[Rust] refactored codegen of primitive array encoding to accept slice instead of array

Author: Michael Ward

sbe-tool/src/main/java/uk/co/real_logic/sbe/generation/rust/LibRsDef.java

@@ -276,9 +276,9 @@ static void generateWriteBuf(final Writer writer, final ByteOrder byteOrder) thr
         indent(writer, 2, "dest.clone_from_slice(src);\n");
         indent(writer, 2, "len\n");
         indent(writer, 1, "}\n");
-
         indent(writer, 0, "}\n");
 
+        // impl From<WriteBuf> for &[u8]
         indent(writer, 0, "impl<%s> From<&%1$s mut %2$s<%1$s>> for &%1$s mut [u8] {\n", BUF_LIFETIME, WRITE_BUF_TYPE);
         indent(writer, 1, "#[inline]\n");
         indent(writer, 1, "fn from(buf: &%s mut %2$s<%1$s>) -> &%1$s mut [u8] {\n", BUF_LIFETIME, WRITE_BUF_TYPE);

sbe-tool/src/main/java/uk/co/real_logic/sbe/generation/rust/RustGenerator.java

@@ -383,18 +383,21 @@ private static void generatePrimitiveEncoder(
             indent(sb, level, "/// - encodedLength: %d\n", typeToken.encodedLength());
             indent(sb, level, "/// - version: %d\n", typeToken.version());
             indent(sb, level, "#[inline]\n");
-            indent(sb, level, "pub fn %s(&mut self, value: &[%s; %d]) {\n",
+            indent(sb, level, "pub fn %s(&mut self, value: &[%s]) {\n",
                 formatFunctionName(name),
-                rustPrimitiveType,
-                arrayLength);
+                rustPrimitiveType);
 
             // NB: must create variable 'offset' before calling mutable self.get_buf_mut()
             indent(sb, level + 1, "let offset = self.%s;\n", getBufOffset(typeToken));
             indent(sb, level + 1, "let buf = self.get_buf_mut();\n");
 
             if (rustPrimitiveType.equals("u8"))
             {
-                indent(sb, level + 1, "buf.put_bytes_at(offset, value);\n");
+                indent(sb, level + 1, "let mid = %d.min(value.len());\n", arrayLength);
+                indent(sb, level + 1, "buf.put_slice_at(offset, value.split_at(mid).0);\n");
+                indent(sb, level + 1, "for i in mid..%d {\n", arrayLength);
+                indent(sb, level + 2, "buf.put_u8_at(offset + (i * 1), %s_u8);\n", encoding.applicableNullValue());
+                indent(sb, level + 1, "}\n");
                 indent(sb, level, "}\n\n");
                 return;
             }