Track actual bytes read in read operations

Add functionality to determine the actual number of bytes read during
read operations, making it possible to detect when a read was truncated
because it went past the end of the file.

Changes:
- Modified file_tree_read() to calculate and return actual_bytes via
  new output parameter
- Updated metadata server to send actual_bytes in READ_SUCCESS messages
- Added bytes_read field to ToastyResult structure
- Modified client to parse, store, and report actual bytes read
- Updated toasty_read() to return the actual number of bytes read
  instead of always returning 0
- Fixed web server to use bytes_read field instead of non-existent
  count field

This allows clients to distinguish between:
- Reading zeros because the file is sparse (has holes)
- Reading past the end of the file (truncated read)

src/client.c

@@ -116,6 +116,7 @@ typedef struct {
     int ranges_head;
     int ranges_count;
     int num_pending;
+    int actual_bytes; // For reads: actual number of bytes that can be read
 
     // Write fields
     SHA256 *hashes;
@@ -1006,12 +1007,22 @@ static void process_event_for_read(ToastyFS *toasty,
             return;
         }
 
+        // Read actual bytes that can be read
+        uint32_t actual_bytes;
+        if (!binary_read(&reader, &actual_bytes, sizeof(actual_bytes))) {
+            toasty->operations[opidx].result = (ToastyResult) { .type=TOASTY_RESULT_READ_ERROR, .user=toasty->operations[opidx].user };
+            return;
+        }
+
+        // Store actual_bytes for later use
+        toasty->operations[opidx].actual_bytes = actual_bytes;
+
         // Calculate which chunks we need
         int off = toasty->operations[opidx].off;
         int len = toasty->operations[opidx].len;
 
         if (len == 0) {
-            toasty->operations[opidx].result = (ToastyResult) { .type=TOASTY_RESULT_READ_SUCCESS, .user=toasty->operations[opidx].user };
+            toasty->operations[opidx].result = (ToastyResult) { .type=TOASTY_RESULT_READ_SUCCESS, .user=toasty->operations[opidx].user, .bytes_read=0 };
             return;
         }
 
@@ -1166,7 +1177,7 @@ static void process_event_for_read(ToastyFS *toasty,
         } else {
             // No chunks to download
             sys_free(ranges);
-            toasty->operations[opidx].result = (ToastyResult) { .type=TOASTY_RESULT_READ_SUCCESS, .user=toasty->operations[opidx].user };
+            toasty->operations[opidx].result = (ToastyResult) { .type=TOASTY_RESULT_READ_SUCCESS, .user=toasty->operations[opidx].user, .bytes_read=toasty->operations[opidx].actual_bytes };
         }
 
     } else {
@@ -1241,7 +1252,7 @@ static void process_event_for_read(ToastyFS *toasty,
         if (toasty->operations[opidx].num_pending == 0) {
             sys_free(toasty->operations[opidx].ranges);
             toasty->operations[opidx].ranges = NULL;
-            toasty->operations[opidx].result = (ToastyResult) { .type=TOASTY_RESULT_READ_SUCCESS, .user=toasty->operations[opidx].user };
+            toasty->operations[opidx].result = (ToastyResult) { .type=TOASTY_RESULT_READ_SUCCESS, .user=toasty->operations[opidx].user, .bytes_read=toasty->operations[opidx].actual_bytes };
         }
     }
 }
@@ -2360,8 +2371,9 @@ int toasty_read(ToastyFS *toasty, ToastyString path,
         return -1;
     }
 
+    int bytes_read = result.bytes_read;
     toasty_free_result(&result);
-    return 0; // TODO: return the number of bytes read?
+    return bytes_read;
 }
 
 int toasty_write(ToastyFS *toasty, ToastyString path,

src/file_tree.c

@@ -411,7 +411,7 @@ int file_tree_write(FileTree *ft, string path,
 
 int file_tree_read(FileTree *ft, string path,
     uint64_t off, uint64_t len, uint64_t *chunk_size,
-    SHA256 *hashes, int max_hashes)
+    SHA256 *hashes, int max_hashes, uint64_t *actual_bytes)
 {
     int num_comps;
     string comps[MAX_COMPS];
@@ -432,6 +432,18 @@ int file_tree_read(FileTree *ft, string path,
 
     *chunk_size = f->chunk_size;
 
+    // Calculate file size (number of chunks * chunk size)
+    uint64_t file_size = f->num_chunks * f->chunk_size;
+
+    // Calculate actual bytes that can be read
+    if (off >= file_size) {
+        *actual_bytes = 0;
+    } else if (off + len > file_size) {
+        *actual_bytes = file_size - off;
+    } else {
+        *actual_bytes = len;
+    }
+
     if (len == 0)
         return 0;
 

src/file_tree.h

@@ -56,7 +56,7 @@ int    file_tree_list          (FileTree *ft, string path, ListItem *items, int
 int    file_tree_create_entity (FileTree *ft, string path, bool is_dir, uint64_t chunk_size);
 int    file_tree_delete_entity (FileTree *ft, string path);
 int    file_tree_write         (FileTree *ft, string path, uint64_t off, uint64_t len, uint32_t num_chunks, uint32_t chunk_size, SHA256 *prev_hashes, SHA256 *hashes, SHA256 *removed_hashes, int *num_removed);
-int    file_tree_read          (FileTree *ft, string path, uint64_t off, uint64_t len, uint64_t *chunk_size, SHA256 *hashes, int max_hashes);
+int    file_tree_read          (FileTree *ft, string path, uint64_t off, uint64_t len, uint64_t *chunk_size, SHA256 *hashes, int max_hashes, uint64_t *actual_bytes);
 string file_tree_strerror      (int code);
 int    file_tree_serialize     (FileTree *ft, int (*flush_fn)(char*,int,void*), void *flush_data);
 int    file_tree_deserialize   (FileTree *ft, int (*read_fn)(char*,int,void*), void *read_data);

src/metadata_server.c

@@ -406,8 +406,9 @@ process_client_read(MetadataServer *state, int conn_idx, ByteView msg)
     #define MAX_READ_HASHES 128
 
     uint64_t chunk_size;
+    uint64_t actual_bytes;
     SHA256 hashes[MAX_READ_HASHES];
-    int ret = file_tree_read(&state->file_tree, path, offset, length, &chunk_size, hashes, MAX_READ_HASHES);
+    int ret = file_tree_read(&state->file_tree, path, offset, length, &chunk_size, hashes, MAX_READ_HASHES, &actual_bytes);
 
     if (ret < 0) {
 
@@ -439,6 +440,14 @@ process_client_read(MetadataServer *state, int conn_idx, ByteView msg)
         uint32_t tmp = chunk_size;
         message_write(&writer, &tmp, sizeof(tmp));
 
+        // Send the actual number of bytes that can be read
+        if (actual_bytes > UINT32_MAX) {
+            message_writer_free(&writer);
+            return -1;
+        }
+        uint32_t tmp_actual = actual_bytes;
+        message_write(&writer, &tmp_actual, sizeof(tmp_actual));
+
         uint32_t num_hashes = ret;
         message_write(&writer, &num_hashes, sizeof(num_hashes));