Add function to determine the size of final unixfs DAG given raw bytes

[masih]

It would be fantastic to have a function that given the size of raw bytes would cheaply and quickly calculate the size of the final unixfs DAG. This would be useful in cases where the final DAG will be written out into a fixed sized bucket and the user wants to guarantee that each bucket will have the full raw bytes, e.g., FileCoin pieces of size 32GiB.

Other uses of this include pre-allocation of resources or more efficient buffer management depending on the final DAG size for large-scale data intensive applications.

[willscott]

is what you want the size of the dag when serialized as a car? (including a carv1 header?)

[masih]

CAR sections only, for a given LinkPrototype please (though I see that's fixed?, which is fine).

[willscott]

• Is there a reason not to include the carv1 header?

• there are fixed expected cid prefixes for both the raw leaves and intermediate nodes. both types of cids used serialize to 36 bytes.

[masih]

Is there a reason not to include the carv1 header?

In my specific usecase, a CAR may contain multiple unixfs DAGs.