fix(sdk-trace-base): avoid keeping non-string status.message on Span#setStatus()

CHANGELOG.md

@@ -17,6 +17,8 @@ For semantic convention package changes, see the [semconv CHANGELOG](packages/se
 
 ### :bug: (Bug Fix)
 
+* fix(sdk-trace-base): avoid keeping non-string `status.message` on `Span#setStatus()` [#4999](https://github.com/open-telemetry/opentelemetry-js/pull/4999) @pichlermarc
+
 ### :books: (Refine Doc)
 
 ### :house: (Internal)

packages/opentelemetry-sdk-trace-base/src/Span.ts

@@ -226,7 +226,19 @@ export class Span implements APISpan, ReadableSpan {
 
   setStatus(status: SpanStatus): this {
     if (this._isSpanEnded()) return this;
-    this.status = status;
+    this.status = { ...status };
+
+    // When using try-catch, the caught "error" is of type `any`. When then assigning `any` to `status.message`,
+    // TypeScript will not error. While this can happen during use of any API, it is more common on Span#setStatus()
+    // as it's likely used in a catch-block. Therefore, we validate if `status.message` is actually a string, null, or
+    // undefined to avoid an incorrect type causing issues downstream.
+    if (this.status.message != null && typeof status.message !== 'string') {
+      diag.warn(
+        `Dropping invalid status.message of type '${typeof status.message}', expected 'string'`
+      );
+      delete this.status.message;
+    }
+
     return this;
   }
 

packages/opentelemetry-sdk-trace-base/test/common/Span.test.ts

@@ -853,6 +853,32 @@ describe('Span', () => {
       message: 'This is an error',
     });
     span.end();
+
+    assert.strictEqual(span.status.code, SpanStatusCode.ERROR);
+    assert.strictEqual(span.status.message, 'This is an error');
+  });
+
+  it('should drop non-string status message', function () {
+    const warnStub = sinon.spy(diag, 'warn');
+    const span = new Span(
+      tracer,
+      ROOT_CONTEXT,
+      name,
+      spanContext,
+      SpanKind.CLIENT
+    );
+    span.setStatus({
+      code: SpanStatusCode.ERROR,
+      message: new Error('this is not a string') as any,
+    });
+    span.end();
+
+    assert.strictEqual(span.status.code, SpanStatusCode.ERROR);
+    assert.strictEqual(span.status.message, undefined);
+    sinon.assert.calledOnceWithExactly(
+      warnStub,
+      "Dropping invalid status.message of type 'object', expected 'string'"
+    );
   });
 
   it('should return ReadableSpan', () => {