Previously we allowed access to the credentials store only indirectly
through the Disco object, and that's fine for callers that only need to
_read_ credentials, but more specialized callers like "terraform login"
and "terraform logout" need more information in order to be transparent
to the user about what they are going to do and where the credentials
are going to be stored.
This PR improves the error handling so we can provide better feedback about any service discovery errors that occured.
Additionally it adds logic to test for specific versions when discovering a service using `service.vN`. This will enable more informational errors which can indicate any version incompatibilities.
By adding this method you now only have to pass a `*disco.Disco` object around in order to do discovery and use any configured credentials for the discovered hosts.
Of course you can also still pass around both a `*disco.Disco` and a `auth.CredentialsSource` object if there is a need or a reason for that!
Extend the discovery timeout from 4 seconds to 11 seconds. This gives a
little more time for a slow host to response. The duration of 11s
keeps the delay reasonable, and puts it just after the default TLS
handshake timeout of 10s for easier differentiation of the error cases.
The default network-based discovery is not desirable for all situations,
so this mechanism allows callers to provide a services map for a given
hostname that was obtained some other way (caller-defined) which will then
cause network-based discovery to be skipped and the given map to be
returned verbatim.
For the same reason the disco tests need to override the http.Transport,
other test fixtures will need to as well. Provide a field to override
the default httpTransport.
Update all references to the version values to use the new package.
The VersionString function was left in the terraform package
specifically for the aws provider, which is vendored. We can remove that
last call once the provider is updated.
Although service discovery metadata is usually not sensitive, a service
host may wish to produce different results depending on the requesting
user, such as if users are migrating between two different implementations
that are both running concurrently for some period.
This package implements our Terraform-native Service discovery protocol,
which allows us to find the base URL for a particular service given a
hostname that was already validated and normalized by the svchost package.
Martin Atkins