implement conditional put/patch

Signed-off-by: Alexander Onnikov <Alexander.Onnikov@xored.com>

tests/src/head.rs

@@ -64,3 +64,48 @@ pub async fn head_known_with_jsonpatch() -> eyre::Result<()> {
 
     Ok(())
 }
+
+#[tanu::test]
+pub async fn head_conditional() -> eyre::Result<()> {
+    let key = random_key();
+    let text = random_text(1024);
+
+    let http = Client::new();
+
+    let res = http.key_put(&key).body(text.clone()).send().await?;
+    check!(res.status().is_success());
+
+    let res = http.key_head(&key).send().await?;
+    check!(res.status().is_success());
+    let etag = res.header("etag").expect("ETag not found");
+
+    // Test without If-None-Match (normal GET)
+    let res = http.key_head(&key).send().await?;
+    check!(res.status().is_success());
+
+    // Test with If-None-Match: *
+    let res = http
+        .key_head(&key)
+        .header("If-None-Match", "*")
+        .send()
+        .await?;
+    check_eq!(res.status(), http::StatusCode::NOT_MODIFIED);
+
+    // Test with correct ETag
+    let res = http
+        .key_head(&key)
+        .header("If-None-Match", etag)
+        .send()
+        .await?;
+    check_eq!(res.status(), http::StatusCode::NOT_MODIFIED);
+
+    // Test with incorrect ETag
+    let res = http
+        .key_head(&key)
+        .header("If-None-Match", "\"invalid-etag\"")
+        .send()
+        .await?;
+    check!(res.status().is_success());
+
+    Ok(())
+}