Pls Help!! How to get an outpoint in a transaction? #blockchain

[HoBzY]

https://developer.bitcoin.org/reference/transactions.html#raw-transaction-format
https://developer.bitcoin.org/reference/transactions.html#outpoint-the-specific-part-of-a-specific-output

How to get an outpoint in a transaction?
I'm trying to parse the structure of an unprocessed transaction.

How to get this c997a5e56e104102fa209c6a852dd90660a20b2d9c352423edce25857fcd3704 hash?

Code:

0100000055bd840a78798ad0da853f68974f3d183e2bd1db6a842c1feecf222a00000000ff104ccb05421ab93e63f8c3ce5c2c2e9dbb37de2764b3a3175c8166562cac7d51b96a49ffff001d283e9e70

02

01000000 01 0000000000000000000000000000000000000000000000000000000000000000 ffffffff 07 04ffff001d0102 ffffffff 0100f2052a010000 00 43 4104d46c4968bde02899d2aa0963367c7a6ce34eec332b32e42e5f3407e052d64ac625da6f0718e7b302140434bd725706957c092db53805b821a85b23a7ac61725bac 00000000

01000000

01

   Outpoint: The Specific Part Of A Specific Output
       c997a5e56e104102fa209c6a852dd90660a20b2d9c352423edce25857fcd3704

00000000

48

47304402204e45e16932b8af514961a1d3a1a25fdf3f4f7732e9d624c6c61548ab5fb8cd410220181522ec8eca07de4860a4acdd12909d831cc56cbbac4622082221a8768d1d0901

ffffffff

02

00ca9a3b00000000

434104ae1a62fe09c5f51b13905f07f06b99a2f7159b2225f374cd378d71302fa28414e7aab37397f554a7df5f142c21c1b7303b8a0626f1baded5c72a704f7e6cd84cac00286bee00000000

43410411db93e1dcdb8a016b49840f8c53bc1eb68a382e97b1482ecad7b148a6909a5cb2e0eaddfb84ccf9744464f82e160bfa9b8b64f9d4c03f999b8643f656b412a3ac00000000

Help me figure it out.
Can you give an example of generating this hash?

[NotATether]

The long string you posted starting with c997... is he transactions ID of the spent output. The 00000000 immediately following it indicates it was the first output of this transaction that has been spent (beware - this and other fields might stored in big-endian, so endian conversion might be necessary)

[HoBzY]

The long string you posted starting with c997... is he transactions ID of the spent output. The 00000000 immediately following it indicates it was the first output of this transaction that has been spent (beware - this and other fields might stored in big-endian, so endian conversion might be necessary)

How does it look in code? well, creating such a hash

[BitMaxz]

Are you talking about Raw/Hex transaction? Thats the link you provided above.

If you want to generate unsigned raw/hex transaction Electrum watch-only wallet have this option just import the public or Btc address that you own to Electrum wallet then make a transaction it should generate a raw/hex transaction.

Or you can use this https://coinb.in/#newTransaction to generate unsigned raw/hex transaction.

What exactly wallet did you generate this hash c997a5e56e104102fa209c6a852dd90660a20b2d9c352423edce25857fcd3704?

[pooya87]

You have to first parse/deserialize the transaction, so you either have to read the first link you posted (raw-transaction-format) to learn how to do it or find a library that does this.
Then you'll have a transaction that has a list of inputs (tx_in), in each input you will have a transaction hash and an index. The combination of these two is the outpoint.

That hash in each outpoint is the double SHA256 hash of the transaction that contains the output (or coins) you are spending.
That index is the index of that output (or coin) inside the previous transaction's output (tx_out) list.

[nc50lc]

How to get an outpoint in a transaction?
I'm trying to parse the structure of an unprocessed transaction.
-snip-
Help me figure it out.
Can you give an example of generating this hash?

Here's an example then:
Let's say you want to spend the first output of this transaction: blockstream.info/tx/4aca2e7e393b04e6b9dfbafd8bc2605c5547c49bb7de55029b76da8f884a4306
The short version is, that's the TXID that should be used in your transaction input's outpoint.

The long version is, you can get that by hashing (SHA256D) the to-be-spent RAW transaction;
for SegWit, witness data should be omitted first.
getrawtransaction 4aca2e7e393b04e6b9dfbafd8bc2605c5547c49bb7de55029b76da8f884a4306:

Code:

02000000

 ↓----Witness----↓
0001
 ↑----Witness----↑

01
edbc78c31ef4beb3f99727513772c95438ab938d0e9e012fb63c21d971d59eed
16000000
17
160014bfe3f2baee0e4e0acb9a09564d85f95f64a08644
fdffffff
02
a086010000000000
22
5120c7da8b195d9e93cb321000adfd2c56ffe30969780cf4e09b782966e38d76761d
70e1080000000000
16
0014eee8c12b1093ef4780509809116f931b1fc6ea5a

 ↓----Witness----↓
02473044022002a98b8b8745339ddeb3d485e240035ab4e42e5836ea3cbe6b324a13cd8b8334022062e8e047e1dcb4a7d9f826ca8194be66a116108021fe7e7139fec22ef5f677b6012102dcfa3aff14e12c8eb96f3cf03880aca6ba451798533f58bd30de8eac93fc047c
 ↑----Witness----↑

dc8b0b00

Without the witnesses, you'll be left with:

Code:

0200000001edbc78c31ef4beb3f99727513772c95438ab938d0e9e012fb63c21d971d59eed1600000017160014bfe3f2baee0e4e0acb9a09564d85f95f64a08644fdffffff02a086010000000000225120c7da8b195d9e93cb321000adfd2c56ffe30969780cf4e09b782966e38d76761d70e1080000000000160014eee8c12b1093ef4780509809116f931b1fc6ea5adc8b0b00

SHA256:                    19911b5338814ae41175533e224bfdadbe1319f78c194659baaa4ac80fbb9f91
SHA256:                    06434a888fda769b0255deb79bc447555c60c28bfdbadfb9e6043b397e2eca4a
Reverse byte order: 4aca2e7e393b04e6b9dfbafd8bc2605c5547c49bb7de55029b76da8f884a4306

A few references:

• Transaction data: learnmeabitcoin.com/technical/transaction-data
• TXID: https://learnmeabitcoin.com/technical/txid
• Witnesses: https://learnmeabitcoin.com/technical/transaction-weight

[HoBzY]

How to get an outpoint in a transaction?
I'm trying to parse the structure of an unprocessed transaction.
-snip-
Help me figure it out.
Can you give an example of generating this hash?

Here's an example then:
Let's say you want to spend the first output of this transaction: blockstream.info/tx/4aca2e7e393b04e6b9dfbafd8bc2605c5547c49bb7de55029b76da8f884a4306
The short version is, that's the TXID that should be used in your transaction input's outpoint.

The long version is, you can get that by hashing (SHA256D) the to-be-spent RAW transaction;
for SegWit, witness data should be omitted first.
getrawtransaction 4aca2e7e393b04e6b9dfbafd8bc2605c5547c49bb7de55029b76da8f884a4306:

Code:

02000000

 ↓----Witness----↓
0001
 ↑----Witness----↑

01
edbc78c31ef4beb3f99727513772c95438ab938d0e9e012fb63c21d971d59eed
16000000
17
160014bfe3f2baee0e4e0acb9a09564d85f95f64a08644
fdffffff
02
a086010000000000
22
5120c7da8b195d9e93cb321000adfd2c56ffe30969780cf4e09b782966e38d76761d
70e1080000000000
16
0014eee8c12b1093ef4780509809116f931b1fc6ea5a

 ↓----Witness----↓
02473044022002a98b8b8745339ddeb3d485e240035ab4e42e5836ea3cbe6b324a13cd8b8334022062e8e047e1dcb4a7d9f826ca8194be66a116108021fe7e7139fec22ef5f677b6012102dcfa3aff14e12c8eb96f3cf03880aca6ba451798533f58bd30de8eac93fc047c
 ↑----Witness----↑

dc8b0b00

Without the witnesses, you'll be left with:

Code:

0200000001edbc78c31ef4beb3f99727513772c95438ab938d0e9e012fb63c21d971d59eed1600000017160014bfe3f2baee0e4e0acb9a09564d85f95f64a08644fdffffff02a086010000000000225120c7da8b195d9e93cb321000adfd2c56ffe30969780cf4e09b782966e38d76761d70e1080000000000160014eee8c12b1093ef4780509809116f931b1fc6ea5adc8b0b00

SHA256:                    19911b5338814ae41175533e224bfdadbe1319f78c194659baaa4ac80fbb9f91
SHA256:                    06434a888fda769b0255deb79bc447555c60c28bfdbadfb9e6043b397e2eca4a
Reverse byte order: 4aca2e7e393b04e6b9dfbafd8bc2605c5547c49bb7de55029b76da8f884a4306

A few references:

• Transaction data: learnmeabitcoin.com/technical/transaction-data
• TXID: https://learnmeabitcoin.com/technical/txid
• Witnesses: https://learnmeabitcoin.com/technical/transaction-weight

This is understandable, but how to get this hash from json?

ed9ed571d9213cb62f019e0e8d93ab3854c97237512797f9b3bef41ec378bced

Code:

{
    "hash": "4aca2e7e393b04e6b9dfbafd8bc2605c5547c49bb7de55029b76da8f884a4306",
    "ver": 2,
    "vin_sz": 1,
    "vout_sz": 2,
    "size": 257,
    "weight": 701,
    "fee": 500,
    "relayed_by": "0.0.0.0",
    "lock_time": 756700,
    "tx_index": 220354657254222,
    "double_spend": false,
    "time": 1664710026,
    "block_index": 756701,
    "block_height": 756701,
    "inputs": [
        {
            "sequence": 4294967293,
            "witness": "02473044022002a98b8b8745339ddeb3d485e240035ab4e42e5836ea3cbe6b324a13cd8b8334022062e8e047e1dcb4a7d9f826ca8194be66a116108021fe7e7139fec22ef5f677b6012102dcfa3aff14e12c8eb96f3cf03880aca6ba451798533f58bd30de8eac93fc047c",
            "script": "160014bfe3f2baee0e4e0acb9a09564d85f95f64a08644",
            "index": 0,
            "prev_out": {
                "tx_index": 8364599542013591,
                "value": 682500,
                "n": 22,
                "type": 0,
                "spent": true,
                "script": "a91453f6e374ee53ef349d5293c49547438bb55f8b7a87",
                "spending_outpoints": [
                    {
                        "tx_index": 220354657254222,
                        "n": 0
                    }
                ],
                "addr": "39Lymaa222Ryp9DMdDcRviYcBijTJS2e5j"
            }
        }
    ],
    "out": [
        {
            "type": 0,
            "spent": true,
            "value": 100000,
            "spending_outpoints": [
                {
                    "tx_index": 6930009354916659,
                    "n": 0
                }
            ],
            "n": 0,
            "tx_index": 220354657254222,
            "script": "5120c7da8b195d9e93cb321000adfd2c56ffe30969780cf4e09b782966e38d76761d",
            "addr": "bc1pcldgkx2an6fukvssqzkl6tzkll3sj6tcpn6wpxmc99nw8rtkwcws04nvas"
        },
        {
            "type": 0,
            "spent": true,
            "value": 582000,
            "spending_outpoints": [
                {
                    "tx_index": 3451925364636683,
                    "n": 41
                }
            ],
            "n": 1,
            "tx_index": 220354657254222,
            "script": "0014eee8c12b1093ef4780509809116f931b1fc6ea5a",
            "addr": "bc1qam5vz2csj0h50qzsnqy3zmunrv0ud6j6m9szd7"
        }
    ]
}

[nc50lc]

-snip-

This is understandable, but how to get this hash from json?

ed9ed571d9213cb62f019e0e8d93ab3854c97237512797f9b3bef41ec378bced

Code:

{
    "hash": "4aca2e7e393b04e6b9dfbafd8bc2605c5547c49bb7de55029b76da8f884a4306",
...
}

It's already in json format so the transaction's txid should be already available.
In that specific case, it's the line that I left in the code snippet, it's the same as the one in my example.

Now I saw where the confusion is.
The "hash" ed9ed571d9213cb62f019e0e8d93ab3854c97237512797f9b3bef41ec378bced is the txid of the input of that example transaction.
You can't get that hash from that transaction's sha256d result, it's only referencing that txid (& vout) to find the UTXO that it's trying to spend.

What we want to get is the hash 4aca2e7e393b04e6b9dfbafd8bc2605c5547c49bb7de55029b76da8f884a4306 in order to spend the example output.
Like here, where it's spent: blockstream.info/tx/13fb6a1f56cd383ecbf90fd5b9463553f2fa4cacff34eb5ba99d991e4f74f6c4
As you can see, the first input is referencing 4aca2e7e393b04e6b9dfbafd8bc2605c5547c49bb7de55029b76da8f884a4306 (vout: 0).

[HoBzY]

-snip-

This is understandable, but how to get this hash from json?

ed9ed571d9213cb62f019e0e8d93ab3854c97237512797f9b3bef41ec378bced

Code:

{
    "hash": "4aca2e7e393b04e6b9dfbafd8bc2605c5547c49bb7de55029b76da8f884a4306",
...
}

It's already in json format so the transaction's txid should be already available.
In that specific case, it's the line that I left in the code snippet, it's the same as the one in my example.

Now I saw where the confusion is.
The "hash" ed9ed571d9213cb62f019e0e8d93ab3854c97237512797f9b3bef41ec378bced is the txid of the input of that example transaction.
You can't get that hash from that transaction's sha256d result, it's only referencing that txid (& vout) to find the UTXO that it's trying to spend.

What we want to get is the hash 4aca2e7e393b04e6b9dfbafd8bc2605c5547c49bb7de55029b76da8f884a4306 in order to spend the example output.
Like here, where it's spent: blockstream.info/tx/13fb6a1f56cd383ecbf90fd5b9463553f2fa4cacff34eb5ba99d991e4f74f6c4
As you can see, the first input is referencing 4aca2e7e393b04e6b9dfbafd8bc2605c5547c49bb7de55029b76da8f884a4306 (vout: 0).

Well, my goal is to study the blockchain, or rather, how mining and all its structures work, but I'm stuck on this txid, I can't figure out how to get it to add it to the structure chain and send RPC. I'm learning blockchain in less than a week
I take the json object itself from blockchain.info

Code:

    "inputs": [
        {
            "sequence": 4294967293,
            "witness": "02473044022002a98b8b8745339ddeb3d485e240035ab4e42e5836ea3cbe6b324a13cd8b8334022062e8e047e1dcb4a7d9f826ca8194be66a116108021fe7e7139fec22ef5f677b6012102dcfa3aff14e12c8eb96f3cf03880aca6ba451798533f58bd30de8eac93fc047c",
            "script": "160014bfe3f2baee0e4e0acb9a09564d85f95f64a08644",
            "index": 0,
            "prev_out": {
                "tx_index": 8364599542013591,
                "value": 682500,
                "n": 22,
                "type": 0,
                "spent": true,
                "script": "a91453f6e374ee53ef349d5293c49547438bb55f8b7a87",
                "spending_outpoints": [
                    {
                        "tx_index": 220354657254222,
                        "n": 0
                    }
                ],
                "addr": "39Lymaa222Ryp9DMdDcRviYcBijTJS2e5j"
            }
        }
    ],

I understand that 'tx_index = 220354657254222' is responsible for txid, but I don't understand how to get that hex txid is needed from it

[nc50lc]

I take the json object itself from blockchain.info

Code:

-snip-

You can't get it from that transaction.
You can get it from this transaction: blockstream.info/tx/ed9ed571d9213cb62f019e0e8d93ab3854c97237512797f9b3bef41ec378bced?output:22 which is what that outpoint is referring to.

You or your wallet should already know that hash in order to "add it to the structure", you can't get it from the transaction being built
For example, you can get a txid from your wallet's inbound transactions which you can also get with listunspent RPC, then use the txid of the one you want to spend as the outpoint.

[HoBzY]

I take the json object itself from blockchain.info

Code:

-snip-

You can't get it from that transaction.
You can get it from this transaction: blockstream.info/tx/ed9ed571d9213cb62f019e0e8d93ab3854c97237512797f9b3bef41ec378bced?output:22 which is what that outpoint is referring to.

You or your wallet should already know that hash in order to "add it to the structure", you can't get it from the transaction being built
For example, you can get a txid from your wallet's inbound transactions which you can also get with listunspent RPC, then use the txid of the one you want to spend as the outpoint.

ok thanks good forum)