First working version

.gitignore

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+/target

.vscode/tasks.json

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+{
+	"version": "2.0.0",
+	"tasks": [
+		{
+			"type": "cargo",
+			"command": "build",
+			"problemMatcher": [
+				"$rustc"
+			],
+			"group": {
+				"kind": "build",
+				"isDefault": true
+			},
+			"label": "rust: cargo build"
+		},
+		{
+			"type": "cargo",
+			"command": "run",
+			"problemMatcher": [
+				"$rustc"
+			],
+			"label": "rust: cargo run"
+		}
+	]
+}

Cargo.toml

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+[package]
+name = "quick_kv"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

README.md

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+## Future development
+
+**Update**
+Add support for update command
+
+**Metadata**
+Serialize and deserialize metadata on start
+
+**Add cache**
+- on read create cache (no size limit)
+- invalidate cache on write (all of it)
+
+**Better cache**
+- invalidate single cache entry
+- cache limit - remove least access element on read
+
+**Remove elements**
+Add support for delete command 
+Set of free blocks
+Write use one of the free blocks

create_pages.py

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+#!/usr/bin/env python3
+
+import sys
+
+page_size = 1024
+filename = "page.db"
+
+def generate_page(value):
+  b = []
+  pattern = 0x41 + value
+
+  for i in range(page_size):
+    b.append(chr(pattern))
+
+  return ''.join(b)
+
+def main():
+  with open(filename, "w") as fh:
+
+    for x in range(0, 20):
+      fh.write(generate_page(x))
+
+
+if __name__ == "__main__":
+  sys.exit(main())

src/error.rs

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+#[derive(Debug)]
+pub enum Error {
+    NamespaceNotFound,
+    FileTooSmall,
+    InvalidValueLen,
+    PageReadOverflow,
+    KeyNotFound,
+    ValueToLarge,
+    DataFileSeek,
+    DataFileWrite
+}

src/lib.rs

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+pub mod storage;
+mod page;
+mod metadata;
+mod error;

src/main.rs

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+use quick_kv::storage::Storage;
+
+
+fn main() {
+    let namespace = String::from("test");
+    let mut storage = Storage::new(namespace);
+
+    let values = [
+        ("test1", vec![0x41; 8]),
+        ("test2", vec![0x42; 12]),
+        ("test3", vec![0x43; 1020]),
+        ("test4", vec![0x44; 16]),
+    ];
+
+    for (key, value) in values {
+        storage.write(&String::from(key), &value).unwrap();
+    }
+
+    let keys = [
+        "test1",
+        "test2",
+        "test3",
+        "test4",
+        "test5"
+    ];
+
+    for key in keys {
+        let value = match storage.read(&String::from(key)) {
+            Ok(v) => v,
+            Err(e) => {
+                // Handle error
+                eprintln!("[{:?}] Key \"{}\" not found", e, &key);
+                return;
+            }
+        };
+
+        println!("Value read: 0x{:x} times {}", value[0], value.len());
+    }
+
+}

src/metadata.rs

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+use std::collections::HashMap;
+
+const PAGE_SIZE: u64 = 1024;
+
+#[derive(Debug, Clone, Copy)]
+pub struct Location {
+  offset: u64,
+  length: u64,
+}
+
+#[derive(Debug)]
+pub struct Metadata {
+  index: HashMap<String, Location>,
+  pub write_cursor: u64,
+}
+
+
+impl Location {
+  pub fn new(offset:u64, length:u64) -> Location {
+    Location {
+      offset,
+      length
+    }
+  }
+
+  pub fn get_offset(self) -> u64 {
+    self.offset
+  }
+
+  pub fn len(self) -> u64 {
+    self.length
+  }
+
+  pub fn get_page_offset(self) -> u64 {
+    // zero out last 10 bits
+    self.offset & !(PAGE_SIZE - 1)
+  }
+
+  pub fn get_relative_offset(self) -> u64 {
+    // keep last 10 bits
+    self.offset & !(PAGE_SIZE - 1)
+  }
+}
+
+impl Metadata {
+  pub fn new(namespace: String) -> Metadata {
+    // if file exist, deserialize metadata
+    // otherwise, create empty one
+
+    Metadata {
+      index: HashMap::new(),
+      write_cursor: 0,
+    }
+  }
+
+  pub fn get_write_cursor(&self) -> u64 {
+    self.write_cursor
+  }
+
+  pub fn update_write_cursor(&mut self, new_cursor: u64) {
+    self.write_cursor = new_cursor;
+  }
+
+  pub fn get_item_location(&self, key: &String) -> Option<&Location> {
+    self.index.get(key)
+  }
+
+  pub fn set_item_location(&mut self, name: &String, location: Location) {
+    self.index.insert(name.to_owned(), location);
+  }
+}
+
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn page_offset() {
+      let location_1 = Location {
+        offset: 536,
+        length: 10
+      };
+      let location_2 = Location {
+        offset: 1536,
+        length: 10
+      };
+
+      assert_eq!(location_1.get_page_offset(), 0);
+      assert_eq!(location_2.get_page_offset(), 1024);
+    }
+}

src/page.rs

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+
+pub const PAGE_SIZE: u64 = 1024;
+
+#[derive(Debug)]
+ pub struct Page {
+  offset: u64,
+  access_count: usize,
+  pub data: Vec<u8>,
+}
+
+impl Page {
+  pub fn new() -> Page {
+    Page {
+      offset: 0,
+      access_count: 0,
+      data: Vec::with_capacity(PAGE_SIZE as usize),
+    }
+  }
+}
+
+impl Default for Page {
+  fn default() -> Self {
+    Page::new()
+  }
+}