Extract ParseDescriptorRange

So as to be consistently informative when the checks fail, and
to protect against unintentional divergence among the checks.

src/rpc/blockchain.cpp

@@ -2224,8 +2224,7 @@ UniValue scantxoutset(const JSONRPCRequest& request)
                 desc_str = desc_uni.get_str();
                 UniValue range_uni = find_value(scanobject, "range");
                 if (!range_uni.isNull()) {
-                    range = ParseRange(range_uni);
-                    if (range.first < 0 || (range.second >> 31) != 0 || range.second >= range.first + 1000000) throw JSONRPCError(RPC_INVALID_PARAMETER, "range out of range");
+                    range = ParseDescriptorRange(range_uni);
                 }
             } else {
                 throw JSONRPCError(RPC_INVALID_PARAMETER, "Scan object needs to be either a string or an object");

src/rpc/misc.cpp

@@ -23,6 +23,7 @@
 #include <warnings.h>
 
 #include <stdint.h>
+#include <tuple>
 #ifdef HAVE_MALLOC_INFO
 #include <malloc.h>
 #endif
@@ -214,18 +215,7 @@ UniValue deriveaddresses(const JSONRPCRequest& request)
     int64_t range_end = 0;
 
     if (request.params.size() >= 2 && !request.params[1].isNull()) {
-        auto range = ParseRange(request.params[1]);
-        if (range.first < 0) {
-            throw JSONRPCError(RPC_INVALID_PARAMETER, "Range should be greater or equal than 0");
-        }
-        if ((range.second >> 31) != 0) {
-            throw JSONRPCError(RPC_INVALID_PARAMETER, "End of range is too high");
-        }
-        if (range.second >= range.first + 1000000) {
-            throw JSONRPCError(RPC_INVALID_PARAMETER, "Range is too large");
-        }
-        range_begin = range.first;
-        range_end = range.second;
+        std::tie(range_begin, range_end) = ParseDescriptorRange(request.params[1]);
     }
 
     FlatSigningProvider provider;

src/rpc/util.cpp

@@ -8,6 +8,8 @@
 #include <tinyformat.h>
 #include <util/strencodings.h>
 
+#include <tuple>
+
 InitInterfaces* g_rpc_interfaces = nullptr;
 
 // Converts a hex string to a public key if possible
@@ -529,7 +531,7 @@ std::string RPCArg::ToString(const bool oneline) const
     assert(false);
 }
 
-std::pair<int64_t, int64_t> ParseRange(const UniValue& value)
+static std::pair<int64_t, int64_t> ParseRange(const UniValue& value)
 {
     if (value.isNum()) {
         return {0, value.get_int64()};
@@ -542,3 +544,19 @@ std::pair<int64_t, int64_t> ParseRange(const UniValue& value)
     }
     throw JSONRPCError(RPC_INVALID_PARAMETER, "Range must be specified as end or as [begin,end]");
 }
+
+std::pair<int64_t, int64_t> ParseDescriptorRange(const UniValue& value)
+{
+    int64_t low, high;
+    std::tie(low, high) = ParseRange(value);
+    if (low < 0) {
+        throw JSONRPCError(RPC_INVALID_PARAMETER, "Range should be greater or equal than 0");
+    }
+    if ((high >> 31) != 0) {
+        throw JSONRPCError(RPC_INVALID_PARAMETER, "End of range is too high");
+    }
+    if (high >= low + 1000000) {
+        throw JSONRPCError(RPC_INVALID_PARAMETER, "Range is too large");
+    }
+    return {low, high};
+}

src/rpc/util.h

@@ -39,7 +39,7 @@ RPCErrorCode RPCErrorFromTransactionError(TransactionError terr);
 UniValue JSONRPCTransactionError(TransactionError terr, const std::string& err_string = "");
 
 //! Parse a JSON range specified as int64, or [int64, int64]
-std::pair<int64_t, int64_t> ParseRange(const UniValue& value);
+std::pair<int64_t, int64_t> ParseDescriptorRange(const UniValue& value);
 
 struct RPCArg {
     enum class Type {

src/wallet/rpcdump.cpp

@@ -22,6 +22,7 @@
 #include <wallet/rpcwallet.h>
 
 #include <stdint.h>
+#include <tuple>
 
 #include <boost/algorithm/string.hpp>
 #include <boost/date_time/posix_time/posix_time.hpp>
@@ -1144,12 +1145,7 @@ static UniValue ProcessImportDescriptor(ImportData& import_data, std::map<CKeyID
         if (!data.exists("range")) {
             throw JSONRPCError(RPC_INVALID_PARAMETER, "Descriptor is ranged, please specify the range");
         }
-        auto range = ParseRange(data["range"]);
-        range_start = range.first;
-        range_end = range.second;
-        if (range_start < 0 || (range_end >> 31) != 0 || range_end - range_start >= 1000000) {
-            throw JSONRPCError(RPC_INVALID_PARAMETER, "Invalid descriptor range specified");
-        }
+        std::tie(range_start, range_end) = ParseDescriptorRange(data["range"]);
     }
 
     const UniValue& priv_keys = data.exists("keys") ? data["keys"].get_array() : UniValue();