Add basic `BufferBlockReader` definition

server/src/kvengine/encoding.rs

@@ -0,0 +1,78 @@
+/*
+ * Created on Thu Jul 01 2021
+ *
+ * This file is a part of Skytable
+ * Skytable (formerly known as TerrabaseDB or Skybase) is a free and open-source
+ * NoSQL database written by Sayan Nandan ("the Author") with the
+ * vision to provide flexibility in data modelling without compromising
+ * on performance, queryability or scalability.
+ *
+ * Copyright (c) 2021, Sayan Nandan <ohsayan@outlook.com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program. If not, see <https://www.gnu.org/licenses/>.
+ *
+*/
+
+//! Functions for validating the encoding of objects
+
+use std::ptr;
+
+pub struct BufferBlockReader<const N: usize> {
+    buffer_ptr: *const u8,
+    len: usize,
+    len_after_step: usize,
+    idx: usize,
+}
+
+impl<const N: usize> BufferBlockReader<N> {
+    pub const fn new(buffer: &[u8]) -> Self {
+        Self {
+            buffer_ptr: buffer.as_ptr(),
+            len: buffer.len(),
+            len_after_step: if buffer.len() < N {
+                0
+            } else {
+                buffer.len() - N
+            },
+            idx: 0,
+        }
+    }
+    pub const fn block_index(&self) -> usize {
+        self.idx
+    }
+    pub const fn has_full_block(&self) -> bool {
+        self.idx < self.len_after_step
+    }
+    pub fn full_block(&self) -> &u8 {
+        unsafe {
+            // UNSAFE(@ohsayan): We're dereferencing a ptr that we know will not be null
+            // because the len of the buffer gurantees that
+            &*self.buffer_ptr.add(self.idx)
+        }
+    }
+    pub unsafe fn get_remaining(&self, dst: *mut u8) -> usize {
+        if self.len == self.idx {
+            0
+        } else {
+            {
+                ptr::write_bytes(dst, 0x20, N);
+                ptr::copy_nonoverlapping(self.buffer_ptr.add(self.idx), dst, self.len - self.idx);
+            }
+            self.len - self.idx
+        }
+    }
+    pub fn advance(&mut self) {
+        self.idx += N
+    }
+}

server/src/kvengine/mod.rs

@@ -33,6 +33,7 @@ use crate::coredb::htable::MapSingleReference;
 use crate::coredb::htable::SharedValue;
 use core::sync::atomic::AtomicBool;
 use core::sync::atomic::Ordering;
+mod encoding;
 
 const ORD_RELAXED: Ordering = Ordering::Relaxed;
 
@@ -86,6 +87,11 @@ pub enum DdlError {
     TableNotEmpty,
 }
 
+/// Errors arising from trying to manipulate data
+pub enum ManipError {
+    EncodingError,
+}
+
 impl Default for KVEngine {
     fn default() -> Self {
         // by default, we don't care about the encoding scheme unless explicitly
@@ -139,6 +145,7 @@ impl KVEngine {
     pub fn truncate_table(&self) {
         self.table.clear()
     }
+    /// Get the value for a given key if it exists
     pub fn get(&self, key: impl AsRef<[u8]>) -> Option<MapSingleReference<Data, Data>> {
         self.table.get(key.as_ref())
     }