Improve error handling for old Peppi files

src/io/peppi/mod.rs

@@ -13,26 +13,33 @@ pub use de::read;
 pub use ser::write;
 
 /// Current version of the Peppi format
-pub const CURRENT_VERSION: Version = Version(2, 0);
+pub const CURRENT_VERSION: Version = Version(2, 0, 0);
 
-/// Peppi files are TAR archives, and are guaranteed to start with `peppi.json`
+/// Minimum supported version of the Peppi format for reading
+pub const MIN_VERSION: Version = Version(2, 0, 0);
+
+/// Peppi files are TAR archives, guaranteed to start with `peppi.json`
 pub const FILE_SIGNATURE: [u8; 10] = [0x70, 0x65, 0x70, 0x70, 0x69, 0x2e, 0x6a, 0x73, 0x6f, 0x6e];
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord, Deserialize, Serialize)]
-pub struct Version(pub u8, pub u8);
+pub struct Version(pub u8, pub u8, pub u8);
 
 impl fmt::Display for Version {
 	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-		write!(f, "{}.{}", self.0, self.1)
+		write!(f, "{}.{}.{}", self.0, self.1, self.2)
 	}
 }
 
 impl str::FromStr for Version {
 	type Err = Error;
 	fn from_str(s: &str) -> Result<Self> {
 		let mut i = s.split('.');
-		match (i.next(), i.next(), i.next()) {
-			(Some(major), Some(minor), None) => Ok(Version(parse_u8(major)?, parse_u8(minor)?)),
+		match (i.next(), i.next(), i.next(), i.next()) {
+			(Some(major), Some(minor), Some(revision), None) => Ok(Version(
+				parse_u8(major)?,
+				parse_u8(minor)?,
+				parse_u8(revision)?,
+			)),
 			_ => Err(err!("invalid Peppi version: {}", s.to_string())),
 		}
 	}
@@ -60,13 +67,9 @@ pub struct Peppi {
 }
 
 pub fn assert_current_version(version: Version) -> Result<()> {
-	if version == CURRENT_VERSION {
-		Ok(())
+	if version < MIN_VERSION {
+		Err(err!("unsupported version ({} < {})", version, MIN_VERSION))
 	} else {
-		Err(err!(
-			"unsupported version ({} != {})",
-			version,
-			CURRENT_VERSION
-		))
+		Ok(())
 	}
 }