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Version: v1.4

The blob Contract

The blob contract is one of the core contracts on each IOTA Smart Contracts chain.

The objective of the blob contract is to maintain an on-chain registry of blobs. A blob is a collection of named chunks of binary data.

<fieldName1>: <binaryChunk1>
<fieldName2>: <binaryChunk2>
...
<fieldNameN>: <binaryChunkN>

Both names and chunks are arbitrarily long byte slices.

Blobs can be used to store arbitrary data like, for example, a collection of Wasm binaries needed to deploy a smart contract.

Each blob in the registry is referenced by its hash. The hash is deterministically calculated from the concatenation of all pieces:

blobHash = hash( fieldName1 || binaryChunk1 || fieldName2 || binaryChunk2 || ... || fieldNameN || binaryChunkN)

Usually, field names are short strings, but their interpretation is use-case specific.

Two predefined field names are interpreted by the VM while deploying smart contracts from binary:

  • fieldname = "v" is interpreted as the VM type.
  • fieldname = "p" is interpreted as the smart contract program binary.

If the field "v" is equal to the string "wasmtime", the binary chunk of "p" is interpreted as WebAssembly binary, executable by the Wasmtime interpreter.

The blob describing a smart contract may contain extra fields (ignored by the VM), for example:

"v" : VM type
"p" : smart contract program binary
"d" : data schema for data exchange between smart contract and outside sources and consumers
"s" : program sources in .zip format

Entry Points​

storeBlob()​

Stores a new blob in the registry.

Parameters​

The key/value pairs of the received parameters are interpreted as the field/chunk pairs of the blob.

Returns​

  • hash ([32]byte): The hash of the stored blob.

Views​

getBlobInfo(hash BlobHash)​

Returns the size of each chunk of the blob.

Parameters​

  • hash ([32]byte): The hash of the blob.

Returns​

<fieldName1>: <size of the dataChunk1> (uint32)
...
<fieldNameN>: <size of the dataChunkN> (uint32)

getBlobField(hash BlobHash, field BlobField)​

Returns the chunk associated with the given blob field name.

Parameters​

  • hash ([32]byte): The hash of the blob.
  • field ([]byte): The field name.

Returns​

  • bytes ([]byte): The chunk associated with the given field name.

listBlobs()​

Returns a list of pairs blob hash: total size of chunks (uint32) for all blobs in the registry.