How do I get the public keys from a transaction javascript

Question

I am developing a site as college project and I cannot seem to understand how to implement StrKey to get the public key from a transaction.

I can decode the xdr but cannot seem to understand how to retrieve the public key from the xdr. For example Stellar Laboratory can do it no problem but I am unable to do the same.

Current xdr extracted in json form

   {
  "_attributes": {
    "tx": {
      "_attributes": {
        "sourceAccount": {
          "_switch": {
            "name": "publicKeyTypeEd25519",
            "value": 0
          },
          "_arm": "ed25519",
          "_armType": {
            "_length": 32,
            "_padding": 0
          },
          "_value": {
            "type": "Buffer",
            "data": [
              158,
              100,
              0,
              66,
              51,
              202,
              169,
              13,
              252,
              113,
              147,
              154,
              22,
              72,
              191,
              147,
              44,
              51,
              52,
              139,
              186,
              201,
              238,
              207,
              158,
              21,
              238,
              196,
              232,
              12,
              24,
              245
            ]
          }
        },
        "fee": 100,
        "seqNum": {
          "low": 22,
          "high": 14586787,
          "unsigned": true
        },
        "memo": {
          "_switch": {
            "name": "memoNone",
            "value": 0
          },
          "_arm": {},
          "_armType": {}
        },
        "operations": [
          {
            "_attributes": {
              "body": {
                "_switch": {
                  "name": "payment",
                  "value": 1
                },
                "_arm": "paymentOp",
                "_value": {
                  "_attributes": {
                    "destination": {
                      "_switch": {
                        "name": "publicKeyTypeEd25519",
                        "value": 0
                      },
                      "_arm": "ed25519",
                      "_armType": {
                        "_length": 32,
                        "_padding": 0
                      },
                      "_value": {
                        "type": "Buffer",
                        "data": [
                          19,
                          172,
                          96,
                          157,
                          239,
                          173,
                          223,
                          213,
                          79,
                          53,
                          53,
                          74,
                          225,
                          128,
                          93,
                          200,
                          48,
                          132,
                          54,
                          241,
                          50,
                          52,
                          38,
                          8,
                          193,
                          2,
                          69,
                          110,
                          219,
                          39,
                          252,
                          94
                        ]
                      }
                    },
                    "asset": {
                      "_switch": {
                        "name": "assetTypeNative",
                        "value": 0
                      },
                      "_arm": {},
                      "_armType": {}
                    },
                    "amount": {
                      "low": 100000000,
                      "high": 0,
                      "unsigned": false
                    }
                  }
                }
              }
            }
          }
        ],
        "ext": {
          "_switch": 0,
          "_arm": {},
          "_armType": {}
        }
      }
    },
    "signatures": [
      {
        "_attributes": {
          "hint": {
            "type": "Buffer",
            "data": [
              232,
              12,
              24,
              245
            ]
          },
          "signature": {
            "type": "Buffer",
            "data": [
              44,
              124,
              174,
              242,
              133,
              116,
              34,
              80,
              134,
              45,
              23,
              241,
              165,
              87,
              193,
              165,
              157,
              98,
              25,
              65,
              73,
              191,
              148,
              19,
              80,
              30,
              136,
              190,
              113,
              237,
              116,
              79,
              150,
              194,
              58,
              160,
              237,
              188,
              99,
              96,
              140,
              85,
              91,
              24,
              0,
              88,
              245,
              66,
              28,
              26,
              26,
              75,
              243,
              52,
              18,
              6,
              117,
              227,
              92,
              49,
              21,
              60,
              242,
              3
            ]
          }
        }
      }
    ]
  }
}

Edit: I was able to solve this by using

StrKey.encodeEd25519PublicKey()

and going to the locations(in the decoded xdr)

._attributes.tx._attributes.sourceAccount._value and
._attributes.tx._attributes.operations[i]._attributes.body._value._attributes.destination._value

Thank you for your help guys!

Answer 1

I'd let the SDK decode the XDR for you, and take it from there.

const tx = new StellarSdk.Transaction(tx_xdr);

From here on you have the source accounts in tx.source and tx.operations[i].source, for 0 < i < tx.operations.length.

Easy peasy!

Answer 2

I'm not familiar with the JS SDK, but I believe you need to take the array value of sourceAccount/_value/data (or destination/_value/data on the payment operation) and construct the public key from KeyPair.fromRawEd25519Seed(seed)