From 655763a9a7d55b1618d4df6f1b2f606ff16c04dc Mon Sep 17 00:00:00 2001
From: Thad House <ThadHouse@users.noreply.github.com>
Date: Sun, 3 Mar 2019 15:43:04 -0800
Subject: [PATCH] Limit length of message sent to DS SendError call (#1618)

If total length is over 65536, the packet will get thrown out.
This can be a problem in stack overflow cases (e.g. infinite recursion).
---
 .../main/native/athena/FRCDriverStation.cpp   | 39 ++++++++++++++++++-
 1 file changed, 37 insertions(+), 2 deletions(-)

diff --git a/hal/src/main/native/athena/FRCDriverStation.cpp b/hal/src/main/native/athena/FRCDriverStation.cpp
index 5409ad056f..018196313b 100644
--- a/hal/src/main/native/athena/FRCDriverStation.cpp
+++ b/hal/src/main/native/athena/FRCDriverStation.cpp
@@ -292,8 +292,43 @@ int32_t HAL_SendError(HAL_Bool isError, int32_t errorCode, HAL_Bool isLVCode,
   }
   int retval = 0;
   if (i == KEEP_MSGS || (curTime - prevMsgTime[i]) >= std::chrono::seconds(1)) {
-    retval = FRC_NetworkCommunication_sendError(isError, errorCode, isLVCode,
-                                                details, location, callStack);
+    wpi::StringRef detailsRef{details};
+    wpi::StringRef locationRef{location};
+    wpi::StringRef callStackRef{callStack};
+
+    // 1 tag, 4 timestamp, 2 seqnum
+    // 2 numOccur, 4 error code, 1 flags, 6 strlen
+    // 1 extra needed for padding on Netcomm end.
+    size_t baseLength = 21;
+
+    if (baseLength + detailsRef.size() + locationRef.size() +
+            callStackRef.size() <=
+        65536) {
+      // Pass through
+      retval = FRC_NetworkCommunication_sendError(isError, errorCode, isLVCode,
+                                                  details, location, callStack);
+    } else if (baseLength + detailsRef.size() > 65536) {
+      // Details too long, cut both location and stack
+      auto newLen = 65536 - baseLength;
+      std::string newDetails{details, newLen};
+      char empty = '\0';
+      retval = FRC_NetworkCommunication_sendError(
+          isError, errorCode, isLVCode, newDetails.c_str(), &empty, &empty);
+    } else if (baseLength + detailsRef.size() + locationRef.size() > 65536) {
+      // Location too long, cut stack
+      auto newLen = 65536 - baseLength - detailsRef.size();
+      std::string newLocation{location, newLen};
+      char empty = '\0';
+      retval = FRC_NetworkCommunication_sendError(
+          isError, errorCode, isLVCode, details, newLocation.c_str(), &empty);
+    } else {
+      // Stack too long
+      auto newLen = 65536 - baseLength - detailsRef.size() - locationRef.size();
+      std::string newCallStack{callStack, newLen};
+      retval = FRC_NetworkCommunication_sendError(isError, errorCode, isLVCode,
+                                                  details, location,
+                                                  newCallStack.c_str());
+    }
     if (printMsg) {
       if (location && location[0] != '\0') {
         wpi::errs() << (isError ? "Error" : "Warning") << " at " << location