h2-mod/deps/curl/docs/IPFS.md

IPFS

For an overview about IPFS, visit the IPFS project site.

In IPFS there are two protocols. IPFS and IPNS (their workings are explained in detail here). The ideal way to access data on the IPFS network is through those protocols. For example to access the Big Buck Bunny video the ideal way to access it is like: ipfs://bafybeigagd5nmnn2iys2f3doro7ydrevyr2mzarwidgadawmamiteydbzi

IPFS Gateways

IPFS Gateway acts as a bridge between traditional HTTP clients and IPFS. IPFS Gateway specifications of HTTP semantics can be found here.

Deserialized responses

By default, a gateway acts as a bridge between traditional HTTP clients and IPFS and performs necessary hash verification and deserialization. Through such gateway, users can download files, directories, and other content-addressed data stored with IPFS or IPNS as if they were stored in a traditional web server.

Verifiable responses

By explicitly requesting application/vnd.ipld.raw or application/vnd.ipld.car responses, by means defined in Trustless Gateway Specification, the user is able to fetch raw content-addressed data and perform hash verification themselves.

This enables users to use untrusted, public gateways without worrying they might return invalid/malicious bytes.

IPFS and IPNS protocol handling

There are various ways to access data from the IPFS network. One such way is through the concept of public "gateways". The short version is that entities can offer gateway services. An example here that is hosted by Protocol Labs (who also makes IPFS) is dweb.link and ipfs.io. Both sites expose gateway functionality. Getting a file through ipfs.io looks like this: https://ipfs.io/ipfs/bafybeigagd5nmnn2iys2f3doro7ydrevyr2mzarwidgadawmamiteydbzi

If you were to be running your own IPFS node then you, by default, also have a local gateway running. In it's default configuration the earlier example would then also work in this link: http://127.0.0.1:8080/ipfs/bafybeigagd5nmnn2iys2f3doro7ydrevyr2mzarwidgadawmamiteydbzi

cURL handling of the IPFS protocols

The IPFS integration in cURL hides this gateway logic for you. So instead of providing a full URL to a file on IPFS like this:

curl http://127.0.0.1:8080/ipfs/bafybeigagd5nmnn2iys2f3doro7ydrevyr2mzarwidgadawmamiteydbzi

You can provide it with the IPFS protocol instead:

curl ipfs://bafybeigagd5nmnn2iys2f3doro7ydrevyr2mzarwidgadawmamiteydbzi

With the IPFS protocol way of asking a file, cURL still needs to know the gateway. curl essentially just rewrites the IPFS based URL to a gateway URL.

IPFS_GATEWAY environment variable

If the IPFS_GATEWAY environment variable is found, it's value is used as gateway.

Automatic gateway detection

When you provide no additional details to cURL then cURL will:

1. First look for the IPFS_GATEWAY environment variable and use that if it's set.
2. Look for the file: ~/.ipfs/gateway. If it can find that file then it means that you have a local gateway running and that file contains the URL to your local gateway.

If cURL fails you'll be presented with an error message and a link to this page to the option most applicable to solving the issue.

--ipfs-gateway argument

You can also provide a --ipfs-gateway argument to cURL. This overrules any other gateway setting. curl won't fallback to the other options if the provided gateway didn't work.

Gateway redirects

A gateway could redirect to another place. For example, dweb.link redirects path based requests to subdomain based ones. So a request to:

curl ipfs://bafybeigagd5nmnn2iys2f3doro7ydrevyr2mzarwidgadawmamiteydbzi --ipfs-gateway https://dweb.link

Which would be translated to:

https://dweb.link/ipfs/bafybeigagd5nmnn2iys2f3doro7ydrevyr2mzarwidgadawmamiteydbzi

Will redirect to:

https://bafybeigagd5nmnn2iys2f3doro7ydrevyr2mzarwidgadawmamiteydbzi.ipfs.dweb.link

If you trust this behavior from your gateway of choice then passing the -L option will follow the redirect.

Error messages and hints

Depending on the arguments, cURL could present the user with an error.

Gateway file and environment variable

cURL tried to look for the file: ~/.ipfs/gateway but couldn't find it. It also tried to look for the IPFS_GATEWAY environment variable but couldn't find that either. This happens when no extra arguments are passed to cURL and letting it try to figure it out automatically.

Any IPFS implementation that has gateway support should expose it's URL in ~/.ipfs/gateway. If you are already running a gateway, make sure it exposes the file where cURL expects to find it.

Alternatively you could set the IPFS_GATEWAY environment variable or pass the --ipfs-gateway flag to the cURL command.

Malformed gateway URL

The command executed evaluates in an invalid URL. This could be anywhere in the URL, but a likely point is a wrong gateway URL.

Inspect your URL. Alternatively opt to go for the automatic gateway detection.