pkg/download: for downloading files into tmp

cmd/podman needs that functionality as well, so I figured it makes sense
to break it into a separate package to reduce code clones.

Signed-off-by: Valentin Rothberg <rothberg@redhat.com>

common/libimage/download.go

@@ -1,46 +0,0 @@
-package libimage
-
-import (
-	"fmt"
-	"io"
-	"io/ioutil"
-	"net/http"
-	"os"
-
-	"github.com/pkg/errors"
-)
-
-// tmpdir returns a path to a temporary directory.
-func tmpdir() string {
-	tmpdir := os.Getenv("TMPDIR")
-	if tmpdir == "" {
-		tmpdir = "/var/tmp"
-	}
-
-	return tmpdir
-}
-
-// downloadFromURL downloads an image in the format "https:/example.com/myimage.tar"
-// and temporarily saves in it $TMPDIR/importxyz, which is deleted after the image is imported
-func (r *Runtime) downloadFromURL(source string) (string, error) {
-	fmt.Printf("Downloading from %q\n", source)
-
-	outFile, err := ioutil.TempFile(r.systemContext.BigFilesTemporaryDir, "import")
-	if err != nil {
-		return "", errors.Wrap(err, "error creating file")
-	}
-	defer outFile.Close()
-
-	response, err := http.Get(source) // nolint:noctx
-	if err != nil {
-		return "", errors.Wrapf(err, "error downloading %q", source)
-	}
-	defer response.Body.Close()
-
-	_, err = io.Copy(outFile, response.Body)
-	if err != nil {
-		return "", errors.Wrapf(err, "error saving %s to %s", source, outFile.Name())
-	}
-
-	return outFile.Name(), nil
-}

common/libimage/import.go

@@ -2,9 +2,11 @@ package libimage
 
 import (
 	"context"
+	"fmt"
 	"net/url"
 	"os"
 
+	"github.com/containers/common/pkg/download"
 	storageTransport "github.com/containers/image/v5/storage"
 	tarballTransport "github.com/containers/image/v5/tarball"
 	v1 "github.com/opencontainers/image-spec/specs-go/v1"
@@ -61,7 +63,8 @@ func (r *Runtime) Import(ctx context.Context, path string, options *ImportOption
 	u, err := url.ParseRequestURI(path)
 	if err == nil && u.Scheme != "" {
 		// If source is a URL, download the file.
-		file, err := r.downloadFromURL(path)
+		fmt.Printf("Downloading from %q\n", path)
+		file, err := download.FromURL(r.systemContext.BigFilesTemporaryDir, path)
 		if err != nil {
 			return "", err
 		}

common/libimage/runtime.go

@@ -21,6 +21,16 @@ import (
 // Faster than the standard library, see https://github.com/json-iterator/go.
 var json = jsoniter.ConfigCompatibleWithStandardLibrary
 
+// tmpdir returns a path to a temporary directory.
+func tmpdir() string {
+	tmpdir := os.Getenv("TMPDIR")
+	if tmpdir == "" {
+		tmpdir = "/var/tmp"
+	}
+
+	return tmpdir
+}
+
 // RuntimeOptions allow for creating a customized Runtime.
 type RuntimeOptions struct {
 	// The base system context of the runtime which will be used throughout

common/pkg/download/download.go

@@ -0,0 +1,31 @@
+package download
+
+import (
+	"fmt"
+	"io"
+	"io/ioutil"
+	"net/http"
+)
+
+// FromURL downloads the specified source to a file in tmpdir (OS defaults if
+// empty).
+func FromURL(tmpdir, source string) (string, error) {
+	tmp, err := ioutil.TempFile(tmpdir, "")
+	if err != nil {
+		return "", fmt.Errorf("creating temporary download file: %w", err)
+	}
+	defer tmp.Close()
+
+	response, err := http.Get(source) // nolint:noctx
+	if err != nil {
+		return "", fmt.Errorf("downloading %s: %w", source, err)
+	}
+	defer response.Body.Close()
+
+	_, err = io.Copy(tmp, response.Body)
+	if err != nil {
+		return "", fmt.Errorf("copying %s to %s: %w", source, tmp.Name(), err)
+	}
+
+	return tmp.Name(), nil
+}