fix(util-body-length-node): restrict fs calls to fs.ReadStream objects (#1735)

Author: kuhe

.changeset/odd-rats-reflect.md

@@ -0,0 +1,5 @@
+---
+"@smithy/util-body-length-node": patch
+---
+
+restrict fs calls to fs.ReadStream instances

packages/util-body-length-node/src/calculateBodyLength.spec.ts

@@ -84,11 +84,9 @@ describe(calculateBodyLength.name, () => {
 
     it("should handle stream created using fd.createReadStream", async () => {
       const fd = await fs.promises.open(__filename, "r");
-      if ((fd as any).createReadStream) {
-        const fdReadStream = (fd as any).createReadStream();
-        expect(calculateBodyLength(fdReadStream)).toEqual(fileSize);
-        fdReadStream.close();
-      }
+      const fdReadStream = fd.createReadStream();
+      expect(calculateBodyLength(fdReadStream)).toEqual(fileSize);
+      fdReadStream.close();
     });
   });
 

packages/util-body-length-node/src/calculateBodyLength.ts

@@ -1,4 +1,11 @@
-import { fstatSync, lstatSync } from "fs";
+import { fstatSync, lstatSync, ReadStream } from "node:fs";
+
+/**
+ * @internal
+ */
+type HasFileDescriptor = {
+  fd: number;
+};
 
 /**
  * @internal
@@ -16,12 +23,13 @@ export const calculateBodyLength = (body: any): number | undefined => {
     return body.size;
   } else if (typeof body.start === "number" && typeof body.end === "number") {
     return body.end + 1 - body.start;
-  } else if (typeof body.path === "string" || Buffer.isBuffer(body.path)) {
-    // handles fs readable streams
-    return lstatSync(body.path).size;
-  } else if (typeof body.fd === "number") {
-    // handles fd readable streams
-    return fstatSync(body.fd).size;
+  } else if (body instanceof ReadStream) {
+    // the previous use case where start and end are numbers is also potentially a ReadStream.
+    if (body.path != null) {
+      return lstatSync(body.path).size;
+    } else if (typeof (body as ReadStream & HasFileDescriptor).fd === "number") {
+      return fstatSync((body as ReadStream & HasFileDescriptor).fd).size;
+    }
   }
   throw new Error(`Body Length computation failed for ${body}`);
 };