Tweaks to enable reuse of CreateMetadata for rasters

main.go

@@ -249,7 +249,7 @@ func main() {
 	tileJSON.MinZoom = zooms[0]
 	tileJSON.MaxZoom = zooms[len(zooms)-1]
 
-	tiles := listTiles(zooms, tileJSON)
+	tiles := ListTiles(zooms, tileJSON)
 	if args.TilesFile != "" {
 		extraTiles, err := tilesFromFile(args.TilesFile)
 		if err != nil {
@@ -271,7 +271,7 @@ func main() {
 		numWorkers = tileLen
 	}
 	// round robin the tiles so workers are hitting similar geospatial entries and zoom at the same time
-	rrTiles := roundRobinTiles(tiles, numWorkers)
+	rrTiles := RoundRobinTiles(tiles, numWorkers)
 	for i := 0; i < numWorkers; i++ {
 		wg.Add(1)
 		workerTiles := rrTiles[i]

mbtiles.go

@@ -11,17 +11,32 @@ import (
 
 type MbTilesMetadata map[string]string
 
+type MbTilesFormat string
+
+const (
+	Pbf  MbTilesFormat = "pbf"
+	Jpg  MbTilesFormat = "jpg"
+	Png  MbTilesFormat = "png"
+	WebP MbTilesFormat = "webp"
+)
+
 type CreateMetadataOptions struct {
 	Filename string
 	Version  string
+	Format   MbTilesFormat
 }
 
 // CreateMetadata generates the (name,value) metadata pairs for .mbtiles files.
 // Since name is required, it falls back to the filename if not provided.
+// format is also required, so it falls back to pbf if not provided.
 func CreateMetadata(tj *TileJSON, opts CreateMetadataOptions) MbTilesMetadata {
+	format := opts.Format
+	if string(format) == "" {
+		format = Pbf
+	}
 	meta := MbTilesMetadata{
 		"name":   tj.Name,
-		"format": "pbf",
+		"format": string(format),
 		"type":   "baselayer",
 	}
 	if tj.Name == "" && opts.Filename != "" {
@@ -59,10 +74,15 @@ func CreateMetadata(tj *TileJSON, opts CreateMetadataOptions) MbTilesMetadata {
 		}
 		meta["center"] = center
 	}
-	metaJSONField := CreateMetadataJSON(tj)
-	if metaJSONBytes, err := json.Marshal(metaJSONField); err == nil {
-		meta["json"] = string(metaJSONBytes)
+
+	// mbtiles spec requires the json field for vector format and it's not meaningful for rasters
+	if opts.Format == Pbf {
+		metaJSONField := CreateMetadataJSON(tj)
+		if metaJSONBytes, err := json.Marshal(metaJSONField); err == nil {
+			meta["json"] = string(metaJSONBytes)
+		}
 	}
+
 	return meta
 }
 

writers.go

@@ -173,6 +173,7 @@ func NewWriters(args Args, tj *TileJSON) (writer TileWriter, bulkWriter TileBulk
 		meta := CreateMetadata(tj, CreateMetadataOptions{
 			Filename: args.TileJSON,
 			Version:  args.Version,
+			Format: Pbf,
 		})
 		err = mbWriter.BulkWriteMetadata(meta)
 		return