From 8fbf5bef60568cd4dcd56921c37be64b8234d9bb Mon Sep 17 00:00:00 2001
From: Patric Stout <truebrain@openttd.org>
Date: Wed, 9 Dec 2020 17:13:34 +0100
Subject: Fix: workarounds for two emscripten bugs in the network stack

---
 src/network/core/address.cpp      | 12 ++++++++++++
 src/network/core/os_abstraction.h | 22 ++++++++++++++++++++++
 src/network/core/tcp_listen.h     |  3 +++
 src/network/core/udp.cpp          |  3 +++
 4 files changed, 40 insertions(+)

(limited to 'src')

diff --git a/src/network/core/address.cpp b/src/network/core/address.cpp
index 1aaa0b5fb..2e00b5b19 100644
--- a/src/network/core/address.cpp
+++ b/src/network/core/address.cpp
@@ -267,6 +267,18 @@ SOCKET NetworkAddress::Resolve(int family, int socktype, int flags, SocketList *
 			this->address_length = (int)runp->ai_addrlen;
 			assert(sizeof(this->address) >= runp->ai_addrlen);
 			memcpy(&this->address, runp->ai_addr, runp->ai_addrlen);
+#ifdef __EMSCRIPTEN__
+			/* Emscripten doesn't zero sin_zero, but as we compare addresses
+			 * to see if they are the same address, we need them to be zero'd.
+			 * Emscripten is, as far as we know, the only OS not doing this.
+			 *
+			 * https://github.com/emscripten-core/emscripten/issues/12998
+			 */
+			if (this->address.ss_family == AF_INET) {
+				sockaddr_in *address_ipv4 = (sockaddr_in *)&this->address;
+				memset(address_ipv4->sin_zero, 0, sizeof(address_ipv4->sin_zero));
+			}
+#endif
 			break;
 		}
 
diff --git a/src/network/core/os_abstraction.h b/src/network/core/os_abstraction.h
index be8b8f919..8aa072aef 100644
--- a/src/network/core/os_abstraction.h
+++ b/src/network/core/os_abstraction.h
@@ -151,6 +151,28 @@ typedef unsigned long in_addr_t;
 
 #endif /* OS/2 */
 
+#ifdef __EMSCRIPTEN__
+/**
+ * Emscripten doesn't set 'addrlen' for accept(), getsockname(), getpeername()
+ * and recvfrom(), which confuses other functions and causes them to crash.
+ * This function needs to be called after these four functions to make sure
+ * 'addrlen' is patched up.
+ *
+ * https://github.com/emscripten-core/emscripten/issues/12996
+ *
+ * @param address The address returned by those four functions.
+ * @return The correct value for addrlen.
+ */
+static inline socklen_t FixAddrLenForEmscripten(struct sockaddr_storage &address)
+{
+	switch (address.ss_family) {
+		case AF_INET6: return sizeof(struct sockaddr_in6);
+		case AF_INET: return sizeof(struct sockaddr_in);
+		default: NOT_REACHED();
+	}
+}
+#endif
+
 /**
  * Try to set the socket into non-blocking mode.
  * @param d The socket to set the non-blocking more for.
diff --git a/src/network/core/tcp_listen.h b/src/network/core/tcp_listen.h
index d2982363e..1f073aa73 100644
--- a/src/network/core/tcp_listen.h
+++ b/src/network/core/tcp_listen.h
@@ -42,6 +42,9 @@ public:
 			socklen_t sin_len = sizeof(sin);
 			SOCKET s = accept(ls, (struct sockaddr*)&sin, &sin_len);
 			if (s == INVALID_SOCKET) return;
+#ifdef __EMSCRIPTEN__
+			sin_len = FixAddrLenForEmscripten(sin);
+#endif
 
 			SetNonBlocking(s); // XXX error handling?
 
diff --git a/src/network/core/udp.cpp b/src/network/core/udp.cpp
index 57352412b..aa6d39cbb 100644
--- a/src/network/core/udp.cpp
+++ b/src/network/core/udp.cpp
@@ -129,6 +129,9 @@ void NetworkUDPSocketHandler::ReceivePackets()
 			/* Did we get the bytes for the base header of the packet? */
 			if (nbytes <= 0) break;    // No data, i.e. no packet
 			if (nbytes <= 2) continue; // Invalid data; try next packet
+#ifdef __EMSCRIPTEN__
+			client_len = FixAddrLenForEmscripten(client_addr);
+#endif
 
 			NetworkAddress address(client_addr, client_len);
 			p.PrepareToRead();
-- 
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