保存解析对象后退出Async.waterfall函数

Question

I have an async function inside my aws-lambda function that works great.

It does this:

1. grabs an image ('download' function),

2. crops and resizes it to a thumbnail ('transform' function),

3. uploads that thumbnail to a new bucket ('upload' function),

4. Updates a venue object (this is a Parse object) with the url to that thumbnail ('updateVenue' function)

5. Lastly, it creates a new scene object (this is also a parse object) ('saveScene' function).

**I left out the code specifying what the venueObj and sceneObj is to make it simpler as i do not believe that is the problem.

My problem is that after the updateVenue function has been logged as successfully completed, the next log is: Process exited before completing request. Aka the saveScene function never gets called.

Even when I flip the order of the updateVenue and saveScene functions, the process is exited after the first Parse function - saveScene is completed. Therefore, I believe the error is in the way I am calling these.

Also I am using context.succeed() ,maybe that has something to do with it?

// 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

I believe you just have to invoke next within updateVenue and saveScence. async.waterfall passes a callback to each function in the series, where you are currently using next . If you need to pass data to the next fn, you pass it as the second argument to the callback.

Here's an example of how this would apply in updateVenue :

   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
   },...

Hope that helps!

Answer 2

I found out how to solve this. Unfortunately I wasn't able to keep the functions separate, however, I was able to imbed the second one into the completion block of the first one:

// 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");
            }


        );