From 0c55a15ce17ac4ba97151acfcd2d9f54bfba1bc6 Mon Sep 17 00:00:00 2001
From: Christopher Faulet <cfaulet@haproxy.com>
Date: Thu, 4 Jul 2019 10:03:28 +0200
Subject: [PATCH] BUG/MINOR: contrib/prometheus-exporter: Don't try to add
 empty data blocks

When the response buffer is full and nothing more can be inserted, it is
important to not try to insert an empty data block. Otherwise, when the function
channel_add_input() is called, the flag CF_READ_PARTIAL is set on the response
channel while nothing was read and the stream is uselessly woken up. Finally, we
have loop while the response buffer is full.

This patch must be backported to 2.0.
---
 .../prometheus-exporter/service-prometheus.c  | 32 ++++++++++++-------
 1 file changed, 20 insertions(+), 12 deletions(-)

diff --git a/contrib/prometheus-exporter/service-prometheus.c b/contrib/prometheus-exporter/service-prometheus.c
index b57af9944..2aafd4d87 100644
--- a/contrib/prometheus-exporter/service-prometheus.c
+++ b/contrib/prometheus-exporter/service-prometheus.c
@@ -1408,9 +1408,11 @@ static int promex_dump_global_metrics(struct appctx *appctx, struct htx *htx)
 	}
 
   end:
-	if (!htx_add_data_atonce(htx, out))
-		return -1; /* Unexpected and unrecoverable error */
-	channel_add_input(chn, out.len);
+	if (out.len) {
+		if (!htx_add_data_atonce(htx, out))
+			return -1; /* Unexpected and unrecoverable error */
+		channel_add_input(chn, out.len);
+	}
 	return ret;
   full:
 	ret = 0;
@@ -1586,9 +1588,11 @@ static int promex_dump_front_metrics(struct appctx *appctx, struct htx *htx)
 	}
 
   end:
-	if (!htx_add_data_atonce(htx, out))
-		return -1; /* Unexpected and unrecoverable error */
-	channel_add_input(chn, out.len);
+	if (out.len) {
+		if (!htx_add_data_atonce(htx, out))
+			return -1; /* Unexpected and unrecoverable error */
+		channel_add_input(chn, out.len);
+	}
 	return ret;
   full:
 	ret = 0;
@@ -1804,9 +1808,11 @@ static int promex_dump_back_metrics(struct appctx *appctx, struct htx *htx)
 	}
 
   end:
-	if (!htx_add_data_atonce(htx, out))
-		return -1; /* Unexpected and unrecoverable error */
-	channel_add_input(chn, out.len);
+	if (out.len) {
+		if (!htx_add_data_atonce(htx, out))
+			return -1; /* Unexpected and unrecoverable error */
+		channel_add_input(chn, out.len);
+	}
 	return ret;
   full:
 	ret = 0;
@@ -1998,9 +2004,11 @@ static int promex_dump_srv_metrics(struct appctx *appctx, struct htx *htx)
 
 
   end:
-	if (!htx_add_data_atonce(htx, out))
-		return -1; /* Unexpected and unrecoverable error */
-	channel_add_input(chn, out.len);
+	if (out.len) {
+		if (!htx_add_data_atonce(htx, out))
+			return -1; /* Unexpected and unrecoverable error */
+		channel_add_input(chn, out.len);
+	}
 	return ret;
   full:
 	ret = 0;