mirror of
https://github.com/ethereum/solidity
synced 2023-10-03 13:03:40 +00:00
Promote metadata to its own chapter (split from miscellaneous)
This commit is contained in:
parent
fbe24da159
commit
b1a7281ee9
@ -144,6 +144,7 @@ Contents
|
||||
solidity-in-depth.rst
|
||||
security-considerations.rst
|
||||
using-the-compiler.rst
|
||||
metadata.rst
|
||||
abi-spec.rst
|
||||
style-guide.rst
|
||||
common-patterns.rst
|
||||
|
144
docs/metadata.rst
Normal file
144
docs/metadata.rst
Normal file
@ -0,0 +1,144 @@
|
||||
#################
|
||||
Contract Metadata
|
||||
#################
|
||||
|
||||
.. index:: metadata, contract verification
|
||||
|
||||
The Solidity compiler automatically generates a JSON file, the
|
||||
contract metadata, that contains information about the current contract.
|
||||
It can be used to query the compiler version, the sources used, the ABI
|
||||
and NatSpec documentation in order to more safely interact with the contract
|
||||
and to verify its source code.
|
||||
|
||||
The compiler appends a Swarm hash of the metadata file to the end of the
|
||||
bytecode (for details, see below) of each contract, so that you can retrieve
|
||||
the file in an authenticated way without having to resort to a centralized
|
||||
data provider.
|
||||
|
||||
Of course, you have to publish the metadata file to Swarm (or some other service)
|
||||
so that others can access it. The file can be output by using ``solc --metadata``
|
||||
and the file will be called ``ContractName_meta.json``.
|
||||
It will contain Swarm references to the source code, so you have to upload
|
||||
all source files and the metadata file.
|
||||
|
||||
The metadata file has the following format. The example below is presented in a
|
||||
human-readable way. Properly formatted metadata should use quotes correctly,
|
||||
reduce whitespace to a minimum and sort the keys of all objects to arrive at a
|
||||
unique formatting.
|
||||
Comments are of course also not permitted and used here only for explanatory purposes.
|
||||
|
||||
.. code-block:: none
|
||||
|
||||
{
|
||||
// Required: The version of the metadata format
|
||||
version: "1",
|
||||
// Required: Source code language, basically selects a "sub-version"
|
||||
// of the specification
|
||||
language: "Solidity",
|
||||
// Required: Details about the compiler, contents are specific
|
||||
// to the language.
|
||||
compiler: {
|
||||
// Required for Solidity: Version of the compiler
|
||||
version: "0.4.6+commit.2dabbdf0.Emscripten.clang",
|
||||
// Optional: Hash of the compiler binary which produced this output
|
||||
keccak256: "0x123..."
|
||||
},
|
||||
// Required: Compilation source files/source units, keys are file names
|
||||
sources:
|
||||
{
|
||||
"myFile.sol": {
|
||||
// Required: keccak256 hash of the source file
|
||||
"keccak256": "0x123...",
|
||||
// Required (unless "content" is used, see below): Sorted URL(s)
|
||||
// to the source file, protocol is more or less arbitrary, but a
|
||||
// Swarm URL is recommended
|
||||
"urls": [ "bzzr://56ab..." ]
|
||||
},
|
||||
"mortal": {
|
||||
// Required: keccak256 hash of the source file
|
||||
"keccak256": "0x234...",
|
||||
// Required (unless "url" is used): literal contents of the source file
|
||||
"content": "contract mortal is owned { function kill() { if (msg.sender == owner) selfdestruct(owner); } }"
|
||||
}
|
||||
},
|
||||
// Required: Compiler settings
|
||||
settings:
|
||||
{
|
||||
// Required for Solidity: Sorted list of remappings
|
||||
remappings: [ ":g/dir" ],
|
||||
// Optional: Optimizer settings (enabled defaults to false)
|
||||
optimizer: {
|
||||
enabled: true,
|
||||
runs: 500
|
||||
},
|
||||
// Required for Solidity: File and name of the contract or library this
|
||||
// metadata is created for.
|
||||
compilationTarget: {
|
||||
"myFile.sol": "MyContract"
|
||||
},
|
||||
// Required for Solidity: Addresses for libraries used
|
||||
libraries: {
|
||||
"MyLib": "0x123123..."
|
||||
}
|
||||
},
|
||||
// Required: Generated information about the contract.
|
||||
output:
|
||||
{
|
||||
// Required: ABI definition of the contract
|
||||
abi: [ ... ],
|
||||
// Required: NatSpec user documentation of the contract
|
||||
userdoc: [ ... ],
|
||||
// Required: NatSpec developer documentation of the contract
|
||||
devdoc: [ ... ],
|
||||
}
|
||||
}
|
||||
|
||||
.. note::
|
||||
Note the ABI definition above has no fixed order. It can change with compiler versions.
|
||||
|
||||
.. note::
|
||||
Since the bytecode of the resulting contract contains the metadata hash, any change to
|
||||
the metadata will result in a change of the bytecode. Furthermore, since the metadata
|
||||
includes a hash of all the sources used, a single whitespace change in any of the source
|
||||
codes will result in a different metadata, and subsequently a different bytecode.
|
||||
|
||||
Encoding of the Metadata Hash in the Bytecode
|
||||
=============================================
|
||||
|
||||
Because we might support other ways to retrieve the metadata file in the future,
|
||||
the mapping ``{"bzzr0": <Swarm hash>}`` is stored
|
||||
`CBOR <https://tools.ietf.org/html/rfc7049>`_-encoded. Since the beginning of that
|
||||
encoding is not easy to find, its length is added in a two-byte big-endian
|
||||
encoding. The current version of the Solidity compiler thus adds the following
|
||||
to the end of the deployed bytecode::
|
||||
|
||||
0xa1 0x65 'b' 'z' 'z' 'r' '0' 0x58 0x20 <32 bytes swarm hash> 0x00 0x29
|
||||
|
||||
So in order to retrieve the data, the end of the deployed bytecode can be checked
|
||||
to match that pattern and use the Swarm hash to retrieve the file.
|
||||
|
||||
Usage for Automatic Interface Generation and NatSpec
|
||||
====================================================
|
||||
|
||||
The metadata is used in the following way: A component that wants to interact
|
||||
with a contract (e.g. Mist) retrieves the code of the contract, from that
|
||||
the Swarm hash of a file which is then retrieved.
|
||||
That file is JSON-decoded into a structure like above.
|
||||
|
||||
The component can then use the ABI to automatically generate a rudimentary
|
||||
user interface for the contract.
|
||||
|
||||
Furthermore, Mist can use the userdoc to display a confirmation message to the user
|
||||
whenever they interact with the contract.
|
||||
|
||||
Usage for Source Code Verification
|
||||
==================================
|
||||
|
||||
In order to verify the compilation, sources can be retrieved from Swarm
|
||||
via the link in the metadata file.
|
||||
The compiler of the correct version (which is checked to be part of the "official" compilers)
|
||||
is invoked on that input with the specified settings. The resulting
|
||||
bytecode is compared to the data of the creation transaction or ``CREATE`` opcode data.
|
||||
This automatically verifies the metadata since its hash is part of the bytecode.
|
||||
Excess data corresponds to the constructor input data, which should be decoded
|
||||
according to the interface and presented to the user.
|
@ -221,150 +221,6 @@ This means the following source mappings represent the same information:
|
||||
|
||||
``1:2:1;:9;2::2;;``
|
||||
|
||||
*****************
|
||||
Contract Metadata
|
||||
*****************
|
||||
|
||||
The Solidity compiler automatically generates a JSON file, the
|
||||
contract metadata, that contains information about the current contract.
|
||||
It can be used to query the compiler version, the sources used, the ABI
|
||||
and NatSpec documentation in order to more safely interact with the contract
|
||||
and to verify its source code.
|
||||
|
||||
The compiler appends a Swarm hash of the metadata file to the end of the
|
||||
bytecode (for details, see below) of each contract, so that you can retrieve
|
||||
the file in an authenticated way without having to resort to a centralized
|
||||
data provider.
|
||||
|
||||
Of course, you have to publish the metadata file to Swarm (or some other service)
|
||||
so that others can access it. The file can be output by using ``solc --metadata``
|
||||
and the file will be called ``ContractName_meta.json``.
|
||||
It will contain Swarm references to the source code, so you have to upload
|
||||
all source files and the metadata file.
|
||||
|
||||
The metadata file has the following format. The example below is presented in a
|
||||
human-readable way. Properly formatted metadata should use quotes correctly,
|
||||
reduce whitespace to a minimum and sort the keys of all objects to arrive at a
|
||||
unique formatting.
|
||||
Comments are of course also not permitted and used here only for explanatory purposes.
|
||||
|
||||
.. code-block:: none
|
||||
|
||||
{
|
||||
// Required: The version of the metadata format
|
||||
version: "1",
|
||||
// Required: Source code language, basically selects a "sub-version"
|
||||
// of the specification
|
||||
language: "Solidity",
|
||||
// Required: Details about the compiler, contents are specific
|
||||
// to the language.
|
||||
compiler: {
|
||||
// Required for Solidity: Version of the compiler
|
||||
version: "0.4.6+commit.2dabbdf0.Emscripten.clang",
|
||||
// Optional: Hash of the compiler binary which produced this output
|
||||
keccak256: "0x123..."
|
||||
},
|
||||
// Required: Compilation source files/source units, keys are file names
|
||||
sources:
|
||||
{
|
||||
"myFile.sol": {
|
||||
// Required: keccak256 hash of the source file
|
||||
"keccak256": "0x123...",
|
||||
// Required (unless "content" is used, see below): Sorted URL(s)
|
||||
// to the source file, protocol is more or less arbitrary, but a
|
||||
// Swarm URL is recommended
|
||||
"urls": [ "bzzr://56ab..." ]
|
||||
},
|
||||
"mortal": {
|
||||
// Required: keccak256 hash of the source file
|
||||
"keccak256": "0x234...",
|
||||
// Required (unless "url" is used): literal contents of the source file
|
||||
"content": "contract mortal is owned { function kill() { if (msg.sender == owner) selfdestruct(owner); } }"
|
||||
}
|
||||
},
|
||||
// Required: Compiler settings
|
||||
settings:
|
||||
{
|
||||
// Required for Solidity: Sorted list of remappings
|
||||
remappings: [ ":g/dir" ],
|
||||
// Optional: Optimizer settings (enabled defaults to false)
|
||||
optimizer: {
|
||||
enabled: true,
|
||||
runs: 500
|
||||
},
|
||||
// Required for Solidity: File and name of the contract or library this
|
||||
// metadata is created for.
|
||||
compilationTarget: {
|
||||
"myFile.sol": "MyContract"
|
||||
},
|
||||
// Required for Solidity: Addresses for libraries used
|
||||
libraries: {
|
||||
"MyLib": "0x123123..."
|
||||
}
|
||||
},
|
||||
// Required: Generated information about the contract.
|
||||
output:
|
||||
{
|
||||
// Required: ABI definition of the contract
|
||||
abi: [ ... ],
|
||||
// Required: NatSpec user documentation of the contract
|
||||
userdoc: [ ... ],
|
||||
// Required: NatSpec developer documentation of the contract
|
||||
devdoc: [ ... ],
|
||||
}
|
||||
}
|
||||
|
||||
.. note::
|
||||
Note the ABI definition above has no fixed order. It can change with compiler versions.
|
||||
|
||||
.. note::
|
||||
Since the bytecode of the resulting contract contains the metadata hash, any change to
|
||||
the metadata will result in a change of the bytecode. Furthermore, since the metadata
|
||||
includes a hash of all the sources used, a single whitespace change in any of the source
|
||||
codes will result in a different metadata, and subsequently a different bytecode.
|
||||
|
||||
Encoding of the Metadata Hash in the Bytecode
|
||||
=============================================
|
||||
|
||||
Because we might support other ways to retrieve the metadata file in the future,
|
||||
the mapping ``{"bzzr0": <Swarm hash>}`` is stored
|
||||
`CBOR <https://tools.ietf.org/html/rfc7049>`_-encoded. Since the beginning of that
|
||||
encoding is not easy to find, its length is added in a two-byte big-endian
|
||||
encoding. The current version of the Solidity compiler thus adds the following
|
||||
to the end of the deployed bytecode::
|
||||
|
||||
0xa1 0x65 'b' 'z' 'z' 'r' '0' 0x58 0x20 <32 bytes swarm hash> 0x00 0x29
|
||||
|
||||
So in order to retrieve the data, the end of the deployed bytecode can be checked
|
||||
to match that pattern and use the Swarm hash to retrieve the file.
|
||||
|
||||
Usage for Automatic Interface Generation and NatSpec
|
||||
====================================================
|
||||
|
||||
The metadata is used in the following way: A component that wants to interact
|
||||
with a contract (e.g. Mist) retrieves the code of the contract, from that
|
||||
the Swarm hash of a file which is then retrieved.
|
||||
That file is JSON-decoded into a structure like above.
|
||||
|
||||
The component can then use the ABI to automatically generate a rudimentary
|
||||
user interface for the contract.
|
||||
|
||||
Furthermore, Mist can use the userdoc to display a confirmation message to the user
|
||||
whenever they interact with the contract.
|
||||
|
||||
Usage for Source Code Verification
|
||||
==================================
|
||||
|
||||
In order to verify the compilation, sources can be retrieved from Swarm
|
||||
via the link in the metadata file.
|
||||
The compiler of the correct version (which is checked to be part of the "official" compilers)
|
||||
is invoked on that input with the specified settings. The resulting
|
||||
bytecode is compared to the data of the creation transaction or ``CREATE`` opcode data.
|
||||
This automatically verifies the metadata since its hash is part of the bytecode.
|
||||
Excess data corresponds to the constructor input data, which should be decoded
|
||||
according to the interface and presented to the user.
|
||||
|
||||
|
||||
***************
|
||||
Tips and Tricks
|
||||
***************
|
||||
|
Loading…
Reference in New Issue
Block a user