From 5d741b9d41224bc739878a5aa5c9e628879113e6 Mon Sep 17 00:00:00 2001
From: chrysn <chrysn@fsfe.org>
Date: Thu, 2 Mar 2023 09:15:51 +0100
Subject: [PATCH 1/3] pkg/tinydtls: Set buffer size as required for gcoap

---
 pkg/tinydtls/Makefile | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/pkg/tinydtls/Makefile b/pkg/tinydtls/Makefile
index 973f44dbc1996..79cb15cfcc29e 100644
--- a/pkg/tinydtls/Makefile
+++ b/pkg/tinydtls/Makefile
@@ -18,3 +18,18 @@ all:
 ifeq (llvm,$(TOOLCHAIN))
   CFLAGS += -Wno-format-nonliteral
 endif
+
+ifneq (,$(filter gcoap,$(USEMODULE)))
+    # Configuring the buffer large enough that a full Gcoap packet can be
+    # encrypted or decrypted.
+
+    # This is the default in gcoap.h, which we don't have access to, so it is copied over.
+    CONFIG_GCOAP_PDU_BUF_SIZE := $(or $(CONFIG_GCOAP_PDU_BUF_SIZE),128)
+
+    # If there were another way to set up DTLS_MAX_BUF, we'd need to set the
+    # maximum of these here.
+    #
+    # 29 bytes are the overhead measured with Wireshark on packets exchanged in
+    # default configuration; adding some to be safe against variable size fields.
+    CFLAGS += "-DDTLS_MAX_BUF=($(CONFIG_GCOAP_PDU_BUF_SIZE) + 36)"
+endif

From f7a83a7edcf4bcbd317dc338ff143aefb51691a5 Mon Sep 17 00:00:00 2001
From: chrysn <chrysn@fsfe.org>
Date: Thu, 2 Mar 2023 09:16:09 +0100
Subject: [PATCH 2/3] tinydtls: Reduce default verbosity

---
 pkg/tinydtls/Makefile | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/pkg/tinydtls/Makefile b/pkg/tinydtls/Makefile
index 79cb15cfcc29e..4d6bdd1002666 100644
--- a/pkg/tinydtls/Makefile
+++ b/pkg/tinydtls/Makefile
@@ -33,3 +33,8 @@ ifneq (,$(filter gcoap,$(USEMODULE)))
     # default configuration; adding some to be safe against variable size fields.
     CFLAGS += "-DDTLS_MAX_BUF=($(CONFIG_GCOAP_PDU_BUF_SIZE) + 36)"
 endif
+
+# TinyDTLS emits several messages during connection establishment at the info
+# level; this is way more verbose than common in RIOT.
+TINYDTLS_LOG_LEVEL ?= LOG_WARNING
+CFLAGS += -DLOG_LEVEL=$(TINYDTLS_LOG_LEVEL)

From f2d5928ee5b01c28d0e0aca719e5e1336f6c07fb Mon Sep 17 00:00:00 2001
From: chrysn <chrysn@fsfe.org>
Date: Tue, 28 Feb 2023 16:06:39 +0100
Subject: [PATCH 3/3] dtls, tinydtls: Raise default number of connections

---
 pkg/tinydtls/Kconfig          | 1 +
 pkg/tinydtls/Makefile.include | 6 ++++++
 sys/include/net/dtls.h        | 6 ++++++
 3 files changed, 13 insertions(+)

diff --git a/pkg/tinydtls/Kconfig b/pkg/tinydtls/Kconfig
index 14ef675737e44..daf62b0fb1862 100644
--- a/pkg/tinydtls/Kconfig
+++ b/pkg/tinydtls/Kconfig
@@ -38,6 +38,7 @@ config DTLS_CONTEXT_MAX
 
 config DTLS_PEER_MAX
     int "Max number of peers"
+    default 2 if KCONFIG_USEMODULE_GCOAP_DTLS
     default 1
     help
         The maximum number of DTLS peers.
diff --git a/pkg/tinydtls/Makefile.include b/pkg/tinydtls/Makefile.include
index fda2825bd6ef4..79245a2b986a5 100644
--- a/pkg/tinydtls/Makefile.include
+++ b/pkg/tinydtls/Makefile.include
@@ -63,6 +63,12 @@ endif
 PEER_MAX := $(or $(CONFIG_DTLS_PEER_MAX),$(patsubst -DCONFIG_DTLS_PEER_MAX=%,%,$(filter -DCONFIG_DTLS_PEER_MAX=%,$(CFLAGS))))
 ifneq (,$(PEER_MAX))
     CFLAGS += -DDTLS_PEER_MAX=$(PEER_MAX)
+else ifneq (,$(filter gcoap_dtls,$(USEMODULE)))
+    # The default value in sys/include/net/dtls.h for CONFIG_DTLS_PEER_MAX is 2
+    # when gcoap_dtls is active, otherwise 1. As the default in tinydtls is 1,
+    # we need to set it explicitly if the dtls.h default value deviates from
+    # the tinydtls default.
+    CFLAGS += -DDTLS_PEER_MAX=2
 endif
 
 HANDSHAKE_MAX := $(or $(CONFIG_DTLS_HANDSHAKE_MAX),$(patsubst -DCONFIG_DTLS_HANDSHAKE_MAX=%,%,$(filter -DCONFIG_DTLS_HANDSHAKE_MAX=%,$(CFLAGS))))
diff --git a/sys/include/net/dtls.h b/sys/include/net/dtls.h
index bfc9dada4e8ab..1e5571dacebc3 100644
--- a/sys/include/net/dtls.h
+++ b/sys/include/net/dtls.h
@@ -36,6 +36,8 @@
 #ifndef NET_DTLS_H
 #define NET_DTLS_H
 
+#include "modules.h"
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -44,8 +46,12 @@ extern "C" {
  * @brief The maximum number DTLS peers (i.e. sessions)
  */
 #ifndef CONFIG_DTLS_PEER_MAX
+#if IS_USED(MODULE_GCOAP_DTLS)
+#define CONFIG_DTLS_PEER_MAX       (2)
+#else
 #define CONFIG_DTLS_PEER_MAX       (1)
 #endif
+#endif
 
 #ifdef __cplusplus
 }