[milo] Refactor all html knowledge out of backends.

milo/buildsource/id.go

+// Copyright 2017 The LUCI Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+package buildsource
+
+import (
+        "golang.org/x/net/context"
+
+        "github.com/luci/luci-go/milo/api/resp"
+)
+
+// ID represents a universal 'build' ID. Each subpackage of buildsource
+// implements an ID (as the type BuildID, e.g. swarming.BuildID), which has
+// buildsource-specific fields, but always implements this ID interface.
+//
+// The frontend constructs an ID from the appropriate buildsource, then calls
+// its .Get() method to get the generic MiloBuild representation.
+type ID interface {
+        Get(c context.Context) (*resp.MiloBuild, error)
+
+        // GetLog is only implemented by swarming; this is for serving the deprecated
+        //   swarming/task/<id>/steps/<logname>
+        // API. Once that's removed, this should be removed as well.
+        GetLog(c context.Context, logname string) (text string, closed bool, err error)
+}