Docker build-push action: Error while parsing json secret

I have a secret file secret.json:

{
  "key1": "value_1",
  "key2": "value_2"
}

and a simple Dockerfile ./src/Dockerfile:

# syntax=docker/dockerfile:1
FROM debian:stable-20230904-slim AS downloader

RUN apt update && apt install -y jq

RUN --mount=type=secret,id=secrets \
    cat /run/secrets/secrets | jq -r '.key1'

When I call the GitHub action

      - name: Build
        uses: docker/build-push-action@v5
        with:
          context: './src/'
          tags: foo/bar:latest
          secret-files: |
            "secrets=./secret.json"  

I receive the following error:

parse error: Invalid numeric literal at line 2, column 7

I tried to base64 encode the json file before passing it to the action and then decode and parse it inside the Dockerfile, but the result is the same. It seems like the double quote characters disappear when the file is read from inside the Docker build and push action

[stage-0 2/2] RUN --mount=type=secret,id=secrets     cat /run/secrets/secrets | sed 's/./&‌/g'

{‌

k‌e‌y‌1‌:‌ ‌v‌a‌l‌u‌e‌_‌1‌,‌
k‌e‌y‌2‌:‌ ‌v‌a‌l‌u‌e‌_‌2‌

}

Tried to reproduce your scenario but it worked fine.

Most probably, you're generating your secret.json and it's not valid JSON to begin with. You need to verify this after generating it. Fixing that part should fix this too.

Here are the details of my test:

Directory structure:

repo
- docker-secrets-test
  - Dockerfile
  - secrets.json

secrets.json

{
    "key1": "value_1",
    "key2": "value_2"
}

Dockerfile

# syntax=docker/dockerfile:1

FROM debian:stable-20230904-slim

RUN apt update && apt install -y jq
RUN \
    --mount=type=secret,id=secrets \
    cat /run/secrets/secrets | jq -r '.key1' > secret.txt

.github/workflows/ci-docker-secrets-test.yml

name: docker_secrets_test

on: workflow_dispatch

jobs:
  ci:
    runs-on: ubuntu-latest

    services:
      registry:
        image: registry:2
        ports:
          - 5000:5000

    steps:
    - name: Checkout
      uses: actions/checkout@v4

    - name: Set up QEMU
      uses: docker/setup-qemu-action@v3

    - name: Set up Docker Buildx
      uses: docker/setup-buildx-action@v3
      with:
        driver-opts: network=host

    - name: Build and push
      uses: docker/build-push-action@v5
      with:
        context: ./docker-secrets-test
        push: true
        tags: localhost:5000/docker-secrets-test:latest
        secret-files: |
          "secrets=./docker-secrets-test/secrets.json"

    - name: Check
      run: |
        docker run --rm localhost:5000/docker-secrets-test:latest cat secret.txt

Output: