Improve documentation of error codes

docs/error_codes.md

@@ -1,42 +1,108 @@
 ## Error codes
 
 ### General init related
-- `GS000`: `Could not finish initialization`
-- `GS001`: `Threshold needs to be defined`
+- **GS000: Could not finish initialization**
+
+- **GS001: Threshold needs to be defined**   
+Threshold is `equal to zero`, some error could happen during the Safe setup.
 
 ### General gas/ execution related
-- `GS010`: `Not enough gas to execute Safe transaction`
-- `GS011`: `Could not pay gas costs with ether`
-- `GS012`: `Could not pay gas costs with token`
-- `GS013`: `Safe transaction failed when gasPrice and safeTxGas were 0`
+- **GS010: Not enough gas to execute Safe transaction**  
+SafeTxGas is too high or gas limit is too low to execute the transaction, keep in mind that we require some gas, at least `2500` is needed for events and at least `500` to perform code until execution.  
+
+- **GS011: Could not pay gas costs with ether**   
+There are not enough funds of `ether` to execute the transaction.   
+Make sure that you have enough funds of `ether` or choose other token with enough funds setting it in `gasToken`.  
+
+- **GS012: Could not pay gas costs with token**  
+There are not enough funds of the token choosen on `gasToken` to execute the transaction.      
+Make sure you have enough of the gasToken or set it to `address(0)` if you want use ether.  
+
+- **GS013: Safe transaction failed when gasPrice and safeTxGas were 0**  
+Transaction is not succesful, this could be for due to multiple reasons.
 
 ### General signature validation related
-- `GS020`: `Signatures data too short`
-- `GS021`: `Invalid contract signature location: inside static part`
-- `GS022`: `Invalid contract signature location: length not present`
-- `GS023`: `Invalid contract signature location: data not complete`
-- `GS024`: `Invalid contract signature provided`
-- `GS025`: `Hash has not been approved`
-- `GS026`: `Invalid owner provided`
+- **GS020: Signatures data too short**  
+The length of required signatures is less than 65*threeshold.
+Each signature has a constant length of 65 bytes `{32-bytes r}{32-bytes s}{1-byte v}`. If more data is necessary it can be appended to the end. 
+More information about signatures:   
+https://docs.gnosis-safe.io/contracts/signatures
+
+- **GS021: Invalid contract signature location:** inside static part  
+Wrong contract `v=0` signature because `s` value is pointing inside the static part, instead to dynamic part (should point to the corresponding data signature).   
+Review the value of `s` to point to the beginning of the correct signature.  
+More information about signatures:  
+https://docs.gnosis-safe.io/contracts/signatures  
+
+- **GS022: Invalid contract signature location:** length not present  
+Wrong contract `v=0` signature because `s` value is greater than the last position of signatures (it's pointing to empty value).   
+Review `s` value points to the correct data signature position or add the missing data signature.   
+More information about contract signature:  
+https://docs.gnosis-safe.io/contracts/signatures  
+
+- **GS023: Invalid contract signature location:** data not complete  
+Wrong contract `v=0` signature because `startingPosition + contractSignatureLen` is out of bounds.   
+
+- **GS024: Invalid contract signature provided**  
+The `EIP-1271` signature provided is wrong.  
+If you don't want to use this type of signature review the `v` value (0 for a contract signature).   
+The `hash` to generate the `signature` must be calculated by the account address provided in `r` value.  
+More information about signatures:  
+https://docs.gnosis-safe.io/contracts/signatures     
+https://eips.ethereum.org/EIPS/eip-1271   
+
+- **GS025: Hash has not been approved**  
+The owner provided on `r` has not pre-approved the safeTxHash.     
+To pre-approve the safeTxHash call `approveHash` with the safeTxHash calculated by the owner.   
+This error could happen also if the nonce has changed and therefore the safeTxHash is different than expected.  
+
+- **GS026: Invalid owner provided**   
+The owner provided doesn't exist for the `Safe`   
+Review that the signing owners are owners of the Safe and signatures are correctly sorted ascending by the owner (without `EIP-55` encoding).
 
 ### General auth related
-- `GS030`: `Only owners can approve a hash`
-- `GS031`: `Method can only be called from this contract`
+- **GS030`: Only owners can approve a hash**  
+The sender is not an owner.   
+Review that a correct owner is being used.   
+
+- **GS031: Method can only be called from this contract**  
 
 ### Module management related
-- `GS100`: `Modules have already been initialized`
-- `GS101`: `Invalid module address provided`
-- `GS102`: `Module has already been added`
-- `GS103`: `Invalid prevModule, module pair provided`
-- `GS104`: `Method can only be called from an enabled module`
+- **GS100: Modules have already been initialized**  
+`setupModules` can only be called once.   
+
+- **GS101: Invalid module address provided**  
+A module address cannot be zero address `address(0)` or sentinel address `address(1)`.    
+
+- **GS102: Module has already been added**   
+
+- **GS103: Invalid prevModule, module pair provided**  
+`prevModule` is not the previous element to `module` in the module list.   
+
+- **GS104: Method can only be called from an enabled module** 
+
 
 ### Owner management related
-- `GS200`: `Owners have already been setup`
-- `GS201`: `Threshold cannot exceed owner count`
-- `GS202`: `Threshold needs to be greater than 0`
-- `GS203`: `Invalid owner address provided`
-- `GS204`: `Address is already an owner`
-- `GS205`: `Invalid prevOwner, owner pair provided`
+- **GS200: Owners have already been setup**   
+`setupOwners` can only be called once.  
+If you want to add, swap or remove an owner use the corresponding method:  
+    - `adOwnerWithThreshold` 
+    - `swapOwner`  
+    - `removeOwner`    
+
+- **GS201: Threshold cannot exceed owner count**   
+Sender is trying to configure a threshold greater than the total of owners or trying to remove an owner when the threshold is equals to the total of owners.   
+
+- **GS202: Threshold needs to be greater than 0**  
+Sender is calling `changeThreshold` with 0.   
+
+- **GS203: Invalid owner address provided**  
+The owner address provided cannot be `address(0)`, sentinel address `address(1)` or the current `safe` address.  
+
+- **GS204: Address is already an owner**  
+
+- **GS205: Invalid prevOwner, owner pair provided**  
+`prevOwner` is not the previous element to `owner` in the owner list.   
 
 ### Guard management related
 - `GS300`: `Guard does not implement IERC165`