signer/fourbyte: add support for nested types in selectors (#24407)

This replaces the simple selector parser in signer/fourbyte with one that
can actually handle most types. The new parser is added in accounts/abi
to also make it useable elsewhere.

accounts/abi/selector_parser.go

@@ -0,0 +1,152 @@
+package abi
+
+import (
+	"fmt"
+)
+
+type SelectorMarshaling struct {
+	Name   string               `json:"name"`
+	Type   string               `json:"type"`
+	Inputs []ArgumentMarshaling `json:"inputs"`
+}
+
+func isDigit(c byte) bool {
+	return c >= '0' && c <= '9'
+}
+
+func isAlpha(c byte) bool {
+	return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z')
+}
+
+func isIdentifierSymbol(c byte) bool {
+	return c == '$' || c == '_'
+}
+
+func parseToken(unescapedSelector string, isIdent bool) (string, string, error) {
+	if len(unescapedSelector) == 0 {
+		return "", "", fmt.Errorf("empty token")
+	}
+	firstChar := unescapedSelector[0]
+	position := 1
+	if !(isAlpha(firstChar) || (isIdent && isIdentifierSymbol(firstChar))) {
+		return "", "", fmt.Errorf("invalid token start: %c", firstChar)
+	}
+	for position < len(unescapedSelector) {
+		char := unescapedSelector[position]
+		if !(isAlpha(char) || isDigit(char) || (isIdent && isIdentifierSymbol(char))) {
+			break
+		}
+		position++
+	}
+	return unescapedSelector[:position], unescapedSelector[position:], nil
+}
+
+func parseIdentifier(unescapedSelector string) (string, string, error) {
+	return parseToken(unescapedSelector, true)
+}
+
+func parseElementaryType(unescapedSelector string) (string, string, error) {
+	parsedType, rest, err := parseToken(unescapedSelector, false)
+	if err != nil {
+		return "", "", fmt.Errorf("failed to parse elementary type: %v", err)
+	}
+	// handle arrays
+	for len(rest) > 0 && rest[0] == '[' {
+		parsedType = parsedType + string(rest[0])
+		rest = rest[1:]
+		for len(rest) > 0 && isDigit(rest[0]) {
+			parsedType = parsedType + string(rest[0])
+			rest = rest[1:]
+		}
+		if len(rest) == 0 || rest[0] != ']' {
+			return "", "", fmt.Errorf("failed to parse array: expected ']', got %c", unescapedSelector[0])
+		}
+		parsedType = parsedType + string(rest[0])
+		rest = rest[1:]
+	}
+	return parsedType, rest, nil
+}
+
+func parseCompositeType(unescapedSelector string) ([]interface{}, string, error) {
+	if len(unescapedSelector) == 0 || unescapedSelector[0] != '(' {
+		return nil, "", fmt.Errorf("expected '(', got %c", unescapedSelector[0])
+	}
+	parsedType, rest, err := parseType(unescapedSelector[1:])
+	if err != nil {
+		return nil, "", fmt.Errorf("failed to parse type: %v", err)
+	}
+	result := []interface{}{parsedType}
+	for len(rest) > 0 && rest[0] != ')' {
+		parsedType, rest, err = parseType(rest[1:])
+		if err != nil {
+			return nil, "", fmt.Errorf("failed to parse type: %v", err)
+		}
+		result = append(result, parsedType)
+	}
+	if len(rest) == 0 || rest[0] != ')' {
+		return nil, "", fmt.Errorf("expected ')', got '%s'", rest)
+	}
+	return result, rest[1:], nil
+}
+
+func parseType(unescapedSelector string) (interface{}, string, error) {
+	if len(unescapedSelector) == 0 {
+		return nil, "", fmt.Errorf("empty type")
+	}
+	if unescapedSelector[0] == '(' {
+		return parseCompositeType(unescapedSelector)
+	} else {
+		return parseElementaryType(unescapedSelector)
+	}
+}
+
+func assembleArgs(args []interface{}) ([]ArgumentMarshaling, error) {
+	arguments := make([]ArgumentMarshaling, 0)
+	for i, arg := range args {
+		// generate dummy name to avoid unmarshal issues
+		name := fmt.Sprintf("name%d", i)
+		if s, ok := arg.(string); ok {
+			arguments = append(arguments, ArgumentMarshaling{name, s, s, nil, false})
+		} else if components, ok := arg.([]interface{}); ok {
+			subArgs, err := assembleArgs(components)
+			if err != nil {
+				return nil, fmt.Errorf("failed to assemble components: %v", err)
+			}
+			arguments = append(arguments, ArgumentMarshaling{name, "tuple", "tuple", subArgs, false})
+		} else {
+			return nil, fmt.Errorf("failed to assemble args: unexpected type %T", arg)
+		}
+	}
+	return arguments, nil
+}
+
+// ParseSelector converts a method selector into a struct that can be JSON encoded
+// and consumed by other functions in this package.
+// Note, although uppercase letters are not part of the ABI spec, this function
+// still accepts it as the general format is valid.
+func ParseSelector(unescapedSelector string) (SelectorMarshaling, error) {
+	name, rest, err := parseIdentifier(unescapedSelector)
+	if err != nil {
+		return SelectorMarshaling{}, fmt.Errorf("failed to parse selector '%s': %v", unescapedSelector, err)
+	}
+	args := []interface{}{}
+	if len(rest) >= 2 && rest[0] == '(' && rest[1] == ')' {
+		rest = rest[2:]
+	} else {
+		args, rest, err = parseCompositeType(rest)
+		if err != nil {
+			return SelectorMarshaling{}, fmt.Errorf("failed to parse selector '%s': %v", unescapedSelector, err)
+		}
+	}
+	if len(rest) > 0 {
+		return SelectorMarshaling{}, fmt.Errorf("failed to parse selector '%s': unexpected string '%s'", unescapedSelector, rest)
+	}
+
+	// Reassemble the fake ABI and constuct the JSON
+	fakeArgs, err := assembleArgs(args)
+	if err != nil {
+		return SelectorMarshaling{}, fmt.Errorf("failed to parse selector: %v", err)
+	}
+
+	return SelectorMarshaling{name, "function", fakeArgs}, nil
+}