29 files changed, 1143 insertions, 66 deletions
diff --git a/src/util/asmap.h b/src/util/asmap.h
index b31e639bb5..d0588bc8c3 100644
--- a/src/util/asmap.h
+++ b/src/util/asmap.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2019 The Bitcoin Core developers
+// Copyright (c) 2019-2020 The Bitcoin Core developers
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
diff --git a/src/util/check.h b/src/util/check.h
index 9edf394492..bc62da3440 100644
--- a/src/util/check.h
+++ b/src/util/check.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2019 The Bitcoin Core developers
+// Copyright (c) 2019-2020 The Bitcoin Core developers
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
@@ -46,7 +46,7 @@ class NonFatalCheckError : public std::runtime_error
 #error "Cannot compile without assertions!"
 #endif
 
-/** Helper for Assert(). TODO remove in C++14 and replace `decltype(get_pure_r_value(val))` with `T` (templated lambda) */
+/** Helper for Assert() */
 template <typename T>
 T get_pure_r_value(T&& val)
 {
@@ -54,6 +54,22 @@ T get_pure_r_value(T&& val)
 }
 
 /** Identity function. Abort if the value compares equal to zero */
-#define Assert(val) [&]() -> decltype(get_pure_r_value(val)) { auto&& check = (val); assert(#val && check); return std::forward<decltype(get_pure_r_value(val))>(check); }()
+#define Assert(val) ([&]() -> decltype(get_pure_r_value(val)) { auto&& check = (val); assert(#val && check); return std::forward<decltype(get_pure_r_value(val))>(check); }())
+
+/**
+ * Assume is the identity function.
+ *
+ * - Should be used to run non-fatal checks. In debug builds it behaves like
+ *   Assert()/assert() to notify developers and testers about non-fatal errors.
+ *   In production it doesn't warn or log anything.
+ * - For fatal errors, use Assert().
+ * - For non-fatal errors in interactive sessions (e.g. RPC or command line
+ *   interfaces), CHECK_NONFATAL() might be more appropriate.
+ */
+#ifdef ABORT_ON_FAILED_ASSUME
+#define Assume(val) Assert(val)
+#else
+#define Assume(val) ((void)(val))
+#endif
 
 #endif // BITCOIN_UTIL_CHECK_H
diff --git a/src/util/epochguard.h b/src/util/epochguard.h
new file mode 100644
index 0000000000..1570ec4eb4
--- /dev/null
+++ b/src/util/epochguard.h
@@ -0,0 +1,91 @@
+// Copyright (c) 2009-2010 Satoshi Nakamoto
+// Copyright (c) 2009-2020 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_UTIL_EPOCHGUARD_H
+#define BITCOIN_UTIL_EPOCHGUARD_H
+
+#include <threadsafety.h>
+
+#include <cassert>
+
+/** Epoch: RAII-style guard for using epoch-based graph traversal algorithms.
+ *     When walking ancestors or descendants, we generally want to avoid
+ * visiting the same transactions twice. Some traversal algorithms use
+ * std::set (or setEntries) to deduplicate the transaction we visit.
+ * However, use of std::set is algorithmically undesirable because it both
+ * adds an asymptotic factor of O(log n) to traversals cost and triggers O(n)
+ * more dynamic memory allocations.
+ *     In many algorithms we can replace std::set with an internal mempool
+ * counter to track the time (or, "epoch") that we began a traversal, and
+ * check + update a per-transaction epoch for each transaction we look at to
+ * determine if that transaction has not yet been visited during the current
+ * traversal's epoch.
+ *     Algorithms using std::set can be replaced on a one by one basis.
+ * Both techniques are not fundamentally incompatible across the codebase.
+ * Generally speaking, however, the remaining use of std::set for mempool
+ * traversal should be viewed as a TODO for replacement with an epoch based
+ * traversal, rather than a preference for std::set over epochs in that
+ * algorithm.
+ */
+
+class LOCKABLE Epoch
+{
+private:
+    uint64_t m_raw_epoch = 0;
+    bool m_guarded = false;
+
+public:
+    Epoch() = default;
+    Epoch(const Epoch&) = delete;
+    Epoch& operator=(const Epoch&) = delete;
+
+    bool guarded() const { return m_guarded; }
+
+    class Marker
+    {
+    private:
+        uint64_t m_marker = 0;
+
+        // only allow modification via Epoch member functions
+        friend class Epoch;
+        Marker& operator=(const Marker&) = delete;
+    };
+
+    class SCOPED_LOCKABLE Guard
+    {
+    private:
+        Epoch& m_epoch;
+
+    public:
+        explicit Guard(Epoch& epoch) EXCLUSIVE_LOCK_FUNCTION(epoch) : m_epoch(epoch)
+        {
+            assert(!m_epoch.m_guarded);
+            ++m_epoch.m_raw_epoch;
+            m_epoch.m_guarded = true;
+        }
+        ~Guard() UNLOCK_FUNCTION()
+        {
+            assert(m_epoch.m_guarded);
+            ++m_epoch.m_raw_epoch; // ensure clear separation between epochs
+            m_epoch.m_guarded = false;
+        }
+    };
+
+    bool visited(Marker& marker) const EXCLUSIVE_LOCKS_REQUIRED(*this)
+    {
+        assert(m_guarded);
+        if (marker.m_marker < m_raw_epoch) {
+            // marker is from a previous epoch, so this is its first visit
+            marker.m_marker = m_raw_epoch;
+            return false;
+        } else {
+            return true;
+        }
+    }
+};
+
+#define WITH_FRESH_EPOCH(epoch) const Epoch::Guard PASTE2(epoch_guard_, __COUNTER__)(epoch)
+
+#endif // BITCOIN_UTIL_EPOCHGUARD_H
diff --git a/src/util/error.cpp b/src/util/error.cpp
index 6c94b80683..48c81693f3 100644
--- a/src/util/error.cpp
+++ b/src/util/error.cpp
@@ -1,4 +1,4 @@
-// Copyright (c) 2010-2019 The Bitcoin Core developers
+// Copyright (c) 2010-2020 The Bitcoin Core developers
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
@@ -31,6 +31,10 @@ bilingual_str TransactionErrorString(const TransactionError err)
             return Untranslated("Specified sighash value does not match value stored in PSBT");
         case TransactionError::MAX_FEE_EXCEEDED:
             return Untranslated("Fee exceeds maximum configured by user (e.g. -maxtxfee, maxfeerate)");
+        case TransactionError::EXTERNAL_SIGNER_NOT_FOUND:
+            return Untranslated("External signer not found");
+        case TransactionError::EXTERNAL_SIGNER_FAILED:
+            return Untranslated("External signer failed to sign");
         // no default case, so the compiler can warn about missing cases
     }
     assert(false);
diff --git a/src/util/error.h b/src/util/error.h
index b9830c9eea..4cc35eb1fd 100644
--- a/src/util/error.h
+++ b/src/util/error.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2010-2019 The Bitcoin Core developers
+// Copyright (c) 2010-2020 The Bitcoin Core developers
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
@@ -30,6 +30,8 @@ enum class TransactionError {
     PSBT_MISMATCH,
     SIGHASH_MISMATCH,
     MAX_FEE_EXCEEDED,
+    EXTERNAL_SIGNER_NOT_FOUND,
+    EXTERNAL_SIGNER_FAILED,
 };
 
 bilingual_str TransactionErrorString(const TransactionError error);
diff --git a/src/util/fees.cpp b/src/util/fees.cpp
index 1855c0bc90..cbefe18dbb 100644
--- a/src/util/fees.cpp
+++ b/src/util/fees.cpp
@@ -1,5 +1,5 @@
 // Copyright (c) 2009-2010 Satoshi Nakamoto
-// Copyright (c) 2009-2019 The Bitcoin Core developers
+// Copyright (c) 2009-2020 The Bitcoin Core developers
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
diff --git a/src/util/fees.h b/src/util/fees.h
index 3f1c33ad9c..9ef2389d3e 100644
--- a/src/util/fees.h
+++ b/src/util/fees.h
@@ -1,5 +1,5 @@
 // Copyright (c) 2009-2010 Satoshi Nakamoto
-// Copyright (c) 2009-2019 The Bitcoin Core developers
+// Copyright (c) 2009-2020 The Bitcoin Core developers
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 #ifndef BITCOIN_UTIL_FEES_H
diff --git a/src/util/getuniquepath.cpp b/src/util/getuniquepath.cpp
new file mode 100644
index 0000000000..9839d2f624
--- /dev/null
+++ b/src/util/getuniquepath.cpp
@@ -0,0 +1,10 @@
+#include <random.h>
+#include <fs.h>
+#include <util/strencodings.h>
+
+fs::path GetUniquePath(const fs::path& base)
+{
+    FastRandomContext rnd;
+    fs::path tmpFile = base / HexStr(rnd.randbytes(8));
+    return tmpFile;
+}
+\ No newline at end of file
diff --git a/src/util/getuniquepath.h b/src/util/getuniquepath.h
new file mode 100644
index 0000000000..e0c6147876
--- /dev/null
+++ b/src/util/getuniquepath.h
@@ -0,0 +1,19 @@
+// Copyright (c) 2021 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_UTIL_GETUNIQUEPATH_H
+#define BITCOIN_UTIL_GETUNIQUEPATH_H
+
+#include <fs.h>
+
+/**
+ * Helper function for getting a unique path
+ *
+ * @param[in] base  Base path
+ * @returns base joined with a random 8-character long string.
+ * @post Returned path is unique with high probability.
+ */
+fs::path GetUniquePath(const fs::path& base);
+
+#endif // BITCOIN_UTIL_GETUNIQUEPATH_H
+\ No newline at end of file
diff --git a/src/util/golombrice.h b/src/util/golombrice.h
index 425e7f6681..67d262406f 100644
--- a/src/util/golombrice.h
+++ b/src/util/golombrice.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2018-2019 The Bitcoin Core developers
+// Copyright (c) 2018-2020 The Bitcoin Core developers
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
diff --git a/src/util/hasher.cpp b/src/util/hasher.cpp
new file mode 100644
index 0000000000..5900daf050
--- /dev/null
+++ b/src/util/hasher.cpp
@@ -0,0 +1,19 @@
+// Copyright (c) 2019 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <random.h>
+#include <util/hasher.h>
+
+#include <limits>
+
+SaltedTxidHasher::SaltedTxidHasher() : k0(GetRand(std::numeric_limits<uint64_t>::max())), k1(GetRand(std::numeric_limits<uint64_t>::max())) {}
+
+SaltedOutpointHasher::SaltedOutpointHasher() : k0(GetRand(std::numeric_limits<uint64_t>::max())), k1(GetRand(std::numeric_limits<uint64_t>::max())) {}
+
+SaltedSipHasher::SaltedSipHasher() : m_k0(GetRand(std::numeric_limits<uint64_t>::max())), m_k1(GetRand(std::numeric_limits<uint64_t>::max())) {}
+
+size_t SaltedSipHasher::operator()(const Span<const unsigned char>& script) const
+{
+    return CSipHasher(m_k0, m_k1).Write(script.data(), script.size()).Finalize();
+}
diff --git a/src/util/hasher.h b/src/util/hasher.h
new file mode 100644
index 0000000000..fa2fea30d8
--- /dev/null
+++ b/src/util/hasher.h
@@ -0,0 +1,99 @@
+// Copyright (c) 2019 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_UTIL_HASHER_H
+#define BITCOIN_UTIL_HASHER_H
+
+#include <crypto/siphash.h>
+#include <primitives/transaction.h>
+#include <uint256.h>
+
+class SaltedTxidHasher
+{
+private:
+    /** Salt */
+    const uint64_t k0, k1;
+
+public:
+    SaltedTxidHasher();
+
+    size_t operator()(const uint256& txid) const {
+        return SipHashUint256(k0, k1, txid);
+    }
+};
+
+class SaltedOutpointHasher
+{
+private:
+    /** Salt */
+    const uint64_t k0, k1;
+
+public:
+    SaltedOutpointHasher();
+
+    /**
+     * This *must* return size_t. With Boost 1.46 on 32-bit systems the
+     * unordered_map will behave unpredictably if the custom hasher returns a
+     * uint64_t, resulting in failures when syncing the chain (#4634).
+     *
+     * Having the hash noexcept allows libstdc++'s unordered_map to recalculate
+     * the hash during rehash, so it does not have to cache the value. This
+     * reduces node's memory by sizeof(size_t). The required recalculation has
+     * a slight performance penalty (around 1.6%), but this is compensated by
+     * memory savings of about 9% which allow for a larger dbcache setting.
+     *
+     * @see https://gcc.gnu.org/onlinedocs/gcc-9.2.0/libstdc++/manual/manual/unordered_associative.html
+     */
+    size_t operator()(const COutPoint& id) const noexcept {
+        return SipHashUint256Extra(k0, k1, id.hash, id.n);
+    }
+};
+
+struct FilterHeaderHasher
+{
+    size_t operator()(const uint256& hash) const { return ReadLE64(hash.begin()); }
+};
+
+/**
+ * We're hashing a nonce into the entries themselves, so we don't need extra
+ * blinding in the set hash computation.
+ *
+ * This may exhibit platform endian dependent behavior but because these are
+ * nonced hashes (random) and this state is only ever used locally it is safe.
+ * All that matters is local consistency.
+ */
+class SignatureCacheHasher
+{
+public:
+    template <uint8_t hash_select>
+    uint32_t operator()(const uint256& key) const
+    {
+        static_assert(hash_select <8, "SignatureCacheHasher only has 8 hashes available.");
+        uint32_t u;
+        std::memcpy(&u, key.begin()+4*hash_select, 4);
+        return u;
+    }
+};
+
+struct BlockHasher
+{
+    // this used to call `GetCheapHash()` in uint256, which was later moved; the
+    // cheap hash function simply calls ReadLE64() however, so the end result is
+    // identical
+    size_t operator()(const uint256& hash) const { return ReadLE64(hash.begin()); }
+};
+
+class SaltedSipHasher
+{
+private:
+    /** Salt */
+    const uint64_t m_k0, m_k1;
+
+public:
+    SaltedSipHasher();
+
+    size_t operator()(const Span<const unsigned char>& script) const;
+};
+
+#endif // BITCOIN_UTIL_HASHER_H
diff --git a/src/util/macros.h b/src/util/macros.h
index 36ea87c0fe..0887c80fd7 100644
--- a/src/util/macros.h
+++ b/src/util/macros.h
@@ -8,4 +8,11 @@
 #define PASTE(x, y) x ## y
 #define PASTE2(x, y) PASTE(x, y)
 
+/**
+ * Converts the parameter X to a string after macro replacement on X has been performed.
+ * Don't merge these into one macro!
+ */
+#define STRINGIZE(X) DO_STRINGIZE(X)
+#define DO_STRINGIZE(X) #X
+
 #endif // BITCOIN_UTIL_MACROS_H
diff --git a/src/util/memory.h b/src/util/memory.h
index 4d73b32869..f21b81bade 100644
--- a/src/util/memory.h
+++ b/src/util/memory.h
@@ -1,5 +1,5 @@
 // Copyright (c) 2009-2010 Satoshi Nakamoto
-// Copyright (c) 2009-2018 The Bitcoin Core developers
+// Copyright (c) 2009-2020 The Bitcoin Core developers
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
diff --git a/src/util/message.cpp b/src/util/message.cpp
index e1d5cff48c..73948e4ff1 100644
--- a/src/util/message.cpp
+++ b/src/util/message.cpp
@@ -31,7 +31,7 @@ MessageVerificationResult MessageVerify(
         return MessageVerificationResult::ERR_INVALID_ADDRESS;
     }
 
-    if (boost::get<PKHash>(&destination) == nullptr) {
+    if (std::get_if<PKHash>(&destination) == nullptr) {
         return MessageVerificationResult::ERR_ADDRESS_NO_KEY;
     }
 
diff --git a/src/util/moneystr.cpp b/src/util/moneystr.cpp
index 1bc8d02eab..3f9ce7dce4 100644
--- a/src/util/moneystr.cpp
+++ b/src/util/moneystr.cpp
@@ -9,13 +9,17 @@
 #include <util/strencodings.h>
 #include <util/string.h>
 
-std::string FormatMoney(const CAmount& n)
+std::string FormatMoney(const CAmount n)
 {
     // Note: not using straight sprintf here because we do NOT want
     // localized number formatting.
-    int64_t n_abs = (n > 0 ? n : -n);
-    int64_t quotient = n_abs/COIN;
-    int64_t remainder = n_abs%COIN;
+    static_assert(COIN > 1);
+    int64_t quotient = n / COIN;
+    int64_t remainder = n % COIN;
+    if (n < 0) {
+        quotient = -quotient;
+        remainder = -remainder;
+    }
     std::string str = strprintf("%d.%08d", quotient, remainder);
 
     // Right-trim excess zeros before the decimal point:
diff --git a/src/util/moneystr.h b/src/util/moneystr.h
index da7f673cda..2aedbee358 100644
--- a/src/util/moneystr.h
+++ b/src/util/moneystr.h
@@ -17,7 +17,7 @@
 /* Do not use these functions to represent or parse monetary amounts to or from
  * JSON but use AmountFromValue and ValueFromAmount for that.
  */
-std::string FormatMoney(const CAmount& n);
+std::string FormatMoney(const CAmount n);
 /** Parse an amount denoted in full coins. E.g. "0.0034" supplied on the command line. **/
 [[nodiscard]] bool ParseMoney(const std::string& str, CAmount& nRet);
 
diff --git a/src/util/readwritefile.cpp b/src/util/readwritefile.cpp
new file mode 100644
index 0000000000..a45c41d367
--- /dev/null
+++ b/src/util/readwritefile.cpp
@@ -0,0 +1,47 @@
+// Copyright (c) 2015-2020 The Bitcoin Core developers
+// Copyright (c) 2017 The Zcash developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <fs.h>
+
+#include <limits>
+#include <stdio.h>
+#include <string>
+#include <utility>
+
+std::pair<bool,std::string> ReadBinaryFile(const fs::path &filename, size_t maxsize=std::numeric_limits<size_t>::max())
+{
+    FILE *f = fsbridge::fopen(filename, "rb");
+    if (f == nullptr)
+        return std::make_pair(false,"");
+    std::string retval;
+    char buffer[128];
+    do {
+        const size_t n = fread(buffer, 1, sizeof(buffer), f);
+        // Check for reading errors so we don't return any data if we couldn't
+        // read the entire file (or up to maxsize)
+        if (ferror(f)) {
+            fclose(f);
+            return std::make_pair(false,"");
+        }
+        retval.append(buffer, buffer+n);
+    } while (!feof(f) && retval.size() <= maxsize);
+    fclose(f);
+    return std::make_pair(true,retval);
+}
+
+bool WriteBinaryFile(const fs::path &filename, const std::string &data)
+{
+    FILE *f = fsbridge::fopen(filename, "wb");
+    if (f == nullptr)
+        return false;
+    if (fwrite(data.data(), 1, data.size(), f) != data.size()) {
+        fclose(f);
+        return false;
+    }
+    if (fclose(f) != 0) {
+        return false;
+    }
+    return true;
+}
diff --git a/src/util/readwritefile.h b/src/util/readwritefile.h
new file mode 100644
index 0000000000..1dab874b38
--- /dev/null
+++ b/src/util/readwritefile.h
@@ -0,0 +1,28 @@
+// Copyright (c) 2015-2020 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_UTIL_READWRITEFILE_H
+#define BITCOIN_UTIL_READWRITEFILE_H
+
+#include <fs.h>
+
+#include <limits>
+#include <string>
+#include <utility>
+
+/** Read full contents of a file and return them in a std::string.
+ * Returns a pair <status, string>.
+ * If an error occurred, status will be false, otherwise status will be true and the data will be returned in string.
+ *
+ * @param maxsize Puts a maximum size limit on the file that is read. If the file is larger than this, truncated data
+ *         (with len > maxsize) will be returned.
+ */
+std::pair<bool,std::string> ReadBinaryFile(const fs::path &filename, size_t maxsize=std::numeric_limits<size_t>::max());
+
+/** Write contents of std::string to a file.
+ * @return true on success.
+ */
+bool WriteBinaryFile(const fs::path &filename, const std::string &data);
+
+#endif /* BITCOIN_UTIL_READWRITEFILE_H */
diff --git a/src/util/sock.cpp b/src/util/sock.cpp
new file mode 100644
index 0000000000..e13c52a16a
--- /dev/null
+++ b/src/util/sock.cpp
@@ -0,0 +1,327 @@
+// Copyright (c) 2020-2021 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <compat.h>
+#include <logging.h>
+#include <threadinterrupt.h>
+#include <tinyformat.h>
+#include <util/sock.h>
+#include <util/system.h>
+#include <util/time.h>
+
+#include <codecvt>
+#include <cwchar>
+#include <locale>
+#include <stdexcept>
+#include <string>
+
+#ifdef USE_POLL
+#include <poll.h>
+#endif
+
+static inline bool IOErrorIsPermanent(int err)
+{
+    return err != WSAEAGAIN && err != WSAEINTR && err != WSAEWOULDBLOCK && err != WSAEINPROGRESS;
+}
+
+Sock::Sock() : m_socket(INVALID_SOCKET) {}
+
+Sock::Sock(SOCKET s) : m_socket(s) {}
+
+Sock::Sock(Sock&& other)
+{
+    m_socket = other.m_socket;
+    other.m_socket = INVALID_SOCKET;
+}
+
+Sock::~Sock() { Reset(); }
+
+Sock& Sock::operator=(Sock&& other)
+{
+    Reset();
+    m_socket = other.m_socket;
+    other.m_socket = INVALID_SOCKET;
+    return *this;
+}
+
+SOCKET Sock::Get() const { return m_socket; }
+
+SOCKET Sock::Release()
+{
+    const SOCKET s = m_socket;
+    m_socket = INVALID_SOCKET;
+    return s;
+}
+
+void Sock::Reset() { CloseSocket(m_socket); }
+
+ssize_t Sock::Send(const void* data, size_t len, int flags) const
+{
+    return send(m_socket, static_cast<const char*>(data), len, flags);
+}
+
+ssize_t Sock::Recv(void* buf, size_t len, int flags) const
+{
+    return recv(m_socket, static_cast<char*>(buf), len, flags);
+}
+
+bool Sock::Wait(std::chrono::milliseconds timeout, Event requested, Event* occurred) const
+{
+#ifdef USE_POLL
+    pollfd fd;
+    fd.fd = m_socket;
+    fd.events = 0;
+    if (requested & RECV) {
+        fd.events |= POLLIN;
+    }
+    if (requested & SEND) {
+        fd.events |= POLLOUT;
+    }
+
+    if (poll(&fd, 1, count_milliseconds(timeout)) == SOCKET_ERROR) {
+        return false;
+    }
+
+    if (occurred != nullptr) {
+        *occurred = 0;
+        if (fd.revents & POLLIN) {
+            *occurred |= RECV;
+        }
+        if (fd.revents & POLLOUT) {
+            *occurred |= SEND;
+        }
+    }
+
+    return true;
+#else
+    if (!IsSelectableSocket(m_socket)) {
+        return false;
+    }
+
+    fd_set fdset_recv;
+    fd_set fdset_send;
+    FD_ZERO(&fdset_recv);
+    FD_ZERO(&fdset_send);
+
+    if (requested & RECV) {
+        FD_SET(m_socket, &fdset_recv);
+    }
+
+    if (requested & SEND) {
+        FD_SET(m_socket, &fdset_send);
+    }
+
+    timeval timeout_struct = MillisToTimeval(timeout);
+
+    if (select(m_socket + 1, &fdset_recv, &fdset_send, nullptr, &timeout_struct) == SOCKET_ERROR) {
+        return false;
+    }
+
+    if (occurred != nullptr) {
+        *occurred = 0;
+        if (FD_ISSET(m_socket, &fdset_recv)) {
+            *occurred |= RECV;
+        }
+        if (FD_ISSET(m_socket, &fdset_send)) {
+            *occurred |= SEND;
+        }
+    }
+
+    return true;
+#endif /* USE_POLL */
+}
+
+void Sock::SendComplete(const std::string& data,
+                        std::chrono::milliseconds timeout,
+                        CThreadInterrupt& interrupt) const
+{
+    const auto deadline = GetTime<std::chrono::milliseconds>() + timeout;
+    size_t sent{0};
+
+    for (;;) {
+        const ssize_t ret{Send(data.data() + sent, data.size() - sent, MSG_NOSIGNAL)};
+
+        if (ret > 0) {
+            sent += static_cast<size_t>(ret);
+            if (sent == data.size()) {
+                break;
+            }
+        } else {
+            const int err{WSAGetLastError()};
+            if (IOErrorIsPermanent(err)) {
+                throw std::runtime_error(strprintf("send(): %s", NetworkErrorString(err)));
+            }
+        }
+
+        const auto now = GetTime<std::chrono::milliseconds>();
+
+        if (now >= deadline) {
+            throw std::runtime_error(strprintf(
+                "Send timeout (sent only %u of %u bytes before that)", sent, data.size()));
+        }
+
+        if (interrupt) {
+            throw std::runtime_error(strprintf(
+                "Send interrupted (sent only %u of %u bytes before that)", sent, data.size()));
+        }
+
+        // Wait for a short while (or the socket to become ready for sending) before retrying
+        // if nothing was sent.
+        const auto wait_time = std::min(deadline - now, std::chrono::milliseconds{MAX_WAIT_FOR_IO});
+        Wait(wait_time, SEND);
+    }
+}
+
+std::string Sock::RecvUntilTerminator(uint8_t terminator,
+                                      std::chrono::milliseconds timeout,
+                                      CThreadInterrupt& interrupt) const
+{
+    const auto deadline = GetTime<std::chrono::milliseconds>() + timeout;
+    std::string data;
+    bool terminator_found{false};
+
+    // We must not consume any bytes past the terminator from the socket.
+    // One option is to read one byte at a time and check if we have read a terminator.
+    // However that is very slow. Instead, we peek at what is in the socket and only read
+    // as many bytes as possible without crossing the terminator.
+    // Reading 64 MiB of random data with 262526 terminator chars takes 37 seconds to read
+    // one byte at a time VS 0.71 seconds with the "peek" solution below. Reading one byte
+    // at a time is about 50 times slower.
+
+    for (;;) {
+        char buf[512];
+
+        const ssize_t peek_ret{Recv(buf, sizeof(buf), MSG_PEEK)};
+
+        switch (peek_ret) {
+        case -1: {
+            const int err{WSAGetLastError()};
+            if (IOErrorIsPermanent(err)) {
+                throw std::runtime_error(strprintf("recv(): %s", NetworkErrorString(err)));
+            }
+            break;
+        }
+        case 0:
+            throw std::runtime_error("Connection unexpectedly closed by peer");
+        default:
+            auto end = buf + peek_ret;
+            auto terminator_pos = std::find(buf, end, terminator);
+            terminator_found = terminator_pos != end;
+
+            const size_t try_len{terminator_found ? terminator_pos - buf + 1 :
+                                                    static_cast<size_t>(peek_ret)};
+
+            const ssize_t read_ret{Recv(buf, try_len, 0)};
+
+            if (read_ret < 0 || static_cast<size_t>(read_ret) != try_len) {
+                throw std::runtime_error(
+                    strprintf("recv() returned %u bytes on attempt to read %u bytes but previous "
+                              "peek claimed %u bytes are available",
+                              read_ret, try_len, peek_ret));
+            }
+
+            // Don't include the terminator in the output.
+            const size_t append_len{terminator_found ? try_len - 1 : try_len};
+
+            data.append(buf, buf + append_len);
+
+            if (terminator_found) {
+                return data;
+            }
+        }
+
+        const auto now = GetTime<std::chrono::milliseconds>();
+
+        if (now >= deadline) {
+            throw std::runtime_error(strprintf(
+                "Receive timeout (received %u bytes without terminator before that)", data.size()));
+        }
+
+        if (interrupt) {
+            throw std::runtime_error(strprintf(
+                "Receive interrupted (received %u bytes without terminator before that)",
+                data.size()));
+        }
+
+        // Wait for a short while (or the socket to become ready for reading) before retrying.
+        const auto wait_time = std::min(deadline - now, std::chrono::milliseconds{MAX_WAIT_FOR_IO});
+        Wait(wait_time, RECV);
+    }
+}
+
+bool Sock::IsConnected(std::string& errmsg) const
+{
+    if (m_socket == INVALID_SOCKET) {
+        errmsg = "not connected";
+        return false;
+    }
+
+    char c;
+    switch (Recv(&c, sizeof(c), MSG_PEEK)) {
+    case -1: {
+        const int err = WSAGetLastError();
+        if (IOErrorIsPermanent(err)) {
+            errmsg = NetworkErrorString(err);
+            return false;
+        }
+        return true;
+    }
+    case 0:
+        errmsg = "closed";
+        return false;
+    default:
+        return true;
+    }
+}
+
+#ifdef WIN32
+std::string NetworkErrorString(int err)
+{
+    wchar_t buf[256];
+    buf[0] = 0;
+    if(FormatMessageW(FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS | FORMAT_MESSAGE_MAX_WIDTH_MASK,
+            nullptr, err, MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
+            buf, ARRAYSIZE(buf), nullptr))
+    {
+        return strprintf("%s (%d)", std::wstring_convert<std::codecvt_utf8_utf16<wchar_t>,wchar_t>().to_bytes(buf), err);
+    }
+    else
+    {
+        return strprintf("Unknown error (%d)", err);
+    }
+}
+#else
+std::string NetworkErrorString(int err)
+{
+    char buf[256];
+    buf[0] = 0;
+    /* Too bad there are two incompatible implementations of the
+     * thread-safe strerror. */
+    const char *s;
+#ifdef STRERROR_R_CHAR_P /* GNU variant can return a pointer outside the passed buffer */
+    s = strerror_r(err, buf, sizeof(buf));
+#else /* POSIX variant always returns message in buffer */
+    s = buf;
+    if (strerror_r(err, buf, sizeof(buf)))
+        buf[0] = 0;
+#endif
+    return strprintf("%s (%d)", s, err);
+}
+#endif
+
+bool CloseSocket(SOCKET& hSocket)
+{
+    if (hSocket == INVALID_SOCKET)
+        return false;
+#ifdef WIN32
+    int ret = closesocket(hSocket);
+#else
+    int ret = close(hSocket);
+#endif
+    if (ret) {
+        LogPrintf("Socket close failed: %d. Error: %s\n", hSocket, NetworkErrorString(WSAGetLastError()));
+    }
+    hSocket = INVALID_SOCKET;
+    return ret != SOCKET_ERROR;
+}
diff --git a/src/util/sock.h b/src/util/sock.h
new file mode 100644
index 0000000000..ecebb84205
--- /dev/null
+++ b/src/util/sock.h
@@ -0,0 +1,166 @@
+// Copyright (c) 2020-2021 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_UTIL_SOCK_H
+#define BITCOIN_UTIL_SOCK_H
+
+#include <compat.h>
+#include <threadinterrupt.h>
+#include <util/time.h>
+
+#include <chrono>
+#include <string>
+
+/**
+ * Maximum time to wait for I/O readiness.
+ * It will take up until this time to break off in case of an interruption.
+ */
+static constexpr auto MAX_WAIT_FOR_IO = 1s;
+
+/**
+ * RAII helper class that manages a socket. Mimics `std::unique_ptr`, but instead of a pointer it
+ * contains a socket and closes it automatically when it goes out of scope.
+ */
+class Sock
+{
+public:
+    /**
+     * Default constructor, creates an empty object that does nothing when destroyed.
+     */
+    Sock();
+
+    /**
+     * Take ownership of an existent socket.
+     */
+    explicit Sock(SOCKET s);
+
+    /**
+     * Copy constructor, disabled because closing the same socket twice is undesirable.
+     */
+    Sock(const Sock&) = delete;
+
+    /**
+     * Move constructor, grab the socket from another object and close ours (if set).
+     */
+    Sock(Sock&& other);
+
+    /**
+     * Destructor, close the socket or do nothing if empty.
+     */
+    virtual ~Sock();
+
+    /**
+     * Copy assignment operator, disabled because closing the same socket twice is undesirable.
+     */
+    Sock& operator=(const Sock&) = delete;
+
+    /**
+     * Move assignment operator, grab the socket from another object and close ours (if set).
+     */
+    virtual Sock& operator=(Sock&& other);
+
+    /**
+     * Get the value of the contained socket.
+     * @return socket or INVALID_SOCKET if empty
+     */
+    virtual SOCKET Get() const;
+
+    /**
+     * Get the value of the contained socket and drop ownership. It will not be closed by the
+     * destructor after this call.
+     * @return socket or INVALID_SOCKET if empty
+     */
+    virtual SOCKET Release();
+
+    /**
+     * Close if non-empty.
+     */
+    virtual void Reset();
+
+    /**
+     * send(2) wrapper. Equivalent to `send(this->Get(), data, len, flags);`. Code that uses this
+     * wrapper can be unit-tested if this method is overridden by a mock Sock implementation.
+     */
+    virtual ssize_t Send(const void* data, size_t len, int flags) const;
+
+    /**
+     * recv(2) wrapper. Equivalent to `recv(this->Get(), buf, len, flags);`. Code that uses this
+     * wrapper can be unit-tested if this method is overridden by a mock Sock implementation.
+     */
+    virtual ssize_t Recv(void* buf, size_t len, int flags) const;
+
+    using Event = uint8_t;
+
+    /**
+     * If passed to `Wait()`, then it will wait for readiness to read from the socket.
+     */
+    static constexpr Event RECV = 0b01;
+
+    /**
+     * If passed to `Wait()`, then it will wait for readiness to send to the socket.
+     */
+    static constexpr Event SEND = 0b10;
+
+    /**
+     * Wait for readiness for input (recv) or output (send).
+     * @param[in] timeout Wait this much for at least one of the requested events to occur.
+     * @param[in] requested Wait for those events, bitwise-or of `RECV` and `SEND`.
+     * @param[out] occurred If not nullptr and `true` is returned, then upon return this
+     * indicates which of the requested events occurred. A timeout is indicated by return
+     * value of `true` and `occurred` being set to 0.
+     * @return true on success and false otherwise
+     */
+    virtual bool Wait(std::chrono::milliseconds timeout,
+                      Event requested,
+                      Event* occurred = nullptr) const;
+
+    /* Higher level, convenience, methods. These may throw. */
+
+    /**
+     * Send the given data, retrying on transient errors.
+     * @param[in] data Data to send.
+     * @param[in] timeout Timeout for the entire operation.
+     * @param[in] interrupt If this is signaled then the operation is canceled.
+     * @throws std::runtime_error if the operation cannot be completed. In this case only some of
+     * the data will be written to the socket.
+     */
+    virtual void SendComplete(const std::string& data,
+                              std::chrono::milliseconds timeout,
+                              CThreadInterrupt& interrupt) const;
+
+    /**
+     * Read from socket until a terminator character is encountered. Will never consume bytes past
+     * the terminator from the socket.
+     * @param[in] terminator Character up to which to read from the socket.
+     * @param[in] timeout Timeout for the entire operation.
+     * @param[in] interrupt If this is signaled then the operation is canceled.
+     * @return The data that has been read, without the terminating character.
+     * @throws std::runtime_error if the operation cannot be completed. In this case some bytes may
+     * have been consumed from the socket.
+     */
+    virtual std::string RecvUntilTerminator(uint8_t terminator,
+                                            std::chrono::milliseconds timeout,
+                                            CThreadInterrupt& interrupt) const;
+
+    /**
+     * Check if still connected.
+     * @param[out] err The error string, if the socket has been disconnected.
+     * @return true if connected
+     */
+    virtual bool IsConnected(std::string& errmsg) const;
+
+private:
+    /**
+     * Contained socket. `INVALID_SOCKET` designates the object is empty.
+     */
+    SOCKET m_socket;
+};
+
+/** Return readable error string for a network error code */
+std::string NetworkErrorString(int err);
+
+/** Close socket and set hSocket to INVALID_SOCKET */
+bool CloseSocket(SOCKET& hSocket);
+
+#endif // BITCOIN_UTIL_SOCK_H
diff --git a/src/util/strencodings.h b/src/util/strencodings.h
index 8ee43c620b..98379e9138 100644
--- a/src/util/strencodings.h
+++ b/src/util/strencodings.h
@@ -17,8 +17,6 @@
 #include <string>
 #include <vector>
 
-#define ARRAYLEN(array)     (sizeof(array)/sizeof((array)[0]))
-
 /** Used by SanitizeString() */
 enum SafeChars
 {
@@ -166,7 +164,7 @@ bool TimingResistantEqual(const T& a, const T& b)
 }
 
 /** Parse number as fixed point according to JSON number syntax.
- * See http://json.org/number.gif
+ * See https://json.org/number.gif
  * @returns true on success, false on error.
  * @note The result must be in the range (-10^18,10^18), otherwise an overflow error will trigger.
  */
diff --git a/src/util/string.h b/src/util/string.h
index 5ffdc80d88..b26facc502 100644
--- a/src/util/string.h
+++ b/src/util/string.h
@@ -25,6 +25,14 @@
     return str.substr(front, end - front + 1);
 }
 
+[[nodiscard]] inline std::string RemovePrefix(const std::string& str, const std::string& prefix)
+{
+    if (str.substr(0, prefix.size()) == prefix) {
+        return str.substr(prefix.size());
+    }
+    return str;
+}
+
 /**
  * Join a list of items
  *
diff --git a/src/util/system.cpp b/src/util/system.cpp
index 5f30136fa2..71453eed81 100644
--- a/src/util/system.cpp
+++ b/src/util/system.cpp
@@ -3,14 +3,16 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
-#include <sync.h>
 #include <util/system.h>
 
-#ifdef HAVE_BOOST_PROCESS
+#ifdef ENABLE_EXTERNAL_SIGNER
 #include <boost/process.hpp>
-#endif // HAVE_BOOST_PROCESS
+#endif // ENABLE_EXTERNAL_SIGNER
 
 #include <chainparamsbase.h>
+#include <sync.h>
+#include <util/check.h>
+#include <util/getuniquepath.h>
 #include <util/strencodings.h>
 #include <util/string.h>
 #include <util/translation.h>
@@ -123,7 +125,7 @@ void ReleaseDirectoryLocks()
 
 bool DirIsWritable(const fs::path& directory)
 {
-    fs::path tmpFile = directory / fs::unique_path();
+    fs::path tmpFile = GetUniquePath(directory);
 
     FILE* file = fsbridge::fopen(tmpFile, "a");
     if (!file) return false;
@@ -310,8 +312,22 @@ bool ArgsManager::ParseParameters(int argc, const char* const argv[], std::strin
             key[0] = '-';
 #endif
 
-        if (key[0] != '-')
+        if (key[0] != '-') {
+            if (!m_accept_any_command && m_command.empty()) {
+                // The first non-dash arg is a registered command
+                Optional<unsigned int> flags = GetArgFlags(key);
+                if (!flags || !(*flags & ArgsManager::COMMAND)) {
+                    error = strprintf("Invalid command '%s'", argv[i]);
+                    return false;
+                }
+            }
+            m_command.push_back(key);
+            while (++i < argc) {
+                // The remaining args are command args
+                m_command.push_back(argv[i]);
+            }
             break;
+        }
 
         // Transform --foo to -foo
         if (key.length() > 1 && key[1] == '-')
@@ -359,6 +375,26 @@ Optional<unsigned int> ArgsManager::GetArgFlags(const std::string& name) const
     return nullopt;
 }
 
+std::optional<const ArgsManager::Command> ArgsManager::GetCommand() const
+{
+    Command ret;
+    LOCK(cs_args);
+    auto it = m_command.begin();
+    if (it == m_command.end()) {
+        // No command was passed
+        return std::nullopt;
+    }
+    if (!m_accept_any_command) {
+        // The registered command
+        ret.command = *(it++);
+    }
+    while (it != m_command.end()) {
+        // The unregistered command and args (if any)
+        ret.args.push_back(*(it++));
+    }
+    return ret;
+}
+
 std::vector<std::string> ArgsManager::GetArgs(const std::string& strArg) const
 {
     std::vector<std::string> result;
@@ -398,7 +434,7 @@ bool ArgsManager::GetSettingsPath(fs::path* filepath, bool temp) const
     }
     if (filepath) {
         std::string settings = GetArg("-settings", BITCOIN_SETTINGS_FILENAME);
-        *filepath = fs::absolute(temp ? settings + ".tmp" : settings, GetDataDir(/* net_specific= */ true));
+        *filepath = fsbridge::AbsPathJoin(GetDataDir(/* net_specific= */ true), temp ? settings + ".tmp" : settings);
     }
     return true;
 }
@@ -504,8 +540,22 @@ void ArgsManager::ForceSetArg(const std::string& strArg, const std::string& strV
     m_settings.forced_settings[SettingName(strArg)] = strValue;
 }
 
+void ArgsManager::AddCommand(const std::string& cmd, const std::string& help, const OptionsCategory& cat)
+{
+    Assert(cmd.find('=') == std::string::npos);
+    Assert(cmd.at(0) != '-');
+
+    LOCK(cs_args);
+    m_accept_any_command = false; // latch to false
+    std::map<std::string, Arg>& arg_map = m_available_args[cat];
+    auto ret = arg_map.emplace(cmd, Arg{"", help, ArgsManager::COMMAND});
+    Assert(ret.second); // Fail on duplicate commands
+}
+
 void ArgsManager::AddArg(const std::string& name, const std::string& help, unsigned int flags, const OptionsCategory& cat)
 {
+    Assert((flags & ArgsManager::COMMAND) == 0); // use AddCommand
+
     // Split arg name from its help param
     size_t eq_index = name.find('=');
     if (eq_index == std::string::npos) {
@@ -1047,27 +1097,36 @@ bool FileCommit(FILE *file)
         LogPrintf("%s: FlushFileBuffers failed: %d\n", __func__, GetLastError());
         return false;
     }
-#else
-    #if HAVE_FDATASYNC
-    if (fdatasync(fileno(file)) != 0 && errno != EINVAL) { // Ignore EINVAL for filesystems that don't support sync
-        LogPrintf("%s: fdatasync failed: %d\n", __func__, errno);
-        return false;
-    }
-    #elif defined(MAC_OSX) && defined(F_FULLFSYNC)
+#elif defined(MAC_OSX) && defined(F_FULLFSYNC)
     if (fcntl(fileno(file), F_FULLFSYNC, 0) == -1) { // Manpage says "value other than -1" is returned on success
         LogPrintf("%s: fcntl F_FULLFSYNC failed: %d\n", __func__, errno);
         return false;
     }
-    #else
+#elif HAVE_FDATASYNC
+    if (fdatasync(fileno(file)) != 0 && errno != EINVAL) { // Ignore EINVAL for filesystems that don't support sync
+        LogPrintf("%s: fdatasync failed: %d\n", __func__, errno);
+        return false;
+    }
+#else
     if (fsync(fileno(file)) != 0 && errno != EINVAL) {
         LogPrintf("%s: fsync failed: %d\n", __func__, errno);
         return false;
     }
-    #endif
 #endif
     return true;
 }
 
+void DirectoryCommit(const fs::path &dirname)
+{
+#ifndef WIN32
+    FILE* file = fsbridge::fopen(dirname, "r");
+    if (file) {
+        fsync(fileno(file));
+        fclose(file);
+    }
+#endif
+}
+
 bool TruncateFile(FILE *file, unsigned int length) {
 #if defined(WIN32)
     return _chsize(_fileno(file), length) == 0;
@@ -1188,7 +1247,7 @@ void runCommand(const std::string& strCommand)
 }
 #endif
 
-#ifdef HAVE_BOOST_PROCESS
+#ifdef ENABLE_EXTERNAL_SIGNER
 UniValue RunCommandParseJSON(const std::string& str_command, const std::string& str_std_in)
 {
     namespace bp = boost::process;
@@ -1223,7 +1282,7 @@ UniValue RunCommandParseJSON(const std::string& str_command, const std::string&
 
     return result_json;
 }
-#endif // HAVE_BOOST_PROCESS
+#endif // ENABLE_EXTERNAL_SIGNER
 
 void SetupEnvironment()
 {
@@ -1302,7 +1361,7 @@ fs::path AbsPathForConfigVal(const fs::path& path, bool net_specific)
     if (path.is_absolute()) {
         return path;
     }
-    return fs::absolute(path, GetDataDir(net_specific));
+    return fsbridge::AbsPathJoin(GetDataDir(net_specific), path);
 }
 
 void ScheduleBatchPriority()
diff --git a/src/util/system.h b/src/util/system.h
index 78ebf751bf..de47b93b6e 100644
--- a/src/util/system.h
+++ b/src/util/system.h
@@ -35,8 +35,6 @@
 #include <utility>
 #include <vector>
 
-#include <boost/thread/condition_variable.hpp> // for boost::thread_interrupted
-
 class UniValue;
 
 // Application startup time (used for uptime calculation)
@@ -56,11 +54,23 @@ bool error(const char* fmt, const Args&... args)
 }
 
 void PrintExceptionContinue(const std::exception *pex, const char* pszThread);
+
+/**
+ * Ensure file contents are fully committed to disk, using a platform-specific
+ * feature analogous to fsync().
+ */
 bool FileCommit(FILE *file);
+
+/**
+ * Sync directory contents. This is required on some environments to ensure that
+ * newly created files are committed to disk.
+ */
+void DirectoryCommit(const fs::path &dirname);
+
 bool TruncateFile(FILE *file, unsigned int length);
 int RaiseFileDescriptorLimit(int nMinFD);
 void AllocateFileRange(FILE *file, unsigned int offset, unsigned int length);
-bool RenameOver(fs::path src, fs::path dest);
+[[nodiscard]] bool RenameOver(fs::path src, fs::path dest);
 bool LockDirectory(const fs::path& directory, const std::string lockfile_name, bool probe_only=false);
 void UnlockDirectory(const fs::path& directory, const std::string& lockfile_name);
 bool DirIsWritable(const fs::path& directory);
@@ -98,7 +108,7 @@ std::string ShellEscape(const std::string& arg);
 #if HAVE_SYSTEM
 void runCommand(const std::string& strCommand);
 #endif
-#ifdef HAVE_BOOST_PROCESS
+#ifdef ENABLE_EXTERNAL_SIGNER
 /**
  * Execute a command which returns JSON, and parse the result.
  *
@@ -107,7 +117,7 @@ void runCommand(const std::string& strCommand);
  * @return parsed JSON
  */
 UniValue RunCommandParseJSON(const std::string& str_command, const std::string& str_std_in="");
-#endif // HAVE_BOOST_PROCESS
+#endif // ENABLE_EXTERNAL_SIGNER
 
 /**
  * Most paths passed as configuration arguments are treated as relative to
@@ -156,7 +166,7 @@ struct SectionInfo
 class ArgsManager
 {
 public:
-    enum Flags {
+    enum Flags : uint32_t {
         // Boolean options can accept negation syntax -noOPTION or -noOPTION=1
         ALLOW_BOOL = 0x01,
         ALLOW_INT = 0x02,
@@ -171,6 +181,7 @@ public:
         NETWORK_ONLY = 0x200,
         // This argument's value is sensitive (such as a password).
         SENSITIVE = 0x400,
+        COMMAND = 0x800,
     };
 
 protected:
@@ -183,9 +194,11 @@ protected:
 
     mutable RecursiveMutex cs_args;
     util::Settings m_settings GUARDED_BY(cs_args);
+    std::vector<std::string> m_command GUARDED_BY(cs_args);
     std::string m_network GUARDED_BY(cs_args);
     std::set<std::string> m_network_only_args GUARDED_BY(cs_args);
     std::map<OptionsCategory, std::map<std::string, Arg>> m_available_args GUARDED_BY(cs_args);
+    bool m_accept_any_command GUARDED_BY(cs_args){true};
     std::list<SectionInfo> m_config_sections GUARDED_BY(cs_args);
 
     [[nodiscard]] bool ReadConfigStream(std::istream& stream, const std::string& filepath, std::string& error, bool ignore_invalid_keys = false);
@@ -236,6 +249,20 @@ public:
      */
     const std::list<SectionInfo> GetUnrecognizedSections() const;
 
+    struct Command {
+        /** The command (if one has been registered with AddCommand), or empty */
+        std::string command;
+        /**
+         * If command is non-empty: Any args that followed it
+         * If command is empty: The unregistered command and any args that followed it
+         */
+        std::vector<std::string> args;
+    };
+    /**
+     * Get the command and command args (returns std::nullopt if no command provided)
+     */
+    std::optional<const Command> GetCommand() const;
+
     /**
      * Return a vector of strings of the given argument
      *
@@ -322,6 +349,11 @@ public:
     void AddArg(const std::string& name, const std::string& help, unsigned int flags, const OptionsCategory& cat);
 
     /**
+     * Add subcommand
+     */
+    void AddCommand(const std::string& cmd, const std::string& help, const OptionsCategory& cat);
+
+    /**
      * Add many hidden arguments
      */
     void AddHiddenArgs(const std::vector<std::string>& args);
@@ -438,11 +470,6 @@ template <typename Callable> void TraceThread(const char* name,  Callable func)
         func();
         LogPrintf("%s thread exit\n", name);
     }
-    catch (const boost::thread_interrupted&)
-    {
-        LogPrintf("%s thread interrupt\n", name);
-        throw;
-    }
     catch (const std::exception& e) {
         PrintExceptionContinue(&e, name);
         throw;
diff --git a/src/util/time.cpp b/src/util/time.cpp
index e96972fe12..e6f0986a39 100644
--- a/src/util/time.cpp
+++ b/src/util/time.cpp
@@ -7,8 +7,11 @@
 #include <config/bitcoin-config.h>
 #endif
 
+#include <compat.h>
 #include <util/time.h>
 
+#include <util/check.h>
+
 #include <atomic>
 #include <boost/date_time/posix_time/posix_time.hpp>
 #include <ctime>
@@ -18,7 +21,7 @@
 
 void UninterruptibleSleep(const std::chrono::microseconds& n) { std::this_thread::sleep_for(n); }
 
-static std::atomic<int64_t> nMockTime(0); //!< For unit testing
+static std::atomic<int64_t> nMockTime(0); //!< For testing
 
 int64_t GetTime()
 {
@@ -30,6 +33,49 @@ int64_t GetTime()
     return now;
 }
 
+bool ChronoSanityCheck()
+{
+    // std::chrono::system_clock.time_since_epoch and time_t(0) are not guaranteed
+    // to use the Unix epoch timestamp, prior to C++20, but in practice they almost
+    // certainly will. Any differing behavior will be assumed to be an error, unless
+    // certain platforms prove to consistently deviate, at which point we'll cope
+    // with it by adding offsets.
+
+    // Create a new clock from time_t(0) and make sure that it represents 0
+    // seconds from the system_clock's time_since_epoch. Then convert that back
+    // to a time_t and verify that it's the same as before.
+    const time_t time_t_epoch{};
+    auto clock = std::chrono::system_clock::from_time_t(time_t_epoch);
+    if (std::chrono::duration_cast<std::chrono::seconds>(clock.time_since_epoch()).count() != 0) {
+        return false;
+    }
+
+    time_t time_val = std::chrono::system_clock::to_time_t(clock);
+    if (time_val != time_t_epoch) {
+        return false;
+    }
+
+    // Check that the above zero time is actually equal to the known unix timestamp.
+    struct tm epoch;
+#ifdef HAVE_GMTIME_R
+    if (gmtime_r(&time_val, &epoch) == nullptr) {
+#else
+    if (gmtime_s(&epoch, &time_val) != 0) {
+#endif
+        return false;
+    }
+
+    if ((epoch.tm_sec != 0)  ||
+       (epoch.tm_min  != 0)  ||
+       (epoch.tm_hour != 0)  ||
+       (epoch.tm_mday != 1)  ||
+       (epoch.tm_mon  != 0)  ||
+       (epoch.tm_year != 70)) {
+        return false;
+    }
+    return true;
+}
+
 template <typename T>
 T GetTime()
 {
@@ -44,35 +90,43 @@ template std::chrono::seconds GetTime();
 template std::chrono::milliseconds GetTime();
 template std::chrono::microseconds GetTime();
 
+template <typename T>
+static T GetSystemTime()
+{
+    const auto now = std::chrono::duration_cast<T>(std::chrono::system_clock::now().time_since_epoch());
+    assert(now.count() > 0);
+    return now;
+}
+
 void SetMockTime(int64_t nMockTimeIn)
 {
+    Assert(nMockTimeIn >= 0);
     nMockTime.store(nMockTimeIn, std::memory_order_relaxed);
 }
 
-int64_t GetMockTime()
+void SetMockTime(std::chrono::seconds mock_time_in)
+{
+    nMockTime.store(mock_time_in.count(), std::memory_order_relaxed);
+}
+
+std::chrono::seconds GetMockTime()
 {
-    return nMockTime.load(std::memory_order_relaxed);
+    return std::chrono::seconds(nMockTime.load(std::memory_order_relaxed));
 }
 
 int64_t GetTimeMillis()
 {
-    int64_t now = (boost::posix_time::microsec_clock::universal_time() -
-                   boost::posix_time::ptime(boost::gregorian::date(1970,1,1))).total_milliseconds();
-    assert(now > 0);
-    return now;
+    return int64_t{GetSystemTime<std::chrono::milliseconds>().count()};
 }
 
 int64_t GetTimeMicros()
 {
-    int64_t now = (boost::posix_time::microsec_clock::universal_time() -
-                   boost::posix_time::ptime(boost::gregorian::date(1970,1,1))).total_microseconds();
-    assert(now > 0);
-    return now;
+    return int64_t{GetSystemTime<std::chrono::microseconds>().count()};
 }
 
 int64_t GetSystemTimeInSeconds()
 {
-    return GetTimeMicros()/1000000;
+    return int64_t{GetSystemTime<std::chrono::seconds>().count()};
 }
 
 std::string FormatISO8601DateTime(int64_t nTime) {
@@ -114,3 +168,16 @@ int64_t ParseISO8601DateTime(const std::string& str)
         return 0;
     return (ptime - epoch).total_seconds();
 }
+
+struct timeval MillisToTimeval(int64_t nTimeout)
+{
+    struct timeval timeout;
+    timeout.tv_sec  = nTimeout / 1000;
+    timeout.tv_usec = (nTimeout % 1000) * 1000;
+    return timeout;
+}
+
+struct timeval MillisToTimeval(std::chrono::milliseconds ms)
+{
+    return MillisToTimeval(count_milliseconds(ms));
+}
diff --git a/src/util/time.h b/src/util/time.h
index af934e423b..7ebcaaa339 100644
--- a/src/util/time.h
+++ b/src/util/time.h
@@ -6,9 +6,13 @@
 #ifndef BITCOIN_UTIL_TIME_H
 #define BITCOIN_UTIL_TIME_H
 
+#include <compat.h>
+
+#include <chrono>
 #include <stdint.h>
 #include <string>
-#include <chrono>
+
+using namespace std::chrono_literals;
 
 void UninterruptibleSleep(const std::chrono::microseconds& n);
 
@@ -22,8 +26,16 @@ void UninterruptibleSleep(const std::chrono::microseconds& n);
  * This helper is used to convert durations before passing them over an
  * interface that doesn't support std::chrono (e.g. RPC, debug log, or the GUI)
  */
-inline int64_t count_seconds(std::chrono::seconds t) { return t.count(); }
-inline int64_t count_microseconds(std::chrono::microseconds t) { return t.count(); }
+constexpr int64_t count_seconds(std::chrono::seconds t) { return t.count(); }
+constexpr int64_t count_milliseconds(std::chrono::milliseconds t) { return t.count(); }
+constexpr int64_t count_microseconds(std::chrono::microseconds t) { return t.count(); }
+
+using SecondsDouble = std::chrono::duration<double, std::chrono::seconds::period>;
+
+/**
+ * Helper to count the seconds in any std::chrono::duration type
+ */
+inline double CountSecondsDouble(SecondsDouble t) { return t.count(); }
 
 /**
  * DEPRECATED
@@ -38,10 +50,19 @@ int64_t GetTimeMicros();
 /** Returns the system time (not mockable) */
 int64_t GetSystemTimeInSeconds(); // Like GetTime(), but not mockable
 
-/** For testing. Set e.g. with the setmocktime rpc, or -mocktime argument */
+/**
+ * DEPRECATED
+ * Use SetMockTime with chrono type
+ *
+ * @param[in] nMockTimeIn Time in seconds.
+ */
 void SetMockTime(int64_t nMockTimeIn);
+
+/** For testing. Set e.g. with the setmocktime rpc, or -mocktime argument */
+void SetMockTime(std::chrono::seconds mock_time_in);
+
 /** For testing */
-int64_t GetMockTime();
+std::chrono::seconds GetMockTime();
 
 /** Return system time (or mocked time, if set) */
 template <typename T>
@@ -55,4 +76,17 @@ std::string FormatISO8601DateTime(int64_t nTime);
 std::string FormatISO8601Date(int64_t nTime);
 int64_t ParseISO8601DateTime(const std::string& str);
 
+/**
+ * Convert milliseconds to a struct timeval for e.g. select.
+ */
+struct timeval MillisToTimeval(int64_t nTimeout);
+
+/**
+ * Convert milliseconds to a struct timeval for e.g. select.
+ */
+struct timeval MillisToTimeval(std::chrono::milliseconds ms);
+
+/** Sanity check epoch match normal Unix epoch */
+bool ChronoSanityCheck();
+
 #endif // BITCOIN_UTIL_TIME_H
diff --git a/src/util/trace.h b/src/util/trace.h
new file mode 100644
index 0000000000..9c92cb10e7
--- /dev/null
+++ b/src/util/trace.h
@@ -0,0 +1,45 @@
+// Copyright (c) 2020 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_UTIL_TRACE_H
+#define BITCOIN_UTIL_TRACE_H
+
+#ifdef ENABLE_TRACING
+
+#include <sys/sdt.h>
+
+#define TRACE(context, event) DTRACE_PROBE(context, event)
+#define TRACE1(context, event, a) DTRACE_PROBE1(context, event, a)
+#define TRACE2(context, event, a, b) DTRACE_PROBE2(context, event, a, b)
+#define TRACE3(context, event, a, b, c) DTRACE_PROBE3(context, event, a, b, c)
+#define TRACE4(context, event, a, b, c, d) DTRACE_PROBE4(context, event, a, b, c, d)
+#define TRACE5(context, event, a, b, c, d, e) DTRACE_PROBE5(context, event, a, b, c, d, e)
+#define TRACE6(context, event, a, b, c, d, e, f) DTRACE_PROBE6(context, event, a, b, c, d, e, f)
+#define TRACE7(context, event, a, b, c, d, e, f, g) DTRACE_PROBE7(context, event, a, b, c, d, e, f, g)
+#define TRACE8(context, event, a, b, c, d, e, f, g, h) DTRACE_PROBE8(context, event, a, b, c, d, e, f, g, h)
+#define TRACE9(context, event, a, b, c, d, e, f, g, h, i) DTRACE_PROBE9(context, event, a, b, c, d, e, f, g, h, i)
+#define TRACE10(context, event, a, b, c, d, e, f, g, h, i, j) DTRACE_PROBE10(context, event, a, b, c, d, e, f, g, h, i, j)
+#define TRACE11(context, event, a, b, c, d, e, f, g, h, i, j, k) DTRACE_PROBE11(context, event, a, b, c, d, e, f, g, h, i, j, k)
+#define TRACE12(context, event, a, b, c, d, e, f, g, h, i, j, k, l) DTRACE_PROBE12(context, event, a, b, c, d, e, f, g, h, i, j, k, l)
+
+#else
+
+#define TRACE(context, event)
+#define TRACE1(context, event, a)
+#define TRACE2(context, event, a, b)
+#define TRACE3(context, event, a, b, c)
+#define TRACE4(context, event, a, b, c, d)
+#define TRACE5(context, event, a, b, c, d, e)
+#define TRACE6(context, event, a, b, c, d, e, f)
+#define TRACE7(context, event, a, b, c, d, e, f, g)
+#define TRACE8(context, event, a, b, c, d, e, f, g, h)
+#define TRACE9(context, event, a, b, c, d, e, f, g, h, i)
+#define TRACE10(context, event, a, b, c, d, e, f, g, h, i, j)
+#define TRACE11(context, event, a, b, c, d, e, f, g, h, i, j, k)
+#define TRACE12(context, event, a, b, c, d, e, f, g, h, i, j, k, l)
+
+#endif
+
+
+#endif /* BITCOIN_UTIL_TRACE_H */
diff --git a/src/util/translation.h b/src/util/translation.h
index 695d6dac96..99899ef3c2 100644
--- a/src/util/translation.h
+++ b/src/util/translation.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2019 The Bitcoin Core developers
+// Copyright (c) 2019-2020 The Bitcoin Core developers
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.