Angular2下载的pdf文件没有内容

Question

MVC控制器方法返回一个pdf文件：

   public ActionResult GetLetterHistoryBatchPdf(int letterBatchID)
        {
            return File(System.IO.File.OpenRead(@"\\ThePath\thepdf.pdf"), "application/pdf");

}

angular2服务：

getData(source_url: string, parameters: Parameter[]): Observable<any[]> {
        let headers = new Headers({ 'X-Requested-With': 'XMLHttpRequest' });
        let options = new RequestOptions({ headers: headers });

        if (parameters.length > 0) {
            let params: URLSearchParams = new URLSearchParams();

            for (var index = 0; index < parameters.length; index++) {
                params.set(parameters[index].name, parameters[index].value);
            }

            return this.http.get(source_url, { search: params, headers: headers })
                .map(this.extractData)
                .catch(this.handleError);
        }
        else {
            return this.http.get(source_url, { headers: headers })
                .map(this.extractData)
                .catch(this.handleError);
        }
    }

extracting received response:

    private extractData(response: Response) {
        let body: any;

        let contentType = response.headers.get('content-type');
        console.log(contentType);

        if (contentType.includes('application/json')){
             body = response.json();
        }
        if (contentType.includes('text/csv')) {
            let buffer: any = [];
            buffer.push(response._body);
            let blob = new Blob(buffer, { type: 'text/csv' });
            return  blob;
        }
        if (contentType.includes('application/pdf')) {
            return response;
        }
        return body.data || {};
    }

保存对角度组件中文件的响应：

this.myCommonService.getData(actionUrl, params)
            .subscribe(data => {
                var link = document.createElement('a');
                document.body.appendChild(link);
                link.style = 'display: none';
                let mediaType = 'application/pdf';
                let buff = data.arrayBuffer();
                let blob = new Blob(buff, { type: mediaType });
                let url = window.URL.createObjectURL(blob);
                console.log(url);
                link.href = url;
                link.download = 'mailedletterhistory_' + this.currentLetterBatchID + '.pdf';
                link.click();
                window.URL.revokeObjectURL(url);
            },
            error => this.errorMessage = <any>error, () => function () {
            } ());

在上面的方法中，数据是响应并且具有带有pdf数据的_body。但下载的文件没有内容（页面为空白）。

有什么想法吗？