cache: Support artifacts compressed with xz

Switches to "github.com/h2non/filetype/matchers" for MIME type matching
and uses "github.com/ulikunitz/xz" for xz decompression.

go.mod

@@ -40,6 +40,7 @@ require (
 	github.com/gorilla/websocket v1.4.1 // indirect
 	github.com/grpc-ecosystem/go-grpc-middleware v1.1.0 // indirect
 	github.com/grpc-ecosystem/grpc-gateway v1.12.1 // indirect
+	github.com/h2non/filetype v1.0.12
 	github.com/hashicorp/go-azure-helpers v0.10.0
 	github.com/hashicorp/go-plugin v1.0.1
 	github.com/hashicorp/go-retryablehttp v0.6.4 // indirect
@@ -98,6 +99,7 @@ require (
 	github.com/terraform-providers/terraform-provider-openstack v1.25.0
 	github.com/terraform-providers/terraform-provider-random v1.3.2-0.20190925210718-83518d96ae4f
 	github.com/terraform-providers/terraform-provider-vsphere v0.0.0
+	github.com/ulikunitz/xz v0.5.6
 	github.com/vincent-petithory/dataurl v0.0.0-20191104211930-d1553a71de50
 	github.com/vmware/govmomi v0.22.1
 	go.uber.org/atomic v1.5.1 // indirect

go.sum

@@ -1214,6 +1214,8 @@ github.com/grpc-ecosystem/grpc-gateway v1.9.4/go.mod h1:vNeuVxBJEsws4ogUvrchl83t
 github.com/grpc-ecosystem/grpc-gateway v1.9.5/go.mod h1:vNeuVxBJEsws4ogUvrchl83t/GYV9WGTSLVdBhOQFDY=
 github.com/grpc-ecosystem/grpc-gateway v1.12.1 h1:zCy2xE9ablevUOrUZc3Dl72Dt+ya2FNAvC2yLYMHzi4=
 github.com/grpc-ecosystem/grpc-gateway v1.12.1/go.mod h1:8XEsbTttt/W+VvjtQhLACqCisSPWTxCZ7sBRjU6iH9c=
+github.com/h2non/filetype v1.0.12 h1:yHCsIe0y2cvbDARtJhGBTD2ecvqMSTvlIcph9En/Zao=
+github.com/h2non/filetype v1.0.12/go.mod h1:319b3zT68BvV+WRj7cwy856M2ehB3HqNOt6sy1HndBY=
 github.com/hailocab/go-hostpool v0.0.0-20160125115350-e80d13ce29ed/go.mod h1:tMWxXQ9wFIaZeTI9F+hmhFiGpFmhOHzyShyFUhRm0H4=
 github.com/hashicorp/aws-sdk-go-base v0.4.0 h1:zH9hNUdsS+2G0zJaU85ul8D59BGnZBaKM+KMNPAHGwk=
 github.com/hashicorp/aws-sdk-go-base v0.4.0/go.mod h1:eRhlz3c4nhqxFZJAahJEFL7gh6Jyj5rQmQc7F9eHFyQ=

pkg/tfvars/internal/cache/cache.go

@@ -12,8 +12,10 @@ import (
 	"os"
 	"path/filepath"
 
+	"github.com/h2non/filetype/matchers"
 	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
+	"github.com/ulikunitz/xz"
 
 	"golang.org/x/sys/unix"
 )
@@ -21,7 +23,6 @@ import (
 const (
 	applicationName = "openshift-installer"
 	imageDataType   = "image"
-	gzipFileType    = "application/x-gzip"
 )
 
 // getCacheDir returns a local path of the cache, where the installer should put the data:
@@ -119,18 +120,25 @@ func cacheFile(reader io.Reader, filePath string, sha256Checksum string) (err er
 	}
 
 	reader = io.MultiReader(bytes.NewReader(buf), reader)
-	fileType := http.DetectContentType(buf)
+	switch {
-	logrus.Debugf("content type of %s is %s", filePath, fileType)
+	case matchers.Gz(buf):
-	switch fileType {
+		logrus.Debug("decompressing the image archive as gz")
-	case gzipFileType:
 		uncompressor, err := gzip.NewReader(reader)
 		if err != nil {
 			return err
 		}
 		defer uncompressor.Close()
 		reader = uncompressor
+	case matchers.Xz(buf):
+		logrus.Debug("decompressing the image archive as xz")
+		uncompressor, err := xz.NewReader(reader)
+		if err != nil {
+			return err
+		}
+		reader = uncompressor
 	default:
 		// No need for an interposer otherwise
+		logrus.Debug("no known archive format detected for image, assuming no decompression necessary")
 	}
 
 	// Wrap the reader in TeeReader to calculate sha256 checksum on the fly