Support encoding and decoding of custom types

Readme.md

@@ -19,12 +19,12 @@ Usage
 
 ```nim
 import contractabi
-import stint
 
 # encode unsigned integers, booleans, enums
 AbiEncoder.encode(42'u8)
 
 # encode uint256
+import stint
 AbiEncoder.encode(42.u256)
 
 # encode byte arrays and sequences
@@ -42,6 +42,21 @@ AbiDecoder.decode(bytes, seq[uint8])
 
 # decode tuples
 AbiDecoder.decode(bytes, (uint32, bool, seq[byte]) )
+
+# add support for encoding of custom types
+import questionable/results
+
+type CustomType = object
+  a: uint16
+  b: string
+
+func encode(encoder: var AbiEncoder, custom: CustomType) =
+  encoder.write( (custom.a, custom.b) )
+
+func decode(decoder: var AbiDecoder, T: type CustomType): ?!T =
+  let (a, b) = ?decoder.read( (uint16, string) )
+  success CustomType(a: a, b: b)
+
 ```
 
 [1]: https://docs.soliditylang.org/en/latest/abi-spec.html

contractabi/decoding.nim

@@ -146,9 +146,6 @@ func decode[T: tuple](decoder: var AbiDecoder, _: typedesc[T]): ?!T =
   decoder.finishTuple()
   success tupl
 
-func read*(decoder: var AbiDecoder, T: type): ?!T =
-  decoder.decode(T)
-
 func finish(decoder: var AbiDecoder): ?!void =
   doAssert decoder.stack.len == 1, "not all tuples were finished"
   doAssert decoder.last mod 32 == 0, "encoding invariant broken"
@@ -183,3 +180,6 @@ func decode*(_: type AbiDecoder, bytes: seq[byte], T: type): ?!T =
   var value = ?decoder.decode(T)
   ?decoder.finish()
   success value
+
+func read*(decoder: var AbiDecoder, T: type): ?!T =
+  decoder.decode(T)

tests/contractabi/testCustomTypes.nim

@@ -0,0 +1,25 @@
+import std/unittest
+import pkg/questionable/results
+import contractabi
+
+type CustomType = object
+  a: uint16
+  b: string
+
+func encode(encoder: var AbiEncoder, custom: CustomType) =
+  encoder.write( (custom.a, custom.b) )
+
+func decode(decoder: var AbiDecoder, T: type CustomType): ?!T =
+  let (a, b) = ?decoder.read( (uint16, string) )
+  success CustomType(a: a, b: b)
+
+suite "custom types":
+
+  let custom = CustomType(a: 42, b: "ultimate answer")
+
+  test "can be encoded":
+    check AbiEncoder.encode(custom) == AbiEncoder.encode( (custom.a, custom.b) )
+
+  test "can be decoded":
+    let encoding = AbiEncoder.encode(custom)
+    check AbiDecoder.decode(encoding, CustomType) == success custom

tests/testAll.nim

@@ -1,4 +1,5 @@
 import ./contractabi/testEncoding
 import ./contractabi/testDecoding
+import ./contractabi/testCustomTypes
 
 {.warning[UnusedImport]:off.}