153 lines
4.2 KiB
Markdown
153 lines
4.2 KiB
Markdown
---
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id: tezos-specific
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title: Tezos Domain-Specific Operations
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---
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LIGO is a programming language for writing Tezos smart contracts. It
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would be a little odd if it did not have any Tezos specific
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functions. This page will tell you about them.
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## Pack and Unpack
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Michelson provides the `PACK` and `UNPACK` instructions for data
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serialization. The instruction `PACK` converts Michelson data
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structures into a binary format, and `UNPACK` reverses that
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transformation. This functionality can be accessed from within LIGO.
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> ⚠️ `PACK` and `UNPACK` are Michelson instructions that are intended
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> to be used by people that really know what they are doing. There are
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> several risks and failure cases, such as unpacking a lambda from an
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> untrusted source, and most of which are beyond the scope of this
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> document. Do not use these functions without doing your homework
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> first.
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<!--DOCUSAURUS_CODE_TABS-->
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<!--PascaLIGO-->
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```pascaligo group=a
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function id_string (const p : string) : option (string) is block {
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const packed : bytes = bytes_pack (p)
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} with (bytes_unpack (packed): option (string))
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```
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<!--CameLIGO-->
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```cameligo group=a
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let id_string (p : string) : string option =
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let packed: bytes = Bytes.pack p in
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(Bytes.unpack packed : string option)
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```
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<!--ReasonLIGO-->
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```reasonligo group=a
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let id_string = (p : string) : option (string) => {
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let packed : bytes = Bytes.pack (p);
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(Bytes.unpack(packed) : option (string));
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};
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```
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<!--END_DOCUSAURUS_CODE_TABS-->
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## Hashing Keys
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It is often desirable to hash a public key. In Michelson, certain data
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structures such as maps will not allow the use of the `key` type. Even
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if this were not the case, hashes are much smaller than keys, and
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storage on blockchains comes at a cost premium. You can hash keys with
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a predefined functions returning a value of type `key_hash`.
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<!--DOCUSAURUS_CODE_TABS-->
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<!--PascaLIGO-->
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```pascaligo group=b
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function check_hash_key (const kh1 : key_hash; const k2 : key) : bool * key_hash is
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block {
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var ret : bool := False;
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var kh2 : key_hash := crypto_hash_key (k2);
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if kh1 = kh2 then ret := True else skip
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} with (ret, kh2)
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```
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<!--CameLIGO-->
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```cameligo group=b
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let check_hash_key (kh1, k2 : key_hash * key) : bool * key_hash =
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let kh2 : key_hash = Crypto.hash_key k2 in
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if kh1 = kh2 then true, kh2 else false, kh2
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```
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<!--ReasonLIGO-->
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```reasonligo group=b
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let check_hash_key = ((kh1, k2) : (key_hash, key)) : (bool, key_hash) => {
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let kh2 : key_hash = Crypto.hash_key(k2);
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if (kh1 == kh2) { (true, kh2); } else { (false, kh2); }
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};
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```
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<!--END_DOCUSAURUS_CODE_TABS-->
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## Checking Signatures
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Sometimes a contract will want to check that a message has been signed
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by a particular key. For example, a point-of-sale system might want a
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customer to sign a transaction so it can be processed
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asynchronously. You can do this in LIGO using the `key` and
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`signature` types.
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> ⚠️ There is no way to *generate* a signed message in LIGO. This is
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> because that would require storing a private key on chain, at which
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> point it is not... private anymore.
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<!--DOCUSAURUS_CODE_TABS-->
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<!--PascaLIGO-->
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```pascaligo group=c
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function check_signature
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(const pk : key;
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const signed : signature;
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const msg : bytes) : bool
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is crypto_check (pk, signed, msg)
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```
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<!--CameLIGO-->
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```cameligo group=c
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let check_signature (pk, signed, msg : key * signature * bytes) : bool =
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Crypto.check pk signed msg
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```
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<!--ReasonLIGO-->
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```reasonligo group=c
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let check_signature =
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((pk, signed, msg) : (key, signature, bytes)) : bool => {
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Crypto.check (pk, signed, msg);
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};
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```
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<!--END_DOCUSAURUS_CODE_TABS-->
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## Contract's Own Address
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Often you want to get the address of the contract being executed. You
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can do it with `self_address`.
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> ⚠️ Due to limitations in Michelson, `self_address` in a contract is
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> only allowed at the entrypoint level, that is, at the
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> top-level. Using it in an embedded function will cause an error.
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<!--DOCUSAURUS_CODE_TABS-->
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<!--PascaLIGO-->
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```pascaligo group=d
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const current_addr : address = self_address
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```
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<!--CameLIGO-->
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```cameligo group=d
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let current_addr : address = Current.self_address
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```
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<!--ReasonLIGO-->
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```reasonligo group=d
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let current_addr : address = Current.self_address;
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```
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<!--END_DOCUSAURUS_CODE_TABS-->
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