Decoding rpc's getblocktemplate coinbase data and building my own

Technical Support
1

Having this raw tx, can someone help me decode it?0400008085202f89010000000000000000000000000000000000000000000000000000000000000000ffffffff
050358760500ffffffff0200ca9a3b000000001976a91488cb6934df9df5ed9538e07d3be38d208e15bedf88ac80b2e60e0000000017a91435943aa429273fe3f78d50a0f24c09e4f7184bde8700000000000000000000000000000000000000

04000080 header
85202f89 nVersionGroupId
01 tx in count
0000000000000000000000000000000000000000000000000000000000000000 prevOutpTxId
ffffffff prev outpoint index
05 bytes in coinbase
03 bytes height
587605 height
00
ffffffff sequence
02 tx out count
00ca9a3b00000000 amount 1
19 bytes in script 1
76a91488cb6934df9df5ed9538e07d3be38d208e15bedf88ac script 1
80b2e60e00000000 amount 2
17 bytes in script 2
a91435943aa429273fe3f78d50a0f24c09e4f7184bde87 script 2
00000000 lock time
00000000 n expiry height
0000000000000000 value balance
000000 ??? no idea

also I was able to generate (for other block height) my own programatically and got:
0400008085202f89010000000000000000000000000000000000000000000000000000000000000000ffffffff3203f67605004f5a502068747470733a2f2f6769746875622e636f6d2f4a4b4b4742452f6f70656e2d7a636173682d706f6f6c000000000200ca9a3b000000001976a914a98aa7b041f3b1fa81c6bc6e51d335dfd18531ab88ac80b2e60e0000000017a914ec6138507d3f43685012a3a7300afdc0a07ad7c3870000000000000000000000000000000000

which goes
04000080
85202f89
01
0000000000000000000000000000000000000000000000000000000000000000
ffffffff
32
03
f37605
00
4f5a502068747470733a2f2f6769746875622e636f6d2f4a4b4b4742452f6f70656e2d7a636173682d706f6f6c
00000000
02
00ca9a3b00000000
19
76a914a98aa7b041f3b1fa81c6bc6e51d335dfd18531ab88ac
80b2e60e00000000
17
a914ec6138507d3f43685012a3a7300afdc0a07ad7c387
00000000
00000000
0000000000000000
00

however this tx appended to raw block gets rejected, any clue what are those last “00”? Also it doesn’t decode with cli, unless I append “0000”, why do I need them? But I’m getting “Block decode failed” anyways, is it possible to check the exact reason? Blocks with coinbasetxn.data from rpc appended go through.

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2

The transparent txin in the first tx is a coinbase input, described here. Your parsing gets out of sync in the coinbase script; remember that it has 5 bytes, so the script is 0358760500, with an empty “coinbase field”. Then the sequence field of that input is ffffffff, and the tx_out_count CompactSize is the following byte 02.

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3

Thank you, you’re right I got lost there. Could you please also explain what are the trailing zeros? I can’t figure it out from the protocol.pdf.

Also got my cbtxn sorted, blocks are getting accepted, but I’m blindly appending those zeros.

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4

In the case of a fully transparent v4 transaction, the vectors vShieldedSpend, vShieldedOutput, and vJoinSplit are empty, and the fields joinSplitPubKey, joinSplitSig, and bindingSig are omitted. But we still must encode the lengths nShieldedSpend, nShieldedOutput, and nJoinSplit. So that’s three zero CompactSizes, hence three zero bytes.

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5

That makes perfect sense, didn’t know they are required, probably misread something. Thank you for your time.

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