构建AWS Lambda触发器：文件上传至S3后自动执行操作的完整指南"

import aws from 'aws-sdk';
import fs from 'fs';

const s3 = new aws.S3();

export class S3Utils {
    static downloadFileFromS3 = function (bucket: string, fileKey: string, filePath: string) {
        console.log('downloading', bucket, fileKey, filePath);
        return new Promise((resolve, reject) => {
            const file = fs.createWriteStream(filePath),
                stream = s3
                    .getObject({
                        Bucket: bucket,
                        Key: fileKey
                    })
                    .createReadStream();
            stream.on('error', reject);
            file.on('error', reject);
            file.on('finish', () => {
                console.log('downloaded', bucket, fileKey);
                resolve(filePath);
            });
            stream.pipe(file);
        });
    };

    static uploadFileToS3 = function (
        bucket: string,
        fileKey: string,
        filePath: string,
        contentType: string
    ) {
        console.log('uploading', bucket, fileKey, filePath);
        return s3
            .upload({
                Bucket: bucket,
                Key: fileKey,
                Body: fs.createReadStream(filePath),
                ACL: 'private',
                ContentType: contentType
            })
            .promise();
    };

    static cleanDownloadedFile = async (filePath: string) => {
        await fs.unlink(filePath, (err) => {
            console.log('temporary file deleted ');
        });
    };
}

import { S3CreateEvent, Context } from 'aws-lambda';
import path from 'path';
import os from 'os';
import { S3Utils } from '../utils/s3-utils';

const supportedFormats = ['csv', 'xlsx'];

function extractS3Info(event: S3CreateEvent) {
    const eventRecord = event.Records && event.Records[0];
    const bucket = eventRecord.s3.bucket.name;
    const { key } = eventRecord.s3.object;
    return { bucket, key };
}

exports.handler = async (event: S3CreateEvent, context: Context) => {
    try {
        const s3Info = extractS3Info(event);
        const id = context.awsRequestId;
        const extension = path.extname(s3Info.key).toLowerCase();
        const tempFile = path.join(os.tmpdir(), id + extension);
        const extensionWithoutDot = extension.slice(1);

        console.log('converting', s3Info.bucket, ':', s3Info.key, 'using', tempFile);
        if (!supportedFormats.includes(extensionWithoutDot)) {
            throw new Error(`unsupported file type ${extension}`);
        }
        await S3Utils.downloadFileFromS3(s3Info.bucket, s3Info.key, tempFile);
        // 进行你想要的文件操作
        // contentType = `image/${extensionWithoutDot}`;
        // await S3Utils.uploadFileToS3(OUTPUT_BUCKET, s3Info.key, tempFile, contentType);
        await S3Utils.cleanDownloadedFile(tempFile);
    } catch (err) {
        console.log(JSON.stringify(err));
    }
};

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: AWS SAM demo Lambda react to file uploaded to s3

Globals:
    Function:
        Runtime: nodejs14.x
        Timeout: 30

Resources:
    S3BucketToRespond:
        Type: AWS::S3::Bucket
        Properties:
            BucketName: 'Dummy-Bucket'
    
    LambdaThatWillReactToFileUpload:
        Type: AWS::Serverless::Function
        Properties:
            CodeUri: src/s3-file-upload-reaction
            Handler: app.handler
            Events:
                FileUploadedToS3:
                    Type: S3
                    Properties:
                        Bucket: !Ref S3BucketToRespond
                        Events: s3:ObjectCreated:*

    ReadS3BucketPolicy:
        Type: AWS::IAM::Policy
        Properties:
            PolicyName: ReadS3BucketPolicy
            PolicyDocument:
                Version: '2012-10-17'
                Statement:
                    - Effect: Allow
                      Action:
                          - s3:GetObject
                      Resource:
                          - !Sub '${S3BucketToRespond.Arn}/*'
            Roles:
                - !Ref LambdaThatWillReactToFileUploadRole

sam deploy --guided

sam logs -n LambdaThatWillReactToFileUpload --stack-name sam-lambda-trigger-s3-file-upload --tail