GODT-35: New pmapi client and manager using resty

pkg/pmapi/manager_download.go

@@ -0,0 +1,51 @@
+package pmapi
+
+import (
+	"io/ioutil"
+
+	"github.com/ProtonMail/gopenpgp/v2/crypto"
+)
+
+// DownloadAndVerify downloads a file and its signature from the given locations `file` and `sig`.
+// The file and its signature are verified using the given keyring `kr`.
+// If the file is verified successfully, it can be read from the returned reader.
+// TLS fingerprinting is used to verify that connections are only made to known servers.
+func (m *manager) DownloadAndVerify(kr *crypto.KeyRing, url, sig string) ([]byte, error) {
+	fb, err := m.fetchFile(url)
+	if err != nil {
+		return nil, err
+	}
+
+	sb, err := m.fetchFile(sig)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := kr.VerifyDetached(
+		crypto.NewPlainMessage(fb),
+		crypto.NewPGPSignature(sb),
+		crypto.GetUnixTime(),
+	); err != nil {
+		return nil, err
+	}
+
+	return fb, nil
+}
+
+func (m *manager) fetchFile(url string) ([]byte, error) {
+	res, err := m.rc.R().SetDoNotParseResponse(true).Get(url)
+	if err != nil {
+		return nil, err
+	}
+
+	b, err := ioutil.ReadAll(res.RawBody())
+	if err != nil {
+		return nil, err
+	}
+
+	if err := res.RawBody().Close(); err != nil {
+		return nil, err
+	}
+
+	return b, nil
+}