Implement getURL of instance MonadHttp IO

[soulomoon]

Now the builtins.fetchurl would be done
Also I unmask the test files
It might close #258 as real implementation
related #1034

[soulomoon]

It seems a lot of name conflict between Effects.hs and hnix store

[soulomoon]

It's my mistake, the reason is that the addTextToStore and makefixouput use different hash object for hashing a name:

• text: text:sha256:37268335dd6931045bdcdf92623ff819a64244b53d0e746d438797349d4da578:/nix/store:test
• makefixouput: fixed:out:sha256:37268335dd6931045bdcdf92623ff819a64244b53d0e746d438797349d4da578: -> b2ddea1e93007908327ef4403126f8e9caa57c4c3d19ea11e382a5d18e9ede62 -> output:out:sha256:b2ddea1e93007908327ef4403126f8e9caa57c4c3d19ea11e382a5d18e9ede62:/nix/store:test

where 37268335dd6931045bdcdf92623ff819a64244b53d0e746d438797349d4da578 is hash of the content.
Here is the problem, how do I add the text along with fixed output through hnix store

[Anton-Latukha]

You can open hnix-store reports during work.

It is much more malleable, we can shape API there to fit with hnix.

Also would thank if details as in #1051 (comment) would end-up noted in the source code.

[soulomoon]

How nix implement fetchurl break down into(source) :

• download the file content. Native http.
• compute hash and path: It is sufficient to use the current makeFixedOutputPath from hnix-store
• add to store (Implementation under remote store). Current addToStore api from hnix-store lacking functionality to send string to daemon. Current addToStore API from hnix-store is too limited, we should shape it hnix-store#176
• if hash provided, compare the hash

[soulomoon]

hnix-store api for addToStore does seems a bit off comparing to nix, we should shape API as in nix.

[soulomoon]

The work should continue after haskell-nix/hnix-store#177 is merged or haskell-nix/hnix-store#176 is solved.