test(outputs.prometheus_client): Add tests for content-type header (#16559)

plugins/inputs/prometheus/README.md

@@ -127,19 +127,6 @@ and `bearer_token_string` option. See the
   # Default is 60 minutes.
   # cache_refresh_interval = 60
 
-  ## Scrape Services available in Consul Catalog
-  # [inputs.prometheus.consul]
-  #   enabled = true
-  #   agent = "http://localhost:8500"
-  #   query_interval = "5m"
-
-  #   [[inputs.prometheus.consul.query]]
-  #     name = "a service name"
-  #     tag = "a service tag"
-  #     url = 'http://{{if ne .ServiceAddress ""}}{{.ServiceAddress}}{{else}}{{.Address}}{{end}}:{{.ServicePort}}/{{with .ServiceMeta.metrics_path}}{{.}}{{else}}metrics{{end}}'
-  #     [inputs.prometheus.consul.query.tags]
-  #       host = "{{.Node}}"
-
   ## Use bearer token for authorization. ('bearer_token' takes priority)
   # bearer_token = "/path/to/bearer/token"
   ## OR
@@ -186,6 +173,19 @@ and `bearer_token_string` option. See the
   ## This option allows you to report the status of prometheus requests.
   # enable_request_metrics = false
 
+  ## Scrape Services available in Consul Catalog
+  # [inputs.prometheus.consul]
+  #   enabled = true
+  #   agent = "http://localhost:8500"
+  #   query_interval = "5m"
+
+  #   [[inputs.prometheus.consul.query]]
+  #     name = "a service name"
+  #     tag = "a service tag"
+  #     url = 'http://{{if ne .ServiceAddress ""}}{{.ServiceAddress}}{{else}}{{.Address}}{{end}}:{{.ServicePort}}/{{with .ServiceMeta.metrics_path}}{{.}}{{else}}metrics{{end}}'
+  #     [inputs.prometheus.consul.query.tags]
+  #       host = "{{.Node}}"
+
   ## Control pod scraping based on pod namespace annotations
   ## Pass and drop here act like tagpass and tagdrop, but instead
   ## of filtering metrics they filters pod candidates for scraping

plugins/inputs/prometheus/sample.conf

@@ -102,19 +102,6 @@
   # Default is 60 minutes.
   # cache_refresh_interval = 60
 
-  ## Scrape Services available in Consul Catalog
-  # [inputs.prometheus.consul]
-  #   enabled = true
-  #   agent = "http://localhost:8500"
-  #   query_interval = "5m"
-
-  #   [[inputs.prometheus.consul.query]]
-  #     name = "a service name"
-  #     tag = "a service tag"
-  #     url = 'http://{{if ne .ServiceAddress ""}}{{.ServiceAddress}}{{else}}{{.Address}}{{end}}:{{.ServicePort}}/{{with .ServiceMeta.metrics_path}}{{.}}{{else}}metrics{{end}}'
-  #     [inputs.prometheus.consul.query.tags]
-  #       host = "{{.Node}}"
-
   ## Use bearer token for authorization. ('bearer_token' takes priority)
   # bearer_token = "/path/to/bearer/token"
   ## OR
@@ -161,6 +148,19 @@
   ## This option allows you to report the status of prometheus requests.
   # enable_request_metrics = false
 
+  ## Scrape Services available in Consul Catalog
+  # [inputs.prometheus.consul]
+  #   enabled = true
+  #   agent = "http://localhost:8500"
+  #   query_interval = "5m"
+
+  #   [[inputs.prometheus.consul.query]]
+  #     name = "a service name"
+  #     tag = "a service tag"
+  #     url = 'http://{{if ne .ServiceAddress ""}}{{.ServiceAddress}}{{else}}{{.Address}}{{end}}:{{.ServicePort}}/{{with .ServiceMeta.metrics_path}}{{.}}{{else}}metrics{{end}}'
+  #     [inputs.prometheus.consul.query.tags]
+  #       host = "{{.Node}}"
+
   ## Control pod scraping based on pod namespace annotations
   ## Pass and drop here act like tagpass and tagdrop, but instead
   ## of filtering metrics they filters pod candidates for scraping

plugins/outputs/prometheus_client/prometheus_client_test.go

@@ -0,0 +1,123 @@
+package prometheus_client
+
+import (
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/influxdata/telegraf/testutil"
+)
+
+func TestLandingPage(t *testing.T) {
+	output := PrometheusClient{
+		Listen:            ":0",
+		CollectorsExclude: []string{"process"},
+		MetricVersion:     1,
+		Log:               &testutil.Logger{Name: "outputs.prometheus_client"},
+	}
+	expected := "Telegraf Output Plugin: Prometheus Client"
+
+	require.NoError(t, output.Init())
+	require.NoError(t, output.Connect())
+
+	u, err := url.Parse(fmt.Sprintf("http://%s/", output.url.Host))
+	require.NoError(t, err)
+
+	resp, err := http.Get(u.String())
+	require.NoError(t, err)
+	defer resp.Body.Close()
+
+	actual, err := io.ReadAll(resp.Body)
+	require.NoError(t, err)
+	require.Equal(t, expected, strings.TrimSpace(string(actual)))
+}
+
+func TestFormatHeader(t *testing.T) {
+	tests := []struct {
+		name     string
+		accept   string
+		expected string
+	}{
+		{
+			name:     "invalid accept ",
+			accept:   "applications/json",
+			expected: "text/plain; version=0.0.4; charset=utf-8; escaping=underscores",
+		},
+		{
+			name:     "no accept header",
+			expected: "text/plain; version=0.0.4; charset=utf-8; escaping=underscores",
+		},
+		{
+			name:     "text no version",
+			accept:   "text/plain",
+			expected: "text/plain; version=0.0.4; charset=utf-8; escaping=underscores",
+		},
+		{
+			name:     "text with version 0.0.4",
+			accept:   "text/plain; version=0.0.4",
+			expected: "text/plain; version=0.0.4; charset=utf-8; escaping=underscores",
+		},
+		{
+			name:     "protobuf text format",
+			accept:   "application/vnd.google.protobuf; proto=io.prometheus.client.MetricFamily; encoding=text",
+			expected: "application/vnd.google.protobuf; proto=io.prometheus.client.MetricFamily; encoding=text; escaping=underscores",
+		},
+		{
+			name:     "protobuf compact text format",
+			accept:   "application/vnd.google.protobuf; proto=io.prometheus.client.MetricFamily; encoding=compact-text",
+			expected: "application/vnd.google.protobuf; proto=io.prometheus.client.MetricFamily; encoding=compact-text; escaping=underscores",
+		},
+		{
+			name:     "protobuf delimited format",
+			accept:   "application/vnd.google.protobuf; proto=io.prometheus.client.MetricFamily; encoding=delimited",
+			expected: "application/vnd.google.protobuf; proto=io.prometheus.client.MetricFamily; encoding=delimited; escaping=underscores",
+		},
+		{
+			name:     "multiple accept preferring protobuf",
+			accept:   "application/vnd.google.protobuf; proto=io.prometheus.client.MetricFamily; encoding=delimited, text/plain",
+			expected: "application/vnd.google.protobuf; proto=io.prometheus.client.MetricFamily; encoding=delimited; escaping=underscores",
+		},
+		{
+			name:     "multiple accept preferring text",
+			accept:   "text/plain, application/vnd.google.protobuf; proto=io.prometheus.client.MetricFamily; encoding=delimited",
+			expected: "text/plain; version=0.0.4; charset=utf-8; escaping=underscores",
+		},
+	}
+
+	// Setup the plugin
+	plugin := PrometheusClient{
+		Listen: ":0",
+		Log:    testutil.Logger{Name: "outputs.prometheus_client"},
+	}
+	require.NoError(t, plugin.Init())
+	require.NoError(t, plugin.Connect())
+
+	// Get the plugin's address so we can send data to it
+	addr := fmt.Sprintf("http://%s/metrics", plugin.url.Host)
+
+	// Run the actual tests
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// Construct a request with the given "Accept" header
+			req, err := http.NewRequest("GET", addr, nil)
+			require.NoError(t, err)
+			if tt.accept != "" {
+				req.Header.Add("Accept", tt.accept)
+			}
+
+			// Get the metrics
+			resp, err := http.DefaultClient.Do(req)
+			require.NoError(t, err)
+			defer resp.Body.Close()
+
+			// Test the result
+			require.NotEmpty(t, resp.Body)
+			require.Equal(t, tt.expected, resp.Header.Get("Content-Type"))
+		})
+	}
+}

plugins/outputs/prometheus_client/prometheus_client_v1_test.go

@@ -5,7 +5,6 @@ import (
 	"io"
 	"net/http"
 	"net/http/httptest"
-	"net/url"
 	"regexp"
 	"strings"
 	"testing"
@@ -496,32 +495,3 @@ rpc_duration_seconds_count 2693
 		})
 	}
 }
-
-func TestLandingPage(t *testing.T) {
-	logger := testutil.Logger{Name: "outputs.prometheus_client"}
-	output := PrometheusClient{
-		Listen:            ":0",
-		CollectorsExclude: []string{"process"},
-		MetricVersion:     1,
-		Log:               logger,
-	}
-	expected := "Telegraf Output Plugin: Prometheus Client"
-
-	err := output.Init()
-	require.NoError(t, err)
-
-	err = output.Connect()
-	require.NoError(t, err)
-
-	u, err := url.Parse(fmt.Sprintf("http://%s/", output.url.Host))
-	require.NoError(t, err)
-
-	resp, err := http.Get(u.String())
-	require.NoError(t, err)
-	defer resp.Body.Close()
-
-	actual, err := io.ReadAll(resp.Body)
-	require.NoError(t, err)
-
-	require.Equal(t, expected, strings.TrimSpace(string(actual)))
-}