variable sized object header

Author: samuelcolvin

crates/batson/examples/read_file.rs

@@ -40,7 +40,11 @@ cargo run --example read_file file.json [path]
     let output_json2 = batson_to_json_string(&batson).expect("failed to convert batson to JSON");
     println!("JSON unchanged after re-encoding: {:?}", output_json == output_json2);
 
-    println!("\n\noutput json:\n{}", output_json);
+    if output_json.len() < 2000 {
+        println!("\n\noutput json:\n{}", output_json);
+    } else {
+        println!("\n\noutput json is too long to display");
+    }
 }
 
 fn to_batson_path(s: &str) -> BatsonPath {

crates/batson/src/array.rs

@@ -144,17 +144,17 @@ pub(crate) fn encode_array(encoder: &mut Encoder, array: &JsonArray) -> EncodeRe
     } else if let Some(packed_array) = PackedArray::new(array) {
         match packed_array {
             PackedArray::Header(array) => {
-                encoder.push(Category::HeaderArray.encode_with(array.len() as u8));
+                encoder.encode_length(Category::HeaderArray, array.len())?;
                 // no alignment necessary, it's a vec of u8
                 encoder.extend(&array);
             }
             PackedArray::I64(array) => {
-                encoder.push(Category::I64Array.encode_with(array.len() as u8));
+                encoder.encode_length(Category::I64Array, array.len())?;
                 encoder.align::<i64>();
                 encoder.extend(bytemuck::cast_slice(&array));
             }
             PackedArray::U8(array) => {
-                encoder.push(Category::U8Array.encode_with(array.len() as u8));
+                encoder.encode_length(Category::U8Array, array.len())?;
                 // no alignment necessary, it's a vec of u8
                 encoder.extend(&array);
             }

crates/batson/src/encoder.rs

@@ -48,6 +48,10 @@ impl Encoder {
         self.data.len()
     }
 
+    pub fn reset_position(&mut self, position: usize) {
+        self.data.truncate(position);
+    }
+
     pub fn encode_null(&mut self) {
         let h = Category::Primitive.encode_with(Primitive::Null as u8);
         self.push(h);
@@ -141,19 +145,27 @@ impl Encoder {
                     self.push(cat.encode_with(Length::U8 as u8));
                     self.push(s);
                 } else if let Ok(int) = u16::try_from(len) {
-                    self.push(cat.encode_with(Length::U16 as u8));
-                    self.extend(&int.to_le_bytes());
-                } else if let Ok(int) = u32::try_from(len) {
-                    self.push(cat.encode_with(Length::U32 as u8));
-                    self.extend(&int.to_le_bytes());
+                    self.encode_len_u16(cat, int);
                 } else {
-                    return Err(EncodeError::StrTooLong);
+                    self.encode_len_u32(cat, len)?;
                 }
             }
         }
         Ok(())
     }
 
+    pub fn encode_len_u16(&mut self, cat: Category, int: u16) {
+        self.push(cat.encode_with(Length::U16 as u8));
+        self.extend(&int.to_le_bytes());
+    }
+
+    pub fn encode_len_u32(&mut self, cat: Category, len: usize) -> EncodeResult<()> {
+        self.push(cat.encode_with(Length::U32 as u8));
+        let int = u32::try_from(len).map_err(|_| EncodeError::StrTooLong)?;
+        self.extend(&int.to_le_bytes());
+        Ok(())
+    }
+
     pub fn push(&mut self, h: u8) {
         self.data.push(h);
     }

crates/batson/src/errors.rs

@@ -9,6 +9,7 @@ pub type EncodeResult<T> = Result<T, EncodeError>;
 #[derive(Debug, Copy, Clone)]
 pub enum EncodeError {
     StrTooLong,
+    ObjectTooLarge,
 }
 
 pub type DecodeResult<T> = Result<T, DecodeError>;