accounts/abi: allow abi: tags when unpacking structs

Go code users can now tag event struct members with `abi:` to specify in what fields the event will be de-serialized.

See PR ethereum#16648 for details.

Author: gballet

accounts/abi/argument.go

@@ -111,9 +111,14 @@ func (arguments Arguments) unpackTuple(v interface{}, marshalledValues []interfa
 	if err := requireUnpackKind(value, typ, kind, arguments); err != nil {
 		return err
 	}
-	// If the output interface is a struct, make sure names don't collide
+
+	// If the interface is a struct, get of abi->struct_field mapping
+
+	var abi2struct map[string]string
 	if kind == reflect.Struct {
-		if err := requireUniqueStructFieldNames(arguments); err != nil {
+		var err error
+		abi2struct, err = mapAbiToStructFields(arguments, value)
+		if err != nil {
 			return err
 		}
 	}
@@ -123,9 +128,10 @@ func (arguments Arguments) unpackTuple(v interface{}, marshalledValues []interfa
 
 		switch kind {
 		case reflect.Struct:
-			err := unpackStruct(value, reflectValue, arg)
-			if err != nil {
-				return err
+			if structField, ok := abi2struct[arg.Name]; ok {
+				if err := set(value.FieldByName(structField), reflectValue, arg); err != nil {
+					return err
+				}
 			}
 		case reflect.Slice, reflect.Array:
 			if value.Len() < i {
@@ -151,17 +157,22 @@ func (arguments Arguments) unpackAtomic(v interface{}, marshalledValues []interf
 	if len(marshalledValues) != 1 {
 		return fmt.Errorf("abi: wrong length, expected single value, got %d", len(marshalledValues))
 	}
+
 	elem := reflect.ValueOf(v).Elem()
 	kind := elem.Kind()
 	reflectValue := reflect.ValueOf(marshalledValues[0])
 
+	var abi2struct map[string]string
 	if kind == reflect.Struct {
-		//make sure names don't collide
-		if err := requireUniqueStructFieldNames(arguments); err != nil {
+		var err error
+		if abi2struct, err = mapAbiToStructFields(arguments, elem); err != nil {
 			return err
 		}
-
-		return unpackStruct(elem, reflectValue, arguments[0])
+		arg := arguments.NonIndexed()[0]
+		if structField, ok := abi2struct[arg.Name]; ok {
+			return set(elem.FieldByName(structField), reflectValue, arg)
+		}
+		return nil
 	}
 
 	return set(elem, reflectValue, arguments.NonIndexed()[0])
@@ -277,18 +288,3 @@ func capitalise(input string) string {
 	}
 	return strings.ToUpper(input[:1]) + input[1:]
 }
-
-//unpackStruct extracts each argument into its corresponding struct field
-func unpackStruct(value, reflectValue reflect.Value, arg Argument) error {
-	name := capitalise(arg.Name)
-	typ := value.Type()
-	for j := 0; j < typ.NumField(); j++ {
-		// TODO read tags: `abi:"fieldName"`
-		if typ.Field(j).Name == name {
-			if err := set(value.Field(j), reflectValue, arg); err != nil {
-				return err
-			}
-		}
-	}
-	return nil
-}

accounts/abi/event_test.go

@@ -58,12 +58,28 @@ var jsonEventPledge = []byte(`{
   "type": "event"
 }`)
 
+var jsonEventMixedCase = []byte(`{
+	"anonymous": false,
+	"inputs": [{
+		"indexed": false, "name": "value", "type": "uint256"
+	  }, {
+		"indexed": false, "name": "_value", "type": "uint256"
+	  }, {
+		"indexed": false, "name": "Value", "type": "uint256"
+	}],
+	"name": "MixedCase",
+	"type": "event"
+  }`)
+
 // 1000000
 var transferData1 = "00000000000000000000000000000000000000000000000000000000000f4240"
 
 // "0x00Ce0d46d924CC8437c806721496599FC3FFA268", 2218516807680, "usd"
 var pledgeData1 = "00000000000000000000000000ce0d46d924cc8437c806721496599fc3ffa2680000000000000000000000000000000000000000000000000000020489e800007573640000000000000000000000000000000000000000000000000000000000"
 
+// 1000000,2218516807680,1000001
+var mixedCaseData1 = "00000000000000000000000000000000000000000000000000000000000f42400000000000000000000000000000000000000000000000000000020489e8000000000000000000000000000000000000000000000000000000000000000f4241"
+
 func TestEventId(t *testing.T) {
 	var table = []struct {
 		definition   string
@@ -121,6 +137,27 @@ func TestEventTupleUnpack(t *testing.T) {
 		Value *big.Int
 	}
 
+	type EventTransferWithTag struct {
+		// this is valid because `value` is not exportable,
+		// so value is only unmarshalled into `Value1`.
+		value  *big.Int
+		Value1 *big.Int `abi:"value"`
+	}
+
+	type BadEventTransferWithSameFieldAndTag struct {
+		Value  *big.Int
+		Value1 *big.Int `abi:"value"`
+	}
+
+	type BadEventTransferWithDuplicatedTag struct {
+		Value1 *big.Int `abi:"value"`
+		Value2 *big.Int `abi:"value"`
+	}
+
+	type BadEventTransferWithEmptyTag struct {
+		Value *big.Int `abi:""`
+	}
+
 	type EventPledge struct {
 		Who      common.Address
 		Wad      *big.Int
@@ -133,9 +170,16 @@ func TestEventTupleUnpack(t *testing.T) {
 		Currency [3]byte
 	}
 
+	type EventMixedCase struct {
+		Value1 *big.Int `abi:"value"`
+		Value2 *big.Int `abi:"_value"`
+		Value3 *big.Int `abi:"Value"`
+	}
+
 	bigint := new(big.Int)
 	bigintExpected := big.NewInt(1000000)
 	bigintExpected2 := big.NewInt(2218516807680)
+	bigintExpected3 := big.NewInt(1000001)
 	addr := common.HexToAddress("0x00Ce0d46d924CC8437c806721496599FC3FFA268")
 	var testCases = []struct {
 		data     string
@@ -158,6 +202,34 @@ func TestEventTupleUnpack(t *testing.T) {
 		jsonEventTransfer,
 		"",
 		"Can unpack ERC20 Transfer event into slice",
+	}, {
+		transferData1,
+		&EventTransferWithTag{},
+		&EventTransferWithTag{Value1: bigintExpected},
+		jsonEventTransfer,
+		"",
+		"Can unpack ERC20 Transfer event into structure with abi: tag",
+	}, {
+		transferData1,
+		&BadEventTransferWithDuplicatedTag{},
+		&BadEventTransferWithDuplicatedTag{},
+		jsonEventTransfer,
+		"struct: abi tag in 'Value2' already mapped",
+		"Can not unpack ERC20 Transfer event with duplicated abi tag",
+	}, {
+		transferData1,
+		&BadEventTransferWithSameFieldAndTag{},
+		&BadEventTransferWithSameFieldAndTag{},
+		jsonEventTransfer,
+		"abi: multiple variables maps to the same abi field 'value'",
+		"Can not unpack ERC20 Transfer event with a field and a tag mapping to the same abi variable",
+	}, {
+		transferData1,
+		&BadEventTransferWithEmptyTag{},
+		&BadEventTransferWithEmptyTag{},
+		jsonEventTransfer,
+		"struct: abi tag in 'Value' is empty",
+		"Can not unpack ERC20 Transfer event with an empty tag",
 	}, {
 		pledgeData1,
 		&EventPledge{},
@@ -216,6 +288,13 @@ func TestEventTupleUnpack(t *testing.T) {
 		jsonEventPledge,
 		"abi: cannot unmarshal tuple into map[string]interface {}",
 		"Can not unpack Pledge event into map",
+	}, {
+		mixedCaseData1,
+		&EventMixedCase{},
+		&EventMixedCase{Value1: bigintExpected, Value2: bigintExpected2, Value3: bigintExpected3},
+		jsonEventMixedCase,
+		"",
+		"Can unpack abi variables with mixed case",
 	}}
 
 	for _, tc := range testCases {
@@ -227,7 +306,7 @@ func TestEventTupleUnpack(t *testing.T) {
 				assert.Nil(err, "Should be able to unpack event data.")
 				assert.Equal(tc.expected, tc.dest, tc.name)
 			} else {
-				assert.EqualError(err, tc.error)
+				assert.EqualError(err, tc.error, tc.name)
 			}
 		})
 	}

accounts/abi/reflect.go

@@ -19,6 +19,7 @@ package abi
 import (
 	"fmt"
 	"reflect"
+	"strings"
 )
 
 // indirect recursively dereferences the value until it either gets the value
@@ -111,18 +112,101 @@ func requireUnpackKind(v reflect.Value, t reflect.Type, k reflect.Kind,
 	return nil
 }
 
-// requireUniqueStructFieldNames makes sure field names don't collide
-func requireUniqueStructFieldNames(args Arguments) error {
-	exists := make(map[string]bool)
+// mapAbiToStringField maps abi to struct fields.
+// first round: for each Exportable field that contains a `abi:""` tag
+//   and this field name exists in the arguments, pair them together.
+// second round: for each argument field that has not been already linked,
+//   find what variable is expected to be mapped into, if it exists and has not been
+//   used, pair them.
+func mapAbiToStructFields(args Arguments, value reflect.Value) (map[string]string, error) {
+
+	typ := value.Type()
+
+	abi2struct := make(map[string]string)
+	struct2abi := make(map[string]string)
+
+	// first round ~~~
+	for i := 0; i < typ.NumField(); i++ {
+		structFieldName := typ.Field(i).Name
+
+		// skip private struct fields.
+		if structFieldName[:1] != strings.ToUpper(structFieldName[:1]) {
+			continue
+		}
+
+		// skip fields that have no abi:"" tag.
+		var ok bool
+		var tagName string
+		if tagName, ok = typ.Field(i).Tag.Lookup("abi"); !ok {
+			continue
+		}
+
+		// check if tag is empty.
+		if tagName == "" {
+			return nil, fmt.Errorf("struct: abi tag in '%s' is empty", structFieldName)
+		}
+
+		// check which argument field matches with the abi tag.
+		found := false
+		for _, abiField := range args.NonIndexed() {
+			if abiField.Name == tagName {
+				if abi2struct[abiField.Name] != "" {
+					return nil, fmt.Errorf("struct: abi tag in '%s' already mapped", structFieldName)
+				}
+				// pair them
+				abi2struct[abiField.Name] = structFieldName
+				struct2abi[structFieldName] = abiField.Name
+				found = true
+			}
+		}
+
+		// check if this tag has been mapped.
+		if !found {
+			return nil, fmt.Errorf("struct: abi tag '%s' defined but not found in abi", tagName)
+		}
+
+	}
+
+	// second round ~~~
 	for _, arg := range args {
-		field := capitalise(arg.Name)
-		if field == "" {
-			return fmt.Errorf("abi: purely underscored output cannot unpack to struct")
+
+		abiFieldName := arg.Name
+		structFieldName := capitalise(abiFieldName)
+
+		if structFieldName == "" {
+			return nil, fmt.Errorf("abi: purely underscored output cannot unpack to struct")
 		}
-		if exists[field] {
-			return fmt.Errorf("abi: multiple outputs mapping to the same struct field '%s'", field)
+
+		// this abi has already been paired, skip it... unless there exists another, yet unassigned
+		// struct field with the same field name. If so, raise an error:
+		//    abi: [ { "name": "value" } ]
+		//    struct { Value  *big.Int , Value1 *big.Int `abi:"value"`}
+		if abi2struct[abiFieldName] != "" {
+			if abi2struct[abiFieldName] != structFieldName &&
+				struct2abi[structFieldName] == "" &&
+				value.FieldByName(structFieldName).IsValid() {
+				return nil, fmt.Errorf("abi: multiple variables maps to the same abi field '%s'", abiFieldName)
+			}
+			continue
 		}
-		exists[field] = true
+
+		// return an error if this struct field has already been paired.
+		if struct2abi[structFieldName] != "" {
+			return nil, fmt.Errorf("abi: multiple outputs mapping to the same struct field '%s'", structFieldName)
+		}
+
+		if value.FieldByName(structFieldName).IsValid() {
+			// pair them
+			abi2struct[abiFieldName] = structFieldName
+			struct2abi[structFieldName] = abiFieldName
+		} else {
+			// not paired, but annotate as used, to detect cases like
+			//   abi : [ { "name": "value" }, { "name": "_value" } ]
+			//   struct { Value *big.Int }
+			struct2abi[structFieldName] = abiFieldName
+		}
+
 	}
-	return nil
+
+	return abi2struct, nil
 }