...

ourdb/src/backend.rs

@@ -14,9 +14,7 @@ pub const HEADER_SIZE: usize = 12;
 impl OurDB {
     /// Selects and opens a database file for read/write operations
     pub(crate) fn db_file_select(&mut self, file_nr: u16) -> Result<(), Error> {
-        if file_nr > 65535 {
-            return Err(Error::InvalidOperation("File number needs to be < 65536".to_string()));
-        }
+        // No need to check if file_nr > 65535 as u16 can't exceed that value
 
         let path = self.path.join(format!("{}.db", file_nr));
 
@@ -53,6 +51,18 @@ impl OurDB {
 
     /// Gets the file number to use for the next write operation
     pub(crate) fn get_file_nr(&mut self) -> Result<u16, Error> {
+        // For keysize 2, 3, or 4, we can only use file_nr 0
+        if self.lookup.keysize() <= 4 {
+            let path = self.path.join("0.db");
+            
+            if !path.exists() {
+                self.create_new_db_file(0)?;
+            }
+            
+            return Ok(0);
+        }
+        
+        // For keysize 6, we can use multiple files
         let path = self.path.join(format!("{}.db", self.last_used_file_nr));
         
         if !path.exists() {
@@ -254,7 +264,7 @@ impl OurDB {
             
             // Read and process records
             let mut buffer = vec![0u8; 1024]; // Read in chunks
-            let mut position = 0;
+            let mut _position = 0;
             
             while let Ok(bytes_read) = src_file.read(&mut buffer) {
                 if bytes_read == 0 {
@@ -265,7 +275,7 @@ impl OurDB {
                 // This is a simplified version - in a real implementation,
                 // you would need to handle records that span chunk boundaries
                 
-                position += bytes_read;
+                _position += bytes_read;
             }
             
             // TODO: Implement proper record copying and position updating

ourdb/src/lib.rs

@@ -37,7 +37,11 @@ pub struct OurDBConfig {
     pub incremental_mode: bool,
     /// Maximum file size (default: 500MB)
     pub file_size: Option<u32>,
-    /// Lookup table key size
+    /// Lookup table key size (default: 4)
+    /// - 2: For databases with < 65,536 records (single file)
+    /// - 3: For databases with < 16,777,216 records (single file)
+    /// - 4: For databases with < 4,294,967,296 records (single file)
+    /// - 6: For large databases requiring multiple files (default)
     pub keysize: Option<u8>,
 }
 

ourdb/src/location.rs

@@ -27,10 +27,10 @@ impl Location {
 
         // Create padded bytes
         let mut padded = vec![0u8; keysize as usize];
-        let start_idx = keysize as usize - bytes.len();
-        if start_idx < 0 {
+        if bytes.len() > keysize as usize {
             return Err(Error::InvalidOperation("Input bytes exceed keysize".to_string()));
         }
+        let start_idx = keysize as usize - bytes.len();
 
         for (i, &b) in bytes.iter().enumerate() {
             if i + start_idx < padded.len() {

ourdb/src/lookup.rs

@@ -13,10 +13,10 @@ pub struct LookupConfig {
     /// Size of the lookup table
     pub size: u32,
     /// Size of each entry in bytes (2-6)
-    /// - 2: For databases with < 65,536 records
-    /// - 3: For databases with < 16,777,216 records
-    /// - 4: For databases with < 4,294,967,296 records
-    /// - 6: For large databases requiring multiple files
+    /// - 2: For databases with < 65,536 records (single file)
+    /// - 3: For databases with < 16,777,216 records (single file)
+    /// - 4: For databases with < 4,294,967,296 records (single file)
+    /// - 6: For large databases requiring multiple files 
     pub keysize: u8,
     /// Path for disk-based lookup
     pub lookuppath: String,
@@ -37,6 +37,11 @@ pub struct LookupTable {
 }
 
 impl LookupTable {
+    /// Returns the keysize of this lookup table
+    pub fn keysize(&self) -> u8 {
+        self.keysize
+    }
+
     /// Creates a new lookup table with the given configuration
     pub fn new(config: LookupConfig) -> Result<Self, Error> {
         // Verify keysize is valid