Fix render of AssetCode12 to JSON when shorter than 5 chars (#358)

src/curr/str.rs

@@ -291,10 +291,21 @@ impl core::str::FromStr for AssetCode12 {
 
 impl core::fmt::Display for AssetCode12 {
     fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
-        if let Some(last_idx) = self.0.iter().rposition(|c| *c != 0) {
-            for b in escape_bytes::Escape::new(&self.0[..=last_idx]) {
-                write!(f, "{}", b as char)?;
-            }
+        // AssetCode12's are always rendered as at least 5 characters, because
+        // any asset code shorter than 5 characters is an AssetCode4.
+        // AssetCode12 contains a fixed length 12-byte array, and the constant
+        // and slices in this function never operate out-of-bounds because of
+        // that.
+        const MIN_LENGTH: usize = 5;
+        let len = MIN_LENGTH
+            + self
+                .0
+                .iter()
+                .skip(MIN_LENGTH)
+                .rposition(|c| *c != 0)
+                .map_or(0, |last_idx| last_idx + 1);
+        for b in escape_bytes::Escape::new(&self.0[..len]) {
+            write!(f, "{}", b as char)?;
         }
         Ok(())
     }

tests/str.rs

@@ -450,11 +450,11 @@ fn asset_code_12_from_str() {
 #[test]
 #[rustfmt::skip]
 fn asset_code_12_to_string() {
-    assert_eq!(AssetCode12(*b"\0\0\0\0\0\0\0\0\0\0\0\0").to_string(), "");
-    assert_eq!(AssetCode12(*b"a\0\0\0\0\0\0\0\0\0\0\0").to_string(), "a");
-    assert_eq!(AssetCode12(*b"ab\0\0\0\0\0\0\0\0\0\0").to_string(), "ab");
-    assert_eq!(AssetCode12(*b"abc\0\0\0\0\0\0\0\0\0").to_string(), "abc");
-    assert_eq!(AssetCode12(*b"abcd\0\0\0\0\0\0\0\0").to_string(), "abcd");
+    assert_eq!(AssetCode12(*b"\0\0\0\0\0\0\0\0\0\0\0\0").to_string(), r"\0\0\0\0\0");
+    assert_eq!(AssetCode12(*b"a\0\0\0\0\0\0\0\0\0\0\0").to_string(), r"a\0\0\0\0");
+    assert_eq!(AssetCode12(*b"ab\0\0\0\0\0\0\0\0\0\0").to_string(), r"ab\0\0\0");
+    assert_eq!(AssetCode12(*b"abc\0\0\0\0\0\0\0\0\0").to_string(), r"abc\0\0");
+    assert_eq!(AssetCode12(*b"abcd\0\0\0\0\0\0\0\0").to_string(), r"abcd\0");
     assert_eq!(AssetCode12(*b"abcde\0\0\0\0\0\0\0").to_string(), "abcde");
     assert_eq!(AssetCode12(*b"abcdef\0\0\0\0\0\0").to_string(), "abcdef");
     assert_eq!(AssetCode12(*b"abcdefg\0\0\0\0\0").to_string(), "abcdefg");
@@ -465,10 +465,10 @@ fn asset_code_12_to_string() {
     assert_eq!(AssetCode12(*b"abcdefghijkl").to_string(), "abcdefghijkl");
 
     // Preserve as much of the code as possible, even if it contains nul bytes.
-    assert_eq!(AssetCode12(*b"a\0cd\0\0\0\0\0\0\0\0").to_string(), r"a\0cd");
+    assert_eq!(AssetCode12(*b"a\0cd\0\0\0\0\0\0\0\0").to_string(), r"a\0cd\0");
 
     // Replace bytes that are not valid utf8 with the replacement character � and preserve length.
-    assert_eq!(AssetCode12(*b"a\xc3\x28d\0\0\0\0\0\0\0\0").to_string(), r"a\xc3(d");
+    assert_eq!(AssetCode12(*b"a\xc3\x28d\0\0\0\0\0\0\0\0").to_string(), r"a\xc3(d\0");
     assert_eq!(AssetCode12(*b"a\xc3\xc3\x28d\0\0\0\0\0\0\0").to_string(), r"a\xc3\xc3(d");
 }
 
@@ -502,11 +502,11 @@ fn asset_code_to_string() {
     assert_eq!(AssetCode::CreditAlphanum4(AssetCode4(*b"abc\0")).to_string(), "abc");
     assert_eq!(AssetCode::CreditAlphanum4(AssetCode4(*b"abcd")).to_string(), "abcd");
 
-    assert_eq!(AssetCode::CreditAlphanum12(AssetCode12(*b"\0\0\0\0\0\0\0\0\0\0\0\0")).to_string(), "");
-    assert_eq!(AssetCode::CreditAlphanum12(AssetCode12(*b"a\0\0\0\0\0\0\0\0\0\0\0")).to_string(), "a");
-    assert_eq!(AssetCode::CreditAlphanum12(AssetCode12(*b"ab\0\0\0\0\0\0\0\0\0\0")).to_string(), "ab");
-    assert_eq!(AssetCode::CreditAlphanum12(AssetCode12(*b"abc\0\0\0\0\0\0\0\0\0")).to_string(), "abc");
-    assert_eq!(AssetCode::CreditAlphanum12(AssetCode12(*b"abcd\0\0\0\0\0\0\0\0")).to_string(), "abcd");
+    assert_eq!(AssetCode::CreditAlphanum12(AssetCode12(*b"\0\0\0\0\0\0\0\0\0\0\0\0")).to_string(), r"\0\0\0\0\0");
+    assert_eq!(AssetCode::CreditAlphanum12(AssetCode12(*b"a\0\0\0\0\0\0\0\0\0\0\0")).to_string(), r"a\0\0\0\0");
+    assert_eq!(AssetCode::CreditAlphanum12(AssetCode12(*b"ab\0\0\0\0\0\0\0\0\0\0")).to_string(), r"ab\0\0\0");
+    assert_eq!(AssetCode::CreditAlphanum12(AssetCode12(*b"abc\0\0\0\0\0\0\0\0\0")).to_string(), r"abc\0\0");
+    assert_eq!(AssetCode::CreditAlphanum12(AssetCode12(*b"abcd\0\0\0\0\0\0\0\0")).to_string(), r"abcd\0");
     assert_eq!(AssetCode::CreditAlphanum12(AssetCode12(*b"abcde\0\0\0\0\0\0\0")).to_string(), "abcde");
     assert_eq!(AssetCode::CreditAlphanum12(AssetCode12(*b"abcdef\0\0\0\0\0\0")).to_string(), "abcdef");
     assert_eq!(AssetCode::CreditAlphanum12(AssetCode12(*b"abcdefg\0\0\0\0\0")).to_string(), "abcdefg");
@@ -518,11 +518,11 @@ fn asset_code_to_string() {
 
     // Preserve as much of the code as possible, even if it contains nul bytes.
     assert_eq!(AssetCode::CreditAlphanum4(AssetCode4(*b"a\0cd")).to_string(), r"a\0cd");
-    assert_eq!(AssetCode::CreditAlphanum12(AssetCode12(*b"a\0cd\0\0\0\0\0\0\0\0")).to_string(), r"a\0cd");
+    assert_eq!(AssetCode::CreditAlphanum12(AssetCode12(*b"a\0cd\0\0\0\0\0\0\0\0")).to_string(), r"a\0cd\0");
 
     // Replace bytes that are not valid utf8 with the replacement character � and preserve length.
     assert_eq!(AssetCode::CreditAlphanum4(AssetCode4(*b"a\xc3\x28d")).to_string(), r"a\xc3(d");
-    assert_eq!(AssetCode::CreditAlphanum12(AssetCode12(*b"a\xc3\x28d\0\0\0\0\0\0\0\0")).to_string(), r"a\xc3(d");
+    assert_eq!(AssetCode::CreditAlphanum12(AssetCode12(*b"a\xc3\x28d\0\0\0\0\0\0\0\0")).to_string(), r"a\xc3(d\0");
     assert_eq!(AssetCode::CreditAlphanum12(AssetCode12(*b"a\xc3\xc3\x28d\0\0\0\0\0\0\0")).to_string(), r"a\xc3\xc3(d");
 }