Don't duplicate queued storage diffs

- currently, if we don't recognize the same diff several times (e.g.
  if you restart the storage diff watcher pointed at the same file),
  we'll add the same row to the queue on each run.
- these changes assure we only queue an unrecognized diff once.

db/migrations/00024_create_queued_storage.sql

@@ -5,7 +5,8 @@ CREATE TABLE public.queued_storage (
   block_hash    BYTEA,
   contract      BYTEA,
   storage_key   BYTEA,
-  storage_value BYTEA
+  storage_value BYTEA,
+  UNIQUE (block_height, block_hash, contract, storage_key, storage_value)
 );
 
 -- +goose Down

db/schema.sql

@@ -2,8 +2,8 @@
 -- PostgreSQL database dump
 --
 
--- Dumped from database version 11.2
--- Dumped by pg_dump version 11.2
+-- Dumped from database version 11.3
+-- Dumped by pg_dump version 11.3
 
 SET statement_timeout = 0;
 SET lock_timeout = 0;
@@ -12,6 +12,7 @@ SET client_encoding = 'UTF8';
 SET standard_conforming_strings = on;
 SELECT pg_catalog.set_config('search_path', '', false);
 SET check_function_bodies = false;
+SET xmloption = content;
 SET client_min_messages = warning;
 SET row_security = off;
 
@@ -789,6 +790,14 @@ ALTER TABLE ONLY public.eth_nodes
     ADD CONSTRAINT nodes_pkey PRIMARY KEY (id);
 
 
+--
+-- Name: queued_storage queued_storage_block_height_block_hash_contract_storage_key_key; Type: CONSTRAINT; Schema: public; Owner: -
+--
+
+ALTER TABLE ONLY public.queued_storage
+    ADD CONSTRAINT queued_storage_block_height_block_hash_contract_storage_key_key UNIQUE (block_height, block_hash, contract, storage_key, storage_value);
+
+
 --
 -- Name: queued_storage queued_storage_pkey; Type: CONSTRAINT; Schema: public; Owner: -
 --

libraries/shared/storage/storage_queue.go

@@ -38,7 +38,7 @@ func NewStorageQueue(db *postgres.DB) StorageQueue {
 func (queue StorageQueue) Add(row utils.StorageDiffRow) error {
 	_, err := queue.db.Exec(`INSERT INTO public.queued_storage (contract,
 		block_hash, block_height, storage_key, storage_value) VALUES
-		($1, $2, $3, $4, $5)`, row.Contract.Bytes(), row.BlockHash.Bytes(),
+		($1, $2, $3, $4, $5) ON CONFLICT DO NOTHING`, row.Contract.Bytes(), row.BlockHash.Bytes(),
 		row.BlockHeight, row.StorageKey.Bytes(), row.StorageValue.Bytes())
 	return err
 }

libraries/shared/storage/storage_queue_test.go

@@ -49,11 +49,22 @@ var _ = Describe("Storage queue", func() {
 		Expect(addErr).NotTo(HaveOccurred())
 	})
 
-	It("adds a storage row to the db", func() {
-		var result utils.StorageDiffRow
-		getErr := db.Get(&result, `SELECT contract, block_hash, block_height, storage_key, storage_value FROM public.queued_storage`)
-		Expect(getErr).NotTo(HaveOccurred())
-		Expect(result).To(Equal(row))
+	Describe("Add", func() {
+		It("adds a storage row to the db", func() {
+			var result utils.StorageDiffRow
+			getErr := db.Get(&result, `SELECT contract, block_hash, block_height, storage_key, storage_value FROM public.queued_storage`)
+			Expect(getErr).NotTo(HaveOccurred())
+			Expect(result).To(Equal(row))
+		})
+
+		It("does not duplicate storage rows", func() {
+			addErr := queue.Add(row)
+			Expect(addErr).NotTo(HaveOccurred())
+			var count int
+			getErr := db.Get(&count, `SELECT count(*) FROM public.queued_storage`)
+			Expect(getErr).NotTo(HaveOccurred())
+			Expect(count).To(Equal(1))
+		})
 	})
 
 	It("deletes storage row from db", func() {