95 lines
3.0 KiB
C
95 lines
3.0 KiB
C
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/*
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* Copyright (c) 2015-present, Facebook, Inc.
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* All rights reserved.
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*
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* This source code is licensed under the BSD-style license found in the
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* LICENSE file in the root directory of this source tree. An additional grant
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* of patent rights can be found in the PATENTS file in the same directory.
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*/
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#pragma once
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#include <string>
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#include <jni.h>
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#include <fb/visibility.h>
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namespace facebook {
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namespace jni {
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namespace detail {
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void utf8ToModifiedUTF8(const uint8_t* bytes, size_t len, uint8_t* modified, size_t modifiedLength);
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size_t modifiedLength(const std::string& str);
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size_t modifiedLength(const uint8_t* str, size_t* length);
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std::string modifiedUTF8ToUTF8(const uint8_t* modified, size_t len) noexcept;
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std::string utf16toUTF8(const uint16_t* utf16Bytes, size_t len) noexcept;
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}
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// JNI represents strings encoded with modified version of UTF-8. The difference between UTF-8 and
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// Modified UTF-8 is that the latter support only 1-byte, 2-byte, and 3-byte formats. Supplementary
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// character (4 bytes in unicode) needs to be represented in the form of surrogate pairs. To create
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// a Modified UTF-8 surrogate pair that Dalvik would understand we take 4-byte unicode character,
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// encode it with UTF-16 which gives us two 2 byte chars (surrogate pair) and then we encode each
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// pair as UTF-8. This result in 2 x 3 byte characters. To convert modified UTF-8 to standard
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// UTF-8, this mus tbe reversed.
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//
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// The second difference is that Modified UTF-8 is encoding NUL byte in 2-byte format.
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//
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// In order to avoid complex error handling, only a minimum of validity checking is done to avoid
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// crashing. If the input is invalid, the output may be invalid as well.
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//
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// Relevant links:
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// - http://docs.oracle.com/javase/7/docs/technotes/guides/jni/spec/functions.html
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// - https://docs.oracle.com/javase/6/docs/api/java/io/DataInput.html#modified-utf-8
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class FBEXPORT LocalString {
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public:
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// Assumes UTF8 encoding and make a required convertion to modified UTF-8 when the string
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// contains unicode supplementary characters.
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explicit LocalString(const std::string& str);
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explicit LocalString(const char* str);
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jstring string() const {
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return m_string;
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}
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~LocalString();
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private:
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jstring m_string;
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};
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// JString to UTF16 extractor using RAII idiom
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class JStringUtf16Extractor {
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public:
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JStringUtf16Extractor(JNIEnv* env, jstring javaString)
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: env_(env)
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, javaString_(javaString)
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, utf16String_(nullptr) {
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if (env_ && javaString_) {
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utf16String_ = env_->GetStringCritical(javaString_, nullptr);
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}
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}
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~JStringUtf16Extractor() {
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if (utf16String_) {
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env_->ReleaseStringCritical(javaString_, utf16String_);
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}
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}
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operator const jchar* () const {
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return utf16String_;
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}
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private:
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JNIEnv* env_;
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jstring javaString_;
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const jchar* utf16String_;
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};
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// The string from JNI is converted to standard UTF-8 if the string contains supplementary
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// characters.
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FBEXPORT std::string fromJString(JNIEnv* env, jstring str);
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} }
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