Bugfix: fix IPC messages writes with low buffer sizes (Thanks jasper, dcoppa)

Use the following command to reproduce this bug:

    echo 4096 | sudo tee /proc/sys/net/core/wmem_default

Then just switch workspaces with some windows on it and i3bar would
exit due to malformed IPC messages.

This bug hits OpenBSD users (and possibly other BSDs) due to their lower
default buffer size.

fixes #896

1 files changed, 7 insertions, 5 deletions

diff --git a/libi3/ipc_send_message.c b/libi3/ipc_send_message.c
index 850fbdd2..88d87a6a 100644
--- a/libi3/ipc_send_message.c
+++ b/libi3/ipc_send_message.c
@@ -10,6 +10,7 @@
 #include <unistd.h>
 #include <stdint.h>
 #include <err.h>
+#include <errno.h>
 
 #include <i3/ipc.h>
 
@@ -38,14 +39,15 @@ int ipc_send_message(int sockfd, uint32_t message_size,
     memcpy(walk, payload, message_size);
 
     int sent_bytes = 0;
-    int bytes_to_go = buffer_size;
-    while (sent_bytes < bytes_to_go) {
-        int n = write(sockfd, msg + sent_bytes, bytes_to_go);
-        if (n == -1)
+    while (sent_bytes < buffer_size) {
+        int n = write(sockfd, msg + sent_bytes, buffer_size - sent_bytes);
+        if (n == -1) {
+            if (errno == EAGAIN)
+                continue;
             return -1;
+        }
 
         sent_bytes += n;
-        bytes_to_go -= n;
     }
 
     return 0;