packer: First pass at Artifact interface

packer/artifact.go

+package packer
+
+// An Artifact is the result of a build, and is the metadata that documents
+// what a builder actually created. The exact meaning of the contents is
+// specific to each builder, but this interface is used to communicate back
+// to the user the result of a build.
+type Artifact interface {
+	// Returns the ID of the builder that was used to create this artifact.
+	// This is the internal ID of the builder and should be unique to every
+	// builder. This can be used to identify what the contents of the
+	// artifact actually are.
+	BuilderId() string
+
+	// Returns the set of files that comprise this artifact. If an
+	// artifact is not made up of files, then this will be empty.
+	Files() []string
+
+	// The ID for the artifact, if it has one. This is not guaranteed to
+	// be unique every run (like a GUID), but simply provide an identifier
+	// for the artifact that may be meaningful in some way. For example,
+	// for Amazon EC2, this value might be the AMI ID.
+	Id() string
+
+	// Returns human-readable output that describes the artifact created.
+	// This is used for UI output. It can be multiple lines.
+	String() string
+}