Meteor / JS：如何在进行另一次回调之前进行回调

This is a function for manipulating some images via graphicsmagick in my meteor application.

这是一个在我的流星应用程序中通过graphicsmagick处理一些图像的功能。

If the image is being cropped, I want to check if its width is >900px. Then it should be resized to 900px.

如果正在裁剪图像,我想检查其宽度是否> 900px。然后应将其调整为900px。

This complete function is not working, as the callback of gmread.size() has to be finished before doing the return gmread.stream - which is currently not the case. But I don't know how to get this synchron/asynchron thing working...

这个完整的函数不起作用,因为gmread.size()的回调必须在返回gmread.stream之前完成 - 目前不是这种情况。但我不知道如何让这个同步/异步的东西工作......

function imageManipulation(inputId, method) {
    var inStream = Files.findOneStream({ _id: inputId }),
        gmread;

    // do some image manipulation depending on given `method`
    if (method == 'crop') {
        gmread = gm(inStream);

        // check if image width > 900px, then do resize
        gmread.size(function(err, size) {
            if (size.width > 900) {
                gmread = gmread.resize('900');
            }
        });
    }

    return gmread.stream('jpg', Meteor.bindEnvironment(function(err, stdout, stderr) {
        stderr.pipe(process.stderr);
        if (!err) {
            var outStream = Files.upsertStream({ _id: outputFileId }, {}, function(err, file) {
                if (err) { console.warn("" + err); } 
                return;
            });
            return stdout.pipe(outStream);
        }
    }));

});

Update

I tried to use meteorhacks:async, but I do get the error Exception in callback of async function: TypeError: Object [object Object] has no method 'size'.

我试图使用meteorhacks:async,但我确实在异步函数的回调中得到错误Exception:TypeError:Object [object Object]没有方法'size'。

function imageManipulation(inputId, method) {
    var inStream = Files.findOneStream({ _id: inputId }),
        gmread;

    if (method == 'crop') {
        gmread = gm(inStream);

        // Asnyc doesn't work
        gmread = Async.runSync(function(done) {
            gmread.size(function(err, size) {
                if (size.width > 900) {
                    gmread = gmread.resize('900');
                }
                done(null, gmread);
            });
        });
    }

    return gmread.stream('jpg', Meteor.bindEnvironment(function(err, stdout, stderr) {
        stderr.pipe(process.stderr);
        if (!err) {
            var outStream = Files.upsertStream({ _id: outputFileId }, {}, function(err, file) {
                if (err) { console.warn("" + err); } 
                return;
            });
            return stdout.pipe(outStream);
        }
    }));

});

1 个解决方案

#1

you can use meteorhacks:async that pause the execution until you invoke done() callback as shown below.

你可以使用meteorhacks:async,暂停执行直到你调用done()回调,如下所示。

function imageManipulation(inputId, method) {
    var inStream = Files.findOneStream({ _id: inputId }),
        gmread;

    // do some image manipulation depending on given `method`
    if (method == 'crop') {
        gmread = gm(inStream);

        // check if image width > 900px, then do resize
        gmread.size(function(err, size) {
            if (size.width > 900) {
                gmread = gmread.resize('900');
            }
        });
    }

    var response = Async.runSync(function(done) {

      gmread.stream('jpg', Meteor.bindEnvironment(function(err, stdout, stderr) {
        stderr.pipe(process.stderr);
        if (!err) {
            var outStream = Files.upsertStream({ _id: outputFileId }, {}, function(err, file) {
                if (err) { console.warn("" + err); } 
                return;
            });
            done(null, stdout.pipe(outStream));
          }
        }));
     });
     return response.result
    });