Split gRPC and HTTP error utility into seperate packages

[austinvazquez]

Issue:

#4

Description:

By having a seperate packages, users can consume base package without pulling gRPC or HTTP as a dependency if not required.

This approach creates errgrpc and errhttp. The imports for users would be the following:

import (
    "github.com/containerd/errdefs"
    "github.com/containerd/errdefs/errgrpc"
    "github.com/containerd/errdefs/errhttp"
)

Other approaches considered:

Top level grpc and http packages. The imports for users would be the following:

import (
    "github.com/containerd/errdefs"
    "github.com/containerd/errdefs/grpc"
    "github.com/containerd/errdefs/http"
)

My thought was this may clutter the top level directory, but this may be acceptable as the number of protocol packages would be finite.

Testing:

Adds basic unit tests for there and back again error conversions for gRPC and HTTP error packages.

[AkihiroSuda]

errdefs.FromGRPC should be now called like grpc.ToNative ?

[austinvazquez]

Yeah, grpc.FromGRPC can be redundant. grpc.ToNative is nice naming imo. Pushed to try it out.

[cpuguy83]

Nit: maybe grpcerror or something?
I just dislike having package name conflicts that makes goimports trip up.

[dmcgowan]

Thanks for doing the split

Top level grpc and http packages. The imports for users would be the following:

+1 to keeping it at the top. I see pkg more for packages that could live on their own or not directly extending the root package.

Nit: maybe grpcerror or something?

+1 for keeping err (or error) in the package name (not the directory name). Maybe to be like...

import (
    "github.com/containerd/errdefs"
    errgrpc "github.com/containerd/errdefs/grpc"
    errhttp "github.com/containerd/errdefs/http"
)

?

@cpuguy83 that what you were thinking?

[cpuguy83]

Not really, but that's fine.
For me I just end up fighting with goimports constantly with packages that have the same name and have to manually write the import statement.

[austinvazquez]

@cpuguy83, @dmcgowan thanks for the suggestions. Pushed changes to address. Landed with errXXX package naming to avoid conflicts with common packages like http and grpc. LMK your thoughts.

[dmcgowan]

Ok, works for me