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MESSAGE_TYPES.md

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CosmWasm message types

CosmWasm uses JSON to send data from the host to the Wasm contract and to handle results from the Wasm contract. Such JSON messages are created in the client, typically some JavaScript-based application. There the usage of JSON feels very natural for developers. However, JSON has significant limitations such as the lack of a native binary type and inconsistent support for integers > 53 bit. For this reason, the CosmWasm standard library cosmwasm-std ships types that ensure good user experience in JSON. The following table shows both standard Rust types as well as cosmwasm_std types and how they are encoded in JSON.

Rust type JSON type1 Example Note
bool true or false true
u32/i32 number 123
u64/i64 number 123456 Supported in Rust and Go. Other implementations (jq, JavaScript) do not support the full uint64/int64 range.
u128/i128 number 340282366920938463463374607431768211455, -2766523308300312711084346401884294402 Supported in Rust. Other implementations do not support the full range. This used to be serialized as a string in serde-json-wasm. See Dev Note #4: u128/i128 serialization. If you have any code relying on that serialization, switch to Uint128 / Int128.
usize/isize number 123456 🚫 Don't use this type because it has a different size in unit tests (64 bit) and Wasm (32 bit). Also it tends to issue float instructions such that the contracts cannot be uploaded.
String string "foo"
&str string "foo" 🚫 Unsupported since message types must be owned (DeserializeOwned)
Option<T> null or JSON type of T null, {"foo":12}
Vec<T> array of JSON type of T ["one", "two", "three"] (Vec<String>), [true, false] (Vec<bool>)
Vec<u8> array of numbers from 0 to 255 [187, 61, 11, 250] ⚠️ Discouraged as this encoding is not as compact as it can be. See Binary.
struct MyType { … } object {"foo":12}
Uint64/Int64 string containing number "1234321", "-1234321" Used to support full uint64/int64 range in all implementations
Uint128/Int128 string containing number "1234321", "-1234321"
Uint256/Int256 string containing number "1234321", "-1234321"
Uint512/Int512 string containing number "1234321", "-1234321"
Decimal string containing decimal number "55.6584"
Decimal256 string containing decimal number "55.6584"
Binary string containing base64 data "MTIzCg=="
HexBinary string containing hex data "b5d7d24e428c"
Timestamp string containing nanoseconds since epoch "1677687687000000000"
Order string containing order variant "ascending" or "descending"

Footnotes

  1. https://www.json.org/ ↩