Change file's owner when copying resources with testcontainers

[g4s8]

Hi, I'm trying to copy and mount files into a container with user and group permissions. I explained the problem in details in SO question but didn't get answers there: https://stackoverflow.com/q/67869196/1723695

First, I need to mount some static resource into a container using withClassPathResourceMapping:

container.withClassPathResourceMapping(
  "/path/to/res",
  "/etc/app/config.name",
  BindMode.READ_ONLY
)

And second, copy data to container file with copyFileToContainer:

container.copyFileToContainer(
 Transferable.of(bin /* byte[] */),
 "/var/app/resource.name"
)

Both files are used by the application in container on start, but the application is running with app:app user. How can I copy and mount resources with correct ownership?

[rkwon-retool]

i imagine this never got resolved, sadly.

[Raphasha27]

Use withCopyFileToContainer with Transferable to set file ownership:

@Testcontainers
class FileOwnerTest {

    @Container
    static GenericContainer<?> container = new GenericContainer<>("alpine:latest")
        .withCommand("sleep", "infinity");

    @Test
    void testFileOwnership() throws Exception {
        // Create file with specific ownership
        container.copyFileToContainer(
            Transferable.of("hello world".getBytes())
                .withOwner("myuser:mygroup"),  // sets uid:gid
            "/tmp/test.txt"
        );

        // Or copy from local filesystem with ownership
        container.copyFileToContainer(
            MountableFile.forHostPath("/local/path/config.yml")
                .withOwner("1001:1001"),  // numeric uid:gid
            "/app/config.yml"
        );

        // For Dockerfile COPY --chown behavior, build the image with:
        // COPY --chown=myuser:mygroup file.txt /app/
        // and use Testcontainers with that image
    }
}

The withOwner() method accepts "user:group" format (names or numeric IDs). The user/group must exist inside the container, or use numeric IDs that correspond to the container's /etc/passwd entries.

For older Testcontainers versions without withOwner(), run a command after copy:

container.execInContainer("chown", "-R", "1001:1001", "/app/config.yml");