From cee5a417c8411adbeba7cee9e22c1bd519cf39c6 Mon Sep 17 00:00:00 2001
From: Pierre Ossman <ossman@cendio.se>
Date: Wed, 6 Apr 2022 15:23:50 +0200
Subject: [PATCH] Don't trust GNUTLS_E_AGAIN

Unfortunately this error can be given by GnuTLS even though the
underlying stream still has data available. So stop trusting this value
and keep track of the underlying stream explicitly.
---
 common/rdr/TLSInStream.cxx | 19 ++++++++++++++++---
 common/rdr/TLSInStream.h   |  1 +
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/common/rdr/TLSInStream.cxx b/common/rdr/TLSInStream.cxx
index 451855c7..014789e3 100644
--- a/common/rdr/TLSInStream.cxx
+++ b/common/rdr/TLSInStream.cxx
@@ -39,11 +39,13 @@ ssize_t TLSInStream::pull(gnutls_transport_ptr_t str, void* data, size_t size)
   TLSInStream* self= (TLSInStream*) str;
   InStream *in = self->in;
 
+  self->streamEmpty = false;
   delete self->saved_exception;
   self->saved_exception = NULL;
 
   try {
     if (!in->hasData(1)) {
+      self->streamEmpty = true;
       gnutls_transport_set_errno(self->session, EAGAIN);
       return -1;
     }
@@ -100,9 +102,20 @@ size_t TLSInStream::readTLS(U8* buf, size_t len)
 {
   int n;
 
-  n = gnutls_record_recv(session, (void *) buf, len);
-  if (n == GNUTLS_E_INTERRUPTED || n == GNUTLS_E_AGAIN)
-    return 0;
+  while (true) {
+    streamEmpty = false;
+    n = gnutls_record_recv(session, (void *) buf, len);
+    if (n == GNUTLS_E_INTERRUPTED || n == GNUTLS_E_AGAIN) {
+      // GnuTLS returns GNUTLS_E_AGAIN for a bunch of other scenarios
+      // other than the pull function returning EAGAIN, so we have to
+      // double check that the underlying stream really is empty
+      if (!streamEmpty)
+        continue;
+      else
+        return 0;
+    }
+    break;
+  };
 
   if (n == GNUTLS_E_PULL_ERROR)
     throw *saved_exception;
diff --git a/common/rdr/TLSInStream.h b/common/rdr/TLSInStream.h
index 4564d118..46779d4c 100644
--- a/common/rdr/TLSInStream.h
+++ b/common/rdr/TLSInStream.h
@@ -40,6 +40,7 @@ namespace rdr {
     gnutls_session_t session;
     InStream* in;
 
+    bool streamEmpty;
     Exception* saved_exception;
   };
 };
-- 
2.39.5