在Google Cloud Storage上将PDF转换为PNG [英] Convert PDF to PNG on Google Cloud Storage
问题描述
我想从上传到Google存储桶中的不同文件创建PNG缩略图.目前，我的目标是图像和PDF.对于图像，功能正常，但是对于PDF，我无法使其正常工作. 想法是从存储桶中下载文件，执行该工作，然后将新文件(PNG缩略图)上传到存储桶.
I want to create a PNG thumbnail from different files which are uploaded on a Google Storage bucket. For the moment, I am targeting images and PDFs. For images the functions works fine, but for PDFs I cannot make it work. The idea is to download the file from the bucket, do the job and then upload the new file (the PNG thumbnail) to the bucket.
因此，我正在检查上传文件的类型，如果文件是图像，则使用createImageFromImage函数进行转换，如果是PDF，则使用createImageFromPDF.
So I am doing a check to see the type of the uploaded file and if the file is an image I am doing the conversion with the createImageFromImage function and if it's PDF, I am using createImageFromPDF.
主要功能:
const gm = require('gm').subClass({imageMagick: true});
const fs = require('fs');
const path = require('path');
const {Storage} = require('@google-cloud/storage');
const storage = new Storage();
const im = require('imagemagick');
exports.generatePreviewImage = event => {
const object = event.data || event; // Node 6: event.data === Node 8+: event
const file = storage.bucket(object.bucket).file(object.name);
const filePath = `gs://${object.bucket}/${object.name}`;
// Ignore already-resized files (to prevent re-invoking this function)
if (file.name.endsWith('-thumb.png')) {
console.log(`The image ${file.name} is already resized.`);
return;
} else {
console.log(`Analyzing ${file.name}.`);
// Check the file extension
if(object.contentType.startsWith('image/')) { // It's an image
console.log("This is an image!")
return createImageFromImage(file);
} else if (object.contentType === 'application/pdf') { // It's a PDF
console.log("This is a PDF file!")
return createImageFromPDF(file);
} else {
return;
}
}
};
createImageFromImage(file)-起作用
createImageFromImage(file) - which works
function createImageFromImage(file) {
const tempLocalPath = `/tmp/${path.parse(file.name).base}`;
// Download file from bucket.
return file
.download({destination: tempLocalPath})
.catch(err => {
console.error('Failed to download file.', err);
return Promise.reject(err);
})
.then(() => {
console.log(
`Image ${file.name} has been downloaded to ${tempLocalPath}.`
);
// Resize the image using ImageMagick.
return new Promise((resolve, reject) => {
gm(tempLocalPath)
.resize(250)
.setFormat('png')
.write(tempLocalPath, (err, stdout) => {
if (err) {
console.error('Failed to resize the image.', err);
reject(err);
} else {
resolve(stdout);
}
});
});
})
.then(() => {
console.log(`Image ${file.name} has been resized.`);
// Get the name of the file without the file extension and mark the result as resized, to avoid re-triggering this function.
const newName = `${path.parse(file.name).name}-thumb.png`;
// Upload the Blurred image back into the bucket.
return file.bucket
.upload(tempLocalPath, {destination: newName})
.catch(err => {
console.error('Failed to upload resized image.', err);
return Promise.reject(err);
});
})
.then(() => {
console.log(`Resized image has been uploaded to ${file.name}.`);
// Delete the temporary file.
return new Promise((resolve, reject) => {
fs.unlink(tempLocalPath, err => {
if (err) {
reject(err);
} else {
resolve();
}
});
});
});
}
createImageFromPDF(file)-不起作用
createImageFromPDF(file) - which doesn't work
function createImageFromPDF(file) {
const tempLocalPath = `/tmp/${path.parse(file.name).base}`;
return file
.download({destination: tempLocalPath}) // Download file from bucket.
.catch(err => {
console.error('Failed to download file.', err);
return Promise.reject(err);
})
.then(() => { // Convert the file to PDF.
console.log(`File ${file.name} has been downloaded to ${tempLocalPath}.`);
return new Promise((resolve, reject) => {
im.convert([tempLocalPath, '-resize', '250x250', `${path.parse(file.name).name}-thumb.png`],
function(err, stdout) {
if (err) {
reject(err);
} else {
resolve(stdout);
}
});
});
})
.then(() => { // Upload the new image to the bucket
console.log(`File ${file.name} has been resized.`);
// Get the name of the file without the file extension and mark the result as resized, to avoid re-triggering this function.
const newName = `${path.parse(file.name).name}-thumb.png`;
// Upload the Blurred image back into the bucket.
return file.bucket
.upload(tempLocalPath, {destination: newName})
.catch(err => {
console.error('Failed to upload resized image.', err);
return Promise.reject(err);
});
})
.then(() => { // Delete the temporary file.
console.log(`Resized image has been uploaded to ${file.name}.`);
return new Promise((resolve, reject) => {
fs.unlink(tempLocalPath, err => {
if (err) {
reject(err);
} else {
resolve();
}
});
});
});
}
我从im.convert收到一条错误消息:
Command failed: convert: no images defined 'test1-thumb.png' @ error/convert.c/ConvertImageCommand/3210.
我不确定这是否是从PDF文件创建PNG缩略图的正确方法，但我尝试了其他解决方案，但均未成功.请告知我我做错了.谢谢！
I get an error from im.convert which says:
Command failed: convert: no images defined 'test1-thumb.png' @ error/convert.c/ConvertImageCommand/3210.
I am not sure if this is the right way to create a PNG thumbnail from a PDF file, I tried other solutions without success. Please advise what I am doing wrong. Thanks!
推荐答案
我刚刚意识到gm可以处理ImageMagick，而您已经做到了(使用.subClass({imageMagick: true}))，那么为什么还要麻烦另一个包装器呢?
I just realized gm can handle ImageMagick, and you already do it (using .subClass({imageMagick: true})), so why bother with another wrapper?
无论如何，我只是尝试了这一点:
Anyway, I just tried this:
const gm = require('gm').subClass({imageMagick: true});
const file = './test.pdf';
gm(file)
.resize(250, 250)
.setFormat('png')
.write(file, (err) => {
if (err) console.log('FAILED', err);
else console.log('SUCCESS');
});
它指出了一些未授权"错误，因为最初禁用了PDF处理-请参见此-但在我完成之后根据建议编辑了/etc/ImageMagick*/policy.xml，效果很好.
It stated some "not authorized" error because PDF processing is originally disabled - see this - but after I've edited /etc/ImageMagick*/policy.xml as suggested, it worked perfectly.
这篇关于在Google Cloud Storage上将PDF转换为PNG的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
