[Android] Fix accessing network interfaces information (#62780)

* Re-enable tests

* Dynamically load getifaddrs if necessary

* Prevent redeclaration of the ifaddrs struct

* Fix typo

* Do not close the dynamic library

* Enable the fixed functional tests in CI

* Reduce code duplication for obtaining libc file name

* Simplify usage of the function pointers

* Move typedefs

* Rename the _ensure_ function

* Remove fptr typedefs

* Update comment

* Add missing include

* Update comment

* Remove unnecessary comment

* Move static variable

* Remove unnecessary change

* Move LIBC_FILENAME to the utilities header

* Avoid error if constant is undefined

* Conditionally include ifaddrs

* Try to fix cmake_symbol_exists issue for browser

* Minor tweaks

* Try different way of detecting getifaddrs

* Use the hack only for Android builds

* Revert "Move LIBC_FILENAME to the utilities header"

This reverts commit 4e67687.

* Revert "Reduce code duplication for obtaining libc file name"

This reverts commit aca15d1.

* Simplify opening libc

* Update code style

* Fix race condition

* Prevent race condition

* Switch locking implementation for a lock-free implementation

* Enable unit test for Android

* Try using weak symbols

* Fix function name

* Revert "Fix function name"

This reverts commit f927aae.

* Revert "Try using weak symbols"

This reverts commit 46d3ede.

* Refactor code to use pthread_once

src/libraries/Native/Unix/Common/pal_config.h.in

@@ -12,6 +12,7 @@
 #cmakedefine01 HAVE_F_FULLFSYNC
 #cmakedefine01 HAVE_O_CLOEXEC
 #cmakedefine01 HAVE_GETIFADDRS
+#cmakedefine01 HAVE_IFADDRS
 #cmakedefine01 HAVE_UTSNAME_DOMAINNAME
 #cmakedefine01 HAVE_STAT64
 #cmakedefine01 HAVE_FORK

src/libraries/Native/Unix/System.Native/pal_interfaceaddresses.c

@@ -11,7 +11,13 @@
 #include <stdlib.h>
 #include <sys/types.h>
 #include <assert.h>
+#if HAVE_IFADDRS || HAVE_GETIFADDRS
 #include <ifaddrs.h>
+#endif
+#if !HAVE_GETIFADDRS && TARGET_ANDROID
+#include <dlfcn.h>
+#include <pthread.h>
+#endif
 #include <net/if.h>
 #include <netinet/in.h>
 #include <string.h>
@@ -55,7 +61,6 @@
 #endif
 #endif
 
-#if HAVE_GETIFADDRS
 // Convert mask to prefix length e.g. 255.255.255.0 -> 24
 // mask parameter is pointer to buffer where address starts and length is
 // buffer length e.g. 4 for IPv4 and 16 for IPv6.
@@ -95,14 +100,67 @@ static inline uint8_t mask2prefix(uint8_t* mask, int length)
 
     return len;
 }
+
+#if !HAVE_IFADDRS && TARGET_ANDROID
+// This structure is exactly the same as struct ifaddrs defined in ifaddrs.h but since the header
+// might not be available (e.g., in bionics used in Android before API 24) we need to mirror it here
+// so that we can dynamically load the getifaddrs function and use it.
+struct ifaddrs
+{
+	struct ifaddrs *ifa_next;
+	char *ifa_name;
+	unsigned int ifa_flags;
+	struct sockaddr *ifa_addr;
+	struct sockaddr *ifa_netmask;
+	union
+	{
+		struct sockaddr *ifu_broadaddr;
+		struct sockaddr *ifu_dstaddr;
+	} ifa_ifu;
+	void *ifa_data;
+};
+#endif
+
+#if !HAVE_GETIFADDRS && TARGET_ANDROID
+// Try to load the getifaddrs and freeifaddrs functions manually.
+// This workaround is necessary on Android prior to API 24 and it can be removed once
+// we drop support for earlier Android versions.
+static int (*getifaddrs)(struct ifaddrs**) = NULL;
+static void (*freeifaddrs)(struct ifaddrs*) = NULL;
+
+static void try_loading_getifaddrs()
+{
+    void *libc = dlopen("libc.so", RTLD_NOW);
+    if (libc)
+    {
+        getifaddrs = (int (*)(struct ifaddrs**)) dlsym(libc, "getifaddrs");
+        freeifaddrs = (void (*)(struct ifaddrs*)) dlsym(libc, "freeifaddrs");
+    }
+}
+
+static bool ensure_getifaddrs_is_loaded()
+{
+    static pthread_once_t getifaddrs_is_loaded = PTHREAD_ONCE_INIT;
+    pthread_once(&getifaddrs_is_loaded, try_loading_getifaddrs);
+    return getifaddrs != NULL && freeifaddrs != NULL;
+}
 #endif
 
 int32_t SystemNative_EnumerateInterfaceAddresses(void* context,
                                                IPv4AddressFound onIpv4Found,
                                                IPv6AddressFound onIpv6Found,
                                                LinkLayerAddressFound onLinkLayerFound)
 {
-#if HAVE_GETIFADDRS
+#if !HAVE_GETIFADDRS && TARGET_ANDROID
+    // Workaround for Android API < 24
+    if (!ensure_getifaddrs_is_loaded())
+    {
+        errno = ENOTSUP;
+        return -1;
+    }
+#endif
+
+#if HAVE_GETIFADDRS || TARGET_ANDROID
     struct ifaddrs* headAddr;
     if (getifaddrs(&headAddr) == -1)
     {
@@ -235,7 +293,7 @@ int32_t SystemNative_EnumerateInterfaceAddresses(void* context,
     freeifaddrs(headAddr);
     return 0;
 #else
-    // Not supported on e.g. Android. Also, prevent a compiler error because parameters are unused
+    // Not supported. Also, prevent a compiler error because parameters are unused
     (void)context;
     (void)onIpv4Found;
     (void)onIpv6Found;
@@ -247,7 +305,16 @@ int32_t SystemNative_EnumerateInterfaceAddresses(void* context,
 
 int32_t SystemNative_GetNetworkInterfaces(int32_t * interfaceCount, NetworkInterfaceInfo **interfaceList, int32_t * addressCount, IpAddressInfo **addressList )
 {
-#if HAVE_GETIFADDRS
+#if !HAVE_GETIFADDRS && TARGET_ANDROID
+    // Workaround for Android API < 24
+    if (!ensure_getifaddrs_is_loaded())
+    {
+        errno = ENOTSUP;
+        return -1;
+    }
+#endif
+
+#if HAVE_GETIFADDRS || TARGET_ANDROID
     struct ifaddrs* head;   // Pointer to block allocated by getifaddrs().
     struct ifaddrs* ifaddrsEntry;
     IpAddressInfo *ai;
@@ -453,7 +520,7 @@ int32_t SystemNative_GetNetworkInterfaces(int32_t * interfaceCount, NetworkInter
 
     return 0;
 #else
-    // Not supported on e.g. Android. Also, prevent a compiler error because parameters are unused
+    // Not supported. Also, prevent a compiler error because parameters are unused
     (void)interfaceCount;
     (void)interfaceList;
     (void)addressCount;

src/libraries/Native/Unix/configure.cmake

@@ -7,6 +7,7 @@ include(CheckStructHasMember)
 include(CheckSymbolExists)
 include(CheckTypeSize)
 include(CheckLibraryExists)
+include(CheckFunctionExists)
 
 # CMP0075 Include file check macros honor CMAKE_REQUIRED_LIBRARIES.
 if(POLICY CMP0075)
@@ -141,6 +142,18 @@ check_c_source_compiles(
     "
     HAVE_FLOCK64)
 
+check_c_source_compiles(
+    "
+    #include <sys/types.h>
+    #include <ifaddrs.h>
+    int main(void)
+    {
+        struct ifaddrs ia;
+        return 0;
+    }
+    "
+    HAVE_IFADDRS)
+
 check_symbol_exists(
     O_CLOEXEC
     fcntl.h
@@ -156,9 +169,8 @@ check_symbol_exists(
     fcntl.h
     HAVE_F_FULLFSYNC)
 
-check_symbol_exists(
+check_function_exists(
     getifaddrs
-    ifaddrs.h
     HAVE_GETIFADDRS)
 
 check_symbol_exists(

src/libraries/System.Net.NetworkInformation/tests/FunctionalTests/IPGlobalPropertiesTest.cs

@@ -26,6 +26,7 @@ public IPGlobalPropertiesTest(ITestOutputHelper output)
         }
 
         [Fact]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/50567", TestPlatforms.Android)]
         public void IPGlobalProperties_AccessAllMethods_NoErrors()
         {
             IPGlobalProperties gp = IPGlobalProperties.GetIPGlobalProperties();
@@ -51,6 +52,7 @@ public void IPGlobalProperties_AccessAllMethods_NoErrors()
 
         [Theory]
         [MemberData(nameof(Loopbacks))]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/50567", TestPlatforms.Android)]
         public void IPGlobalProperties_TcpListeners_Succeed(IPAddress address)
         {
             using (var server = new Socket(address.AddressFamily, SocketType.Stream, ProtocolType.Tcp))
@@ -77,6 +79,7 @@ public void IPGlobalProperties_TcpListeners_Succeed(IPAddress address)
         [Theory]
         [ActiveIssue("https://github.com/dotnet/runtime/issues/34690", TestPlatforms.Windows, TargetFrameworkMonikers.Netcoreapp, TestRuntimes.Mono)]
         [MemberData(nameof(Loopbacks))]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/50567", TestPlatforms.Android)]
         public async Task IPGlobalProperties_TcpActiveConnections_Succeed(IPAddress address)
         {
             using (var server = new Socket(address.AddressFamily, SocketType.Stream, ProtocolType.Tcp))
@@ -106,6 +109,7 @@ public async Task IPGlobalProperties_TcpActiveConnections_Succeed(IPAddress addr
         }
 
         [Fact]
+        [ActiveIssue("https://github.com/dotnet/runtime/issues/50567", TestPlatforms.Android)]
         public void IPGlobalProperties_TcpActiveConnections_NotListening()
         {
             TcpConnectionInformation[] tcpCconnections = IPGlobalProperties.GetIPGlobalProperties().GetActiveTcpConnections();
@@ -116,7 +120,6 @@ public void IPGlobalProperties_TcpActiveConnections_NotListening()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/50567", TestPlatforms.Android)]
         public async Task GetUnicastAddresses_NotEmpty()
         {
             IPGlobalProperties props = IPGlobalProperties.GetIPGlobalProperties();

src/libraries/System.Net.NetworkInformation/tests/FunctionalTests/NetworkInterfaceBasicTest.cs

@@ -20,7 +20,6 @@ public NetworkInterfaceBasicTest(ITestOutputHelper output)
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/50567", TestPlatforms.Android)]
         public void BasicTest_GetNetworkInterfaces_AtLeastOne()
         {
             Assert.NotEqual<int>(0, NetworkInterface.GetAllNetworkInterfaces().Length);
@@ -57,7 +56,7 @@ public void BasicTest_AccessInstanceProperties_NoExceptions()
         }
 
         [Fact]
-        [PlatformSpecific(TestPlatforms.Linux)]  // Some APIs are not supported on Linux
+        [PlatformSpecific(TestPlatforms.Linux|TestPlatforms.Android)]  // Some APIs are not supported on Linux and Android
         public void BasicTest_AccessInstanceProperties_NoExceptions_Linux()
         {
             foreach (NetworkInterface nic in NetworkInterface.GetAllNetworkInterfaces())
@@ -132,7 +131,6 @@ public void BasicTest_AccessInstanceProperties_NoExceptions_Bsd()
 
         [Fact]
         [Trait("IPv4", "true")]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/50567", TestPlatforms.Android)]
         public void BasicTest_StaticLoopbackIndex_MatchesLoopbackNetworkInterface()
         {
             Assert.True(Capability.IPv4Support());
@@ -156,7 +154,6 @@ public void BasicTest_StaticLoopbackIndex_MatchesLoopbackNetworkInterface()
 
         [Fact]
         [Trait("IPv4", "true")]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/50567", TestPlatforms.Android)]
         public void BasicTest_StaticLoopbackIndex_ExceptionIfV4NotSupported()
         {
             Assert.True(Capability.IPv4Support());
@@ -166,7 +163,6 @@ public void BasicTest_StaticLoopbackIndex_ExceptionIfV4NotSupported()
 
         [Fact]
         [Trait("IPv6", "true")]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/50567", TestPlatforms.Android)]
         public void BasicTest_StaticIPv6LoopbackIndex_MatchesLoopbackNetworkInterface()
         {
             Assert.True(Capability.IPv6Support());
@@ -191,7 +187,6 @@ public void BasicTest_StaticIPv6LoopbackIndex_MatchesLoopbackNetworkInterface()
 
         [Fact]
         [Trait("IPv6", "true")]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/50567", TestPlatforms.Android)]
         public void BasicTest_StaticIPv6LoopbackIndex_ExceptionIfV6NotSupported()
         {
             Assert.True(Capability.IPv6Support());
@@ -272,7 +267,6 @@ public void BasicTest_GetIPInterfaceStatistics_Success_Bsd()
 
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/50567", TestPlatforms.Android)]
         public void BasicTest_GetIsNetworkAvailable_Success()
         {
             Assert.True(NetworkInterface.GetIsNetworkAvailable());
@@ -284,7 +278,6 @@ public void BasicTest_GetIsNetworkAvailable_Success()
         [SkipOnPlatform(TestPlatforms.iOS | TestPlatforms.MacCatalyst | TestPlatforms.tvOS, "Not supported on Browser, iOS, MacCatalyst, or tvOS.")]
         [InlineData(false)]
         [InlineData(true)]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/50567", TestPlatforms.Android)]
         public async Task NetworkInterface_LoopbackInterfaceIndex_MatchesReceivedPackets(bool ipv6)
         {
             using (var client = new Socket(SocketType.Dgram, ProtocolType.Udp))

src/libraries/tests.proj

@@ -88,7 +88,6 @@
 
     <!-- PSNE -->
     <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Console/tests/System.Console.Tests.csproj" />
-    <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Net.NetworkInformation/tests/FunctionalTests/System.Net.NetworkInformation.Functional.Tests.csproj" />
     <ProjectExclusions Include="$(MSBuildThisFileDirectory)System.Net.Primitives/tests/FunctionalTests/System.Net.Primitives.Functional.Tests.csproj" />
 
     <!-- Crashes on CI (possibly flakey) -->

src/mono/cmake/config.h.in

@@ -620,6 +620,9 @@
 /* Have getifaddrs */
 #cmakedefine HAVE_GETIFADDRS 1
 
+/* Have struct ifaddrs */
+#cmakedefine HAVE_IFADDRS 1
+
 /* Have access */
 #cmakedefine HAVE_ACCESS 1