Add JSON RPC hex strings support

nimbus/rpc/hexstrings.nim

@@ -0,0 +1,103 @@
+# Nimbus
+# Copyright (c) 2018 Status Research & Development GmbH
+# Licensed under either of
+#  * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE))
+#  * MIT license ([LICENSE-MIT](LICENSE-MIT))
+# at your option.
+# This file may not be copied, modified, or distributed except according to
+# those terms.
+
+## This module implements the Ethereum hexadecimal string formats for JSON
+## See: https://github.com/ethereum/wiki/wiki/JSON-RPC#hex-value-encoding
+
+type
+  HexQuantityStr* = distinct string
+  HexDataStr* = distinct string
+
+# Hex validation
+
+template stripLeadingZeros(value: string): string =
+  var cidx = 0
+  # ignore the last character so we retain '0' on zero value
+  while cidx < value.len - 1 and value[cidx] == '0':
+    cidx.inc
+  value[cidx .. ^1]
+
+proc encodeQuantity*(value: SomeUnsignedInt): string =
+  var hValue = value.toHex.stripLeadingZeros
+  result = "0x" & hValue
+
+template hasHexHeader*(value: string): bool =
+  if value != "" and value[0] == '0' and value[1] in {'x', 'X'} and value.len > 2: true
+  else: false
+
+template isHexChar*(c: char): bool =
+  if  c notin {'0'..'9'} and
+      c notin {'a'..'f'} and
+      c notin {'A'..'F'}: false
+  else: true
+
+proc validateHexQuantity*(value: string): bool =
+  if not value.hasHexHeader:
+    return false
+  # No leading zeros
+  if value[2] == '0': return false
+  for i in 2 ..< value.len:
+    let c = value[i]
+    if not c.isHexChar:
+      return false
+  return true
+
+proc validateHexData*(value: string): bool =
+  if not value.hasHexHeader:
+    return false
+  # Must be even number of digits
+  if value.len mod 2 != 0: return false
+  # Leading zeros are allowed
+  for i in 2 ..< value.len:
+    let c = value[i]
+    if not c.isHexChar:
+      return false
+  return true
+
+# Initialisation
+
+proc hexQuantityStr*(value: string): HexQuantityStr =
+  if not value.validateHexQuantity:
+    raise newException(ValueError, "Invalid hex quantity format for Ethereum: " & value)
+  else:
+    result = value.HexQuantityStr
+
+proc hexDataStr*(value: string): HexDataStr =
+  if not value.validateHexData:
+    raise newException(ValueError, "Invalid hex data format for Ethereum: " & value)
+  else:
+    result = value.HexDataStr
+
+# Converters for use in RPC
+
+import json
+from json_rpc/rpcserver import expect
+
+proc `%`*(value: HexQuantityStr): JsonNode =
+  result = %(value.string)
+
+proc `%`*(value: HexDataStr): JsonNode =
+  result = %(value.string)
+
+proc fromJson*(n: JsonNode, argName: string, result: var HexQuantityStr) =
+  # Note that '0x' is stripped after validation
+  n.kind.expect(JString, argName)
+  let hexStr = n.getStr()
+  if not hexStr.validateHexQuantity:
+    raise newException(ValueError, "Parameter \"" & argName & "\" value is not valid as an Ethereum hex quantity \"" & hexStr & "\"")
+  result = hexStr[2..hexStr.high].hexQuantityStr
+
+proc fromJson*(n: JsonNode, argName: string, result: var HexDataStr) =
+  # Note that '0x' is stripped after validation
+  n.kind.expect(JString, argName)
+  let hexStr = n.getStr()
+  if not hexStr.validateHexData:
+    raise newException(ValueError, "Parameter \"" & argName & "\" value is not valid as a Ethereum data \"" & hexStr & "\"")
+  result = hexStr[2..hexStr.high].hexDataStr
+