type_to_string: add secp256k1_ecdsa_signature.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

bitcoin/signature.c

@@ -4,6 +4,7 @@
 #include "shadouble.h"
 #include "signature.h"
 #include "tx.h"
+#include "type_to_string.h"
 #include "utils.h"
 #include <assert.h>
 #include <ccan/cast/cast.h>
@@ -254,3 +255,13 @@ bool sig_valid(const secp256k1_ecdsa_signature *sig)
 		return true;
 	return false;
 }
+
+static char *signature_to_hexstr(const tal_t *ctx,
+				 const secp256k1_ecdsa_signature *sig)
+{
+	u8 der[72];
+	size_t len = signature_to_der(der, sig);
+
+	return tal_hexstr(ctx, der, len);
+}
+REGISTER_TYPE_TO_STRING(secp256k1_ecdsa_signature, signature_to_hexstr);

type_to_string.h

@@ -21,6 +21,7 @@ union printable_types {
 	const secp256k1_pubkey *secp256k1_pubkey;
 	const struct channel_id *channel_id;
 	const struct privkey *privkey;
+	const secp256k1_ecdsa_signature *secp256k1_ecdsa_signature;
 	const char *charp_;
 };