[browser] native - no sockets, no threads, no blocking by pavelsavara · Pull Request #123962 · dotnet/runtime

pavelsavara · 2026-02-03T20:38:00Z

dotnet-policy-service · 2026-02-03T20:39:04Z

Tagging subscribers to this area: @karelz, @dotnet/ncl
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Copilot

Pull request overview

This pull request adds support for the browser (WASM) target by providing stub implementations for features not available in the browser environment, specifically: no sockets, no threads, and no blocking operations.

Changes:

Added browser-specific stub implementations for networking, interface addresses, network statistics, and console APIs
Updated error messages in WASM-specific files from "WASI" to "WASM" for clarity
Modified CoreCLR PAL to prevent blocking operations and thread suspension in single-threaded WASM
Updated build configuration to disable socket support for browser targets and include browser-specific source files
Added perftracing configuration for browser builds

Reviewed changes

Copilot reviewed 20 out of 21 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
src/native/libs/System.Native/pal_signal_wasm.c	Updated error messages from "WASI" to "WASM"
src/native/libs/System.Native/pal_networkstatistics_wasm.c	New file with stub implementations returning "not supported" for network statistics APIs
src/native/libs/System.Native/pal_networking_browser.c	New file with comprehensive stub implementations for all networking APIs, returning ENOTSUP
src/native/libs/System.Native/pal_io.c	Added early return for pipe() on WASM targets with ENOTSUP
src/native/libs/System.Native/pal_interfaceaddresses_browser.c	New file with stub implementations for interface enumeration APIs
src/native/libs/System.Native/pal_dynamicload_wasm.c	Updated error messages from "WASI" to "WASM"
src/native/libs/System.Native/pal_console_wasm.c	New console implementation for WASM with some working features (stdin/isatty) and stubs for unsupported features
src/native/libs/System.Native/CMakeLists.txt	Updated build configuration to differentiate between browser and WASI targets, using browser-specific source files
src/native/eventpipe/ds-ipc-pal-websocket.c	Added string duplication helper functions for eventpipe
src/mono/mono/profiler/log.c	Changed sys/socket.h include guard from HOST_WIN32 to HAVE_SYS_SOCKET_H
src/mono/mono/profiler/helper.c	Changed sys/socket.h include guard from HOST_WIN32 to HAVE_SYS_SOCKET_H
src/mono/mono/profiler/CMakeLists.txt	Disabled AOT profiler for browser targets
src/mono/mono/mini/cfgdump.c	Added guard for sys/socket.h include
src/mono/browser/runtime/dotnet.d.ts	Formatting fix: removed space before parentheses in function signatures
src/coreclr/pal/src/thread/threadsusp.cpp	Added guard to prevent thread suspension in single-threaded WASM
src/coreclr/pal/src/thread/thread.cpp	Added guard to prevent CREATE_SUSPENDED flag in single-threaded WASM
src/coreclr/pal/src/synchmgr/wait.cpp	Added guards to prevent blocking waits and made Sleep return immediately in WASM
src/coreclr/pal/src/synchmgr/synchmanager.cpp	Added assertion to prevent waiting on non-signaled objects in WASM
src/coreclr/pal/src/debug/debug.cpp	Added WASM-specific implementation of PAL_ProbeMemory using emscripten heap size
eng/native/tryrun.browser.cmake	Disabled HAVE_SYS_SOCKET_H for browser targets
eng/native.wasm.targets	Added perftracing configuration flags for browser builds

src/coreclr/pal/src/debug/debug.cpp

src/native/libs/System.Native/pal_console_wasm.c

src/mono/mono/mini/cfgdump.c

src/coreclr/pal/src/debug/debug.cpp

src/coreclr/pal/src/thread/thread.cpp

src/coreclr/pal/src/synchmgr/synchmanager.cpp

src/coreclr/pal/src/debug/debug.cpp

pavelsavara · 2026-02-04T00:10:11Z

Whole this PR makes emscripten emulator smaller only by 20KB of JavaScript - from 154KB to 134KB.
And only 4KB of .wasm with -O3. Those are CoreCLR numbers, it will have similar impact for Mono but I have not measured it yet.

I hoped for more, I'm not sure I want to merge this...

pavelsavara · 2026-02-04T00:47:28Z

These are JS emulators of mmap that are slow and terrible, we should not use them in CoreCLR

adding _mmap_js (referenced by root reference (e.g. compiled C/C++ code))
adding _msync_js (referenced by root reference (e.g. compiled C/C++ code))
adding _munmap_js (referenced by root reference (e.g. compiled C/C++ code))

The rest of the JS support is OK. See https://gist.github.com/pavelsavara/f11dd1078548a16fc923de444f1c9d9b

All the symbols in the wasm files are https://gist.github.com/pavelsavara/b7653066a83554168739558630d34847

Among them these caught my eye

GetNativeSwiftPhysicalLowering

GetThreadStaticsByIndex
SwitchStackAndExecuteHandler
Thread::HandleThreadAbort
ThreadNative_Abort
ThreadNative_ResetAbort
ThreadNative_Start
ThreadSuspend::LockThreadStore

WKS::gc_heap and SVR::gc_heap

COMDouble
COMSingle
COMDelegate
OleVariant
RealCOMPlusThrow

jkotas · 2026-02-04T00:57:04Z

These are JS emulators of mmap that are slow and terrible, we should not use them in CoreCLR

#117813 is the main offender.

Copilot

Pull request overview

Copilot reviewed 26 out of 27 changed files in this pull request and generated 7 comments.

src/native/libs/System.Native/pal_console_wasm.c

src/mono/mono/mini/cfgdump.c

src/native/libs/System.Native/pal_networking_browser.c

src/mono/sample/wasm/browser/native.sh

src/coreclr/pal/src/debug/debug.cpp

Copilot

Pull request overview

Copilot reviewed 25 out of 26 changed files in this pull request and generated 4 comments.

src/native/libs/System.Native/pal_networking_browser.c

src/mono/sample/wasm/browser/native.sh

src/mono/sample/wasm/browser/linkLibs.rrsp

src/mono/sample/wasm/browser/core-emcc-link.rrsp

Copilot

Pull request overview

Copilot reviewed 27 out of 28 changed files in this pull request and generated 6 comments.

Copilot · 2026-02-06T12:33:53Z

src/native/libs/System.Native/pal_networking_browser.c

+
+#include <errno.h>
+#include <string.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+// Error codes from pal_errno.h
+#define Error_ENOTSUP 95
+#define Error_EFAULT 14
+#define Error_EAFNOSUPPORT 97
+#define Error_EINVAL 22
+#define Error_EBADF 9
+#define Error_SUCCESS 0
+


The Error_* constants are hard-coded to raw Unix errno values (e.g., ENOTSUP=95, EFAULT=14). System.Native APIs are expected to return PAL Error enum values (see pal_error_common.h), which are different (e.g., Error_ENOTSUP is 0x1003D). Returning raw errno values here will be misinterpreted by managed code. Use the shared PAL Error constants (include pal_errno.h / pal_error_common.h) instead of redefining them.

Suggested change

#include <errno.h>

#include <string.h>

#include <stdlib.h>

#include <unistd.h>

// Error codes from pal_errno.h

#define Error_ENOTSUP 95

#define Error_EFAULT 14

#define Error_EAFNOSUPPORT 97

#define Error_EINVAL 22

#define Error_EBADF 9

#define Error_SUCCESS 0

#include "pal_errno.h"

#include <errno.h>

#include <string.h>

#include <stdlib.h>

#include <unistd.h>

Copilot · 2026-02-06T12:33:53Z

src/native/libs/System.Native/pal_networking_browser.c

+    if (createdSocket == NULL)
+    {
+        return Error_EFAULT;
+    }
+
+    // Allocate fake socket structure
+    FakeSocket* fs = (FakeSocket*)malloc(sizeof(FakeSocket));
+    if (fs == NULL)
+    {
+        *createdSocket = -1;
+        return Error_EFAULT;
+    }
+
+    fs->addressFamily = addressFamily;
+    fs->socketType = socketType;
+    fs->protocolType = protocolType;
+    fs->isListening = 0;
+    fs->magic = FAKE_SOCKET_MAGIC;
+
+    *createdSocket = (intptr_t)fs;
+    return Error_SUCCESS;


SystemNative_Socket returns a malloc'ed pointer cast to intptr_t as the "socket" handle. In the rest of System.Native (and managed code), sockets are treated as OS file descriptors (see ToFileDescriptor casts/asserts). Returning a pointer here risks invalid close()/fcntl usage (pointer truncation) and makes resource lifetime undefined (e.g., only freed in SystemNative_Shutdown). Consider returning Error_ENOTSUP (and setting *createdSocket = -1) so callers fail predictably, or ensure the handle is a real fd compatible with the existing PAL contract.

Suggested change

if (createdSocket == NULL)

{

return Error_EFAULT;

}

// Allocate fake socket structure

FakeSocket* fs = (FakeSocket*)malloc(sizeof(FakeSocket));

if (fs == NULL)

{

*createdSocket = -1;

return Error_EFAULT;

}

fs->addressFamily = addressFamily;

fs->socketType = socketType;

fs->protocolType = protocolType;

fs->isListening = 0;

fs->magic = FAKE_SOCKET_MAGIC;

*createdSocket = (intptr_t)fs;

return Error_SUCCESS;

(void)addressFamily;

(void)socketType;

(void)protocolType;

if (createdSocket == NULL)

{

return Error_EFAULT;

}

*createdSocket = -1;

return Error_ENOTSUP;

Copilot · 2026-02-06T12:33:54Z

src/native/libs/System.Native/pal_networking_browser.c

+int32_t SystemNative_SetSockOpt(
+    intptr_t socket, int32_t socketOptionLevel, int32_t socketOptionName, uint8_t* optionValue, int32_t optionLen)
+{
+    FakeSocket* fs = GetFakeSocket(socket);
+    if (fs == NULL)
+    {
+        return Error_EBADF;
+    }
+
+    (void)socketOptionLevel;
+    (void)socketOptionName;
+    (void)optionValue;
+    (void)optionLen;
+    // Pretend setting options succeeds
+    return Error_SUCCESS;
+}
+
+int32_t SystemNative_SetRawSockOpt(
+    intptr_t socket, int32_t socketOptionLevel, int32_t socketOptionName, uint8_t* optionValue, int32_t optionLen)
+{
+    FakeSocket* fs = GetFakeSocket(socket);
+    if (fs == NULL)
+    {
+        return Error_EBADF;
+    }
+
+    (void)socketOptionLevel;
+    (void)socketOptionName;
+    (void)optionValue;
+    (void)optionLen;
+    // Pretend setting options succeeds
+    return Error_SUCCESS;
+}


SystemNative_SetSockOpt / SystemNative_SetRawSockOpt currently return success unconditionally for a fake socket. If socket options are not actually supported in the browser target, reporting success can cause managed code to continue under incorrect assumptions. Prefer returning Error_ENOTSUP (or only succeeding for an explicitly documented no-op subset) to keep behavior consistent with other unsupported networking APIs in this file.

Copilot · 2026-02-06T12:33:54Z

src/native/libs/System.Native/pal_networkstatistics_wasm.c

+int32_t SystemNative_GetTcpGlobalStatistics(TcpGlobalStatistics* retStats)
+{
+    if (retStats == NULL)
+    {
+        return -1;
+    }
+    memset(retStats, 0, sizeof(TcpGlobalStatistics));
+    return -1; // Not supported
+}
+
+int32_t SystemNative_GetIPv4GlobalStatistics(IPv4GlobalStatistics* retStats)
+{
+    if (retStats == NULL)
+    {
+        return -1;
+    }
+    memset(retStats, 0, sizeof(IPv4GlobalStatistics));
+    return -1; // Not supported


These stubs return -1 for unsupported operations but don't set errno (ENOTSUP/EFAULT). The existing fallback implementations in pal_networkstatistics.c set errno=ENOTSUP before returning -1, and managed callers may rely on errno/GetLastPInvokeError for exception details. Set errno appropriately on all failure returns (including the NULL retStats case).

Copilot · 2026-02-06T12:33:54Z

src/native/libs/System.Native/pal_networkstatistics_wasm.c

+    return 0;
+}
+
+int32_t SystemNative_GetActiveTcpConnectionInfos(NativeTcpConnectionInformation* infos, int32_t* infoCount)
+{
+    (void)infos;
+    if (infoCount != NULL)
+    {
+        *infoCount = 0;
+    }
+    return 0;
+}
+
+int32_t SystemNative_GetEstimatedUdpListenerCount(void)
+{
+    return 0;
+}
+
+int32_t SystemNative_GetActiveUdpListeners(IPEndPointInfo* infos, int32_t* infoCount)
+{
+    (void)infos;
+    if (infoCount != NULL)
+    {
+        *infoCount = 0;
+    }
+    return 0;


The "estimated/active" count APIs return 0 (success) in this stub implementation. On other platforms, when network statistics aren't supported, these return -1 with errno=ENOTSUP (see pal_networkstatistics.c fallback). Returning 0 changes semantics from "not supported" to "supported with empty data", which can lead to incorrect behavior in managed code. Align these with the existing not-supported contract (return -1 and set errno=ENOTSUP).

Suggested change

return 0;

}

int32_t SystemNative_GetActiveTcpConnectionInfos(NativeTcpConnectionInformation* infos, int32_t* infoCount)

{

(void)infos;

if (infoCount != NULL)

{

*infoCount = 0;

}

return 0;

}

int32_t SystemNative_GetEstimatedUdpListenerCount(void)

{

return 0;

}

int32_t SystemNative_GetActiveUdpListeners(IPEndPointInfo* infos, int32_t* infoCount)

{

(void)infos;

if (infoCount != NULL)

{

*infoCount = 0;

}

return 0;

errno = ENOTSUP;

return -1;

}

int32_t SystemNative_GetActiveTcpConnectionInfos(NativeTcpConnectionInformation* infos, int32_t* infoCount)

{

(void)infos;

(void)infoCount;

errno = ENOTSUP;

return -1;

}

int32_t SystemNative_GetEstimatedUdpListenerCount(void)

{

errno = ENOTSUP;

return -1;

}

int32_t SystemNative_GetActiveUdpListeners(IPEndPointInfo* infos, int32_t* infoCount)

{

(void)infos;

(void)infoCount;

errno = ENOTSUP;

return -1;

Copilot · 2026-02-06T12:33:54Z

src/native/libs/System.Native/pal_interfaceaddresses_browser.c

+int32_t SystemNative_GetNetworkInterfaces(int32_t* interfaceCount, NetworkInterfaceInfo** interfaces, int32_t* addressCount, IpAddressInfo** addressList)
+{
+    if (interfaceCount == NULL || interfaces == NULL || addressCount == NULL || addressList == NULL)
+    {


When argument validation fails (returning -1), this stub doesn't set errno. Other System.Native APIs typically set errno (e.g., EFAULT) to enable managed code to surface a meaningful P/Invoke error. Set errno=EFAULT (or another appropriate value) before returning -1 for invalid pointer arguments.

Suggested change

{

{

errno = EFAULT;

# Conflicts: # src/native/corehost/corehost.proj # src/native/libs/build-native.proj

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pavelsavara added 5 commits February 3, 2026 14:20

initial

3c4db7c

aquire emsdk for coreCLR

864e9c3

first pass

75b667b

fix mono

eae8e05

more

0dffd94

pavelsavara added this to the 11.0.0 milestone Feb 3, 2026

pavelsavara self-assigned this Feb 3, 2026

pavelsavara added arch-wasm WebAssembly architecture area-System.Net.Sockets os-browser Browser variant of arch-wasm labels Feb 3, 2026

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fix

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pavelsavara added 3 commits February 4, 2026 15:45

fix

e80dd23

Merge branch 'main' into browser_no_sockets

e8b0c0e

simulate socket structure

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pavelsavara and others added 4 commits February 4, 2026 20:28

fix

24de2fa

fix

f54b25e

fix

b3511bf

Fix AcquireEmscriptenSdk for MonoAOTOffsets builds

cebded0

build-analysis bot mentioned this pull request Feb 5, 2026

Android System.Security.Cryptography test failure: Signing key verifies the CRL #119023

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pavelsavara added 2 commits February 5, 2026 13:31

feedback

92ad5b3

Merge branch 'main' into browser_no_sockets

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feedback, merge

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Merge branch 'main' into browser_no_sockets

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fix

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pavelsavara added 6 commits February 6, 2026 14:17

Merge branch 'aquire_emsdk' into browser_no_sockets

e705933

conditional native.wasm.targets

4af2615

fix

0edd5fa

whitespace

48a9aa6

fix

93693eb

Merge branch 'aquire_emsdk' into browser_no_sockets

c61f7c1

# Conflicts: # src/native/corehost/corehost.proj # src/native/libs/build-native.proj

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pavelsavara commented Feb 3, 2026 •

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