implemented read

fat-bits/src/iter.rs

@@ -22,7 +22,7 @@ impl<'a> ClusterChainReader<'a> {
         }
     }
 
-    fn next_cluster(&mut self) -> bool {
+    fn move_to_next_cluster(&mut self) -> bool {
         let Some(next_cluster) = self.next_cluster else {
             return false;
         };
@@ -37,12 +37,33 @@ impl<'a> ClusterChainReader<'a> {
 
         true
     }
+
+    pub fn skip(&mut self, n: u64) -> u64 {
+        let mut bytes_to_skip = n;
+
+        while bytes_to_skip > self.sub_slice.len() as u64 {
+            bytes_to_skip -= self.sub_slice.len() as u64;
+            if !self.move_to_next_cluster() {
+                // ran out of bytes to seek
+                return n - bytes_to_skip;
+            }
+        }
+
+        if bytes_to_skip != 0 {
+            bytes_to_skip -= self.sub_slice.skip(bytes_to_skip as usize) as u64;
+        }
+
+        // n should absolutely be zero here
+        assert_eq!(bytes_to_skip, 0);
+
+        n
+    }
 }
 
-impl<'a> Read for ClusterChainReader<'a> {
+impl Read for ClusterChainReader<'_> {
     fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
         if self.sub_slice.is_empty() {
-            if !self.next_cluster() {
+            if !self.move_to_next_cluster() {
                 return Ok(0);
             }
         }

fat-bits/src/lib.rs

@@ -11,7 +11,7 @@ mod datetime;
 pub mod dir;
 pub mod fat;
 pub mod fs_info;
-mod iter;
+pub mod iter;
 mod subslice;
 mod utils;
 
@@ -240,7 +240,7 @@ impl FatFs {
         Ok(data)
     }
 
-    fn chain_reader(&self, first_cluster: u32) -> impl Read {
+    fn chain_reader(&'_ self, first_cluster: u32) -> iter::ClusterChainReader<'_> {
         iter::ClusterChainReader::new(self, first_cluster)
     }
 
@@ -274,4 +274,10 @@ impl FatFs {
 
         DirIter::new(Box::new(cluster_iter))
     }
+
+    pub fn file_reader(&self, first_cluster: u32) -> iter::ClusterChainReader<'_> {
+        assert!(first_cluster >= 2);
+
+        self.chain_reader(first_cluster)
+    }
 }

fat-bits/src/subslice.rs

@@ -104,16 +104,21 @@ impl SubSlice<'_> {
         self.fat_fs
     }
 
-    pub fn fat_fs_mut(&self) -> &FatFs {
-        self.fat_fs
-    }
-
     pub fn is_empty(&self) -> bool {
         self.len() == 0
     }
     pub fn len(&self) -> usize {
         self.len
     }
+
+    pub fn skip(&mut self, n: usize) -> usize {
+        let n = n.min(self.len());
+
+        self.offset += n as u64;
+        self.len -= n;
+
+        n
+    }
 }
 
 impl<'a> SubSlice<'a> {