Emit by frame directly

Author: gyuheon0h

datadog-crashtracker/src/runtime_callback.rs

@@ -355,12 +355,43 @@ unsafe fn emit_frame_as_json(
     // to a valid RuntimeStackFrame.
     let frame_ref = &*frame;
 
-    // TODO: this allocates a new StackFrame. Avoid this by just emitting the JSON directly here.
-    let stack_frame: StackFrame = frame_ref.into();
+    write!(writer, "{{")?;
 
-    // Serialize to JSON and write
-    let json = serde_json::to_string(&stack_frame).map_err(std::io::Error::other)?;
-    writeln!(writer, "{}", json)?;
+    let mut first_field = true;
+
+    if let Ok(Some(function_name)) = frame_ref.function_name.try_to_string_option() {
+        write!(
+            writer,
+            "\"function\": \"{}\"",
+            function_name.replace('"', "\\\"")
+        )?;
+        first_field = false;
+    }
+
+    if let Ok(Some(file_name)) = frame_ref.file_name.try_to_string_option() {
+        if !first_field {
+            write!(writer, ", ")?;
+        }
+        write!(writer, "\"file\": \"{}\"", file_name.replace('"', "\\\""))?;
+        first_field = false;
+    }
+
+    if frame_ref.line_number != 0 {
+        if !first_field {
+            write!(writer, ", ")?;
+        }
+        write!(writer, "\"line\": {}", frame_ref.line_number)?;
+        first_field = false;
+    }
+
+    if frame_ref.column_number != 0 {
+        if !first_field {
+            write!(writer, ", ")?;
+        }
+        write!(writer, "\"column\": {}", frame_ref.column_number)?;
+    }
+
+    writeln!(writer, "}}")?;
     Ok(())
 }