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Fix failing to serialize Collection or Map with inaccessible constructor #1902

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Marcono1234
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@Marcono1234 Marcono1234 commented Jun 4, 2021

Fixes #1875

Note that this introduces an incompatibility:
Projects which previously relied on UnsafeReflectionAccessor making internal members accessible will now encounter warnings or exceptions when the Java Platform Module System does not allow access. These projects should write their own TypeAdapters, or temporarily use java --add-opens ....
This "resolves" #1540, in the sense that that issue is not a problem with Gson, and that this pull request further strengthens this standpoint.
(In theory this change could be omitted from this pull request while still solving #1875, but it would render the added unit test ineffective.)

Marcono1234 added 2 commits Jun 3, 2021
Revert google#1218

Usage of sun.misc.Unsafe to change internal AccessibleObject.override field
to suppress JPMS warnings goes against the intentions of the JPMS and does not
work anymore in newer versions, see google#1540.
Therefore remove it and instead create a descriptive exception when making a
member accessible fails. If necessary users can also still use `java` command
line flags to open external modules.
Also remove tests which rely on Java implementation details.
@google-cla google-cla bot added the cla: yes label Jun 4, 2021
Marcono1234 added 2 commits Jun 4, 2021
This also avoids a confusing stack trace, since the previously caught
exception might have had a complete unrelated stack trace.
// New exception is created every time to avoid keeping reference
// to exception with potentially long stack trace, causing a
// memory leak
throw new JsonIOException(exceptionMessage);
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@Marcono1234 Marcono1234 Nov 6, 2021

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JsonIOException thrown here and in ReflectionHelper is not fitting very well, but Gson has currently no better fitting exception type.
(maybe the whole Gson exception hierarchy should be refactored in the future)

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Marcono1234 commented Nov 6, 2021

@eamonnmcmanus could you please have a look at this pull request? The fixed issue (#1875) causes problems for some legit usages of certain JDK types.

If you want I can also split off the removal of UnsafeReflectionAccessor; though ultimately it should be removed either way because it circumvents JDK module system restrictions and is ineffective in the latest JDK versions anyway (see pull request description).

import com.google.gson.annotations.SerializedName;

@SuppressWarnings("serial")
public final class ThrowableFunctionalTest extends TestCase {
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@Marcono1234 Marcono1234 Nov 6, 2021

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Has been removed because it relies on JDK internals.

@@ -53,21 +53,6 @@ public void testRecursiveResolveSimple() {
assertNotNull(adapter);
}

/**
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@Marcono1234 Marcono1234 Nov 6, 2021

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Have been removed because they rely on JDK internals.

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@eamonnmcmanus eamonnmcmanus left a comment

This looks very helpful, thanks! I have mostly nits. Also a merge is needed.

// should be acceptable because this only retrieves enum constants, but does not expose anything else
Field[] constantFields = AccessController.doPrivileged(new PrivilegedAction<Field[]>() {
@Override public Field[] run() {
Field[] fields = classOfT.getDeclaredFields();
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@Marcono1234 Marcono1234 Nov 9, 2021

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Have changed this to also run getDeclaredFields() in privileged context because it can throw a SecurityException as well.

Not directly related to the other changes of this pull request, but I was having a look at other cases where a SecurityManager could be an issue.
Sorry for this delayed change after the pull request approval. If you want I can also put that in a separate pull request.

@Marcono1234 Marcono1234 force-pushed the marcono1234/inaccessible-object-exception branch from eafcffc to 9140460 Compare Nov 9, 2021
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Marcono1234 commented Nov 9, 2021

Sorry for these changes after your approval; I tried adding back the Maven toolchain usage, but unfortunately even with version range it apparently requires to explicitly configure toolchains. Therefore I have removed that commit again and force-pushed; you can see the changes by clicking on the "force-pushed" text here:
force-pushed text screenshot

Also just to be sure there is no misunderstanding; these changes might cause backward compability issues for Gson users running < JDK 12 who rely on Gson's Unsafe usage for making fields and constructors accessible to which they should not have any access, because this pull request removes that code.
However, on the other hand these versions < JDK 12 will by default permit illegal access for the module system (was changed in Java 16 to deny by default, see JDK-8255363), so unless the users explicitly changed this behavior, the worse thing they will experience is warnings about illegal access on the console.

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eamonnmcmanus commented Nov 9, 2021

This looks fine now.

@eamonnmcmanus eamonnmcmanus merged commit b0595c5 into google:master Nov 9, 2021
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@Marcono1234 Marcono1234 deleted the marcono1234/inaccessible-object-exception branch Nov 10, 2021
tibor-universe pushed a commit to getuniverse/gson that referenced this pull request Nov 21, 2021
…tor (google#1902)

* Remove UnsafeReflectionAccessor

Revert google#1218

Usage of sun.misc.Unsafe to change internal AccessibleObject.override field
to suppress JPMS warnings goes against the intentions of the JPMS and does not
work anymore in newer versions, see google#1540.
Therefore remove it and instead create a descriptive exception when making a
member accessible fails. If necessary users can also still use `java` command
line flags to open external modules.

* Fix failing to serialize Collection or Map with inaccessible constructor

Also remove tests which rely on Java implementation details.

* Don't keep reference to access exception of ConstructorConstructor

This also avoids a confusing stack trace, since the previously caught
exception might have had a complete unrelated stack trace.

* Remove Maven toolchain requirement

* Address review feedback

* Add back test for Security Manager
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InaccessibleObjectException with JDK 16
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