[receiver/datadogreceiver] add json handling for the api/v2/series endpoint (open-telemetry#36218)

<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
#### Description
Adding json handling for the `api/v2/series` endpoint. The datadog api
client libraries use json messages, however only protobuf messages are
currently supported in the` api/v2/series` endpoint, so requests fail
with `proto: illegal wireType 6`

If `Content-Type: application/json` is set, then we handle the json
message. Otherwise, we handle the protobuf message.

<!-- Issue number (e.g. open-telemetry#1234) or full URL to issue, if applicable. -->
#### Link to tracking issue
Fixes
open-telemetry#36079

<!--Describe what testing was performed and which tests were added.-->
#### Testing
Added test with a json metric payload that now passes.

Additionally, I also tested these changes in my own image and confirmed
that the datadog api client libraries can now successfully ship metrics
to the `api/v2/series` endpoint.

I also confirmed with the following curl:

```
curl -X POST \
  -H "Content-Type: application/json" \
  -H "DD-API-KEY: your_api_key_here" \
  -d '{
    "series": [
      {
        "resources": [
          {
            "name": "dummyhost",
            "type": "host"
          }
        ],
        "tags": ["env:test"],
        "metric": "test.metric",
        "points": [
          {
            "timestamp": 1730829575,
            "value": 1.0
          }
        ],
        "type": 3
      }
    ]
  }' \
  https://datadog-receiver/api/v2/series
{"errors":[]}
```

---------

Co-authored-by: Sean Marciniak <30928402+MovieStoreGuy@users.noreply.github.com>

Author: 2 people

.chloggen/36079-add-datadog-json-handling.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: 'enhancement'
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: 'datadogreceiver'
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: "Add json handling for the `api/v2/series` endpoint in the datadogreceiver"
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [36079]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

receiver/datadogreceiver/internal/translator/series.go

@@ -4,6 +4,7 @@
 package translator // import "github.com/open-telemetry/opentelemetry-collector-contrib/receiver/datadogreceiver/internal/translator"
 
 import (
+	"encoding/json"
 	"io"
 	"net/http"
 	"strings"
@@ -27,19 +28,27 @@ type SeriesList struct {
 	Series []datadogV1.Series `json:"series"`
 }
 
-// TODO: add handling for JSON format in additional to protobuf?
 func (mt *MetricsTranslator) HandleSeriesV2Payload(req *http.Request) (mp []*gogen.MetricPayload_MetricSeries, err error) {
 	buf := GetBuffer()
 	defer PutBuffer(buf)
 	if _, err := io.Copy(buf, req.Body); err != nil {
 		return mp, err
 	}
 
+	contentType := req.Header.Get("Content-Type")
+
 	pl := new(gogen.MetricPayload)
-	if err := pl.Unmarshal(buf.Bytes()); err != nil {
-		return mp, err
-	}
 
+	// handle json messages if set, otherwise handle protobuf
+	if contentType == "application/json" {
+		if err := json.Unmarshal(buf.Bytes(), &pl); err != nil {
+			return mp, err
+		}
+	} else {
+		if err := pl.Unmarshal(buf.Bytes()); err != nil {
+			return mp, err
+		}
+	}
 	return pl.GetSeries(), nil
 }
 

receiver/datadogreceiver/receiver_test.go

@@ -459,6 +459,85 @@ func TestDatadogMetricsV2_EndToEnd(t *testing.T) {
 	assert.Equal(t, pcommon.Timestamp(1636629071*1_000_000_000), metric.Sum().DataPoints().At(1).StartTimestamp())
 }
 
+func TestDatadogMetricsV2_EndToEndJSON(t *testing.T) {
+	cfg := createDefaultConfig().(*Config)
+	cfg.Endpoint = "localhost:0" // Using a randomly assigned address
+	sink := new(consumertest.MetricsSink)
+
+	dd, err := newDataDogReceiver(
+		cfg,
+		receivertest.NewNopSettings(),
+	)
+	require.NoError(t, err, "Must not error when creating receiver")
+	dd.(*datadogReceiver).nextMetricsConsumer = sink
+
+	require.NoError(t, dd.Start(context.Background(), componenttest.NewNopHost()))
+	defer func() {
+		require.NoError(t, dd.Shutdown(context.Background()))
+	}()
+
+	metricsPayloadV2 := []byte(`{
+		"series": [
+			{
+				"metric": "system.load.1",
+				"type": 1,
+				"points": [
+					{
+						"timestamp": 1636629071,
+						"value":     1.5
+					},
+					{
+						"timestamp": 1636629081,
+						"value":     2.0
+					}
+				],
+				"resources": [
+					{
+						"name": "dummyhost",
+						"type": "host"
+					}
+				]
+			}
+		]
+	}`)
+
+	req, err := http.NewRequest(
+		http.MethodPost,
+		fmt.Sprintf("http://%s/api/v2/series", dd.(*datadogReceiver).address),
+		io.NopCloser(bytes.NewReader(metricsPayloadV2)),
+	)
+
+	req.Header.Set("Content-Type", "application/json")
+
+	require.NoError(t, err, "Must not error when creating request")
+
+	resp, err := http.DefaultClient.Do(req)
+	require.NoError(t, err, "Must not error performing request")
+
+	body, err := io.ReadAll(resp.Body)
+	require.NoError(t, multierr.Combine(err, resp.Body.Close()), "Must not error when reading body")
+	require.JSONEq(t, `{"errors": []}`, string(body), "Expected JSON response to be `{\"errors\": []}`, got %s", string(body))
+	require.Equal(t, http.StatusAccepted, resp.StatusCode)
+
+	mds := sink.AllMetrics()
+	require.Len(t, mds, 1)
+	got := mds[0]
+	require.Equal(t, 1, got.ResourceMetrics().Len())
+	metrics := got.ResourceMetrics().At(0).ScopeMetrics().At(0).Metrics()
+	assert.Equal(t, 1, metrics.Len())
+	metric := metrics.At(0)
+	assert.Equal(t, pmetric.MetricTypeSum, metric.Type())
+	assert.Equal(t, "system.load.1", metric.Name())
+	assert.Equal(t, pmetric.AggregationTemporalityDelta, metric.Sum().AggregationTemporality())
+	assert.False(t, metric.Sum().IsMonotonic())
+	assert.Equal(t, pcommon.Timestamp(1636629071*1_000_000_000), metric.Sum().DataPoints().At(0).Timestamp())
+	assert.Equal(t, 1.5, metric.Sum().DataPoints().At(0).DoubleValue())
+	assert.Equal(t, pcommon.Timestamp(0), metric.Sum().DataPoints().At(0).StartTimestamp())
+	assert.Equal(t, pcommon.Timestamp(1636629081*1_000_000_000), metric.Sum().DataPoints().At(1).Timestamp())
+	assert.Equal(t, 2.0, metric.Sum().DataPoints().At(1).DoubleValue())
+	assert.Equal(t, pcommon.Timestamp(1636629071*1_000_000_000), metric.Sum().DataPoints().At(1).StartTimestamp())
+}
+
 func TestDatadogSketches_EndToEnd(t *testing.T) {
 	cfg := createDefaultConfig().(*Config)
 	cfg.Endpoint = "localhost:0" // Using a randomly assigned address