Update swagger API specification (#1782)

# Summary

This PR drops the outdated former swagger.yaml/json and introduced
automatic API document generation from Go code.
The generated code is also used to generate documentation/markdown for
the community page,
as well as enable the Woodpecker server to serve a Swagger Web UI for
manual tinkering.

I did opt-in for gin-swagger, a middleware for the Gin framework, to
ease implementation and have a sophisticated output.
This middleware only produces Swagger v2 specs. AFAIK the newer OpenApi
3x tooling is not yet that mature,
so I guess that's fine for now.

## Implemenation notes

- former swagger.json files removed
- former // swagger godocs removed
- introduced new dependency gin-swagger, which uses godoc annotations on
top of Gin Handler functions.
- reworked Makefile to automatically generate Go code for the server
- introduce new dependency go-swagger, to generate Markdown for
documentation purposes
- add a Swagger Web UI, incl. capabilities for manual API exploration
- consider relative root paths in the implementation
- write documentation for all exposed API endpoints
- incl. API docs in the community website (auto-generated)
- provide developer documentation, for the Woodpecker authors
- no other existing logic/code was intentionally changed

---------

close #292

---------

Co-authored-by: qwerty287 <80460567+qwerty287@users.noreply.github.com>
Co-authored-by: 6543 <6543@obermui.de>

cmd/server/main.go

@@ -20,6 +20,7 @@ import (
 
 	_ "github.com/joho/godotenv/autoload"
 	"github.com/urfave/cli/v2"
+	_ "github.com/woodpecker-ci/woodpecker/cmd/server/docs"
 
 	"github.com/woodpecker-ci/woodpecker/version"
 )
@@ -32,6 +33,8 @@ func main() {
 	app.Action = run
 	app.Flags = flags
 
+	setupSwaggerStaticConfig()
+
 	if err := app.Run(os.Args); err != nil {
 		_, _ = fmt.Fprintln(os.Stderr, err)
 		os.Exit(1)

cmd/server/swagger.go

@@ -0,0 +1,38 @@
+// Copyright 2023 Woodpecker Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package main
+
+import (
+	"github.com/woodpecker-ci/woodpecker/cmd/server/docs"
+	"github.com/woodpecker-ci/woodpecker/version"
+)
+
+// generate docs/docs/20-usage/90-rest-api.md via:
+//go:generate go run woodpecker_docs_gen.go swagger.go
+
+// setupSwaggerStaticConfig initializes static content only (contacts, title and description)
+// for dynamic configuration of e.g. hostname, etc. see router.setupSwaggerConfigAndRoutes
+//
+//	@contact.name	Woodpecker CI Community
+//	@contact.url	https://woodpecker-ci.org/
+func setupSwaggerStaticConfig() {
+	docs.SwaggerInfo.BasePath = "/api"
+	docs.SwaggerInfo.InfoInstanceName = "api"
+	docs.SwaggerInfo.Title = "Woodpecker CI API"
+	docs.SwaggerInfo.Version = version.String()
+	docs.SwaggerInfo.Description = "Woodpecker is a simple CI engine with great extensibility.\n" +
+		"To get a personal access token (PAT) for authentication, please log in your Woodpecker server,\n" +
+		"and go to you personal profile page, by clicking the user icon at the top right."
+}

cmd/server/woodpecker_docs_gen.go

@@ -0,0 +1,134 @@
+// Copyright 2023 Woodpecker Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// ************************************************************************************************
+// This is a generator tool, to update the Markdown documentation for the woodpecker-ci.org website
+// ************************************************************************************************
+
+//go:build generate
+// +build generate
+
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"path"
+	"strings"
+	"time"
+
+	"github.com/go-swagger/go-swagger/generator"
+
+	"github.com/woodpecker-ci/woodpecker/cmd/server/docs"
+)
+
+const restApiMarkdownInto = `
+# REST API
+
+Woodpecker offers a comprehensive REST API, so you can integrate easily with from and with other tools.
+
+## API specification
+
+Starting with Woodpecker v1.0.0 a Swagger v2 API specification is served by the Woodpecker Server.
+The typical URL looks like "http://woodpecker-host/swagger/doc.json", where you can fetch the API specification.
+
+## Swagger API UI
+
+Starting with Woodpecker v1.0.0 a Swagger web user interface (UI) is served by the Woodpecker Server.
+Typically, you can open "http://woodpecker-host/swagger/index.html" in your browser, to explore the API documentation.
+
+# API endpoint summary
+
+This is a summary of available API endpoints.
+Please, keep in mind this documentation reflects latest development changes
+and might differ from your used server version.
+Its recommended to consult the Swagger API UI of your Woodpecker server,
+where you also have the chance to do manual exploration and live testing.
+
+`
+
+func main() {
+	setupSwaggerStaticConfig()
+
+	specFile := createTempFileWithSwaggerSpec()
+	defer os.Remove(specFile)
+	markdown := generateTempMarkdown(specFile)
+
+	f, err := os.Create(path.Join("..", "..", "docs", "docs", "20-usage", "90-rest-api.md"))
+	if err != nil {
+		panic(err)
+	}
+	defer f.Close()
+	_, err = f.WriteString(restApiMarkdownInto)
+	if err != nil {
+		panic(err)
+	}
+	_, err = f.WriteString(readGeneratedMarkdownAndSkipIntro(markdown))
+	if err != nil {
+		panic(err)
+	}
+}
+
+func createTempFileWithSwaggerSpec() string {
+	f, err := os.CreateTemp(os.TempDir(), "swagger.json")
+	if err != nil {
+		panic(err)
+	}
+	defer f.Close()
+	_, err = f.WriteString(docs.SwaggerInfo.ReadDoc())
+	if err != nil {
+		panic(err)
+	}
+	return f.Name()
+}
+
+func generateTempMarkdown(specFile string) string {
+	// HINT: we MUST use underscores, since the library tends to rename things
+	tempFile := fmt.Sprintf("woodpecker_api_%d.md", time.Now().UnixMilli())
+	markdownFile := path.Join(os.TempDir(), tempFile)
+
+	opts := generator.GenOpts{
+		GenOptsCommon: generator.GenOptsCommon{
+			Spec: specFile,
+		},
+	}
+	// TODO: contrib upstream a GenerateMarkdown that use io.Reader and io.Writer
+	err := generator.GenerateMarkdown(markdownFile, []string{}, []string{}, &opts)
+	if err != nil {
+		panic(err)
+	}
+
+	data, err := os.ReadFile(markdownFile)
+	if err != nil {
+		panic(err)
+	}
+	defer os.Remove(markdownFile)
+
+	return string(data)
+}
+
+func readGeneratedMarkdownAndSkipIntro(markdown string) string {
+	scanner := bufio.NewScanner(strings.NewReader(markdown))
+	sb := strings.Builder{}
+	foundActualContentStart := false
+	for scanner.Scan() {
+		text := scanner.Text()
+		foundActualContentStart = foundActualContentStart || (strings.HasPrefix(text, "##") && strings.Contains(strings.ToLower(text), "all endpoints"))
+		if foundActualContentStart {
+			sb.WriteString(text + "\n")
+		}
+	}
+	return sb.String()
+}