
| [f-dag-pb-json]: https://dweb.link/ipfs/bafkreidmwhhm6myajxlpu7kofe3aqwf4ezxxn46cp5fko7mb6x74g4k5nm | ||
| [rfc8259-sec12]: https://datatracker.ietf.org/doc/html/rfc8259#section-12 | ||
| [rfc8949-sec10]: https://datatracker.ietf.org/doc/html/rfc8949#section-10 | ||
| [dag-json-spec]: https://ipld.io/specs/codecs/dag-json/spec/ | ||
| [dag-cbor-spec]: https://ipld.io/specs/codecs/dag-cbor/spec/ |
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