保存 Parse 对象后退出 Async.waterfall 函数

Question

我的 aws-lambda 函数中有一个异步函数，效果很好。

这样做：

1. 抓取图片（“下载”功能），

2. 裁剪并将其调整为缩略图（“转换”功能），

3. 将该缩略图上传到新存储桶（“上传”功能），

4. 使用缩略图的 url 更新场地对象（这是一个 Parse 对象）（'updateVenue' 函数）

5. 最后，它创建一个新的场景对象（这也是一个解析对象）（'saveScene' 函数）。

**我省略了指定场地对象和场景对象的代码以使其更简单，因为我认为这不是问题。

我的问题是在 updateVenue 函数被记录为成功完成后，下一个日志是：Process exited before completed request.也就是 saveScene 函数永远不会被调用。

即使我颠倒了 updateVenue 和 saveScene 函数的顺序，在第一个 Parse 函数 - saveScene 完成后，该过程也会退出。因此，我认为错误在于我调用这些的方式。

我也在使用 context.succeed() ，也许这与它有关？

// Download the image from S3, transform, and upload to a different S3 bucket.
        async.waterfall([
            function download(next) {
                // Download the image from S3 into a buffer.
                s3.getObject({
                        Bucket: srcBucket,
                        Key: srcKey
                    },
                    next);
                },
            function transform(response, next) {
                gm(response.Body).size(function(err, size) {
                    // Infer the scaling factor to avoid stretching the image unnaturally.
                    WIDTH = size.width;
                    HEIGHT = size.height;


                    if (WIDTH > HEIGHT) {
                        var side = HEIGHT;
                    }
                    else{
                        var side = WIDTH;
                    }

                    var scalingFactor = Math.min(
                                    MAX_WIDTH / side,
                                    MAX_HEIGHT / side
                                );
                                var width  = scalingFactor * side;
                                var height = scalingFactor * side;

                    // Transform the image buffer in memory.
                    this.gravity("Center").crop(side, side).resize(width, height)
                        .toBuffer(imageType, function(err, buffer) {
                            if (err) {
                                next(err); 
                                console.log(err);
                            } else {
                                next(null, response.ContentType, buffer);

                            }
                        });


                });
            },
            function upload(contentType, data, next) {
                // Stream the transformed image to a different S3 bucket.
                s3.putObject({
                        Bucket: dstBucket,
                        Key: dstKey,
                        Body: data,
                        ContentType: contentType
                    },
                    next);
            },
            function updateVenue(next) {
                venueObj.save(null, {
                  success: function(response){
                    console.log('Updated Venue thumbnail succesfully: ', response);
                    context.succeed();
                    next
                  },
                  error: function(response, error){
                      console.log('Failed to update Venue thumbnail, with error code: ' + error.description);
                      context.fail();
                      next
                  }
                }); // end of venueObj.save
            },
            function saveScene(next) {
                sceneObj.save(null, {
                  success: function(response){
                    console.log('Saved sceneObj succesfully: ', response);
                    context.succeed();
                    next
                  },
                  error: function(response, error){
                      console.log('Failed to create new sceneObj, with error code: ' + error.description);
                      context.fail();
                      next 
                  }
                }); // end of sceneObj.save
            }
            ], function (err) {
                if (err) {
                    console.error(
                        'Unable to resize ' + srcBucket + '/' + srcKey +
                        ' and upload to ' + dstBucket + '/' + dstKey +
                        ' due to an error: ' + err
                    );
                } else {
                    console.log(
                        'Successfully resized ' + srcBucket + '/' + srcKey +
                        ' and uploaded to ' + dstBucket + '/' + dstKey
                    );
                }

                callback(null, "message");
            }


        );

Answer 1

我相信您只需要在 updateVenue 和 saveScence 中调用 next。 async.waterfall 将回调传递给系列中的每个函数，您当前正在使用next。如果您需要将数据传递给下一个 fn，请将其作为第二个参数传递给回调。

这是一个如何在updateVenue 中应用的示例：

   function updateVenue(next) {
       return venueObj.save(null, {
           success: function(response){
               console.log('Updated Venue thumbnail succesfully: ',    response);
               return next(null, response);
           },
           error: function(response, error){
               console.log('Failed to update Venue thumbnail, with error code: ' + error.description);
               return next(error);
           }
       }); // end of venueObj.save
   },...

希望有帮助！

Answer 2

我发现了如何解决这个问题。不幸的是，我无法将函数分开，但是，我能够将第二个函数嵌入到第一个函数的完成块中：

// Download the image from S3, transform, and upload to a different S3 bucket.
        async.waterfall([
            function download(next) {
                // Download the image from S3 into a buffer.
                s3.getObject({
                        Bucket: srcBucket,
                        Key: srcKey
                    },
                    next);
                },
            function transform(response, next) {
                gm(response.Body).size(function(err, size) {
                    // Infer the scaling factor to avoid stretching the image unnaturally.
                    WIDTH = size.width;
                    HEIGHT = size.height;


                    if (WIDTH > HEIGHT) {
                        var side = HEIGHT;
                    }
                    else{
                        var side = WIDTH;
                    }

                    var scalingFactor = Math.min(
                                    MAX_WIDTH / side,
                                    MAX_HEIGHT / side
                                );
                                var width  = scalingFactor * side;
                                var height = scalingFactor * side;

                    // Transform the image buffer in memory.
                    this.gravity("Center").crop(side, side).resize(width, height)
                        .toBuffer(imageType, function(err, buffer) {
                            if (err) {
                                next(err); 
                                console.log(err);
                            } else {
                                next(null, response.ContentType, buffer);

                            }
                        });


                });
            },
            function upload(contentType, data, next) {
                // Stream the transformed image to a different S3 bucket.
                s3.putObject({
                        Bucket: dstBucket,
                        Key: dstKey,
                        Body: data,
                        ContentType: contentType
                    },
                    next);
            },
            function updateVenue(next) {
                venueObj.save(null, {
                  success: function(response){
                    console.log('Updated Venue thumbnail succesfully: ', response);
                    sceneObj.save(null, {
                      success: function(response){
                        console.log('Saved sceneObj succesfully: ', response);
                        context.succeed();
                        next
                      },
                      error: function(response, error){
                          console.log('Failed to create new sceneObj, with error code: ' + error.description);
                          context.fail();
                          next 
                      }
                    }); // end of sceneObj.save

                  },
                  error: function(response, error){
                      console.log('Failed to update Venue thumbnail, with error code: ' + error.description);
                      context.fail();
                      next
                  }
                }); // end of venueObj.save
            }
            ], function (err) {
                if (err) {
                    console.error(
                        'Unable to resize ' + srcBucket + '/' + srcKey +
                        ' and upload to ' + dstBucket + '/' + dstKey +
                        ' due to an error: ' + err
                    );
                } else {
                    console.log(
                        'Successfully resized ' + srcBucket + '/' + srcKey +
                        ' and uploaded to ' + dstBucket + '/' + dstKey
                    );
                }

                callback(null, "message");
            }


        );