From a3e713ace8b6dd97b6048b267e51e74f5a386f5f Mon Sep 17 00:00:00 2001
From: Patrick Strateman <patrick.strateman@gmail.com>
Date: Wed, 10 Feb 2021 15:15:55 -0500
Subject: [PATCH] net: latch IBD across restarts

this prevents a network wide failure in the event that all or most listening
nodes are restarted at approximately the same time
---
 src/test/util/validation.cpp |  1 +
 src/validation.cpp           | 15 +++++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/src/test/util/validation.cpp b/src/test/util/validation.cpp
index 1aed492c3c037..24083bd98d0ca 100644
--- a/src/test/util/validation.cpp
+++ b/src/test/util/validation.cpp
@@ -11,6 +11,7 @@
 void TestChainState::ResetIbd()
 {
     m_cached_finished_ibd = false;
+    fs::remove(GetDataDir() / ".ibd_complete");
     assert(IsInitialBlockDownload());
 }
 
diff --git a/src/validation.cpp b/src/validation.cpp
index 8f7d36bfd3ffb..5a5899a7ee2a3 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -16,6 +16,7 @@
 #include <consensus/validation.h>
 #include <cuckoocache.h>
 #include <flatfile.h>
+#include <fs.h>
 #include <hash.h>
 #include <index/txindex.h>
 #include <logging.h>
@@ -1294,8 +1295,11 @@ void CChainState::InitCoinsCache(size_t cache_size_bytes)
 // `const` so that `CValidationInterface` clients (which are given a `const CChainState*`)
 // can call it.
 //
+// The file .ibd_complete is used to latch the datadir to IBD false across restarts
+//
 bool CChainState::IsInitialBlockDownload() const
 {
+    static const fs::path latch_filename = GetDataDir() / ".ibd_complete";
     // Optimization: pre-test latch before taking the lock.
     if (m_cached_finished_ibd.load(std::memory_order_relaxed))
         return false;
@@ -1303,6 +1307,11 @@ bool CChainState::IsInitialBlockDownload() const
     LOCK(cs_main);
     if (m_cached_finished_ibd.load(std::memory_order_relaxed))
         return false;
+    if (fs::exists(latch_filename)) {
+        LogPrintf("Leaving InitialBlockDownload (latching to false)\n");
+        m_cached_finished_ibd.store(true, std::memory_order_relaxed);
+        return false;
+    }
     if (fImporting || fReindex)
         return true;
     if (m_chain.Tip() == nullptr)
@@ -1312,6 +1321,12 @@ bool CChainState::IsInitialBlockDownload() const
     if (m_chain.Tip()->GetBlockTime() < (GetTime() - nMaxTipAge))
         return true;
     LogPrintf("Leaving InitialBlockDownload (latching to false)\n");
+    FILE* f = fsbridge::fopen(latch_filename, "wb");
+    if (f) {
+        fclose(f);
+    } else {
+        LogPrintf("Failed to write %s\n", latch_filename.string().c_str());
+    }
     m_cached_finished_ibd.store(true, std::memory_order_relaxed);
     return false;
 }