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Fixed the native crash happening on Android. #116

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Fixed the native crash happening on Android. #116

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069e1b2
Fixed the native crash happening on Android.
MohitMaliDeveloper Jan 17, 2025
5fd942d
Removed the redundant check to check whether the native object is nul…
MohitMaliDeveloper Jan 20, 2025
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2 changes: 1 addition & 1 deletion lib/src/main/cpp/libzim/archive.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -183,7 +183,7 @@ METHOD(jboolean, hasIllustration, jint size) {
GETTER(jlongArray, getIllustrationSizes)

METHOD(jobject, getEntryByPath__Ljava_lang_String_2, jstring path) {
return BUILD_WRAPPER("org/kiwix/libzim/Entry", THIS->getEntryByPath(TO_C(path)));
return BUILD_WRAPPER("org/kiwix/libzim/Entry", SAFE_THIS->getEntryByPath(TO_C(path)));
} CATCH_EXCEPTION(nullptr)

METHOD(jobject, getEntryByPath__I, jint index) {
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13 changes: 13 additions & 0 deletions lib/src/main/cpp/macros.h
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Expand Up @@ -27,6 +27,16 @@

#define THIS getPtr<NATIVE_TYPE>(env, thisObj)

#define SAFE_THIS \
({ \
auto ptr = getPtr<NATIVE_TYPE>(env, thisObj); \
if (!ptr) { \
throwException(env, "java/lang/IllegalStateException", "The native object has already been disposed."); \
return nullptr; \
} \
ptr; \
})
Comment on lines +31 to +38
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I can't see how this could work in the pre-C++-14 language standard that I am more or less familiar with. SAFE_THIS has to be an expression but it doesn't seem to expand to code that can be considered an expression according to the language specification. I tried to quickly skim through https://en.cppreference.com/w/cpp/language/expressions but couldn't find anything that allows to consider this code valid in modern c++.

In other words, I am puzzled how this code compiles (in the context of the change in lib/src/main/cpp/libzim/archive.cpp).

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@MohitMaliFtechiz MohitMaliFtechiz Jan 18, 2025 •
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@veloman-yunkan This code is made by @mgautierfr, he can better explain this, and i am not very much familiar with C++.

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I think that @veloman-yunkan understand how it works :)

#define FOO BAR make every instance of FOO literally replaced by BAR.

So something like THIS->getEntryByPath(...) is replaced by getPtr<NATIVE_TYPE>(env, thisObj)->getEntryByPath(...). And it compiles because getPtr is a function returning a pointer.

With your define of SAFE_THIS we have SAFE_THIS->getEntryByPath(...) replaced by:

 ({ 
        auto ptr = getPtr<NATIVE_TYPE>(env, thisObj); 
        if (!ptr) { 
            throwException(env, "java/lang/IllegalStateException", "The native object has already been disposed."); 
            return nullptr; 
        } 
        ptr; 
    })->getEntryByPath(...)

And, as @veloman-yunkan, I don't know how this code can be compiled.

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With your define of SAFE_THIS we have SAFE_THIS->getEntryByPath(...) replaced by:

@mgautierfr SAFE_THIS also uses the getPtr<NATIVE_TYPE>(env, thisObj) to get the pointer, and if this method returns the nullptr it throws the error which will be caught in the archive.cpp.

METHOD(jobject, getEntryByPath__Ljava_lang_String_2, jstring path) {
  return BUILD_WRAPPER("org/kiwix/libzim/Entry", SAFE_THIS->getEntryByPath(TO_C(path)));
} CATCH_EXCEPTION(nullptr)

Also, in the archive.cpp SAFE_THIS returns the archive.

Screenshot from 2025-01-21 17-41-04

I think that's why this code was compiled without any error.


#define METHOD0(retType, name) \
JNIEXPORT retType JNICALL BUILD_METHOD(TYPENAME, name) ( \
JNIEnv* env, jobject thisObj) try
Expand Down Expand Up @@ -59,4 +69,7 @@ catch(const zim::ZimFileFormatError& e) { \
} catch(const std::exception& e) { \
throwException(env, "java/lang/Exception", e.what()); \
return RET; \
} catch(...) { \
throwException(env, "java/lang/Error", "Unknown native exception occurred."); \
return RET; \
}
3 changes: 3 additions & 0 deletions lib/src/main/cpp/utils.h
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Expand Up @@ -104,6 +104,9 @@ shared_ptr<T> getPtr(JNIEnv* env, jobject thisObj, const char* handleName = "nat
jclass thisClass = env->GetObjectClass(thisObj);
jfieldID fidNumber = env->GetFieldID(thisClass, handleName, "J");
auto handle = reinterpret_cast<shared_ptr<T>*>(env->GetLongField(thisObj, fidNumber));
if (handle == nullptr) {
return nullptr;
}
return *handle;
}
#define GET_PTR(NATIVE_TYPE) getPtr<NATIVE_TYPE>(env, thisObj)
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