In order to watch out for lost bytes in a pipe I encountered this segfault.
It seems that the readEnd is already closed when rawRead = fread is
called (uncomment the eof line).

How do I keep the pipe open?

```piperawreadsegfault.d (linux)
import std.stdio;
import std.process;

void main ()
{
   auto dev_zero = File ("/dev/zero", "r");
   auto dev_null = File ("/dev/null", "w");
   auto p = pipe ();
   auto proc1 = spawnProcess (["dd", "bs=4096", "count=2"],
      dev_zero, p.writeEnd);
   auto proc2 = spawnProcess (["dd", "bs=4096", "count=1"],
      p.readEnd, dev_null);
   auto res2 = wait (proc2);
   auto res1 = wait (proc1);
   stderr.writeln ("res1 = ", res1, ", res2 = ", res2);
//  stderr.writeln (p.readEnd.eof);
   ubyte [1] u;
   auto n = p.readEnd.rawRead (u);
}
```

$ dmd -g piperawreadsegfault
$ gdb ./piperawreadsegfault
(gdb) r
Starting program: /tmp/k/piperawreadsegfault
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
2+0 records in
2+0 records out
8192 bytes (8.2 kB) copied, 2.487e-05 s, 329 MB/s
1+0 records in
1+0 records out
4096 bytes (4.1 kB) copied, 2.0234e-05 s, 202 MB/s
res1 = 0, res2 = 0

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff7054f99 in fread () from /lib64/libc.so.6
(gdb) bt
#0  0x00007ffff7054f99 in fread () from /lib64/libc.so.6
#1  0x000000000048fd96 in std.stdio() (obj=..., f=0x0) at [...]/dmd2/linux/bin64/../../src/phobos/std/stdio.d:4383
#2  0x000000000048fcb7 in std.stdio.File() (this=..., buffer=...)
    at [...]/dmd2/linux/bin64/../../src/phobos/std/stdio.d:1036
#3  0x000000000048f10a in D main () at piperawreadsegfault.d:18
[...]

On Wednesday, 17 March 2021 at 23:08:07 UTC, kdevel wrote:
> In order to watch out for lost bytes in a pipe I encountered this segfault.
> It seems that the readEnd is already closed when rawRead = fread is
> called (uncomment the eof line).
>
> [...]

Have you tried "scope(exit) wait(" instead?

On Thursday, 18 March 2021 at 07:55:01 UTC, Imperatorn wrote:
[...]
> Have you tried "scope(exit) wait(" instead?

Yes. Does not make a difference. For the segfault I have filed Issue 21728

On Wednesday, 17 March 2021 at 23:08:07 UTC, kdevel wrote:
[...]
> How do I keep the pipe open?

Having the readEnd and writeEnd closed in the parent is usually
the right thing to to. spawnProcess closes the ends which is
documented:

| Note that if you pass a File object that is not one of the standard
| input/output/error streams of the parent process, that stream will
| by default be closed in the parent process when this function returns.
| See the Config documentation below for information about how to disable
| this behaviour. [1]

[1] https://dlang.org/phobos/std_process.html#spawnProcess