Category Archives: Guides

Upload an Image to S3 Using Post and a Presigned Url

Hi everyone,

Today I’ve been converting my “PUT” upload to S3 to a “POST”. The main motivator for this was to restrict the file size of uploads using a signed policy. Unfortunately this was a pretty tedious process and the error responses from S3 were very vague. Thankfully it’s working now and here’s what I needed to do!

Here’s an excerpt from my nodejs lambda function that generates the presigned url:

/* Creates a pre-signed upload url and then stores a reference in a table */
exports.createUploadUrl = async params => {

    var { databaseHandler, bucketHandler } = params;

    // Create id for upload
    var uploadId = uuidv4();

    // Retrieve pre-signed url
    var bucketDataPromise = createPresignedPostPromise({
        Bucket: process.env.BUCKET_UPLOADS,
        Expires: 60 * 60,
        Conditions: [            
            ["content-length-range", 0, 300000], // 300kb
            [ "eq", "$key", uploadId],
            [ "eq", "$Content-Type", 'image/jpeg' ],
        ]
    });

    // var ddbData = await ddbDataPromise;
    var bucketData = await bucketDataPromise;

    // Wait for database handler to complete operation and then return
    return Helpers.generateResponse({
        data: {
            uploadData: bucketData,
            additionalFields: {
                key: uploadId,
                "Content-Type": 'image/jpeg',
            },
        },
        statusCode: 200
    });
}

You can then retrieve the upload details using a request like the following (Python):

resp = requests.put("https://f86caxqe9f.execute-api.ap-southeast-2.amazonaws.com/Prod/images", data=open(path, 'rb'))

This will return a response similar to the following:

{
    "messages": [],
    "data": {
        "uploadUrl": {
            "url": "YOUR UPLOAD URL",
            "fields": {
                "bucket": "YOUR BUCKET",
                "X-Amz-Algorithm": "AWS4-HMAC-SHA256",
                "X-Amz-Credential": "XXX",
                "X-Amz-Date": "20190107T125044Z",
                "X-Amz-Security-Token": "SECURITY_TOKEN",
                "Policy": "YOUR BASE64 ENCODED POLICY",
                "X-Amz-Signature": "SIGNATURE"
            }
        },
        "uploadId": "UPLOAD_ID"
    }
}

And once you have those details you can use them to upload the image:

# Attempt to retrieve upload url etc
json = resp.json()
data = json["data"]
uploadUrl = data["uploadData"]["url"]
uploadFields = data["uploadData"]["fields"]
uploadFields.update(data["additionalFields"])

try:
    print("Uploading image...",end='')
    headers = {'Content-Type': 'multipart/form-data' }
    files = { 'file': open(path, 'rb')}
    resp = requests.post(uploadUrl, data=uploadFields, files=files)

    # Only show content if there's an error
    if resp.status_code == 200:
        print("Uploaded")
    else:  
        print("ERROR")                          
        print(repr(resp))
        print(repr(resp.content))

except Exception as e:
    print("\r\nFailed to upload image.")
    print("Upload data:")
    print(repr(uploadFields))
    print("Exception:")
    print(repr(e))
    traceback.print_exc()

Hopefully that’s been able to help you out, but feel free to let me know in the comments below if you need more info!

Thanks to these links for the info:
https://stackoverflow.com/a/35923104/522859
https://stackoverflow.com/a/49311831/522859

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Cognito Auth with AWS SAM

Hi everyone,

I’ve spent today implementing Cognito with AWS SAM and it took quite a while to work out what needed to be done – unfortunately there’s a lot of conflicting doco out there. Posting a sample template just in case it’s able to help anyone else out.

The first thing to do is to explicitly define you rest API. By default AWS SAM will generate one with a default logical id of ServerlessRestApi. You’ll need to override this:

Resources:
  # See links for more info
  # Referencing cognito authorizer: https://github.com/awslabs/serverless-application-model/issues/512#issuecomment-411284092
  # Logical id is auto generated: https://github.com/awslabs/serverless-application-model/blob/master/docs/internals/generated_resources.rst#api
  # Sample template.yml: https://github.com/awslabs/serverless-application-model/blob/release/v1.8.0/examples/2016-10-31/api_cognito_auth/template.yaml
  MyCustomApi:
    Type: "AWS::Serverless::Api"
    Properties:
      StageName: Prod
      Auth: # We will eventually define other auth options here such as Usage Plans/Api Keys, AWS_IAM, and Resource Policies
        DefaultAuthorizer: MyCustomCognitoAuthorizer
        Authorizers:
          MyCustomCognitoAuthorizer:
            UserPoolArn: !GetAtt MyCustomCognitoUserPool.Arn # Can be a string, or array
            # Identity: # Optional
              # Header: ... # Optional; Default: Authorization
              # ValidationExpression: ...  # Optional; ensures the request header matches a pattern before checking in with the Authorizer endpoint; is there a default we can set for Cognito User Pools Auth?

You’ll also need to create a user pool and client:

# Creating a cognito user pool - https://github.com/awslabs/serverless-application-model/blob/master/examples/2016-10-31/api_cognito_auth/template.yaml
  MyCustomCognitoUserPool:
    Type: AWS::Cognito::UserPool
    Properties:
      UserPoolName: !Ref CognitoUserPoolName
      # LambdaConfig:
        # PreSignUp: !GetAtt PreSignupLambdaFunction.Arn
      Policies:
        PasswordPolicy:
          MinimumLength: 8
      UsernameAttributes:
        - email
      Schema:
        - AttributeDataType: String
          Name: email
          Required: false

  MyCustomCognitoUserPoolClient:
    Type: AWS::Cognito::UserPoolClient
    Properties:
      UserPoolId: !Ref MyCustomCognitoUserPool
      ClientName: !Ref CognitoUserPoolClientName
      GenerateSecret: false

You then add the api id and the auth attribute to each of your function properties. If you’ve used the default authorizer property when defining the associated api you can override it by using authorizer: none.

GetBreedFunction:
    Type: AWS::Serverless::Function
    Properties:
      Handler: breed.getBreedHandler
      Policies: arn:aws:iam::aws:policy/AmazonDynamoDBFullAccess
      Runtime: nodejs8.10
      Environment:
        Variables:
          TABLE_CAT_BREED: !Ref CatBreedTable
      Events:
        GetEvent:
          Type: Api
          Properties:
            Path: /breed/{breedId}
            Method: get
            RestApiId: !Ref MyCustomCustomApi
            Auth:
              Authorizer: NONE

Hopefully that’s able to help you out. If you run into any trouble I found the following link pretty useful: https://github.com/awslabs/serverless-application-model/blob/release/v1.8.0/examples/2016-10-31/api_cognito_auth/template.yaml

AWS SAM Cheat Sheet/Quick Reference

Hi everyone,

This will just be a living cheat sheet or quick reference for using AWS SAM with nodejs. I’ll add to it as I find things that are useful or I might need again.

General AWS SAM Info:

Description Example More
Validate template sam validate
Start AWS Sam Locally https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/serverless-quick-start.html
Access config variable in Lambda const CAT_BREED_TABLE = process.env.CAT_BREED_TABLE; https://stackoverflow.com/a/48491845/522859
Dynamically reference another resource in template.yml CAT_BREED_TABLE: !Ref DynamoDbCatBreedTable https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference-ref.html

Dynamo DB Local Info:

Description Example More
Create table aws dynamodb create-table –table-name CatBreeds –attribute-definitions AttributeName=CatBreedId,AttributeType=S –key-schema AttributeName=CatBreedId,KeyType=HASH –provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5
–endpoint-url http://192.168.0.31:8000
https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Tools.CLI.html
List Tables aws dynamodb list-tables –endpoint-url http://192.168.0.31:8000 https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Tools.CLI.html
List All Rows in Table aws dynamodb scan –table-name PestinatorTable –endpoint-url http://192.168.0.31:8000 https://stackoverflow.com/a/52236600/522859

Node.js Info:

Description Example More
Run tests npm test

Create DynamoDB Table – AWS CLI

Hi everyone,

A quick example of how to create a dynamodb table using the AWS CLI:

aws dynamodb create-table --table-name CatBreeds --attribute-definitions AttributeName=CatBreedId,AttributeType=S --key-schema AttributeName=CatBreedId,KeyType=HASH --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5

For more info the following AWS page helped me: https://docs.aws.amazon.com/cli/latest/reference/dynamodb/create-table.html

Update Wireless Info on Raspberry Pi

Hi everyone,

Just a quick post on how to configure wireless info on a raspberry pi. To start with, open the config file:

sudo nano /etc/wpa_supplicant/wpa_supplicant.conf

You can then add any number of connections to the file with varying priorities:

ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1
country=AU

network={
        ssid="Mobile Network"
        psk="YOUR_PASSWORD"
        key_mgmt=WPA-PSK
        priority=2
}

network={
        ssid="Home Network"
        psk="YOUR_PASSWORD"
        key_mgmt=WPA-PSK
        priority=10
}

Then save the file. Your raspberry pi will now connect to the network with the highest priority first (home network), when that’s not available it will use the network with the lower priority (mobile network).

The official doco is actually pretty good for this use case if you need more info: https://www.raspberrypi.org/documentation/configuration/wireless/wireless-cli.md

Fetch As Google Error – ReactJs

Hi everyone,

I ran into the following error while using “fetch as Google” and none of my pages were being indexed correctly:

Uncaught TypeError: undefined is not a function

It took a while to find a solution but after some Googling I found that GoogleBot currently uses Chrome v41. You can download the mini installer of Chromium v41 which will run in parallel with your existing Chrome version: https://www.googleapis.com/download/storage/v1/b/chromium-browser-snapshots/o/Win%2F310958%2Fmini_installer.exe?generation=1420864313749000&alt=media

After downloading Chromium you can just debug normally via the console. In my case, Chrome v41 didn’t like the following command:

document.head.append(script);

If you’re using a front-end framework like ReactJS, AngularJS or Vue you’ll often just need to add babel polyfill:


npm install babel-core --save-dev

Then add this as the first line in your entry point e.g. index.js:

import 'babel-core/polyfill';

It’s important that the polyfill import is added as the first line otherwise anything added before it won’t work.

If you’re getting an error about Headers, you may also need to install the following:

npm install whatwg-fetch --save

Add then add this import just below your babel polyfill:

import 'whatwg-fetch'

Thanks to tomekrudzki on Reddit for the link to Chromium v41: Chrome 41 the key to successful website rendering