rpc: Accept scientific notation for monetary amounts in JSON

Add a function `ParseFixedPoint` that parses numbers according
to the JSON number specification and returns a 64-bit integer.

Then this in `AmountFromValue`, rather than `ParseMoney`.

Also add lots of tests (thanks to @jonasschnelli for some of them).

Fixes issue #6297.

5 files changed, 215 insertions, 1 deletions

diff --git a/src/rpcserver.cpp b/src/rpcserver.cpp
index 287cfb2f13..aeb51fed56 100644
--- a/src/rpcserver.cpp
+++ b/src/rpcserver.cpp
@@ -124,7 +124,7 @@ CAmount AmountFromValue(const UniValue& value)
     if (!value.isReal() && !value.isNum())
         throw JSONRPCError(RPC_TYPE_ERROR, "Amount is not a number");
     CAmount amount;
-    if (!ParseMoney(value.getValStr(), amount))
+    if (!ParseFixedPoint(value.getValStr(), 8, &amount))
         throw JSONRPCError(RPC_TYPE_ERROR, "Invalid amount");
     if (!MoneyRange(amount))
         throw JSONRPCError(RPC_TYPE_ERROR, "Amount out of range");
diff --git a/src/test/rpc_tests.cpp b/src/test/rpc_tests.cpp
index 9e99ff6286..25599beafc 100644
--- a/src/test/rpc_tests.cpp
+++ b/src/test/rpc_tests.cpp
@@ -142,6 +142,24 @@ BOOST_AUTO_TEST_CASE(rpc_parse_monetary_values)
     BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("1.00000000")), 100000000LL);
     BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("20999999.9999999")), 2099999999999990LL);
     BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("20999999.99999999")), 2099999999999999LL);
+
+    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("1e-8")), COIN/100000000);
+    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("0.1e-7")), COIN/100000000);
+    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("0.01e-6")), COIN/100000000);
+    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("0.0000000000000000000000000000000000000000000000000000000000000000000000000001e+68")), COIN/100000000);
+    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("10000000000000000000000000000000000000000000000000000000000000000e-64")), COIN);
+    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("0.000000000000000000000000000000000000000000000000000000000000000100000000000000000000000000000000000000000000000000000e64")), COIN);
+
+    BOOST_CHECK_THROW(AmountFromValue(ValueFromString("1e-9")), UniValue); //should fail
+    BOOST_CHECK_THROW(AmountFromValue(ValueFromString("0.000000019")), UniValue); //should fail
+    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("0.00000001000000")), 1LL); //should pass, cut trailing 0
+    BOOST_CHECK_THROW(AmountFromValue(ValueFromString("19e-9")), UniValue); //should fail
+    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("0.19e-6")), 19); //should pass, leading 0 is present
+
+    BOOST_CHECK_THROW(AmountFromValue(ValueFromString("92233720368.54775808")), UniValue); //overflow error
+    BOOST_CHECK_THROW(AmountFromValue(ValueFromString("1e+11")), UniValue); //overflow error
+    BOOST_CHECK_THROW(AmountFromValue(ValueFromString("1e11")), UniValue); //overflow error signless
+    BOOST_CHECK_THROW(AmountFromValue(ValueFromString("93e+9")), UniValue); //overflow error
 }
 
 BOOST_AUTO_TEST_CASE(json_parse_errors)
@@ -151,6 +169,9 @@ BOOST_AUTO_TEST_CASE(json_parse_errors)
     // Valid, with leading or trailing whitespace
     BOOST_CHECK_EQUAL(ParseNonRFCJSONValue(" 1.0").get_real(), 1.0);
     BOOST_CHECK_EQUAL(ParseNonRFCJSONValue("1.0 ").get_real(), 1.0);
+
+    BOOST_CHECK_THROW(AmountFromValue(ParseNonRFCJSONValue(".19e-6")), std::runtime_error); //should fail, missing leading 0, therefore invalid JSON
+    BOOST_CHECK_EQUAL(AmountFromValue(ParseNonRFCJSONValue("0.00000000000000000000000000000000000001e+30 ")), 1);
     // Invalid, initial garbage
     BOOST_CHECK_THROW(ParseNonRFCJSONValue("[1.0"), std::runtime_error);
     BOOST_CHECK_THROW(ParseNonRFCJSONValue("a1.0"), std::runtime_error);
diff --git a/src/test/util_tests.cpp b/src/test/util_tests.cpp
index 5cb5894251..e956cc5b90 100644
--- a/src/test/util_tests.cpp
+++ b/src/test/util_tests.cpp
@@ -418,4 +418,70 @@ BOOST_AUTO_TEST_CASE(test_FormatSubVersion)
     BOOST_CHECK_EQUAL(FormatSubVersion("Test", 99900, comments),std::string("/Test:0.9.99(comment1)/"));
     BOOST_CHECK_EQUAL(FormatSubVersion("Test", 99900, comments2),std::string("/Test:0.9.99(comment1; comment2)/"));
 }
+
+BOOST_AUTO_TEST_CASE(test_ParseFixedPoint)
+{
+    int64_t amount = 0;
+    BOOST_CHECK(ParseFixedPoint("0", 8, &amount));
+    BOOST_CHECK_EQUAL(amount, 0LL);
+    BOOST_CHECK(ParseFixedPoint("1", 8, &amount));
+    BOOST_CHECK_EQUAL(amount, 100000000LL);
+    BOOST_CHECK(ParseFixedPoint("0.0", 8, &amount));
+    BOOST_CHECK_EQUAL(amount, 0LL);
+    BOOST_CHECK(ParseFixedPoint("-0.1", 8, &amount));
+    BOOST_CHECK_EQUAL(amount, -10000000LL);
+    BOOST_CHECK(ParseFixedPoint("1.1", 8, &amount));
+    BOOST_CHECK_EQUAL(amount, 110000000LL);
+    BOOST_CHECK(ParseFixedPoint("1.10000000000000000", 8, &amount));
+    BOOST_CHECK_EQUAL(amount, 110000000LL);
+    BOOST_CHECK(ParseFixedPoint("1.1e1", 8, &amount));
+    BOOST_CHECK_EQUAL(amount, 1100000000LL);
+    BOOST_CHECK(ParseFixedPoint("1.1e-1", 8, &amount));
+    BOOST_CHECK_EQUAL(amount, 11000000LL);
+    BOOST_CHECK(ParseFixedPoint("1000", 8, &amount));
+    BOOST_CHECK_EQUAL(amount, 100000000000LL);
+    BOOST_CHECK(ParseFixedPoint("-1000", 8, &amount));
+    BOOST_CHECK_EQUAL(amount, -100000000000LL);
+    BOOST_CHECK(ParseFixedPoint("0.00000001", 8, &amount));
+    BOOST_CHECK_EQUAL(amount, 1LL);
+    BOOST_CHECK(ParseFixedPoint("0.0000000100000000", 8, &amount));
+    BOOST_CHECK_EQUAL(amount, 1LL);
+    BOOST_CHECK(ParseFixedPoint("-0.00000001", 8, &amount));
+    BOOST_CHECK_EQUAL(amount, -1LL);
+    BOOST_CHECK(ParseFixedPoint("1000000000.00000001", 8, &amount));
+    BOOST_CHECK_EQUAL(amount, 100000000000000001LL);
+    BOOST_CHECK(ParseFixedPoint("9999999999.99999999", 8, &amount));
+    BOOST_CHECK_EQUAL(amount, 999999999999999999LL);
+    BOOST_CHECK(ParseFixedPoint("-9999999999.99999999", 8, &amount));
+    BOOST_CHECK_EQUAL(amount, -999999999999999999LL);
+
+    BOOST_CHECK(!ParseFixedPoint("", 8, &amount));
+    BOOST_CHECK(!ParseFixedPoint("-", 8, &amount));
+    BOOST_CHECK(!ParseFixedPoint("a-1000", 8, &amount));
+    BOOST_CHECK(!ParseFixedPoint("-a1000", 8, &amount));
+    BOOST_CHECK(!ParseFixedPoint("-1000a", 8, &amount));
+    BOOST_CHECK(!ParseFixedPoint("-01000", 8, &amount));
+    BOOST_CHECK(!ParseFixedPoint("00.1", 8, &amount));
+    BOOST_CHECK(!ParseFixedPoint(".1", 8, &amount));
+    BOOST_CHECK(!ParseFixedPoint("--0.1", 8, &amount));
+    BOOST_CHECK(!ParseFixedPoint("0.000000001", 8, &amount));
+    BOOST_CHECK(!ParseFixedPoint("-0.000000001", 8, &amount));
+    BOOST_CHECK(!ParseFixedPoint("0.00000001000000001", 8, &amount));
+    BOOST_CHECK(!ParseFixedPoint("-10000000000.00000000", 8, &amount));
+    BOOST_CHECK(!ParseFixedPoint("10000000000.00000000", 8, &amount));
+    BOOST_CHECK(!ParseFixedPoint("-10000000000.00000001", 8, &amount));
+    BOOST_CHECK(!ParseFixedPoint("10000000000.00000001", 8, &amount));
+    BOOST_CHECK(!ParseFixedPoint("-10000000000.00000009", 8, &amount));
+    BOOST_CHECK(!ParseFixedPoint("10000000000.00000009", 8, &amount));
+    BOOST_CHECK(!ParseFixedPoint("-99999999999.99999999", 8, &amount));
+    BOOST_CHECK(!ParseFixedPoint("99999909999.09999999", 8, &amount));
+    BOOST_CHECK(!ParseFixedPoint("92233720368.54775807", 8, &amount));
+    BOOST_CHECK(!ParseFixedPoint("92233720368.54775808", 8, &amount));
+    BOOST_CHECK(!ParseFixedPoint("-92233720368.54775808", 8, &amount));
+    BOOST_CHECK(!ParseFixedPoint("-92233720368.54775809", 8, &amount));
+    BOOST_CHECK(!ParseFixedPoint("1.1e", 8, &amount));
+    BOOST_CHECK(!ParseFixedPoint("1.1e-", 8, &amount));
+    BOOST_CHECK(!ParseFixedPoint("1.", 8, &amount));
+}
+
 BOOST_AUTO_TEST_SUITE_END()
diff --git a/src/utilstrencodings.cpp b/src/utilstrencodings.cpp
index 7d1de7d6a8..7208ca9474 100644
--- a/src/utilstrencodings.cpp
+++ b/src/utilstrencodings.cpp
@@ -538,3 +538,123 @@ int atoi(const std::string& str)
 {
     return atoi(str.c_str());
 }
+
+/** Upper bound for mantissa.
+ * 10^18-1 is the largest arbitrary decimal that will fit in a signed 64-bit integer.
+ * Larger integers cannot consist of arbitrary combinations of 0-9:
+ *
+ *   999999999999999999  1^18-1
+ *  9223372036854775807  (1<<63)-1  (max int64_t)
+ *  9999999999999999999  1^19-1     (would overflow)
+ */
+static const int64_t UPPER_BOUND = 1000000000000000000LL - 1LL;
+
+/** Helper function for ParseFixedPoint */
+static inline bool ProcessMantissaDigit(char ch, int64_t &mantissa, int &mantissa_tzeros)
+{
+    if(ch == '0')
+        ++mantissa_tzeros;
+    else {
+        for (int i=0; i<=mantissa_tzeros; ++i) {
+            if (mantissa > (UPPER_BOUND / 10LL))
+                return false; /* overflow */
+            mantissa *= 10;
+        }
+        mantissa += ch - '0';
+        mantissa_tzeros = 0;
+    }
+    return true;
+}
+
+bool ParseFixedPoint(const std::string &val, int decimals, int64_t *amount_out)
+{
+    int64_t mantissa = 0;
+    int64_t exponent = 0;
+    int mantissa_tzeros = 0;
+    bool mantissa_sign = false;
+    bool exponent_sign = false;
+    int ptr = 0;
+    int end = val.size();
+    int point_ofs = 0;
+
+    if (ptr < end && val[ptr] == '-') {
+        mantissa_sign = true;
+        ++ptr;
+    }
+    if (ptr < end)
+    {
+        if (val[ptr] == '0') {
+            /* pass single 0 */
+            ++ptr;
+        } else if (val[ptr] >= '1' && val[ptr] <= '9') {
+            while (ptr < end && val[ptr] >= '0' && val[ptr] <= '9') {
+                if (!ProcessMantissaDigit(val[ptr], mantissa, mantissa_tzeros))
+                    return false; /* overflow */
+                ++ptr;
+            }
+        } else return false; /* missing expected digit */
+    } else return false; /* empty string or loose '-' */
+    if (ptr < end && val[ptr] == '.')
+    {
+        ++ptr;
+        if (ptr < end && val[ptr] >= '0' && val[ptr] <= '9')
+        {
+            while (ptr < end && val[ptr] >= '0' && val[ptr] <= '9') {
+                if (!ProcessMantissaDigit(val[ptr], mantissa, mantissa_tzeros))
+                    return false; /* overflow */
+                ++ptr;
+                ++point_ofs;
+            }
+        } else return false; /* missing expected digit */
+    }
+    if (ptr < end && (val[ptr] == 'e' || val[ptr] == 'E'))
+    {
+        ++ptr;
+        if (ptr < end && val[ptr] == '+')
+            ++ptr;
+        else if (ptr < end && val[ptr] == '-') {
+            exponent_sign = true;
+            ++ptr;
+        }
+        if (ptr < end && val[ptr] >= '0' && val[ptr] <= '9') {
+            while (ptr < end && val[ptr] >= '0' && val[ptr] <= '9') {
+                if (exponent > (UPPER_BOUND / 10LL))
+                    return false; /* overflow */
+                exponent = exponent * 10 + val[ptr] - '0';
+                ++ptr;
+            }
+        } else return false; /* missing expected digit */
+    }
+    if (ptr != end)
+        return false; /* trailing garbage */
+
+    /* finalize exponent */
+    if (exponent_sign)
+        exponent = -exponent;
+    exponent = exponent - point_ofs + mantissa_tzeros;
+
+    /* finalize mantissa */
+    if (mantissa_sign)
+        mantissa = -mantissa;
+
+    /* convert to one 64-bit fixed-point value */
+    exponent += decimals;
+    if (exponent < 0)
+        return false; /* cannot represent values smaller than 10^-decimals */
+    if (exponent >= 18)
+        return false; /* cannot represent values larger than or equal to 10^(18-decimals) */
+
+    for (int i=0; i < exponent; ++i) {
+        if (mantissa > (UPPER_BOUND / 10LL) || mantissa < -(UPPER_BOUND / 10LL))
+            return false; /* overflow */
+        mantissa *= 10;
+    }
+    if (mantissa > UPPER_BOUND || mantissa < -UPPER_BOUND)
+        return false; /* overflow */
+
+    if (amount_out)
+        *amount_out = mantissa;
+
+    return true;
+}
+
diff --git a/src/utilstrencodings.h b/src/utilstrencodings.h
index 58329b51bb..dcd56751f2 100644
--- a/src/utilstrencodings.h
+++ b/src/utilstrencodings.h
@@ -109,4 +109,11 @@ bool TimingResistantEqual(const T& a, const T& b)
     return accumulator == 0;
 }
 
+/** Parse number as fixed point according to JSON number syntax.
+ * See http://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.
+ */
+bool ParseFixedPoint(const std::string &val, int decimals, int64_t *amount_out);
+
 #endif // BITCOIN_UTILSTRENCODINGS_H