From 074f20f93b0c13c6d5633a39fc5b62435cb8084a Mon Sep 17 00:00:00 2001
From: jyelon <jyelon@gmail.com>
Date: Mon, 3 Apr 2023 15:05:36 -0400
Subject: [PATCH] Fix a subtle bug in the poll code

---
 luprex/cpp/drv/driver-common.cpp | 31 +++++++++++++++++--------------
 1 file changed, 17 insertions(+), 14 deletions(-)

diff --git a/luprex/cpp/drv/driver-common.cpp b/luprex/cpp/drv/driver-common.cpp
index d005e606..49feff6c 100644
--- a/luprex/cpp/drv/driver-common.cpp
+++ b/luprex/cpp/drv/driver-common.cpp
@@ -261,6 +261,7 @@ class Driver {
     // Copy data from the send BIO into the socket.
     //
     // If it detects an error, sets the recent_errno flag.
+    // It is an error to call this when there is nothing in the send BIO.
     //
     void transfer_send_bio_to_socket(ChanInfo &chan) {
         if ((chan.state == CHAN_INACTIVE) || (!chan.recent_error.empty())) {
@@ -270,7 +271,10 @@ class Driver {
         char *data;
         int ndata = BIO_get_mem_data(chan.send_bio, &data);
         if (ndata > DRV_SHORTSTRING_SIZE) ndata = DRV_SHORTSTRING_SIZE;
+
+        // It is an error to call this function when there is nothing in the send BIO.
         assert(ndata > 0);
+
         std::string err;
         int nwrote = socket_send(chan.socket, data, ndata, err);
         // std::cerr << "chan " << chan.chid << " send " << nwrote << " err=" << err << std::endl;
@@ -453,12 +457,6 @@ class Driver {
 
         // Construct the struct pollfd vector.
         int pollsize = 0;
-        for (const auto &p : listen_sockets_) {
-            struct pollfd &pfd = pollvec_[pollsize++];
-            pfd.fd = p.second;
-            pfd.events = POLLIN;
-            pfd.revents = 0;
-        }
         for (const ChanInfo &chan : chans_) {
             struct pollfd &pfd = pollvec_[pollsize++];
             assert(chan.socket != INVALID_SOCKET);
@@ -477,20 +475,19 @@ class Driver {
                 mstimeout = 0;
             }
         }
+        for (const auto &p : listen_sockets_) {
+            struct pollfd &pfd = pollvec_[pollsize++];
+            pfd.fd = p.second;
+            pfd.events = POLLIN;
+            pfd.revents = 0;
+        }
 
         // Do the poll.
         socket_poll(pollvec_.get(), pollsize, mstimeout, err);
         if_error_print_and_exit(err);
 
-        // Check listening sockets.
+        // Advance channels where possible and then check listen sockets.
         int index = 0;
-        for (auto &p : listen_sockets_) {
-            struct pollfd &pfd = pollvec_[index++];
-            if (pfd.revents & (POLLIN | POLLERR)) {
-                accept_connection(p.first, p.second);
-            }
-        }
-        // Advance channels where possible.
         for (ChanInfo &chan : chans_) {
             struct pollfd &pfd = pollvec_[index++];
             if ((pfd.revents & POLLIN) != 0) {
@@ -513,6 +510,12 @@ class Driver {
             chan.nbytes = 0;
             chan.bytes = 0;
         }
+        for (auto &p : listen_sockets_) {
+            struct pollfd &pfd = pollvec_[index++];
+            if (pfd.revents & (POLLIN | POLLERR)) {
+                accept_connection(p.first, p.second);
+            }
+        }
 
         // Delete any newly-inactive channels
         drvutil::remove_marked_items(chans_);