javascript - 使用 graphicsmagick 的 collectionFS 中出现意外的空写入流

Question

我正在使用 CollectionFS 来管理图像。此外，我正在使用 graphicsmagick gm() 来处理图像。

现在我想裁剪已保存的图像。因此，在单击事件上调用服务器方法，该方法执行 crop()。但是在这样做之后，我在集合中找到了一个空图像，其中 size=0 在正确的日期更新。

我不明白，我做错了什么。

shared.js

Images = new FS.Collection("images", {
    stores: [
        new FS.Store.FileSystem("thumbnail", { 
            transformWrite: function(fileObj, readStream, writeStream) {
                gm(readStream, fileObj.name()).autoOrient().resize('96', '96' + '^').gravity('Center').extent('96', '96').stream().pipe(writeStream);
            } 
        }),
        new FS.Store.FileSystem("public"),
    ]
});

server.js

Meteor.methods({
    'crop': function (fileId, selection) {
        var file = Images.findOne({ _id: fileId }),
            read = file.createReadStream('public'),
            write = file.createWriteStream('public');

        gm(read)
            .crop(selection.width, selection.height, selection.left, selection.top)
        .stream()
        .pipe(write);
    }
});

client.js

Template.editor.events({
    'click #crop': function () { 
        var fileId      = '123456789',
            selection   = { height: 100, width: 100, top: 10, left: 10 }; 

        Meteor.call('crop', fileId, selection);
    }
});

更新

按照 Christian 的建议，我正在为 writeStream 使用 tmp 文件，因为 writeStream 不能与 readStream 相同——这导致了空结果。

但是在写入 tmp 文件之后，它的内容必须被复制回公共(public)存储。我该怎么做？

Meteor.methods({
    'crop': function (fileId, selection) {

        var fs   = Meteor.npmRequire('fs'),
            file = Images.findOne({ _id: fileId }),
            read = file.createReadStream('public'),
            filename = '/tmp/gm_' + Date.now(),
            tmp  = fs.createWriteStream(filename);

        gm(read)
            .crop(selection.width, selection.height, selection.left, selection.top)
        .stream()
        .pipe(tmp);

        // After writing to tmp -> copy back to stream and delete tmp-file
    }
});

更新 2我试过这个:

// Add temp store
new FS.Store.FileSystem("temp")

// Method
Meteor.methods({
    'crop': function (fileId, selection) {
        var file  = Images.findOne({ _id: fileId }),
            read  = file.createReadStream('public'),
            temp  = file.createWriteStream('temp');

        gm(read)
            .crop(selection.width, selection.height, selection.left, selection.top)
        .stream()
        .pipe(tmp)
        .on('end', function () {
            var tmpread  = file.createReadStream('temp'),
                write    = file.createWriteStream('public');

            gm(tmpread).stream().pipe(write);
        });

    }
});

Answer 1

您不能读取和写入同一个文件。这相当于

cat test | grep 1 > test

在外壳上。你可以试试看，test 之后会是空的。

您需要在 crop 方法中创建一个中间的临时文件。

---

假设这确实是问题所在，那么这是一种方法(未测试):

var fs = Meteor.npmRequire('fs');
var file = Images.findOne({ _id: fileId }),
var read = file.createReadStream('public'),
var filename = '/tmp/gm_' + Date.now();
var tmp = fs.createWriteStream(filename);

var gmread = gm(read)
    .crop(selection.width, selection.height, selection.left, selection.top)
    .stream();

gmread.on('end', function() {
    // done streaming through GM, copy the result back:
    var tmpread = fs.createReadStream(filename);
    var write = file.createWriteStream('public');
    tmpread.pipe(write);
});

gmread.pipe(tmp);