Disable the CharSpan("literal") footgun (project-chip#30400)

CharSpan("literal") includes the trailing 0 byte in the value which
is almost never what is intended.

examples/all-clusters-app/nxp/mw320/main.cpp

@@ -172,7 +172,7 @@ void InitOTARequestor(void)
     // TODO: instatiate and initialize these values when QueryImageResponse tells us an image is available
     // TODO: add API for OTARequestor to pass QueryImageResponse info to the application to use for OTADownloader init
     // OTAImageProcessor ipParams;
-    // ipParams.imageFile = CharSpan("dnld_img.txt");
+    // ipParams.imageFile = "dnld_img.txt"_span;
     // gImageProcessor.SetOTAImageProcessorParams(ipParams);
     gImageProcessor.SetOTADownloader(&gDownloader);
 

examples/chef/common/stubs.cpp

@@ -186,7 +186,7 @@ class LockManager
         endpoints[0].id = 1;
         uint8_t pin[6]  = { 0x31, 0x32, 0x33, 0x34, 0x35, 0x36 };
         endpoints[0].credentials[0].set(DlCredentialStatus::kOccupied, CredentialTypeEnum::kPin, chip::ByteSpan(pin));
-        endpoints[0].users[0].set(chip::CharSpan("default"), 1, UserStatusEnum::kOccupiedEnabled, UserTypeEnum::kUnrestrictedUser,
+        endpoints[0].users[0].set("default"_span, 1, UserStatusEnum::kOccupiedEnabled, UserTypeEnum::kUnrestrictedUser,
                                   CredentialRuleEnum::kSingle);
         endpoints[0].users[0].addCredential(CredentialTypeEnum::kPin, 1);
     }

src/app/clusters/door-lock-server/door-lock-server.cpp

@@ -1985,7 +1985,7 @@ Status DoorLockServer::clearUser(chip::EndpointId endpointId, chip::FabricIndex
     }
 
     // Remove the user entry
-    if (!emberAfPluginDoorLockSetUser(endpointId, userIndex, kUndefinedFabricIndex, kUndefinedFabricIndex, chip::CharSpan(""), 0,
+    if (!emberAfPluginDoorLockSetUser(endpointId, userIndex, kUndefinedFabricIndex, kUndefinedFabricIndex, ""_span, 0,
                                       UserStatusEnum::kAvailable, UserTypeEnum::kUnrestrictedUser, CredentialRuleEnum::kSingle,
                                       nullptr, 0))
     {

src/app/tests/TestSceneTable.cpp

@@ -102,21 +102,21 @@ static const SceneStorageId sceneId12(kScene6, kGroup4);
 CharSpan empty;
 
 // Scene data
-static const SceneData sceneData1(CharSpan("Scene #1"));
-static const SceneData sceneData2(CharSpan("Scene #2"), 2000);
-static const SceneData sceneData3(CharSpan("Scene #3"), 250);
-static const SceneData sceneData4(CharSpan("Scene num4"), 5000);
+static const SceneData sceneData1("Scene #1"_span);
+static const SceneData sceneData2("Scene #2"_span, 2000);
+static const SceneData sceneData3("Scene #3"_span, 250);
+static const SceneData sceneData4("Scene num4"_span, 5000);
 static const SceneData sceneData5(empty);
-static const SceneData sceneData6(CharSpan("Scene #6"), 3000);
-static const SceneData sceneData7(CharSpan("Scene #7"), 20000);
-static const SceneData sceneData8(CharSpan("NAME TOO LOOONNG!"), 15000);
-static const SceneData sceneData9(CharSpan("Scene #9"), 3000);
-static const SceneData sceneData10(CharSpan("Scene #10"), 1000);
-static const SceneData sceneData11(CharSpan("Scene #11"), 50);
-static const SceneData sceneData12(CharSpan("Scene #12"), 100);
-static const SceneData sceneData13(CharSpan("Scene #13"), 100);
-static const SceneData sceneData14(CharSpan("Scene #14"), 100);
-static const SceneData sceneData15(CharSpan("Scene #15"), 100);
+static const SceneData sceneData6("Scene #6"_span, 3000);
+static const SceneData sceneData7("Scene #7"_span, 20000);
+static const SceneData sceneData8("NAME TOO LOOONNG!"_span, 15000);
+static const SceneData sceneData9("Scene #9"_span, 3000);
+static const SceneData sceneData10("Scene #10"_span, 1000);
+static const SceneData sceneData11("Scene #11"_span, 50);
+static const SceneData sceneData12("Scene #12"_span, 100);
+static const SceneData sceneData13("Scene #13"_span, 100);
+static const SceneData sceneData14("Scene #14"_span, 100);
+static const SceneData sceneData15("Scene #15"_span, 100);
 
 // Scenes
 SceneTableEntry scene1(sceneId1, sceneData1);

src/credentials/FabricTable.cpp

@@ -782,7 +782,7 @@ FabricTable::AddOrUpdateInner(FabricIndex fabricIndex, bool isAddition, Crypto::
     FabricInfo::InitParams newFabricInfo;
     FabricInfo * fabricEntry    = nullptr;
     FabricId fabricIdToValidate = kUndefinedFabricId;
-    CharSpan fabricLabel("");
+    CharSpan fabricLabel;
 
     if (isAddition)
     {

src/credentials/tests/TestFabricTable.cpp

@@ -943,7 +943,7 @@ void TestBasicAddNocUpdateNocFlow(nlTestSuite * inSuite, void * inContext)
     // Sequence 4: Rename fabric index 2, applies immediately when nothing pending
     {
         NL_TEST_ASSERT_EQUALS(inSuite, fabricTable.FabricCount(), 2);
-        NL_TEST_ASSERT_SUCCESS(inSuite, fabricTable.SetFabricLabel(2, CharSpan("roboto")));
+        NL_TEST_ASSERT_SUCCESS(inSuite, fabricTable.SetFabricLabel(2, "roboto"_span));
         NL_TEST_ASSERT_EQUALS(inSuite, fabricTable.FabricCount(), 2);
 
         NL_TEST_ASSERT_EQUALS(inSuite, storage.GetNumKeys(), numStorageAfterUpdate); // Number of keys unchanged

src/lib/support/Span.h

@@ -58,10 +58,25 @@ class Span
     // should be used to construct empty Spans. All other cases involving null are invalid.
     Span(std::nullptr_t null, size_t size) = delete;
 
-    template <class U, size_t N, typename = std::enable_if_t<sizeof(U) == sizeof(T) && std::is_convertible<U *, T *>::value>>
+    // Creates a Span view of a plain array.
+    //
+    // Note that this constructor template explicitly excludes `const char[]`, see below.
+    template <
+        class U, size_t N,
+        std::enable_if_t<!std::is_same_v<U, const char> && sizeof(U) == sizeof(T) && std::is_convertible_v<U *, T *>, bool> = true>
     constexpr explicit Span(U (&databuf)[N]) : mDataBuf(databuf), mDataLen(N)
     {}
 
+    // Explicitly disallow the creation of a CharSpan from a `const char[]` to prevent the
+    // creation of spans from string literals that incorrectly include the trailing '\0' byte.
+    // If CharSpan("Hi!") were allowed, it would be a span of length 4, not 3 as intended.
+    //
+    // To create a CharSpan literal, use the `_span` operator instead, e.g. "Hi!"_span.
+    template <
+        class U, size_t N,
+        std::enable_if_t<std::is_same_v<U, const char> && 1 == sizeof(T) && std::is_convertible_v<const char *, T *>, bool> = true>
+    constexpr explicit Span(U (&databuf)[N]) = delete;
+
     // Creates a (potentially mutable) Span view of an std::array
     template <class U, size_t N, typename = std::enable_if_t<sizeof(U) == sizeof(T) && std::is_convertible<U *, T *>::value>>
     constexpr Span(std::array<U, N> & arr) : mDataBuf(arr.data()), mDataLen(N)

src/lib/support/tests/TestSpan.cpp

@@ -299,6 +299,11 @@ static void TestLiteral(nlTestSuite * inSuite, void * inContext)
     NL_TEST_ASSERT(inSuite, literal.size() == 3);
     NL_TEST_ASSERT(inSuite, literal.data_equal(CharSpan::fromCharString("HI!")));
     NL_TEST_ASSERT(inSuite, ""_span.size() == 0);
+
+    // These should be compile errors -- if they were allowed they would produce
+    // a CharSpan that includes the trailing '\0' byte in the value.
+    // constexpr CharSpan disallowed1("abcd");
+    // constexpr CharSpan disallowed2{ "abcd" };
 }
 
 static void TestConversionConstructors(nlTestSuite * inSuite, void * inContext)

src/lib/support/tests/TestTlvJson.cpp

@@ -133,8 +133,7 @@ void TestConverter(nlTestSuite * inSuite, void * inContext)
                       "   \"value\" : 1.0\n"
                       "}\n");
 
-    const char charBuf[] = "hello";
-    CharSpan charSpan(charBuf);
+    CharSpan charSpan = "hello"_span;
     EncodeAndValidate(charSpan,
                       "{\n"
                       "   \"value\" : \"hello\"\n"