services/horizon: Ignore ConnectionTimeout in txsub (#2818)

This commit changes the behaviour of `--connection-timeout` config
param. After this change, it is ignored in `txsub` so if the value is
less than 30s, `txsub` will still timeout after 30s.

If Horizon admin wants to set `--connection-timeout` to a small value it
will likely affect `txsub` system because it requires at least 5 seconds
on average to report the status of the transaction when it's included in
the ledger.

Currently the code ignores timeout for all `POST` requests to avoid
having to parse the route from request URL.

services/horizon/CHANGELOG.md

@@ -12,6 +12,7 @@ file. This project adheres to [Semantic Versioning](http://semver.org/).x
   - `core-db-max-open-connections`
   - `core-db-max-idle-connections`
 * HAL response population is implemented using Go `strings` package instead of `regexp`, improving its performance.  
+* The `--connection-timeout` param is ignored in `POST /transactions`. The requests sent to that endpoint will always timeout after 30 seconds.
 
 ## v1.5.0
 

services/horizon/cmd/root.go

@@ -206,7 +206,7 @@ var configOpts = support.ConfigOptions{
 		OptType:        types.Int,
 		FlagDefault:    55,
 		CustomSetValue: support.SetDuration,
-		Usage:          "defines the timeout of connection after which 504 response will be sent or stream will be closed, if Horizon is behind a load balancer with idle connection timeout, this should be set to a few seconds less that idle timeout",
+		Usage:          "defines the timeout of connection after which 504 response will be sent or stream will be closed, if Horizon is behind a load balancer with idle connection timeout, this should be set to a few seconds less that idle timeout, does not apply to POST /transactions",
 	},
 	&support.ConfigOption{
 		Name:        "per-hour-rate-limit",

services/horizon/internal/middleware.go

@@ -114,7 +114,10 @@ func timeoutMiddleware(timeout time.Duration) func(next http.Handler) http.Handl
 				}
 			}()
 
-			r = r.WithContext(ctx)
+			// txsub has a custom timeout
+			if r.Method != http.MethodPost {
+				r = r.WithContext(ctx)
+			}
 			next.ServeHTTP(mw, r)
 		}
 		return http.HandlerFunc(fn)