[FFmpeg-devel] [PATCH] gdigrab: Allow capturing a window by its handle

[FFmpeg-devel] [PATCH] gdigrab: Allow capturing a window by its handle

[Lena via ffmpeg-devel]

x11grab can capture windows by their ID, but gdigrab can only capture 
windows by their names, internally calling FindWindowW to lookup its handle.

This patch simply allows the user to specify a window handle directly.
Signed-off-by: Lena <lena@nihil.gay>
---
  libavdevice/gdigrab.c | 6 +++++-
  1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/libavdevice/gdigrab.c b/libavdevice/gdigrab.c
index c069232472..05d3c0c929 100644
--- a/libavdevice/gdigrab.c
+++ b/libavdevice/gdigrab.c
@@ -273,9 +273,13 @@ gdigrab_read_header(AVFormatContext *s1)
          }
      } else if (!strcmp(filename, "desktop")) {
          hwnd = NULL;
+    } else if (!strncmp(filename, "hwnd=", 5)) {
+        name = filename + 5;
+        +        hwnd = strtol(name, NULL, 0);
      } else {
          av_log(s1, AV_LOG_ERROR,
-               "Please use \"desktop\" or \"title=<windowname>\" to 
specify your target.\n");
+               "Please use \"desktop\", \"title=<windowname>\" or 
\"hwnd=<hwnd>\" to specify your target.\n");
          ret = AVERROR(EIO);
          goto error;
      }
-- 
2.43.0

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Re: [FFmpeg-devel] [PATCH] gdigrab: Allow capturing a window by its handle

[Andreas Rheinhardt]

Lena via ffmpeg-devel:
> x11grab can capture windows by their ID, but gdigrab can only capture
> windows by their names, internally calling FindWindowW to lookup its
> handle.
> 
> This patch simply allows the user to specify a window handle directly.
> Signed-off-by: Lena <lena@nihil.gay>
> ---
>  libavdevice/gdigrab.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/libavdevice/gdigrab.c b/libavdevice/gdigrab.c
> index c069232472..05d3c0c929 100644
> --- a/libavdevice/gdigrab.c
> +++ b/libavdevice/gdigrab.c
> @@ -273,9 +273,13 @@ gdigrab_read_header(AVFormatContext *s1)
>          }
>      } else if (!strcmp(filename, "desktop")) {
>          hwnd = NULL;
> +    } else if (!strncmp(filename, "hwnd=", 5)) {
> +        name = filename + 5;
> +        +        hwnd = strtol(name, NULL, 0);

This won't even compile due to the extra '+'.

>      } else {
>          av_log(s1, AV_LOG_ERROR,
> -               "Please use \"desktop\" or \"title=<windowname>\" to
> specify your target.\n");
> +               "Please use \"desktop\", \"title=<windowname>\" or
> \"hwnd=<hwnd>\" to specify your target.\n");
>          ret = AVERROR(EIO);
>          goto error;
>      }

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Re: [FFmpeg-devel] [PATCH] gdigrab: Allow capturing a window by its handle

[Lena via ffmpeg-devel]

I'm so sorry, will resend immediately.


Andreas Rheinhardt via ffmpeg-devel:

> Lena via ffmpeg-devel:
>> x11grab can capture windows by their ID, but gdigrab can only capture
>> windows by their names, internally calling FindWindowW to lookup its
>> handle.
>>
>> This patch simply allows the user to specify a window handle directly.
>> Signed-off-by: Lena <lena@nihil.gay>
>> ---
>>   libavdevice/gdigrab.c | 6 +++++-
>>   1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/libavdevice/gdigrab.c b/libavdevice/gdigrab.c
>> index c069232472..05d3c0c929 100644
>> --- a/libavdevice/gdigrab.c
>> +++ b/libavdevice/gdigrab.c
>> @@ -273,9 +273,13 @@ gdigrab_read_header(AVFormatContext *s1)
>>           }
>>       } else if (!strcmp(filename, "desktop")) {
>>           hwnd = NULL;
>> +    } else if (!strncmp(filename, "hwnd=", 5)) {
>> +        name = filename + 5;
>> +        +        hwnd = strtol(name, NULL, 0);
> This won't even compile due to the extra '+'.
>
>>       } else {
>>           av_log(s1, AV_LOG_ERROR,
>> -               "Please use \"desktop\" or \"title=<windowname>\" to
>> specify your target.\n");
>> +               "Please use \"desktop\", \"title=<windowname>\" or
>> \"hwnd=<hwnd>\" to specify your target.\n");
>>           ret = AVERROR(EIO);
>>           goto error;
>>       }
> _______________________________________________
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> ffmpeg-devel@ffmpeg.org
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>
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> ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe".
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Re: [FFmpeg-devel] [PATCH] gdigrab: Allow capturing a window by its handle

[Lena via ffmpeg-devel]

x11grab can capture windows by their ID, but gdigrab can only capture windows by their names, internally calling FindWindowW to lookup its handle.

This patch simply allows the user to specify a window handle directly.
Signed-off-by: Lena <lena@nihil.gay>
---
 libavdevice/gdigrab.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/libavdevice/gdigrab.c b/libavdevice/gdigrab.c
index c069232472..05d3c0c929 100644
--- a/libavdevice/gdigrab.c
+++ b/libavdevice/gdigrab.c
@@ -273,9 +273,13 @@ gdigrab_read_header(AVFormatContext *s1)
         }
     } else if (!strcmp(filename, "desktop")) {
         hwnd = NULL;
+    } else if (!strncmp(filename, "hwnd=", 5)) {
+        name = filename + 5;
+        
+        hwnd = strtol(name, NULL, 0);
     } else {
         av_log(s1, AV_LOG_ERROR,
-               "Please use \"desktop\" or \"title=<windowname>\" to specify your target.\n");
+               "Please use \"desktop\", \"title=<windowname>\" or \"hwnd=<hwnd>\" to specify your target.\n");
         ret = AVERROR(EIO);
         goto error;
     }
-- 
2.43.0

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Re: [FFmpeg-devel] [PATCH] gdigrab: Allow capturing a window by its handle

[Stefano Sabatini]

On date Monday 2023-12-11 02:52:01 +0100, ffmpeg-devel Mailing List wrote:
> x11grab can capture windows by their ID, but gdigrab can only capture windows by their names, internally calling FindWindowW to lookup its handle.
> 
> This patch simply allows the user to specify a window handle directly.
> Signed-off-by: Lena <lena@nihil.gay>
> ---

>  libavdevice/gdigrab.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)

Missing doc/indevs.texi updates.

> diff --git a/libavdevice/gdigrab.c b/libavdevice/gdigrab.c
> index c069232472..05d3c0c929 100644
> --- a/libavdevice/gdigrab.c
> +++ b/libavdevice/gdigrab.c
> @@ -273,9 +273,13 @@ gdigrab_read_header(AVFormatContext *s1)
>          }
>      } else if (!strcmp(filename, "desktop")) {
>          hwnd = NULL;

> +    } else if (!strncmp(filename, "hwnd=", 5)) {
> +        name = filename + 5;
> +        
> +        hwnd = strtol(name, NULL, 0);

This should fail in case the parsing failed, for this you can check
the second argument (see examples in the code).
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[FFmpeg-devel] [PATCH v2] gdigrab: Allow capturing a window by its handle

[Lena via ffmpeg-devel]

Added the change to the documentation and added error checking on `strtol`, according to the stdlib documentation.

The documentation for `strtol` says that on error, 0 is returned. This makes it impossible to specify a window handle of 0 (the whole desktop), but that case is already covered by the "desktop" input filename, so it should be fine.


x11grab can capture windows by their ID, but gdigrab can only capture windows by their names, internally calling FindWindowW to lookup its handle.

This patch simply allows the user to specify a window handle directly.
Signed-off-by: Lena <lena@nihil.gay>
---
 doc/indevs.texi       |  8 ++++++--
 libavdevice/gdigrab.c | 13 ++++++++++++-
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/doc/indevs.texi b/doc/indevs.texi
index 863536a34d..6da0ccac62 100644
--- a/doc/indevs.texi
+++ b/doc/indevs.texi
@@ -722,7 +722,7 @@ Win32 GDI-based screen capture device.
 
 This device allows you to capture a region of the display on Windows.
 
-There are two options for the input filename:
+There are three options for the input filename:
 @example
 desktop
 @end example
@@ -730,9 +730,13 @@ or
 @example
 title=@var{window_title}
 @end example
+or
+@example
+hwnd=@var{window_hwnd}
+@end example
 
 The first option will capture the entire desktop, or a fixed region of the
-desktop. The second option will instead capture the contents of a single
+desktop. The second and third options will instead capture the contents of a single
 window, regardless of its position on the screen.
 
 For example, to grab the entire desktop using @command{ffmpeg}:
diff --git a/libavdevice/gdigrab.c b/libavdevice/gdigrab.c
index c069232472..f310d8f3d7 100644
--- a/libavdevice/gdigrab.c
+++ b/libavdevice/gdigrab.c
@@ -273,9 +273,20 @@ gdigrab_read_header(AVFormatContext *s1)
         }
     } else if (!strcmp(filename, "desktop")) {
         hwnd = NULL;
+    } else if (!strncmp(filename, "hwnd=", 5)) {
+        name = filename + 5;
+        
+        hwnd = strtol(name, NULL, 0);
+
+        if (hwnd == NULL) {
+            av_log(s1, AV_LOG_ERROR,
+               "Invalid window handle.\n");
+            ret = AVERROR(EINVAL);
+            goto error;
+        }
     } else {
         av_log(s1, AV_LOG_ERROR,
-               "Please use \"desktop\" or \"title=<windowname>\" to specify your target.\n");
+               "Please use \"desktop\", \"title=<windowname>\" or \"hwnd=<hwnd>\" to specify your target.\n");
         ret = AVERROR(EIO);
         goto error;
     }
-- 
2.43.0

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Re: [FFmpeg-devel] [PATCH v2] gdigrab: Allow capturing a window by its handle

[Nicolas George]

Lena via ffmpeg-devel (12023-12-12):
> The documentation for `strtol` says that on error, 0 is returned. This
> makes it impossible to specify a window handle of 0 (the whole
> desktop), but that case is already covered by the "desktop" input
> filename, so it should be fine.

The correct way to test for error in strtol is to check the endptr.

But just use a single sscanf() and %n to see if it reached the end of
the string.

> -There are two options for the input filename:
> +There are three options for the input filename:

“Amongst options for the imput filenames are such elements as:”

;-)

Regards,

-- 
  Nicolas George
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Re: [FFmpeg-devel] [PATCH v2] gdigrab: Allow capturing a window by its handle

[Rémi Denis-Courmont]

Le 12 décembre 2023 16:07:28 GMT+02:00, Nicolas George <george@nsup.org> a écrit :
>Lena via ffmpeg-devel (12023-12-12):
>> The documentation for `strtol` says that on error, 0 is returned. This
>> makes it impossible to specify a window handle of 0 (the whole
>> desktop), but that case is already covered by the "desktop" input
>> filename, so it should be fine.
>
>The correct way to test for error in strtol is to check the endptr.

...and test for overflow errors in errno.m (which shall have been zeroed beforehand). AFAIK, you need to do both if you want strict error detection.

>
>But just use a single sscanf() and %n to see if it reached the end of
>the string.

Don't some distros forbid the use of the n specifier for (debatable) "security reasons"? Or is that only for formatting, and not in scanning?

>> -There are two options for the input filename:
>> +There are three options for the input filename:
>
>“Amongst options for the imput filenames are such elements as:”
>
>;-)
>
>Regards,
>
>-- 
>  Nicolas George
>_______________________________________________
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>
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>ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe".
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Re: [FFmpeg-devel] [PATCH v2] gdigrab: Allow capturing a window by its handle

[Nicolas George]

Rémi Denis-Courmont (12023-12-12):
> ...and test for overflow errors in errno.m (which shall have been
> zeroed beforehand). AFAIK, you need to do both if you want strict
> error detection.

Or we can consider that 30064771114 is just another valid way if writing
42 = 042 = 0x2a. It would be better to check, but it is less critical
than checking for garbage at the and, which itself is less critical than
checking that the number is entirely absent.

> Don't some distros forbid the use of the n specifier for (debatable)
> "security reasons"? Or is that only for formatting, and not in
> scanning?

First time I ear of that. We use %n in quite a few places — not only
code by me — and we did not have a problem.

If there is a real security consideration about %n, I would like a
pointer to the explanations; but I strongly doubt there are, it is just
another conversion specifier with all the usual caveats. If not, and
there are distros who forbid it for no valid reason, then I say to hell
with them.

Regards,

-- 
  Nicolas George
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[FFmpeg-devel] [PATCH v3] gdigrab: Allow capturing a window by its handle

[Lena via ffmpeg-devel]

Updated the wording of the documentation, and added error checking for strtol.

I looked at how other parts of the codebase check for errors on strtol and implemented it that way (iec61883, filter_units_bsf, etc).

As for checking if the string value is larger/smaller than a long, i don't think there's a need, as the documentation says it'd just get set to LONG_MIN/LONG_MAX and fail anyway.


x11grab can capture windows by their ID, but gdigrab can only capture windows by their names, internally calling FindWindowW to lookup its handle.

This patch simply allows the user to specify a window handle directly.
Signed-off-by: Lena <lena@nihil.gay>
---
 doc/indevs.texi       |  8 ++++++--
 libavdevice/gdigrab.c | 15 ++++++++++++++-
 2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/doc/indevs.texi b/doc/indevs.texi
index 863536a34d..a0c684f545 100644
--- a/doc/indevs.texi
+++ b/doc/indevs.texi
@@ -722,7 +722,7 @@ Win32 GDI-based screen capture device.
 
 This device allows you to capture a region of the display on Windows.
 
-There are two options for the input filename:
+Amongst options for the imput filenames are such elements as:
 @example
 desktop
 @end example
@@ -730,9 +730,13 @@ or
 @example
 title=@var{window_title}
 @end example
+or
+@example
+hwnd=@var{window_hwnd}
+@end example
 
 The first option will capture the entire desktop, or a fixed region of the
-desktop. The second option will instead capture the contents of a single
+desktop. The second and third options will instead capture the contents of a single
 window, regardless of its position on the screen.
 
 For example, to grab the entire desktop using @command{ffmpeg}:
diff --git a/libavdevice/gdigrab.c b/libavdevice/gdigrab.c
index c069232472..3153b6f711 100644
--- a/libavdevice/gdigrab.c
+++ b/libavdevice/gdigrab.c
@@ -273,9 +273,22 @@ gdigrab_read_header(AVFormatContext *s1)
         }
     } else if (!strcmp(filename, "desktop")) {
         hwnd = NULL;
+    } else if (!strncmp(filename, "hwnd=", 5)) {
+        name = filename + 5;
+        char *p;
+
+        hwnd = strtol(name, &p, 0);
+
+        if (p == NULL || p == name || p[0] == '\0')
+        {
+            av_log(s1, AV_LOG_ERROR,
+                   "Invalid window handle.\n");
+            ret = AVERROR(EINVAL);
+            goto error;
+        }
     } else {
         av_log(s1, AV_LOG_ERROR,
-               "Please use \"desktop\" or \"title=<windowname>\" to specify your target.\n");
+               "Please use \"desktop\", \"title=<windowname>\" or \"hwnd=<hwnd>\" to specify your target.\n");
         ret = AVERROR(EIO);
         goto error;
     }
-- 
2.43.0

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Re: [FFmpeg-devel] [PATCH v3] gdigrab: Allow capturing a window by its handle

[Stefano Sabatini]

On date Thursday 2023-12-14 11:32:44 +0100, Lena wrote:
> Updated the wording of the documentation, and added error checking for strtol.
> 
> I looked at how other parts of the codebase check for errors on strtol and implemented it that way (iec61883, filter_units_bsf, etc).
> 
> As for checking if the string value is larger/smaller than a long, i don't think there's a need, as the documentation says it'd just get set to LONG_MIN/LONG_MAX and fail anyway.
> 
> 
> x11grab can capture windows by their ID, but gdigrab can only capture windows by their names, internally calling FindWindowW to lookup its handle.
> 
> This patch simply allows the user to specify a window handle directly.
> Signed-off-by: Lena <lena@nihil.gay>
> ---
>  doc/indevs.texi       |  8 ++++++--
>  libavdevice/gdigrab.c | 15 ++++++++++++++-
>  2 files changed, 20 insertions(+), 3 deletions(-)
> 
> diff --git a/doc/indevs.texi b/doc/indevs.texi
> index 863536a34d..a0c684f545 100644
> --- a/doc/indevs.texi
> +++ b/doc/indevs.texi
> @@ -722,7 +722,7 @@ Win32 GDI-based screen capture device.
>  
>  This device allows you to capture a region of the display on Windows.
>  
> -There are two options for the input filename:
> +Amongst options for the imput filenames are such elements as:
>  @example
>  desktop
>  @end example
> @@ -730,9 +730,13 @@ or
>  @example
>  title=@var{window_title}
>  @end example
> +or
> +@example
> +hwnd=@var{window_hwnd}
> +@end example
>  
>  The first option will capture the entire desktop, or a fixed region of the
> -desktop. The second option will instead capture the contents of a single
> +desktop. The second and third options will instead capture the contents of a single
>  window, regardless of its position on the screen.
>  
>  For example, to grab the entire desktop using @command{ffmpeg}:
> diff --git a/libavdevice/gdigrab.c b/libavdevice/gdigrab.c
> index c069232472..3153b6f711 100644
> --- a/libavdevice/gdigrab.c
> +++ b/libavdevice/gdigrab.c
> @@ -273,9 +273,22 @@ gdigrab_read_header(AVFormatContext *s1)
>          }
>      } else if (!strcmp(filename, "desktop")) {
>          hwnd = NULL;
> +    } else if (!strncmp(filename, "hwnd=", 5)) {
> +        name = filename + 5;
> +        char *p;
> +
> +        hwnd = strtol(name, &p, 0);
> +
> +        if (p == NULL || p == name || p[0] == '\0')
> +        {
> +            av_log(s1, AV_LOG_ERROR,

> +                   "Invalid window handle.\n");

Here you can provide some context:
"Invalid window handle '%s', must be an valid integer.", name

Looks good otherwise, thanks.
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[FFmpeg-devel] [PATCH v4] gdigrab: Allow capturing a window by its handle

[Lena via ffmpeg-devel]

Added more context in the error message and did a final test that it all works.

Thanks for the smooth patch submission process!


x11grab can capture windows by their ID, but gdigrab can only capture windows by their names, internally calling FindWindowW to lookup its handle.

This patch simply allows the user to specify a window handle directly.
Signed-off-by: Lena <lena@nihil.gay>
---
 doc/indevs.texi       |  8 ++++++--
 libavdevice/gdigrab.c | 15 ++++++++++++++-
 2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/doc/indevs.texi b/doc/indevs.texi
index 863536a34d..a0c684f545 100644
--- a/doc/indevs.texi
+++ b/doc/indevs.texi
@@ -722,7 +722,7 @@ Win32 GDI-based screen capture device.
 
 This device allows you to capture a region of the display on Windows.
 
-There are two options for the input filename:
+Amongst options for the imput filenames are such elements as:
 @example
 desktop
 @end example
@@ -730,9 +730,13 @@ or
 @example
 title=@var{window_title}
 @end example
+or
+@example
+hwnd=@var{window_hwnd}
+@end example
 
 The first option will capture the entire desktop, or a fixed region of the
-desktop. The second option will instead capture the contents of a single
+desktop. The second and third options will instead capture the contents of a single
 window, regardless of its position on the screen.
 
 For example, to grab the entire desktop using @command{ffmpeg}:
diff --git a/libavdevice/gdigrab.c b/libavdevice/gdigrab.c
index c069232472..aa909a9392 100644
--- a/libavdevice/gdigrab.c
+++ b/libavdevice/gdigrab.c
@@ -273,9 +273,22 @@ gdigrab_read_header(AVFormatContext *s1)
         }
     } else if (!strcmp(filename, "desktop")) {
         hwnd = NULL;
+    } else if (!strncmp(filename, "hwnd=", 5)) {
+        name = filename + 5;
+        char *p;
+
+        hwnd = strtol(name, &p, 0);
+
+        if (p == NULL || p == name || p[0] == '\0')
+        {
+            av_log(s1, AV_LOG_ERROR,
+                   "Invalid window handle '%s', must be an valid integer.\n", name);
+            ret = AVERROR(EINVAL);
+            goto error;
+        }
     } else {
         av_log(s1, AV_LOG_ERROR,
-               "Please use \"desktop\" or \"title=<windowname>\" to specify your target.\n");
+               "Please use \"desktop\", \"title=<windowname>\" or \"hwnd=<hwnd>\" to specify your target.\n");
         ret = AVERROR(EIO);
         goto error;
     }
-- 
2.43.0

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Re: [FFmpeg-devel] [PATCH v4] gdigrab: Allow capturing a window by its handle

[Stefano Sabatini]

On date Sunday 2023-12-17 18:29:33 +0100, Lena wrote:
> Added more context in the error message and did a final test that it all works.
> 
> Thanks for the smooth patch submission process!
> 
> 
> x11grab can capture windows by their ID, but gdigrab can only capture windows by their names, internally calling FindWindowW to lookup its handle.
> 
> This patch simply allows the user to specify a window handle directly.
> Signed-off-by: Lena <lena@nihil.gay>
> ---
>  doc/indevs.texi       |  8 ++++++--
>  libavdevice/gdigrab.c | 15 ++++++++++++++-
>  2 files changed, 20 insertions(+), 3 deletions(-)

Thanks! Applied with a typo fix and a Changelog addition.
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Re: [FFmpeg-devel] [PATCH v2] gdigrab: Allow capturing a window by its handle

[Rémi Denis-Courmont]

Le 13 décembre 2023 12:03:55 GMT+02:00, Nicolas George <george@nsup.org> a écrit :
>Rémi Denis-Courmont (12023-12-12):
>> ...and test for overflow errors in errno.m (which shall have been
>> zeroed beforehand). AFAIK, you need to do both if you want strict
>> error detection.
>
>Or we can consider that 30064771114 is just another valid way if writing
>42 = 042 = 0x2a. It would be better to check, but it is less critical
>than checking for garbage at the and, which itself is less critical than
>checking that the number is entirely absent.

That's completely arbitrary, TBH. Both cases are syntax errors, and there are no particular reasons to tolerate one but not the other. And even if it constitued a sensible distinction, that's simply not how strtoul() handles overflow: it returns ULONG_MAX, not a wrapped-around value.

In this case, both error cases are strong signs of a typing error or corruption.
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