state/api: Introducing bulk operations on units

state/apiserver/units.go

+// Copyright 2013 Canonical Ltd.
+// Licensed under the AGPLv3, see LICENCE file for details.
+
+package apiserver
+
+import "launchpad.net/juju-core/state/api/params"
+
+// srvUnits serves API methods on set of units.
+type srvUnits struct {
+        root *srvRoot
+}
+
+// Get retrieves all the details of list of unit ids.
+func (u *srvUnits) Get(args params.Units) (params.UnitsResults, error) {
+        result := params.UnitsResults{
+                Units: make(map[string]*params.Unit),
+        }
+        for _, name := range args.Names {
+                unit, err := u.root.srv.state.Unit(name)
+                if err != nil {
+                        return params.UnitsResults{}, err
+                }
+                result.Units[name] = stateUnitToParams(unit)

[jameinel, 2013/05/29 10:27:46]

I'm fine with William's comment that we probably want to default to a list of
objects rather than a mapping because of potential conflicts with name.
There are some simplicities of getting back data in exactly the format you use
it, but really we have to read the whole thing in the response. So reading a
list and shoving it into a map locally is really the same overhead as just
reading the map.

However, I notice here that if *any* unit name isn't found, it refuses to answer
all the rest of the request, and it only returns the simple error string. So you
are likely to not even know *which* unit failed.

Because of concurrency, I think we want to rethink the error logic.

Specifically, return:

[{"name": name, "unit": unitdetails, "error": null})

I'm thinking that otherwise if a unit happens to be killed by person X while
person Y is running 'juju status', status will just die, rather than returning
the best information it can get in a snapshot.

With a list of requested results, you have a way to say there was an error
retrieving information about unit "name".

And while there *is* some redundancy in the result, it makes it has a fair bit
of making context clear and error handling pretty straightforward.

+        }
+        return result, nil
+}