From 21d8c5a765c334ce7e52f9b3c82580340815485f Mon Sep 17 00:00:00 2001
From: Anton Kaliaev <anton.kalyaev@gmail.com>
Date: Tue, 3 Mar 2020 17:02:19 +0400
Subject: [PATCH 1/4] rpc: create buffered subscriptions on /subscribe

buffer size: 100

Closes #3935
---
 rpc/core/events.go | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/rpc/core/events.go b/rpc/core/events.go
index 165aa6e54fd..4d87a6797b2 100644
--- a/rpc/core/events.go
+++ b/rpc/core/events.go
@@ -12,6 +12,11 @@ import (
 	rpctypes "github.com/tendermint/tendermint/rpc/lib/types"
 )
 
+const (
+	// Buffer on the Tendermint (server) side to allow some slowness in clients.
+	subCap = 100
+)
+
 // Subscribe for events via WebSocket.
 // More: https://docs.tendermint.com/master/rpc/#/Websocket/subscribe
 func Subscribe(ctx *rpctypes.Context, query string) (*ctypes.ResultSubscribe, error) {
@@ -33,7 +38,7 @@ func Subscribe(ctx *rpctypes.Context, query string) (*ctypes.ResultSubscribe, er
 	subCtx, cancel := context.WithTimeout(ctx.Context(), SubscribeTimeout)
 	defer cancel()
 
-	sub, err := eventBus.Subscribe(subCtx, addr, q)
+	sub, err := eventBus.Subscribe(subCtx, addr, q, subCap)
 	if err != nil {
 		return nil, err
 	}

From 6f6c1b6425d4dab54c569086e9ffa9f73fc2ee97 Mon Sep 17 00:00:00 2001
From: Anton Kaliaev <anton.kalyaev@gmail.com>
Date: Tue, 3 Mar 2020 17:03:57 +0400
Subject: [PATCH 2/4] update changelog

---
 CHANGELOG_PENDING.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/CHANGELOG_PENDING.md b/CHANGELOG_PENDING.md
index f85b63307e3..3bd983a0e61 100644
--- a/CHANGELOG_PENDING.md
+++ b/CHANGELOG_PENDING.md
@@ -24,6 +24,7 @@ Friendly reminder, we have a [bug bounty program](https://hackerone.com/tendermi
 
 ### BUG FIXES:
 
+- [rpc] \#3935 Create buffered subscriptions on `/subscribe` (@melekes)
 - [rpc] [\#4493](https://github.com/tendermint/tendermint/pull/4493) Keep the original subscription "id" field when new RPCs come in (@michaelfig)
 
 - [rpc] [\#4437](https://github.com/tendermint/tendermint/pull/4437) Fix tx_search pagination with ordered results (@erikgrinaker)

From 106a59fde35fb247177217a8395beb23f6cad366 Mon Sep 17 00:00:00 2001
From: Anton Kaliaev <anton.kalyaev@gmail.com>
Date: Thu, 5 Mar 2020 12:04:56 +0400
Subject: [PATCH 3/4] rename subCap to subBufferSize

---
 rpc/core/events.go | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/rpc/core/events.go b/rpc/core/events.go
index 4d87a6797b2..7802f160e60 100644
--- a/rpc/core/events.go
+++ b/rpc/core/events.go
@@ -14,7 +14,7 @@ import (
 
 const (
 	// Buffer on the Tendermint (server) side to allow some slowness in clients.
-	subCap = 100
+	subBufferSize = 100
 )
 
 // Subscribe for events via WebSocket.
@@ -38,7 +38,7 @@ func Subscribe(ctx *rpctypes.Context, query string) (*ctypes.ResultSubscribe, er
 	subCtx, cancel := context.WithTimeout(ctx.Context(), SubscribeTimeout)
 	defer cancel()
 
-	sub, err := eventBus.Subscribe(subCtx, addr, q, subCap)
+	sub, err := eventBus.Subscribe(subCtx, addr, q, subBufferSize)
 	if err != nil {
 		return nil, err
 	}

From 097f15b02aa2d6960c830268ab75fa1b9efcabad Mon Sep 17 00:00:00 2001
From: Anton Kaliaev <anton.kalyaev@gmail.com>
Date: Thu, 5 Mar 2020 12:14:17 +0400
Subject: [PATCH 4/4] add docs

---
 rpc/core/README.md | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/rpc/core/README.md b/rpc/core/README.md
index d767c5f7169..f62d2dbf445 100644
--- a/rpc/core/README.md
+++ b/rpc/core/README.md
@@ -5,3 +5,14 @@
 Requests that return multiple items will be paginated to 30 items by default.
 You can specify further pages with the ?page parameter. You can also set a
 custom page size up to 100 with the ?per_page parameter.
+
+## Subscribing to events
+
+The user can subscribe to events emitted by Tendermint, using `/subscribe`. If
+the maximum number of clients is reached or the client has too many
+subscriptions, an error will be returned. The subscription timeout is 5 sec.
+Each subscription has a buffer to accommodate short bursts of events or some
+slowness in clients. If the buffer gets full, the subscription will be canceled
+("client is not pulling messages fast enough"). If Tendermint exits, all
+subscriptions are canceled ("Tendermint exited"). The user can unsubscribe
+using either `/unsubscribe` or `/unsubscribe_all`.