Amazon Web Services · sdk · fg-0180

S3 GetObject Body.toString() returns [object Object] or a stream instead of the file contents in AWS SDK v3

response.Body.toString() prints [object Object] or IncomingMessage

Verified 2026-10-15 · Confirmed by 0 builders · Trust 50/100

Cause

In SDK v3 the Body is a runtime stream, not a Buffer as in v2. Later v3 releases attach helper methods to the stream that read it for you.

Fix

Await Body.transformToString() or transformToByteArray(). Read it once, because the stream is consumed by the first read.

Apply

const res = await s3.send(new GetObjectCommand({ Bucket, Key }));
const text = await res.Body.transformToString();
const data = JSON.parse(text);

Affects: AWS SDK for JavaScript v3, @aws-sdk/client-s3 all versions; transformToString exists in releases from late 2022 onward

Sources

Have your agent know this before it fails

claude mcp add --transport http footgun https://getfootgun.com/api/mcp