Transaction tracing API

Last updated 8 March 2023
Transaction tracing enables deeper look into smart contract inner calls and account creation calls. It is inspired with the OpenEthereum (Parity) node trace module, which is used in lot of projects.
For now, following JSON-RPC methods are implemented:
trace_block
trace_filter
trace_get
trace_transaction
Currently it is deployed on endpoints for Fantom mainnet and testnet:
​https://rpcapi-tracing.fantom.network​
​https://rpcapi-tracing.testnet.fantom.network​
Start a new go-opera tracing node
Because of stored traces, tracing node requires little bit bigger storage (around 1/4 more).  For more information, please follow README.md file in txtracing branch.
Building
You can check out and build tx tracing release version from git repository (release/txtracing/1.1.2-rc.5): https://github.com/Fantom-foundation/go-opera/tree/release/txtracing/1.1.2-rc.5.
Running
It's recommended to launch new node from scratch with CLI option --tracenode as this flag has to be set to use stored transaction traces.
$ opera --genesis /path/to/genesis.g --tracenode
Enable JSON-RPC API with option trace
--http.api=eth,web3,net,ftm,trace
A complete example command
opera \
    --genesis=/datadir/mainnet-5577-full-mpt.g \
    --port=5050 \
    --maxpeers=200 \
    --datadir=/datadir \
    --http \
    --http.addr=0.0.0.0 \
    --http.port=18545 \
    --http.corsdomain="*" \
    --http.vhosts="*" \
    --ws \
    --ws.addr=0.0.0.0 \
    --ws.port=18546 \
    --ws.origins="*" \
    --nousb \
    --db.preset pbl-1 \
    --tracenode \
    --http.api=eth,web3,net,ftm,trace
Genesis file
For the first start of the node, you have to specify the genesis file, which defines blockchain and contains his history. 
Please select a genesis file ( from this site) with full history ("full-mpt" in filename), if you need transaction traces for history states.
It is recommended to use this genesis file mainnet-5577-full-mpt.g for a full history tracing node.
Import, export and delete
Transaction traces are created on the node while processing transactions and then stored into node database. You can export these traces and import them on other nodes (this feature was introduced since version release/txtracing/1.1.0-rc.4.1). This was added to be able to react to some changes which could change content of the traces without need of doing a full sync of the blockchain again. 
Another way is to delete traces, which are then recreated with next request to them from the rpc api. This option is not recomended as the recreating of the traces in this manner is slower with first request to non-existent transaction trace.
All these operations has to be done with node which is stopped as it is changing data in the core database. For export and delete, you can specify block range, which is narrowing amount of processed transaction traces.
The command for export is export txtraces <filename.gz> <from block> <to block>
opera --tracenode --datadir=/path/to/opera/datadir export txtraces filename.gz 10000000 11000000
For import  it is import txtraces <filename.gz>
opera --tracenode --datadir=/path/to/opera/datadir import txtraces filename.gz
With delete there is no file specified delete txtraces <from block> <to block>
opera --tracenode --datadir=/path/to/opera/datadir delete txtraces 10000000 11000000
Go-Opera version migration
This section contains information about migrating transaction tracing api node to newer go-opera version. It will mention, if you need to resync the node from scratch (because of stored transaction traces) or if node needs only the update of the code to migrate from previous version.
​release/txtracing/1.1.1-rc.2​
​release/txtracing/1.1.1-rc.3 - no resync from 1.1.1-rc.2, just update
release/txtracing/1.1.2-rc.2 - don't use this version
​release/txtracing/1.1.2-rc.5 - resync from all previous versions and see notes below
When using version 1.1.2 you need to add db.preset argument for starting opera command. You can see options for this parameters with opera help command. For standard conditions, please use this option:
db.preset=ldb-1
trace_block
Returns traces created at given block.
Parameters
1.Quantity or Tag - Integer of a block number, or the string 'earliest', 'latest' or 'pending'.
params: [
  "0x22DB3E" // 2284350
]
Returns
Array - Block traces.
Example
Request
curl --data '{"method":"trace_block","params":["0x22DB3E"],"id":1,"jsonrpc":"2.0"}' -H "Content-Type: application/json" -X POST https://rpcapi-tracing.fantom.network
Response
{
   "jsonrpc":"2.0",
   "id":1,
   "result":[
      {
         "action":{
            "callType":"call",
            "from":"0x740c82e9009738b3ab6080e89da964a4704a6cba",
            "to":"0xd4e0aca70d1fe8979e7e1015b30a2085803d0244",
            "value":"0x0",
            "gas":"0x689e",
            "input":"0x6930fd2a0000000000000000000000000000000000000000000000000000000000000608"
         },
         "blockHash":"0x00000ce000001cf16b859ccacc281e32e2c17730ce48b3498bf1f7f05d90fe5c",
         "blockNumber":2284350,
         "result":{
            "gasUsed":"0x688f",
            "output":"0x"
         },
         "subtraces":1,
         "traceAddress":[
            
         ],
         "transactionHash":"0x58846dd2a9fa3ea9e700838db48fd9829ebbc95e103142ac7968f658fd1ed3ac",
         "transactionPosition":0,
         "type":"call"
      },
      {
         "action":{
            "callType":"delegatecall",
            "from":"0xd4e0aca70d1fe8979e7e1015b30a2085803d0244",
            "to":"0x1125eabf1eba69ef00266b7a038141474d8afff1",
            "value":"0x0",
            "gas":"0x125c",
            "input":"0x6930fd2a0000000000000000000000000000000000000000000000000000000000000608"
         },
         "blockHash":"0x00000ce000001cf16b859ccacc281e32e2c17730ce48b3498bf1f7f05d90fe5c",
         "blockNumber":2284350,
         "result":{
            "gasUsed":"0xf62",
            "output":"0x"
         },
         "subtraces":0,
         "traceAddress":[
            0
         ],
         "transactionHash":"0x58846dd2a9fa3ea9e700838db48fd9829ebbc95e103142ac7968f658fd1ed3ac",
         "transactionPosition":0,
         "type":"call"
      }
   ]
}
trace_transaction
Returns all traces of given transaction
Parameters
1.Hash - Transaction hash
params: ["0x58846dd2a9fa3ea9e700838db48fd9829ebbc95e103142ac7968f658fd1ed3ac"]
Returns
Array - Traces of given transaction
Example
Request
curl --data '{"method":"trace_transaction","params":["0x58846dd2a9fa3ea9e700838db48fd9829ebbc95e103142ac7968f658fd1ed3ac"],"id":1,"jsonrpc":"2.0"}' -H "Content-Type: application/json" -X POST https://rpcapi-tracing.fantom.network
trace_filter
Returns traces matching given filter
Parameters
1.Object - The filter object
fromBlock: Quantity or Tag - (optional) From this block.
toBlock: Quantity or Tag - (optional) To this block.
fromAddress: Array - (optional) Sent from these addresses.
toAddress: Address - (optional) Sent to these addresses.
after: Quantity - (optional) The offset trace number
count: Quantity - (optional) Integer number of traces to display in a batch.
params: [{
  "fromBlock": "0x22DB29", // 2284329
  "toBlock": "0x22DB34", // 2284340
  "toAddress": ["0xda7a001b254cd22e46d3eab04d937489c93174c3"],
  "after": 20,
  "count": 10
}]
Returns
Array - Traces matching given filter
Example
Request
curl -H "Content-Type: application/json" -X POST --data '{"method":"trace_filter","params":[{"fromBlock":"0x22DB29", "toBlock":"0x22DB34", "fromAddress":["0xda7a001b254cd22e46d3eab04d937489c93174c3"], "count":10, "after":20}],"id":1,"jsonrpc":"2.0"}'  https://rpcapi-tracing.fantom.network
trace_get
Returns trace at given position.
Parameters
1.Hash - Transaction hash.
2.Array - Index positions of the traces.
params: [
  "0x58846dd2a9fa3ea9e700838db48fd9829ebbc95e103142ac7968f658fd1ed3ac",
  ["0x0"]
]
Returns
Object - Trace object
Example
Request
curl -H "Content-Type: application/json" -X POST --data '{"method":"trace_get","params":["0x58846dd2a9fa3ea9e700838db48fd9829ebbc95e103142ac7968f658fd1ed3ac",["0x0"]],"id":1,"jsonrpc":"2.0"}' https://rpcapi-tracing.fantom.network
debug_traceBlockByNumber
The method returns a full stack trace of all invoked opcodes of all transaction that were included in a block identified by a block number. The parent of this block must be present or it will fail.
Parameters
1.Number - Block number to be traced.
2.Object - (optional) Options for the trace.
tracer: String - (optional) Setting this will enable JavaScript-based transaction tracing, described below.
timeout: String - (optional) Overrides the default timeout of 5 seconds for JavaScript-based tracing calls. Check documentation for ParseDuration for valid values.
Returns
Array - A trace object per transaction inside the block.
Example
curl -H "Content-Type: application/json" -X POST --data '{"method":"debug_traceBlockByNumber","params":["0x2F5DD49"],"id":1,"jsonrpc":"2.0"}' https://rpcapi-tracing.fantom.network
debug_traceBlockByHash
The method returns a full stack trace of all invoked opcodes of all transaction that were included in a block identified by a hash. The parent of this block must be present or it will fail.
Parameters
1.Hash - Hash of the block to be traced.
2.Object - (optional) Options for the trace.
tracer: String - (optional) Setting this will enable JavaScript-based transaction tracing, described below.
timeout: String - (optional) Overrides the default timeout of 5 seconds for JavaScript-based tracing calls. Check documentation for ParseDuration for valid values.
Returns
Array - A trace object per transaction inside thw block.
Example
curl -H "Content-Type: application/json" -X POST --data '{"method":"debug_traceBlockByHash","params":["0x0002825a0000008c2bc8a86b966c34797db3c21916ca033f4bd68461801217d0"],"id":1,"jsonrpc":"2.0"}' https://rpcapi-tracing.fantom.network
debug_traceTransaction
The method will attempt to run the transaction in the exact same manner as it was executed on the network. It will replay any transaction that may have been executed prior to this one on the block before it will finally attempt to execute the transaction that corresponds to the given hash.
Parameters
1.Hash - Hash of the transaction to be traced.
2.Object - (optional) Options for the trace.
tracer: String - (optional) Setting this will enable JavaScript-based transaction tracing, described below.
timeout: String - (optional) Overrides the default timeout of 5 seconds for JavaScript-based tracing calls. Check documentation for ParseDuration for valid values.
Returns
Object - A trace object of the traced transaction.
Example
curl -H "Content-Type: application/json" -X POST --data '{"method":"debug_traceTransaction","params":["0xa6598be1f06b0aff5caddec2685ec53599f064f7b8ff9eaded0a719a378c8802"],"id":1,"jsonrpc":"2.0"}' https://rpcapi-tracing.fantom.network
JavaScript Based Tracer 
Specifying the tracer option in the second argument of the debug tracing calls enables JavaScript based tracing. In this mode, tracer is interpreted as a JavaScript expression that is expected to evaluate to an object which must expose the result and fault methods. There exist 4 additional methods, namely: setup, step, enter, and exit. enter and exit must be present or omitted together.
Setup Method
Method setup is invoked once, in the beginning when the tracer is being constructed for each  transaction being traced. It takes in one argument config, which allows users to pass in options to the tracer. config is to be JSON-decoded for usage and its default value is "{}".
Step Method
Method step is a function that takes two arguments, log and db, and is called for each step of the EVM, or when an error occurs, as a transaction is traced.
log has the following fields:
op: Object, an OpCode object representing the current opcode
stack: Object, a structure representing the EVM execution stack
memory: Object, a structure representing the contract’s memory space
contract: Object, an object representing the account executing the current operation
and the following methods:
getPC() - returns a Number with the current program counter
getGas() - returns a Number with the amount of gas remaining
getCost() - returns the cost of the opcode as a Number
getDepth() - returns the execution depth as a Number
getRefund() - returns the amount to be refunded as a Number
getError() - returns information about the error if one occured, otherwise returns undefined
If error is non-empty, all other fields should be ignored.
For efficiency, the same log object is reused on each execution step, updated with current values; make sure to copy values you want to preserve beyond the current call. 
log.op has the following methods:
isPush() - returns true if the opcode is a PUSHn
toString() - returns the string representation of the opcode
toNumber() - returns the opcode’s number
log.memory has the following methods:
slice(start, stop) - returns the specified segment of memory as a byte slice
getUint(offset) - returns the 32 bytes at the given offset
length() - returns the memory size
log.stack has the following methods:
peek(idx) - returns the idx-th element from the top of the stack (0 is the topmost element) as a big.Int
length() - returns the number of elements in the stack
log.contract has the following methods:
getCaller() - returns the address of the caller
getAddress() - returns the address of the current contract
getValue() - returns the amount of value sent from caller to contract as a big.Int
getInput() - returns the input data passed to the contract
db has the following methods:
getBalance(address) - returns a big.Int with the specified account’s balance
getNonce(address) - returns a Number with the specified account’s nonce
getCode(address) - returns a byte slice with the code for the specified account
getState(address, hash) - returns the state value for the specified account and the specified hash
exists(address) - returns true if the specified address exists
If the step function throws an exception or executes an illegal operation at any point, it will not be called on any further VM steps, and the error will be returned to the caller.
Result Method
Method result is a function that takes two arguments ctx and db, and is expected to return a JSON-serializable value to return to the RPC caller.
ctx is the context in which the transaction is executing and has the following fields:
type - String, one of the two values CALL and CREATE
from - Address, sender of the transaction
to - Address, target of the transaction
input - Buffer, input transaction data
gas - Number, gas budget of the transaction
gasUsed - Number, amount of gas used in executing the transaction (excludes txdata costs)
gasPrice - Number, gas price configured in the transaction being executed
intrinsicGas - Number, intrinsic gas for the transaction being executed
value - big.Int, amount to be transferred in wei
block - Number, block number
output - Buffer, value returned from EVM
time - String, execution runtime
Fault Method
Method fault is a function that takes two arguments, log and db, just like step and is invoked when an error happens during the execution of an opcode which wasn’t reported in step. The method log.getError() has information about the error.
Ender and Exit Methods
Methods enter and exit are respectively invoked on stepping in and out of an internal call. More specifically they are invoked on the CALL variants, CREATE variants and also for the transfer implied by a SELFDESTRUCT.
enter takes a callFrame object as argument which has the following methods:
getType() - returns a string which has the type of the call frame
getFrom() - returns the address of the call frame sender
getTo() - returns the address of the call frame target
getInput() - returns the input as a buffer
getGas() - returns a Number which has the amount of gas provided for the frame
getValue() - returns a big.Int with the amount to be transferred only if available, otherwise undefined
exit takes in a frameResult object which has the following methods:
getGasUsed() - returns amount of gas used throughout the frame as a Number
getOutput() - returns the output as a buffer 
getError() - returns an error if one occured during execution and undefined otherwise
Note that several values are Golang big.Int objects, not JavaScript numbers or JS bigints. As such, they have the same interface as described in the godocs. Their default serialization to JSON is as a Javascript number; to serialize large numbers accurately call .String() on them. For convenience, big.NewInt(x) is provided, and will convert a uint to a Go BigInt.
​
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