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Posted to dev@qpid.apache.org by GitBox <gi...@apache.org> on 2020/09/24 20:06:32 UTC
[GitHub] [qpid-dispatch] jiridanek opened a new pull request #853: WIP: DISPATCH-1783 testing safe_snprintf function
jiridanek opened a new pull request #853:
URL: https://github.com/apache/qpid-dispatch/pull/853
My attempt to rescue code from the following commit in the following PR.
The code has diverged since, and I had to edit manually.
https://github.com/nicob87/qpid-dispatch/commit/4fc99cf08d033817c02bc83a6d74ddb8f87515af
https://github.com/jiridanek/qpid-dispatch/compare/jd_nb_2020_09_24-mocking...nicob87:4fc99cf08d033817c02bc83a6d74ddb8f87515af
https://github.com/apache/qpid-dispatch/pull/684
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[GitHub] [qpid-dispatch] jiridanek edited a comment on pull request #853: WIP: DISPATCH-1783 testing safe_snprintf function
Posted by GitBox <gi...@apache.org>.
jiridanek edited a comment on pull request #853:
URL: https://github.com/apache/qpid-dispatch/pull/853#issuecomment-698563800
There is multiple options how to do this. I've been writing a more complete list, but I only have an example for two.
## preprocessor magic
See the PR
## elfspy
https://github.com/mollismerx/elfspy
The code below, plus need to add a library
```
#include "qdr_doctest.h"
#include "elfspy/SPY.h"
#include "elfspy/Fake.h"
int fake_vsnprintf(char * s, size_t n, const char * format, va_list arg) {
return -1;
}
TEST_CASE("safe_snprintf_vsnprintf_failed") {
const int OUTPUT_SIZE = 128;
const char *TEST_MESSAGE = "something";
const int LEN = strlen(TEST_MESSAGE);
size_t len;
char output[OUTPUT_SIZE];
// weird elfspy boilerplate
char* argv[2] = {(char*)"c_unittests", nullptr};
spy::initialise(0, argv);
// setup the fake, it will be unset when the variables go out of scope
// it changes dynamic linking in the running process, to replace call to vsnprintf in glibc with the fake
auto vsnprintf_ = SPY(&vsnprintf);
auto vsnprintf_fake = spy::fake(vsnprintf_, &fake_vsnprintf);
// alternative way for previous line:
// auto vsnprintf_fake = spy::fake(vsnprintf_, [](auto ...) { return -1; }); // I can haz lambdaz !!!
// run the test, simulating a failed vsnprintf
output[0] = 'a';
len = safe_snprintf(output, LEN+10, TEST_MESSAGE);
CHECK(0 == len);
CHECK('\0' == output[0]);
CHECK("" == output);
}
```
## more possibilities
* use the `__wrap` feature in gnu linker
* libraries similar to elfspy, such as mimick, https://github.com/Snaipe/Mimick
* linking order, just define vsnprintf in the same translation unit as the test and things work out just right
* LD_PRELOAD
* ...
## general consideration
In any case, static functions cannot be mocked in C, and also inlining, when compiler decides to optimize this way, destroys the ability to replace a function. That implies that this kind of tests can be either only run in a debug build, or it has to build a second, `-testing` version of the dispatch library, for this testing. Third option is not to link to the dispatch library and `#include` the needed .c files. That also works, if the surface area tested is small. It encourages creating many smaller ctest test targets, instead of one large one.
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[GitHub] [qpid-dispatch] jiridanek edited a comment on pull request #853: WIP: DISPATCH-1783 testing safe_snprintf function
Posted by GitBox <gi...@apache.org>.
jiridanek edited a comment on pull request #853:
URL: https://github.com/apache/qpid-dispatch/pull/853#issuecomment-698563800
There is multiple options how to do this. I've been writing a more complete list, but I only have an example for two.
## preprocessor magic
See the PR
## elfspy
https://github.com/mollismerx/elfspy
The code below, plus need to add a library
```c++
#include "qdr_doctest.h"
#include "elfspy/SPY.h"
#include "elfspy/Fake.h"
int fake_vsnprintf(char * s, size_t n, const char * format, va_list arg) {
return -1;
}
TEST_CASE("safe_snprintf_vsnprintf_failed") {
const int OUTPUT_SIZE = 128;
const char *TEST_MESSAGE = "something";
const int LEN = strlen(TEST_MESSAGE);
size_t len;
char output[OUTPUT_SIZE];
// weird elfspy boilerplate
char* argv[2] = {(char*)"c_unittests", nullptr};
spy::initialise(0, argv);
// setup the fake, it will be unset when the variables go out of scope
// it changes dynamic linking in the running process, to replace call to vsnprintf in glibc with the fake
auto vsnprintf_ = SPY(&vsnprintf);
auto vsnprintf_fake = spy::fake(vsnprintf_, &fake_vsnprintf);
// alternative way for previous line:
// auto vsnprintf_fake = spy::fake(vsnprintf_, [](auto ...) { return -1; }); // I can haz lambdaz !!!
// run the test, simulating a failed vsnprintf
output[0] = 'a';
len = safe_snprintf(output, LEN+10, TEST_MESSAGE);
CHECK(0 == len);
CHECK('\0' == output[0]);
CHECK("" == output);
}
```
## more possibilities
* use the `__wrap` feature in gnu linker
* libraries similar to elfspy, such as mimick, https://github.com/Snaipe/Mimick
* linking order, just define vsnprintf in the same translation unit as the test and things work out just right
* LD_PRELOAD
* ...
## general consideration
In any case, static functions cannot be mocked in C, and also inlining, when compiler decides to optimize this way, destroys the ability to replace a function. That implies that this kind of tests can be either only run in a debug build, or it has to build a second, `-testing` version of the dispatch library, for this testing. Third option is not to link to the dispatch library and `#include` the needed .c files. That also works, if the surface area tested is small. It encourages creating many smaller ctest test targets, instead of one large one.
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[GitHub] [qpid-dispatch] jiridanek edited a comment on pull request #853: WIP: DISPATCH-1783 testing safe_snprintf function
Posted by GitBox <gi...@apache.org>.
jiridanek edited a comment on pull request #853:
URL: https://github.com/apache/qpid-dispatch/pull/853#issuecomment-698563800
There is multiple options how to do this. I've been writing a more complete list, but I only have an example for two.
## preprocessor magic
See the PR
## elfspy
https://github.com/mollismerx/elfspy
The code below, plus need to add a library
```
#include "qdr_doctest.h"
#include "elfspy/SPY.h"
#include "elfspy/Fake.h"
TEST_CASE("safe_snprintf_vsnprintf_failed") {
const int OUTPUT_SIZE = 128;
const char *TEST_MESSAGE = "something";
const int LEN = strlen(TEST_MESSAGE);
size_t len;
char output[OUTPUT_SIZE];
// weird elfspy boilerplate
char* argv[2] = {(char*)"c_unittests", nullptr};
spy::initialise(0, argv);
// setup the fake, it will be unset when the variables go out of scope
// it changes dynamic linking in the running process, to replace call to vsnprintf in glibc with the fake
auto vsnprintf_ = SPY(&vsnprintf);
auto vsnprintf_fake = spy::fake(vsnprintf_, &fake_vsnprintf);
// alternative way for previous line:
// auto vsnprintf_fake = spy::fake(vsnprintf_, [](auto ...) { return -1; }); // I can haz lambdaz !!!
// run the test, simulating a failed vsnprintf
output[0] = 'a';
len = safe_snprintf(output, LEN+10, TEST_MESSAGE);
CHECK(0 == len);
CHECK('\0' == output[0]);
CHECK("" == output);
}
```
## more possibilities
* use the `__wrap` feature in gnu linker
* libraries similar to elfspy, such as mimick, https://github.com/Snaipe/Mimick
* linking order, just define vsnprintf in the same translation unit as the test and things work out just right
* LD_PRELOAD
* ...
## general consideration
In any case, static functions cannot be mocked in C, and also inlining, when compiler decides to optimize this way, destroys the ability to replace a function. That implies that this kind of tests can be either only run in a debug build, or it has to build a second, `-testing` version of the dispatch library, for this testing. Third option is not to link to the dispatch library and `#include` the needed .c files. That also works, if the surface area tested is small. It encourages creating many smaller ctest test targets, instead of one large one.
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[GitHub] [qpid-dispatch] jiridanek commented on pull request #853: WIP: DISPATCH-1783 testing safe_snprintf function
Posted by GitBox <gi...@apache.org>.
jiridanek commented on pull request #853:
URL: https://github.com/apache/qpid-dispatch/pull/853#issuecomment-701609625
The decision is to pursue dynamic PLT/GOT modification approach, such as elfspy. It is self contained in the test source code, and has the least number of requirements on the compilation process. The disadvantage is that it becomes harder to ma the tests work multiplatform.
There are various other libraries besides elfspy, I examined five so far, but each seems to have at least one significant limitation.
I'll close this PR, since we chose not to use preprocessor solution prototyped here. I will put further updates on the Jira.
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[GitHub] [qpid-dispatch] jiridanek closed pull request #853: WIP: DISPATCH-1783 testing safe_snprintf function
Posted by GitBox <gi...@apache.org>.
jiridanek closed pull request #853:
URL: https://github.com/apache/qpid-dispatch/pull/853
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[GitHub] [qpid-dispatch] jiridanek commented on pull request #853: WIP: DISPATCH-1783 testing safe_snprintf function
Posted by GitBox <gi...@apache.org>.
jiridanek commented on pull request #853:
URL: https://github.com/apache/qpid-dispatch/pull/853#issuecomment-698563800
There is multiple options how to do this. I've been writing a more complete list, but I only have an example for two.
## linking magic
See the PR
## elfspy
https://github.com/mollismerx/elfspy
The code below, plus need to add a library
```
#include "qdr_doctest.h"
#include "elfspy/SPY.h"
#include "elfspy/Fake.h"
TEST_CASE("safe_snprintf_vsnprintf_failed") {
const int OUTPUT_SIZE = 128;
const char *TEST_MESSAGE = "something";
const int LEN = strlen(TEST_MESSAGE);
size_t len;
char output[OUTPUT_SIZE];
// weird elfspy boilerplate
char* argv[2] = {(char*)"c_unittests", nullptr};
spy::initialise(0, argv);
// setup the fake, it will be unset when the variables go out of scope
// it changes dynamic linking in the running process, to replace call to vsnprintf in glibc with the fake
auto vsnprintf_ = SPY(&vsnprintf);
auto vsnprintf_fake = spy::fake(vsnprintf_, &fake_vsnprintf);
// alternative way for previous line:
// auto vsnprintf_fake = spy::fake(vsnprintf_, [](auto ...) { return -1; }); // I can haz lambdaz !!!
// run the test, simulating a failed vsnprintf
output[0] = 'a';
len = safe_snprintf(output, LEN+10, TEST_MESSAGE);
CHECK(0 == len);
CHECK('\0' == output[0]);
CHECK("" == output);
}
```
## more possibilities
* use the `__wrap` feature in gnu linker
* libraries similar to elfspy, such as mimick, https://github.com/Snaipe/Mimick
* linking order, just define vsnprintf in the same translation unit as the test and things work out just right
* LD_PRELOAD
* ...
## general consideration
In any case, static functions cannot be mocked in C, and also inlining, when compiler decides to optimize this way, destroys the ability to replace a function. That implies that this kind of tests can be either only run in a debug build, or it has to build a second, `-testing` version of the dispatch library, for this testing. Third option is not to link to the dispatch library and `#include` the needed .c files. That also works, if the surface area tested is small. It encourages creating many smaller ctest test targets, instead of one large one.
----------------------------------------------------------------
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[GitHub] [qpid-dispatch] jiridanek commented on pull request #853: WIP: DISPATCH-1783 testing safe_snprintf function
Posted by GitBox <gi...@apache.org>.
jiridanek commented on pull request #853:
URL: https://github.com/apache/qpid-dispatch/pull/853#issuecomment-698563800
There is multiple options how to do this. I've been writing a more complete list, but I only have an example for two.
## linking magic
See the PR
## elfspy
https://github.com/mollismerx/elfspy
The code below, plus need to add a library
```
#include "qdr_doctest.h"
#include "elfspy/SPY.h"
#include "elfspy/Fake.h"
TEST_CASE("safe_snprintf_vsnprintf_failed") {
const int OUTPUT_SIZE = 128;
const char *TEST_MESSAGE = "something";
const int LEN = strlen(TEST_MESSAGE);
size_t len;
char output[OUTPUT_SIZE];
// weird elfspy boilerplate
char* argv[2] = {(char*)"c_unittests", nullptr};
spy::initialise(0, argv);
// setup the fake, it will be unset when the variables go out of scope
// it changes dynamic linking in the running process, to replace call to vsnprintf in glibc with the fake
auto vsnprintf_ = SPY(&vsnprintf);
auto vsnprintf_fake = spy::fake(vsnprintf_, &fake_vsnprintf);
// alternative way for previous line:
// auto vsnprintf_fake = spy::fake(vsnprintf_, [](auto ...) { return -1; }); // I can haz lambdaz !!!
// run the test, simulating a failed vsnprintf
output[0] = 'a';
len = safe_snprintf(output, LEN+10, TEST_MESSAGE);
CHECK(0 == len);
CHECK('\0' == output[0]);
CHECK("" == output);
}
```
## more possibilities
* use the `__wrap` feature in gnu linker
* libraries similar to elfspy, such as mimick, https://github.com/Snaipe/Mimick
* linking order, just define vsnprintf in the same translation unit as the test and things work out just right
* LD_PRELOAD
* ...
## general consideration
In any case, static functions cannot be mocked in C, and also inlining, when compiler decides to optimize this way, destroys the ability to replace a function. That implies that this kind of tests can be either only run in a debug build, or it has to build a second, `-testing` version of the dispatch library, for this testing. Third option is not to link to the dispatch library and `#include` the needed .c files. That also works, if the surface area tested is small. It encourages creating many smaller ctest test targets, instead of one large one.
----------------------------------------------------------------
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[GitHub] [qpid-dispatch] jiridanek commented on pull request #853: WIP: DISPATCH-1783 testing safe_snprintf function
Posted by GitBox <gi...@apache.org>.
jiridanek commented on pull request #853:
URL: https://github.com/apache/qpid-dispatch/pull/853#issuecomment-698926372
## linking order solution (first found symbol wins)
https://github.com/apache/qpid-dispatch/blob/b5deb03579a7dedd81a56f32baa3e5f4b5b57136/tests/timer_test.c#L37-L44
(this is already being used in Dispatch in one test)
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[GitHub] [qpid-dispatch] jiridanek edited a comment on pull request #853: WIP: DISPATCH-1783 testing safe_snprintf function
Posted by GitBox <gi...@apache.org>.
jiridanek edited a comment on pull request #853:
URL: https://github.com/apache/qpid-dispatch/pull/853#issuecomment-698563800
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