[build] Add several util units

Adds the following util units and adds them to libbitcoin_util:

- `util/url.cpp` takes `urlDecode` from `httpserver.cpp`
- `util/error.cpp` takes `TransactionErrorString` from
  `node/transaction.cpp` and `AmountHighWarn` and `AmountErrMsg` from
  `ui_interface.cpp`
- `util/fees.cpp` takes `StringForFeeReason` and `FeeModeFromString` from `policy/fees.cpp`
- `util/rbf.cpp` takes `SignalsOptInRBF` from `policy/rbf.cpp`
- 'util/validation.cpp` takes `FormatStateMessage` and `strMessageMagic` from 'validation.cpp`

10 files changed, 245 insertions, 0 deletions

diff --git a/src/util/error.cpp b/src/util/error.cpp
new file mode 100644
index 0000000000..68ffd8b046
--- /dev/null
+++ b/src/util/error.cpp
@@ -0,0 +1,43 @@
+// Copyright (c) 2010-2018 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 <util/error.h>
+
+#include <util/system.h>
+
+std::string TransactionErrorString(const TransactionError err)
+{
+    switch (err) {
+        case TransactionError::OK:
+            return "No error";
+        case TransactionError::MISSING_INPUTS:
+            return "Missing inputs";
+        case TransactionError::ALREADY_IN_CHAIN:
+            return "Transaction already in block chain";
+        case TransactionError::P2P_DISABLED:
+            return "Peer-to-peer functionality missing or disabled";
+        case TransactionError::MEMPOOL_REJECTED:
+            return "Transaction rejected by AcceptToMemoryPool";
+        case TransactionError::MEMPOOL_ERROR:
+            return "AcceptToMemoryPool failed";
+        case TransactionError::INVALID_PSBT:
+            return "PSBT is not sane";
+        case TransactionError::PSBT_MISMATCH:
+            return "PSBTs not compatible (different transactions)";
+        case TransactionError::SIGHASH_MISMATCH:
+            return "Specified sighash value does not match existing value";
+        // no default case, so the compiler can warn about missing cases
+    }
+    assert(false);
+}
+
+std::string AmountHighWarn(const std::string& optname)
+{
+    return strprintf(_("%s is set very high!"), optname);
+}
+
+std::string AmountErrMsg(const char* const optname, const std::string& strValue)
+{
+    return strprintf(_("Invalid amount for -%s=<amount>: '%s'"), optname, strValue);
+}
diff --git a/src/util/error.h b/src/util/error.h
new file mode 100644
index 0000000000..d93309551b
--- /dev/null
+++ b/src/util/error.h
@@ -0,0 +1,38 @@
+// Copyright (c) 2010-2018 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_ERROR_H
+#define BITCOIN_UTIL_ERROR_H
+
+/**
+ * util/error.h is a common place for definitions of simple error types and
+ * string functions. Types and functions defined here should not require any
+ * outside dependencies.
+ *
+ * Error types defined here can be used in different parts of the bitcoin
+ * codebase, to avoid the need to write boilerplate code catching and
+ * translating errors passed across wallet/node/rpc/gui code boundaries.
+ */
+
+#include <string>
+
+enum class TransactionError {
+    OK, //!< No error
+    MISSING_INPUTS,
+    ALREADY_IN_CHAIN,
+    P2P_DISABLED,
+    MEMPOOL_REJECTED,
+    MEMPOOL_ERROR,
+    INVALID_PSBT,
+    PSBT_MISMATCH,
+    SIGHASH_MISMATCH,
+};
+
+std::string TransactionErrorString(const TransactionError error);
+
+std::string AmountHighWarn(const std::string& optname);
+
+std::string AmountErrMsg(const char* const optname, const std::string& strValue);
+
+#endif // BITCOIN_UTIL_ERROR_H
diff --git a/src/util/fees.cpp b/src/util/fees.cpp
new file mode 100644
index 0000000000..5fdaa1284c
--- /dev/null
+++ b/src/util/fees.cpp
@@ -0,0 +1,42 @@
+// Copyright (c) 2009-2010 Satoshi Nakamoto
+// Copyright (c) 2009-2018 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 <policy/fees.h>
+
+#include <string>
+
+std::string StringForFeeReason(FeeReason reason) {
+    static const std::map<FeeReason, std::string> fee_reason_strings = {
+        {FeeReason::NONE, "None"},
+        {FeeReason::HALF_ESTIMATE, "Half Target 60% Threshold"},
+        {FeeReason::FULL_ESTIMATE, "Target 85% Threshold"},
+        {FeeReason::DOUBLE_ESTIMATE, "Double Target 95% Threshold"},
+        {FeeReason::CONSERVATIVE, "Conservative Double Target longer horizon"},
+        {FeeReason::MEMPOOL_MIN, "Mempool Min Fee"},
+        {FeeReason::PAYTXFEE, "PayTxFee set"},
+        {FeeReason::FALLBACK, "Fallback fee"},
+        {FeeReason::REQUIRED, "Minimum Required Fee"},
+        {FeeReason::MAXTXFEE, "MaxTxFee limit"}
+    };
+    auto reason_string = fee_reason_strings.find(reason);
+
+    if (reason_string == fee_reason_strings.end()) return "Unknown";
+
+    return reason_string->second;
+}
+
+bool FeeModeFromString(const std::string& mode_string, FeeEstimateMode& fee_estimate_mode) {
+    static const std::map<std::string, FeeEstimateMode> fee_modes = {
+        {"UNSET", FeeEstimateMode::UNSET},
+        {"ECONOMICAL", FeeEstimateMode::ECONOMICAL},
+        {"CONSERVATIVE", FeeEstimateMode::CONSERVATIVE},
+    };
+    auto mode = fee_modes.find(mode_string);
+
+    if (mode == fee_modes.end()) return false;
+
+    fee_estimate_mode = mode->second;
+    return true;
+}
diff --git a/src/util/fees.h b/src/util/fees.h
new file mode 100644
index 0000000000..fc355ce9c2
--- /dev/null
+++ b/src/util/fees.h
@@ -0,0 +1,16 @@
+// Copyright (c) 2009-2010 Satoshi Nakamoto
+// Copyright (c) 2009-2018 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
+#define BITCOIN_UTIL_FEES_H
+
+#include <string>
+
+enum class FeeEstimateMode;
+enum class FeeReason;
+
+bool FeeModeFromString(const std::string& mode_string, FeeEstimateMode& fee_estimate_mode);
+std::string StringForFeeReason(FeeReason reason);
+
+#endif // BITCOIN_UTIL_FEES_H
diff --git a/src/util/rbf.cpp b/src/util/rbf.cpp
new file mode 100644
index 0000000000..d520a9606d
--- /dev/null
+++ b/src/util/rbf.cpp
@@ -0,0 +1,17 @@
+// Copyright (c) 2016-2018 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 <util/rbf.h>
+
+#include <primitives/transaction.h>
+
+bool SignalsOptInRBF(const CTransaction &tx)
+{
+    for (const CTxIn &txin : tx.vin) {
+        if (txin.nSequence <= MAX_BIP125_RBF_SEQUENCE) {
+            return true;
+        }
+    }
+    return false;
+}
diff --git a/src/util/rbf.h b/src/util/rbf.h
new file mode 100644
index 0000000000..d3ef110628
--- /dev/null
+++ b/src/util/rbf.h
@@ -0,0 +1,18 @@
+// Copyright (c) 2016-2018 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_RBF_H
+#define BITCOIN_UTIL_RBF_H
+
+#include <cstdint>
+
+class CTransaction;
+
+static const uint32_t MAX_BIP125_RBF_SEQUENCE = 0xfffffffd;
+
+// Check whether the sequence numbers on this transaction are signaling
+// opt-in to replace-by-fee, according to BIP 125
+bool SignalsOptInRBF(const CTransaction &tx);
+
+#endif // BITCOIN_UTIL_RBF_H
diff --git a/src/util/url.cpp b/src/util/url.cpp
new file mode 100644
index 0000000000..49eacbf2d0
--- /dev/null
+++ b/src/util/url.cpp
@@ -0,0 +1,21 @@
+// Copyright (c) 2015-2018 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 <util/url.h>
+
+#include <event2/http.h>
+#include <stdlib.h>
+#include <string>
+
+std::string urlDecode(const std::string &urlEncoded) {
+    std::string res;
+    if (!urlEncoded.empty()) {
+        char *decoded = evhttp_uridecode(urlEncoded.c_str(), false, nullptr);
+        if (decoded) {
+            res = std::string(decoded);
+            free(decoded);
+        }
+    }
+    return res;
+}
diff --git a/src/util/url.h b/src/util/url.h
new file mode 100644
index 0000000000..3d7315a338
--- /dev/null
+++ b/src/util/url.h
@@ -0,0 +1,12 @@
+// Copyright (c) 2015-2018 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_URL_H
+#define BITCOIN_UTIL_URL_H
+
+#include <string>
+
+std::string urlDecode(const std::string &urlEncoded);
+
+#endif // BITCOIN_UTIL_URL_H
diff --git a/src/util/validation.cpp b/src/util/validation.cpp
new file mode 100644
index 0000000000..fe1f5a277e
--- /dev/null
+++ b/src/util/validation.cpp
@@ -0,0 +1,20 @@
+// Copyright (c) 2009-2010 Satoshi Nakamoto
+// Copyright (c) 2009-2019 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 <util/validation.h>
+
+#include <consensus/validation.h>
+#include <tinyformat.h>
+
+/** Convert CValidationState to a human-readable message for logging */
+std::string FormatStateMessage(const CValidationState &state)
+{
+    return strprintf("%s%s (code %i)",
+        state.GetRejectReason(),
+        state.GetDebugMessage().empty() ? "" : ", "+state.GetDebugMessage(),
+        state.GetRejectCode());
+}
+
+const std::string strMessageMagic = "Bitcoin Signed Message:\n";
diff --git a/src/util/validation.h b/src/util/validation.h
new file mode 100644
index 0000000000..32559853ee
--- /dev/null
+++ b/src/util/validation.h
@@ -0,0 +1,18 @@
+// Copyright (c) 2009-2010 Satoshi Nakamoto
+// Copyright (c) 2009-2019 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_VALIDATION_H
+#define BITCOIN_UTIL_VALIDATION_H
+
+#include <string>
+
+class CValidationState;
+
+/** Convert CValidationState to a human-readable message for logging */
+std::string FormatStateMessage(const CValidationState &state);
+
+extern const std::string strMessageMagic;
+
+#endif // BITCOIN_UTIL_VALIDATION_H