AWS C Common

Core c99 package for AWS SDK for C. Includes cross-platform primitives, configuration, data structures, and error handling.

License

This library is licensed under the Apache 2.0 License.

Usage

Building

aws-c-common uses CMake for setting up build environments. This library has no non-kernel dependencies so the build is quite simple.

For example:

git clone [email protected]:awslabs/aws-c-common.git aws-c-common
mkdir aws-c-common-build
cd aws-c-common-build
cmake ../aws-c-common
make -j 12
make test
sudo make install

Keep in mind that CMake supports multiple build systems, so for each platform you can pass your own build system as the

-G

cmake -GNinja ../aws-c-common
ninja build
ninja test
sudo ninja install

Or on windows,

cmake -G "Visual Studio 14 2015 Win64" ../aws-c-common
msbuild.exe ALL_BUILD.vcproj

CMake Options

• -DCMAKECLANGTIDY=/path/to/clang-tidy (or just clang-tidy or clang-tidy-7.0 if it is in your PATH) - Runs clang-tidy as part of your build.
• -DENABLESANITIZERS=ON - Enables gcc/clang sanitizers, by default this adds -fsanitizer=address,undefined to the compile flags for projects that call awsadd_sanitizers.
• -DENABLEFUZZTESTS=ON - Includes fuzz tests in the unit test suite. Off by default, because fuzz tests can take a long time. Set -DFUZZTESTSMAX_TIME=N to determine how long to run each fuzz test (default 60s).
• -DCMAKEINSTALLPREFIX=/path/to/install - Standard way of installing to a user defined path. If specified when configuring aws-c-common, ensure the same prefix is specified when configuring other aws-c-* SDKs.
• -DSTATIC_CRT=ON - On MSVC, use /MT(d) to link MSVCRT

API style and conventions

Every API has a specific set of styles and conventions. We'll outline them here. These conventions are followed in every library in the AWS C SDK ecosystem.

Error handling

Every function that returns an

int

AWS_OP_SUCCESS

AWS_OP_ERR

aws_last_error()

aws_error_str()

In addition, you can install both a global and a thread local error handler by using the

aws_set_global_error_handler_fn()

aws_set_thread_local_error_handler_fn()

All error functions are in the

include/aws/common/error.h

Naming

Any function that allocates and initializes an object will be suffixed with

new

aws_myobj_new()

destroy

new

NULL

aws_last_error()

new

destroy

new_x

destroy_x

aws_myobj_new_copy()

aws_myobj_destroy_secure()

Any function that initializes an existing object will be suffixed with

init

aws_myobj_init()

clean_up

init

AWS_OP_SUCCESS

AWS_OP_ERR

init

clean_up

init_x

clean_up_x

aws_myobj_init_static()

aws_myobj_clean_up_secure()

Contributing

If you are contributing to this code-base, first off, THANK YOU!. There are a few things to keep in mind to minimize the pull request turn around time.

Coding "guidelines"

These "guidelines" are followed in every library in the AWS C SDK ecosystem.

Memory Management

• All APIs that need to be able to allocate memory, must take an instance of

  aws_allocator

  and use that. No

  malloc()

  or

  free()

  calls should be made directly.
• If an API does not allocate the memory, it does not free it. All allocations and deallocations should take place at the same level. For example, if a user allocates memory, the user is responsible for freeing it. There will inevitably be a few exceptions to this rule, but they will need significant justification to make it through the code-review.
• All functions that allocate memory must raise an

  AWS_ERROR_OOM

  error code upon allocation failures. If it is a

  new()

  function it should return NULL. If it is an

  init()

  function, it should return

  AWS_OP_ERR

  .

Threading

• Occasionally a thread is necessary. In those cases, prefer for memory not to be shared between threads. If memory must cross a thread barrier it should be a complete ownership hand-off. Bias towards, "if I need a mutex, I'm doing it wrong".
• Do not sleep or block .... ever .... under any circumstances, in non-test-code.
• Do not expose blocking APIs.

Error Handling

• For APIs returning an

  int

  error code. The only acceptable return types are

  AWS_OP_SUCCESS

  and

  AWS_OP_ERR

  . Before returning control to the caller, if you have an error to raise, use the

  aws_raise_error()

  function.
• For APIs returning an allocated instance of an object, return the memory on success, and

  NULL

  on failure. Before returning control to the caller, if you have an error to raise, use the

  aws_raise_error()

  function.

Log Subjects & Error Codes

The logging & error handling infrastructure is designed to support multiple libraries. For this to work, AWS maintained libraries have pre-slotted log subjects & error codes for each library. The currently allocated ranges are:

| Range | Library Name | | --- | --- | | [0x0000, 0x0400) | aws-c-common | | [0x0400, 0x0800) | aws-c-io | | [0x0800, 0x0C00) | aws-c-http | | [0x0C00, 0x1000) | aws-c-compression | | [0x1000, 0x1400) | aws-c-eventstream | | [0x1400, 0x1800) | aws-c-mqtt | | [0x1800, 0x1C00) | aws-c-auth | | [0x1C00, 0x2000) | aws-c-cal | | [0x2000, 0x2400) | aws-crt-cpp | | [0x2400, 0x2800) | aws-crt-java | | [0x2800, 0x2C00) | aws-crt-python | | [0x2C00, 0x3000) | aws-crt-nodejs | | [0x3000, 0x3400) | aws-crt-dotnet | | [0x3400, 0x3800) | aws-c-iot | | [0x3800, 0x3C00) | (reserved for future project) | | [0x3C00, 0x4000) | (reserved for future project) | | [0x4000, 0x4400) | (reserved for future project) | | [0x4400, 0x4800) | (reserved for future project) |

Each library should begin its error and log subject values at the beginning of its range and follow in sequence (don't skip codes). Upon adding an AWS maintained library, a new enum range must be approved and added to the above table.

Testing

We have a high bar for test coverage, and PRs fixing bugs or introducing new functionality need to have tests before they will be accepted. A couple of tips:

Aws Test Harness

We provide a test harness for writing unit tests. This includes an allocator that will fail your test if you have any memory leaks, as well as some

ASSERT

• Create a *.c test file in the tests directory of the project.
• Implement one or more tests with the signature

  int test_case_name(struct aws_allocator *, void *ctx)

• Use the

  AWS_TEST_CASE

  macro to declare the test.
• Include your test in the

  tests/main.c

  file.
• Include your test in the

  tests/CMakeLists.txt

  file.

Coding Style

• No Tabs.
• Indent is 4 spaces.
• K & R style for braces.
• Space after if, before the

  (

  .

• else

  and

  else if

  stay on the same line as the closing brace.

Example:

if (condition) {
    do_something();
} else {
    do_something_else();
}

• Avoid C99 features in header files. For some types such as bool, uint32_t etc..., these are defined if not available for the language standard being used in

  aws/common/common.h

  , so feel free to use them.
• For C++ compatibility, don't put const members in structs.
• Avoid C++ style comments e.g.

  //

  .
• All public API functions need C++ guards and Windows dll semantics.
• Use Unix line endings.
• Where implementation hiding is desired for either ABI or runtime polymorphism reasons, use the

  void *impl

  pattern. v-tables should be the last member in the struct.
• For #ifdef, put a # as the first character on the line and then indent the compilation branches.

Example:

#ifdef FOO
    do_something();

ifdef BAR
do_something_else();
endif
#endif

• For all error code names with the exception of aws-c-common, use

  AWS_ERROR__

  .
• All error strings should be written using correct English grammar.
• SNAKEUPPERCASE constants, macros, and enum members.
• snakelowercase everything else.

• static

  (local file scope) variables that are not

  const

  are prefixed by

  s_

  and lower snake case.
• Global variables not prefixed as

  const

  are prefixed by

  g_

  and lower snake case.
• Thread local variables are prefixed as

  tl_

  and lower snake case.
• Macros and

  const

  variables are upper snake case.
• For constants, prefer anonymous enums.
• Don't typedef structs. It breaks forward declaration ability.
• Don't typedef enums. It breaks forward declaration ability.
• typedef function definitions for use as function pointers as values and suffixed with _fn.

Example:

typedef int(fn_name_fn)(void *);

Not:

typedef int(*fn_name_fn)(void *);

• Every source and header file must have a copyright header (The standard AWS one for apache 2).
• Use standard include guards (e.g. #IFNDEF HEADERNAME #define HEADERNAME etc...).
• Include order should be: the header for the translation unit for the .c file newline header files in a directory in alphabetical order newline header files not in a directory (system and stdlib headers)
• Platform specifics should be handled in c files and partitioned by directory.
• Do not use

  extern inline

  . It's too unpredictable between compiler versions and language standards.
• Namespace all definitions in header files with

  aws_?__

  . Lib name is not always required if a conflict is not likely and it provides better ergonomics.

• init

  ,

  clean_up

  ,

  new

  ,

  destroy

  are suffixed to the function names for their object.

Example:

AWS_COMMON_API

int awsmoduleinit(awsmodulet *module); AWSCOMMONAPI void awsmodulecleanup(awsmodulet *module); AWSCOMMONAPI awsmodulet *awsmodulenew(awsallocatort *allocator); AWSCOMMONAPI void awsmoduledestroy(awsmodule_t *module);

• Avoid c-strings, and don't write code that depends on

  NULL

  terminators. Expose

  struct aws_byte_buf

  APIs and let the user figure it out.
• There is only one valid character encoding-- UTF-8. Try not to ever need to care about character encodings, but where you do, the working assumption should always be UTF-8 unless it's something we don't get a choice in (e.g. a protocol explicitly mandates a character set).
• If you are adding/using a compiler specific keyword, macro, or intrinsic, hide it behind a platform independent macro definition. This mainly applies to header files. Obviously, if you are writing a file that will only be built on a certain platform, you have more liberty on this.
• When checking more than one error condition, check and log each condition separately with a unique message.

Example:

if (options->callback == NULL) {
    AWS_LOGF_ERROR(AWS_LS_SOME_SUBJECT, "Invalid options - callback is null");
    return aws_raise_error(AWS_ERROR_INVALID_ARGUMENT);
}

if (options->allocator == NULL) {
    AWS_LOGF_ERROR(AWS_LS_SOME_SUBJECT, "Invalid options - allocator is null");
    return aws_raise_error(AWS_ERROR_INVALID_ARGUMENT);
}

Not:

if (options->callback == NULL || options->allocator == NULL) {
    AWS_LOGF_ERROR(AWS_LS_SOME_SUBJECT, "Invalid options - something is null");
    return aws_raise_error(AWS_ERROR_INVALID_ARGUMENT);
}