From f395d952bf1b1546532a3ec79510302ff9c8c970 Mon Sep 17 00:00:00 2001
From: 11soda11 <115734183+Sodastream11@users.noreply.github.com>
Date: Thu, 7 May 2026 01:01:56 +0200
Subject: [PATCH 01/23] tool_doswin: don't use `TerminateThread` in stdin relay

It is a dangerous function. Remove usage by only starting
the thread after setup completed successfully.

Ref: https://github.com/curl/curl/pull/21467#discussion_r3173013432
---
 src/tool_doswin.c | 289 +++++++++++++++++++++++++++-------------------
 1 file changed, 173 insertions(+), 116 deletions(-)

diff --git a/src/tool_doswin.c b/src/tool_doswin.c
index a64665bcd9..cf009e4d50 100644
--- a/src/tool_doswin.c
+++ b/src/tool_doswin.c
@@ -30,6 +30,7 @@
 
 #ifdef _WIN32
 #  include "curlx/winapi.h" /* for curlx_win32_random() */
+#  include "curlx/nonblock.h" /* for curlx_nonblock() */
 #  include <tlhelp32.h>
 #elif !defined(__DJGPP__) || (__DJGPP__ < 2)  /* DJGPP 2.0 has _use_lfn() */
 #  define CURL_USE_LFN(f) 0  /* long filenames never available */
@@ -707,59 +708,15 @@ struct win_thread_data {
   /* This is a copy of the true stdin file handle before any redirection. It is
      read by the thread. */
   HANDLE stdin_handle;
-  /* This is the listen socket for the thread. It is closed after the first
-     connection. */
-  curl_socket_t socket_l;
-  /* This is the random number which the background thread will use to verify
-   * the peer. */
-  uint64_t expected_auth_val;
+  /* this is the socket the thread will forward stdin to. It is connected to
+   * the socket which replaces the stdin handle. */
+  curl_socket_t socket_w;
 };
 
 static DWORD WINAPI win_stdin_thread_func(void *thread_data)
 {
   struct win_thread_data *tdata = (struct win_thread_data *)thread_data;
-  struct sockaddr_in clientAddr;
-  int clientAddrLen = sizeof(clientAddr);
-  size_t nread = 0;
-  uint64_t auth_val = 0;
 
-  curl_socket_t socket_w = CURL_ACCEPT(tdata->socket_l,
-                                       (struct sockaddr *)&clientAddr,
-                                       &clientAddrLen);
-
-  if(socket_w == CURL_SOCKET_BAD) {
-    errorf("accept error: %d", SOCKERRNO);
-    goto ThreadCleanup;
-  }
-
-  sclose(tdata->socket_l);
-  tdata->socket_l = CURL_SOCKET_BAD;
-
-  do {
-    ssize_t ret = sread(socket_w, ((unsigned char *)&auth_val) + nread,
-                        sizeof(auth_val) - nread);
-    if(ret <= 0) {
-      if(!ret) {
-        errorf("relay peer disconnected");
-      }
-      else {
-        errorf("read error: %d", SOCKERRNO);
-      }
-
-      goto ThreadCleanup;
-    }
-    nread += ret;
-  } while(nread < sizeof(auth_val));
-
-  if(auth_val != tdata->expected_auth_val) {
-    errorf("relay peer auth failed");
-    goto ThreadCleanup;
-  }
-
-  if(shutdown(socket_w, SHUT_RD)) {
-    errorf("shutdown error: %d", SOCKERRNO);
-    goto ThreadCleanup;
-  }
   for(;;) {
     DWORD n;
     ssize_t nwritten;
@@ -769,34 +726,105 @@ static DWORD WINAPI win_stdin_thread_func(void *thread_data)
       break;
     if(n == 0)
       break;
-    nwritten = swrite(socket_w, buffer, n);
+    nwritten = swrite(tdata->socket_w, buffer, n);
     if(nwritten == -1)
       break;
     if((DWORD)nwritten != n)
       break;
   }
-ThreadCleanup:
-  if(tdata->socket_l != CURL_SOCKET_BAD) {
-    sclose(tdata->socket_l);
-    tdata->socket_l = CURL_SOCKET_BAD;
+
+  if(tdata->socket_w != CURL_SOCKET_BAD) {
+    sclose(tdata->socket_w);
+    tdata->socket_w = CURL_SOCKET_BAD;
+  }
+
+  if(tdata->stdin_handle != NULL) {
+    CloseHandle(tdata->stdin_handle);
+    tdata->stdin_handle = NULL;
   }
-  if(socket_w != CURL_SOCKET_BAD)
-    sclose(socket_w);
 
   curlx_free(tdata);
   return 0;
 }
 
+static int swrite_blocking_on_nonblock(curl_socket_t nonblock_sock,
+                                       unsigned char* data,
+                                       size_t len)
+{
+  fd_set fdwrite;
+  fd_set fdexcep;
+  size_t nwritten = 0;
+
+  FD_ZERO(&fdwrite);
+  FD_ZERO(&fdexcep);
+
+  do {
+    ssize_t ret;
+    FD_SET(nonblock_sock, &fdwrite);
+    FD_SET(nonblock_sock, &fdexcep);
+
+    if(select(0, NULL, &fdwrite, &fdexcep, NULL) <= 0) {
+      errorf("select error: %d", SOCKERRNO);
+      return -1;
+    }
+
+    if(FD_ISSET(nonblock_sock, &fdexcep)) {
+      int sock_err = 0;
+      int sock_err_size = sizeof(sock_err);
+      getsockopt(nonblock_sock, SOL_SOCKET, SO_ERROR,
+                 (char *)&sock_err, &sock_err_size);
+      errorf("connect failure: %d", sock_err);
+      return -1;
+    }
+
+    ret = swrite(nonblock_sock, data + nwritten,
+            len - nwritten);
+
+    if(ret <= 0) {
+      errorf("socket write error: %d", SOCKERRNO);
+      return -1;
+    }
+
+    nwritten += ret;
+  } while(nwritten < len);
+
+  return 0;
+}
+
+static int read_auth_val(curl_socket_t sock,
+                         uint64_t* buf)
+{
+  size_t nread = 0;
+
+  do {
+    ssize_t ret = sread(sock, buf + nread,
+                        sizeof(*buf) - nread);
+    if(ret <= 0) {
+      if(!ret) {
+        errorf("stdin relay peer disconnected");
+      }
+      else {
+        errorf("read error: %d", SOCKERRNO);
+      }
+
+      return -1;
+    }
+    nread += ret;
+  } while(nread < sizeof(*buf));
+
+  return 0;
+}
+
 /* The background thread that reads and buffers the true stdin. */
 curl_socket_t win32_stdin_read_thread(void)
 {
   int rc = 0;
   struct win_thread_data *tdata = NULL;
-  HANDLE stdin_handle = NULL;
-  uint64_t auth_rnd;
-  size_t nwritten = 0;
   static HANDLE stdin_thread = NULL;
   static curl_socket_t socket_r = CURL_SOCKET_BAD;
+  curl_socket_t socket_l = CURL_SOCKET_BAD;
+  uint64_t auth_rnd = 0;
+  uint64_t recvd_val = 1;
 
   if(socket_r != CURL_SOCKET_BAD) {
     assert(stdin_thread);
@@ -815,10 +843,10 @@ curl_socket_t win32_stdin_read_thread(void)
       errorf("curlx_calloc() error");
       break;
     }
-    /* Create the listening socket for the thread. When it starts, it accepts
-     * our connection and begin writing STDIN data to the connection. */
-    tdata->socket_l = CURL_SOCKET(AF_INET, SOCK_STREAM, IPPROTO_TCP);
-    if(tdata->socket_l == CURL_SOCKET_BAD) {
+    /* Create the listening socket. It is used to create the writing socket by
+     * accepting a connection from the reading socket. */
+    socket_l = CURL_SOCKET(AF_INET, SOCK_STREAM, IPPROTO_TCP);
+    if(socket_l == CURL_SOCKET_BAD) {
       errorf("socket() error: %d", SOCKERRNO);
       break;
     }
@@ -828,36 +856,103 @@ curl_socket_t win32_stdin_read_thread(void)
     selfaddr.sin_family = AF_INET;
     selfaddr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
     /* Bind to any available loopback port */
-    if(bind(tdata->socket_l, (const struct sockaddr *)&selfaddr, socksize)) {
+    if(bind(socket_l, (const struct sockaddr *)&selfaddr, socksize)) {
       errorf("bind error: %d", SOCKERRNO);
       break;
     }
 
     /* Retrieve the assigned loopback port/address */
-    if(getsockname(tdata->socket_l, (struct sockaddr *)&selfaddr, &socksize)) {
+    if(getsockname(socket_l, (struct sockaddr *)&selfaddr, &socksize)) {
       errorf("getsockname error: %d", SOCKERRNO);
       break;
     }
 
-    if(listen(tdata->socket_l, 1)) {
+    if(listen(socket_l, 1)) {
       errorf("listen error: %d", SOCKERRNO);
       break;
     }
 
+    /* Create the reading socket */
+    socket_r = CURL_SOCKET(AF_INET, SOCK_STREAM, IPPROTO_TCP);
+    if(socket_r == CURL_SOCKET_BAD) {
+      errorf("socket error: %d", SOCKERRNO);
+      break;
+    }
+
+    /* Hard close the socket on closesocket() */
+    setsockopt(socket_r, SOL_SOCKET, SO_DONTLINGER, 0, 0);
+
+    /* Make the reading socket nonblocking */
+    if(curlx_nonblock(socket_r, TRUE)) {
+      errorf("curlx_nonblock() error");
+      break;
+    }
+
+    /* Connect to the listening socket */
+    if(connect(socket_r, (const struct sockaddr *)&selfaddr, socksize)) {
+      ssize_t sockerrno = SOCKERRNO;
+      if(sockerrno != WSAEWOULDBLOCK) {
+        errorf("connect error: %d", sockerrno);
+        break;
+      }
+    }
+
+    /* Accept the connection on the other end, creating the writing socket
+     * which will be given to the background thread */
+    tdata->socket_w = CURL_ACCEPT(socket_l, NULL, NULL);
+
+    if(tdata->socket_w == CURL_SOCKET_BAD) {
+      errorf("accept error: %d", SOCKERRNO);
+      break;
+    }
+
+    /* We don't need the listening socket anymore */
+    sclose(socket_l);
+    socket_l = CURL_SOCKET_BAD;
+
+    /* Authenticate the reading socket to the writing socket to make sure we don't
+     * leak information.*/
     if(curlx_win32_random((unsigned char *)&auth_rnd, sizeof(auth_rnd))) {
       errorf("curlx_win32_random() error");
       break;
     }
-    tdata->expected_auth_val = auth_rnd;
+
+    if(swrite_blocking_on_nonblock(socket_r, (unsigned char *)&auth_rnd,
+                                   sizeof(auth_rnd)))
+      break;
+
+    if(read_auth_val(tdata->socket_w, &recvd_val))
+      break;
+
+    if(recvd_val != auth_rnd) {
+      errorf("relay peer auth failed");
+      break;
+    }
+
+    if(shutdown(tdata->socket_w, SHUT_RD)) {
+      errorf("shutdown error: %d", SOCKERRNO);
+      break;
+    }
+
+    if(shutdown(socket_r, SHUT_WR)) {
+      errorf("shutdown error: %d", SOCKERRNO);
+      break;
+    }
+
 
     /* Make a copy of the stdin handle to be used by win_stdin_thread_func */
     if(!DuplicateHandle(GetCurrentProcess(), GetStdHandle(STD_INPUT_HANDLE),
-                        GetCurrentProcess(), &stdin_handle,
+                        GetCurrentProcess(), &tdata->stdin_handle,
                         0, FALSE, DUPLICATE_SAME_ACCESS)) {
       errorf("DuplicateHandle error: 0x%08lx", GetLastError());
       break;
     }
-    tdata->stdin_handle = stdin_handle;
+
+    /* Set the stdin handle to read from the socket. */
+    if(SetStdHandle(STD_INPUT_HANDLE, (HANDLE)socket_r) == 0) {
+      errorf("SetStdHandle error: 0x%08lx", GetLastError());
+      break;
+    }
 
     /* Start up the thread. We do not bother keeping a reference to it
        because it runs until program termination. From here on out all reads
@@ -871,72 +966,34 @@ curl_socket_t win32_stdin_read_thread(void)
     }
     tdata = NULL; /* win_stdin_thread_func owns it now */
 
-    /* Connect to the thread and rearrange our own STDIN handles */
-    socket_r = CURL_SOCKET(AF_INET, SOCK_STREAM, IPPROTO_TCP);
-    if(socket_r == CURL_SOCKET_BAD) {
-      errorf("socket error: %d", SOCKERRNO);
-      break;
-    }
-
-    /* Hard close the socket on closesocket() */
-    setsockopt(socket_r, SOL_SOCKET, SO_DONTLINGER, 0, 0);
-
-    if(connect(socket_r, (const struct sockaddr *)&selfaddr, socksize)) {
-      errorf("connect error: %d", SOCKERRNO);
-      break;
-    }
-
-    do {
-      ssize_t ret = swrite(socket_r, ((unsigned char *)&auth_rnd) + nwritten,
-                           sizeof(auth_rnd) - nwritten);
-
-      if(ret <= 0) {
-        errorf("socket write error: %d", SOCKERRNO);
-        goto err;
-      }
-
-      nwritten += ret;
-    } while(nwritten < sizeof(auth_rnd));
-
-    if(shutdown(socket_r, SHUT_WR)) {
-      errorf("shutdown error: %d", SOCKERRNO);
-      break;
-    }
-
-    /* Set the stdin handle to read from the socket. */
-    if(SetStdHandle(STD_INPUT_HANDLE, (HANDLE)socket_r) == 0) {
-      errorf("SetStdHandle error: 0x%08lx", GetLastError());
-      break;
-    }
+    /* Starting the thread is the last thing we do, since there aren't any
+     * reliable ways to close it in case of subsequent errors. */
 
     rc = 1;
   } while(0);
 
-err:
   if(rc != 1) {
-    if(stdin_thread) {
-      TerminateThread(stdin_thread, 1);
-      CloseHandle(stdin_thread);
-      stdin_thread = NULL;
-    }
-
     if(socket_r != CURL_SOCKET_BAD) {
       if(GetStdHandle(STD_INPUT_HANDLE) == (HANDLE)socket_r &&
-         stdin_handle) {
+         tdata && tdata->stdin_handle) {
         /* restore STDIN */
-        SetStdHandle(STD_INPUT_HANDLE, stdin_handle);
-        stdin_handle = NULL;
+        SetStdHandle(STD_INPUT_HANDLE, tdata->stdin_handle);
+        tdata->stdin_handle = NULL;
       }
 
       sclose(socket_r);
       socket_r = CURL_SOCKET_BAD;
     }
 
+
+    if(socket_l != CURL_SOCKET_BAD)
+      sclose(socket_l);
+
     if(tdata) {
       if(tdata->stdin_handle)
         CloseHandle(tdata->stdin_handle);
-      if(tdata->socket_l != CURL_SOCKET_BAD)
-        sclose(tdata->socket_l);
+      if(tdata->socket_w != CURL_SOCKET_BAD)
+        sclose(tdata->socket_w);
 
       curlx_free(tdata);
     }

From 2bfa796c31ce54c16d373b2390107863593f1d40 Mon Sep 17 00:00:00 2001
From: 11soda11 <115734183+Sodastream11@users.noreply.github.com>
Date: Fri, 24 Jul 2026 12:38:25 +0200
Subject: [PATCH 02/23] fix code style

---
 src/tool_doswin.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/tool_doswin.c b/src/tool_doswin.c
index cf009e4d50..ad72db29d0 100644
--- a/src/tool_doswin.c
+++ b/src/tool_doswin.c
@@ -738,7 +738,7 @@ static DWORD WINAPI win_stdin_thread_func(void *thread_data)
     tdata->socket_w = CURL_SOCKET_BAD;
   }
 
-  if(tdata->stdin_handle != NULL) {
+  if(tdata->stdin_handle) {
     CloseHandle(tdata->stdin_handle);
     tdata->stdin_handle = NULL;
   }
@@ -748,7 +748,7 @@ static DWORD WINAPI win_stdin_thread_func(void *thread_data)
 }
 
 static int swrite_blocking_on_nonblock(curl_socket_t nonblock_sock,
-                                       unsigned char* data,
+                                       unsigned char *data,
                                        size_t len)
 {
   fd_set fdwrite;
@@ -910,8 +910,8 @@ curl_socket_t win32_stdin_read_thread(void)
     sclose(socket_l);
     socket_l = CURL_SOCKET_BAD;
 
-    /* Authenticate the reading socket to the writing socket to make sure we don't
-     * leak information.*/
+    /* Authenticate the reading socket to the writing socket to make sure
+     * we don't leak information.*/
     if(curlx_win32_random((unsigned char *)&auth_rnd, sizeof(auth_rnd))) {
       errorf("curlx_win32_random() error");
       break;

From 77265b595d5c3f6b16c48911ce253148f2435538 Mon Sep 17 00:00:00 2001
From: 11soda11 <115734183+Sodastream11@users.noreply.github.com>
Date: Fri, 24 Jul 2026 13:08:01 +0200
Subject: [PATCH 03/23] fix format string

---
 src/tool_doswin.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/tool_doswin.c b/src/tool_doswin.c
index ad72db29d0..8d0ff84b02 100644
--- a/src/tool_doswin.c
+++ b/src/tool_doswin.c
@@ -892,7 +892,7 @@ curl_socket_t win32_stdin_read_thread(void)
     if(connect(socket_r, (const struct sockaddr *)&selfaddr, socksize)) {
       ssize_t sockerrno = SOCKERRNO;
       if(sockerrno != WSAEWOULDBLOCK) {
-        errorf("connect error: %d", sockerrno);
+        errorf("connect error: %lld", sockerrno);
         break;
       }
     }

From c728ac5ed4e6d4a52731f6b6b2482c26f2a5d97e Mon Sep 17 00:00:00 2001
From: 11soda11 <115734183+Sodastream11@users.noreply.github.com>
Date: Sat, 25 Jul 2026 17:55:12 +0200
Subject: [PATCH 04/23] address comments

---
 src/tool_doswin.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/src/tool_doswin.c b/src/tool_doswin.c
index 8d0ff84b02..fa6308f46c 100644
--- a/src/tool_doswin.c
+++ b/src/tool_doswin.c
@@ -890,9 +890,9 @@ curl_socket_t win32_stdin_read_thread(void)
 
     /* Connect to the listening socket */
     if(connect(socket_r, (const struct sockaddr *)&selfaddr, socksize)) {
-      ssize_t sockerrno = SOCKERRNO;
-      if(sockerrno != WSAEWOULDBLOCK) {
-        errorf("connect error: %lld", sockerrno);
+      int sockerr = SOCKERRNO;
+      if(!SOCK_EAGAIN(sockerr)) {
+        errorf("connect error: %d", sockerr);
         break;
       }
     }
@@ -939,7 +939,6 @@ curl_socket_t win32_stdin_read_thread(void)
       break;
     }
 
-
     /* Make a copy of the stdin handle to be used by win_stdin_thread_func */
     if(!DuplicateHandle(GetCurrentProcess(), GetStdHandle(STD_INPUT_HANDLE),
                         GetCurrentProcess(), &tdata->stdin_handle,
@@ -985,7 +984,6 @@ curl_socket_t win32_stdin_read_thread(void)
       socket_r = CURL_SOCKET_BAD;
     }
 
-
     if(socket_l != CURL_SOCKET_BAD)
       sclose(socket_l);
 

From e555532403095972dde0f43df983542cac388aff Mon Sep 17 00:00:00 2001
From: 11soda11 <115734183+Sodastream11@users.noreply.github.com>
Date: Sat, 25 Jul 2026 21:42:13 +0200
Subject: [PATCH 05/23] test

---
 tests/http/test_07_upload.py | 15 +++++++++++++++
 tests/http/testenv/curl.py   |  3 ++-
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/tests/http/test_07_upload.py b/tests/http/test_07_upload.py
index 6cb4d943e1..697fb6b11e 100644
--- a/tests/http/test_07_upload.py
+++ b/tests/http/test_07_upload.py
@@ -713,6 +713,21 @@ class TestUpload:
         # we might send less before the server handshakes.
         assert 0 < earlydata[1] <= (upload_size + 1024), f'{earlydata}\n{r.dump_logs()}'
 
+    @pytest.mark.parametrize("proto", Env.http_protos())
+    @pytest.mark.parametrize("indata", [
+        '', '1', '123\n456andsomething\n\n'
+    ])
+    def test_07_71_upload_async_stdin(self, env: Env, httpd, nghttpx, proto, indata):
+        count = 1
+        curl = CurlClient(env=env)
+        url = f'https://{env.authority_for(env.domain1, proto)}/curltest/put?id=[0-{count-1}]'
+        r = curl.http_put(urls=[url], data=indata, alpn_proto=proto, async_stdin=True)
+        r.check_stats(count=count, http_status=200, exitcode=0)
+        for i in range(count):
+            with open(curl.response_file(i)) as fr:
+                respdata = fr.readlines()
+            assert respdata == [f'{len(indata)}']
+
     def check_downloads(self, client, r, source: List[str], count: int,
                         complete: bool = True):
         for i in range(count):
diff --git a/tests/http/testenv/curl.py b/tests/http/testenv/curl.py
index 2abbbbe49c..5c9f12eeaf 100644
--- a/tests/http/testenv/curl.py
+++ b/tests/http/testenv/curl.py
@@ -811,13 +811,14 @@ class CurlClient:
                  with_headers: bool = False,
                  with_profile: bool = False,
                  suppress_cl: bool = False,
+                 async_stdin: bool = False,
                  extra_args: Optional[List[str]] = None):
         if extra_args is None:
             extra_args = []
         if fdata is not None:
             extra_args.extend(['-T', fdata])
         elif data is not None:
-            extra_args.extend(['-T', '-'])
+            extra_args.extend(['-T', '.' if async_stdin else '-'])
         extra_args.extend([
             '-o', 'download_#1.data',
         ])

From 481e91f8934001979de1727c93fa261d6bdd0716 Mon Sep 17 00:00:00 2001
From: 11soda11 <115734183+Sodastream11@users.noreply.github.com>
Date: Sat, 25 Jul 2026 21:42:13 +0200
Subject: [PATCH 06/23] add test

---
 tests/http/test_07_upload.py | 15 +++++++++++++++
 tests/http/testenv/curl.py   |  3 ++-
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/tests/http/test_07_upload.py b/tests/http/test_07_upload.py
index 6cb4d943e1..697fb6b11e 100644
--- a/tests/http/test_07_upload.py
+++ b/tests/http/test_07_upload.py
@@ -713,6 +713,21 @@ class TestUpload:
         # we might send less before the server handshakes.
         assert 0 < earlydata[1] <= (upload_size + 1024), f'{earlydata}\n{r.dump_logs()}'
 
+    @pytest.mark.parametrize("proto", Env.http_protos())
+    @pytest.mark.parametrize("indata", [
+        '', '1', '123\n456andsomething\n\n'
+    ])
+    def test_07_71_upload_async_stdin(self, env: Env, httpd, nghttpx, proto, indata):
+        count = 1
+        curl = CurlClient(env=env)
+        url = f'https://{env.authority_for(env.domain1, proto)}/curltest/put?id=[0-{count-1}]'
+        r = curl.http_put(urls=[url], data=indata, alpn_proto=proto, async_stdin=True)
+        r.check_stats(count=count, http_status=200, exitcode=0)
+        for i in range(count):
+            with open(curl.response_file(i)) as fr:
+                respdata = fr.readlines()
+            assert respdata == [f'{len(indata)}']
+
     def check_downloads(self, client, r, source: List[str], count: int,
                         complete: bool = True):
         for i in range(count):
diff --git a/tests/http/testenv/curl.py b/tests/http/testenv/curl.py
index 2abbbbe49c..5c9f12eeaf 100644
--- a/tests/http/testenv/curl.py
+++ b/tests/http/testenv/curl.py
@@ -811,13 +811,14 @@ class CurlClient:
                  with_headers: bool = False,
                  with_profile: bool = False,
                  suppress_cl: bool = False,
+                 async_stdin: bool = False,
                  extra_args: Optional[List[str]] = None):
         if extra_args is None:
             extra_args = []
         if fdata is not None:
             extra_args.extend(['-T', fdata])
         elif data is not None:
-            extra_args.extend(['-T', '-'])
+            extra_args.extend(['-T', '.' if async_stdin else '-'])
         extra_args.extend([
             '-o', 'download_#1.data',
         ])

From 1e91bf6e6e449283089b2d46ac174dd78a0c8ff2 Mon Sep 17 00:00:00 2001
From: 11soda11 <115734183+Sodastream11@users.noreply.github.com>
Date: Sun, 26 Jul 2026 13:12:05 +0200
Subject: [PATCH 07/23] more style fixes

---
 src/tool_doswin.c | 15 +++++----------
 1 file changed, 5 insertions(+), 10 deletions(-)

diff --git a/src/tool_doswin.c b/src/tool_doswin.c
index fa6308f46c..6c062ea60b 100644
--- a/src/tool_doswin.c
+++ b/src/tool_doswin.c
@@ -777,8 +777,7 @@ static int swrite_blocking_on_nonblock(curl_socket_t nonblock_sock,
       return -1;
     }
 
-    ret = swrite(nonblock_sock, data + nwritten,
-            len - nwritten);
+    ret = swrite(nonblock_sock, data + nwritten, len - nwritten);
 
     if(ret <= 0) {
       errorf("socket write error: %d", SOCKERRNO);
@@ -791,21 +790,17 @@ static int swrite_blocking_on_nonblock(curl_socket_t nonblock_sock,
   return 0;
 }
 
-static int read_auth_val(curl_socket_t sock,
-                         uint64_t* buf)
+static int read_auth_val(curl_socket_t sock, uint64_t* buf)
 {
   size_t nread = 0;
 
   do {
-    ssize_t ret = sread(sock, buf + nread,
-                        sizeof(*buf) - nread);
+    ssize_t ret = sread(sock, buf + nread, sizeof(*buf) - nread);
     if(ret <= 0) {
-      if(!ret) {
+      if(!ret)
         errorf("stdin relay peer disconnected");
-      }
-      else {
+      else
         errorf("read error: %d", SOCKERRNO);
-      }
 
       return -1;
     }

From 971b83e389329a6cfa5c65904d21f673a6eb29c8 Mon Sep 17 00:00:00 2001
From: 11soda11 <115734183+Sodastream11@users.noreply.github.com>
Date: Mon, 27 Jul 2026 02:42:28 +0200
Subject: [PATCH 08/23] remove useless pytest + unblock test 1498 for windows

---
 tests/data/test1498          |  1 -
 tests/http/test_07_upload.py | 15 ---------------
 tests/http/testenv/curl.py   |  3 +--
 3 files changed, 1 insertion(+), 18 deletions(-)

diff --git a/tests/data/test1498 b/tests/data/test1498
index 67c3f8409d..b6aa35d813 100644
--- a/tests/data/test1498
+++ b/tests/data/test1498
@@ -27,7 +27,6 @@ blablabla
 http
 </server>
 <features>
-!win32
 </features>
 <name>
 HTTP PUT from stdin using period
diff --git a/tests/http/test_07_upload.py b/tests/http/test_07_upload.py
index 697fb6b11e..6cb4d943e1 100644
--- a/tests/http/test_07_upload.py
+++ b/tests/http/test_07_upload.py
@@ -713,21 +713,6 @@ class TestUpload:
         # we might send less before the server handshakes.
         assert 0 < earlydata[1] <= (upload_size + 1024), f'{earlydata}\n{r.dump_logs()}'
 
-    @pytest.mark.parametrize("proto", Env.http_protos())
-    @pytest.mark.parametrize("indata", [
-        '', '1', '123\n456andsomething\n\n'
-    ])
-    def test_07_71_upload_async_stdin(self, env: Env, httpd, nghttpx, proto, indata):
-        count = 1
-        curl = CurlClient(env=env)
-        url = f'https://{env.authority_for(env.domain1, proto)}/curltest/put?id=[0-{count-1}]'
-        r = curl.http_put(urls=[url], data=indata, alpn_proto=proto, async_stdin=True)
-        r.check_stats(count=count, http_status=200, exitcode=0)
-        for i in range(count):
-            with open(curl.response_file(i)) as fr:
-                respdata = fr.readlines()
-            assert respdata == [f'{len(indata)}']
-
     def check_downloads(self, client, r, source: List[str], count: int,
                         complete: bool = True):
         for i in range(count):
diff --git a/tests/http/testenv/curl.py b/tests/http/testenv/curl.py
index 5c9f12eeaf..2abbbbe49c 100644
--- a/tests/http/testenv/curl.py
+++ b/tests/http/testenv/curl.py
@@ -811,14 +811,13 @@ class CurlClient:
                  with_headers: bool = False,
                  with_profile: bool = False,
                  suppress_cl: bool = False,
-                 async_stdin: bool = False,
                  extra_args: Optional[List[str]] = None):
         if extra_args is None:
             extra_args = []
         if fdata is not None:
             extra_args.extend(['-T', fdata])
         elif data is not None:
-            extra_args.extend(['-T', '.' if async_stdin else '-'])
+            extra_args.extend(['-T', '-'])
         extra_args.extend([
             '-o', 'download_#1.data',
         ])

From f5378361eb3aff2a53a60e275f1c1ba4b1f95dca Mon Sep 17 00:00:00 2001
From: 11soda11 <115734183+Sodastream11@users.noreply.github.com>
Date: Mon, 27 Jul 2026 13:43:42 +0200
Subject: [PATCH 09/23] remove features section + unlbock test 2300

---
 .github/workflows/windows.yml | 1 -
 tests/data/test1498           | 2 --
 2 files changed, 3 deletions(-)

diff --git a/.github/workflows/windows.yml b/.github/workflows/windows.yml
index 267a2a108a..d397cb9948 100644
--- a/.github/workflows/windows.yml
+++ b/.github/workflows/windows.yml
@@ -513,7 +513,6 @@ jobs:
               export CURL_TEST_SSH_ENABLE_KEX=diffie-hellman-group-exchange-sha256
             fi
             if [[ "${TFLAGS}" = *'-t'* ]]; then
-              TFLAGS+=' !2300'  # Leaks memory and file handle via tool_doswin.c / win32_stdin_read_thread()
               export CURL_TEST_NO_TASKKILL=1  # experiment to see if it reduces flaky failures
             fi
             if [[ "${MATRIX_INSTALL} " = *'-libssh '* && \
diff --git a/tests/data/test1498 b/tests/data/test1498
index b6aa35d813..362cf7fcf6 100644
--- a/tests/data/test1498
+++ b/tests/data/test1498
@@ -26,8 +26,6 @@ blablabla
 <server>
 http
 </server>
-<features>
-</features>
 <name>
 HTTP PUT from stdin using period
 </name>

From 3621138ffb3d231cc0c61b99212f4fb69d3bfc07 Mon Sep 17 00:00:00 2001
From: 11soda11 <115734183+Sodastream11@users.noreply.github.com>
Date: Mon, 27 Jul 2026 14:31:32 +0200
Subject: [PATCH 10/23] fix error handling bug

---
 src/tool_doswin.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/tool_doswin.c b/src/tool_doswin.c
index 6c062ea60b..c325c42332 100644
--- a/src/tool_doswin.c
+++ b/src/tool_doswin.c
@@ -838,6 +838,8 @@ curl_socket_t win32_stdin_read_thread(void)
       errorf("curlx_calloc() error");
       break;
     }
+    tdata->socket_w = CURL_SOCKET_BAD;
+
     /* Create the listening socket. It is used to create the writing socket by
      * accepting a connection from the reading socket. */
     socket_l = CURL_SOCKET(AF_INET, SOCK_STREAM, IPPROTO_TCP);

From 71e045d3fe3a6280cdb315995f1346693b310dec Mon Sep 17 00:00:00 2001
From: 11soda11 <115734183+Sodastream11@users.noreply.github.com>
Date: Mon, 27 Jul 2026 14:56:21 +0200
Subject: [PATCH 11/23] make tdata static

---
 src/tool_doswin.c | 47 +++++++++++++++++++----------------------------
 1 file changed, 19 insertions(+), 28 deletions(-)

diff --git a/src/tool_doswin.c b/src/tool_doswin.c
index c325c42332..c0c5947622 100644
--- a/src/tool_doswin.c
+++ b/src/tool_doswin.c
@@ -743,7 +743,6 @@ static DWORD WINAPI win_stdin_thread_func(void *thread_data)
     tdata->stdin_handle = NULL;
   }
 
-  curlx_free(tdata);
   return 0;
 }
 
@@ -814,7 +813,10 @@ static int read_auth_val(curl_socket_t sock, uint64_t* buf)
 curl_socket_t win32_stdin_read_thread(void)
 {
   int rc = 0;
-  struct win_thread_data *tdata = NULL;
+  static struct win_thread_data tdata = {
+    .socket_w = CURL_SOCKET_BAD,
+    .stdin_handle = NULL
+  };
   static HANDLE stdin_thread = NULL;
   static curl_socket_t socket_r = CURL_SOCKET_BAD;
   curl_socket_t socket_l = CURL_SOCKET_BAD;
@@ -831,15 +833,6 @@ curl_socket_t win32_stdin_read_thread(void)
     curl_socklen_t socksize = 0;
     struct sockaddr_in selfaddr;
 
-    /* Prepare handles for thread */
-    tdata = (struct win_thread_data *)
-      curlx_calloc(1, sizeof(struct win_thread_data));
-    if(!tdata) {
-      errorf("curlx_calloc() error");
-      break;
-    }
-    tdata->socket_w = CURL_SOCKET_BAD;
-
     /* Create the listening socket. It is used to create the writing socket by
      * accepting a connection from the reading socket. */
     socket_l = CURL_SOCKET(AF_INET, SOCK_STREAM, IPPROTO_TCP);
@@ -896,9 +889,9 @@ curl_socket_t win32_stdin_read_thread(void)
 
     /* Accept the connection on the other end, creating the writing socket
      * which will be given to the background thread */
-    tdata->socket_w = CURL_ACCEPT(socket_l, NULL, NULL);
+    tdata.socket_w = CURL_ACCEPT(socket_l, NULL, NULL);
 
-    if(tdata->socket_w == CURL_SOCKET_BAD) {
+    if(tdata.socket_w == CURL_SOCKET_BAD) {
       errorf("accept error: %d", SOCKERRNO);
       break;
     }
@@ -918,7 +911,7 @@ curl_socket_t win32_stdin_read_thread(void)
                                    sizeof(auth_rnd)))
       break;
 
-    if(read_auth_val(tdata->socket_w, &recvd_val))
+    if(read_auth_val(tdata.socket_w, &recvd_val))
       break;
 
     if(recvd_val != auth_rnd) {
@@ -926,7 +919,7 @@ curl_socket_t win32_stdin_read_thread(void)
       break;
     }
 
-    if(shutdown(tdata->socket_w, SHUT_RD)) {
+    if(shutdown(tdata.socket_w, SHUT_RD)) {
       errorf("shutdown error: %d", SOCKERRNO);
       break;
     }
@@ -938,7 +931,7 @@ curl_socket_t win32_stdin_read_thread(void)
 
     /* Make a copy of the stdin handle to be used by win_stdin_thread_func */
     if(!DuplicateHandle(GetCurrentProcess(), GetStdHandle(STD_INPUT_HANDLE),
-                        GetCurrentProcess(), &tdata->stdin_handle,
+                        GetCurrentProcess(), &tdata.stdin_handle,
                         0, FALSE, DUPLICATE_SAME_ACCESS)) {
       errorf("DuplicateHandle error: 0x%08lx", GetLastError());
       break;
@@ -955,12 +948,11 @@ curl_socket_t win32_stdin_read_thread(void)
        from the stdin handle or file descriptor 0 is reading from the
        socket that is fed by the thread. */
     stdin_thread = CreateThread(NULL, 0, win_stdin_thread_func,
-                                tdata, 0, NULL);
+                                &tdata, 0, NULL);
     if(!stdin_thread) {
       errorf("CreateThread error: 0x%08lx", GetLastError());
       break;
     }
-    tdata = NULL; /* win_stdin_thread_func owns it now */
 
     /* Starting the thread is the last thing we do, since there aren't any
      * reliable ways to close it in case of subsequent errors. */
@@ -969,12 +961,14 @@ curl_socket_t win32_stdin_read_thread(void)
   } while(0);
 
   if(rc != 1) {
+    /* we rely on the background thread not running at this point, as there
+     * could be TOCTOU bugs otherwise */
     if(socket_r != CURL_SOCKET_BAD) {
       if(GetStdHandle(STD_INPUT_HANDLE) == (HANDLE)socket_r &&
-         tdata && tdata->stdin_handle) {
+         tdata.stdin_handle) {
         /* restore STDIN */
-        SetStdHandle(STD_INPUT_HANDLE, tdata->stdin_handle);
-        tdata->stdin_handle = NULL;
+        SetStdHandle(STD_INPUT_HANDLE, tdata.stdin_handle);
+        tdata.stdin_handle = NULL;
       }
 
       sclose(socket_r);
@@ -984,14 +978,11 @@ curl_socket_t win32_stdin_read_thread(void)
     if(socket_l != CURL_SOCKET_BAD)
       sclose(socket_l);
 
-    if(tdata) {
-      if(tdata->stdin_handle)
-        CloseHandle(tdata->stdin_handle);
-      if(tdata->socket_w != CURL_SOCKET_BAD)
-        sclose(tdata->socket_w);
+    if(tdata.stdin_handle)
+      CloseHandle(tdata.stdin_handle);
+    if(tdata.socket_w != CURL_SOCKET_BAD)
+      sclose(tdata.socket_w);
 
-      curlx_free(tdata);
-    }
 
     return CURL_SOCKET_BAD;
   }

From 9ae25134831466f99d139029d6bb60080f64433b Mon Sep 17 00:00:00 2001
From: Emanuel Krollmann <115734183+11soda11@users.noreply.github.com>
Date: Mon, 27 Jul 2026 16:50:25 +0200
Subject: [PATCH 12/23] fix tdata init literal

---
 src/tool_doswin.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/src/tool_doswin.c b/src/tool_doswin.c
index c0c5947622..8552011942 100644
--- a/src/tool_doswin.c
+++ b/src/tool_doswin.c
@@ -813,10 +813,7 @@ static int read_auth_val(curl_socket_t sock, uint64_t* buf)
 curl_socket_t win32_stdin_read_thread(void)
 {
   int rc = 0;
-  static struct win_thread_data tdata = {
-    .socket_w = CURL_SOCKET_BAD,
-    .stdin_handle = NULL
-  };
+  static struct win_thread_data tdata = { CURL_SOCKET_BAD, NULL };
   static HANDLE stdin_thread = NULL;
   static curl_socket_t socket_r = CURL_SOCKET_BAD;
   curl_socket_t socket_l = CURL_SOCKET_BAD;

From ff2192990226ec6ddcea1862fc5c94ac3d710843 Mon Sep 17 00:00:00 2001
From: Emanuel Krollmann <115734183+11soda11@users.noreply.github.com>
Date: Mon, 27 Jul 2026 16:55:03 +0200
Subject: [PATCH 13/23] fix init again

---
 src/tool_doswin.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/tool_doswin.c b/src/tool_doswin.c
index 8552011942..070e405118 100644
--- a/src/tool_doswin.c
+++ b/src/tool_doswin.c
@@ -813,7 +813,8 @@ static int read_auth_val(curl_socket_t sock, uint64_t* buf)
 curl_socket_t win32_stdin_read_thread(void)
 {
   int rc = 0;
-  static struct win_thread_data tdata = { CURL_SOCKET_BAD, NULL };
+  static struct win_thread_data tdata =
+    (struct win_thread_data){ CURL_SOCKET_BAD, NULL };
   static HANDLE stdin_thread = NULL;
   static curl_socket_t socket_r = CURL_SOCKET_BAD;
   curl_socket_t socket_l = CURL_SOCKET_BAD;

From 50b4999ea6ba5210562ef5e7e5edb693922f0177 Mon Sep 17 00:00:00 2001
From: Emanuel Krollmann <115734183+11soda11@users.noreply.github.com>
Date: Mon, 27 Jul 2026 16:59:29 +0200
Subject: [PATCH 14/23] switch order

---
 src/tool_doswin.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/src/tool_doswin.c b/src/tool_doswin.c
index 070e405118..23bb432ffb 100644
--- a/src/tool_doswin.c
+++ b/src/tool_doswin.c
@@ -813,8 +813,7 @@ static int read_auth_val(curl_socket_t sock, uint64_t* buf)
 curl_socket_t win32_stdin_read_thread(void)
 {
   int rc = 0;
-  static struct win_thread_data tdata =
-    (struct win_thread_data){ CURL_SOCKET_BAD, NULL };
+  static struct win_thread_data tdata = { NULL, CURL_SOCKET_BAD };
   static HANDLE stdin_thread = NULL;
   static curl_socket_t socket_r = CURL_SOCKET_BAD;
   curl_socket_t socket_l = CURL_SOCKET_BAD;

From a7a9ea6d459b8eafcd161cba1c694b8d30c7e362 Mon Sep 17 00:00:00 2001
From: Emanuel Krollmann <115734183+11soda11@users.noreply.github.com>
Date: Mon, 27 Jul 2026 17:04:25 +0200
Subject: [PATCH 15/23] remove duplicate empty line

---
 src/tool_doswin.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/src/tool_doswin.c b/src/tool_doswin.c
index 23bb432ffb..87c6ae3887 100644
--- a/src/tool_doswin.c
+++ b/src/tool_doswin.c
@@ -980,7 +980,6 @@ curl_socket_t win32_stdin_read_thread(void)
     if(tdata.socket_w != CURL_SOCKET_BAD)
       sclose(tdata.socket_w);
 
-
     return CURL_SOCKET_BAD;
   }
 

From 984d3bef520daf4a22310c15a3967bebef32102f Mon Sep 17 00:00:00 2001
From: 11soda11 <115734183+Sodastream11@users.noreply.github.com>
Date: Tue, 28 Jul 2026 03:26:55 +0200
Subject: [PATCH 16/23] fix valgrind errors

---
 src/tool_doswin.c | 43 ++++++++++++++++++++++---------------------
 1 file changed, 22 insertions(+), 21 deletions(-)

diff --git a/src/tool_doswin.c b/src/tool_doswin.c
index 87c6ae3887..6333464460 100644
--- a/src/tool_doswin.c
+++ b/src/tool_doswin.c
@@ -704,45 +704,50 @@ static void init_terminal(void)
 #ifdef USE_WINSOCK
 /* The following STDIN non - blocking read techniques are heavily inspired
    by nmap and ncat (https://nmap.org/ncat/) */
-struct win_thread_data {
+static struct win_thread_data {
   /* This is a copy of the true stdin file handle before any redirection. It is
      read by the thread. */
   HANDLE stdin_handle;
   /* this is the socket the thread will forward stdin to. It is connected to
    * the socket which replaces the stdin handle. */
   curl_socket_t socket_w;
-};
+} tdata = { NULL, CURL_SOCKET_BAD };
+
+static void cleanup_tdata(void)
+{
+  if(tdata.stdin_handle) {
+    CloseHandle(tdata.stdin_handle);
+    tdata.stdin_handle = NULL;
+  }
+
+  if(tdata.socket_w != CURL_SOCKET_BAD) {
+    sclose(tdata.socket_w);
+    tdata.socket_w = CURL_SOCKET_BAD;
+  }
+}
 
 static DWORD WINAPI win_stdin_thread_func(void *thread_data)
 {
-  struct win_thread_data *tdata = (struct win_thread_data *)thread_data;
+  (void)thread_data;
+
+  atexit(cleanup_tdata);
 
   for(;;) {
     DWORD n;
     ssize_t nwritten;
     char buffer[BUFSIZ];
 
-    if(!ReadFile(tdata->stdin_handle, buffer, sizeof(buffer), &n, NULL))
+    if(!ReadFile(tdata.stdin_handle, buffer, sizeof(buffer), &n, NULL))
       break;
     if(n == 0)
       break;
-    nwritten = swrite(tdata->socket_w, buffer, n);
+    nwritten = swrite(tdata.socket_w, buffer, n);
     if(nwritten == -1)
       break;
     if((DWORD)nwritten != n)
       break;
   }
 
-  if(tdata->socket_w != CURL_SOCKET_BAD) {
-    sclose(tdata->socket_w);
-    tdata->socket_w = CURL_SOCKET_BAD;
-  }
-
-  if(tdata->stdin_handle) {
-    CloseHandle(tdata->stdin_handle);
-    tdata->stdin_handle = NULL;
-  }
-
   return 0;
 }
 
@@ -813,7 +818,6 @@ static int read_auth_val(curl_socket_t sock, uint64_t* buf)
 curl_socket_t win32_stdin_read_thread(void)
 {
   int rc = 0;
-  static struct win_thread_data tdata = { NULL, CURL_SOCKET_BAD };
   static HANDLE stdin_thread = NULL;
   static curl_socket_t socket_r = CURL_SOCKET_BAD;
   curl_socket_t socket_l = CURL_SOCKET_BAD;
@@ -945,7 +949,7 @@ curl_socket_t win32_stdin_read_thread(void)
        from the stdin handle or file descriptor 0 is reading from the
        socket that is fed by the thread. */
     stdin_thread = CreateThread(NULL, 0, win_stdin_thread_func,
-                                &tdata, 0, NULL);
+                                NULL, 0, NULL);
     if(!stdin_thread) {
       errorf("CreateThread error: 0x%08lx", GetLastError());
       break;
@@ -975,10 +979,7 @@ curl_socket_t win32_stdin_read_thread(void)
     if(socket_l != CURL_SOCKET_BAD)
       sclose(socket_l);
 
-    if(tdata.stdin_handle)
-      CloseHandle(tdata.stdin_handle);
-    if(tdata.socket_w != CURL_SOCKET_BAD)
-      sclose(tdata.socket_w);
+    cleanup_tdata();
 
     return CURL_SOCKET_BAD;
   }

From 13f10b2fe0ee03ea47a26d9c8b9f032bc58e16d8 Mon Sep 17 00:00:00 2001
From: 11soda11 <115734183+Sodastream11@users.noreply.github.com>
Date: Tue, 28 Jul 2026 04:16:11 +0200
Subject: [PATCH 17/23] second try with atexit

---
 src/tool_doswin.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/tool_doswin.c b/src/tool_doswin.c
index 6333464460..390d0aba91 100644
--- a/src/tool_doswin.c
+++ b/src/tool_doswin.c
@@ -730,7 +730,6 @@ static DWORD WINAPI win_stdin_thread_func(void *thread_data)
 {
   (void)thread_data;
 
-  atexit(cleanup_tdata);
 
   for(;;) {
     DWORD n;
@@ -834,6 +833,12 @@ curl_socket_t win32_stdin_read_thread(void)
     curl_socklen_t socksize = 0;
     struct sockaddr_in selfaddr;
 
+    /* prevent mem leak warnings */
+    if(atexit(&cleanup_tdata)) {
+      errorf("atexit() error");
+      break;
+    }
+
     /* Create the listening socket. It is used to create the writing socket by
      * accepting a connection from the reading socket. */
     socket_l = CURL_SOCKET(AF_INET, SOCK_STREAM, IPPROTO_TCP);

From f89318e65c3ce15a7aa49108210824cb1771e25b Mon Sep 17 00:00:00 2001
From: Emanuel Krollmann <115734183+11soda11@users.noreply.github.com>
Date: Tue, 28 Jul 2026 05:04:17 +0200
Subject: [PATCH 18/23] remove duplicate newline

---
 src/tool_doswin.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/src/tool_doswin.c b/src/tool_doswin.c
index 390d0aba91..c4c2f696c6 100644
--- a/src/tool_doswin.c
+++ b/src/tool_doswin.c
@@ -730,7 +730,6 @@ static DWORD WINAPI win_stdin_thread_func(void *thread_data)
 {
   (void)thread_data;
 
-
   for(;;) {
     DWORD n;
     ssize_t nwritten;

From 8266ff2354fc11015f9412f739580b113954dfa4 Mon Sep 17 00:00:00 2001
From: 11soda11 <115734183+Sodastream11@users.noreply.github.com>
Date: Wed, 29 Jul 2026 00:26:03 +0200
Subject: [PATCH 19/23] fix buffer overflow + duplicate fds inside fd_set

---
 src/tool_doswin.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/tool_doswin.c b/src/tool_doswin.c
index c4c2f696c6..c195742e3a 100644
--- a/src/tool_doswin.c
+++ b/src/tool_doswin.c
@@ -759,10 +759,11 @@ static int swrite_blocking_on_nonblock(curl_socket_t nonblock_sock,
 
   FD_ZERO(&fdwrite);
   FD_ZERO(&fdexcep);
+  FD_SET(nonblock_sock, &fdwrite);
 
   do {
     ssize_t ret;
-    FD_SET(nonblock_sock, &fdwrite);
+
     FD_SET(nonblock_sock, &fdexcep);
 
     if(select(0, NULL, &fdwrite, &fdexcep, NULL) <= 0) {
@@ -797,7 +798,7 @@ static int read_auth_val(curl_socket_t sock, uint64_t* buf)
   size_t nread = 0;
 
   do {
-    ssize_t ret = sread(sock, buf + nread, sizeof(*buf) - nread);
+    ssize_t ret = sread(sock, (unsigned char*)buf + nread, sizeof(*buf) - nread);
     if(ret <= 0) {
       if(!ret)
         errorf("stdin relay peer disconnected");

From bc1999e217069f6f8c53deb55e689795b0f43799 Mon Sep 17 00:00:00 2001
From: 11soda11 <115734183+Sodastream11@users.noreply.github.com>
Date: Wed, 29 Jul 2026 00:29:55 +0200
Subject: [PATCH 20/23] checksrc fix

---
 src/tool_doswin.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/tool_doswin.c b/src/tool_doswin.c
index c195742e3a..0a81692cd0 100644
--- a/src/tool_doswin.c
+++ b/src/tool_doswin.c
@@ -798,7 +798,8 @@ static int read_auth_val(curl_socket_t sock, uint64_t* buf)
   size_t nread = 0;
 
   do {
-    ssize_t ret = sread(sock, (unsigned char*)buf + nread, sizeof(*buf) - nread);
+    ssize_t ret = sread(sock, (unsigned char *)buf + nread,
+                        sizeof(*buf) - nread);
     if(ret <= 0) {
       if(!ret)
         errorf("stdin relay peer disconnected");

From 7f0458823d5e0aee49a040d48a73cf96ec9ef142 Mon Sep 17 00:00:00 2001
From: 11soda11 <115734183+Sodastream11@users.noreply.github.com>
Date: Wed, 29 Jul 2026 00:52:23 +0200
Subject: [PATCH 21/23] naming changes + default value for selfaddr

---
 src/tool_doswin.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/src/tool_doswin.c b/src/tool_doswin.c
index 0a81692cd0..d218e0dd83 100644
--- a/src/tool_doswin.c
+++ b/src/tool_doswin.c
@@ -751,7 +751,7 @@ static DWORD WINAPI win_stdin_thread_func(void *thread_data)
 
 static int swrite_blocking_on_nonblock(curl_socket_t nonblock_sock,
                                        unsigned char *data,
-                                       size_t len)
+                                       size_t nbytes)
 {
   fd_set fdwrite;
   fd_set fdexcep;
@@ -780,7 +780,7 @@ static int swrite_blocking_on_nonblock(curl_socket_t nonblock_sock,
       return -1;
     }
 
-    ret = swrite(nonblock_sock, data + nwritten, len - nwritten);
+    ret = swrite(nonblock_sock, data + nwritten, nbytes - nwritten);
 
     if(ret <= 0) {
       errorf("socket write error: %d", SOCKERRNO);
@@ -788,18 +788,18 @@ static int swrite_blocking_on_nonblock(curl_socket_t nonblock_sock,
     }
 
     nwritten += ret;
-  } while(nwritten < len);
+  } while(nwritten < nbytes);
 
   return 0;
 }
 
-static int read_auth_val(curl_socket_t sock, uint64_t* buf)
+static int read_auth_val(curl_socket_t sock, uint64_t* auth_val_ptr)
 {
   size_t nread = 0;
 
   do {
-    ssize_t ret = sread(sock, (unsigned char *)buf + nread,
-                        sizeof(*buf) - nread);
+    ssize_t ret = sread(sock, (unsigned char *)auth_val_ptr + nread,
+                        sizeof(*auth_val_ptr) - nread);
     if(ret <= 0) {
       if(!ret)
         errorf("stdin relay peer disconnected");
@@ -809,7 +809,7 @@ static int read_auth_val(curl_socket_t sock, uint64_t* buf)
       return -1;
     }
     nread += ret;
-  } while(nread < sizeof(*buf));
+  } while(nread < sizeof(*auth_val_ptr));
 
   return 0;
 }
@@ -832,7 +832,7 @@ curl_socket_t win32_stdin_read_thread(void)
 
   do {
     curl_socklen_t socksize = 0;
-    struct sockaddr_in selfaddr;
+    struct sockaddr_in selfaddr = {0};
 
     /* prevent mem leak warnings */
     if(atexit(&cleanup_tdata)) {

From 5635e6b94de7f8ee7c2a1883139ea9f0678d8362 Mon Sep 17 00:00:00 2001
From: 11soda11 <115734183+Sodastream11@users.noreply.github.com>
Date: Wed, 29 Jul 2026 01:08:00 +0200
Subject: [PATCH 22/23] add EAGAIN check on write to nonblock sock

---
 src/tool_doswin.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/tool_doswin.c b/src/tool_doswin.c
index d218e0dd83..b8a94ebc4d 100644
--- a/src/tool_doswin.c
+++ b/src/tool_doswin.c
@@ -759,6 +759,7 @@ static int swrite_blocking_on_nonblock(curl_socket_t nonblock_sock,
 
   FD_ZERO(&fdwrite);
   FD_ZERO(&fdexcep);
+
   FD_SET(nonblock_sock, &fdwrite);
 
   do {
@@ -783,6 +784,9 @@ static int swrite_blocking_on_nonblock(curl_socket_t nonblock_sock,
     ret = swrite(nonblock_sock, data + nwritten, nbytes - nwritten);
 
     if(ret <= 0) {
+      if(SOCK_EAGAIN(SOCKERRNO))
+        continue;
+
       errorf("socket write error: %d", SOCKERRNO);
       return -1;
     }

From c8cd3ef1960cc0fda415a82f96f095a736caeb80 Mon Sep 17 00:00:00 2001
From: 11soda11 <115734183+Sodastream11@users.noreply.github.com>
Date: Wed, 29 Jul 2026 18:39:03 +0200
Subject: [PATCH 23/23] address further comments

---
 src/tool_doswin.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/tool_doswin.c b/src/tool_doswin.c
index b8a94ebc4d..4c2ab885a1 100644
--- a/src/tool_doswin.c
+++ b/src/tool_doswin.c
@@ -750,7 +750,7 @@ static DWORD WINAPI win_stdin_thread_func(void *thread_data)
 }
 
 static int swrite_blocking_on_nonblock(curl_socket_t nonblock_sock,
-                                       unsigned char *data,
+                                       const unsigned char *data,
                                        size_t nbytes)
 {
   fd_set fdwrite;
@@ -836,7 +836,7 @@ curl_socket_t win32_stdin_read_thread(void)
 
   do {
     curl_socklen_t socksize = 0;
-    struct sockaddr_in selfaddr = {0};
+    struct sockaddr_in selfaddr;
 
     /* prevent mem leak warnings */
     if(atexit(&cleanup_tdata)) {