Commit 73aef6edfe
modified archive.ReplaceFileTarWrapper to set the Name field in the tar header,
if the field was not set.
That change exposed an issue in how a Dockerfile from stdin was sent to the daemon.
When attempting to build using a build-context, and a Dockerfile from stdin, the
following happened:
```bash
mkdir build-stdin && cd build-stdin && echo hello > hello.txt
DOCKER_BUILDKIT=0 docker build --no-cache -t foo -f- . <<'EOF'
FROM alpine
COPY . .
EOF
Sending build context to Docker daemon 2.607kB
Error response from daemon: dockerfile parse error line 1: unknown instruction: .DOCKERIGNORE
```
Removing the `-t foo`, oddly lead to a different failure:
```bash
DOCKER_BUILDKIT=0 docker build --no-cache -f- . <<'EOF'
FROM alpine
COPY . .
EOF
Sending build context to Docker daemon 2.581kB
Error response from daemon: Cannot locate specified Dockerfile: .dockerfile.701d0d71fb1497d6a7ce
```
From the above, it looks like the tar headers got mangled, causing (in the first
case) the daemon to use the build-context tar as a plain-text file, and therefore
parsing it as Dockerfile, and in the second case, causing it to not being able to
find the Dockerfile in the context.
I noticed that both TarModifierFuncs were using the same `hdrTmpl` struct, which
looks to caused them to step on each other's toes. Changing them to each initialize
their own struct made the issue go away.
After this change:
```bash
DOCKER_BUILDKIT=0 docker build --no-cache -t foo -f- . <<'EOF'
FROM alpine
COPY . .
EOF
Sending build context to Docker daemon 2.607kB
Step 1/2 : FROM alpine
---> d4ff818577bc
Step 2/2 : COPY . .
---> 556f745e6938
Successfully built 556f745e6938
Successfully tagged foo:latest
DOCKER_BUILDKIT=0 docker build --no-cache -f- . <<'EOF'
FROM alpine
COPY . .
EOF
Sending build context to Docker daemon 2.607kB
Step 1/2 : FROM alpine
---> d4ff818577bc
Step 2/2 : COPY . .
---> aaaee43bec5e
Successfully built aaaee43bec5e
```
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
847aef321e