docs(gateway) clarify scope of blocks in car responses #489
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SgtPooki
approved these changes
Feb 3, 2025
2color
reviewed
Feb 4, 2025
| @@ -151,8 +151,8 @@ content type parameters. | |||
| For example: | |||
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| - [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://en.wikipedia.org/wiki/Tar_(computing)) – returns UnixFS tree (files and directories) as a [TAR](https://en.wikipedia.org/wiki/Tar_(computing)) stream. Returned tree starts at a root item which name is the same as the requested CID. Produces 400 Bad Request for content that is not UnixFS. | |||
| - [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 with implicit or explicit [`dag-scope`](https://specs.ipfs.tech/http-gateways/trustless-gateway/#dag-scope-request-query-parameter) for blocks at the terminus of the specified path and the blocks required to traverse path segments from root CID to the terminus. | |||
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I find this line and how dag-scope influences it to be a bit confusing.
- If you don't pass an explicit
dag-scopeit will default toall, returning the terminus block the "entire contiguous DAG that begins at the end of the path query". But what is meant by that?
For example: if you request application/vnd.ipld.car with the path bafy...jomu/assets/logo.png in the following DAG
How will dag-scope influence the response?
all: root blockbafy...jomu,assetsdir blockbafy...idcm, logo.png blockbafy...wwoiand raw data blocks.block: This would need the same blocks asallin order to "verify the specified path segments."
What am I misunderstanding?
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correct on all, you get 7 blocks
block gives you the same as all minus the children of bafy...wwoi, so 3 blocks, you're asking it specifically for the bafy...wwoi block but the protocol gives you a trustless/verifiable path from the CID you've given it down to that particular block.
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Aims to close #488 by reiterating at https://specs.ipfs.tech/http-gateways/path-gateway/#accept-request-header what we have in https://specs.ipfs.tech/http-gateways/trustless-gateway/#dag-scope-request-query-parameter
TLDR is that we ALWAYS include parents in CAR responses (/ipfs/cid/foo/bar will include
bardag + minimal set of blocks to walk fromcid→foo→bar)While we are at it, lmk if https://specs.ipfs.tech/http-gateways/trustless-gateway/#dag-scope-request-query-parameter can be improved as well.