Fix incorrect parsing of a single b3 header (#190)

gh-189

Author: nosan

propagation/b3/spancontext.go

@@ -120,7 +120,7 @@ func ParseSingleHeader(contextHeader string) (*model.SpanContext, error) {
 			pos = 16
 		}
 
-		low, err := strconv.ParseUint(contextHeader[pos+1:pos+16], 16, 64)
+		low, err := strconv.ParseUint(contextHeader[pos:pos+16], 16, 64)
 		if err != nil {
 			return nil, ErrInvalidTraceIDValue
 		}

propagation/b3/spancontext_test.go

@@ -21,30 +21,19 @@ import (
 )
 
 func TestParseHeaderSuccess(t *testing.T) {
-	trueVal := true
-	falseVal := false
-	ParentIDVal := model.ID(456)
-
 	testCases := []struct {
 		header          string
 		expectedContext *model.SpanContext
 		expectedErr     error
 	}{
 		{"d", &model.SpanContext{Debug: true}, nil},
-		{"1", &model.SpanContext{Sampled: &trueVal}, nil},
+		{"1", &model.SpanContext{Sampled: pointerBool(true)}, nil},
 		{"000000000000007b00000000000001c8-000000000000007b", &model.SpanContext{TraceID: model.TraceID{High: 123, Low: 456}, ID: model.ID(123)}, nil},
-		{"000000000000007b00000000000001c8-000000000000007b-0", &model.SpanContext{TraceID: model.TraceID{High: 123, Low: 456}, ID: model.ID(123), Sampled: &falseVal}, nil},
-		{
-			"000000000000007b00000000000001c8-000000000000007b-1-00000000000001c8",
-			&model.SpanContext{
-				TraceID:  model.TraceID{High: 123, Low: 456},
-				ID:       model.ID(123),
-				ParentID: &ParentIDVal,
-				Sampled:  &trueVal,
-			},
-			nil,
-		},
+		{"000000000000007b00000000000001c8-000000000000007b-0", &model.SpanContext{TraceID: model.TraceID{High: 123, Low: 456}, ID: model.ID(123), Sampled: pointerBool(false)}, nil},
+		{"000000000000007b00000000000001c8-000000000000007b-1-00000000000001c8", &model.SpanContext{TraceID: model.TraceID{High: 123, Low: 456}, ID: model.ID(123), ParentID: pointerID(model.ID(456)), Sampled: pointerBool(true)}, nil},
 		{"", nil, ErrEmptyContext},
+		{"80f198ee56343ba864fe8b2a57d3eff7-e457b5a2e4d86bd1-1-05e3ac9a4f6e3b90", &model.SpanContext{TraceID: model.TraceID{High: 9291375655657946024, Low: 7277407061855694839}, ID: model.ID(16453819474850114513), ParentID: pointerID(model.ID(424372568660523920)), Sampled: pointerBool(true)}, nil},
+		{"d4c3c787ce202dc5-77c6a763a5a72544-0-6a3211d95bed2c99", &model.SpanContext{TraceID: model.TraceID{High: 0, Low: 15331316942592028101}, ID: model.ID(8630769782324929860), ParentID: pointerID(model.ID(7652198342103739545)), Sampled: pointerBool(false)}, nil},
 	}
 
 	for _, testCase := range testCases {
@@ -95,24 +84,20 @@ func TestParseHeaderFails(t *testing.T) {
 }
 
 func TestBuildHeader(t *testing.T) {
-	trueVal := true
-	falseVal := false
-	ParentIDVal := model.ID(456)
-
 	testCases := []struct {
 		context        model.SpanContext
 		expectedHeader string
 	}{
 		{model.SpanContext{ID: model.ID(123)}, ""},
 		{model.SpanContext{Debug: true}, "d"},
-		{model.SpanContext{Sampled: &trueVal}, "1"},
+		{model.SpanContext{Sampled: pointerBool(true)}, "1"},
 		{model.SpanContext{TraceID: model.TraceID{High: 123, Low: 456}, ID: model.ID(123)}, "000000000000007b00000000000001c8-000000000000007b"},
-		{model.SpanContext{TraceID: model.TraceID{High: 123, Low: 456}, ID: model.ID(123), Sampled: &falseVal}, "000000000000007b00000000000001c8-000000000000007b-0"},
+		{model.SpanContext{TraceID: model.TraceID{High: 123, Low: 456}, ID: model.ID(123), Sampled: pointerBool(false)}, "000000000000007b00000000000001c8-000000000000007b-0"},
 		{model.SpanContext{
 			TraceID:  model.TraceID{High: 123, Low: 456},
 			ID:       model.ID(123),
-			ParentID: &ParentIDVal,
-			Sampled:  &falseVal,
+			ParentID: pointerID(model.ID(456)),
+			Sampled:  pointerBool(false),
 		}, "000000000000007b00000000000001c8-000000000000007b-0-00000000000001c8"},
 	}
 
@@ -123,3 +108,11 @@ func TestBuildHeader(t *testing.T) {
 		}
 	}
 }
+
+func pointerID(value model.ID) *model.ID {
+	return &value
+}
+
+func pointerBool(value bool) *bool {
+	return &value
+}