Handle EAGAIN in SSL_get_error

Author: WillChilds-Klein

ssl/ssl_lib.cc

@@ -143,6 +143,7 @@
 #include <algorithm>
 
 #include <assert.h>
+#include <errno.h>
 #include <limits.h>
 #include <stdlib.h>
 #include <string.h>
@@ -1375,8 +1376,11 @@ int SSL_get_error(const SSL *ssl, int ret_code) {
     }
     // An EOF was observed which violates the protocol, and the underlying
     // transport does not participate in the error queue. Bubble up to the
-    // caller.
-    return SSL_ERROR_SYSCALL;
+    // caller. If errno is non-zero due to temporariy unavailability (e.g.
+    // non-blocking socket), continue with normal logic.
+    if (errno != 0 && errno != EAGAIN && errno != EWOULDBLOCK) {
+      return SSL_ERROR_SYSCALL;
+    }
   }
 
   switch (ssl->s3->rwstate) {