From 1ee3b92fdd2b9bcfc94364c1d297502730dc24c8 Mon Sep 17 00:00:00 2001
From: Marko Mikulicic <mkm@influxdata.com>
Date: Wed, 16 Feb 2022 05:14:34 +0100
Subject: [PATCH] feat: Add telegraf.influxdata.com/global-tag-literal-

---
 sidecar.go      | 29 +++++++++++++++++++++++++++++
 sidecar_test.go | 40 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 69 insertions(+)

diff --git a/sidecar.go b/sidecar.go
index 9d8cb53..3fb148c 100644
--- a/sidecar.go
+++ b/sidecar.go
@@ -53,6 +53,8 @@ const (
 	TelegrafEnvSecretKeyRefPrefix = "telegraf.influxdata.com/env-secretkeyref-"
 	// TelegrafEnvLiteralPrefix allows adding a literal to the telegraf sidecar in the form of an environment variable
 	TelegrafEnvLiteralPrefix = "telegraf.influxdata.com/env-literal-"
+	// TelegrafGlobalTagLiteralPrefix allows adding a literal global tag to the telegraf sidecar config
+	TelegrafGlobalTagLiteralPrefix = "telegraf.influxdata.com/global-tag-literal-"
 	// TelegrafImage allows specifying a custom telegraf image to be used in the sidecar container
 	TelegrafImage = "telegraf.influxdata.com/image"
 	// TelegrafRequestsCPU allows specifying custom CPU resource requests
@@ -273,6 +275,33 @@ func (h *sidecarHandler) assembleConf(pod *corev1.Pod, className string) (telegr
 	}
 	telegrafConf = fmt.Sprintf("%s\n%s", telegrafConf, classData)
 
+	type keyValue struct{ key, value string }
+	var globalTags []keyValue
+	for key, value := range pod.Annotations {
+		if strings.HasPrefix(key, TelegrafGlobalTagLiteralPrefix) {
+			globalTags = append(globalTags, keyValue{strings.TrimPrefix(key, TelegrafGlobalTagLiteralPrefix), value})
+		}
+	}
+	// Go maps aren't ordered; we want a stable config output, to simplify tests among other things
+	sort.Slice(globalTags, func(i, j int) bool { return globalTags[i].key < globalTags[j].key })
+
+	if len(globalTags) > 0 {
+		globalTagsText := "[global_tags]\n"
+		for _, i := range globalTags {
+			globalTagsText = fmt.Sprintf("%s  %s = %q\n", globalTagsText, i.key, i.value)
+		}
+
+		// inject globalTagsText at the top of an existing "[global_tags]" section
+		// or create one.
+		// Edge case / caveat: This doesn't handle when the class config file starts with "[global_tags]
+		// TODO(mkm): yak shave: change this whole method to manipulate a real toml instead of fiddling with strings.
+		//            currently blocked on inability of github.com/influxdata/toml to render the AST back to string.
+		if !strings.Contains(telegrafConf, "[global_tags]\n") {
+			telegrafConf = fmt.Sprintf("%s\n%s", telegrafConf, "[global_tags]\n")
+		}
+		telegrafConf = strings.ReplaceAll(telegrafConf, "[global_tags]\n", globalTagsText)
+	}
+
 	if _, err := toml.Parse([]byte(telegrafConf)); err != nil {
 		return "", fmt.Errorf("resulting Telegraf is not a valid file: %v", err)
 	}
diff --git a/sidecar_test.go b/sidecar_test.go
index d091a7a..af82181 100644
--- a/sidecar_test.go
+++ b/sidecar_test.go
@@ -277,6 +277,46 @@ func Test_assembleConf(t *testing.T) {
 [[inputs.internal]]
 `,
 		},
+		{
+			name: "handle global_tags",
+			pod: &corev1.Pod{
+				ObjectMeta: metav1.ObjectMeta{
+					Annotations: map[string]string{
+						TelegrafGlobalTagLiteralPrefix + "foo": "bar",
+					},
+				},
+			},
+			wantConfig: `[global_tags]
+  foo = "bar"`,
+		},
+		{
+			name: "handle global_tags multiple",
+			pod: &corev1.Pod{
+				ObjectMeta: metav1.ObjectMeta{
+					Annotations: map[string]string{
+						TelegrafGlobalTagLiteralPrefix + "foo": "bar",
+						TelegrafGlobalTagLiteralPrefix + "baz": "quz",
+					},
+				},
+			},
+			wantConfig: `[global_tags]
+  baz = "quz"
+  foo = "bar"`,
+		},
+		{
+			name: "handle global_tags existing",
+			pod: &corev1.Pod{
+				ObjectMeta: metav1.ObjectMeta{
+					Annotations: map[string]string{
+						TelegrafRawInput:                       "[global_tags]\n  a = \"b\"",
+						TelegrafGlobalTagLiteralPrefix + "foo": "bar",
+					},
+				},
+			},
+			wantConfig: `[global_tags]
+  foo = "bar"
+  a = "b"`,
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {