improve the quality of starlark docs by executing them as tests (#8020)

plugins/processors/starlark/README.md

@@ -9,7 +9,7 @@ Existing Python code is unlikely to work unmodified.  The execution environment
 is sandboxed, and it is not possible to do I/O operations such as reading from
 files or sockets.
 
-The Starlark [specification][] has details about the syntax and available
+The **[Starlark specification][]** has details about the syntax and available
 functions.
 
 Telegraf minimum version: Telegraf 1.15.0
@@ -44,7 +44,7 @@ def apply(metric):
 ```
 
 For a list of available types and functions that can be used in the code, see
-the Starlark [specification][].
+the [Starlark specification][].
 
 In addition to these, the following InfluxDB-specific
 types and functions are exposed to the script.
@@ -149,14 +149,17 @@ Attempting to modify the global scope will fail with an error.
 
 ### Examples
 
-- [ratio](/plugins/processors/starlark/testdata/ratio.star)
-- [rename](/plugins/processors/starlark/testdata/rename.star)
-- [scale](/plugins/processors/starlark/testdata/scale.star)
-- [number logic](/plugins/processors/starlark/testdata/number_logic.star)
-- [pivot](/plugins/processors/starlark/testdata/pivot.star)
+- [ratio](/plugins/processors/starlark/testdata/ratio.star) - Compute the ratio of two integer fields
+- [rename](/plugins/processors/starlark/testdata/rename.star) - Rename tags or fields using a name mapping.
+- [scale](/plugins/processors/starlark/testdata/scale.star) - Multiply any field by a number
+- [number logic](/plugins/processors/starlark/testdata/number_logic.star) - transform a numerical value to another numerical value
+- [pivot](/plugins/processors/starlark/testdata/pivot.star) - Pivots a key's value to be the key for another key.
+- [value filter](plugins/processors/starlark/testdata/value_filter.star) - remove a metric based on a field value.
 
-Open a [PR](https://github.com/influxdata/telegraf/compare) to add any other useful Starlark examples. 
+[All examples](/plugins/processors/starlark/testdata) are in the testdata folder.
 
-[specification]: https://github.com/google/starlark-go/blob/master/doc/spec.md
+Open a Pull Request to add any other useful Starlark examples.
+
+[Starlark specification]: https://github.com/google/starlark-go/blob/master/doc/spec.md
 [string]: https://github.com/google/starlark-go/blob/master/doc/spec.md#strings
 [dict]: https://github.com/google/starlark-go/blob/master/doc/spec.md#dictionaries

plugins/processors/starlark/starlark_test.go

@@ -1,10 +1,16 @@
 package starlark
 
 import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"strings"
 	"testing"
 	"time"
 
 	"github.com/influxdata/telegraf"
+	"github.com/influxdata/telegraf/plugins/parsers"
 	"github.com/influxdata/telegraf/testutil"
 	"github.com/stretchr/testify/require"
 )
@@ -2787,3 +2793,72 @@ def apply(metric):
 		})
 	}
 }
+func TestAllScriptTestData(t *testing.T) {
+	// can be run from multiple folders
+	paths := []string{"testdata", "plugins/processors/starlark/testdata"}
+	for _, testdataPath := range paths {
+		filepath.Walk(testdataPath, func(path string, info os.FileInfo, err error) error {
+			if info == nil || info.IsDir() {
+				return nil
+			}
+			fn := path
+			t.Run(fn, func(t *testing.T) {
+				b, err := ioutil.ReadFile(fn)
+				require.NoError(t, err)
+				lines := strings.Split(string(b), "\n")
+				inputMetrics := parseMetricsFrom(t, lines, "Example Input:")
+				outputMetrics := parseMetricsFrom(t, lines, "Example Output:")
+				plugin := &Starlark{
+					Script: fn,
+					Log:    testutil.Logger{},
+				}
+				require.NoError(t, plugin.Init())
+
+				acc := &testutil.Accumulator{}
+
+				err = plugin.Start(acc)
+				require.NoError(t, err)
+
+				for _, m := range inputMetrics {
+					err = plugin.Add(m, acc)
+					require.NoError(t, err)
+				}
+
+				err = plugin.Stop()
+				require.NoError(t, err)
+
+				testutil.RequireMetricsEqual(t, outputMetrics, acc.GetTelegrafMetrics(), testutil.SortMetrics(), testutil.IgnoreTime())
+			})
+			return nil
+		})
+	}
+}
+
+var parser, _ = parsers.NewInfluxParser() // literally never returns errors.
+
+// parses metric lines out of line protocol following a header, with a trailing blank line
+func parseMetricsFrom(t *testing.T, lines []string, header string) (metrics []telegraf.Metric) {
+	require.NotZero(t, len(lines), "Expected some lines to parse from .star file, found none")
+	startIdx := -1
+	endIdx := len(lines)
+	for i := range lines {
+		if strings.TrimLeft(lines[i], "# ") == header {
+			startIdx = i + 1
+			break
+		}
+	}
+	require.NotEqual(t, -1, startIdx, fmt.Sprintf("Header %q must exist in file", header))
+	for i := startIdx; i < len(lines); i++ {
+		line := strings.TrimLeft(lines[i], "# ")
+		if line == "" || line == "'''" {
+			endIdx = i
+			break
+		}
+	}
+	for i := startIdx; i < endIdx; i++ {
+		m, err := parser.ParseLine(strings.TrimLeft(lines[i], "# "))
+		require.NoError(t, err, fmt.Sprintf("Expected to be able to parse %q metric, but found error", header))
+		metrics = append(metrics, m)
+	}
+	return metrics
+}

plugins/processors/starlark/testdata/number_logic.star

@@ -2,9 +2,10 @@
 # Example: Set  any 'status' field between 1 and 6 to a value of 0
 #
 # Example Input:
-# lb, http_method=GET status=5 1465839830100400201
+# lb,http_method=GET status=5i 1465839830100400201
+#
 # Example Output:
-# lb, http_method=GET status=0 1465839830100400201
+# lb,http_method=GET status=0i 1465839830100400201
 
 
 def apply(metric):

plugins/processors/starlark/testdata/pivot.star

@@ -3,10 +3,10 @@ Pivots a key's value to be the key for another key.
 In this example it pivots the value of key `sensor`
 to be the key of the value in key `value`
 
-Input: 
-temperature sensor=001A0,value=111.48
+Example Input:
+temperature sensor="001A0",value=111.48
 
-Output: 
+Example Output:
 temperature 001A0=111.48
 '''
 

plugins/processors/starlark/testdata/ratio.star

@@ -4,8 +4,9 @@
 #
 # Example Input:
 # memory,host=hostname used=11038756864.4948,total=17179869184.1221 1597255082000000000
+#
 # Example Output:
-# memory, host=hostname used=11038756864.4948,total=17179869184.1221,usage=64.254021647 1597255082000000000
+# memory,host=hostname used=11038756864.4948,total=17179869184.1221,usage=64.25402164701573 1597255082000000000
 
 def apply(metric):
     used = float(metric.fields['used'])

plugins/processors/starlark/testdata/rename.star

@@ -2,6 +2,7 @@
 #
 # Example Input:
 # measurement,host=hostname lower=0,upper=100 1597255410000000000
+#
 # Example Output:
 # measurement,host=hostname min=0,max=100 1597255410000000000
 
@@ -15,4 +16,8 @@ def apply(metric):
         if k in renames:
             metric.tags[renames[k]] = v
             metric.tags.pop(k)
+    for k, v in metric.fields.items():
+        if k in renames:
+            metric.fields[renames[k]] = v
+            metric.fields.pop(k)
     return metric

plugins/processors/starlark/testdata/scale.star

@@ -2,6 +2,7 @@
 #
 # Example Input:
 # modbus,host=hostname Current=1.22,Energy=0,Frequency=60i,Power=0,Voltage=123.9000015258789 1554079521000000000
+#
 # Example Output:
 # modbus,host=hostname Current=12.2,Energy=0,Frequency=60i,Power=0,Voltage=1239.000015258789 1554079521000000000
 

plugins/processors/starlark/testdata/value_filter.star

@@ -0,0 +1,18 @@
+# Filter metrics by value
+'''
+In this example we look at the `value` field of the metric.
+If the value is zeor, we delete all the fields, effectively dropping the metric.
+
+Example Input:
+temperature sensor="001A0",value=111.48
+temperature sensor="001B0",value=0.0
+
+Example Output:
+temperature sensor="001A0",value=111.48
+'''
+
+def apply(metric):
+    if metric.fields["value"] == 0.0:
+        # removing all fields deletes a metric
+        metric.fields.clear()
+    return metric