vcf/io/writer/header/record/value: Validate unstructured header recor…

…d value

This disallows unstructured header record values to be empty or start
with a structured header record marker (`<`). See _The Variant Call
Format Specification: VCFv4.4 and BCFv2.2_ (2024-04-20) § 1.4
"Meta-information lines".

noodles-vcf/CHANGELOG.md

@@ -10,6 +10,12 @@
     header line by line. This makes it so that it is no longer required to read
     the entire raw header into memory before parsing.
 
+  * vcf/io/writer/header/record/value: Disallow unstructured header records to
+    be empty or start with a structured header record marker (`<`).
+
+    See _The Variant Call Format Specification: VCFv4.4 and BCFv2.2_
+    (2024-04-20) § 1.4 "Meta-information lines".
+
   * vcf/io/writer/record/reference_bases: Resolve IUPAC ambiguity codes
     ([#268]).
 

noodles-vcf/src/io/writer/header/record/value.rs

@@ -12,5 +12,45 @@ pub(super) fn write_string<W>(writer: &mut W, s: &str) -> io::Result<()>
 where
     W: Write,
 {
-    writer.write_all(s.as_bytes())
+    // § 1.4 "Meta-information lines" (2024-04-20): "An _unstructured_ meta-information line
+    // consists of [...] a _value_ (which may not be empty and must not start with a '<'
+    // character)..."
+    fn is_valid(s: &str) -> bool {
+        const LESS_THAN_SIGN: char = '<';
+        s.chars().next().is_some_and(|c| c != LESS_THAN_SIGN)
+    }
+
+    if is_valid(s) {
+        writer.write_all(s.as_bytes())
+    } else {
+        Err(io::Error::new(
+            io::ErrorKind::InvalidInput,
+            "invalid unstructured header record value",
+        ))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_write_string() -> io::Result<()> {
+        let mut buf = Vec::new();
+
+        write_string(&mut buf, "ndls")?;
+        assert_eq!(buf, b"ndls");
+
+        assert!(matches!(
+            write_string(&mut buf, ""),
+            Err(e) if e.kind() == io::ErrorKind::InvalidInput
+        ));
+
+        assert!(matches!(
+            write_string(&mut buf, "<"),
+            Err(e) if e.kind() == io::ErrorKind::InvalidInput
+        ));
+
+        Ok(())
+    }
 }