Add OpenAPI documentation page

.gitignore

@@ -1 +1,2 @@
-.DS_Store
+.DS_Store
+tmp

cmd/fauxrpc/cmd_run.go

@@ -4,15 +4,22 @@ import (
 	"errors"
 	"fmt"
 	"log"
-	"log/slog"
 	"net/http"
+	"os"
+	"strings"
 
 	"connectrpc.com/grpcreflect"
 	"connectrpc.com/vanguard"
+	plugin_go "github.com/golang/protobuf/protoc-gen-go/plugin"
 	"github.com/sudorandom/fauxrpc/private/protobuf"
+	"github.com/sudorandom/protoc-gen-connect-openapi/converter"
 	"golang.org/x/net/http2"
 	"golang.org/x/net/http2/h2c"
+	"google.golang.org/protobuf/proto"
+	"google.golang.org/protobuf/reflect/protodesc"
 	"google.golang.org/protobuf/reflect/protoreflect"
+	"google.golang.org/protobuf/types/pluginpb"
+	"gopkg.in/yaml.v3"
 )
 
 type RunCmd struct {
@@ -34,8 +41,9 @@ func (c *RunCmd) Run(globals *Globals) error {
 	}
 
 	// TODO: Add --no-reflection option
+	// TODO: Add --no-openapi option
 	// TODO: Load descriptors from stdin (assume protocol descriptors in binary format)
-	// TODO: way more options for data generator, including a stub service for registering stubs
+	// TODO: add a stub service for registering stubs
 
 	serviceNames := []string{}
 	vgservices := []*vanguard.Service{}
@@ -58,12 +66,112 @@ func (c *RunCmd) Run(globals *Globals) error {
 	mux.Handle("/", transcoder)
 	mux.Handle(grpcreflect.NewHandlerV1(reflector))
 	mux.Handle(grpcreflect.NewHandlerV1Alpha(reflector))
+
+	// OpenAPI Stuff
+	resp, err := convertToOpenAPISpec(registry)
+	if err != nil {
+		return err
+	}
+	mux.Handle("GET /fauxrpc.openapi.html", singleFileHandler(openapiHTML))
+	mux.Handle("GET /fauxrpc.openapi.yaml", singleFileHandler(resp.File[0].GetContent()))
+
 	server := &http.Server{
 		Addr:    c.Addr,
 		Handler: h2c.NewHandler(mux, &http2.Server{}),
 	}
 
-	slog.Info(fmt.Sprintf("Listening on http://%s", c.Addr))
-	slog.Info(fmt.Sprintf("See available methods: buf curl --http2-prior-knowledge http://%s --list-methods", c.Addr))
+	fmt.Printf("FauxRPC (%s)", fullVersion())
+	fmt.Printf("Listening on http://%s\n", c.Addr)
+	fmt.Printf("OpenAPI documentation: http://%s/fauxrpc.openapi.html\n", c.Addr)
+	fmt.Println()
+	fmt.Println("Example Commands:")
+	fmt.Printf("$ buf curl --http2-prior-knowledge http://%s --list-methods\n", c.Addr)
+	fmt.Printf("$ buf curl --http2-prior-knowledge http://%s/[METHOD_NAME]\n", c.Addr)
 	return server.ListenAndServe()
 }
+
+func convertToOpenAPISpec(registry *protobuf.ServiceRegistry) (*pluginpb.CodeGeneratorResponse, error) {
+	req := new(plugin_go.CodeGeneratorRequest)
+	files := registry.Files()
+	files.RangeFiles(func(fd protoreflect.FileDescriptor) bool {
+		if fd.Services().Len() > 0 {
+			req.FileToGenerate = append(req.FileToGenerate, string(fd.Path()))
+		}
+		req.ProtoFile = append(req.ProtoFile, protodesc.ToFileDescriptorProto(fd.ParentFile()))
+		return true
+	})
+	openapiBaseFile, err := os.CreateTemp("", "base.*.openapi.yaml")
+	if err != nil {
+		return nil, err
+	}
+	defer openapiBaseFile.Close()
+
+	descBuilder := strings.Builder{}
+	descBuilder.WriteString("This is a [FauxRPC](https://fauxrpc.com/) server that is currently hosting the following services:\n")
+	registry.ForEachService(func(sd protoreflect.ServiceDescriptor) {
+		descBuilder.WriteString("- ")
+		descBuilder.WriteString(string(sd.FullName()))
+		descBuilder.WriteByte('\n')
+	})
+	descBuilder.WriteByte('\n')
+	descBuilder.WriteString("FauxRPC is a mock server that supports gRPC, gRPC-Web, Connect and HTTP/JSON transcoding.")
+
+	base := openAPIBase{
+		OpenAPI: "3.1.0",
+		Info: openAPIBaseInfo{
+			Title:       "FauxRPC Generated Documentation",
+			Description: descBuilder.String(),
+			Version:     strings.TrimPrefix(version, "v"),
+		},
+	}
+	b, err := yaml.Marshal(base)
+	if err != nil {
+		return nil, err
+	}
+	if _, err := openapiBaseFile.Write(b); err != nil {
+		return nil, err
+	}
+
+	req.Parameter = proto.String(fmt.Sprintf("path=all.openapi.yaml,base=%s", openapiBaseFile.Name()))
+
+	return converter.Convert(req)
+}
+
+func singleFileHandler(content string) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprint(w, content)
+	}
+}
+
+const openapiHTML = `
+<!doctype html>
+<html lang="en">
+  <head>
+    <meta charset="utf-8">
+    <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
+    <title>Elements in HTML</title>
+    <!-- Embed elements Elements via Web Component -->
+    <script src="https://unpkg.com/@stoplight/elements/web-components.min.js"></script>
+    <link rel="stylesheet" href="https://unpkg.com/@stoplight/elements/styles.min.css">
+  </head>
+  <body>
+
+    <elements-api
+      apiDescriptionUrl="/fauxrpc.openapi.yaml"
+      router="hash"
+      layout="sidebar"
+    />
+
+  </body>
+</html>
+`
+
+type openAPIBaseInfo struct {
+	Description string `yaml:"description"`
+	Title       string `yaml:"title"`
+	Version     string `yaml:"version"`
+}
+type openAPIBase struct {
+	OpenAPI string          `yaml:"openapi"`
+	Info    openAPIBaseInfo `yaml:"info"`
+}

cmd/fauxrpc/main.go

@@ -77,5 +77,5 @@ func (n *staticNames) Names() []string {
 }
 
 func fullVersion() string {
-	return fmt.Sprintf("fauxrpc: %s (%s) @ %s; %s", version, commit, date, runtime.Version())
+	return fmt.Sprintf("%s (%s) @ %s; %s", version, commit, date, runtime.Version())
 }

go.mod

@@ -13,24 +13,34 @@ require (
 	github.com/alecthomas/kong v0.9.0
 	github.com/brianvoe/gofakeit/v7 v7.0.4
 	github.com/bufbuild/protocompile v0.14.0
-	github.com/bufbuild/protovalidate-go v0.6.3
+	github.com/bufbuild/protovalidate-go v0.6.4
 	github.com/bufbuild/protoyaml-go v0.1.11
 	github.com/golang/protobuf v1.5.4
 	github.com/stretchr/testify v1.9.0
-	golang.org/x/net v0.26.0
+	github.com/sudorandom/protoc-gen-connect-openapi v0.8.10
+	golang.org/x/net v0.28.0
 	google.golang.org/protobuf v1.34.2
+	gopkg.in/yaml.v3 v3.0.1
 )
 
 require (
 	github.com/antlr4-go/antlr/v4 v4.13.1 // indirect
+	github.com/bahlo/generic-list-go v0.2.0 // indirect
+	github.com/buger/jsonparser v1.1.1 // indirect
 	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/dprotaso/go-yit v0.0.0-20240618133044-5a0af90af097 // indirect
 	github.com/google/cel-go v0.21.0 // indirect
+	github.com/google/gnostic v0.7.0 // indirect
+	github.com/google/gnostic-models v0.6.9-0.20230804172637-c7be7c783f49 // indirect
+	github.com/lmittmann/tint v1.0.5 // indirect
+	github.com/mailru/easyjson v0.7.7 // indirect
+	github.com/pb33f/libopenapi v0.16.14 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
 	github.com/stoewer/go-strcase v1.3.0 // indirect
+	github.com/vmware-labs/yaml-jsonpath v0.3.2 // indirect
+	github.com/wk8/go-ordered-map/v2 v2.1.8 // indirect
 	golang.org/x/exp v0.0.0-20240808152545-0cdaa3abc0fa // indirect
-	golang.org/x/sys v0.22.0 // indirect
 	golang.org/x/text v0.17.0 // indirect
 	google.golang.org/genproto/googleapis/api v0.0.0-20240814211410-ddb44dafa142 // indirect
 	google.golang.org/genproto/googleapis/rpc v0.0.0-20240814211410-ddb44dafa142 // indirect
-	gopkg.in/yaml.v3 v3.0.1 // indirect
 )