Remove a superfluous array copy from several String ctors.
All of the String constructors that take a Charset to decode bytes
ultimately go through StringFactory.newStringFromBytes. For Charsets
other than UTF-8, ISO-8859-1, and US-ASCII, this method does a
System.arraycopy of the bytes it gets from Charset.decode. The comment
claims that this is to trim the array, and to defend against the
Charset keeping a reference to the buffer it returns and modifying it
and so violating String's immutability.
However, the byte array is then passed to newStringFromChars, a native
method which itself takes a copy of the correct number of bytes from
the array it's given (see ultimately,
SetStringCountAndValueVisitorFromCharArray in
//art/runtime/mirror/string-inl.h). Therefore, the previous copy is
unnecessary.
There is a test for exactly this case,
libcore.java.lang.StringTest#testStringFromCharset_MaliciousCharset,
which uses a charset that modifies the CharBuffer after it's been
returned, and asserts that this doesn't change the String, and it
passes with this change.
Bug: 111178950
Test: `cts-tradefed run commandAndExit cts-dev -m CtsLibcoreTestCases`
Change-Id: I7e18467da764d8f0fec1359a6abcbde9d6b45972
1 file changed