Option to build without SCTP/ICE/DTLS/NICE/JUICE

[ungive]

I'm using this library only for WebSocket connectivity and it would be nice to be able to use it without all of the WebRTC-specific initialization and background threads. This mainly creates two SCTP background threads that aren't needed for WebSockets. I was at least able to compile it and all my tests that used WebSockets passed without it.

To keep a record, here are the changes I made:

src/impl/init.cpp

:100644 100644 0a332feb 00000000 M	src/impl/init.cpp

diff --git a/src/impl/init.cpp b/src/impl/init.cpp
index 0a332feb..dca78540 100644
--- a/src/impl/init.cpp
+++ b/src/impl/init.cpp
@@ -9,10 +9,10 @@
 #include "init.hpp"
 #include "certificate.hpp"
 #include "dtlstransport.hpp"
-#include "icetransport.hpp"
+// #include "icetransport.hpp"
 #include "internals.hpp"
 #include "pollservice.hpp"
-#include "sctptransport.hpp"
+// #include "sctptransport.hpp"
 #include "threadpool.hpp"
 #include "tls.hpp"
 #include "utils.hpp"
@@ -99,13 +99,12 @@ std::shared_future<void> Init::cleanup() {
 void Init::setThreadPoolSize(unsigned int count) {
 	std::lock_guard lock(mMutex);
 	mThreadPoolSize = count;
-
 }
 
 void Init::setSctpSettings(SctpSettings s) {
 	std::lock_guard lock(mMutex);
-	if (mGlobal)
-		SctpTransport::SetSettings(s);
+	// if (mGlobal)
+	// 	SctpTransport::SetSettings(s);
 
 	mCurrentSctpSettings = std::move(s); // store for next init
 }
@@ -124,7 +123,8 @@ void Init::doInit() {
 		throw std::runtime_error("WSAStartup failed, error=" + std::to_string(WSAGetLastError()));
 #endif
 
-	unsigned int count = mThreadPoolSize > 0 ? mThreadPoolSize : std::thread::hardware_concurrency();
+	unsigned int count =
+	    mThreadPoolSize > 0 ? mThreadPoolSize : std::thread::hardware_concurrency();
 	count = std::max(count, MIN_THREADPOOL_SIZE);
 	PLOG_DEBUG << "Spawning " << count << " threads";
 	ThreadPool::Instance().spawn(count);
@@ -141,16 +141,19 @@ void Init::doInit() {
 	openssl::init();
 #endif
 
-	SctpTransport::Init();
-	SctpTransport::SetSettings(mCurrentSctpSettings);
-	DtlsTransport::Init();
+	// SctpTransport::Init();
+	// SctpTransport::SetSettings(mCurrentSctpSettings);
+
+	// DtlsTransport::Init();
+
 #if RTC_ENABLE_WEBSOCKET
 	TlsTransport::Init();
 #endif
 #if RTC_ENABLE_MEDIA
 	DtlsSrtpTransport::Init();
 #endif
-	IceTransport::Init();
+
+	// IceTransport::Init();
 }
 
 void Init::doCleanup() {
@@ -169,15 +172,17 @@ void Init::doCleanup() {
 	PollService::Instance().join();
 #endif
 
-	SctpTransport::Cleanup();
-	DtlsTransport::Cleanup();
+	// SctpTransport::Cleanup();
+	// DtlsTransport::Cleanup();
+
 #if RTC_ENABLE_WEBSOCKET
 	TlsTransport::Cleanup();
 #endif
 #if RTC_ENABLE_MEDIA
 	DtlsSrtpTransport::Cleanup();
 #endif
-	IceTransport::Cleanup();
+
+	// IceTransport::Cleanup();
 
 #ifdef _WIN32
 	WSACleanup();

In CMakeLists.txt I commented out these lines:

if(USE_SYSTEM_USRSCTP)
	find_package(Usrsctp REQUIRED)
else()
	option(sctp_build_shared_lib OFF)
	option(sctp_build_programs OFF)
	option(sctp_inet OFF)
	option(sctp_inet6 OFF)
	option(sctp_werror OFF)
	set(CMAKE_POLICY_DEFAULT_CMP0077 NEW)
	add_subdirectory(deps/usrsctp EXCLUDE_FROM_ALL)
	if (MSYS OR MINGW)
		target_compile_definitions(usrsctp PUBLIC -DSCTP_STDINT_INCLUDE=<stdint.h>)
	endif()
	add_library(Usrsctp::Usrsctp ALIAS usrsctp)

	if(INSTALL_DEPS_LIBS)
		install(TARGETS usrsctp EXPORT LibDataChannelTargets)
		# Fix directories
		set_target_properties(usrsctp PROPERTIES INTERFACE_INCLUDE_DIRECTORIES "")
		target_include_directories(usrsctp INTERFACE
			$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/deps/usrsctp/usrsctplib>
			$<INSTALL_INTERFACE:>)
	endif()
endif()

if (USE_NICE)
	find_package(LibNice REQUIRED)
	target_compile_definitions(datachannel PRIVATE USE_NICE=1)
	target_compile_definitions(datachannel-static PRIVATE USE_NICE=1)
	target_link_libraries(datachannel PRIVATE LibNice::LibNice)
	target_link_libraries(datachannel-static PRIVATE LibNice::LibNice)
else()
	target_compile_definitions(datachannel PRIVATE USE_NICE=0)
	target_compile_definitions(datachannel-static PRIVATE USE_NICE=0)
	if(USE_SYSTEM_JUICE)
		find_package(LibJuice 1.7.0 REQUIRED)
		target_compile_definitions(datachannel PRIVATE RTC_SYSTEM_JUICE=1)
		target_compile_definitions(datachannel-static PRIVATE RTC_SYSTEM_JUICE=1)
		target_link_libraries(datachannel PRIVATE LibJuice::LibJuice)
		target_link_libraries(datachannel-static PRIVATE LibJuice::LibJuice)
	else()
		add_subdirectory(deps/libjuice EXCLUDE_FROM_ALL)
		if(INSTALL_DEPS_LIBS)
			install(TARGETS juice EXPORT LibDataChannelTargets)
		endif()
		target_compile_definitions(datachannel PRIVATE RTC_SYSTEM_JUICE=0)
		target_compile_definitions(datachannel-static PRIVATE RTC_SYSTEM_JUICE=0)
		target_link_libraries(datachannel PRIVATE LibJuice::LibJuice)
		target_link_libraries(datachannel-static PRIVATE LibJuice::LibJuiceStatic)
	endif()
endif()

I also removed any linking with Usrsctp::Usrsctp.

I think it's very possible to add a few CMake options to exclude all of these things. I'm happy to make a PR, but someone would definitely have to look over it as I'm not very well versed with WebRTC.