internal/getproviders: Stub NetworkMirrorSource

This is a placeholder for later implementation of a mirror source that
talks to a particular remote HTTP server and expects it to implement the
provider mirror protocol.

internal/getproviders/network_mirror_source.go

@@ -0,0 +1,39 @@
+package getproviders
+
+import (
+	"fmt"
+
+	svchost "github.com/hashicorp/terraform-svchost"
+
+	"github.com/hashicorp/terraform/addrs"
+)
+
+// NetworkMirrorSource is a source that reads providers and their metadata
+// from an HTTP server implementing the Terraform network mirror protocol.
+type NetworkMirrorSource struct {
+	host svchost.Hostname
+}
+
+var _ Source = (*NetworkMirrorSource)(nil)
+
+// NewNetworkMirrorSource constructs and returns a new network-based
+// mirror source that will expect to find a mirror service on the given
+// host.
+func NewNetworkMirrorSource(host svchost.Hostname) *NetworkMirrorSource {
+	return &NetworkMirrorSource{
+		host: host,
+	}
+}
+
+// AvailableVersions retrieves the available versions for the given provider
+// from the network mirror.
+func (s *NetworkMirrorSource) AvailableVersions(provider addrs.Provider) (VersionList, error) {
+	return nil, fmt.Errorf("Network provider mirror is not supported in this version of Terraform")
+}
+
+// PackageMeta checks to see if the network mirror contains a copy of the
+// distribution package for the given provider version on the given target,
+// and returns the metadata about it if so.
+func (s *NetworkMirrorSource) PackageMeta(provider addrs.Provider, version Version, target Platform) (PackageMeta, error) {
+	return PackageMeta{}, fmt.Errorf("Network provider mirror is not supported in this version of Terraform")
+}