Content-Encoding header getting added multiple times when compressing data

[dhruv-nudge]

I am manually compressing response like this and then sending to the FE

if ((this.headers['accept-encoding'] as string)?.includes('zstd') && stringified.length > 2048) {
	this.responseHeaders.push({ key: 'Content-Encoding', value: 'zstd' });
	compress(Buffer.from(stringified), 1).then(result => this.send(result, statusCode));
} else {
	this.send(stringified, statusCode);
}

private send(responseBody: string | Buffer, statusCode: HttpStatus) {
    this.uResponse.cork(() => {
	    this.uResponse.writeStatus(statusCode);
	    this.responseHeaders.forEach(it => {
		    this.uResponse.writeHeader(it.key, it.value);
	    });
	    this.uResponse.writeHeader('Access-Control-Allow-Methods', this.uResponse.method);
	    this.uResponse.end(responseBody);
    });
}

But for some reason, this header is being added 8 times, which is causing the API to fail. Any idea why this might be happening?