From f6330ce9679409259834e59c8a109d8337b3a69f Mon Sep 17 00:00:00 2001
From: Paul Hauner <paul@paulhauner.com>
Date: Thu, 20 Sep 2018 17:36:23 +1000
Subject: [PATCH] Add ClientDB `exists()` method

---
 lighthouse/db/disk_db.rs | 15 +++++++++++++++
 lighthouse/db/traits.rs  |  3 +++
 2 files changed, 18 insertions(+)

diff --git a/lighthouse/db/disk_db.rs b/lighthouse/db/disk_db.rs
index e4ebdedec..d0f6eb970 100644
--- a/lighthouse/db/disk_db.rs
+++ b/lighthouse/db/disk_db.rs
@@ -107,6 +107,21 @@ impl ClientDB for DiskDB {
             Some(handle) => self.db.put_cf(handle, key, val).map_err(|e| e.into())
         }
     }
+
+    /// Return true if some key exists in some column.
+    fn exists(&self, col: &str, key: &[u8])
+        -> Result<bool, DBError>
+    {
+        /*
+         * I'm not sure if this is the correct way to read if some
+         * block exists. Naievely I would expect this to unncessarily
+         * copy some data, but I could be wrong.
+         */
+        match self.db.cf_handle(col) {
+            None => Err(DBError{ message: "Unknown column".to_string() }),
+            Some(handle) => Ok(self.db.get_cf(handle, key)?.is_some())
+        }
+    }
 }
 
 
diff --git a/lighthouse/db/traits.rs b/lighthouse/db/traits.rs
index 97759d3b7..35feda243 100644
--- a/lighthouse/db/traits.rs
+++ b/lighthouse/db/traits.rs
@@ -26,5 +26,8 @@ pub trait ClientDB: Sync + Send {
 
     fn put(&self, col: &str, key: &[u8], val: &[u8])
         -> Result<(), DBError>;
+
+    fn exists(&self, col: &str, key: &[u8])
+        -> Result<bool, DBError>;
 }