Bug: Error with binary files sent through api

[mjkubba]

Description:

When sending file (postman or frontend) to backend lambda through API Gateway I'm getting an error while doing local testing with sam local start-api
UnicodeDecodeError while processing HTTP request: 'utf-8' codec can't decode byte 0xb5 in position 473: invalid start byte.
While the deployed application behave normally with an actual API Gateway and Lambda

Steps to reproduce:

template:

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: >
  GAPP-debug

Globals:
  Function:
    Timeout: 360

Resources:
  gappbeapi:
    Type: AWS::Serverless::HttpApi
    Properties:
      CorsConfiguration:
        AllowOrigins:
          - "*"
        AllowMethods:
          - GET
          - POST
          - OPTIONS
        AllowHeaders:
          - Content-Type
          - Accept
          - Access-Control-Allow-Headers
          - Access-Control-Request-Method
          - Access-Control-Request-Headers
          - Authorization
  gappbe:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri: fulfillment/ful_deployment_package.zip
      Handler: index.lambda_handler
      Runtime: python3.13
      Architectures:
        - x86_64
      Events:
        HelloWorld:
          Type: HttpApi
          Properties:
            Path: /sendData
            Method: POST
            ApiId: !Ref gappbeapi
      Policies:
      - Statement:
        - Sid: lambda
          Effect: Allow
          Action:
          - lambda:InvokeFunction
          Resource: arn:aws:lambda:us-east-1:*:function:*

python code example:

# index.py


def lambda_handler(event, context):

    print("do things here")
    try:
        if not event:
            raise ValueError("Empty event object")



        return "All good"

    except Exception as e:
        return "Bad response"

curl:

curl --location 'http://127.0.0.1:3000/sendData' \
--form 'cxName="postman"' \
--form 'email="emailpost"' \
--form 'vafile=@"/Users/xxxx/Downloads/somefile.pdf"'

Observed result:

○ → sam local start-api --debug
2025-03-10 09:20:34,406 | No config file found in this directory.
2025-03-10 09:20:34,408 | OSError occurred while reading TOML file: [Errno 2] No such file or directory: '/Users/mjkubba/workspace/debug/samconfig.toml'
2025-03-10 09:20:34,409 | Config file location: /Users/mjkubba/workspace/debug/samconfig.toml
2025-03-10 09:20:34,410 | Config file '/Users/mjkubba/workspace/debug/samconfig.toml' does not exist
2025-03-10 09:20:34,412 | Using SAM Template at /Users/mjkubba/workspace/debug/template.yaml
2025-03-10 09:20:34,430 | OSError occurred while reading TOML file: [Errno 2] No such file or directory: '/Users/mjkubba/workspace/debug/samconfig.toml'
2025-03-10 09:20:34,431 | Using config file: samconfig.toml, config environment: default
2025-03-10 09:20:34,431 | Expand command line arguments to:
2025-03-10 09:20:34,431 | --template_file=/Users/mjkubba/workspace/debug/template.yaml --host=127.0.0.1 --port=3000 --static_dir=public
--layer_cache_basedir=/Users/mjkubba/.aws-sam/layers-pkg --container_host=localhost --container_host_interface=127.0.0.1
2025-03-10 09:20:34,492 | local start-api command is called
2025-03-10 09:20:34,726 | No Parameters detected in the template
2025-03-10 09:20:34,745 | There is no customer defined id or cdk path defined for resource gappbeapi, so we will use the resource logical id as the resource id
2025-03-10 09:20:34,745 | There is no customer defined id or cdk path defined for resource gappbe, so we will use the resource logical id as the resource id
2025-03-10 09:20:34,746 | 0 stacks found in the template
2025-03-10 09:20:34,746 | No Parameters detected in the template
2025-03-10 09:20:34,756 | There is no customer defined id or cdk path defined for resource gappbeapi, so we will use the resource logical id as the resource id
2025-03-10 09:20:34,756 | There is no customer defined id or cdk path defined for resource gappbe, so we will use the resource logical id as the resource id
2025-03-10 09:20:34,757 | 2 resources found in the stack
2025-03-10 09:20:34,757 | Found Serverless function with name='gappbe' and CodeUri='fulfillment/ful_deployment_package.zip'
2025-03-10 09:20:34,758 | --base-dir is not presented, adjusting uri fulfillment/ful_deployment_package.zip relative to /Users/mjkubba/workspace/debug/template.yaml
2025-03-10 09:20:34,758 | Skip building zip function: gappbe
2025-03-10 09:20:36,121 | Detected Inline Swagger definition
2025-03-10 09:20:36,123 | Parsing Swagger document using 3.0 specification
2025-03-10 09:20:36,123 | Found '0' authorizers in resource 'gappbeapi'
2025-03-10 09:20:36,124 | Lambda function integration not found in Swagger document at path='/sendData' method='post'
2025-03-10 09:20:36,124 | Found '0' APIs in resource 'gappbeapi'
2025-03-10 09:20:36,124 | authorizer not found or disabled, returning early
2025-03-10 09:20:36,125 | Found '1' API Events in Serverless function with name 'gappbe'
2025-03-10 09:20:36,125 | Removed duplicates from '1' Explicit APIs and '0' Implicit APIs to produce '1' APIs
2025-03-10 09:20:36,125 | 1 APIs found in the template
2025-03-10 09:20:36,129 | Mounting gappbe at http://127.0.0.1:3000/sendData [POST, OPTIONS]
2025-03-10 09:20:36,129 | You can now browse to the above endpoints to invoke your functions. You do not need to restart/reload SAM CLI while working on your functions, changes will
be reflected instantly/automatically. If you used sam build before running local commands, you will need to re-run sam build for the changes to be picked up. You only need to restart
SAM CLI if you update your AWS SAM template
2025-03-10 09:20:36,130 | Localhost server is starting up. Multi-threading = True
2025-03-10 09:20:36,130 | Setting SIGTERM interrupt handler
2025-03-10 09:20:36 WARNING: This is a development server. Do not use it in a production deployment. Use a production WSGI server instead.
 * Running on http://127.0.0.1:3000
2025-03-10 09:20:36 Press CTRL+C to quit
2025-03-10 09:20:41,076 | UnicodeDecodeError while processing HTTP request: 'utf-8' codec can't decode byte 0xb5 in position 473: invalid start byte
2025-03-10 09:20:41,077 | Lambda execution failed ()
2025-03-10 09:20:41 127.0.0.1 - - [10/Mar/2025 09:20:41] "POST /sendData HTTP/1.1" 502 -

Expected result:

passing in the file as binary to lambda for processing

Additional environment details (Ex: Windows, Mac, Amazon Linux etc)

○ → sam --info
{
  "version": "1.133.0",
  "system": {
    "python": "3.13.2",
    "os": "macOS-14.7.4-arm64-arm-64bit-Mach-O"
  },
  "additional_dependencies": {
    "docker_engine": "27.3.1",
    "aws_cdk": "2.44.0 (build bf32cb1)",
    "terraform": "1.10.5"
  },
  "available_beta_feature_env_vars": [
    "SAM_CLI_BETA_FEATURES",
    "SAM_CLI_BETA_BUILD_PERFORMANCE",
    "SAM_CLI_BETA_TERRAFORM_SUPPORT",
    "SAM_CLI_BETA_RUST_CARGO_LAMBDA"
  ]
}

1. OS: macOS
2. sam --version: 1.133.0
3. AWS region: us-east-1

[clamb-dunbar]

I'm seeing similar issues; though using
Runtime: nodejs20.x

[vicheey]

The issue happens in event_constructor.py #137 when SAM tries to decode request contains file in pdf or others format.