1 files changed, 56 insertions, 0 deletions
diff --git a/monitor/database.go b/monitor/database.go
new file mode 100644
index 0000000..7a0ead1
--- /dev/null
+++ b/monitor/database.go
@@ -0,0 +1,56 @@
+package monitor
+
+import (
+	"fmt"
+	"io/ioutil"
+	"log"
+	"net/http"
+
+	"golang.org/x/mod/sumdb/note"
+	"golang.org/x/mod/sumdb/tlog"
+)
+
+type Database struct {
+	URL string
+	Key string
+}
+
+func (db *Database) readRemote(path string) ([]byte, error) {
+	log.Printf("GET %s", path)
+	resp, err := http.Get("https://" + db.URL + path)
+	if err != nil {
+		return nil, err
+	}
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("get %s: expected HTTP OK but got %s", path, resp.Status)
+	}
+	if resp.ContentLength > 1e6 {
+		return nil, fmt.Errorf("get %s: body too large (%d bytes)", path, resp.ContentLength)
+	}
+	defer resp.Body.Close()
+	body, err := ioutil.ReadAll(resp.Body)
+	if err != nil {
+		return nil, fmt.Errorf("get %s: %v", err)
+	}
+	return body, nil
+}
+
+func (db *Database) VerifyNote(msg []byte) (*note.Note, error) {
+	verifier, err := note.NewVerifier(db.Key)
+	if err != nil {
+		return nil, err
+	}
+	return note.Open(msg, note.VerifierList(verifier))
+}
+
+func (db *Database) FetchSTH() (tlog.Tree, error) {
+	resp, err := db.readRemote("/latest")
+	if err != nil {
+		return tlog.Tree{}, err
+	}
+	note, err := db.VerifyNote(resp)
+	if err != nil {
+		return tlog.Tree{}, err
+	}
+	return tlog.ParseTree([]byte(note.Text))
+}