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Tools/SmartCheck/Solidity/Rules/SOLIDITY_ERC20_FUNCTIONS_ALWAYS_RETURN_FALSE.md

+# Analysis of Smart Contract Security Vulnerabilities and Tools ![](https://img.shields.io/badge/-Live-brightgreen)
+![](https://img.shields.io/badge/Batch-UG21CYS-lightgreen) ![](https://img.shields.io/badge/Batch-PG21CYS-green) ![](https://img.shields.io/badge/Batch-UG22CYS-lightgreen) ![](https://img.shields.io/badge/Batch-PG21CYS-green) ![](https://img.shields.io/badge/Batch-PhD-darkgreen) ![](https://img.shields.io/badge/-B_RIG-darkgreen)<br/>   ![](https://img.shields.io/badge/BlockchainCourse-21CY712-green)  ![](https://img.shields.io/badge/-M.Tech_Dissertation-blue) ![](https://img.shields.io/badge/Focus-Smart_Contract_Security-yellow) <br/>
+![](https://img.shields.io/badge/Blockchain-Ethereum-blue)   <br/> 
+![](https://img.shields.io/badge/Language-Solidity-blue)
+
+## SOLIDITY_ERC20_FUNCTIONS_ALWAYS_RETURN_FALSE
+### Rule Description
+The <code>transfer</code>, <code>transferFrom</code> or <code>approve</code> functions do not return <code>true</code> for any values of input parameters.
+### Solidity-Rules
+
+![](https://img.shields.io/badge/Pattern_ID-b180ca-gold) ![](https://img.shields.io/badge/Severity-2-brown) 
+
+```
+//contractDefinition
+                        [
+                            identifier[matches(text()[1], "token|erc20", "i")]
+                            or inheritanceSpecifier/userDefinedTypeName/identifier[matches(text()[1], "token|erc20", "i")]
+                        ]
+                    //functionDefinition
+                        [block/statement]
+                        [identifier[matches(text()[1], "^transfer$|^transferFrom$|^approve$")]]
+                        [returnsParameters/parameterList/parameter/typeName/elementaryTypeName[matches(text()[1], "bool")]]
+                        [not(block/statement//returnStatement)]
+                        [count(returnsParameters/parameterList/parameter) = 1]
+                        [
+                            returnsParameters/parameterList/parameter/identifier
+                                [not(text()[1]
+                                    = ancestor::functionDefinition/block//expression
+                                        [matches(text()[1], "=")]/expression[1]//identifier)
+                                ]
+                            or returnsParameters/parameterList/parameter[not(identifier)]
+                        ]
+```
+
+### Sample Code
+
+```
+pragma solidity 0.4.24;
+
+contract TestToken {
+    // <yes> <report> SOLIDITY_ERC20_FUNCTIONS_ALWAYS_RETURN_FALSE b180ca
+    function approve(address _spender, uint _value) returns (bool success) {
+    	if (_value < 20 wei) throw;
+    }
+    // <yes> <report> SOLIDITY_ERC20_FUNCTIONS_ALWAYS_RETURN_FALSE b180ca
+    function transferFrom(address _spender, uint _value) returns (bool) {
+        require(_value > 10 wei);
+    }
+}
+contract TestToken2 {
+    function transferFrom(address _spender, uint _value) returns (bool success) {
+        require(_value > 10 wei);
+        success = true;
+    }
+}
+
+contract TestToken3 {
+    function transferFrom(address _spender, uint _value) returns (bool) {
+        require(_value > 10 wei);
+        return true;
+    }
+    function transfer(address _spender, uint _value) returns (bool success) {
+    	if (_value < 20 wei) revert();
+    	return false;
+    }
+    function transferTokens(address _spender, uint _value) returns (bool success) {
+        if (_value < 20 wei) revert();
+    }
+    function approve(address _to, uint256 _value) returns (bool);
+ }
+```
+
+### Abstract Syntax Tree 
+
+[Click Here](https://astexplorer.net/#/gist/65609430a00dea52c532b93bcb634f5b/1bc08a00c8138494fa5997e7f8fbc84f2714d80c) to view the AST for the above code. Code generated from AST Explorer using _solidity-parser-antlr-0.4.11_
+
+### Code Result
+
+```
+SOLIDITY_DEPRECATED_CONSTRUCTIONS
+patternId: 49bd2a
+severity: 1
+line: 6
+column: 26
+content: throw
+
+ruleId: SOLIDITY_ERC20_APPROVE
+patternId: af782c
+severity: 2
+line: 5
+column: 4
+content: functionapprove(address_spender,uint_value)returns(boolsuccess){if(_value<20wei)throw;}
+
+ruleId: SOLIDITY_ERC20_FUNCTIONS_ALWAYS_RETURN_FALSE
+patternId: b180ca
+severity: 2
+line: 5
+column: 4
+content: functionapprove(address_spender,uint_value)returns(boolsuccess){if(_value<20wei)throw;}
+
+ruleId: SOLIDITY_ERC20_FUNCTIONS_ALWAYS_RETURN_FALSE
+patternId: b180ca
+severity: 2
+line: 9
+column: 4
+content: functiontransferFrom(address_spender,uint_value)returns(bool){require(_value>10wei);}
+
+ruleId: SOLIDITY_ERC20_FUNCTIONS_ALWAYS_RETURN_FALSE
+patternId: b180ca
+severity: 2
+line: 29
+column: 4
+content: functiontransferTokens(address_spender,uint_value)returns(boolsuccess){if(_value<20wei)revert();}
+
+ruleId: SOLIDITY_FUNCTIONS_RETURNS_TYPE_AND_NO_RETURN
+patternId: 47acc2
+severity: 1
+line: 9
+column: 4
+content: functiontransferFrom(address_spender,uint_value)returns(bool){require(_value>10wei);}
+
+ruleId: SOLIDITY_FUNCTIONS_RETURNS_TYPE_AND_NO_RETURN
+patternId: 58bdd3
+severity: 1
+line: 5
+column: 4
+content: functionapprove(address_spender,uint_value)returns(boolsuccess){if(_value<20wei)throw;}
+
+ruleId: SOLIDITY_FUNCTIONS_RETURNS_TYPE_AND_NO_RETURN
+patternId: 58bdd3
+severity: 1
+line: 29
+column: 4
+content: functiontransferTokens(address_spender,uint_value)returns(boolsuccess){if(_value<20wei)revert();}
+
+ruleId: SOLIDITY_REVERT_REQUIRE
+patternId: c56b12
+severity: 1
+line: 6
+column: 5
+content: if(_value<20wei)throw;
+
+ruleId: SOLIDITY_REVERT_REQUIRE
+patternId: c56b12
+severity: 1
+line: 26
+column: 5
+content: if(_value<20wei)revert();
+
+ruleId: SOLIDITY_REVERT_REQUIRE
+patternId: c56b12
+severity: 1
+line: 30
+column: 8
+content: if(_value<20wei)revert();
+
+ruleId: SOLIDITY_VISIBILITY
+patternId: 910067
+severity: 1
+line: 5
+column: 4
+content: functionapprove(address_spender,uint_value)returns(boolsuccess){if(_value<20wei)throw;}
+
+ruleId: SOLIDITY_VISIBILITY
+patternId: 910067
+severity: 1
+line: 9
+column: 4
+content: functiontransferFrom(address_spender,uint_value)returns(bool){require(_value>10wei);}
+
+ruleId: SOLIDITY_VISIBILITY
+patternId: 910067
+severity: 1
+line: 14
+column: 4
+content: functiontransferFrom(address_spender,uint_value)returns(boolsuccess){require(_value>10wei);success=true;}
+
+ruleId: SOLIDITY_VISIBILITY
+patternId: 910067
+severity: 1
+line: 21
+column: 4
+content: functiontransferFrom(address_spender,uint_value)returns(bool){require(_value>10wei);returntrue;}
+
+ruleId: SOLIDITY_VISIBILITY
+patternId: 910067
+severity: 1
+line: 25
+column: 4
+content: functiontransfer(address_spender,uint_value)returns(boolsuccess){if(_value<20wei)revert();returnfalse;}
+
+ruleId: SOLIDITY_VISIBILITY
+patternId: 910067
+severity: 1
+line: 29
+column: 4
+content: functiontransferTokens(address_spender,uint_value)returns(boolsuccess){if(_value<20wei)revert();}
+
+ruleId: SOLIDITY_VISIBILITY
+patternId: 910067
+severity: 1
+line: 32
+column: 4
+content: functionapprove(address_to,uint256_value)returns(bool);
+
+SOLIDITY_VISIBILITY :7
+SOLIDITY_ERC20_FUNCTIONS_ALWAYS_RETURN_FALSE :3
+SOLIDITY_DEPRECATED_CONSTRUCTIONS :1
+SOLIDITY_REVERT_REQUIRE :3
+SOLIDITY_FUNCTIONS_RETURNS_TYPE_AND_NO_RETURN :3
+SOLIDITY_ERC20_APPROVE :1
+
+```