chore(manifest): add manifest validation boilerplate (aws#2815)

<!-- Provide summary of changes -->
Part of aws#2818. This PR adds boilerplate for new manifest validation for LB svc. Also added validation for mutually exclusive fields. Will add for the other workload types, advanced type validation, and consolidate existing validations in following PRs
<!-- Issue number, if available. E.g. "Fixes aws#31", "Addresses aws#42, 77" -->

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the Apache 2.0 License..

internal/pkg/manifest/errors.go

@@ -5,6 +5,8 @@ package manifest
 
 import (
 	"fmt"
+
+	"github.com/dustin/go-humanize/english"
 )
 
 // ErrInvalidWorkloadType occurs when a user requested a manifest template type that doesn't exist.
@@ -50,3 +52,39 @@ func (e *ErrUnknownProvider) Is(target error) bool {
 	_, ok := target.(*ErrUnknownProvider)
 	return ok
 }
+
+type errFieldMustBeSpecified struct {
+	missingField      string
+	conditionalFields []string
+}
+
+func (e *errFieldMustBeSpecified) Error() string {
+	errMsg := fmt.Sprintf(`"%s" must be specified`, e.missingField)
+	if len(e.conditionalFields) == 0 {
+		return errMsg
+	}
+	return fmt.Sprintf(`%s if "%s" %s specified`, errMsg, english.WordSeries(e.conditionalFields, "or"),
+		english.PluralWord(len(e.conditionalFields), "is", "are"))
+}
+
+type errFieldMutualExclusive struct {
+	firstField  string
+	secondField string
+	mustExist   bool
+}
+
+func (e *errFieldMutualExclusive) Error() string {
+	if e.mustExist {
+		return fmt.Sprintf(`must specify one of "%s" and "%s"`, e.firstField, e.secondField)
+	}
+	return fmt.Sprintf(`must specify one, not both, of "%s" and "%s"`, e.firstField, e.secondField)
+}
+
+type errMinGreaterThanMax struct {
+	min int
+	max int
+}
+
+func (e *errMinGreaterThanMax) Error() string {
+	return fmt.Sprintf("min value %d cannot be greater than max value %d", e.min, e.max)
+}

internal/pkg/manifest/storage.go

@@ -11,8 +11,7 @@ import (
 )
 
 var (
-	errUnmarshalEFSOpts        = errors.New(`cannot unmarshal efs field into bool or map`)
-	errInvalidEFSConfiguration = errors.New(`must specify one, not both, of "uid/gid" and "id/root_dir/auth"`)
+	errUnmarshalEFSOpts = errors.New(`cannot unmarshal "efs" field into bool or map`)
 )
 
 // Storage represents the options for external and native storage.
@@ -154,7 +153,10 @@ func (e *EFSVolumeConfiguration) unsetUIDConfig() {
 
 func (e *EFSVolumeConfiguration) isValid() error {
 	if !e.EmptyBYOConfig() && !e.EmptyUIDConfig() {
-		return errInvalidEFSConfiguration
+		return &errFieldMutualExclusive{
+			firstField:  "uid/gid",
+			secondField: "id/root_dir/auth",
+		}
 	}
 	return nil
 }

internal/pkg/manifest/svc.go

@@ -33,7 +33,7 @@ var ServiceTypes = []string{
 	WorkerServiceType,
 }
 
-// Range contains either a Range or a range configuration for Autoscaling ranges
+// Range contains either a Range or a range configuration for Autoscaling ranges.
 type Range struct {
 	Value       *IntRangeBand // Mutually exclusive with RangeConfig
 	RangeConfig RangeConfig
@@ -44,17 +44,12 @@ func (r *Range) IsEmpty() bool {
 	return r.Value == nil && r.RangeConfig.IsEmpty()
 }
 
-// Parse extracts the min and max from RangeOpts
+// Parse extracts the min and max from RangeOpts.
 func (r *Range) Parse() (min int, max int, err error) {
-	if r.Value != nil && !r.RangeConfig.IsEmpty() {
-		return 0, 0, errInvalidRangeOpts
-	}
-
 	if r.Value != nil {
 		return r.Value.Parse()
 	}
-
-	return *r.RangeConfig.Min, *r.RangeConfig.Max, nil
+	return aws.IntValue(r.RangeConfig.Min), aws.IntValue(r.RangeConfig.Max), nil
 }
 
 // UnmarshalYAML overrides the default YAML unmarshaling logic for the RangeOpts
@@ -206,12 +201,18 @@ func (a *AdvancedCount) hasAutoscaling() bool {
 func (a *AdvancedCount) IsValid() error {
 	// Spot translates to desiredCount; cannot specify with autoscaling
 	if a.Spot != nil && a.hasAutoscaling() {
-		return errInvalidAdvancedCount
+		return &errFieldMutualExclusive{
+			firstField:  "spot",
+			secondField: "range/cpu_percentage/memory_percentage/requests/response_time",
+		}
 	}
 
 	// Range must be specified if using autoscaling
 	if a.Range.IsEmpty() && (a.CPU != nil || a.Memory != nil || a.Requests != nil || a.ResponseTime != nil) {
-		return errInvalidAutoscaling
+		return &errFieldMustBeSpecified{
+			missingField:      "range",
+			conditionalFields: []string{"cpu_percentage", "memory_percentage", "requests", "response_time"},
+		}
 	}
 
 	return nil

internal/pkg/manifest/svc_test.go

@@ -474,13 +474,19 @@ func TestCount_UnmarshalYAML(t *testing.T) {
   range: 1-10
   spot: 3
 `),
-			wantedError: errInvalidAdvancedCount,
+			wantedError: &errFieldMutualExclusive{
+				firstField:  "spot",
+				secondField: "range/cpu_percentage/memory_percentage/requests/response_time",
+			},
 		},
 		"Error if autoscaling specified without range": {
 			inContent: []byte(`count:
   cpu_percentage: 30
 `),
-			wantedError: errInvalidAutoscaling,
+			wantedError: &errFieldMustBeSpecified{
+				missingField:      "range",
+				conditionalFields: []string{"cpu_percentage", "memory_percentage", "requests", "response_time"},
+			},
 		},
 		"Error if unmarshalable": {
 			inContent: []byte(`count: badNumber
@@ -562,20 +568,16 @@ func TestRange_Parse(t *testing.T) {
 
 		wantedMin int
 		wantedMax int
-		wantedErr error
 	}{
-		"error when both range and RangeConfig specified": {
+		"success with range value": {
 			input: Range{
 				Value: &mockRange,
-				RangeConfig: RangeConfig{
-					Min: aws.Int(1),
-					Max: aws.Int(3),
-				},
 			},
 
-			wantedErr: errInvalidRangeOpts,
+			wantedMin: 1,
+			wantedMax: 10,
 		},
-		"success": {
+		"success with range config": {
 			input: Range{
 				RangeConfig: RangeConfig{
 					Min: aws.Int(2),
@@ -591,13 +593,9 @@ func TestRange_Parse(t *testing.T) {
 		t.Run(name, func(t *testing.T) {
 			gotMin, gotMax, err := tc.input.Parse()
 
-			if tc.wantedErr != nil {
-				require.EqualError(t, err, tc.wantedErr.Error())
-			} else {
-				require.NoError(t, err)
-				require.Equal(t, tc.wantedMin, gotMin)
-				require.Equal(t, tc.wantedMax, gotMax)
-			}
+			require.NoError(t, err)
+			require.Equal(t, tc.wantedMin, gotMin)
+			require.Equal(t, tc.wantedMax, gotMax)
 		})
 	}
 }
@@ -814,7 +812,10 @@ func TestAdvancedCount_IsValid(t *testing.T) {
 				Requests: aws.Int(1000),
 			},
 
-			expectedErr: errInvalidAdvancedCount,
+			expectedErr: &errFieldMutualExclusive{
+				firstField:  "spot",
+				secondField: "range/cpu_percentage/memory_percentage/requests/response_time",
+			},
 		},
 		"invalid with spot count and range": {
 			input: &AdvancedCount{
@@ -824,7 +825,10 @@ func TestAdvancedCount_IsValid(t *testing.T) {
 				},
 			},
 
-			expectedErr: errInvalidAdvancedCount,
+			expectedErr: &errFieldMutualExclusive{
+				firstField:  "spot",
+				secondField: "range/cpu_percentage/memory_percentage/requests/response_time",
+			},
 		},
 		"invalid with spot count and range config": {
 			input: &AdvancedCount{
@@ -838,7 +842,10 @@ func TestAdvancedCount_IsValid(t *testing.T) {
 				},
 			},
 
-			expectedErr: errInvalidAdvancedCount,
+			expectedErr: &errFieldMutualExclusive{
+				firstField:  "spot",
+				secondField: "range/cpu_percentage/memory_percentage/requests/response_time",
+			},
 		},
 		"invalid with autoscaling fields and no range": {
 			input: &AdvancedCount{
@@ -847,7 +854,10 @@ func TestAdvancedCount_IsValid(t *testing.T) {
 				Requests: aws.Int(1000),
 			},
 
-			expectedErr: errInvalidAutoscaling,
+			expectedErr: &errFieldMustBeSpecified{
+				missingField:      "range",
+				conditionalFields: []string{"cpu_percentage", "memory_percentage", "requests", "response_time"},
+			},
 		},
 	}
 	for name, tc := range testCases {