Add a string splitter class

src/lib/support/BUILD.gn

@@ -132,6 +132,7 @@ static_library("support") {
     "SetupDiscriminator.h",
     "SortUtils.h",
     "StateMachine.h",
+    "StringSplitter.h",
     "ThreadOperationalDataset.cpp",
     "ThreadOperationalDataset.h",
     "TimeUtils.cpp",

src/lib/support/StringSplitter.h

@@ -0,0 +1,88 @@
+/*
+ *
+ *    Copyright (c) 2023 Project CHIP Authors
+ *    All rights reserved.
+ *
+ *    Licensed under the Apache License, Version 2.0 (the "License");
+ *    you may not use this file except in compliance with the License.
+ *    You may obtain a copy of the License at
+ *
+ *        http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *    Unless required by applicable law or agreed to in writing, software
+ *    distributed under the License is distributed on an "AS IS" BASIS,
+ *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *    See the License for the specific language governing permissions and
+ *    limitations under the License.
+ */
+#pragma once
+
+#include <lib/support/Span.h>
+
+namespace chip {
+
+/// Provides the ability to split a given string by a character.
+///
+/// Converts things like:
+///   "a,b,c" split by ',': "a", "b", "c"
+///   ",b,c" split by ',': "", "b", "c"
+///   "a,,c" split by ',': "a", "", "c"
+///   "a," split by ',': "a", ""
+///   ",a" split by ',': "", "a"
+///
+///
+/// WARNING: WILL DESTRUCTIVELY MODIFY THE STRING IN PLACE
+///
+class StringSplitter
+{
+public:
+    StringSplitter(const char * s, char separator) : mNext(s), mSeparator(separator)
+    {
+        if ((mNext != nullptr) && (*mNext == '\0'))
+        {
+            mNext = nullptr; // end of string right away
+        }
+    }
+
+    /// Returns the next character san
+    ///
+    /// out - contains the next element or a nullptr/0 sized span if
+    ///       no elements available
+    ///
+    /// Returns true if an element is available, false otherwise.
+    bool Next(CharSpan & out)
+    {
+        if (mNext == nullptr)
+        {
+            out = CharSpan();
+            return false; // nothing left
+        }
+
+        const char * end = mNext;
+        while ((*end != '\0') && (*end != mSeparator))
+        {
+            end++;
+        }
+
+        if (*end != '\0')
+        {
+            // intermediate element
+            out   = CharSpan(mNext, static_cast<size_t>(end - mNext));
+            mNext = end + 1;
+        }
+        else
+        {
+            // last element
+            out   = CharSpan::fromCharString(mNext);
+            mNext = nullptr;
+        }
+
+        return true;
+    }
+
+protected:
+    const char * mNext; // start of next element to return by Next()
+    const char mSeparator;
+};
+
+} // namespace chip

src/lib/support/tests/BUILD.gn

@@ -47,6 +47,7 @@ chip_test_suite("tests") {
     "TestSpan.cpp",
     "TestStateMachine.cpp",
     "TestStringBuilder.cpp",
+    "TestStringSplitter.cpp",
     "TestTestPersistentStorageDelegate.cpp",
     "TestThreadOperationalDataset.cpp",
     "TestTimeUtils.cpp",
@@ -65,6 +66,9 @@ chip_test_suite("tests") {
 
     # TODO(#21255): work-around for SimpleStateMachine constructor issue.
     "-Wno-uninitialized",
+
+    # TestStringSplitter intentionally validates string overflows.
+    "-Wno-stringop-truncation",
   ]
 
   public_deps = [

src/lib/support/tests/TestStringSplitter.cpp

@@ -0,0 +1,153 @@
+/*
+ *
+ *    Copyright (c) 2023 Project CHIP Authors
+ *
+ *    Licensed under the Apache License, Version 2.0 (the "License");
+ *    you may not use this file except in compliance with the License.
+ *    You may obtain a copy of the License at
+ *
+ *        http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *    Unless required by applicable law or agreed to in writing, software
+ *    distributed under the License is distributed on an "AS IS" BASIS,
+ *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *    See the License for the specific language governing permissions and
+ *    limitations under the License.
+ */
+#include <lib/support/StringSplitter.h>
+#include <lib/support/UnitTestRegistration.h>
+
+#include <nlunit-test.h>
+
+namespace {
+
+using namespace chip;
+
+void TestStrdupSplitter(nlTestSuite * inSuite, void * inContext)
+{
+    CharSpan out;
+
+    // empty string handling
+    {
+        StringSplitter splitter("", ',');
+
+        // next stays at nullptr
+        NL_TEST_ASSERT(inSuite, !splitter.Next(out));
+        NL_TEST_ASSERT(inSuite, out.data() == nullptr);
+        NL_TEST_ASSERT(inSuite, !splitter.Next(out));
+        NL_TEST_ASSERT(inSuite, out.data() == nullptr);
+        NL_TEST_ASSERT(inSuite, !splitter.Next(out));
+        NL_TEST_ASSERT(inSuite, out.data() == nullptr);
+    }
+
+    // single item
+    {
+        StringSplitter splitter("single", ',');
+
+        NL_TEST_ASSERT(inSuite, splitter.Next(out));
+        NL_TEST_ASSERT(inSuite, out.data_equal(CharSpan::fromCharString("single")));
+
+        // next stays at nullptr also after valid data
+        NL_TEST_ASSERT(inSuite, !splitter.Next(out));
+        NL_TEST_ASSERT(inSuite, out.data() == nullptr);
+        NL_TEST_ASSERT(inSuite, !splitter.Next(out));
+        NL_TEST_ASSERT(inSuite, out.data() == nullptr);
+    }
+
+    // multi-item
+    {
+        StringSplitter splitter("one,two,three", ',');
+
+        NL_TEST_ASSERT(inSuite, splitter.Next(out));
+        NL_TEST_ASSERT(inSuite, out.data_equal(CharSpan::fromCharString("one")));
+        NL_TEST_ASSERT(inSuite, splitter.Next(out));
+        NL_TEST_ASSERT(inSuite, out.data_equal(CharSpan::fromCharString("two")));
+        NL_TEST_ASSERT(inSuite, splitter.Next(out));
+        NL_TEST_ASSERT(inSuite, out.data_equal(CharSpan::fromCharString("three")));
+        NL_TEST_ASSERT(inSuite, !splitter.Next(out));
+        NL_TEST_ASSERT(inSuite, out.data() == nullptr);
+    }
+
+    // mixed
+    {
+        StringSplitter splitter("a**bc*d,e*f", '*');
+
+        NL_TEST_ASSERT(inSuite, splitter.Next(out));
+        NL_TEST_ASSERT(inSuite, out.data_equal(CharSpan::fromCharString("a")));
+        NL_TEST_ASSERT(inSuite, splitter.Next(out));
+        NL_TEST_ASSERT(inSuite, out.data_equal(CharSpan::fromCharString("")));
+        NL_TEST_ASSERT(inSuite, splitter.Next(out));
+        NL_TEST_ASSERT(inSuite, out.data_equal(CharSpan::fromCharString("bc")));
+        NL_TEST_ASSERT(inSuite, splitter.Next(out));
+        NL_TEST_ASSERT(inSuite, out.data_equal(CharSpan::fromCharString("d,e")));
+        NL_TEST_ASSERT(inSuite, splitter.Next(out));
+        NL_TEST_ASSERT(inSuite, out.data_equal(CharSpan::fromCharString("f")));
+        NL_TEST_ASSERT(inSuite, !splitter.Next(out));
+    }
+
+    // some edge cases
+    {
+        StringSplitter splitter(",", ',');
+        // Note that even though "" is nullptr right away, "," becomes two empty strings
+        NL_TEST_ASSERT(inSuite, splitter.Next(out));
+        NL_TEST_ASSERT(inSuite, out.data_equal(CharSpan::fromCharString("")));
+        NL_TEST_ASSERT(inSuite, splitter.Next(out));
+        NL_TEST_ASSERT(inSuite, out.data_equal(CharSpan::fromCharString("")));
+        NL_TEST_ASSERT(inSuite, !splitter.Next(out));
+    }
+    {
+        StringSplitter splitter("log,", ',');
+        NL_TEST_ASSERT(inSuite, splitter.Next(out));
+        NL_TEST_ASSERT(inSuite, out.data_equal(CharSpan::fromCharString("log")));
+        NL_TEST_ASSERT(inSuite, splitter.Next(out));
+        NL_TEST_ASSERT(inSuite, out.data_equal(CharSpan::fromCharString("")));
+        NL_TEST_ASSERT(inSuite, !splitter.Next(out));
+    }
+    {
+        StringSplitter splitter(",log", ',');
+        NL_TEST_ASSERT(inSuite, splitter.Next(out));
+        NL_TEST_ASSERT(inSuite, out.data_equal(CharSpan::fromCharString("")));
+        NL_TEST_ASSERT(inSuite, splitter.Next(out));
+        NL_TEST_ASSERT(inSuite, out.data_equal(CharSpan::fromCharString("log")));
+        NL_TEST_ASSERT(inSuite, !splitter.Next(out));
+    }
+    {
+        StringSplitter splitter(",,,", ',');
+        NL_TEST_ASSERT(inSuite, splitter.Next(out));
+        NL_TEST_ASSERT(inSuite, out.data_equal(CharSpan::fromCharString("")));
+        NL_TEST_ASSERT(inSuite, splitter.Next(out));
+        NL_TEST_ASSERT(inSuite, out.data_equal(CharSpan::fromCharString("")));
+        NL_TEST_ASSERT(inSuite, splitter.Next(out));
+        NL_TEST_ASSERT(inSuite, out.data_equal(CharSpan::fromCharString("")));
+        NL_TEST_ASSERT(inSuite, splitter.Next(out));
+        NL_TEST_ASSERT(inSuite, out.data_equal(CharSpan::fromCharString("")));
+        NL_TEST_ASSERT(inSuite, !splitter.Next(out));
+    }
+}
+
+void TestNullResilience(nlTestSuite * inSuite, void * inContext)
+{
+    {
+        StringSplitter splitter(nullptr, ',');
+        CharSpan span;
+        NL_TEST_ASSERT(inSuite, !splitter.Next(span));
+        NL_TEST_ASSERT(inSuite, span.data() == nullptr);
+    }
+}
+
+const nlTest sTests[] = {
+    NL_TEST_DEF("TestSplitter", TestStrdupSplitter),       //
+    NL_TEST_DEF("TestNullResilience", TestNullResilience), //
+    NL_TEST_SENTINEL()                                     //
+};
+
+} // namespace
+
+int TestStringSplitter()
+{
+    nlTestSuite theSuite = { "StringSplitter", sTests, nullptr, nullptr };
+    nlTestRunner(&theSuite, nullptr);
+    return nlTestRunnerStats(&theSuite);
+}
+
+CHIP_REGISTER_TEST_SUITE(TestStringSplitter)