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12_2_Accessing_Bitcoind_with_C.md
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@ -2,7 +2,7 @@
> **NOTE:** This is a draft in progress, so that I can get some feedback from early reviewers. It is not yet ready for learning. > **NOTE:** This is a draft in progress, so that I can get some feedback from early reviewers. It is not yet ready for learning.
Though command-line `curl` is the easiest way to access the `bitcoind` directly, there are [many other options](https://en.bitcoin.it/wiki/API_reference_(JSON-RPC)) for doing so and most of them support more fully featured programming languages. The best package for doing so in C is currently [libbitcoinrpc](https://github.com/gitmarek/libbitcoinrpc/blob/master/README.md). It uses a `curl` library for accessing the data and it uses the somewhat clunky `jansson` library for decoding JSON. The advantage of a full programming language over command-line `curl` for writing more complex code should be obvious. Though command-line `curl` is the easiest way to access the `bitcoind` directly, there are [many other options](https://en.bitcoin.it/wiki/API_reference_(JSON-RPC)) for doing so and most of them support more fully featured programming languages. The best package for doing so in C is currently [libbitcoinrpc](https://github.com/gitmarek/libbitcoinrpc/blob/master/README.md). It uses a `curl` library for accessing the data and it uses the somewhat clunky `jansson` library for decoding the JSON.
## Set Up libbitcoinrpc ## Set Up libbitcoinrpc
@ -19,11 +19,11 @@ $ cd libbitcoinrpc-master/
### Compile libbitcoinrpc ### Compile libbitcoinrpc
You'll probably need to adjust your `$PATH`, so that you can access `/sbin/ldconfig`: Before you can compile and install the package, you'll probably need to adjust your `$PATH`, so that you can access `/sbin/ldconfig`:
``` ```
$ PATH="/sbin:$PATH" $ PATH="/sbin:$PATH"
``` ```
For a Ubunto system, you'll also want to adjust the `INSTALL_LIBPATH` in the `Makefile` to install to `/usr/lib` instead of `/usr/local/lib`: For a Ubunto system, you'll also want to adjust the `INSTALL_LIBPATH` in the `libbitcoinrpc` `Makefile` to install to `/usr/lib` instead of `/usr/local/lib`:
``` ```
INSTALL_LIBPATH := $(INSTALL_PREFIX)/usr/lib INSTALL_LIBPATH := $(INSTALL_PREFIX)/usr/lib
``` ```
@ -44,7 +44,7 @@ $ sudo make install
### Setup Your Code ### Setup Your Code
Make sure that your code files include the appropriate headers: To use `libbitcoinrpc`, make sure that your code files include the appropriate headers:
``` ```
#include <jansson.h> #include <jansson.h>
#include <bitcoinrpc.h> #include <bitcoinrpc.h>
@ -56,13 +56,13 @@ $ cc mybitcoinclient.c -lbitcoinrpc -ljansson -o rpcclient
### Build Your Connection ### Build Your Connection
There are just a few steps involved with building the connection to your `bitcoind` server. Building the connection to your `bitcoind` server takes a few simple steps.
First, you initialize the library: First, initialize the library:
``` ```
bitcoinrpc_global_init(); bitcoinrpc_global_init();
``` ```
Then you connect to your `bitcoind`. The four arguments for `bitcoinrpc_cl_init_params` are username, password, IP address, and port. As usual, you should extract the user and password from `~/.bitcoin/bitcoin.conf`, while IP address 127.0.0.1 and port 18332 should be correct for the standard testnet setup described in this documents. Then connect to your `bitcoind`. The four arguments for `bitcoinrpc_cl_init_params` are username, password, IP address, and port. As usual, you should extract the user and password from `~/.bitcoin/bitcoin.conf`, while IP address 127.0.0.1 and port 18332 should be correct for the standard testnet setup described in this documents.
``` ```
bitcoinrpc_cl_t *rpc_client; bitcoinrpc_cl_t *rpc_client;
rpc_client = bitcoinrpc_cl_init_params ("bitcoinrpc", "d8340efbcd34e312044c8431c59c792c", "127.0.0.1", 18332); rpc_client = bitcoinrpc_cl_init_params ("bitcoinrpc", "d8340efbcd34e312044c8431c59c792c", "127.0.0.1", 18332);
@ -72,11 +72,66 @@ rpc_client = bitcoinrpc_cl_init_params ("bitcoinrpc", "d8340efbcd34e312044c8431c
If `rpc_client` is successful, then you can go. If `rpc_client` is successful, then you can go.
When you're all done with everything, you should close your connection: Later, when you're all done with your `bitcoind` connection, you should close it:
``` ```
bitcoinrpc_global_cleanup(); bitcoinrpc_global_cleanup();
``` ```
#### Test Your Connection
Appendix I shows the complete code for a test of a `bitcoind` connection.
### Make an RPC Call
In order to use an RPC method in `bitcoinrpc`, you must initialize a variable of type `bitcoinrpc_method_t`. You do so with the appropriate value for the method you want to use, all of which are listed in the [bitcoinrpc Reference](https://github.com/gitmarek/libbitcoinrpc/blob/master/doc/reference.md).
```
bitcoinrpc_method_t *getmininginfo = NULL;
getmininginfo = bitcoinrpc_method_init(BITCOINRPC_METHOD_GETMININGINFO);
```
Usually you would set parameters here, but `getmininginfo` requires no parameters, so you can skip that for now.
Two more objects are required, a "response object" and an "error object". They're created via standard `bitcoinrpc` function calls:
```
bitcoinrpc_resp_t *btcresponse = NULL;
btcresponse = bitcoinrpc_resp_init();
bitcoinrpc_err_t btcerror;
```
And now you can put it all together to make a `getmininginfo` RPC call:
```
bitcoinrpc_call (rpc_client, getmininginfo, btcresponse, &btcerror);
```
### Output Your Response
Retrieve the output of your call as a JSON object with `bitcoinrpc_resp_get`.
```
json_t *jsonresponse = NULL;
jsonresponse = bitcoinrpc_resp_get (btcresponse);
```
If you want to output the complete JSON results of the RPC call, you can do so with a simple invocation of `json_dumps`, from the `jansson` library:
```
printf ("%s\n", json_dumps (j, JSON_INDENT(2)));
```
However since your now writing complete programs, you're probably going to want to do more subtle work, such as pulling out individual JSON values for specific usage. The [jansson Reference](https://jansson.readthedocs.io/en/2.10/apiref.html) details how to do so.
You can drill down to the `result` JSON object:
```
json_t *jsonresult = NULL;
jsonresult = json_object_get(jsonresponse,"result");
printf ("%s\n", json_dumps (jsonresult, JSON_INDENT(2)));
```
Alternatively, you can drill down to an individual item like `blocks`:
```
json_t *jsonblocks = NULL;
jsonresult = json_object_get(jsonresult,"blocks");
int blocks;
blocks = json_integer_value(jsonresult);
printf("Block Count: %d\n",blocks);
```
Appendix II has an example of this complete code, with the variable initiatialization all rearranged to the top, and with cleanup of the JSON objects.
[[SUMMARY]]
## Appendix I: Testing a Bitcoind Connection
Here's the complete code for a test of the connection to `bitcoind`. Here's the complete code for a test of the connection to `bitcoind`.
``` ```
@ -90,8 +145,7 @@ int main(void) {
bitcoinrpc_global_init(); bitcoinrpc_global_init();
bitcoinrpc_cl_t *rpc_client; bitcoinrpc_cl_t *rpc_client;
rpc_client = bitcoinrpc_cl_init_params ("bitcoinrpc", "d8340efbcd34e312044c843 rpc_client = bitcoinrpc_cl_init_params ("bitcoinrpc", "d8340efbcd34e312044c8431c59c792c", "127.0.0.1", 18332);
1c59c792c", "127.0.0.1", 18332);
if (rpc_client) { if (rpc_client) {
@ -107,64 +161,14 @@ int main(void) {
} }
``` ```
Test it out to make sure everything is working: You can compile and run this as follows:
``` ```
$ cc testbitcoin.c -lbitcoinrpc -ljansson -o testbitcoin $ cc testbitcoin.c -lbitcoinrpc -ljansson -o testbitcoin
$ ./testbitcoin $ ./testbitcoin
Successfully connected to server! Successfully connected to server!
``` ```
### Make an RPC Call ## Appendix II: Getting Mining Info
In order to you an RPC method in `bitcoinrpc`, you must initialize a variable of type `bitcoinrpc_method_t`. You do so with the appropriate value for the method you want to use, all of which are listed in the [bitcoinrpc Reference](https://github.com/gitmarek/libbitcoinrpc/blob/master/doc/reference.md), which includes all of the `bitcoinrpc` constants, including RPC calls and error messages.
```
bitcoinrpc_method_t *getmininginfo = NULL;
getmininginfo = bitcoinrpc_method_init(BITCOINRPC_METHOD_GETMININGINFO);
```
Usually you would set parameters here, but in this get, `getmininginfo` requires no parameters, so we can skip that.
Two more objects are required, a "response object" and an "error object". They're created via standard `bitcoinrpc` function calls:
```
bitcoinrpc_resp_t *btcresponse = NULL;
btcresponse = bitcoinrpc_resp_init();
bitcoinrpc_err_t btcerror;
```
And now you can put it all together to make a `getmininginfo` RPC call:
```
bitcoinrpc_call (rpc_client, getmininginfo, btcresponse, &btcerror);
```
### Output Your Response
Retrieve the output of your call with `bitcoinrpc_resp_get`.
```
json_t *jsonresponse = NULL;
jsonresponse = bitcoinrpc_resp_get (btcresponse);
```
If you want to output the complete JSON results of the RPC call, you can do so with a simple invocation of `json_dumps`, from the `jansson` library:
```
fprintf (stderr, "%s\n", json_dumps (j, JSON_INDENT(2)));
```
However since your now writing complete programs, you're probably going to want to do more subtle work, such as pulling out individual JSON values for specific usage. The [jansson Reference](https://jansson.readthedocs.io/en/2.10/apiref.html) tells how to do so.
You can then drill down to the `result` JSON object:
```
json_t *jsonresult = NULL;
jsonresult = json_object_get(jsonresponse,"result");
fprintf (stderr, "%s\n", json_dumps (jsonresult, JSON_INDENT(2)));
```
Finall, you can drill down to an individual item like `blocks`:
```
json_t *jsonblocks = NULL;
jsonresult = json_object_get(jsonresult,"blocks");
int blocks;
blocks = json_integer_value(jsonresult);
printf("Block Count: %d\n",blocks);
```
[[SUMMARY]]
[[APPENDIX 1: First Code]]
[[APPENDIX 2: First Code]] [[APPENDIX 2: First Code]]
[[clean up organizing of initialization of variables]] [[clean up organizing of initialization of variables]]
[[FREE up the JSON objects]] [[FREE up the JSON objects]]