在供应商目录中使用google.golang.org/grpc时出错

Question

I am having issues using google.golang.org/grpc from vendor directory and I get the below error

cannot use &metadata.HeaderMD (type *"google.golang.org/grpc/metadata".MD) as type *"project1/vendor/google.golang.org/grpc/metadata".MD in argument to grpc.Header

I get the error though I am using the necessary version of the package which I copied from my gopath. But, when I delete the golang.google.org/grpc folder from vendor my project fetches the dependency from gopath and it works fine though the one gopath is a copy of when I have in vendor directory and every other library in vendor directory works fine except grpc.

Answer 1

When you created project1/vendor/google.golang.org/grpc, it means that for packages under project1/..., an import of google.golang.org/gprc/... will be transparently remapped to the vendor version.

Any packages outside of project1 will continue to import the non-vendored google.golang.org/grpc/... packages. While the vendored package might be a copy of the upstream, Go treats them as independent packages. So the types they contain are not equivalent.

What has most likely happened is that one of your non-vendored dependencies imports the grpc package and uses its types in its public API. When you make use of that API from project1, you get the upstream type which can't be assigned to variables using the vendored types.

There's two possible solutions to this problem:

1. Vendor all of your dependencies that make use of what you've already vendored.

2. If you're using Go >= 1.11, switch to the newer Go module build system. This will let you continue to control when you upgrade your dependencies without having the project1/vendor/... tree to confuse the type system.