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Developer Notes

Style guide C++

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. We are sticking to the Google C++ Style Guide.

This includes aiming for a maximum line length of 80 characters.

There are a few additional rules:

  • 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.

    • Variable (including function arguments) and namespace names are all lowercase, and may use _ to separate words (snake_case).
      • Class member variables have a m_ prefix.
      • Public struct member variables don't have m_ prefix.
      • Global variables have a g_ prefix.
    • Constant names are all uppercase, and use _ to separate words.
    • Class names, function names and method names are UpperCamelCase (PascalCase). Do not prefix class names with C.

  • Includes. Make sure to always use <> notation instead of the "". This is done mostly for consistency with the current codebase.

  • Forward declarations. Forward declarations of classes and structs are allowed and welcome, especially when they solve circular dependencies problem or increase recompilation time. But note that forward declarations of functions and templated classes are prohibited according to Google Style Guide.

  • If-Statements.

    • Always use braces around if statements, even blocks that contain just one statement.
    • Prefer early return as a guard clause 
      if (!smth) {
  return;
}

// continue with the valid case

  • namespace.

    • files in src/ don't have namespace
    • files in src/directory have directory namespace
    • avoid nested directories/namespaces

  • Uniform initialization. Rationale: Uniform initialization isn't.

    • In call sites: Use parentheses to initialize in all cases. Use braces only for the specific behavior that braces provide.
    • When declaring classes: Avoid writing class interfaces in which an ambiguity between uniform initialization and list-initializer syntax might arise.

  • 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.
    • Do not use the scope resolution unless it is required (that is: use Type instead of ::Type if not ambigious otherwise)

You can check the code for style violations by running test/lint/lint-clang-format.py. Use the --help option to get more info how to use it.

Copy the contrib/githooks/pre-commit file to your .git/hooks directory and make it executable to automatically apply the defined style on your commits. If you don't want automatic changes, adapt the options of the call in the pre-commit file.

Style guide Python

Refer to /test/functional/README.md#style-guidelines. You can check the code for style violations by running test/lint/lint-python.sh.

UNIT-E tag

In case of comments and TODOs that are pertinent only to the UNIT-E code please create a code comment like:

//UNIT-E: very specific comment about unit-e

Doxygen comments

To facilitate the generation of documentation, use doxygen-compatible comment blocks for functions, methods and fields.

For example, to describe a function use:

//! \brief one-line description
//!
//! ... optional long description ...
//! @param[in] arg1    A description
//! @param[in] arg2    Another argument description
//! @pre Precondition for function...
bool function(int arg1, const char *arg2) {

To describe a class use the same construct above the class definition:

//! \brief one-line description
//!
//! 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:

//! Detailed description
int var;

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.

Development tips and tricks

compiling for debugging

Run configure with the --enable-debug option, then make. Or run configure with CXXFLAGS="-g -ggdb -O0" or whatever debug flags you need.

compiling for gprof profiling

Run configure with the --enable-gprof option, then make.

debug.log

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).

testnet and regtest modes

Run with the -testnet option to run with "play unites" 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.

DEBUG_LOCKORDER

unit-e is a multithreaded application, and deadlocks or other multithreading bugs can be very difficult to track down. Compiling with -DDEBUG_LOCKORDER (configure CXXFLAGS="-DDEBUG_LOCKORDER -g") 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 suppressions file

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_unite
$ valgrind --suppressions=contrib/valgrind.supp --leak-check=full \
      --show-leak-kinds=all src/test/test_unite --log_level=test_suite
$ valgrind -v --leak-check=full src/unit-e -printtoconsole

compiling for test coverage

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_unite.coverage/index.html`.

Sanitizers

unit-e 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:

Locking/mutex usage notes

The code is multi-threaded, and uses mutexes and the LOCK/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 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 CKeyStore class and its cs_KeyStore lock for example).

Threads

  • 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 7182.

  • 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.

  • ThreadFlushWalletDB : Close the wallet.dat file if it hasn't been used in 500ms.

  • ThreadRPCServer : Remote procedure call handler, listens on port 7181 for connections and services them.

  • unite-proposer : Proposes new blocks using the open wallets balance as stake.

  • unite-snapshot : Creates snapshots and deletes outdated ones

  • Shutdown : Does an orderly shutdown of everything.

Ignoring IDE/editor files

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 unit-e, 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.

Development guidelines

A few non-style-related recommendations for developers, as well as points to pay attention to for reviewers of unit-e code.

General unit-e

  • 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

Wallet

  • Make sure that no crashes happen with run-time option -disablewallet.

    • Rationale: In RPC code that conditionally uses the wallet (such as 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

    • Rationale: Otherwise compilation of the disable-wallet build will fail in environments without BerkeleyDB

General C++

  • Assertions should not have side-effects

    • Rationale: Even though the source code is set to refuse to compile with assertions disabled, having side-effects in assertions is unexpected and makes the code harder to understand

  • If you use the .h, you must link the .cpp

    • Rationale: Include files define the interface for the code in implementation files. Including one but not linking the other is confusing. Please avoid that. Moving functions from the .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.

    • Rationale: This avoids memory and resource leaks, and ensures exception safety

C++ data structures

  • Never use the std::map [] syntax when reading from a map, but instead use .find()

    • Rationale: [] 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)

    • Rationale: Behavior is undefined. In C++ parlor this means "may reformat the universe", in practice this has resulted in at least one hard-to-debug crash bug

  • 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

  • Make sure that constructors initialize all fields. If this is skipped for a good reason (i.e., optimization on the critical path), add an explicit comment about this

    • Rationale: Ensure determinism by avoiding accidental use of uninitialized values. Also, static analyzers balk about this.

  • By default, declare single-argument constructors explicit.

    • Rationale: This is a precaution to avoid unintended conversions that might arise when single-argument constructors are used as implicit conversion functions.

  • 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

    • Rationale: Easier to understand what is happening, thus easier to spot mistakes, even for those that are not language lawyers

Strings and formatting

  • Be careful of LogPrint versus LogPrintf. LogPrint takes a category argument, LogPrintf does not.

    • Rationale: Confusion of these can result in runtime exceptions due to formatting mismatch, and it is easy to get wrong because of subtly similar naming

  • Use std::string, avoid C string manipulation functions

    • Rationale: C++ string handling is marginally safer, less scope for buffer overflows and surprises with \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

    • Rationale: These functions do overflow checking, and avoid pesky locale issues

  • 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

    • Rationale: unit-e uses tinyformat, which is type safe. Leave them out to avoid confusion

Variable names

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 mode;
}

AddressBookPage::AddressBookPage(Mode _mode) :
      mode(_mode)
...

When using nested cycles, do not name the inner cycle variable the same as in upper cycle etc.

Threads and synchronization

  • 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);
{
    ...
}

Source code organization

  • 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

    • Rationale: Shorter and simpler header files are easier to read, and reduce compile time

  • 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. One exception is that a .cpp file does not need to re-include the includes already included in its corresponding .h file.

    • Rationale: Excluding headers because they are already indirectly included results in compilation failures when those indirect dependencies change. Furthermore, it obscures what the real code dependencies are.

  • Don't import anything into the global namespace (using namespace ...). Use fully specified types such as std::string.

    • Rationale: Avoids symbol conflicts

  • 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

  • Prefer #include <primitives/transaction.h> bracket syntax instead of #include "primitives/transactions.h" quote syntax when possible.

    • Rationale: Bracket syntax is less ambiguous because the preprocessor searches a fixed list of include directories without taking location of the source file into account. This allows quoted includes to stand out more when the location of the source file actually is relevant.

Subtrees

Several parts of the repository are git subtrees of software maintained elsewhere. They are managed with git-subtree.

Some of these are maintained by active developers of Bitcoin Core, some are external projects without a tight relationship to Bitcoin Core.

Changes on the parts of the code which are pulled in as a git subtree are ideally done through contributions to the original upstream and then pulled in via subtree updates in bitcoin upstream and then merged to unit-e with a bitcoin merge.

Where this is too slow changes might also be done via pull request to the Bitcoin Core version of the code. See the bitcoin developer notes for their policies on that.

If something needs to be merged urgently we create a fork of the repo where the subtree is coming from, apply the patches there and merge that as subtree from our fork. This makes it clear where changes are coming from and it keeps the integrity of the git subtrees in the unit-e repository without local changes.

Current subtrees

You can list the git subtrees of a repo with the command

git log | grep git-subtree-dir | awk '{ print $2 }' | sort | uniq

These are the current subtrees and where they are coming from:

Checking subtrees

There is a tool in test/lint/git-subtree-check.sh to check a subtree directory for consistency with its upstream repository. Run it for example as:

$ test/lint/git-subtree-check.sh src/secp256k1
src/secp256k1 in HEAD currently refers to tree 8ae830321a35bc7499991d5428bec2b231f0f154
src/secp256k1 in HEAD was last updated in commit 520d78e7c9698245e8da1509661922068ffe67ed (tree 8ae830321a35bc7499991d5428bec2b231f0f154)
src/secp256k1 in HEAD was last updated to upstream commit f43d43b1a4b9d2eb426d131f9a9b756de6a2cce2 (tree 8ae830321a35bc7499991d5428bec2b231f0f154)
GOOD

Updating subtrees

Git subtrees are updated from the upstream repos as they are listed above using the git subtree command:

git subtree pull --prefix src/${prefix} ${remote_repo} ${ref} --squash

The remote_repo is the URL or path to the upstream repo, ref is the branch. The commits are squashed so that a subtree update consists of a commit containing all changes since the last update and a merge commit pulling in this commit into the code base.

Git and GitHub tips

  • 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:dtr-org/unit-e.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.

GitHub issues

We use GitHub issues as a way to report bugs or feature requests and track work. See our conventions for GitHub issues for details. These are used across all unit-e related repos.

We use labels to classify and categorize issues and pull requests. The labels are defined in a YAML file and applied to GitHub via the API. Here is an overview of all labels used in the unit-e repository.

GitHub labels

Scripted diffs

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:

  • start the commit message with scripted-diff: (and then a description of the diff on the same line)
  • in the commit message include the bash script between lines containing just the following text:
    • -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.

RPC interface guidelines

A few guidelines for introducing and reviewing new RPC interfaces:

  • Method naming: use consecutive lower-case names such as getrawtransaction and submitblock

    • Rationale: Consistency with existing interface.

  • Argument naming: use snake case fee_delta (and not, e.g. camel case feeDelta)

    • Rationale: Consistency with existing interface.

  • 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 is prioritisetransaction 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.

    • Rationale: Avoids surprises when switching to name-based arguments. Missing name-based arguments are passed as '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 unit-e-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.

    • Rationale: If not, the call can not be used with name-based arguments.

  • 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.

    • Rationale: Troubleshooting a node in safe mode is difficult if half the RPCs don't work.

  • Add every non-string RPC argument (method, idx, name) to the table vRPCConvertParams in rpc/parameter_conversion.cpp.

    • Rationale: unit-e-cli uses 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.

    • Rationale: as well as complicating the implementation and interfering with the introduction of multi-wallet, wallet and non-wallet code should be separated to avoid introducing circular dependencies between code units.

  • Try to make the RPC response a JSON object.

    • Rationale: If a RPC response is not a JSON object then it is harder to avoid API breakage if new data in the response is needed.

  • 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.

    • Rationale: In previous versions of unit-e, the wallet was always in-sync with the chainstate (by virtue of them all being updated in the same cs_main lock). In order to maintain the behavior that wallet RPCs return results as of at least the highest best-known block an RPC client may be aware of prior to entering a wallet RPC call, we must block until the wallet is caught up to the chainstate as of the RPC call's entry. This also makes the API much easier for RPC clients to reason about.

  • 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.