.NET Min API Lambda经API Gateway返回S3 PDF至Angular仅本地可用

本地运行正常，但通过API Gateway部署到云端后，前端下载的PDF打开提示"File does not begin with '%PDF-'"。Windows环境下，本地启动Angular前端和.NET Min API后端（双localhost）时，PDF下载始终正常。

.NET代码 #

Controller #

[HttpGet("DownloadPDF")]
public async Task<IActionResult> DownloadPDF(string filepath)
{
    /*
     * How To Contribute
     * Call the DownloadPDF function. Pass in your S3 bucket's name and the object's name, or filepath, you want to retrieve.
    */
    
    //Create a memory stream. 
    MemoryStream memoryStream = new MemoryStream();

    //Get PDF from S3 in binary form.
    using (var getPDFResponseStream = await _domain.DownloadPDF(Environment.GetEnvironmentVariable("bucketName"), filepath))
    {
       //Copy bytes from start position 0 to end position y.
       await getPDFResponseStream.CopyToAsync(memoryStream); 
    }

    //Reset the Position property to the beginning.
    memoryStream.Seek(0, SeekOrigin.Begin);

    //Return the binary to the front end.
    return File(memoryStream, MediaTypeNames.Application.Pdf, "dummyPDF.pdf");
}

Domain #

public async Task<Stream> DownloadPDF(string bucketName, string filePath)
{
    /*
     * How To Contribute
     * The filePath string must equal the object name inside the s3 bucket.
     */
    return (await AmazonS3Service.DownloadObjectFromBucketAsync(bucketName, filePath)).ResponseStream;
}

AmazonS3Service #

public static async Task<GetObjectResponse> DownloadObjectFromBucketAsync(
         string bucketName,
         string objectName)
{
    /*
     * Assume a valid IAM role with STS before making S3 call.
     */
    var becomeAuthorizedForS3 = await AmazonSTSService.AssumeRoleAsync(Environment.GetEnvironmentVariable("roleToBeAssumed"));

    //Create an AmazonS3Client
    using AmazonS3Client s3Client = new AmazonS3Client(becomeAuthorizedForS3.Credentials.AccessKeyId, becomeAuthorizedForS3.Credentials.SecretAccessKey, becomeAuthorizedForS3.Credentials.SessionToken, Amazon.RegionEndpoint.USEast1);

    // Create a GetObject request.
    var request = new GetObjectRequest
    {
        BucketName = bucketName,
        Key = objectName,
    };

    // Issue request and return control to calling method. 
    return await s3Client.GetObjectAsync(request);
}

Angular代码 #

HTTP Service #

downloadPDF$ = (filePath: string | undefined) => {
    const url = `${this.basePath}${this.downloadPDFResource}?filePath=${filePath}`;
    return this.http.get(url, {responseType: 'blob'})
}

Component Method #

downloadPDF() {
    let mockFilePath = 'sample_w2.pdf';
    this.taxService.downloadPDF$(mockFilePath).subscribe({
      next: (pdfDataLump: Blob) => {
        saveAs(pdfDataLump, mockPageLink) //npm i file-saver
      },
    });
}

尝试过在Notepad++中编辑下载的PDF，在编码字符串前添加'%PDF-'，但结果PDF损坏，提示"This file is damaged and could not be repaired."。

内容的提问来源于stack exchange，提问作者InstructionDecode