Fix regression when parsing numbers in Push request (#10550)

**What this PR does / why we need it**:
Even though the[ Loki HTTP API docs for the push endpoint][1] state that
the stream label values should be strings, we previously didn't enforce
this requirement. With #9694, we
started enforcing this requirement, and that broke some users.

In this PR we are reverting this type of assertion and adding a bunch of
tests to avoid the regression in the future.

[1]:
https://grafana.com/docs/loki/latest/reference/api/#push-log-entries-to-loki

(cherry picked from commit 5ab9515)

pkg/loghttp/query.go

@@ -69,15 +69,8 @@ func (s *LogProtoStream) UnmarshalJSON(data []byte) error {
 	err := jsonparser.ObjectEach(data, func(key, val []byte, ty jsonparser.ValueType, _ int) error {
 		switch string(key) {
 		case "stream":
-			labels := make(LabelSet)
-			err := jsonparser.ObjectEach(val, func(key, val []byte, dataType jsonparser.ValueType, _ int) error {
-				if dataType != jsonparser.String {
-					return jsonparser.MalformedStringError
-				}
-				labels[string(key)] = string(val)
-				return nil
-			})
-			if err != nil {
+			var labels LabelSet
+			if err := labels.UnmarshalJSON(val); err != nil {
 				return err
 			}
 			s.Labels = labels.String()

pkg/util/unmarshal/unmarshal_test.go

@@ -7,6 +7,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/prometheus/prometheus/model/labels"
 	"github.com/stretchr/testify/require"
 
 	"github.com/grafana/loki/pkg/loghttp"
@@ -15,24 +16,28 @@ import (
 	"github.com/grafana/loki/pkg/util/marshal"
 )
 
-// covers requests to /loki/api/v1/push
-var pushTests = []struct {
-	expected []logproto.Stream
-	actual   string
-}{
-	{
-		[]logproto.Stream{
-			{
-				Entries: []logproto.Entry{
-					{
-						Timestamp: time.Unix(0, 123456789012345),
-						Line:      "super line",
+func Test_DecodePushRequest(t *testing.T) {
+	// covers requests to /loki/api/v1/push
+	for _, tc := range []struct {
+		name        string
+		expected    []logproto.Stream
+		expectedErr bool
+		actual      string
+	}{
+		{
+			name: "basic",
+			expected: []logproto.Stream{
+				{
+					Entries: []logproto.Entry{
+						{
+							Timestamp: time.Unix(0, 123456789012345),
+							Line:      "super line",
+						},
 					},
+					Labels: labels.FromStrings("test", "test").String(),
 				},
-				Labels: `{test="test"}`,
 			},
-		},
-		`{
+			actual: `{
 			"streams": [
 				{
 					"stream": {
@@ -44,24 +49,25 @@ var pushTests = []struct {
 				}
 			]
 		}`,
-	},
-	{
-		[]logproto.Stream{
-			{
-				Entries: []logproto.Entry{
-					{
-						Timestamp: time.Unix(0, 123456789012345),
-						Line:      "super line",
-						StructuredMetadata: []logproto.LabelAdapter{
-							{Name: "a", Value: "1"},
-							{Name: "b", Value: "2"},
+		},
+		{
+			name: "with structured metadata",
+			expected: []logproto.Stream{
+				{
+					Entries: []logproto.Entry{
+						{
+							Timestamp: time.Unix(0, 123456789012345),
+							Line:      "super line",
+							StructuredMetadata: []logproto.LabelAdapter{
+								{Name: "a", Value: "1"},
+								{Name: "b", Value: "2"},
+							},
 						},
 					},
+					Labels: labels.FromStrings("test", "test").String(),
 				},
-				Labels: `{test="test"}`,
 			},
-		},
-		`{
+			actual: `{
 			"streams": [
 				{
 					"stream": {
@@ -73,18 +79,100 @@ var pushTests = []struct {
 				}
 			]
 		}`,
-	},
-}
+		},
 
-func Test_DecodePushRequest(t *testing.T) {
-	for i, pushTest := range pushTests {
-		var actual logproto.PushRequest
-		closer := io.NopCloser(strings.NewReader(pushTest.actual))
+		// The following test cases are added to cover a regression. Even though the Loki HTTP API
+		// docs for the push endpoint state that the stream label values should be strings, we
+		// previously didn't enforce this requirement.
+		// With https://github.com/grafana/loki/pull/9694, we started enforcing this requirement
+		// and that broke some users. We are adding these test cases to ensure that we don't
+		// enforce this requirement in the future. Note that we may want to enforce this requirement
+		// in a future major release, in which case we should modify these test cases.
+		{
+			name: "number in stream label value",
+			expected: []logproto.Stream{
+				{
+					Entries: []logproto.Entry{
+						{
+							Timestamp: time.Unix(0, 123456789012345),
+							Line:      "super line",
+						},
+					},
+					Labels: labels.FromStrings("test", "test", "number", "123").String(),
+				},
+			},
+			actual: `{
+			"streams": [
+				{
+					"stream": {
+						"test": "test",
+						"number": 123
+					},
+					"values":[
+						[ "123456789012345", "super line" ]
+					]
+				}
+			]
+		}`,
+		},
+		{
+			name:        "string without quotes in stream label value",
+			expectedErr: true,
+			actual: `{
+			"streams": [
+				{
+					"stream": {
+						"test": "test",
+						"text": None
+					},
+					"values":[
+						[ "123456789012345", "super line" ]
+					]
+				}
+			]
+		}`,
+		},
+		{
+			name: "json object in stream label value",
+			expected: []logproto.Stream{
+				{
+					Entries: []logproto.Entry{
+						{
+							Timestamp: time.Unix(0, 123456789012345),
+							Line:      "super line",
+						},
+					},
+					Labels: labels.FromStrings("test", "test", "text", "{ \"a\": \"b\" }").String(),
+				},
+			},
+			actual: `{
+			"streams": [
+				{
+					"stream": {
+						"test": "test",
+						"text": { "a": "b" }
+					},
+					"values":[
+						[ "123456789012345", "super line" ]
+					]
+				}
+			]
+		}`,
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			var actual logproto.PushRequest
+			closer := io.NopCloser(strings.NewReader(tc.actual))
 
-		err := DecodePushRequest(closer, &actual)
-		require.NoError(t, err)
+			err := DecodePushRequest(closer, &actual)
+			if tc.expectedErr {
+				require.Error(t, err)
+				return
+			}
+			require.NoError(t, err)
 
-		require.Equalf(t, pushTest.expected, actual.Streams, "Push Test %d failed", i)
+			require.Equal(t, tc.expected, actual.Streams)
+		})
 	}
 }