Expose builder buffer capacity accessors

arrow-array/src/builder/generic_bytes_builder.rs

@@ -231,16 +231,31 @@ impl<T: ByteArrayType> GenericByteBuilder<T> {
         self.value_builder.as_slice()
     }
 
+    /// Returns the current values buffer capacity, in bytes.
+    pub fn values_capacity(&self) -> usize {
+        self.value_builder.capacity()
+    }
+
     /// Returns the current offsets buffer as a slice
     pub fn offsets_slice(&self) -> &[T::Offset] {
         self.offsets_builder.as_slice()
     }
 
+    /// Returns the current offsets buffer capacity, in offsets.
+    pub fn offsets_capacity(&self) -> usize {
+        self.offsets_builder.capacity()
+    }
+
     /// Returns the current null buffer as a slice
     pub fn validity_slice(&self) -> Option<&[u8]> {
         self.null_buffer_builder.as_slice()
     }
 
+    /// Returns the current null buffer allocated capacity, in bytes.
+    pub fn validity_capacity(&self) -> usize {
+        self.null_buffer_builder.allocated_size()
+    }
+
     /// Returns the current null buffer as a mutable slice
     pub fn validity_slice_mut(&mut self) -> Option<&mut [u8]> {
         self.null_buffer_builder.as_slice_mut()

arrow-array/src/builder/generic_list_builder.rs

@@ -355,10 +355,20 @@ where
         self.offsets_builder.as_slice()
     }
 
+    /// Returns the current offsets buffer capacity, in offsets.
+    pub fn offsets_capacity(&self) -> usize {
+        self.offsets_builder.capacity()
+    }
+
     /// Returns the current null buffer as a slice
     pub fn validity_slice(&self) -> Option<&[u8]> {
         self.null_buffer_builder.as_slice()
     }
+
+    /// Returns the current null buffer allocated capacity, in bytes.
+    pub fn validity_capacity(&self) -> usize {
+        self.null_buffer_builder.allocated_size()
+    }
 }
 
 impl<O, B, V, E> Extend<Option<V>> for GenericListBuilder<O, B>

arrow-array/src/builder/primitive_builder.rs

@@ -361,6 +361,11 @@ impl<T: ArrowPrimitiveType> PrimitiveBuilder<T> {
         self.null_buffer_builder.as_slice()
     }
 
+    /// Returns the current null buffer allocated capacity, in bytes.
+    pub fn validity_capacity(&self) -> usize {
+        self.null_buffer_builder.allocated_size()
+    }
+
     /// Returns the current null buffer as a mutable slice
     pub fn validity_slice_mut(&mut self) -> Option<&mut [u8]> {
         self.null_buffer_builder.as_slice_mut()

arrow-array/src/builder/struct_builder.rs

@@ -314,6 +314,11 @@ impl StructBuilder {
     pub fn validity_slice(&self) -> Option<&[u8]> {
         self.null_buffer_builder.as_slice()
     }
+
+    /// Returns the current null buffer allocated capacity, in bytes.
+    pub fn validity_capacity(&self) -> usize {
+        self.null_buffer_builder.allocated_size()
+    }
 }
 
 #[cfg(test)]