simplify converting asn1string

in combination with the previous commit this makes it easier to get an
asn1string from a `&str` and convert it to a der encoding with a asn1
type tag.

openssl/src/asn1.rs

@@ -430,6 +430,30 @@ foreign_type_and_impl_send_sync! {
     pub struct Asn1StringRef;
 }
 
+impl Asn1String {
+    /// Converts a `&str` to an `Asn1String`.
+    pub fn from_str(data: &str) -> Result<Self, ErrorStack> {
+        unsafe {
+            let s = cvt_p(ffi::ASN1_STRING_type_new(Asn1Type::IA5STRING.as_raw()))?;
+            ffi::ASN1_STRING_set(s, data.as_ptr().cast(), data.len().try_into().unwrap());
+            Ok(Self::from_ptr(s))
+        }
+    }
+
+    /// Converts the Asn1String to the ASN.1 representation with a IA5String tag
+    pub fn as_asn1type_der(&self) -> Result<Vec<u8>, ErrorStack> {
+        unsafe {
+            let typ = cvt_p(ffi::ASN1_TYPE_new()).unwrap();
+            ffi::ASN1_TYPE_set(typ, ffi::V_ASN1_IA5STRING, self.0.cast());
+
+            let len = cvt(ffi::i2d_ASN1_TYPE(typ, ptr::null_mut()))?;
+            let mut buf = vec![0; len as usize];
+            crate::cvt(ffi::i2d_ASN1_TYPE(typ, &mut buf.as_mut_ptr()))?;
+            Ok(buf)
+        }
+    }
+}
+
 impl Asn1StringRef {
     /// Converts the ASN.1 underlying format to UTF8
     ///