server: use etag for vecs instead of date modified

crates/brk_vec/src/traits/any.rs

@@ -1,6 +1,4 @@
-use std::time::Duration;
-
-use brk_core::{Result, Version};
+use brk_core::Version;
 
 use super::{BoxedVecIterator, StoredIndex, StoredType};
 
@@ -11,9 +9,23 @@ pub trait AnyVec: Send + Sync {
     fn is_empty(&self) -> bool {
         self.len() == 0
     }
-    fn modified_time(&self) -> Result<Duration>;
     fn index_type_to_string(&self) -> &'static str;
     fn value_type_to_size_of(&self) -> usize;
+    fn etag(&self, to: Option<i64>) -> String {
+        let len = self.len();
+        format!(
+            "{}-{:?}",
+            to.map_or(len, |to| {
+                if to.is_negative() {
+                    len.checked_sub(to.unsigned_abs() as usize)
+                        .unwrap_or_default()
+                } else {
+                    to as usize
+                }
+            }),
+            self.version()
+        )
+    }
 }
 
 pub trait AnyIterableVec<I, T>: AnyVec {

crates/brk_vec/src/traits/generic.rs

@@ -3,7 +3,6 @@ use std::{
     io::{self, Seek, SeekFrom, Write},
     path::{Path, PathBuf},
     sync::Arc,
-    time::{self, Duration},
 };
 
 use arc_swap::ArcSwap;
@@ -168,12 +167,4 @@ where
     fn flush(&mut self) -> Result<()>;
 
     fn truncate_if_needed(&mut self, index: I) -> Result<()>;
-
-    fn modified_time_(&self) -> Result<Duration> {
-        Ok(self
-            .file()
-            .metadata()?
-            .modified()?
-            .duration_since(time::UNIX_EPOCH)?)
-    }
 }