add openconnect_disable_dtls() API function

This also adds the API function to the Java bindings.

The immediate motivation is that there are a lot of Android users with
MTU-related issues (https://github.com/cernekee/ics-openconnect), and
disabling UDP/DTLS/ESP is a good temporary band-aid.

Signed-off-by: Daniel Lenski <dlenski@gmail.com>

java/src/org/infradead/libopenconnect/LibOpenConnect.java

@@ -151,6 +151,8 @@ public synchronized native void setMobileInfo(String mobilePlatformVersion,
 	public synchronized native int setAllowInsecureCrypto(boolean isEnabled);
 	public synchronized native void setSystemTrust(boolean isEnabled);
 	public synchronized native int setProtocol(String protocol);
+	public synchronized native void disableDTLS();
+	public synchronized native void disableIPv6();
 
 	/* connection info */
 

jni.c

@@ -1011,6 +1011,16 @@ JNIEXPORT void JNICALL Java_org_infradead_libopenconnect_LibOpenConnect_disableI
 	openconnect_disable_ipv6(ctx->vpninfo);
 }
 
+JNIEXPORT void JNICALL Java_org_infradead_libopenconnect_LibOpenConnect_disableDTLS(
+	JNIEnv *jenv, jobject jobj)
+{
+	struct libctx *ctx = getctx(jenv, jobj);
+
+	if (!ctx)
+		return;
+	openconnect_disable_dtls(ctx->vpninfo);
+}
+
 JNIEXPORT void JNICALL Java_org_infradead_libopenconnect_LibOpenConnect_setCertExpiryWarning(
 	JNIEnv *jenv, jobject jobj, jint arg)
 {

libopenconnect.map.in

@@ -113,6 +113,7 @@ OPENCONNECT_5_7 {
 	openconnect_set_cookie;
 	openconnect_set_allow_insecure_crypto;
 	openconnect_get_auth_expiration;
+	openconnect_disable_dtls;
 } OPENCONNECT_5_6;
 
 OPENCONNECT_PRIVATE {

library.c

@@ -557,6 +557,11 @@ void openconnect_disable_ipv6(struct openconnect_info *vpninfo)
 	vpninfo->disable_ipv6 = 1;
 }
 
+void openconnect_disable_dtls(struct openconnect_info *vpninfo)
+{
+	vpninfo->dtls_state = DTLS_DISABLED;
+}
+
 int openconnect_set_cafile(struct openconnect_info *vpninfo, const char *cafile)
 {
 	UTF8CHECK(cafile);

openconnect.h

@@ -40,6 +40,7 @@ extern "C" {
  *  - Add openconnect_set_cookie()
  *  - Add openconnect_set_allow_insecure_crypto()
  *  - Add openconnect_get_auth_expiration()
+ *  - Add openconnect_disable_dtls()
  *
  * API version 5.6 (v8.06; 2020-03-31):
  *  - Add openconnect_set_trojan_interval()
@@ -550,6 +551,7 @@ int openconnect_set_cookie(struct openconnect_info *, const char *);
 void openconnect_clear_cookie(struct openconnect_info *);
 
 void openconnect_disable_ipv6(struct openconnect_info *vpninfo);
+void openconnect_disable_dtls(struct openconnect_info *vpninfo);
 void openconnect_reset_ssl(struct openconnect_info *vpninfo);
 int openconnect_parse_url(struct openconnect_info *vpninfo, const char *url);
 void openconnect_set_cert_expiry_warning(struct openconnect_info *vpninfo,