Add Flatbuffer Schema Support

internal/generateFlatbuffer.test.ts

@@ -0,0 +1,129 @@
+import { generateFlatbuffer } from "./generateFlatbuffer";
+import { exampleEnum, exampleMessage } from "./testFixtures";
+
+describe("generateFlatBuffer", () => {
+  it("generates Message .fbs files", () => {
+    expect(generateFlatbuffer(exampleMessage)).toMatchInlineSnapshot(`
+    "// Generated by https://github.com/foxglove/schemas
+
+    include "ByteVectorForNesting.fbs";
+    include "Duration.fbs";
+    include "ExampleEnum.fbs";
+    include "NestedMessage.fbs";
+    include "Time.fbs";
+
+    namespace foxglove;
+
+    /// An example type
+    table ExampleMessage {
+      /// duration field
+      field_duration:Duration;
+
+      /// time field
+      field_time:Time;
+
+      /// boolean field
+      field_boolean:bool;
+
+      /// bytes field
+      field_bytes:[byte];
+
+      /// float64 field
+      field_float64:double;
+
+      /// uint32 field
+      field_uint32:uint;
+
+      /// string field
+      field_string:string;
+
+      /// duration array field
+      field_duration_array:[Duration];
+
+      /// time array field
+      field_time_array:[Time];
+
+      /// boolean array field
+      field_boolean_array:[bool];
+
+      /// bytes array field
+      field_bytes_array:[ByteVectorForNesting];
+
+      /// float64 array field
+      field_float64_array:[double];
+
+      /// uint32 array field
+      field_uint32_array:[uint];
+
+      /// string array field
+      field_string_array:[string];
+
+      /// duration fixed-length array field
+      /// length 3
+      field_duration_fixed_array:[Duration];
+
+      /// time fixed-length array field
+      /// length 3
+      field_time_fixed_array:[Time];
+
+      /// boolean fixed-length array field
+      /// length 3
+      field_boolean_fixed_array:[bool];
+
+      /// bytes fixed-length array field
+      /// length 3
+      field_bytes_fixed_array:[ByteVectorForNesting];
+
+      /// float64 fixed-length array field
+      /// length 3
+      field_float64_fixed_array:[double];
+
+      /// uint32 fixed-length array field
+      /// length 3
+      field_uint32_fixed_array:[uint];
+
+      /// string fixed-length array field
+      /// length 3
+      field_string_fixed_array:[string];
+
+      /// An enum field
+      field_enum:ExampleEnum;
+
+      /// An enum array field
+      field_enum_array:[ExampleEnum];
+
+      /// A nested field
+      field_nested:foxglove.NestedMessage;
+
+      /// A nested array field
+      /// With
+      /// a
+      /// very
+      /// long
+      /// description
+      field_nested_array:[foxglove.NestedMessage];
+    }
+
+    root_type ExampleMessage;
+    "
+    `);
+  });
+  it("generates Enum .fbs files", () => {
+    expect(generateFlatbuffer(exampleEnum)).toMatchInlineSnapshot(`
+    "// Generated by https://github.com/foxglove/schemas
+
+    namespace foxglove;
+
+    /// An example enum
+    enum ExampleEnum : byte {
+      /// Value A
+      A = 1,
+
+      /// Value B
+      B = 2,
+    }
+
+    "
+    `);
+  });
+});

internal/generateFlatbuffer.ts

@@ -0,0 +1,137 @@
+import { FoxgloveMessageField, FoxglovePrimitive, FoxgloveSchema } from "./types";
+
+// Flatbuffer only supports nested vectors via table
+export const BYTE_VECTOR_FB = `table ByteVectorForNesting {
+  data:[byte];
+}
+
+root_type ByteVectorForNesting;
+`;
+
+// Same as protobuf wellknown types
+export const TIME_FB = `struct Time {
+  sec:long;
+  nsec:int;
+}
+`;
+
+export const DURATION_FB = `struct Duration {
+  sec:long;
+  nsec:int;
+}
+`;
+
+// fields that would benefit from having a default of 1
+const defaultOneNumberFields = new Set(["x", "y", "z", "r", "g", "b", "a", "w"]);
+function isDefaultOneField(field: FoxgloveMessageField): boolean {
+  return (
+    field.type.type === "primitive" &&
+    field.type.name === "float64" &&
+    defaultOneNumberFields.has(field.name)
+  );
+}
+
+function primitiveToFlatbuffer(type: Exclude<FoxglovePrimitive, "time" | "duration">) {
+  switch (type) {
+    case "uint32":
+      return "uint";
+    case "bytes":
+      return "[byte]";
+    case "string":
+      return "string";
+    case "boolean":
+      return "bool";
+    case "float64":
+      return "double";
+  }
+}
+
+export function generateFlatbuffer(schema: FoxgloveSchema): string {
+  let definition;
+  const imports = new Set<string>();
+  switch (schema.type) {
+    case "enum": {
+      const fields = schema.values.map(({ name, value, description }) => {
+        if (description != undefined) {
+          return `/// ${description}\n  ${name} = ${value},`;
+        } else {
+          return `${name} = ${value},`;
+        }
+      });
+
+      // `///` comments required to show up in compiled flatbuffer schemas
+      definition = `/// ${schema.description}\nenum ${schema.name} : byte {\n  ${fields.join(
+        "\n\n  ",
+      )}\n}\n`;
+      break;
+    }
+    case "message": {
+      const fields = schema.fields.map((field) => {
+        const isArray = field.array != undefined;
+
+        let type;
+        switch (field.type.type) {
+          case "enum":
+            type = field.type.enum.name;
+            imports.add(field.type.enum.name);
+            break;
+          case "nested":
+            type = `foxglove.${field.type.schema.name}`;
+            imports.add(field.type.schema.name);
+            break;
+          case "primitive":
+            if (field.type.name === "time") {
+              type = "Time";
+              imports.add(`Time`);
+            } else if (field.type.name === "duration") {
+              type = "Duration";
+              imports.add(`Duration`);
+            } else if (field.type.name === "bytes" && isArray) {
+              type = "ByteVectorForNesting";
+              imports.add("ByteVectorForNesting");
+            } else {
+              type = primitiveToFlatbuffer(field.type.name);
+            }
+            break;
+        }
+        let lengthComment;
+
+        if (typeof field.array === "number") {
+          // can't specify length of vector outside of struct, all of these are tables
+          lengthComment = `  /// length ${field.array}\n`;
+        }
+        return `${field.description
+          .trim()
+          .split("\n")
+          .map((line) => `  /// ${line}\n`)
+          .join("")}${
+          // can't have inline comments, so the lengthComment needs to be above
+          lengthComment ?? ""
+          // convert field.name to lowercase for flatbuffer compilation compliance
+        }  ${field.name.toLowerCase()}:${isArray ? `[${type}]` : type}${
+          isDefaultOneField(field) ? ` = 1.0` : ""
+        };`;
+      });
+
+      definition = `/// ${schema.description}\ntable ${schema.name} {\n${fields.join(
+        "\n\n",
+      )}\n}\n\nroot_type ${schema.name};`;
+      break;
+    }
+  }
+
+  const outputSections = [
+    `// Generated by https://github.com/foxglove/schemas`,
+
+    Array.from(imports)
+      .sort()
+      .map((name) => `include "${name}.fbs";`)
+      .join("\n"),
+
+    `namespace foxglove;`,
+
+    definition,
+  ].filter(Boolean);
+
+  return outputSections.join("\n\n") + "\n";
+}