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
.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.enum class
is preferred over enum
where possible. Scoped enumerations avoid two potential pitfalls/problems with traditional C++ enumerations: implicit conversions to int, and name clashes due to enumerators being exported to the surrounding scope.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 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.stack.nl/~dimitri/doxygen/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.stack.nl/~dimitri/doxygen/manual/docblocks.html, but if possible use one of the above styles.
Documentation can be generated with make docs
and cleaned up with make clean-docs
.
Refer to /test/functional/README.md#style-guidelines.
Run configure with --enable-debug
to add additional compiler flags that
produce better debugging builds.
Run configure with the --enable-gprof
option, then make.
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.
Run with the -testnet
option to run with "play litecoins" 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.
Litecoin 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.
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_litecoin
$ valgrind --suppressions=contrib/valgrind.supp --leak-check=full \
--show-leak-kinds=all src/test/test_litecoin --log_level=test_suite
$ valgrind -v --leak-check=full src/litecoind -printtoconsole
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_litecoin.coverage/index.html`.
Sanitizers
Litecoin 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=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 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 CBasicKeyStore
class
and its cs_KeyStore
lock for example).
ThreadScriptCheck : Verifies block scripts.
ThreadImport : Loads blocks from blk*.dat files or bootstrap.dat.
StartNode : Starts other threads.
ThreadDNSAddressSeed : Loads addresses of peers from the DNS.
ThreadMapPort : Universal plug-and-play startup/shutdown
ThreadSocketHandler : Sends/Receives data from peers on port 9333.
ThreadOpenAddedConnections : Opens network connections to added nodes.
ThreadOpenConnections : Initiates new connections to peers.
ThreadMessageHandler : Higher-level message handling (sending and receiving).
DumpAddresses : Dumps IP addresses of nodes to peers.dat.
ThreadRPCServer : Remote procedure call handler, listens on port 9332 for connections and services them.
Shutdown : Does an orderly shutdown of everything.
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 Litecoin 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 Litecoin Core code.
New features should be exposed on RPC first, then can be made available in the GUI
Make sure pull requests pass Travis 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
.
validateaddress
) it is easy to forget that global pointer pwalletMain
can be nullptr. See test/functional/disablewallet.py
for functional tests
exercising the API with -disablewallet
Include 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.
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 char
s, 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
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 localeUse 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
Although the shadowing warning (-Wshadow
) is not enabled by default (it prevents issues rising
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.
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.
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:
{
TRY_LOCK(cs_vNodes, lockNodes);
...
}
Wrong:
TRY_LOCK(cs_vNodes, lockNodes);
{
...
}
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.
namespace mynamespace {
...
} // namespace mynamespace
namespace {
...
} // namespace
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.
#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 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 Litecoin 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 Litecoin 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
to check a subtree directory for consistency with
its upstream repository.
Current subtrees include:
src/leveldb
src/libsecp256k1
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 Litecoin'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 $(pidof litecoind) |\
awk 'BEGIN { fd=0; mem=0; } /ldb$/ { 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 Litecoin's copy of LevelDB. In general you should be wary of any upstream changes affecting what data is returned from LevelDB queries.
For resolving merge/rebase conflicts, it can be useful to enable diff3 style using
git config merge.conflictstyle diff3
. Instead of
<<<
yours
===
theirs
>>>
you will see
<<<
yours
|||
original
===
theirs
>>>
This may make it much clearer what caused the conflict. In this style, you can often just look at what changed between original and theirs, and mechanically apply that to yours (or the other way around).
When reviewing patches which change indentation in C++ files, use git diff -w
and git show -w
. This makes
the diff algorithm ignore whitespace changes. This feature is also available on github.com, by adding ?w=1
at the end of any URL which shows a diff.
When reviewing patches that change symbol names in many places, use git diff --word-diff
. This will instead
of showing the patch as deleted/added lines, show deleted/added words.
When reviewing patches that move code around, try using
git diff --patience commit~:old/file.cpp commit:new/file/name.cpp
, and ignoring everything except the
moved body of code which should show up as neither +
or -
lines. In case it was not a pure move, this may
even work when combined with the -w
or --word-diff
options described above.
When looking at other's pull requests, it may make sense to add the following section to your .git/config
file:
[remote "upstream-pull"]
fetch = +refs/pull/*:refs/remotes/upstream-pull/*
url = git@github.com:litecoin-project/litecoin.git
This will add an upstream-pull
remote to your git repository, which can be fetched using git fetch --all
or git fetch upstream-pull
. Afterwards, you can use upstream-pull/NUMBER/head
in arguments to git show
,
git checkout
and anywhere a commit id would be acceptable to see the changes from pull request NUMBER.
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 Travis 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's 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
Commit bb81e173
is an example of a scripted-diff.
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 litecoin-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
.
litecoin-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.