Add the discovery flag and method, along with model package

cmd/tap-incident/cmd/app.go

@@ -28,9 +28,10 @@ var (
 	app = kingpin.New("tap-incident", "Extract data from incident.io for use with Singer").Version(versionStanza())
 
 	// Global flags
-	debug       = app.Flag("debug", "Enable debug logging").Default("false").Bool()
-	configFile  = app.Flag("config", "Configuration file").ExistingFile()
-	catalogFile = app.Flag("catalog", "If set, allows filtering which streams would be synced").ExistingFile()
+	debug         = app.Flag("debug", "Enable debug logging").Default("false").Bool()
+	configFile    = app.Flag("config", "Configuration file").ExistingFile()
+	catalogFile   = app.Flag("catalog", "If set, allows filtering which streams would be synced").ExistingFile()
+	discoveryMode = app.Flag("discover", "If set, only outputs the catalog and exits").Default("false").Bool()
 )
 
 func Run(ctx context.Context) (err error) {
@@ -79,7 +80,11 @@ func Run(ctx context.Context) (err error) {
 	// can be streamed separately.
 	ol := tap.NewOutputLogger(os.Stdout)
 
-	err = tap.Run(ctx, logger, ol, cl)
+	if *discoveryMode {
+		err = tap.Discover(ctx, logger, ol)
+	} else {
+		err = tap.Sync(ctx, logger, ol, cl)
+	}
 	if err != nil {
 		return err
 	}

go.mod

@@ -5,6 +5,7 @@ go 1.21
 require (
 	github.com/alecthomas/kingpin/v2 v2.3.2
 	github.com/deepmap/oapi-codegen v1.12.4
+	github.com/fatih/structs v1.1.0
 	github.com/ghodss/yaml v1.0.0
 	github.com/go-kit/log v0.2.0
 	github.com/go-ozzo/ozzo-validation v3.6.0+incompatible

go.sum

@@ -20,6 +20,8 @@ github.com/deepmap/oapi-codegen v1.12.4/go.mod h1:3lgHGMu6myQ2vqbbTXH2H1o4eXFTGn
 github.com/fatih/color v1.7.0/go.mod h1:Zm6kSWBoL9eyXnKyktHP6abPY2pDugNf5KwzbycvMj4=
 github.com/fatih/color v1.12.0 h1:mRhaKNwANqRgUBGKmnI5ZxEk7QXmjQeCcuYFMX2bfcc=
 github.com/fatih/color v1.12.0/go.mod h1:ELkj/draVOlAH/xkhN6mQ50Qd0MPOk5AAr3maGEBuJM=
+github.com/fatih/structs v1.1.0 h1:Q7juDM0QtcnhCpeyLGQKyg4TOIghuNXrkL32pHAUMxo=
+github.com/fatih/structs v1.1.0/go.mod h1:9NiDSp5zOcgEDl+j00MP/WkGVPOlPRLejGD8Ga6PJ7M=
 github.com/getkin/kin-openapi v0.107.0 h1:bxhL6QArW7BXQj8NjXfIJQy680NsMKd25nwhvpCXchg=
 github.com/getkin/kin-openapi v0.107.0/go.mod h1:9Dhr+FasATJZjS4iOLvB0hkaxgYdulrNYm2e9epLWOo=
 github.com/ghodss/yaml v1.0.0 h1:wQHKEahhL6wmXdzwWG11gIVCkOv05bNOh+Rxn0yngAk=

model/schema.go

@@ -0,0 +1,90 @@
+package model
+
+import (
+	"strings"
+
+	"github.com/fatih/structs"
+)
+
+// Schema is a JSON schema for a stream.
+type Schema struct {
+	// Type is the type of the schema, e.g. "object" - for some reason singer docs
+	// have this as an array and often nullable eg: `"type": ["null", "object"]`
+	Type []string `json:"type"`
+	// HasAdditionalProperties indicates whether the schema allows additional properties
+	// not defined in the schema.
+	HasAdditionalProperties bool `json:"additionalProperties"`
+	// Properties is a map of property names to their schema.
+	Properties map[string]Property `json:"properties"`
+}
+
+// Property is a property in a JSON schema.
+type Property struct {
+	// Types is a list of types that this property can be, e.g. "string" or "integer".
+	Types []string `json:"type"`
+	// CustomFormat	is a custom format for this property, e.g. "date-time".
+	CustomFormat string `json:"format,omitempty"`
+	// For nested structures a property can have its own properties.
+	Properties map[string]Property `json:"properties,omitempty"`
+	// For array structures we define the type of the items in the array
+	Items *ArrayItem `json:"items,omitempty"`
+}
+
+// ArrayItem is the type and properties of an item in an array.
+type ArrayItem struct {
+	Type       string              `json:"type"`
+	Properties map[string]Property `json:"properties,omitempty"`
+}
+
+func (s Property) IsBoolean() bool {
+	return s.hasType("boolean")
+}
+
+func (s Property) IsNumber() bool {
+	return s.hasType("number")
+}
+
+func (s Property) IsInteger() bool {
+	return s.hasType("integer")
+}
+
+func (s Property) hasType(typeName string) bool {
+	for _, t := range s.Types {
+		if strings.EqualFold(t, typeName) {
+			return true
+		}
+	}
+	return false
+}
+
+func (s Property) IsDateTime() bool {
+	return s.CustomFormat == "date-time"
+}
+
+// As a shortcut for simple leaf nodes we can just dump everything (we can also dump everything higher level probably too)
+// If we're just going to dump everything why bother with serialisers? Good question.
+// a) Initial thoughts were that we want some control on the fields we output potentially - for example
+// ignoring deprecated fields.
+// b) We also might need to be cleverer when it comes to catalog config that enables / disables optional fields
+// in the output.
+//
+// Keeping this as a single callsite so it's easy to find where we're doing this in future.
+func DumpToMap(input interface{}) map[string]any {
+	structs.DefaultTagName = "json"
+	return structs.Map(input)
+}
+
+func AsOptional(p Property) Property {
+	p.Types = append(p.Types, "null")
+	return p
+}
+
+func AsArray(p Property) Property {
+	return Property{
+		Types: []string{"array"},
+		Items: &ArrayItem{
+			Type:       "object",
+			Properties: p.Properties,
+		},
+	}
+}

tap/catalog.go

@@ -0,0 +1,43 @@
+package tap
+
+import "github.com/incident-io/singer-tap/model"
+
+// A catalog can contain several streams or "entries"
+type CatalogEntry struct {
+	// Name of the stream
+	Stream string `json:"stream"`
+
+	// Unique identifier for this stream
+	// Allows for multiple sources that have duplicate stream names
+	TapStreamID string `json:"tap_stream_id"`
+
+	// The given schema for this stream
+	Schema model.Schema `json:"schema"`
+
+	// Optional metadata for this stream
+	// Metadata *[]Metadata `json:"metadata,omitempty"`
+}
+
+// Actual catalog that we export
+// contains an array of all our streams
+type Catalog struct {
+	Streams []CatalogEntry `json:"streams"`
+}
+
+func NewCatalog(streams map[string]Stream) *Catalog {
+	entries := []CatalogEntry{}
+
+	for name, stream := range streams {
+		catalogEntry := CatalogEntry{
+			Stream:      name,
+			TapStreamID: name,
+			Schema:      *stream.Output().Schema,
+		}
+
+		entries = append(entries, catalogEntry)
+	}
+
+	return &Catalog{
+		Streams: entries,
+	}
+}

tap/output.go

@@ -4,7 +4,8 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
-	"strings"
+
+	"github.com/incident-io/singer-tap/model"
 )
 
 // OutputType is the type of Singer tap output for each message.
@@ -29,7 +30,7 @@ type Output struct {
 	// Stream is the name of the stream, e.g. "users"
 	Stream string `json:"stream,omitempty"`
 	// Schema is the schema of the stream, if Type == "SCHEMA", in JSON schema format.
-	Schema *Schema `json:"schema,omitempty"`
+	Schema *model.Schema `json:"schema,omitempty"`
 	// Record is a record from the stream, if Type == "RECORD".
 	Record map[string]any `json:"record,omitempty"`
 	// TimeExtracted is the time that this record was extracted, if Type == "RECORD".
@@ -46,50 +47,6 @@ type Output struct {
 	BookmarkProperties []string `json:"bookmark_properties,omitempty"`
 }
 
-// Schema is a JSON schema for a stream.
-type Schema struct {
-	// Type is the type of the schema, e.g. "object"
-	Type []string `json:"type"`
-	// HasAdditionalProperties indicates whether the schema allows additional properties
-	// not defined in the schema.
-	HasAdditionalProperties bool `json:"additionalProperties"`
-	// Properties is a map of property names to their schema.
-	Properties map[string]Property `json:"properties"`
-}
-
-// Property is a property in a JSON schema.
-type Property struct {
-	// Types is a list of types that this property can be, e.g. "string" or "integer".
-	Types []string `json:"type"`
-	// CustomFormat	is a custom format for this property, e.g. "date-time".
-	CustomFormat string `json:"format,omitempty"`
-}
-
-func (s Property) IsBoolean() bool {
-	return s.hasType("boolean")
-}
-
-func (s Property) IsNumber() bool {
-	return s.hasType("number")
-}
-
-func (s Property) IsInteger() bool {
-	return s.hasType("integer")
-}
-
-func (s Property) hasType(typeName string) bool {
-	for _, t := range s.Types {
-		if strings.EqualFold(t, typeName) {
-			return true
-		}
-	}
-	return false
-}
-
-func (s Property) IsDateTime() bool {
-	return s.CustomFormat == "date-time"
-}
-
 // OutputLogger is a logger that logs to STDOUT in the format expected by the downstream
 // Singer target.
 type OutputLogger struct {
@@ -113,3 +70,17 @@ func (o *OutputLogger) Log(op *Output) error {
 
 	return nil
 }
+
+func (o *OutputLogger) CataLog(catalog *Catalog) error {
+	data, err := json.Marshal(catalog)
+	if err != nil {
+		return err
+	}
+
+	_, err = fmt.Fprintln(o.w, string(data))
+	if err != nil {
+		return err
+	}
+
+	return nil
+}

tap/stream_incidents.go

@@ -5,6 +5,7 @@ import (
 
 	kitlog "github.com/go-kit/log"
 	"github.com/incident-io/singer-tap/client"
+	"github.com/incident-io/singer-tap/model"
 	"github.com/pkg/errors"
 	"github.com/samber/lo"
 )
@@ -20,9 +21,9 @@ func (s *StreamIncidents) Output() *Output {
 	return &Output{
 		Type:   OutputTypeSchema,
 		Stream: "incidents",
-		Schema: &Schema{
+		Schema: &model.Schema{
 			Type: []string{"object"},
-			Properties: map[string]Property{
+			Properties: map[string]model.Property{
 				"id": {
 					Types: []string{"string"},
 				},

tap/tap.go

@@ -8,7 +8,7 @@ import (
 	"github.com/incident-io/singer-tap/client"
 )
 
-func Run(ctx context.Context, logger kitlog.Logger, ol *OutputLogger, cl *client.ClientWithResponses) error {
+func Sync(ctx context.Context, logger kitlog.Logger, ol *OutputLogger, cl *client.ClientWithResponses) error {
 	for name, stream := range streams {
 		logger := kitlog.With(logger, "stream", name)
 
@@ -40,3 +40,13 @@ func Run(ctx context.Context, logger kitlog.Logger, ol *OutputLogger, cl *client
 
 	return nil
 }
+
+func Discover(ctx context.Context, logger kitlog.Logger, ol *OutputLogger) error {
+	catalog := NewCatalog(streams)
+
+	if err := ol.CataLog(catalog); err != nil {
+		return err
+	}
+
+	return nil
+}