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# Tendermint Encoding (Pre-Amino) |
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## PubKeys and Addresses |
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PubKeys are prefixed with a type-byte, followed by the raw bytes of the public |
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key. |
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Two keys are supported with the following type bytes: |
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``` |
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TypeByteEd25519 = 0x1 |
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TypeByteSecp256k1 = 0x2 |
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``` |
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``` |
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// TypeByte: 0x1 |
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type PubKeyEd25519 [32]byte |
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func (pub PubKeyEd25519) Encode() []byte { |
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return 0x1 | pub |
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} |
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func (pub PubKeyEd25519) Address() []byte { |
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// NOTE: the length (0x0120) is also included |
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return RIPEMD160(0x1 | 0x0120 | pub) |
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} |
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// TypeByte: 0x2 |
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// NOTE: OpenSSL compressed pubkey (x-cord with 0x2 or 0x3) |
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type PubKeySecp256k1 [33]byte |
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func (pub PubKeySecp256k1) Encode() []byte { |
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return 0x2 | pub |
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} |
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func (pub PubKeySecp256k1) Address() []byte { |
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return RIPEMD160(SHA256(pub)) |
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} |
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``` |
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See https://github.com/tendermint/go-crypto/blob/v0.5.0/pub_key.go for more. |
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## Binary Serialization (go-wire) |
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Tendermint aims to encode data structures in a manner similar to how the corresponding Go structs |
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are laid out in memory. |
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Variable length items are length-prefixed. |
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While the encoding was inspired by Go, it is easily implemented in other languages as well, given its intuitive design. |
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XXX: This is changing to use real varints and 4-byte-prefixes. |
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See https://github.com/tendermint/go-wire/tree/sdk2. |
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### Fixed Length Integers |
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Fixed length integers are encoded in Big-Endian using the specified number of bytes. |
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So `uint8` and `int8` use one byte, `uint16` and `int16` use two bytes, |
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`uint32` and `int32` use 3 bytes, and `uint64` and `int64` use 4 bytes. |
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Negative integers are encoded via twos-complement. |
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Examples: |
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```go |
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encode(uint8(6)) == [0x06] |
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encode(uint32(6)) == [0x00, 0x00, 0x00, 0x06] |
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encode(int8(-6)) == [0xFA] |
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encode(int32(-6)) == [0xFF, 0xFF, 0xFF, 0xFA] |
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``` |
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### Variable Length Integers |
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Variable length integers are encoded as length-prefixed Big-Endian integers. |
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The length-prefix consists of a single byte and corresponds to the length of the encoded integer. |
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Negative integers are encoded by flipping the leading bit of the length-prefix to a `1`. |
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Zero is encoded as `0x00`. It is not length-prefixed. |
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Examples: |
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```go |
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encode(uint(6)) == [0x01, 0x06] |
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encode(uint(70000)) == [0x03, 0x01, 0x11, 0x70] |
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encode(int(-6)) == [0xF1, 0x06] |
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encode(int(-70000)) == [0xF3, 0x01, 0x11, 0x70] |
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encode(int(0)) == [0x00] |
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``` |
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### Strings |
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An encoded string is length-prefixed followed by the underlying bytes of the string. |
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The length-prefix is itself encoded as an `int`. |
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The empty string is encoded as `0x00`. It is not length-prefixed. |
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Examples: |
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```go |
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encode("") == [0x00] |
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encode("a") == [0x01, 0x01, 0x61] |
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encode("hello") == [0x01, 0x05, 0x68, 0x65, 0x6C, 0x6C, 0x6F] |
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encode("¥") == [0x01, 0x02, 0xC2, 0xA5] |
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``` |
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### Arrays (fixed length) |
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An encoded fix-lengthed array is the concatenation of the encoding of its elements. |
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There is no length-prefix. |
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Examples: |
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```go |
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encode([4]int8{1, 2, 3, 4}) == [0x01, 0x02, 0x03, 0x04] |
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encode([4]int16{1, 2, 3, 4}) == [0x00, 0x01, 0x00, 0x02, 0x00, 0x03, 0x00, 0x04] |
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encode([4]int{1, 2, 3, 4}) == [0x01, 0x01, 0x01, 0x02, 0x01, 0x03, 0x01, 0x04] |
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encode([2]string{"abc", "efg"}) == [0x01, 0x03, 0x61, 0x62, 0x63, 0x01, 0x03, 0x65, 0x66, 0x67] |
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``` |
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### Slices (variable length) |
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An encoded variable-length array is length-prefixed followed by the concatenation of the encoding of |
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its elements. |
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The length-prefix is itself encoded as an `int`. |
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An empty slice is encoded as `0x00`. It is not length-prefixed. |
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Examples: |
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```go |
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encode([]int8{}) == [0x00] |
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encode([]int8{1, 2, 3, 4}) == [0x01, 0x04, 0x01, 0x02, 0x03, 0x04] |
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encode([]int16{1, 2, 3, 4}) == [0x01, 0x04, 0x00, 0x01, 0x00, 0x02, 0x00, 0x03, 0x00, 0x04] |
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encode([]int{1, 2, 3, 4}) == [0x01, 0x04, 0x01, 0x01, 0x01, 0x02, 0x01, 0x03, 0x01, 0x4] |
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encode([]string{"abc", "efg"}) == [0x01, 0x02, 0x01, 0x03, 0x61, 0x62, 0x63, 0x01, 0x03, 0x65, 0x66, 0x67] |
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``` |
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### BitArray |
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BitArray is encoded as an `int` of the number of bits, and with an array of `uint64` to encode |
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value of each array element. |
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```go |
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type BitArray struct { |
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Bits int |
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Elems []uint64 |
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} |
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``` |
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### Time |
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Time is encoded as an `int64` of the number of nanoseconds since January 1, 1970, |
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rounded to the nearest millisecond. |
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Times before then are invalid. |
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Examples: |
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```go |
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encode(time.Time("Jan 1 00:00:00 UTC 1970")) == [0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00] |
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encode(time.Time("Jan 1 00:00:01 UTC 1970")) == [0x00, 0x00, 0x00, 0x00, 0x3B, 0x9A, 0xCA, 0x00] // 1,000,000,000 ns |
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encode(time.Time("Mon Jan 2 15:04:05 -0700 MST 2006")) == [0x0F, 0xC4, 0xBB, 0xC1, 0x53, 0x03, 0x12, 0x00] |
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``` |
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### Structs |
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An encoded struct is the concatenation of the encoding of its elements. |
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There is no length-prefix. |
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Examples: |
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```go |
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type MyStruct struct{ |
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A int |
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B string |
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C time.Time |
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} |
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encode(MyStruct{4, "hello", time.Time("Mon Jan 2 15:04:05 -0700 MST 2006")}) == |
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[0x01, 0x04, 0x01, 0x05, 0x68, 0x65, 0x6C, 0x6C, 0x6F, 0x0F, 0xC4, 0xBB, 0xC1, 0x53, 0x03, 0x12, 0x00] |
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``` |
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## Merkle Trees |
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Simple Merkle trees are used in numerous places in Tendermint to compute a cryptographic digest of a data structure. |
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RIPEMD160 is always used as the hashing function. |
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The function `SimpleMerkleRoot` is a simple recursive function defined as follows: |
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```go |
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func SimpleMerkleRoot(hashes [][]byte) []byte{ |
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switch len(hashes) { |
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case 0: |
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return nil |
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case 1: |
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return hashes[0] |
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default: |
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left := SimpleMerkleRoot(hashes[:(len(hashes)+1)/2]) |
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right := SimpleMerkleRoot(hashes[(len(hashes)+1)/2:]) |
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return RIPEMD160(append(left, right)) |
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} |
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} |
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``` |
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Note: we abuse notion and call `SimpleMerkleRoot` with arguments of type `struct` or type `[]struct`. |
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For `struct` arguments, we compute a `[][]byte` by sorting elements of the `struct` according to |
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field name and then hashing them. |
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For `[]struct` arguments, we compute a `[][]byte` by hashing the individual `struct` elements. |
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## JSON (TMJSON) |
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Signed messages (eg. votes, proposals) in the consensus are encoded in TMJSON, rather than TMBIN. |
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TMJSON is JSON where `[]byte` are encoded as uppercase hex, rather than base64. |
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When signing, the elements of a message are sorted by key and the sorted message is embedded in an |
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outer JSON that includes a `chain_id` field. |
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We call this encoding the CanonicalSignBytes. For instance, CanonicalSignBytes for a vote would look |
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like: |
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```json |
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{"chain_id":"my-chain-id","vote":{"block_id":{"hash":DEADBEEF,"parts":{"hash":BEEFDEAD,"total":3}},"height":3,"round":2,"timestamp":1234567890, "type":2} |
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``` |
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Note how the fields within each level are sorted. |
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## Other |
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### MakeParts |
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Encode an object using TMBIN and slice it into parts. |
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```go |
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MakeParts(object, partSize) |
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``` |
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### Part |
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```go |
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type Part struct { |
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Index int |
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Bytes byte[] |
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Proof byte[] |
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} |
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``` |