1 files changed, 95 insertions, 0 deletions
diff --git a/stream/artifact_utils.go b/stream/artifact_utils.go
new file mode 100644
index 0000000..68ae647
--- /dev/null
+++ b/stream/artifact_utils.go
@@ -0,0 +1,95 @@
+package stream
+
+import (
+	"crypto/sha256"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"os"
+	"path"
+	"path/filepath"
+)
+
+// Fetch an artifact, validating its checksum.  If applicable,
+// the artifact will not be decompressed.  Does not
+// validate GPG signature.
+func (a *Artifact) Fetch(w io.Writer) error {
+	resp, err := http.Get(a.Location)
+	if err != nil {
+		return err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return fmt.Errorf("%s returned status: %s", a.Location, resp.Status)
+	}
+	hasher := sha256.New()
+	reader := io.TeeReader(resp.Body, hasher)
+
+	_, err = io.Copy(w, reader)
+	if err != nil {
+		return err
+	}
+
+	// Validate sha256 checksum
+	foundChecksum := fmt.Sprintf("%x", hasher.Sum(nil))
+	if a.Sha256 != foundChecksum {
+		return fmt.Errorf("checksum mismatch for %s; expected=%s found=%s", a.Location, a.Sha256, foundChecksum)
+	}
+
+	return nil
+}
+
+// Name returns the "basename" of the artifact, i.e. the contents
+// after the last `/`.  This can be useful when downloading to a file.
+func (a *Artifact) Name() (string, error) {
+	loc, err := url.Parse(a.Location)
+	if err != nil {
+		return "", fmt.Errorf("failed to parse artifact url: %w", err)
+	}
+	// Note this one uses `path` since even on Windows URLs have forward slashes.
+	return path.Base(loc.Path), nil
+}
+
+// Download fetches the specified artifact and saves it to the target
+// directory.  The full file path will be returned as a string.
+// If the target file path exists, it will be overwritten.
+// If the download fails, the temporary file will be deleted.
+func (a *Artifact) Download(destdir string) (string, error) {
+	name, err := a.Name()
+	if err != nil {
+		return "", err
+	}
+	destfile := filepath.Join(destdir, name)
+	w, err := os.CreateTemp(destdir, ".coreos-artifact-")
+	if err != nil {
+		return "", err
+	}
+	finalized := false
+	defer func() {
+		if !finalized {
+			// Ignore an error to unlink
+			_ = os.Remove(w.Name())
+		}
+	}()
+
+	if err := a.Fetch(w); err != nil {
+		return "", err
+	}
+	if err := w.Sync(); err != nil {
+		return "", err
+	}
+	if err := w.Chmod(0644); err != nil {
+		return "", err
+	}
+	if err := w.Close(); err != nil {
+		return "", err
+	}
+	if err := os.Rename(w.Name(), destfile); err != nil {
+		return "", err
+	}
+	finalized = true
+
+	return destfile, nil
+}