Use TMPDIR when commiting images

Fixes: containers#9825

Currently we are using TMPDIR for storaing temporary files
when building images, but not when you directly commit the images.

This change simply uses the TMPDIR environment variable if set
to store temporary files.

Signed-off-by: Daniel J Walsh <dwalsh@redhat.com>

libpod/image/docker_registry_options.go

@@ -69,6 +69,7 @@ func GetSystemContext(signaturePolicyPath, authFilePath string, forceCompress bo
 	sc.AuthFilePath = authFilePath
 	sc.DirForceCompress = forceCompress
 	sc.DockerRegistryUserAgent = fmt.Sprintf("libpod/%s", podmanVersion.Version)
+	sc.BigFilesTemporaryDir = parse.GetTempDir()
 
 	return sc
 }

libpod/image/image_test.go

@@ -9,6 +9,7 @@ import (
 
 	"github.com/containers/podman/v3/libpod/events"
 	"github.com/containers/podman/v3/pkg/util"
+	podmanVersion "github.com/containers/podman/v3/version"
 	"github.com/containers/storage"
 	"github.com/containers/storage/pkg/reexec"
 	"github.com/opencontainers/go-digest"
@@ -293,3 +294,25 @@ func TestNormalizedTag(t *testing.T) {
 		}
 	}
 }
+
+func TestGetSystemContext(t *testing.T) {
+	sc := GetSystemContext("", "", false)
+	assert.Equal(t, sc.SignaturePolicyPath, "")
+	assert.Equal(t, sc.AuthFilePath, "")
+	assert.Equal(t, sc.DirForceCompress, false)
+	assert.Equal(t, sc.DockerRegistryUserAgent, fmt.Sprintf("libpod/%s", podmanVersion.Version))
+	assert.Equal(t, sc.BigFilesTemporaryDir, "/var/tmp")
+
+	oldtmpdir := os.Getenv("TMPDIR")
+	os.Setenv("TMPDIR", "/mnt")
+	sc = GetSystemContext("/tmp/foo", "/tmp/bar", true)
+	assert.Equal(t, sc.SignaturePolicyPath, "/tmp/foo")
+	assert.Equal(t, sc.AuthFilePath, "/tmp/bar")
+	assert.Equal(t, sc.DirForceCompress, true)
+	assert.Equal(t, sc.BigFilesTemporaryDir, "/mnt")
+	if oldtmpdir != "" {
+		os.Setenv("TMPDIR", oldtmpdir)
+	} else {
+		os.Unsetenv("TMPDIR")
+	}
+}