On Mon, Oct 25, 2021 at 5:04 PM Daniel P. Berrangé <berrange@redhat.com> wrote:
On Mon, Oct 25, 2021 at 04:45:03PM +0300, Nir Soffer wrote:
I'm playing with libnbd go module, planning to use it in a new command[1]
The biggest obstacle for me is that the module is not published in a way that Go developers expect.
The module is listed in: https://pkg.go.dev/github.com/libguestfs/libnbd/golang
But the module actually lives in: https://github.com/libguestfs/libnbd/tree/master/golang/src/libguestfs.org/l...
So the pkg.go.dev page is broken, .e.g no there is no documation or license, and the suggested import is wrong.
The module name is "libguestfs.org/libnbd". But if you try to use it, for example in the (improved) example from libnbd-golang.pod:
$ cat test.go package main
import "fmt" import "libguestfs.org/libnbd"
func main() { h, err := libnbd.Create() if err != nil { panic(err) } defer h.Close() uri := "nbd://localhost" err = h.ConnectUri(uri) if err != nil { panic(err) } size, err := h.GetSize() if err != nil { panic(err) } fmt.Printf("size of %s = %d\n", uri, size) }
$ go mod init example/test go: creating new go.mod: module example/test go: to add module requirements and sums: go mod tidy
$ go mod tidy go: finding module for package libguestfs.org/libnbd example/test imports libguestfs.org/libnbd: cannot find module providing package libguestfs.org/libnbd: unrecognized import path "libguestfs.org/libnbd": reading https://libguestfs.org/libnbd?go-get=1: 404 Not Found
If we use libguestfs.org, https://libguestfs.org/libnbd?go-get=1 should return the expected metadata instead of 404.
But even if "libguestfs.org/libnbd" would work, we cannot use the module from the source since the source is missing the generated files (wrappers.go, binding.go, ...).
It looks like the only ways to use the module are:
- Vendor the go code from the tarball.
I did not try this since I don't want to copy libnbd into source into my project.
- Clone and build libnbd locally, and replace libguestfs.org with the path to your local source
$ go mod edit -replace libguestfs.org/libnbd=../../src/libnbd/golang/src/libguestfs.org/libnbd $ go mod tidy go: found libguestfs.org/libnbd in libguestfs.org/libnbd v0.0.0-00010101000000-000000000000
$ cat go.mod module example/test
go 1.16
replace libguestfs.org/libnbd => ../../src/libnbd/golang/src/libguestfs.org/libnbd
require libguestfs.org/libnbd v0.0.0-00010101000000-000000000000
But the version is wrong - it should be v1.10.0. I think the issue is missing tag: https://golang.org/ref/mod#vcs-version
If a module is defined in a subdirectory within the repository, that is, the module subdirectory portion of the module path is not empty, then each tag name must be prefixed with the module subdirectory, followed by a slash. For example, the module golang.org/x/tools/gopls is defined in the gopls subdirectory of the repository with root path golang.org/x/tools. The version v0.4.0 of that module must have the tag named gopls/v0.4.0 in that repository.
So the linbd project needs a tag like: golang/src/libguestfs.org/libnbd/v1.10.0
Removing the "src/libguestfs.org" directories will clean things up: golang/libnbd/v1.10.0
Go modules are a bit annoying in that they're effectively designed around the use of semver for versioning. Anything from v2.xxxx onwards means you need to put the module code in sub-directory named after the major version number. This means all your apps need to update their imports any time you change major version.
In libvirt's go modules we had to re-create the git repos with new tags based on semver instead of calver, to get out of the ever changing sub-directory trap.
libnbd is lucky that it is still on v1.xxxx, so isn't in the sub-dir naming trap yet.
I feel like as a general rule life is simpler if the Go code is all in a dedicated repo, completely separate from any other non-Go code, and any auto-generated code is committed too, and wired up such that "go gen" will trigger whatever command is needed to re-generate.
Assuming you don't want to change libnbd build system at all though, you could have a separate git repo where you import the generated Go binding at time of each release. It'll still get a little odd when people want to submit bugs/patches, as they will need to know to submit to the main repo, not this import-only repo.
It seems like Go tools are optimized to have each module in its own repo. For my case, I really want to have the go modules in the imageio repo, since the modules are a client library and client command line, and having them inside the repo with the server makes it easier to test. For example I can write tests start the server from source, and testing the client against the server. This ensures that changes in the server will never break the client when all this happens in the CI. Nir