Functions event.isbase64Encoded discrepancy in CLI vs Production

[hrishikesh-k]

Describe the bug:

The production server encodes the function's event.body to base64 except for a few content-types as mentioned here: https://answers.netlify.com/t/changed-behavior-in-function-body-encoding/19000.

When submitting a file using a (non-Netlify) form to a Netlify Function, we have to use multipart/form-data content-type which is encoded according to the above post. Thus, we need to decode it as:

Buffer.from(event.body, 'base64').toString('utf8')

However, when doing the same in CLI, the body is not encoded and available easily as event.body.

It can easily be worked around like:

if (event.isbase64Encoded) {
  Buffer.from(event.body, 'base64').toString('utf8')
} else {
  event.body
}

But, it leads to confusion.

To reproduce:

Steps to reproduce the behavior:

1. Clone this commit: https://github.com/Hrishikesh-K/formFile/tree/1f7d002c18eff4830614d6d405d84cee4dd106e8.
2. Navigate to the cloned repository.
3. Run netlify dev.
4. Try to submit the form with any random file and log event.body. Then, log the same in production environment.

Configuration:

netlify.toml:

[build]
  command = "echo Hi!"
  publish = "dist"

[functions]
  directory = "functions"
  node_bundler = "esbuild"

System info:

  System:
    OS: macOS 11.5.2
    CPU: (12) x64 Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
    Memory: 746.86 MB / 16.00 GB
    Shell: 5.8 - /bin/zsh
  Binaries:
    Node: 16.9.0 - /usr/local/bin/node
    npm: 7.21.1 - /usr/local/bin/npm

Expected behaviour:

The CLI should encode event.body to base64.

Additional context:

Slack discussion (INTERNAL ONLY): https://netlify.slack.com/archives/C023PC3D08J/p1631194079008400

[bettse]

I just ran into this myself recently.
I haven't found where the base64 encoding is happening for production, but I believe the discrepancy in the CLI is in this regex: https://github.com/netlify/cli/blob/main/src/lib/functions/utils.js#L6

I suspect adding multipart/form-data would align the experience.

[bettse]

I tracked down what causes this in production, I'll drop the details in slack (https://netlify.slack.com/archives/C023PC3D08J/p1636131535288700)