创建 lambda 函数以生成 PDF 文件缩略图

Question

我一直在尝试创建一个 AWS 节点 lambda 函数来从 S3 下载 PDF 文件，为该文件的第一页生成缩略图，然后将该缩略图上传回 S3。由于我不是专家，我尝试从 AWS 提供的 Lambda 示例中启发自己来调整图像大小以及在 node.js 中的 PDF 缩略图生成器的 SO 上找到的 node.js，但未能使其工作。 从 S3 下载有效，上传回 S3 有效，但缩略图生成失败。 请参阅下面的代码：

// Download the pdf from S3, create thumbnail, and upload to cache.
	async.waterfall([
		function download(next) {
			// Download the pdf from S3 into a buffer.
			s3.getObject({
					Bucket: BUCKET,
					Key: pdfkey
				},
				next);
			},
		function thumbnail(response, next) {
			gm(response.Body[0]).size(function(err, size) {
				// Transform the image buffer in memory.
				this.resize(requestedwidth, requestedheight).toBuffer(format.toUpperCase(), function(err, buffer) {
					if (err) {
						console.log('failed generating thumbnail');
						next(err);
					} else {
						next(null, response.ContentType, buffer);
					}
				});
			});
		},
		function upload(contentType, data, next) {
			// Stream the thumbnail
			s3.putObject({
					Bucket: BUCKET,
					Key: thumbnailkey,
					ACL:"public-read",
					Body: data,
					ContentType: contentType
				},
				next);
			}
		], function (err) {
			if (err) {
				context.fail(new Error(
					'Unable to create thumbnail for ' + BUCKET + '/' + pdfkey +
					' and upload to ' + BUCKET + '/' + thumbnailkey +
					' due to an error: ' + err
				));
			} else {
				context.succeed(
					'Successfully resized ' + BUCKET + '/' + pdfkey +
					' and uploaded to ' + BUCKET + '/' + thumbnailkey
				);
			}
		}
	);

任何帮助将不胜感激！

Answer 1

这是最终可以运行的代码。以下代码在节点模块中包含以下 4 个库：

• 异步
• 通用
• mktemp
• pdf-图片

：

var async = require('async');
var AWS = require('aws-sdk');
var gm = require('gm').subClass({ imageMagick: true }); // Enable ImageMagick integration. 
var util = require('util');
var fs = require('fs');
var mktemp = require("mktemp");

var BUCKET  = "XXXXXXXXXX";

var s3 = new AWS.S3();
exports.handler = function(event, context) {

var pdfkey = decodeURIComponent(event.pdfkey.replace(/\+/g, " ")); 
var thumbnailkey = decodeURIComponent(event.thumbnailkey.replace(/\+/g, " ")); 
var requestedwidth = event.width;
var requestedheight = event.height;
var shape = event.shape;
var format = event.format;

// Infer the pdf type.
var typeMatch = pdfkey.match(/\.([^.]*)$/);
if (!typeMatch) {
    context.fail(new Error('unable to infer pdf type for key ' + pdfkey));
    return;
}
var fileType = typeMatch[1];
if (fileType != "pdf") {
    context.fail(new Error('skipping non-pdf ' + pdfkey));
    return;
}

// Download the pdf from S3, create thumbnail, and upload to cache.
async.waterfall([
    function download(next) {
        // Download the pdf from S3 into a buffer.
        s3.getObject({
            Bucket: BUCKET,
            Key: pdfkey
        },
        next);
    },
    function thumbnail(response, next) {
        console.log('generating thumbnail');
        var temp_file, image;

        temp_file = mktemp.createFileSync("/tmp/XXXXXXXXXX.pdf");
        fs.writeFileSync(temp_file, response.Body);
        image = gm(temp_file + "[0]").flatten().colorspace("CMYK");

        image.size(function(err, size) {
            if ((requestedwidth > 0) && (requestedheight > 0))
            {

                if (shape == "pad")
                {
                    // Transform the image buffer in memory.
                    this.resize(requestedwidth, requestedheight).gravity('Center').background('transparent').extent(requestedwidth, requestedheight)
                    .toBuffer(format.toUpperCase(), function(err, buffer) {
                        if (err) {
                            next(err);
                        } else {
                            next(null, response.ContentType, buffer);
                        }
                    });
                }
                else
                {
                    // Transform the image buffer in memory.
                    this.resize(requestedwidth, requestedheight)
                    .toBuffer(format.toUpperCase(), function(err, buffer) {
                        if (err) {
                            next(err);
                        } else {
                            next(null, response.ContentType, buffer);
                        }
                    });
                }
            }
            else
            {
                if (requestedwidth > 0)
                {
                    // Transform the image buffer in memory.
                    this.resize(requestedwidth)
                    .toBuffer(format.toUpperCase(), function(err, buffer) {
                        if (err) {
                            next(err);
                        } else {
                            next(null, response.ContentType, buffer);
                        }
                    });

                }
                else
                {
                    // Transform the image buffer in memory.
                    this.resize(null, requestedheight)
                    .toBuffer(format.toUpperCase(), function(err, buffer) {
                        if (err) {
                            next(err);
                        } else {
                            next(null, response.ContentType, buffer);
                        }
                    });
                }
            }
        });
    },
    function upload(contentType, data, next) {
        // Stream the thumbnail
        console.log('uploading thumbnail');
        s3.putObject({
            Bucket: BUCKET,
            Key: thumbnailkey,
            ACL:"public-read",
            Body: data,
            ContentType: "image/" + format
        },
        next);
    }
    ], function (err) {
        if (err) {
            context.fail(new Error(
                'Unable to create thumbnail for ' + BUCKET + '/' + pdfkey +
                ' and upload to ' + BUCKET + '/' + thumbnailkey +
                ' due to an error: ' + err
                ));
        } else {
            context.succeed(
                'Successfully resized ' + BUCKET + '/' + pdfkey +
                ' and uploaded to ' + BUCKET + '/' + thumbnailkey
                );
        }
    }
    );
};