asset: update documentation and fix Create/Renew

Both Create and Renew have things returned from them.

pkg/interop/asset/asset.go

@@ -1,53 +1,97 @@
+/*
+Package asset provides functions to work with regular UTXO assets (like NEO or GAS).
+Mostly these are getters for Asset structure, but you can also create new assets
+and renew them (although it's recommended to use NEP-5 standard for new tokens).
+*/
 package asset
 
-// Package asset provides function signatures that can be used inside
-// smart contracts that are written in the neo-go framework.
-
-// Asset stubs a NEO asset type.
+// Asset represents NEO asset type that is used in interop functions, it's
+// an opaque data structure that you can get data from only using functions from
+// this package. It's similar in function to the Asset class in the Neo .net
+// framework. To be able to use it you either need to get an existing Asset via
+// blockchain.GetAsset function or create a new one via Create.
 type Asset struct{}
 
-// GetAssetID returns the id of the given asset.
+// GetAssetID returns ID (256-bit ID of Register transaction for this asset in BE
+// representation) of the given asset. It uses `Neo.Asset.GetAssetId` syscall
+// internally.
 func GetAssetID(a Asset) []byte {
 	return nil
 }
 
-// GetAssetType returns the type of the given asset.
+// GetAssetType returns type of the given asset as a byte value. The value
+// returned can be interpreted as a bit field with the following meaning:
+//     CreditFlag = 0x40
+//     DutyFlag = 0x80
+//     SystemShare = 0x00
+//     SystemCoin = 0x01
+//     Currency = 0x08
+//     Share = DutyFlag | 0x10
+//     Invoice = DutyFlag | 0x18
+//     Token = CreditFlag | 0x20
+// It uses `Neo.Asset.GetAssetType` syscall internally.
 func GetAssetType(a Asset) byte {
 	return 0x00
 }
 
-// GetAmount returns the amount of the given asset.
+// GetAmount returns the total amount of the given asset as an integer
+// multiplied by 10⁸. This value is the maximum possible circulating quantity of
+// Asset. The function uses `Neo.Asset.GetAmount` syscall internally.
 func GetAmount(a Asset) int {
 	return 0
 }
 
-// GetAvailable returns the available of the given asset.
+// GetAvailable returns the amount of Asset currently available on the
+// blockchain. It uses the same encoding as the result of GetAmount and its
+// value can never exceed the value returned by GetAmount. This function uses
+// `Neo.Asset.GetAvailable` syscall internally.
 func GetAvailable(a Asset) int {
 	return 0
 }
 
-// GetPrecision returns the precision of the given asset.
+// GetPrecision returns precision of the given Asset. It uses
+// `Neo.Asset.GetPrecision` syscall internally.
 func GetPrecision(a Asset) byte {
 	return 0x00
 }
 
-// GetOwner returns the owner of the given asset.
+// GetOwner returns the owner of the given Asset. It's represented as a
+// serialized (in compressed form) public key (33 bytes long). This function
+// uses `Neo.Asset.GetOwner` syscall internally.
 func GetOwner(a Asset) []byte {
 	return nil
 }
 
-// GetAdmin returns the admin of the given asset.
+// GetAdmin returns the admin of the given Asset represented as a 160 bit hash
+// in BE form (contract script hash). Admin can modify attributes of this Asset.
+// This function uses `Neo.Asset.GetAdmin` syscall internally.
 func GetAdmin(a Asset) []byte {
 	return nil
 }
 
-// GetIssuer returns the issuer of the given asset.
+// GetIssuer returns the issuer of the given Asset represented as a 160 bit hash
+// in BE form (contract script hash). Issuer can issue new tokens for this Asset.
+// This function uses `Neo.Asset.GetIssuer` syscall internally.
 func GetIssuer(a Asset) []byte {
 	return nil
 }
 
-// Create registers a new asset on the blockchain.
-func Create(assetType byte, name string, amount int, precision byte, owner, admin, issuer []byte) {}
+// Create registers a new asset on the blockchain (similar to old Register
+// transaction). `assetType` parameter has the same set of possible values as
+// GetAssetType result, `amount` must be multiplied by 10⁸, `precision` limits
+// the smallest possible amount of new Asset to 10⁻ⁿ (where n is precision which
+// can't exceed 8), `owner` is a public key of the owner in compressed serialized
+// form (33 bytes), `admin` and `issuer` should be represented as 20-byte slices
+// storing 160-bit hash in BE form. Created Asset is set to expire in one year,
+// so you need to renew it in time. If successful, this function returns a new
+// Asset. It uses `Neo.Asset.Create` syscall internally.
+func Create(assetType byte, name string, amount int, precision byte, owner, admin, issuer []byte) Asset {
+	return Asset{}
+}
 
-// Renew renews the existence of an asset by the given years.
-func Renew(asset Asset, years int) {}
+// Renew renews (make available for use) existing asset by the specified number
+// of years. It returns the last block number when this asset will be active.
+// It uses `Neo.Asset.Renew` syscall internally.
+func Renew(asset Asset, years int) int {
+	return 0
+}