Extrinsic Encoding differs from initial value

[infinitedaremo]

Retrieving block 4013570 from Polkadot mainnet. The raw extrinsic hexs are as follows:

extrinsics := []string{
"0x280403000b409716f37701",
"0x450284004e4a383d2cc6653e9ede079e04c7fc951f39a45f8e8a1aabff8b1f3d158c284c018ea351924d3e4af2e0f61ac8ffefe3a8c3f7f80755c24551bd514eafcd25744bec3713fda140643af9efe06a12c96c3307bd0d48bcbb99a7edcd0194c473798e00a103000503008a4b192ab4dbe097774f392ead0727dfc35e2a990a012a1a23e5862f3dc4c5660b00ced62c891d",
"0x450284004e4a383d2cc6653e9ede079e04c7fc951f39a45f8e8a1aabff8b1f3d158c284c01a4c8d5127b6945a6eadf8b6cfd7c745509eba002a46649a476875f5c4e7d490d5d2dfafdc7a378669a919f70a5069907ba9b816a0363ad28906014c1fdb8498200a503000503003da4fdbd80ad23cf5efe767f626f6558e4985f462ecdeafbb91accccdc015be50b00a846b4ae0d",
"0x41028400dc9fb8f1c1f200f8787fd517e74d4d8cc58e73633b8e82cca603181604e6620900ee111f10a7c09f7ab535a8eddcc3919e8963f5f79b7ffaf9b9c3387aafb4ae6c345c1510b4d10e2b620bea7a4e4473a7256966e6752c93d2f2bf90d4ef5ae00215000000050000b2385eab057a2c1a757466642edc4d48d3838a2d3b6b04e92a81c2997656ab4a070037f87e06"}

Once the extrinsic is decoded to the Go struct. Attempting to encode it again gives differing values:

d, _ := extrinsic.MarshalJSON()
fmt.Println(string(d))

"0x280403000b409716f37701"
"0x410284004a383d2cc6653e9ede079e04c7fc951f39a45f8e8a1aabff8b1f3d158c284c018ea351924d3e4af2e0f61ac8ffefe3a8c3f7f80755c24551bd514eafcd25744bec3713fda140643af9efe06a12c96c3307bd0d48bcbb99a7edcd0194c473798e00a103000503008a4b192ab4dbe097774f392ead0727dfc35e2a990a012a1a23e5862f3dc4c5660b00ced62c891d"
"0x410284004a383d2cc6653e9ede079e04c7fc951f39a45f8e8a1aabff8b1f3d158c284c01a4c8d5127b6945a6eadf8b6cfd7c745509eba002a46649a476875f5c4e7d490d5d2dfafdc7a378669a919f70a5069907ba9b816a0363ad28906014c1fdb8498200a503000503003da4fdbd80ad23cf5efe767f626f6558e4985f462ecdeafbb91accccdc015be50b00a846b4ae0d"
"0x3d0284009fb8f1c1f200f8787fd517e74d4d8cc58e73633b8e82cca603181604e6620900ee111f10a7c09f7ab535a8eddcc3919e8963f5f79b7ffaf9b9c3387aafb4ae6c345c1510b4d10e2b620bea7a4e4473a7256966e6752c93d2f2bf90d4ef5ae00215000000050000b2385eab057a2c1a757466642edc4d48d3838a2d3b6b04e92a81c2997656ab4a070037f87e06"

Note the inherent extrinsic is as expected but the first 2nd, 3rd and 9th characters are different.

[infinitedaremo]

I think it could potentiialy be down to this line:

func (e *Extrinsic) Decode(decoder scale.Decoder) error {
	// compact length encoding (1, 2, or 4 bytes) (may not be there for Extrinsics older than Jan 11 2019)
	_, err := decoder.DecodeUintCompact()
	if err != nil {
		return err
	}

There is no corresponding encode for a potential length which would explain why only the start of the value is different.

[mikiquantum]

@infinitedaremo The length is prepended at the end of the function:

go-substrate-rpc-client/types/extrinsic.go

Line 242 in 904cb0b

err = encoder.EncodeUintCompact(*big.NewInt(0).SetUint64(uint64(len(eb))))

The reason why is shorter (missing 5th byte 4e, I believe, is because GSRPC hasn't been updated to use MultiAddresses yet, introduced by paritytech/substrate#7380 and I believe Polkadot is running with them now.

We will support it very soon.

[infinitedaremo]

Thats good to hear. In the mean time. Is there a way to get the original extrinsic hash from the current code?

[mikiquantum]

@infinitedaremo Can you elaborate a bit more on this? Do you mean from each extrinsic encoded above, get the correspondent extrinsic hash id?

[infinitedaremo]

Yes. I couldnt find that data anywhere.

[mikiquantum]

@infinitedaremo I believe is just the blake2b256 of the byte array representation of the extrinsic encoded hex:

        h, err := NewBlake2b256(nil)
	assert.NoError(t, err)
	dd := hexutil.MustDecode("0x450284004e4a383d2cc6653e9ede079e04c7fc951f39a45f8e8a1aabff8b1f3d158c284c018ea351924d3e4af2e0f61ac8ffefe3a8c3f7f80755c24551bd514eafcd25744bec3713fda140643af9efe06a12c96c3307bd0d48bcbb99a7edcd0194c473798e00a103000503008a4b192ab4dbe097774f392ead0727dfc35e2a990a012a1a23e5862f3dc4c5660b00ced62c891d")
	_, err = h.Write(dd)
	assert.NoError(t, err)
	r := h.Sum(nil)
	fmt.Printf("%x\n", r)

[cdamian]

Please re-open another issue if there are questions related to this.