Fix 'no TLS' problem with RequestWithoutContentLengthOrTransferEncoding

httplib.h

@@ -9869,7 +9869,11 @@ inline bool Server::read_content_core(
         payload_max_length_ < (std::numeric_limits<size_t>::max)()) {
       socket_t s = strm.socket();
       if (s != INVALID_SOCKET) {
-        // Peek to check if there is any pending data
+        // Use a non-blocking check to see if there is any pending data.
+        // A blocking recv(MSG_PEEK) would deadlock when the client is
+        // waiting for the response (e.g. POST with Connection: close and
+        // no body).
+        if (detail::select_read(s, 0, 0) > 0) {
           char peekbuf[1];
           ssize_t n = ::recv(s, peekbuf, 1, MSG_PEEK);
           if (n > 0) {
@@ -9886,6 +9890,7 @@ inline bool Server::read_content_core(
           }
         }
       }
+    }
     return true;
   }
 #else

justfile

@@ -13,6 +13,9 @@ mbedtls:
     @(cd test && make test_mbedtls && LSAN_OPTIONS=suppressions=lsan_suppressions.txt ./test_mbedtls)
     @(cd test && make proxy_mbedtls)
 
+no_tls:
+    @(cd test && make test_no_tls && ./test_no_tls)
+
 fuzz:
     @(cd test && make fuzz_test)