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, so please use it in new code. Old code will be converted
gradually and a handful of linters will help you to clean up your patches before
submitting them for review. These linters are run automatically when using
arc diff but can also be explicitly called with arc lint.
/.clang-format).
public/protected/private or for namespace.if, for and while.if, for, while).++i is preferred over i++.static_assert is preferred over assert where possible.
Generally; compile-time checking is preferred over run-time checking.ValidateTransaction, AddTransactionToMempool, ConnectBlock)canDoThing, signatureOperations, didThing)m_The naming convention roughly mirrors Microsoft Naming Conventions
C++ Coding Standards should strive to follow the LLVM Coding Standards
Code style example:
// namespaces should be lower_snake_case
namespace foo_bar_bob {
/**
* Class is used for doing classy things. All classes should
* have a doxygen comment describing their PURPOSE. That is to say,
* why they exist. Functional details can be determined from the code.
* @see PerformTask()
*/
class Class {
private:
//! memberVariable's name should be lowerCamelCase, and be a noun.
int m_memberVariable;
public:
/**
* The documentation before a function or class method should follow Doxygen
* spec. The name of the function should start with an english verb which
* indicates the intended purpose of this code.
*
* The function name should be should be CamelCase.
*
* @param[in] s A description
* @param[in] n Another argument description
* @pre Precondition for function...
*/
bool PerformTask(const std::string& s, int n) {
// Use lowerChamelCase for local variables.
bool didMore = false;
// Comment summarizing the intended purpose of this section of code
for (int i = 0; i < n; ++i) {
if (!DidSomethingFail()) {
return false;
}
...
if (IsSomethingElse()) {
DoMore();
didMore = true;
} else {
DoLess();
}
}
return didMore;
}
}
} // namespace foo
To facilitate the generation of documentation, use doxygen-compatible comment blocks for functions, methods and fields.
For example, to describe a function use:
/**
* ... text ...
* @param[in] arg1 A description
* @param[in] arg2 Another argument description
* @pre Precondition for function...
*/
bool function(int arg1, const char *arg2)
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 CAlert
{
To describe a member or variable use:
int var; //!< Detailed description after the member
or
//! Description before the member
int var;
Also OK:
///
/// ... text ...
///
bool function2(int arg1, const char *arg2)
Not OK (used plenty in the current source, but not picked up):
//
// ... text ...
//
A full list of comment syntaxes picked up by doxygen can be found at http://www.doxygen.nl/manual/docblocks.html, but if possible use one of the above styles.
To build doxygen locally to test changes to the Doxyfile or visualize your comments before landing changes:
ninja doc-doxygen
# output goes to doc/doxygen/html/
Refer to functional-tests.md#style-guidelines.
Run cmake with -DCMAKE_BUILD_TYPE=Debug to add additional compiler flags
that produce better debugging builds.
cmake -GNinja .. -DENABLE_HARDENING=OFF -DENABLE_PROFIILING=gprof
If 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.
For details on unit tests, see Compiling/running unit tests.
For details on functional tests, see Functional tests.
Script integration tests are built using src/test/script_tests.cpp:
#define UPDATE_JSON_TESTSscript_build test to cover your test case.ninja check-bitcoin-script_tests<build-dir>/src/script_tests.json.gen to src/test/data/script_tests.json.Please commit your TestBuilder along with your generated test JSON and cleanup the uncommented #define before code review.
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/ (/test/functional) for tests
that run in -regtest mode.
Bitcoin ABC is a multi-threaded application, and deadlocks or other
multi-threading bugs can be very difficult to track down.
The -DCMAKE_BUILD_TYPE=Debug cmake 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.
Defining DEBUG_LOCKCONTENTION adds a “lock” logging category that, when enabled,
logs the location and duration of each lock contention to the debug.log file.
To enable it, run cmake with -DDEBUG_LOCKCONTENTION added to your CPPFLAGS,
e.g. -DCMAKE_CXX_FLAGS="-DDEBUG_LOCKCONTENTION", then build and run bitcoind.
You can then use the -debug=lock configuration option at bitcoind startup or
bitcoin-cli logging '["lock"]' at runtime to turn on lock contention logging.
It can be toggled off again with bitcoin-cli logging [] '["lock"]'.
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 (/contrib/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
LCOV can be used to generate a test coverage report based upon some test targets
execution. Some packages are required to generate the coverage report:
c++filt, gcov, genhtml, lcov and python3.
To install these dependencies on Debian 10:
sudo apt install binutils-common g++ lcov python3
To enable LCOV report generation during test runs:
cmake -GNinja .. -DENABLE_COVERAGE=ON
ninja coverage-check-all
A coverage report will now be accessible at ./check-all.coverage/index.html.
To include branch coverage, you can add the -DENABLE_BRANCH_COVERAGE=ON option
to the cmake command line.
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 StackExchange thread for specific instructions.
Certain kernel parameters may need to be set for perf to be able to inspect the running process’ stack.
$ sudo sysctl -w kernel.perf_event_paranoid=-1
$ sudo sysctl -w kernel.kptr_restrict=0
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:
$ perf record \
-g --call-graph dwarf --per-thread -F 140 \
-p `pgrep bitcoind` -- sleep 60
You could then analyze the results by running
perf report --stdio | c++filt | less
or using a graphical tool like Hotspot.
See the functional test documentation for how to invoke perf within tests.
Bitcoin ABC 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
-DENABLE_SANITIZERS cmake flag, which should be a semicolon 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
cmake -GNinja .. -DENABLE_SANITIZERS="address;undefined"
# Enable the thread sanitizer
cmake -GNinja .. -DENABLE_SANITIZERS=thread
If 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 cmake script will fail with an error when testing the sanitizer flags.
Note that the sanitizers will give a better output if they are run with a Debug build configuration.
There are a number of known problems for which suppressions files are provided
under test/sanitizer_suppressions. These files are intended to be used with
the suppressions option from the sanitizers. If you are using the check-*
targets to run the tests, the suppression options are automatically set.
Otherwise they need to be set manually using environment variables; refer to
your compiler manual for the correct syntax.
The address sanitizer is known to fail in
sha256_sse4::Transform (/src/crypto/sha256_sse4.cpp) which makes it unusable
unless you also use -DCRYPTO_USE_ASM=OFF when running cmake.
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 `-DENABLE_SANITIZERS==”address;thread” will fail in the cmake 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.
Examples:
Build and run the test suite with the address sanitizer enabled:
mkdir build_asan
cd build_asan
cmake -GNinja .. \
-DCMAKE_BUILD_TYPE=Debug \
-DENABLE_SANITIZERS=address \
-DCRYPTO_USE_ASM=OFF
ninja check check-functional
Build and run the test suite with the thread sanitizer enabled (it can take a very long time to complete):
mkdir build_tsan
cd build_tsan
cmake -GNinja .. \
-DCMAKE_BUILD_TYPE=Debug \
-DENABLE_SANITIZERS=thread
ninja check check-functional
Build and run the test suite with the undefined sanitizer enabled:
mkdir build_ubsan
cd build_ubsan
cmake -GNinja .. \
-DCMAKE_BUILD_TYPE=Debug \
-DENABLE_SANITIZERS=undefined
ninja check check-functional
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 -DCMAKE_BUILD_TYPE=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).
bitcoind)main() in bitcoind.cpp. Responsible for starting up and
shutting down the application.b-loadblk)blk*.dat files or -loadblock=<file> on startup.b-scriptch.x)b-http)b-httpworker.x)b-txindex, etc)b-scheduler)b-torcontrol)Net threads:
b-msghand)b-dnsseed)b-upnp)b-net)b-addcon)b-opencon)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 ABC, 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 favorite 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 ABC code.
Make sure that no crashes happen with run-time option -disablewallet.
validateaddress) it is easy to forget that global pointer pwalletMain
can be NULL. See test/functional/disablewallet.py for functional tests
exercising the API with -disablewalletInclude db_cxx.h (BerkeleyDB header) only when ENABLE_WALLET is set
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 errorsUse the RAII (Resource Acquisition Is Initialization) paradigm where possible. For example by using
unique_ptr for allocations in a function.
Use std::make_unique() to construct objects owned by unique_ptrs
std::make_unique is concise and ensures exception safety in complex expressions.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 mapDo 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
class A
{
uint32_t m_count{0};
}
By default, declare single-argument 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 (../src/span.h).void Foo(Span<const int> data);
std::vector<int> vec{1,2,3};
Foo(vec);
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 localeUse ParseInt32, ParseInt64, ParseUInt32, ParseUInt64, ParseDouble from utilstrencodings.h for number parsing
The shadowing warning (-Wshadow) is enabled by default. It prevents issues rising
from using a different variable with the same name.
E.g. in member initializers, prepend _ to the argument name shadowing the
member name:
class AddressBookPage
{
Mode m_mode;
}
AddressBookPage::AddressBookPage(Mode _mode) :
m_mode(_mode)
...
When using nested cycles, do not name the inner cycle variable the same as in upper cycle etc.
Please name variables so that their names do not shadow variables defined in the source code.
Prefer Mutex type to RecursiveMutex one
Consistently use Clang Thread Safety Analysis annotations to get compile-time warnings about potential race conditions or deadlocks in code.
In functions that are declared separately from where they are defined, the thread safety annotations should be added exclusively to the function declaration, to avoid shadowing the declaration’s annotation and cause false positives (lack of compile failure) if a new lock requirement is later added to the declaration but the lock is not taken.
Prefer locks that are in a class rather than global, and that are internal to a class (private or protected) rather than public.
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 CChainState {
protected:
...
Mutex m_chainstate_mutex;
...
public:
...
bool ActivateBestChain(
BlockValidationState& state,
std::shared_ptr<const CBlock> pblock = nullptr)
EXCLUSIVE_LOCKS_REQUIRED(!m_chainstate_mutex)
LOCKS_EXCLUDED(::cs_main);
...
bool PreciousBlock(BlockValidationState& state, CBlockIndex* pindex)
EXCLUSIVE_LOCKS_REQUIRED(!m_chainstate_mutex)
LOCKS_EXCLUDED(::cs_main);
...
}
// validation.cpp
bool CChainState::PreciousBlock(BlockValidationState& state, CBlockIndex* pindex) {
AssertLockNotHeld(m_chainstate_mutex);
AssertLockNotHeld(::cs_main);
{
LOCK(cs_main);
...
}
return ActivateBestChain(state, std::shared_ptr<const CBlock>());
}
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 -DCMAKE_BUILD_TYPE=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:
{
TRY_LOCK(cs_vNodes, lockNodes);
...
}
Wrong:
TRY_LOCK(cs_vNodes, lockNodes);
{
...
}
#!/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:
#!/usr/bin/env bash
Wrong:
#!/bin/bash
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.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.
namespace mynamespace {
...
} // namespace mynamespace
namespace {
...
} // namespace
Header inclusions should use angle brackets (#include <>).
The include path should be relative to the src folder.
e.g.: #include <qt/test/guiutiltests.h>
Native C++ headers should be preferred over C compatibility headers.
e.g.: use <cstdint> instead of <stdint.h>
In order to make the code consistent, header files should be included in the following order, with each section separated by a newline:
All headers should be lexically ordered inside their block.
foo/bar.h should use the include guard identifier BITCOIN_FOO_BAR_H, e.g.#ifndef BITCOIN_FOO_BAR_H
#define BITCOIN_FOO_BAR_H
...
#endif // BITCOIN_FOO_BAR_H
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 interface::Node and interface::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.
src/test/foo_tests.cpp should be named foo_tests. Test suite names must
be unique.Several parts of the repository are software maintained elsewhere.
Changes to these should preferably be sent upstream but bugfixes may also be submitted to Bitcoin ABC so that they can be integrated quickly. Cosmetic changes should be purely taken upstream.
Current third party libraries include:
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 = 0
The 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 ABC’s copy of LevelDB. In general you should be wary of any upstream changes affecting what data is returned from LevelDB queries.
Github is not typically the source of truth for pull requests. See CONTRIBUTING for instructions on setting up your repo correctly.
Similarly, your git remote origin should be set to: ssh://[email protected]:2221/source/bitcoin-abc.git
instead of github.com. See CONTRIBUTING.
For git and GitHub productivity tips, see Productivity Notes.
Release notes should be written for any PR that:
Release notes should be added to the /doc/release-notes.md file, which is archived and cleared after each 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 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 such as signrawtransaction that differ in behavior
based on 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 the UNIX_EPOCH_TIME constant when describing UNIX epoch time or
timestamps in the documentation.
Use fs::path::u8string() and fs::u8path() functions when converting path
to JSON strings, not fs::PathToString and fs::PathFromString
Internal interfaces between parts of the codebase that are meant to be
independent (node, wallet, GUI), are defined in
src/interfaces/ (../src/interfaces/). The main interface classes defined
there are interfaces::Chain (../src/interfaces/chain.h), used by wallet to
access the node’s latest chain state,
interfaces::Node (../src/interfaces/node.h), used by the GUI to control the
node, and interfaces::Wallet (../src/interfaces/wallet.h), used by the GUI
to control an individual wallet. There are also more specialized interface
types like interfaces::Handler (../src/interfaces/handler.h)
interfaces::ChainClient (../src/interfaces/chain.h) 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/ (../src/node/) or
src/wallet/ (../src/wallet/) and just exposed in
src/interfaces/ (../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:
// Good: error output param is last
virtual bool broadcastTransaction(const CTransactionRef& tx, CAmount max_fee, std::string& error) = 0;
// Bad: error output param is between input params
virtual bool broadcastTransaction(const CTransactionRef& tx, std::string& error, CAmount max_fee) = 0;
For friendliness to code generation tools, interface methods should not be overloaded:
Example:
// Good: method names are unique
virtual bool disconnectByAddress(const CNetAddr& net_addr) = 0;
virtual bool disconnectById(NodeId id) = 0;
// Bad: methods are overloaded by type
virtual bool disconnect(const CNetAddr& net_addr) = 0;
virtual bool disconnect(NodeId id) = 0;
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/ (../src/interfaces/), though it did come up for discussion
before in #14635.