Table of Contents
Various coding styles have been used during the history of the codebase, and the result is not very consistent. However, we're now trying to converge to a single style, which is specified below. When writing patches, favor the new style over attempting to mimic the surrounding style, except for move-only commits.
Do not submit patches solely to modify the style of existing code.
Indentation and whitespace rules as specified in src/.clang-format. You can use the provided clang-format-diff script tool to clean up patches automatically before submission.
public/protected/private or for namespace.( this ).if, for and while.if only has a single-statement then-clause, it can appear on the same line as the if, without braces. In every other case, braces are required, and the then and else clauses must appear correctly indented on a new line.Symbol naming conventions. These are preferred in new code, but are not required when doing so would need changes to significant pieces of existing code.
_ to separate words (snake_case).
m_ prefix.g_ prefix._ to separate words.C.src/test/foo_tests.cpp should be named foo_tests. Test suite names must be unique.Miscellaneous
++i is preferred over i++.nullptr is preferred over NULL or (void*)0.static_assert is preferred over assert where possible. Generally; compile-time checking is preferred over run-time checking.Block style example:
int g_count = 0;
namespace foo {
class Class
{
std::string m_name;
public:
bool Function(const std::string& s, int n)
{
// Comment summarising what this section of code does
for (int i = 0; i < n; ++i) {
int total_sum = 0;
// When something fails, return early
if (!Something()) return false;
...
if (SomethingElse(i)) {
total_sum += ComputeSomething(g_count);
} else {
DoSomething(m_name, total_sum);
}
}
// Success return is usually at the end
return true;
}
}
} // namespace fooRefer to /test/functional/README.html#style-guidelines.
Bitcoin Core uses Doxygen to generate its official documentation.
Use Doxygen-compatible comment blocks for functions, methods, and fields.
For example, to describe a function use:
/**
* ... Description ...
*
* @param[in] arg1 input description...
* @param[in] arg2 input description...
* @param[out] arg3 output description...
* @return Return cases...
* @throws Error type and cases...
* @pre Pre-condition for function...
* @post Post-condition for function...
*/
bool function(int arg1, const char *arg2, std::string& arg3)A complete list of @xxx commands can be found at http://www.doxygen.nl/manual/commands.html. As Doxygen recognizes the comments by the delimiters (/** and */ in this case), you don't need to provide any commands for a comment to be valid; just a description text is fine.
To describe a class, use the same construct above the class definition:
/**
* Alerts are for notifying old versions if they become too obsolete and
* need to upgrade. The message is displayed in the status bar.
* @see GetWarnings()
*/
class CAlertTo describe a member or variable use:
or
Also OK:
Not picked up by Doxygen:
Also not picked up by Doxygen:
A full list of comment syntaxes picked up by Doxygen can be found at http://www.doxygen.nl/manual/docblocks.html, but the above styles are favored.
Recommendations:
Avoiding duplicating type and input/output information in function descriptions.
Use backticks (``) to refer to argument names in function and parameter descriptions.
Backticks aren't required when referring to functions Doxygen already knows about; it will build hyperlinks for these automatically. See http://www.doxygen.nl/manual/autolink.html for complete info.
Avoid linking to external documentation; links can break.
Javadoc and all valid Doxygen comments are stripped from Doxygen source code previews (STRIP_CODE_COMMENTS = YES in Doxyfile.in). If you want a comment to be preserved, it must instead use // or /* */.
The documentation can be generated with make docs and cleaned up with make clean-docs. The resulting files are located in doc/doxygen/html; open index.html in that directory to view the homepage.
Before running make docs, you'll need to install these dependencies:
Linux: sudo apt install doxygen graphviz
MacOS: brew install doxygen graphviz
Run configure with --enable-debug to add additional compiler flags that produce better debugging builds.
Run configure with the --enable-gprof option, then make.
debug.logIf the code is behaving strangely, take a look in the debug.log file in the data directory; error and debugging messages are written there.
The -debug=... command-line option controls debugging; running with just -debug or -debug=1 will turn on all categories (and give you a very large debug.log file).
The Qt code routes qDebug() output to debug.log under category "qt": run with -debug=qt to see it.
Run with the -testnet option to run with "play bitcoins" on the test network, if you are testing multi-machine code that needs to operate across the internet.
If you are testing something that can run on one machine, run with the -regtest option. In regression test mode, blocks can be created on-demand; see test/functional/ for tests that run in -regtest mode.
Bitcoin Core is a multi-threaded application, and deadlocks or other multi-threading bugs can be very difficult to track down. The --enable-debug configure option adds -DDEBUG_LOCKORDER to the compiler flags. This inserts run-time checks to keep track of which locks are held and adds warnings to the debug.log file if inconsistencies are detected.
The util file src/util/check.h offers helpers to protect against coding and internal logic bugs. They must never be used to validate user, network or any other input.
assert or Assert should be used to document assumptions when any violation would mean that it is not safe to continue program execution. The code is always compiled with assertions enabled.
CHECK_NONFATAL should be used for recoverable internal logic bugs. On failure, it will throw an exception, which can be caught to recover from the error.
Assume should be used to document assumptions when program execution can safely continue even if the assumption is violated. In debug builds it behaves like Assert/assert to notify developers and testers about nonfatal errors. In production it doesn't warn or log anything, though the expression is always evaluated.
Valgrind is a programming tool for memory debugging, memory leak detection, and profiling. The repo contains a Valgrind suppressions file (valgrind.supp) which includes known Valgrind warnings in our dependencies that cannot be fixed in-tree. Example use:
$ valgrind --suppressions=contrib/valgrind.supp src/test/test_bitcoin
$ valgrind --suppressions=contrib/valgrind.supp --leak-check=full \
--show-leak-kinds=all src/test/test_bitcoin --log_level=test_suite
$ valgrind -v --leak-check=full src/bitcoind -printtoconsole
$ ./test/functional/test_runner.py --valgrind
LCOV can be used to generate a test coverage report based upon make check execution. LCOV must be installed on your system (e.g. the lcov package on Debian/Ubuntu).
To enable LCOV report generation during test runs:
./configure --enable-lcov
make
make cov
# A coverage report will now be accessible at `./test_bitcoin.coverage/index.html`.
Profiling is a good way to get a precise idea of where time is being spent in code. One tool for doing profiling on Linux platforms is called perf, and has been integrated into the functional test framework. Perf can observe a running process and sample (at some frequency) where its execution is.
Perf installation is contingent on which kernel version you're running; see this thread for specific instructions.
Certain kernel parameters may need to be set for perf to be able to inspect the running process's stack.
Make sure you understand the security trade-offs of setting these kernel parameters.
To profile a running bitcoind process for 60 seconds, you could use an invocation of perf record like this:
You could then analyze the results by running:
or using a graphical tool like Hotspot.
See the functional test documentation for how to invoke perf within tests.
Bitcoin Core can be compiled with various "sanitizers" enabled, which add instrumentation for issues regarding things like memory safety, thread race conditions, or undefined behavior. This is controlled with the --with-sanitizers configure flag, which should be a comma separated list of sanitizers to enable. The sanitizer list should correspond to supported -fsanitize= options in your compiler. These sanitizers have runtime overhead, so they are most useful when testing changes or producing debugging builds.
Some examples:
# Enable both the address sanitizer and the undefined behavior sanitizer
./configure --with-sanitizers=address,undefined
# Enable the thread sanitizer
./configure --with-sanitizers=threadIf you are compiling with GCC you will typically need to install corresponding "san" libraries to actually compile with these flags, e.g. libasan for the address sanitizer, libtsan for the thread sanitizer, and libubsan for the undefined sanitizer. If you are missing required libraries, the configure script will fail with a linker error when testing the sanitizer flags.
The test suite should pass cleanly with the thread and undefined sanitizers, but there are a number of known problems when using the address sanitizer. The address sanitizer is known to fail in sha256_sse4::Transform which makes it unusable unless you also use --disable-asm when running configure. We would like to fix sanitizer issues, so please send pull requests if you can fix any errors found by the address sanitizer (or any other sanitizer).
Not all sanitizer options can be enabled at the same time, e.g. trying to build with --with-sanitizers=address,thread will fail in the configure script as these sanitizers are mutually incompatible. Refer to your compiler manual to learn more about these options and which sanitizers are supported by your compiler.
Additional resources:
The code is multi-threaded and uses mutexes and the LOCK and TRY_LOCK macros to protect data structures.
Deadlocks due to inconsistent lock ordering (thread 1 locks cs_main and then cs_wallet, while thread 2 locks them in the opposite order: result, deadlock as each waits for the other to release its lock) are a problem. Compile with -DDEBUG_LOCKORDER (or use --enable-debug) to get lock order inconsistencies reported in the debug.log file.
Re-architecting the core code so there are better-defined interfaces between the various components is a goal, with any necessary locking done by the components (e.g. see the self-contained FillableSigningProvider class and its cs_KeyStore lock for example).
Main thread (bitcoind) : Started from main() in bitcoind.cpp. Responsible for starting up and shutting down the application.
ThreadImport (b-loadblk) : Loads blocks from blk*.dat files or -loadblock=<file> on startup.
ThreadScriptCheck (b-scriptch.x) : Parallel script validation threads for transactions in blocks.
ThreadHTTP (b-http) : Libevent thread to listen for RPC and REST connections.
HTTP worker threads(b-httpworker.x) : Threads to service RPC and REST requests.
Indexer threads (b-txindex, etc) : One thread per indexer.
SchedulerThread (b-scheduler) : Does asynchronous background tasks like dumping wallet contents, dumping addrman and running asynchronous validationinterface callbacks.
TorControlThread (b-torcontrol) : Libevent thread for tor connections.
Net threads:
ThreadMessageHandler (b-msghand) : Application level message handling (sending and receiving). Almost all net_processing and validation logic runs on this thread.
ThreadDNSAddressSeed (b-dnsseed) : Loads addresses of peers from the DNS.
ThreadMapPort (b-upnp) : Universal plug-and-play startup/shutdown.
ThreadSocketHandler (b-net) : Sends/Receives data from peers on port 8333.
ThreadOpenAddedConnections (b-addcon) : Opens network connections to added nodes.
ThreadOpenConnections (b-opencon) : Initiates new connections to peers.
In closed-source environments in which everyone uses the same IDE, it is common to add temporary files it produces to the project-wide .gitignore file.
However, in open source software such as Bitcoin Core, where everyone uses their own editors/IDE/tools, it is less common. Only you know what files your editor produces and this may change from version to version. The canonical way to do this is thus to create your local gitignore. Add this to ~/.gitconfig:
[core]
excludesfile = /home/.../.gitignore_global
(alternatively, type the command git config --global core.excludesfile ~/.gitignore_global on a terminal)
Then put your favourite tool's temporary filenames in that file, e.g.
# NetBeans
nbproject/
Another option is to create a per-repository excludes file .git/info/exclude. These are not committed but apply only to one repository.
If a set of tools is used by the build system or scripts the repository (for example, lcov) it is perfectly acceptable to add its files to .gitignore and commit them.
A few non-style-related recommendations for developers, as well as points to pay attention to for reviewers of Bitcoin Core code.
New features should be exposed on RPC first, then can be made available in the GUI.
Make sure pull requests pass CI before merging.
Rationale: Makes sure that they pass thorough testing, and that the tester will keep passing on the master branch. Otherwise, all new pull requests will start failing the tests, resulting in confusion and mayhem.
Explanation: If the test suite is to be updated for a change, this has to be done first.
Make sure that no crashes happen with run-time option -disablewallet.
Include db_cxx.h (BerkeleyDB header) only when ENABLE_WALLET is set.
For general C++ guidelines, you may refer to the C++ Core Guidelines.
Common misconceptions are clarified in those sections:
Passing (non-)fundamental types in the C++ Core Guideline.
Assertions should not have side-effects.
If you use the .h, you must link the .cpp.
.h to the .cpp should not result in build errors.Use the RAII (Resource Acquisition Is Initialization) paradigm where possible. For example, by using unique_ptr for allocations in a function.
Use MakeUnique() to construct objects owned by unique_ptrs.
MakeUnique is concise and ensures exception safety in complex expressions. MakeUnique is a temporary project local implementation of std::make_unique (C++14).Never use the std::map [] syntax when reading from a map, but instead use .find().
[] does an insert (of the default element) if the item doesn't exist in the map yet. This has resulted in memory leaks in the past, as well as race conditions (expecting read-read behavior). Using [] is fine for writing to a map.Do not compare an iterator from one data structure with an iterator of another data structure (even if of the same type).
Watch out for out-of-bounds vector access. &vch[vch.size()] is illegal, including &vch[0] for an empty vector. Use vch.data() and vch.data() + vch.size() instead.
Vector bounds checking is only enabled in debug mode. Do not rely on it.
Initialize all non-static class members where they are defined. If this is skipped for a good reason (i.e., optimization on the critical path), add an explicit comment about this.
By default, declare constructors explicit.
Use explicitly signed or unsigned chars, or even better uint8_t and int8_t. Do not use bare char unless it is to pass to a third-party API. This type can be signed or unsigned depending on the architecture, which can lead to interoperability problems or dangerous conditions such as out-of-bounds array accesses.
Prefer explicit constructions over implicit ones that rely on 'magical' C++ behavior.
Use Span as function argument when it can operate on any range-like container.
Foo(const vector<int>&) this avoids the need for a (potentially expensive) conversion to vector if the caller happens to have the input stored in another type of container. However, be aware of the pitfalls documented in span.h.Prefer enum class (scoped enumerations) over enum (traditional enumerations) where possible.
int, and name clashes due to enumerators being exported to the surrounding scope.switch statement on an enumeration example:
enum class Tabs {
INFO,
CONSOLE,
GRAPH,
PEERS
};
int GetInt(Tabs tab)
{
switch (tab) {
case Tabs::INFO: return 0;
case Tabs::CONSOLE: return 1;
case Tabs::GRAPH: return 2;
case Tabs::PEERS: return 3;
} // no default case, so the compiler can warn about missing cases
assert(false);
}Rationale: The comment documents skipping default: label, and it complies with clang-format rules. The assertion prevents firing of -Wreturn-type warning on some compilers.
Be careful of LogPrint versus LogPrintf. LogPrint takes a category argument, LogPrintf does not.
Use std::string, avoid C string manipulation functions.
\0 characters. Also, some C string manipulations tend to act differently depending on platform, or even the user locale.Use ParseInt32, ParseInt64, ParseUInt32, ParseUInt64, ParseDouble from utilstrencodings.h for number parsing.
Avoid using locale dependent functions if possible. You can use the provided lint-locale-dependence.sh to check for accidental use of locale dependent functions.
Rationale: Unnecessary locale dependence can cause bugs that are very tricky to isolate and fix.
These functions are known to be locale dependent: alphasort, asctime, asprintf, atof, atoi, atol, atoll, atoq, btowc, ctime, dprintf, fgetwc, fgetws, fprintf, fputwc, fputws, fscanf, fwprintf, getdate, getwc, getwchar, isalnum, isalpha, isblank, iscntrl, isdigit, isgraph, islower, isprint, ispunct, isspace, isupper, iswalnum, iswalpha, iswblank, iswcntrl, iswctype, iswdigit, iswgraph, iswlower, iswprint, iswpunct, iswspace, iswupper, iswxdigit, isxdigit, mblen, mbrlen, mbrtowc, mbsinit, mbsnrtowcs, mbsrtowcs, mbstowcs, mbtowc, mktime, putwc, putwchar, scanf, snprintf, sprintf, sscanf, stoi, stol, stoll, strcasecmp, strcasestr, strcoll, strfmon, strftime, strncasecmp, strptime, strtod, strtof, strtoimax, strtol, strtold, strtoll, strtoq, strtoul, strtoull, strtoumax, strtouq, strxfrm, swprintf, tolower, toupper, towctrans, towlower, towupper, ungetwc, vasprintf, vdprintf, versionsort, vfprintf, vfscanf, vfwprintf, vprintf, vscanf, vsnprintf, vsprintf, vsscanf, vswprintf, vwprintf, wcrtomb, wcscasecmp, wcscoll, wcsftime, wcsncasecmp, wcsnrtombs, wcsrtombs, wcstod, wcstof, wcstoimax, wcstol, wcstold, wcstoll, wcstombs, wcstoul, wcstoull, wcstoumax, wcswidth, wcsxfrm, wctob, wctomb, wctrans, wctype, wcwidth, wprintf
For strprintf, LogPrint, LogPrintf formatting characters don't need size specifiers.
Use .c_str() sparingly. Its only valid use is to pass C++ strings to C functions that take NULL-terminated strings.
Do not use it when passing a sized array (so along with .size()). Use .data() instead to get a pointer to the raw data.
.data() communicates the intent better.Do not use it when passing strings to tfm::format, strprintf, LogPrint[f].
Do not use it to convert to QString. Use QString::fromStdString().
In cases where do you call .c_str(), you might want to additionally check that the string does not contain embedded '\0' characters, because it will (necessarily) truncate the string. This might be used to hide parts of the string from logging or to circumvent checks. If a use of strings is sensitive to this, take care to check the string for embedded NULL characters first and reject it if there are any (see ParsePrechecks in strencodings.cpp for an example).
Although the shadowing warning (-Wshadow) is not enabled by default (it prevents issues arising from using a different variable with the same name), please name variables so that their names do not shadow variables defined in the source code.
When using nested cycles, do not name the inner cycle variable the same as in the upper cycle, etc.
Prefer Mutex type to RecursiveMutex one
Consistently use Clang Thread Safety Analysis annotations to get compile-time warnings about potential race conditions in code. Combine annotations in function declarations with run-time asserts in function definitions:
// txmempool.h
class CTxMemPool
{
public:
...
mutable RecursiveMutex cs;
...
void UpdateTransactionsFromBlock(...) EXCLUSIVE_LOCKS_REQUIRED(::cs_main, cs);
...
}
// txmempool.cpp
void CTxMemPool::UpdateTransactionsFromBlock(...)
{
AssertLockHeld(::cs_main);
AssertLockHeld(cs);
...
}// validation.h
class ChainstateManager
{
public:
...
bool ProcessNewBlock(...) EXCLUSIVE_LOCKS_REQUIRED(!::cs_main);
...
}
// validation.cpp
bool ChainstateManager::ProcessNewBlock(...)
{
AssertLockNotHeld(::cs_main);
...
LOCK(::cs_main);
...
}Build and run tests with -DDEBUG_LOCKORDER to verify that no potential deadlocks are introduced. As of 0.12, this is defined by default when configuring with --enable-debug.
When using LOCK/TRY_LOCK be aware that the lock exists in the context of the current scope, so surround the statement and the code that needs the lock with braces.
OK:
Wrong:
Use #!/usr/bin/env bash instead of obsolete #!/bin/bash.
#!/bin/bash assumes it is always installed to /bin/ which can cause issues;
#!/usr/bin/env bash searches the user's PATH to find the bash binary.
OK:
Wrong:
Implementation code should go into the .cpp file and not the .h, unless necessary due to template usage or when performance due to inlining is critical.
Use only the lowercase alphanumerics (a-z0-9), underscore (_) and hyphen (-) in source code filenames.
grep:ing and auto-completing filenames is easier when using a consistent naming pattern. Potential problems when building on case-insensitive filesystems are avoided when using only lowercase characters in source code filenames.Every .cpp and .h file should #include every header file it directly uses classes, functions or other definitions from, even if those headers are already included indirectly through other headers.
Don't import anything into the global namespace (using namespace ...). Use fully specified types such as std::string.
Terminate namespaces with a comment (// namespace mynamespace). The comment should be placed on the same line as the brace closing the namespace, e.g.
Rationale: Avoids confusion about the namespace context.
Use #include <primitives/transaction.h> bracket syntax instead of #include "primitives/transactions.h" quote syntax.
Use include guards to avoid the problem of double inclusion. The header file foo/bar.h should use the include guard identifier BITCOIN_FOO_BAR_H, e.g.
Do not display or manipulate dialogs in model code (classes *Model).
Avoid adding slow or blocking code in the GUI thread. In particular, do not add new interfaces::Node and interfaces::Wallet method calls, even if they may be fast now, in case they are changed to lock or communicate across processes in the future.
Prefer to offload work from the GUI thread to worker threads (see RPCExecutor in console code as an example) or take other steps (see https://doc.qt.io/archives/qq/qq27-responsive-guis.html) to keep the GUI responsive.
Several parts of the repository are subtrees of software maintained elsewhere.
Some of these are maintained by active developers of Bitcoin Core, in which case changes should probably go directly upstream without being PRed directly against the project. They will be merged back in the next subtree merge.
Others are external projects without a tight relationship with our project. Changes to these should also be sent upstream, but bugfixes may also be prudent to PR against Bitcoin Core so that they can be integrated quickly. Cosmetic changes should be purely taken upstream.
There is a tool in test/lint/git-subtree-check.sh (instructions) to check a subtree directory for consistency with its upstream repository.
Current subtrees include:
src/leveldb
src/crc32c
src/secp256k1
src/crypto/ctaes
src/univalue
Extra care must be taken when upgrading LevelDB. This section explains issues you must be aware of.
In most configurations, we use the default LevelDB value for max_open_files, which is 1000 at the time of this writing. If LevelDB actually uses this many file descriptors, it will cause problems with Bitcoin's select() loop, because it may cause new sockets to be created where the fd value is >= 1024. For this reason, on 64-bit Unix systems, we rely on an internal LevelDB optimization that uses mmap() + close() to open table files without actually retaining references to the table file descriptors. If you are upgrading LevelDB, you must sanity check the changes to make sure that this assumption remains valid.
In addition to reviewing the upstream changes in env_posix.cc, you can use lsof to check this. For example, on Linux this command will show open .ldb file counts:
$ lsof -p $(pidof bitcoind) |\
awk 'BEGIN { fd=0; mem=0; } /ldb$/ { if ($4 == "mem") mem++; else fd++ } END { printf "mem = %s, fd = %s\n", mem, fd}'
mem = 119, fd = 0The mem value shows how many files are mmap'ed, and the fd value shows you many file descriptors these files are using. You should check that fd is a small number (usually 0 on 64-bit hosts).
See the notes in the SetMaxOpenFiles() function in dbwrapper.cc for more details.
It is possible for LevelDB changes to inadvertently change consensus compatibility between nodes. This happened in Bitcoin 0.8 (when LevelDB was first introduced). When upgrading LevelDB, you should review the upstream changes to check for issues affecting consensus compatibility.
For example, if LevelDB had a bug that accidentally prevented a key from being returned in an edge case, and that bug was fixed upstream, the bug "fix" would be an incompatible consensus change. In this situation, the correct behavior would be to revert the upstream fix before applying the updates to Bitcoin's copy of LevelDB. In general, you should be wary of any upstream changes affecting what data is returned from LevelDB queries.
For reformatting and refactoring commits where the changes can be easily automated using a bash script, we use scripted-diff commits. The bash script is included in the commit message and our CI job checks that the result of the script is identical to the commit. This aids reviewers since they can verify that the script does exactly what it is supposed to do. It is also helpful for rebasing (since the same script can just be re-run on the new master commit).
To create a scripted-diff:
scripted-diff: (and then a description of the diff on the same line)-BEGIN VERIFY SCRIPT--END VERIFY SCRIPT-The scripted-diff is verified by the tool test/lint/commit-script-check.sh. The tool's default behavior, when supplied with a commit is to verify all scripted-diffs from the beginning of time up to said commit. Internally, the tool passes the first supplied argument to git rev-list --reverse to determine which commits to verify script-diffs for, ignoring commits that don't conform to the commit message format described above.
For development, it might be more convenient to verify all scripted-diffs in a range A..B, for example:
If you need to replace in multiple files, prefer git ls-files to find or globbing, and git grep to grep, to avoid changing files that are not under version control.
For efficient replacement scripts, reduce the selection to the files that potentially need to be modified, so for example, instead of a blanket git ls-files src | xargs sed -i s/apple/orange/, use git grep -l apple src | xargs sed -i s/apple/orange/.
Also, it is good to keep the selection of files as specific as possible — for example, replace only in directories where you expect replacements — because it reduces the risk that a rebase of your commit by re-running the script will introduce accidental changes.
Some good examples of scripted-diff:
scripted-diff: Rename InitInterfaces to NodeContext uses an elegant script to replace occurrences of multiple terms in all source files.
scripted-diff: Remove g_connman, g_banman globals replaces specific terms in a list of specific source files.
scripted-diff: Replace fprintf with tfm::format does a global replacement but excludes certain directories.
To find all previous uses of scripted diffs in the repository, do:
git log --grep="-BEGIN VERIFY SCRIPT-"
Release notes should be written for any PR that:
Release notes should be added to a PR-specific release note file at /doc/release-notes-<PR number>.html to avoid conflicts between multiple PRs. All release-notes* files are merged into a single /doc/release-notes.html file prior to the release.
A few guidelines for introducing and reviewing new RPC interfaces:
Method naming: use consecutive lower-case names such as getrawtransaction and submitblock.
Argument naming: use snake case fee_delta (and not, e.g. camel case feeDelta)
Use the JSON parser for parsing, don't manually parse integers or strings from arguments unless absolutely necessary.
Rationale: Introduces hand-rolled string manipulation code at both the caller and callee sites, which is error-prone, and it is easy to get things such as escaping wrong. JSON already supports nested data structures, no need to re-invent the wheel.
Exception: AmountFromValue can parse amounts as string. This was introduced because many JSON parsers and formatters hard-code handling decimal numbers as floating-point values, resulting in potential loss of precision. This is unacceptable for monetary values. Always use AmountFromValue and ValueFromAmount when inputting or outputting monetary values. The only exceptions to this are prioritisetransaction and getblocktemplate because their interface is specified as-is in BIP22.
Missing arguments and 'null' should be treated the same: as default values. If there is no default value, both cases should fail in the same way. The easiest way to follow this guideline is to detect unspecified arguments with params[x].isNull() instead of params.size() <= x. The former returns true if the argument is either null or missing, while the latter returns true if is missing, and false if it is null.
Try not to overload methods on argument type. E.g. don't make getblock(true) and getblock("hash") do different things.
Rationale: This is impossible to use with bitcoin-cli, and can be surprising to users.
Exception: Some RPC calls can take both an int and bool, most notably when a bool was switched to a multi-value, or due to other historical reasons. Always have false map to 0 and true to 1 in this case.
Don't forget to fill in the argument names correctly in the RPC command table.
Set okSafeMode in the RPC command table to a sensible value: safe mode is when the blockchain is regarded to be in a confused state, and the client deems it unsafe to do anything irreversible such as send. Anything that just queries should be permitted.
Add every non-string RPC argument (method, idx, name) to the table vRPCConvertParams in rpc/client.cpp.
bitcoin-cli and the GUI debug console use this table to determine how to convert a plaintext command line to JSON. If the types don't match, the method can be unusable from there.A RPC method must either be a wallet method or a non-wallet method. Do not introduce new methods that differ in behavior based on the presence of a wallet.
Try to make the RPC response a JSON object.
Wallet RPCs call BlockUntilSyncedToCurrentChain to maintain consistency with getblockchaininfo's state immediately prior to the call's execution. Wallet RPCs whose behavior does not depend on the current chainstate may omit this call.
Be aware of RPC method aliases and generally avoid registering the same callback function pointer for different RPCs.
Rationale: RPC methods registered with the same function pointer will be considered aliases and only the first method name will show up in the help RPC command list.
Exception: Using RPC method aliases may be appropriate in cases where a new RPC is replacing a deprecated RPC, to avoid both RPCs confusingly showing up in the command list.
Use invalid bech32 addresses (e.g. in the constant array EXAMPLE_ADDRESS) for RPCExamples help documentation.
Use the UNIX_EPOCH_TIME constant when describing UNIX epoch time or timestamps in the documentation.
Internal interfaces between parts of the codebase that are meant to be independent (node, wallet, GUI), are defined in src/interfaces/. The main interface classes defined there are interfaces::Chain, used by wallet to access the node's latest chain state, interfaces::Node, used by the GUI to control the node, and interfaces::Wallet, used by the GUI to control an individual wallet. There are also more specialized interface types like interfaces::Handler interfaces::ChainClient passed to and from various interface methods.
Interface classes are written in a particular style so node, wallet, and GUI code doesn't need to run in the same process, and so the class declarations work more easily with tools and libraries supporting interprocess communication:
Interface classes should be abstract and have methods that are pure virtual. This allows multiple implementations to inherit from the same interface class, particularly so one implementation can execute functionality in the local process, and other implementations can forward calls to remote processes.
Interface method definitions should wrap existing functionality instead of implementing new functionality. Any substantial new node or wallet functionality should be implemented in src/node/ or src/wallet/ and just exposed in src/interfaces/ instead of being implemented there, so it can be more modular and accessible to unit tests.
Interface method parameter and return types should either be serializable or be other interface classes. Interface methods shouldn't pass references to objects that can't be serialized or accessed from another process.
Examples:
// Good: takes string argument and returns interface class pointer
virtual unique_ptr<interfaces::Wallet> loadWallet(std::string filename) = 0;
// Bad: returns CWallet reference that can't be used from another process
virtual CWallet& loadWallet(std::string filename) = 0;// Good: accepts and returns primitive types
virtual bool findBlock(const uint256& hash, int& out_height, int64_t& out_time) = 0;
// Bad: returns pointer to internal node in a linked list inaccessible to
// other processes
virtual const CBlockIndex* findBlock(const uint256& hash) = 0;// Good: takes plain callback type and returns interface pointer
using TipChangedFn = std::function<void(int block_height, int64_t block_time)>;
virtual std::unique_ptr<interfaces::Handler> handleTipChanged(TipChangedFn fn) = 0;
// Bad: returns boost connection specific to local process
using TipChangedFn = std::function<void(int block_height, int64_t block_time)>;
virtual boost::signals2::scoped_connection connectTipChanged(TipChangedFn fn) = 0;For consistency and friendliness to code generation tools, interface method input and inout parameters should be ordered first and output parameters should come last.
Example:
For friendliness to code generation tools, interface methods should not be overloaded:
Example:
For consistency and friendliness to code generation tools, interface method names should be lowerCamelCase and standalone function names should be UpperCamelCase.
Examples:
// Good: lowerCamelCase method name
virtual void blockConnected(const CBlock& block, int height) = 0;
// Bad: uppercase class method
virtual void BlockConnected(const CBlock& block, int height) = 0;// Good: UpperCamelCase standalone function name
std::unique_ptr<Node> MakeNode(LocalInit& init);
// Bad: lowercase standalone function
std::unique_ptr<Node> makeNode(LocalInit& init);Note: This last convention isn't generally followed outside of src/interfaces/, though it did come up for discussion before in #14635.