Support creating operator from URL

[Xuanwo]

Discussed in #1494

^{Originally posted by frostming March 7, 2023}

Proposal

I propose an alternative approach to create an opendal Operator -- from a resource URI(or URL? either is good) string.

I am new to OpenDAL and feel free to close it if it is already a thing -- That's great!

Examples:

let op = Operator::from_uri("file:///tmp")?.finish();

This does the same as

let mut builder = Fs::default();
builder.root("/tmp");
let op: Operator = Operator::create(builder)?.finish();

Another example, HDFS:

let op = Operator::from_uri("hdfs://127.0.0.1:9000/tmp")?.finish();

Advantages

• Of course, this can save us a few lines of initialization code.
• This will also make the configuration easier -- only one config line is needed.
• Language bindings can choose to not expose Builder structs at all. For a minimal interface, an Operator struct is sufficient, service backends can be set up with a primitive string. This will significantly save the effort of supporting a new language.

Possible Solutions

We already have a unique Scheme for each Builder, we can give them a unique URL prefix. The URI will be encoded as follows:

$scheme://$positional_arg1/$positional_arg2?arg1=value1&arg2=value2

Where positional arguments are required parameters for the specific service, such as root for Fs. Specifically, the URI will be parsed with Url::parse, and the query_pairs will be fed to the ::from_iter() method of the corresponding Builder to get a builder object. Thanks to the good API design of OpenDAL, these APIs are ready to do this.

Be aware because all values are URL components, they must be percent-encoded.

Some concerns

For some services that use URL as the parameter themselves, such as IPFS, the resource URI will be a bit different:

ipfs://...... # for http endpoint
ipfss://...... # for https endpoint

And there can be multiple schemes map to the same builder. Both http:// and https:// map to HTTP builder.

This might cause some confusion, so I will leave it to the maintainers to make the choice of how this feature will go.

[jorgehermo9]

Hi, I'm interested in addressing this. Did you start working on this @Xuanwo ? apache/hudi-rs#131 (comment)

[Xuanwo]

Hi, I'm interested in addressing this. Did you start working on this @Xuanwo ? apache/hudi-rs#131 (comment)

Hi, thank you very much for your interest. I'm currently working on a design for this.