Subject: Re: [PATCH v2] mingw: emulate write(2) that fails with a EPIPE

From: Junio C Hamano <[email-masked]>
Date: Thu, 17 Dec 2015 11:22:49 -0800

Johannes Schindelin <[email-masked]> writes:

> On Windows, when writing to a pipe fails, errno is always
> EINVAL. However, Git expects it to be EPIPE.
>
> According to the documentation, there are two cases in which write()
> triggers EINVAL: the buffer is NULL, or the length is odd but the mode
> is 16-bit Unicode (the broken pipe is not mentioned as possible cause).
> Git never sets the file mode to anything but binary, therefore we know
> that errno should actually be EPIPE if it is EINVAL and the buffer is
> not NULL.
>
> See https://msdn.microsoft.com/en-us/library/1570wh78.aspx for more
> details.
>
> This works around t5571.11 failing with v2.6.4 on Windows.
>
> Signed-off-by: Johannes Schindelin <[email-masked]>
> ---
>  compat/mingw.c | 17 +++++++++++++++++
>  compat/mingw.h |  3 +++
>  2 files changed, 20 insertions(+)
>
> diff --git a/compat/mingw.c b/compat/mingw.c
> index 90bdb1e..5edea29 100644
> --- a/compat/mingw.c
> +++ b/compat/mingw.c
> @@ -394,6 +394,23 @@ int mingw_fflush(FILE *stream)
>  	return ret;
>  }
>  
> +#undef write
> +ssize_t mingw_write(int fd, const void *buf, size_t len)
> +{
> +	ssize_t result = write(fd, buf, len);
> +
> +	if (result < 0 && errno == EINVAL && buf) {
> +		/* check if fd is a pipe */
> +		HANDLE h = (HANDLE) _get_osfhandle(fd);
> +		if (GetFileType(h) == FILE_TYPE_PIPE)
> +			errno = EPIPE;
> +		else
> +			errno = EINVAL;
> +	}
> +
> +	return result;
> +}
> +
>  int mingw_access(const char *filename, int mode)
>  {
>  	wchar_t wfilename[MAX_PATH];
> diff --git a/compat/mingw.h b/compat/mingw.h
> index 738865c..57ca477 100644
> --- a/compat/mingw.h
> +++ b/compat/mingw.h
> @@ -210,6 +210,9 @@ FILE *mingw_freopen (const char *filename, const char *otype, FILE *stream);
>  int mingw_fflush(FILE *stream);
>  #define fflush mingw_fflush
>  
> +ssize_t mingw_write(int fd, const void *buf, size_t len);
> +#define write mingw_write
> +
>  int mingw_access(const char *filename, int mode);
>  #undef access
>  #define access mingw_access

PLEASE DON'T DO THE BELOW TO THE SAME MESSAGE AS THE PATCH ITSELF.
"git apply" would not read and understand the next line as a natural
language sentence for obvious reasons.

> Interdiff vs v1:
>
> diff --git a/compat/mingw.c b/compat/mingw.c
> index 90bdb1e..5edea29 100644
> --- a/compat/mingw.c
> +++ b/compat/mingw.c
> @@ -394,6 +394,23 @@ int mingw_fflush(FILE *stream)
>  	return ret;
>  }
>  
> +#undef write
> +ssize_t mingw_write(int fd, const void *buf, size_t len)
> +{
> +	ssize_t result = write(fd, buf, len);
> +
> +	if (result < 0 && errno == EINVAL && buf) {
> +		/* check if fd is a pipe */
> +		HANDLE h = (HANDLE) _get_osfhandle(fd);
> +		if (GetFileType(h) == FILE_TYPE_PIPE)
> +			errno = EPIPE;
> +		else
> +			errno = EINVAL;
> +	}
> +
> +	return result;
> +}
> +
>  int mingw_access(const char *filename, int mode)
>  {
>  	wchar_t wfilename[MAX_PATH];
> diff --git a/compat/mingw.h b/compat/mingw.h
> index 2aca347..57ca477 100644
> --- a/compat/mingw.h
> +++ b/compat/mingw.h
> @@ -210,22 +210,7 @@ FILE *mingw_freopen (const char *filename, const char *otype, FILE *stream);
>  int mingw_fflush(FILE *stream);
>  #define fflush mingw_fflush
>  
> -static inline ssize_t mingw_write(int fd, const void *buf, size_t len)
> -{
> -	ssize_t result = write(fd, buf, len);
> -
> -	if (result < 0 && errno == EINVAL && buf) {
> -		/* check if fd is a pipe */
> -		HANDLE h = (HANDLE) _get_osfhandle(fd);
> -		if (GetFileType(h) == FILE_TYPE_PIPE)
> -			errno = EPIPE;
> -		else
> -			errno = EINVAL;
> -	}
> -
> -	return result;
> -}
> -
> +ssize_t mingw_write(int fd, const void *buf, size_t len);
>  #define write mingw_write
>  
>  int mingw_access(const char *filename, int mode);