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Date: Thu, 29 Nov 2018 10:38:01 +0000
From: Eric Wong <normalperson@yhbt.net>
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Subject: [ruby-core:90160] Re: [Ruby trunk Bug#15356] Rack::Deflater on
 Rails responds with no data on Ruby 2.6.0
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zundan@gmail.com wrote:
> Clarify what I think of causing the problem.

> I'd like to report that a Rails app with `Rack::Deflater`
> enabled responds with a zero-length body on Ruby 2.6.0, to a
> request with `Accept-encoding: gzip` request header. It seems
> to happen at least on `x86_64-linux` (Ubuntu 18.04.1; see
> below for procedure for a reproduction) as well as on
> `universal.x86_64-darwin17` (macOS High Sierra 10.13.6; tested
> about a half year ago).

So you're saying this is not a new problem...

> I suspect some kind of change in
> behavior of pipe or named pipe is causing this.

...Because the only recent change for pipe was enabling
non-blocking by default on *nix; and that only
happened about a week ago on r65922 [Bug #14968]

Anyways, you can try using blocking pipes (one-line change
below), but I suspect the problem is some bad interaction with
Rails and Rack::Deflater (Rack::Deflater does some weird stuff
with block captures)

```
diff --git a/io.c b/io.c
index d59bde93cf..e87e507540 100644
--- a/io.c
+++ b/io.c
@@ -138,7 +138,7 @@ off_t __syscall(quad_t number, ...);
 #if defined(_WIN32)
 #  define RUBY_PIPE_NONBLOCK_DEFAULT    (0)
 #elif defined(O_NONBLOCK)
-#  define RUBY_PIPE_NONBLOCK_DEFAULT    (O_NONBLOCK)
+#  define RUBY_PIPE_NONBLOCK_DEFAULT    (0)
 #else /* any platforms where O_NONBLOCK does not exist? */
 #  define RUBY_PIPE_NONBLOCK_DEFAULT    (0)
 #endif
```

Fwiw, I don't know Rails well, but I use Rack::Deflater
a bunch with Rack (not-Rails) apps on Ruby trunk.