Storage chains: serve transactions over IPFS/bitswap (#7963)

* IPFS server for transactions

* Style

* Indent

* Log message

* CLI option

* Apply suggestions from code review

Co-authored-by: Pierre Krieger <pierre.krieger1708@gmail.com>

* Style

* Style

* Minor fixes

Co-authored-by: Pierre Krieger <pierre.krieger1708@gmail.com>

substrate/primitives/blockchain/src/backend.rs

@@ -215,6 +215,17 @@ pub trait Backend<Block: BlockT>: HeaderBackend<Block> + HeaderMetadata<Block, E
 
 		Ok(None)
 	}
+
+	/// Get single extrinsic by hash.
+	fn extrinsic(
+		&self,
+		hash: &Block::Hash,
+	) -> Result<Option<<Block as BlockT>::Extrinsic>>;
+
+	/// Check if extrinsic exists.
+	fn have_extrinsic(&self, hash: &Block::Hash) -> Result<bool> {
+		Ok(self.extrinsic(hash)?.is_some())
+	}
 }
 
 /// Provides access to the optional cache.

substrate/primitives/database/src/lib.rs

@@ -115,6 +115,11 @@ pub trait Database<H: Clone>: Send + Sync {
 	/// `key` is not currently in the database.
 	fn get(&self, col: ColumnId, key: &[u8]) -> Option<Vec<u8>>;
 
+	/// Check if the value exists in the database without retrieving it.
+	fn contains(&self, col: ColumnId, key: &[u8]) -> bool {
+		self.get(col, key).is_some()
+	}
+
 	/// Call `f` with the value previously stored against `key`.
 	///
 	/// This may be faster than `get` since it doesn't allocate.