kata-types: use pretty TOML encoder for initdata

TOML was chosen for initdata particularly for the ability to include
policy docs and other configuration files without mangling them. The
default TOML encoding renders string values as single-line,
double-quoted strings, effectively depriving us of this feature.

This commit changes the encoding to use `to_string_pretty`, and includes
a test that verifies the desirable aspect of encoding: newlines are kept
verbatim.

Fixes: #11943

Signed-off-by: Markus Rudy <mr@edgeless.systems>

src/libs/kata-types/src/initdata.rs

@@ -209,12 +209,12 @@ pub fn calculate_initdata_digest(
 
 /// Encodes initdata as an annotation
 pub fn encode_initdata(init_data: &InitData) -> String {
-    let toml_str = toml::to_string(&init_data).unwrap();
+    let toml_str = toml::to_string_pretty(&init_data).unwrap();
     create_encoded_input(&toml_str)
 }
 
-/// Decodes initdata annotation
-pub fn decode_initdata(initdata_annotation: &str) -> Result<InitData> {
+/// Decodes a base64-encoded gzipped initdata document to its raw TOML representation.
+fn decode_raw_initdata(initdata_annotation: &str) -> Result<String> {
     // Base64 decode the annotation value
     let b64_decoded =
         base64::decode_config(initdata_annotation, base64::STANDARD).context("base64 decode")?;
@@ -225,7 +225,12 @@ pub fn decode_initdata(initdata_annotation: &str) -> Result<InitData> {
     gz_decoder
         .read_to_string(&mut initdata_str)
         .context("gz decoder failed")?;
+    Ok(initdata_str)
+}
 
+/// Decodes initdata annotation
+pub fn decode_initdata(initdata_annotation: &str) -> Result<InitData> {
+    let initdata_str = decode_raw_initdata(initdata_annotation)?;
     // Return parsed initdata
     let initdata = parse_initdata(&initdata_str).context("parse initdata overrides")?;
 
@@ -509,4 +514,31 @@ key = "value"
         let invalid_data = base64::encode("raw uncompressed data");
         assert!(add_hypervisor_initdata_overrides(&invalid_data).is_err());
     }
+
+    #[test]
+    fn test_pretty_initdata() {
+        let nested_toml = r#"
+algorithm = "sha384"
+version = "0.1.0"
+
+[data]
+"aa.toml" = '''
+[token_configs]
+[token_configs.coco_as]
+url = 'http://kbs-service.xxx.cluster.local:8080'
+
+[token_configs.kbs]
+url = 'http://kbs-service.xxx.cluster.local:8080'
+'''
+        "#;
+        let init_data = parse_initdata(nested_toml).expect("canned initdata document should parse");
+
+        let doc = decode_raw_initdata(&encode_initdata(&init_data))
+            .expect("encoding and decoding again should work");
+        assert!(
+            !doc.contains("\\n"),
+            "the encoded initdata toml should not contain escaped newlines, but does:\n{}",
+            doc
+        )
+    }
 }