问题
Cloud Functions for Firebase has this nice sample where they create a thumbnail for each uploaded image. This is done by making use of ImageMagick.
I tried to convert the sample to convert PDFs to images. This is something ImageMagick can do, but I can't make it work with Cloud Functions for Firebase. I keep getting a code 1 error:
ChildProcessError: `convert /tmp/cd9d0278-16b2-42be-aa3d-45b5adf89332.pdf[0] -density 200 /tmp/cd9d0278-16b2-42be-aa3d-45b5adf89332.pdf` failed with code 1
at ChildProcess.<anonymous> (/user_code/node_modules/child-process-promise/lib/index.js:132:23)
at emitTwo (events.js:106:13)
at ChildProcess.emit (events.js:191:7)
at maybeClose (internal/child_process.js:877:16)
at Socket.<anonymous> (internal/child_process.js:334:11)
at emitOne (events.js:96:13)
at Socket.emit (events.js:188:7)
at Pipe._handle.close [as _onclose] (net.js:498:12)
Of course one possibility is that converting PDFs are simply not supported.
const functions = require('firebase-functions');
const gcs = require('@google-cloud/storage')();
const spawn = require('child-process-promise').spawn;
// [END import]
// [START generateThumbnail]
/**
* When an image is uploaded in the Storage bucket We generate a thumbnail automatically using
* ImageMagick.
*/
// [START generateThumbnailTrigger]
exports.generateThumbnail = functions.storage.object().onChange(event => {
// [END generateThumbnailTrigger]
// [START eventAttributes]
const object = event.data; // The Storage object.
const fileBucket = object.bucket; // The Storage bucket that contains the file.
const filePath = object.name; // File path in the bucket.
const contentType = object.contentType; // File content type.
const resourceState = object.resourceState; // The resourceState is 'exists' or 'not_exists' (for file/folder deletions).
// [END eventAttributes]
// [START stopConditions]
// Exit if this is triggered on a file that is not an image.
if (!contentType.startsWith('application/pdf')) {
console.log('This is not a pdf.');
return;
}
// Get the file name.
const fileName = filePath.split('/').pop();
// Exit if the image is already a thumbnail.
if (fileName.startsWith('thumb_')) {
console.log('Already a Thumbnail.');
return;
}
// Exit if this is a move or deletion event.
if (resourceState === 'not_exists') {
console.log('This is a deletion event.');
return;
}
// [END stopConditions]
// [START thumbnailGeneration]
// Download file from bucket.
const bucket = gcs.bucket(fileBucket);
const tempFilePath = `/tmp/${fileName}`;
return bucket.file(filePath).download({
destination: tempFilePath
}).then(() => {
console.log('Pdf downloaded locally to', tempFilePath);
// Generate a thumbnail of the first page using ImageMagick.
return spawn('convert', [tempFilePath+'[0]' ,'-density', '200', tempFilePath]).then(() => {
console.log('Thumbnail created at', tempFilePath);
// Convert pdf extension to png
const thumbFilePath = filePath.replace('.pdf', 'png');
// Uploading the thumbnail.
return bucket.upload(tempFilePath, {
destination: thumbFilePath
});
});
});
// [END thumbnailGeneration]
});
回答1:
Node modules can install native code that is in the same directory as the Cloud Function's source code. I found that some node libraries on github that do this for ghostscript which is a very useful library for PDF processing:
- Node library that wraps Ghostscript command line: https://github.com/sina-masnadi/node-gs
- Compiled Ghostscript which is used via git submodule: https://github.com/sina-masnadi/lambda-ghostscript
I put lambda-ghostscript into a sub-directory of my functions directory, then add the node-gs as a dependency in my package file like this:
{
"name": "functions",
"dependencies": {
"@google-cloud/storage": "^1.3.1",
"child-process-promise": "^2.2.1",
"firebase-admin": "~5.4.0",
"firebase-functions": "^0.7.2",
"gs": "https://github.com/sina-masnadi/node-gs/tarball/master"
}
}
Then in my index.js file I can just require the node library to easily use ghostscript from JavaScript. Here's the complete code for the Cloud Function that uses a Google Cloud Storage trigger:
const functions = require('firebase-functions');
const gcs = require('@google-cloud/storage')();
const spawn = require('child-process-promise').spawn;
const path = require('path');
const os = require('os');
const fs = require('fs');
var gs = require('gs');
exports.makePNG = functions.storage.object().onChange(event => {
// ignore delete events
if (event.data.resourceState == 'not_exists') return false;
const filePath = event.data.name;
const fileDir = path.dirname(filePath);
const fileName = path.basename(filePath);
const tempFilePath = path.join(os.tmpdir(), fileName);
if (fileName.endsWith('.png')) return false;
if (!fileName.endsWith('.pdf')) return false;
const newName = path.basename(filePath, '.pdf') + '.png';
const tempNewPath = path.join(os.tmpdir(), newName);
// // Download file from bucket.
const bucket = gcs.bucket(event.data.bucket);
return bucket.file(filePath).download({
destination: tempFilePath
}).then(() => {
console.log('Image downloaded locally to', tempFilePath);
return new Promise(function (resolve, reject) {
gs()
.batch()
.nopause()
.option('-r' + 50 * 2)
.option('-dDownScaleFactor=2')
.executablePath('lambda-ghostscript/bin/./gs')
.device('png16m')
.output(tempNewPath)
.input(tempFilePath)
.exec(function (err, stdout, stderr) {
if (!err) {
console.log('gs executed w/o error');
console.log('stdout',stdout);
console.log('stderr',stderr);
resolve();
} else {
console.log('gs error:', err);
reject(err);
}
});
});
}).then(() => {
console.log('PNG created at', tempNewPath);
// Uploading the thumbnail.
return bucket.upload(tempNewPath, {destination: newName});
// Once the thumbnail has been uploaded delete the local file to free up disk space.
}).then(() => {
fs.unlinkSync(tempNewPath);
fs.unlinkSync(tempFilePath);
}).catch((err) => {
console.log('exception:', err);
return err;
});
});
Here's the project on github: https://github.com/ultrasaurus/ghostscript-cloud-function
Disclaimer: This is using compiled native code and I verified experimentally that works for this case, so it is probably fine. I didn't look into the specific compile options and validate if they exactly correct for the Cloud Functions environment.
来源：https://stackoverflow.com/questions/43242998/cloud-functions-for-firebase-converting-pdf-to-image