bug#34341: 26.1; url-retrieve-synchronously returns blank buffer

[Noam Postavsky <npostavs@gmail.com>]

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Eli Zaretskii <eliz@gnu.org> writes:

>> From: Robert Pluim <rpluim@gmail.com>
>> Date: Mon, 06 May 2019 14:15:27 +0200
>> Cc: Laurent Charignon <l.charignon@gmail.com>, 34341@debbugs.gnu.org
>> 
>> >>>>> On Mon, 06 May 2019 08:10:32 -0400, Noam Postavsky <npostavs@gmail.com> said:
>> 
>>     Noam> Thanks, I wasn't aware of this, I'll check if that helps
>>     Noam> later today.  I think it makes sense to backport regardless
>>     Noam> though.

I can confirm that

    (setq gnutls-algorithm-priority "NORMAL:-VERS-TLS1.3") 

avoids the problem on my Arch box (has gnutls v3.6.7).

>> I do too, but last time Eli wasn't too enthusiastic about it.
>
> It's a complex change, and we don't even know whether emacs-26 will be
> used for another "regular" release.  What if we need it for some
> emergency release, for example?  Having to remember there was this
> cherry-pick, and branching from before it, reverting it, is not my
> idea of fun.

I found this smaller change fixes it also.  Is it simple enough to for
emacs-26?  Otherwise, we should set gnutls-algorithm-priority because
(as far as I understand) we have a broken TLS1.3 implementation at the
momement.


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From 6d5f5670443f7adfbd6993173ad997ce25827775 Mon Sep 17 00:00:00 2001
From: Noam Postavsky <npostavs@gmail.com>
Date: Mon, 6 May 2019 19:55:17 -0400
Subject: [PATCH] Handle GNUTLS_E_AGAIN in emacs_gnutls_read (Bug#34341)

* src/gnutls.c (emacs_gnutls_read): Similar to emacs_gnutls_write,
when gnutls_record_recv returns GNUTLS_E_AGAIN set errno to EGAIN.
---
 src/gnutls.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/src/gnutls.c b/src/gnutls.c
index 3c16b6c9c3..b724c3592d 100644
--- a/src/gnutls.c
+++ b/src/gnutls.c
@@ -753,8 +753,15 @@ emacs_gnutls_read (struct Lisp_Process *proc, char *buf, ptrdiff_t nbyte)
     /* The peer closed the connection. */
     return 0;
   else if (emacs_gnutls_handle_error (state, rtnval))
-    /* non-fatal error */
-    return -1;
+    {
+      /* If we get GNUTLS_E_AGAIN, then set errno appropriately so that
+         wait_reading_process_output retries the correct way instead of
+         erroring out.  */
+      if (rtnval == GNUTLS_E_AGAIN)
+        errno = EAGAIN;
+      /* non-fatal error */
+      return -1;
+    }
   else {
     /* a fatal error occurred */
     return 0;
-- 
2.11.0