x509: support DER recovery

include/libwebsockets/lws-x509.h

@@ -42,6 +42,11 @@ enum lws_tls_cert_info {
 	 * same tls backend, ie, OpenSSL or mbedTLS.  The different backends
 	 * produce different, incompatible representations for the same cert.
 	 */
+	LWS_TLS_CERT_INFO_DER_RAW,
+	/**< the certificate's raw DER representation.  If it's too big,
+	 * -1 is returned and the size will be returned in buf->ns.len.
+	 * If the certificate cannot be found -1 is returned and 0 in
+	 * buf->ns.len. */
 };
 
 union lws_tls_cert_info_results {

lib/tls/mbedtls/mbedtls-x509.c

@@ -166,6 +166,19 @@ lws_tls_mbedtls_cert_info(mbedtls_x509_crt *x509, enum lws_tls_cert_info type,
 		}
 		break;
 	}
+	case LWS_TLS_CERT_INFO_DER_RAW:
+
+		buf->ns.len = (int)x509->raw.len;
+
+		if (len < x509->raw.len)
+			/*
+			 * The buffer is too small and the attempt failed, but
+			 * the required object length is in buf->ns.len
+			 */
+			return -1;
+
+		memcpy(buf->ns.name, x509->raw.p, x509->raw.len);
+		break;
 
 	default:
 		return -1;

lib/tls/openssl/openssl-x509.c

@@ -164,6 +164,22 @@ lws_tls_openssl_cert_info(X509 *x509, enum lws_tls_cert_info type,
 #endif
 		return 0;
 	}
+	case LWS_TLS_CERT_INFO_DER_RAW:
+	{
+		int der_len = i2d_X509(x509, NULL);
+		uint8_t *tmp = (uint8_t *)buf->ns.name;
+
+		buf->ns.len = der_len < 0 ? 0 : der_len;
+
+		if (der_len < 0 || (size_t)der_len > len)
+			return -1;
+
+		der_len = i2d_X509(x509, &tmp);
+		if (der_len < 0)
+			return -1;
+
+		return 0;
+	}
 	default:
 		return -1;
 	}