Support for Compressed, Base64-Enc, Inline Content

This patch adds support for local, inline content as compressed, base64
encoded values. For example, the string "Hello, world." can be
compressed with gzip and base64 encoded with the following command:

        $ echo Hello, world. | gzip | base64
        H4sIAG/kFlsAA/NIzcnJ11Eozy/KSdHjAgDXu838DgAAAA==

A Container Linux Config could use the above contents and write them to
the file "/etc/helloworld.txt":

        storage:
          files:
            - path: /etc/helloworld.txt
              filesystem: root
              mode: 0644
              contents:
                base64: true
                compression: gzip
                inline: |
                  H4sIAB/jFlsAA/NIzcnJ11Eozy/KSdHjAgDXu838DgAAAA==

The CT transpiler would transform the above configuration snippet into
the JSON below:

        {
          "filesystem": "root",
          "path": "/etc/srv/kubernetes/pki/apiserver.key",
          "contents": {
              "compression": "gzip",
              "source": "data:;base64,H4sIAB/jFlsAA/NIzcnJ11Eozy/KSdHjAgDXu838DgAAAA==",
              "verification": {}
          },
          "mode": 420
        },

Please note the value of the "source" field -- it uses the data URL
scheme (https://tools.ietf.org/html/rfc2397) to indicate the content
is base64 encoded. The "compression" field indicates the content is
also compressed using gzip. In fact, the following command may be used
to verify the data matches the original "Hello, world." string:

        $ echo H4sIAB/jFlsAA/NIzcnJ11Eozy/KSdHjAgDXu838DgAAAA== | \
          base64 -D | \
          gzip -d
        Hello, world.

Author: akutz

config/types/files.go

@@ -63,9 +63,11 @@ type File struct {
 }
 
 type FileContents struct {
-	Remote Remote `yaml:"remote"`
-	Inline string `yaml:"inline"`
-	Local  string `yaml:"local"`
+	Base64      *bool  `yaml:"base64"`
+	Compression string `yaml:"compression"`
+	Remote      Remote `yaml:"remote"`
+	Inline      string `yaml:"inline"`
+	Local       string `yaml:"local"`
 }
 
 type Remote struct {
@@ -158,11 +160,20 @@ func init() {
 			}
 
 			if file.Contents.Inline != "" {
-				newFile.Contents = ignTypes.FileContents{
-					Source: (&url.URL{
-						Scheme: "data",
-						Opaque: "," + dataurl.EscapeString(file.Contents.Inline),
-					}).String(),
+				if file.Contents.Base64 != nil && *file.Contents.Base64 {
+					newFile.Contents = ignTypes.FileContents{
+						Source: (&url.URL{
+							Scheme: "data",
+							Opaque: ";base64," + file.Contents.Inline,
+						}).String(),
+					}
+				} else {
+					newFile.Contents = ignTypes.FileContents{
+						Source: (&url.URL{
+							Scheme: "data",
+							Opaque: "," + dataurl.EscapeString(file.Contents.Inline),
+						}).String(),
+					}
 				}
 			}
 
@@ -237,7 +248,10 @@ func init() {
 				}
 			}
 
-			newFile.Contents.Compression = file.Contents.Remote.Compression
+			if file.Contents.Compression == "" {
+				file.Contents.Compression = file.Contents.Remote.Compression
+			}
+			newFile.Contents.Compression = file.Contents.Compression
 			newFile.Contents.Verification = convertVerification(file.Contents.Remote.Verification)
 
 			out.Storage.Files = append(out.Storage.Files, newFile)