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diff --git a/locale/pt/LC_MESSAGES/_articles/2021-02-17-ann-fallible-fault-injection-library-for-stress-testing-failure-scenarios.po b/locale/pt/LC_MESSAGES/_articles/2021-02-17-ann-fallible-fault-injection-library-for-stress-testing-failure-scenarios.po new file mode 100644 index 0000000..3dc4a7d --- /dev/null +++ b/locale/pt/LC_MESSAGES/_articles/2021-02-17-ann-fallible-fault-injection-library-for-stress-testing-failure-scenarios.po @@ -0,0 +1,344 @@ +# +msgid "" +msgstr "" + +msgid "" +"title: \"ANN: fallible - Fault injection library for stress-testing failure " +"scenarios\"" +msgstr "" + +msgid "date: 2021-02-17" +msgstr "" + +msgid "layout: post" +msgstr "" + +msgid "lang: en" +msgstr "" + +msgid "" +"ref: ann-fallible-fault-injection-library-for-stress-testing-failure-" +"scenarios" +msgstr "" + +msgid "" +"Yesterday I pushed v0.1.0 of [fallible](https://fallible.euandreh.xyz), a " +"miniscule library for fault-injection and stress-testing C programs." +msgstr "" + +msgid "Existing solutions" +msgstr "" + +msgid "" +"Writing robust code can be challenging, and tools like static analyzers, " +"fuzzers and friends can help you get there with more certainty. As I would " +"try to improve some of my C code and make it more robust, in order to handle" +" system crashes, filled disks, out-of-memory and similar scenarios, I didn't" +" find existing tooling to help me get there as I expected to find. I " +"couldn't find existing tools to help me explicitly stress-test those failure" +" scenarios." +msgstr "" + +msgid "" +"Take the \"[Writing Robust " +"Programs](https://www.gnu.org/prep/standards/standards.html#Semantics)\" " +"section of the GNU Coding Standards:" +msgstr "" + +msgid "" +"Check every system call for an error return, unless you know you wish to " +"ignore errors. (...) Check every call to malloc or realloc to see if it " +"returned NULL." +msgstr "" + +msgid "" +"From a robustness standpoint, this is a reasonable stance: if you want to " +"have a robust program that knows how to fail when you're out of memory and " +"`malloc` returns `NULL`, than you ought to check every call to `malloc`." +msgstr "" + +msgid "Take a sample code snippet for clarity:" +msgstr "" + +msgid "" +"void a_function() {\n" +" char *s1 = malloc(A_NUMBER);\n" +" strcpy(s1, \"some string\");\n" +"\n" +" char *s2 = malloc(A_NUMBER);\n" +" strcpy(s2, \"another string\");\n" +"}\n" +msgstr "" + +msgid "" +"At a first glance, this code is unsafe: if any of the calls to `malloc` " +"returns `NULL`, `strcpy` will be given a `NULL` pointer." +msgstr "" + +msgid "My first instinct was to change this code to something like this:" +msgstr "" + +msgid "" +"@@ -1,7 +1,15 @@\n" +" void a_function() {\n" +" char *s1 = malloc(A_NUMBER);\n" +"+ if (!s1) {\n" +"+ fprintf(stderr, \"out of memory, exitting\\n\");\n" +"+ exit(1);\n" +"+ }\n" +" strcpy(s1, \"some string\");\n" +"\n" +" char *s2 = malloc(A_NUMBER);\n" +"+ if (!s2) {\n" +"+ fprintf(stderr, \"out of memory, exitting\\n\");\n" +"+ exit(1);\n" +"+ }\n" +" strcpy(s2, \"another string\");\n" +" }\n" +msgstr "" + +msgid "" +"As I later found out, there are at least 2 problems with this approach:" +msgstr "" + +msgid "" +"**it doesn't compose**: this could arguably work if `a_function` was `main`." +" But if `a_function` lives inside a library, an `exit(1);` is a inelegant " +"way of handling failures, and will catch the top-level `main` consuming the " +"library by surprise;" +msgstr "" + +msgid "" +"**it gives up instead of handling failures**: the actual handling goes a bit" +" beyond stopping. What about open file handles, in-memory caches, unflushed " +"bytes, etc.?" +msgstr "" + +msgid "" +"If you could force only the second call to `malloc` to fail, " +"[Valgrind](https://www.valgrind.org/) would correctly complain that the " +"program exitted with unfreed memory." +msgstr "" + +msgid "So the last change to make the best version of the above code is:" +msgstr "" + +msgid "" +"@@ -1,15 +1,14 @@\n" +"-void a_function() {\n" +"+bool a_function() {\n" +" char *s1 = malloc(A_NUMBER);\n" +" if (!s1) {\n" +"- fprintf(stderr, \"out of memory, exitting\\n\");\n" +"- exit(1);\n" +"+ return false;\n" +" }\n" +" strcpy(s1, \"some string\");\n" +"\n" +" char *s2 = malloc(A_NUMBER);\n" +" if (!s2) {\n" +"- fprintf(stderr, \"out of memory, exitting\\n\");\n" +"- exit(1);\n" +"+ free(s1);\n" +"+ return false;\n" +" }\n" +" strcpy(s2, \"another string\");\n" +" }\n" +msgstr "" + +msgid "" +"Instead of returning `void`, `a_function` now returns `bool` to indicate " +"whether an error ocurred during its execution. If `a_function` returned a " +"pointer to something, the return value could be `NULL`, or an `int` that " +"represents an error code." +msgstr "" + +msgid "" +"The code is now a) safe and b) failing gracefully, returning the control to " +"the caller to properly handle the error case." +msgstr "" + +msgid "" +"After seeing similar patterns on well designed APIs, I adopted this practice" +" for my own code, but was still left with manually verifying the correctness" +" and robustness of it." +msgstr "" + +msgid "" +"How could I add assertions around my code that would help me make sure the " +"`free(s1);` exists, before getting an error report? How do other people and " +"projects solve this?" +msgstr "" + +msgid "" +"From what I could see, either people a) hope for the best, b) write safe " +"code but don't strees-test it or c) write ad-hoc code to stress it." +msgstr "" + +msgid "" +"The most proeminent case of c) is SQLite: it has a few wrappers around the " +"familiar `malloc` to do fault injection, check for memory limits, add " +"warnings, create shim layers for other environments, etc. All of that, " +"however, is tightly couple with SQLite itself, and couldn't be easily pulled" +" off for using somewhere else." +msgstr "" + +msgid "" +"When searching for it online, an [interesting " +"thread](https://stackoverflow.com/questions/1711170/unit-testing-for-failed-" +"malloc) caught my atention: fail the call to `malloc` for each time it is " +"called, and when the same stacktrace appears again, allow it to proceed." +msgstr "" + +msgid "Implementation" +msgstr "" + +msgid "" +"A working implementation of that already exists: " +"[mallocfail](https://github.com/ralight/mallocfail). It uses `LD_PRELOAD` to" +" replace `malloc` at run-time, computes the SHA of the stacktrace and fails " +"once for each SHA." +msgstr "" + +msgid "" +"I initially envisioned and started implementing something very similar to " +"mallocfail. However I wanted it to go beyond out-of-memory scenarios, and " +"using `LD_PRELOAD` for every possible corner that could fail wasn't a good " +"idea on the long run." +msgstr "" + +msgid "" +"Also, mallocfail won't work together with tools such as Valgrind, who want " +"to do their own override of `malloc` with `LD_PRELOAD`." +msgstr "" + +msgid "" +"I instead went with less automatic things: starting with a " +"`fallible_should_fail(char *filename, int lineno)` function that fails once " +"for each `filename`+`lineno` combination, I created macro wrappers around " +"common functions such as `malloc`:" +msgstr "" + +msgid "" +"void *fallible_malloc(size_t size, const char *const filename, int lineno) {\n" +"#ifdef FALLIBLE\n" +" if (fallible_should_fail(filename, lineno)) {\n" +" return NULL;\n" +" }\n" +"#else\n" +" (void)filename;\n" +" (void)lineno;\n" +"#endif\n" +" return malloc(size);\n" +"}\n" +"\n" +"#define MALLOC(size) fallible_malloc(size, __FILE__, __LINE__)\n" +msgstr "" + +msgid "" +"With this definition, I could replace the calls to `malloc` with `MALLOC` " +"(or any other name that you want to `#define`):" +msgstr "" + +msgid "" +"--- 3.c\t2021-02-17 00:15:38.019706074 -0300\n" +"+++ 4.c\t2021-02-17 00:44:32.306885590 -0300\n" +"@@ -1,11 +1,11 @@\n" +" bool a_function() {\n" +"- char *s1 = malloc(A_NUMBER);\n" +"+ char *s1 = MALLOC(A_NUMBER);\n" +" if (!s1) {\n" +" return false;\n" +" }\n" +" strcpy(s1, \"some string\");\n" +"\n" +"- char *s2 = malloc(A_NUMBER);\n" +"+ char *s2 = MALLOC(A_NUMBER);\n" +" if (!s2) {\n" +" free(s1);\n" +" return false;\n" +msgstr "" + +msgid "" +"With this change, if the program gets compiled with the `-DFALLIBLE` flag " +"the fault-injection mechanism will run, and `MALLOC` will fail once for each" +" `filename`+`lineno` combination. When the flag is missing, `MALLOC` is a " +"very thin wrapper around `malloc`, which compilers could remove entirely, " +"and the `-lfallible` flags can be omitted." +msgstr "" + +msgid "" +"This applies not only to `malloc` or other `stdlib.h` functions. If " +"`a_function` is important or relevant, I could add a wrapper around it too, " +"that checks if `fallible_should_fail` to exercise if its callers are also " +"doing the proper clean-up." +msgstr "" + +msgid "" +"The actual code is just this single function, " +"[`fallible_should_fail`](https://git.euandreh.xyz/fallible/tree/src/fallible.c?id=v0.1.0#n16)," +" which ended-up taking only ~40 lines. In fact, there are more lines of " +"either Makefile (111), README.md (82) or troff (306) on this first version." +msgstr "" + +msgid "" +"The price for such fine-grained control is that this approach requires more " +"manual work." +msgstr "" + +msgid "Usage examples" +msgstr "" + +msgid "`MALLOC` from the `README.md`" +msgstr "" + +msgid "" +"// leaky.c\n" +"#include <string.h>\n" +"#include <fallible_alloc.h>\n" +"\n" +"int main() {\n" +" char *aaa = MALLOC(100);\n" +" if (!aaa) {\n" +" return 1;\n" +" }\n" +" strcpy(aaa, \"a safe use of strcpy\");\n" +"\n" +" char *bbb = MALLOC(100);\n" +" if (!bbb) {\n" +" // free(aaa);\n" +" return 1;\n" +" }\n" +" strcpy(bbb, \"not unsafe, but aaa is leaking\");\n" +"\n" +" free(bbb);\n" +" free(aaa);\n" +" return 0;\n" +"}\n" +msgstr "" + +msgid "" +"Compile with `-DFALLIBLE` and run [`fallible-" +"check.1`](https:/fallible.euandreh.xyz/fallible-check.1.html):" +msgstr "" + +msgid "" +"$ c99 -DFALLIBLE -o leaky leaky.c -lfallible\n" +"$ fallible-check ./leaky\n" +"Valgrind failed when we did not expect it to:\n" +"(...suppressed output...)\n" +"# exit status is 1\n" +msgstr "" + +msgid "Conclusion" +msgstr "" + +msgid "" +"For my personal use, I'll [package](https://git.euandreh.xyz/package-" +"repository/about/) them for GNU Guix and Nix. Packaging it to any other " +"distribution should be trivial, or just downloading the tarball and running " +"`[sudo] make install`." +msgstr "" + +msgid "Patches welcome!" +msgstr "" |