Intermittent error reading preface from client

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I've found a bug and checked that ...

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• ... there are no open or closed issues that are related to my problem

Description

Run buildx.exe build --file C:\Users\Gili\Documents\docker\buildx\src\test\resources\missing someContextPath

Expected behaviour

I am expecting stderr to return:

ERROR: resolve : CreateFile C:\Users\Gili\Documents\docker\buildx\src\test\resources\missing: The system cannot find the file specified.

Actual behaviour

Intermittently, I get this instead:

2025/06/11 15:53:20 http2: server: error reading preface from client //./pipe/dockerDesktopLinuxEngine: file has already been closed
ERROR: resolve : CreateFile C:\Users\Gili\Documents\docker\buildx\src\test\resources\missing: The system cannot find the file specified.

Buildx version

github.com/docker/buildx v0.24.0 d0e5e86c8b88ae4865040bc96917c338f4dd673c

Docker info

I am running buildx directly, not using docker.

Builders list

NAME/NODE                                DRIVER/ENDPOINT                         STATUS    BUILDKIT   PLATFORMS
SwarmIT.demoteLastManager.manager        docker
 \_ SwarmIT.demoteLastManager.manager     \_ SwarmIT.demoteLastManager.manager   running   v0.22.0    linux/amd64 (+3), linux/arm64, linux/arm (+2), linux/ppc64le, (2 more)
default                                  docker
 \_ default                               \_ default                             running   v0.22.0    linux/amd64 (+3), linux/arm64, linux/arm (+2), linux/ppc64le, (2 more)
desktop-linux*                           docker
 \_ desktop-linux                         \_ desktop-linux                       running   v0.22.0    linux/amd64 (+3), linux/arm64, linux/arm (+2), linux/ppc64le, (2 more)
ServiceIT.listTasksFromManager.manager                                           error
ServiceIT.listTasksFromManager.worker                                            error

Cannot load builder ServiceIT.listTasksFromManager.manager: error during connect: Head "https://localhost:33569/_ping": dial tcp [::1]:33569: connectex: No connection could be made because the target machine actively refused it.
Cannot load builder ServiceIT.listTasksFromManager.worker: error during connect: Head "https://localhost:33583/_ping": dial tcp [::1]:33583: connectex: No connection could be made because the target machine actively refused it.

Configuration

The referenced dockerfile does not exist. This is intentional as the integration test being run checks that the error is handled properly on our end.

Build logs

Additional info

No response

Start by reproducing buildx.exe build --file ... missing someContextPath and examine how the build command connects to the Docker Desktop Linux engine over //./pipe/dockerDesktopLinuxEngine. The fix is complete when the intermittent HTTP/2 preface error is no longer emitted and the expected missing-file error remains.