codec2: add setFlexSize() to flexible C2Param

Bug: 165694889
Change-Id: I23847ac72638cbfe4279dd9fcfc47eacc7021e3b
diff --git a/media/codec2/core/include/C2Param.h b/media/codec2/core/include/C2Param.h
index 51d417a..436269a 100644
--- a/media/codec2/core/include/C2Param.h
+++ b/media/codec2/core/include/C2Param.h
@@ -508,6 +508,14 @@
         return _mIndex.setPort(output);
     }
 
+    /// sets the size of this parameter.
+    inline void setSize(size_t size) {
+        if (size < sizeof(C2Param)) {
+            size = 0;
+        }
+        _mSize = c2_min(size, _mSize);
+    }
+
 public:
     /// invalidate this parameter. There is no recovery from this call; e.g. parameter
     /// cannot be 'corrected' to be valid.
diff --git a/media/codec2/core/include/C2ParamDef.h b/media/codec2/core/include/C2ParamDef.h
index 0a33283..8af9fe3 100644
--- a/media/codec2/core/include/C2ParamDef.h
+++ b/media/codec2/core/include/C2ParamDef.h
@@ -270,6 +270,11 @@
         } \
         return 0; \
     } \
+    inline void setFlexCount(size_t count) { \
+        if (count < flexCount()) { \
+            this->setSize(sizeof(_Type) + _Type::FLEX_SIZE * count); \
+        } \
+    } \
 
 /// Mark flexible member variable and make structure flexible.
 #define FLEX(cls, m) \
diff --git a/media/codec2/tests/C2Param_test.cpp b/media/codec2/tests/C2Param_test.cpp
index 564d4d2..c39605a 100644
--- a/media/codec2/tests/C2Param_test.cpp
+++ b/media/codec2/tests/C2Param_test.cpp
@@ -2328,6 +2328,17 @@
         static_assert(std::is_same<decltype(blobValue->m.value), uint8_t[]>::value, "should be uint8_t[]");
         EXPECT_EQ(0, memcmp(blobValue->m.value, "ABCD\0", 6));
         EXPECT_EQ(6u, blobValue->flexCount());
+        blobValue->setFlexCount(7u); // increasing the count does not change it
+        EXPECT_EQ(6u, blobValue->flexCount());
+        blobValue->setFlexCount(2u); // decreasing the count changes it to it
+        EXPECT_EQ(2u, blobValue->flexCount());
+        blobValue->setFlexCount(0u); // can decrease to 0 and blob remains valid
+        EXPECT_EQ(0u, blobValue->flexCount());
+        EXPECT_TRUE(*blobValue);
+        blobValue->invalidate(); // flex params can be invalidated => results in 0 size
+        EXPECT_FALSE(*blobValue);
+        EXPECT_EQ(0u, blobValue->size());
+
         std::vector<C2FieldDescriptor> fields = blobValue->FieldList();
         EXPECT_EQ(1u, fields.size());
         EXPECT_EQ(FD::BLOB, fields.cbegin()->type());