chapter 1 done

src/dal.rs

@@ -0,0 +1,56 @@
+use std::fs::File;
+use std::os::unix::fs::{FileExt, OpenOptionsExt};
+
+pub const PageSize : u32 = 4096;
+pub struct Dal {
+    file : File,
+    pageSize : u32
+}
+
+impl Dal{
+    pub fn new(path : &str, pageSize : u32) -> Self {
+        let file =  std::fs::OpenOptions::new()
+            .create(true)
+            .write(true)
+            .append(true)
+            .mode(0o666)
+            .open(path)
+            .unwrap();
+
+        Dal {
+            file,
+            pageSize
+        }
+    }
+
+    pub fn allocateEmptyPage(&self, pageNumber : Option<u64>) -> Page {
+        Page::new(pageNumber)
+    }
+
+    fn readPage(&self, pageNumber : u64) -> Page {
+        let mut page = self.allocateEmptyPage(Some(pageNumber));
+        let offset = pageNumber * self.pageSize as u64;
+        self.file.read_at(&mut page.data, offset).unwrap();
+        page
+    }
+
+    pub fn writePage(&mut self, page : &mut Page) {
+        let offset = page.pageNumber * self.pageSize as u64;
+        self.file.write_at(&page.data, offset).unwrap();
+    }
+
+}
+
+pub struct Page {
+    pub pageNumber : u64,
+    pub data : Vec<u8>
+}
+
+impl  Page {
+    pub fn new(pageNumber : Option<u64>) -> Self {
+        Page {
+            pageNumber: pageNumber.unwrap_or(0), // if no page number, set to 0
+            data: vec![0_u8;  PageSize as usize] // create a 4kB zero filled vector
+        }
+    }
+}

src/main.rs

@@ -1,3 +1,27 @@
+use crate::dal::Dal;
+
+mod dal;
+
 fn main() {
-    println!("Hello, world!");
+    // initialize Dal
+    let mut dal = Dal::new("giraffe.db", dal::PageSize);
+
+    let mut page_0 = dal.allocateEmptyPage(Some(0));
+
+    writeToPage(&mut page_0.data, "Page 0, hello", 0);
+
+    dal.writePage(&mut page_0);
+
+    let mut page_1 = dal.allocateEmptyPage(Some(1));
+
+    writeToPage(&mut page_1.data, "Page 1, hello", 0);
+
+    // commit page
+    dal.writePage(&mut page_1);
+
+}
+
+fn writeToPage(buffer: &mut[u8],msg : &str, startAt: usize) {
+    // write to buffer from position `startAt`
+    buffer[startAt .. msg.len()].copy_from_slice(msg.as_bytes());
 }