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@ -324,3 +324,340 @@ The entire code, with a _little_ more error-checking appears in the Appendix.
## Summary: Programming Bitcoind with C ## Summary: Programming Bitcoind with C
Using the techniques outlined in [§12.2](12_2_Accessing_Bitcoind_with_C.md) you can write a much more complex program using C calls. This section offers an example, with the first cut of a program that will send money to an address, without your users worrying about where it's coming from, how much they're paying as a fee, or how they get their change back. Obviously, a real-world program would need much better user-input control and error handling, but by outlining how the RPC code works, this section opens up the programming doorways to allow you to take the next step. Using the techniques outlined in [§12.2](12_2_Accessing_Bitcoind_with_C.md) you can write a much more complex program using C calls. This section offers an example, with the first cut of a program that will send money to an address, without your users worrying about where it's coming from, how much they're paying as a fee, or how they get their change back. Obviously, a real-world program would need much better user-input control and error handling, but by outlining how the RPC code works, this section opens up the programming doorways to allow you to take the next step.
## Appendix: Sending to an Address
Here's the complete code for sending funds to someone using C.
WARNING: This code has not been robustly checked. Beyond that, it's to be functionally minimalistic, not containing necessary error-checking. If you use it as a foundation of your own work, be sure to check it carefully and to make it a lot more robust.
```
file: sendtoaddress.c
#include <jansson.h>
#include <bitcoinrpc.h>
#include <string.h>
int main(int argc, char *argv[]) {
/* 1. Request an Address and an Amount */
if (argc != 3) {
printf("ERROR: Only %i arguments! Correct usage is '%s [recipient] [amount]'\n",argc-1,argv[0]);
exit(-1);
}
char *tx_recipient = argv[1];
double tx_amount = atof(argv[2]);
/* 2. Set an Arbitrary Fee */
double tx_fee = 0.0005;
double tx_total = tx_amount + tx_fee;
/* X. Prepare Your RPC */
bitcoinrpc_cl_t *rpc_client;
bitcoinrpc_method_t *rpc_method = NULL;
bitcoinrpc_resp_t *btcresponse = NULL;
bitcoinrpc_err_t btcerror;
json_t *lu_response = NULL;
json_t *lu_result = NULL;
bitcoinrpc_global_init();
rpc_client = bitcoinrpc_cl_init_params ("bitcoinrpc", "73bd45ba60ab8f9ff9846b6404769487", "127.0.0.1", 18332);
if (rpc_client) {
/* 3. Find a UTXO */
rpc_method = bitcoinrpc_method_init(BITCOINRPC_METHOD_LISTUNSPENT);
if (!rpc_method) {
printf("ERROR: Unable to initialize listunspent method!\n");
exit(-1);
}
btcresponse = bitcoinrpc_resp_init();
if (!btcresponse) {
printf("Error: Cannot initialize response object!");
exit(-1);
}
bitcoinrpc_call(rpc_client, rpc_method, btcresponse, &btcerror);
if (btcerror.code != BITCOINRPCE_OK) {
printf("Error: listunspent error code %d [%s]\n", btcerror.code,btcerror.msg);
exit(-1);
}
lu_response = bitcoinrpc_resp_get (btcresponse);
lu_result = json_object_get(lu_response,"result");
int i;
const char *tx_id = 0;
int tx_vout = 0;
double tx_value = 0.0;
for (i = 0 ; i < json_array_size(lu_result) ; i++) {
json_t *lu_data = NULL;
lu_data = json_array_get(lu_result, i);
json_t *lu_value = NULL;
lu_value = json_object_get(lu_data,"amount");
tx_value = json_real_value(lu_value);
if (tx_value > tx_total) {
json_t *lu_txid = NULL;
lu_txid = json_object_get(lu_data,"txid");
tx_id = strdup(json_string_value(lu_txid));
json_t *lu_vout = NULL;
lu_vout = json_object_get(lu_data,"vout");
tx_vout = json_integer_value(lu_vout);
json_decref(lu_value);
json_decref(lu_txid);
json_decref(lu_vout);
json_decref(lu_data);
break;
}
}
json_decref(lu_result);
json_decref(lu_response);
if (!tx_id) {
printf("Very Sad: You don't have any UTXOs larger than %f",tx_total);
exit(-1);
}
bitcoinrpc_method_free(rpc_method);
/* 4. Create a Change Address */
rpc_method = bitcoinrpc_method_init(BITCOINRPC_METHOD_GETRAWCHANGEADDRESS);
if (!rpc_method) {
printf("ERROR: Unable to initialize createrawchangeaddress method!\n");
exit(-1);
}
bitcoinrpc_call(rpc_client, rpc_method, btcresponse, &btcerror);
if (btcerror.code != BITCOINRPCE_OK) {
printf("Error: createrawchangeaddress error code %d [%s]\n", btcerror.code, btcerror.msg);
exit(-1);
}
lu_response = bitcoinrpc_resp_get (btcresponse);
lu_result = json_object_get(lu_response,"result");
char *changeaddress = strdup(json_string_value(lu_result));
json_decref(lu_result);
json_decref(lu_response);
bitcoinrpc_method_free(rpc_method);
/* 5. Create a Raw Transaction */
/* 5.1. Create the Input Parameters */
json_t *inputtxid = NULL;
inputtxid = json_object();
json_object_set_new(inputtxid,"txid",json_string(tx_id));
json_object_set_new(inputtxid,"vout",json_integer(tx_vout));
json_t *inputparams = NULL;
inputparams = json_array();
json_array_append(inputparams,inputtxid);
/* 5.2 Create the Output Parameters */
json_t *outputparams = NULL;
outputparams = json_object();
char tx_amount_string[32];
sprintf(tx_amount_string,"%.8f",tx_amount);
char tx_change_string[32];
sprintf(tx_change_string,"%.8f",tx_value - tx_total);
json_object_set(outputparams,
tx_recipient,
json_string(tx_amount_string));
json_object_set(outputparams,
changeaddress,
json_string(tx_change_string));
/* 5.3 Create the Parameter Array */
json_t *params = NULL;
params = json_array();
json_array_append(params,inputparams);
json_array_append(params,outputparams);
/* 5.4 Make the RPC Call */
rpc_method = bitcoinrpc_method_init(BITCOINRPC_METHOD_CREATERAWTRANSACTION);
if (!rpc_method) {
printf("ERROR: Unable to initialize createrawtransaction method!\n");
exit(-1);
}
if (bitcoinrpc_method_set_params(rpc_method, params) != BITCOINRPCE_OK) {
fprintf (stderr, "Error: Could not set params for createrawtransaction");
}
json_decref(inputtxid);
json_decref(inputparams);
json_decref(outputparams);
json_decref(params);
bitcoinrpc_call(rpc_client, rpc_method, btcresponse, &btcerror);
if (btcerror.code != BITCOINRPCE_OK) {
printf("Error: createrawtransaction error code %d [%s]\n", btcerror.code,btcerror.msg);
exit(-1);
}
lu_response = bitcoinrpc_resp_get(btcresponse);
lu_result = json_object_get(lu_response,"result");
char *tx_rawhex = strdup(json_string_value(lu_result));
json_decref(lu_result);
json_decref(lu_response);
bitcoinrpc_method_free(rpc_method);
/* 6. Sign the Transaction */
params = json_array();
json_array_append_new(params,json_string(tx_rawhex));
rpc_method = bitcoinrpc_method_init(BITCOINRPC_METHOD_SIGNRAWTRANSACTION);
if (!rpc_method) {
printf("ERROR: Unable to initialize signrawtransaction method!\n");
exit(-1);
}
if (bitcoinrpc_method_set_params(rpc_method, params) != BITCOINRPCE_OK) {
fprintf (stderr, "Error: Could not set params for signrawtransaction");
}
json_decref(params);
bitcoinrpc_call(rpc_client, rpc_method, btcresponse, &btcerror);
if (btcerror.code != BITCOINRPCE_OK) {
printf("Error: signrawtransaction error code %d [%s]\n", btcerror.code,btcerror.msg);
exit(-1);
}
lu_response = bitcoinrpc_resp_get(btcresponse);
lu_result = json_object_get(lu_response,"result");
json_t *lu_signature = json_object_get(lu_result,"hex");
char *tx_signrawhex = strdup(json_string_value(lu_signature));
json_decref(lu_signature);
json_decref(lu_result);
json_decref(lu_response);
bitcoinrpc_method_free(rpc_method);
/* 7. Sign the Transaction */
params = json_array();
json_array_append_new(params,json_string(tx_signrawhex));
rpc_method = bitcoinrpc_method_init(BITCOINRPC_METHOD_SENDRAWTRANSACTION);
if (!rpc_method) {
printf("ERROR: Unable to initialize sendrawtransaction method!\n");
exit(-1);
}
if (bitcoinrpc_method_set_params(rpc_method, params) != BITCOINRPCE_OK) {
fprintf (stderr, "Error: Could not set params for sendrawtransaction");
}
json_decref(params);
bitcoinrpc_call(rpc_client, rpc_method, btcresponse, &btcerror);
if (btcerror.code != BITCOINRPCE_OK) {
printf("Error: endrawtransaction error code %d [%s]\n", btcerror.code,btcerror.msg);
exit(-1);
}
lu_response = bitcoinrpc_resp_get(btcresponse);
lu_result = json_object_get(lu_response,"result");
char *tx_newid = strdup(json_string_value(lu_result));
printf("Txid: %s\n",tx_newid);
json_decref(lu_result);
json_decref(lu_response);
bitcoinrpc_method_free(rpc_method);
} else {
printf("ERROR: Failed to connect to server!\n");
}
bitcoinrpc_cl_free(rpc_client);
bitcoinrpc_global_cleanup();
}
```
Compile this as usual:
```
$ cc sendtoaddress.c -lbitcoinrpc -ljansson -o sendtoaddress
```
You can then use it to send funds to an address:
```
$ ./sendtoaddress mwCwTceJvYV27KXBc3NJZys6CjsgsoeHmf .10
Txid: 23f3faea4e1e933e981fe7ed66008f33c00983a865f6ccce9af0005e9670e916
```
You can see information on this transaction that we sent [here](https://live.blockcypher.com/btc-testnet/tx/23f3faea4e1e933e981fe7ed66008f33c00983a865f6ccce9af0005e9670e916/).