Move redirection logic to a separate packagev0.4.0

Also, add an optional ‘-c’ flag to pass the path to a configuration file
that can be used to specify several matching patterns and replacements.

3 files changed, 208 insertions, 0 deletions

diff --git a/pkg/redirector/redirector.go b/pkg/redirector/redirector.go
new file mode 100644
index 0000000..96becb2
--- /dev/null
+++ b/pkg/redirector/redirector.go
@@ -0,0 +1,75 @@
+package redirector
+
+import (
+	"embed"
+	"encoding/json"
+	"log"
+	"net/http"
+	"path"
+	"regexp"
+	"strings"
+	"text/template"
+
+	"go.awhk.org/core"
+)
+
+var DefaultTemplate = template.Must(template.ParseFS(fs, "*.tpl"))
+
+var (
+	filter = core.FilterHTTPMethod(http.MethodGet)
+
+	//go:embed *.tpl
+	fs embed.FS
+)
+
+type Redirector struct {
+	Template     *template.Template
+	Transformers []Transformer
+}
+
+func (h *Redirector) ServeHTTP(w http.ResponseWriter, req *http.Request) {
+	if filter(w, req) {
+		return
+	}
+
+	pkg := path.Join(req.Host, req.URL.Path)
+	for _, t := range h.Transformers {
+		if !t.Pattern.MatchString(pkg) {
+			continue
+		}
+
+		if req.URL.Query().Get("go-get") != "1" {
+			w.Header().Set("Location", "https://pkg.go.dev/"+pkg)
+			w.WriteHeader(http.StatusFound)
+			return
+		}
+
+		repo := t.Pattern.ReplaceAllString(pkg, t.Replacement)
+		w.Header().Set("Content-Type", "text/html; charset=utf-8")
+		w.WriteHeader(http.StatusOK)
+		if err := h.Template.Execute(w, TemplateData{pkg, repo, t.VCS}); err != nil {
+			log.Println("Failed to execute template:", err)
+		}
+		return
+	}
+	w.WriteHeader(http.StatusNotFound)
+}
+
+type Pattern struct{ *regexp.Regexp }
+
+func (pp *Pattern) UnmarshalJSON(data []byte) (err error) {
+	var s string
+	if err = json.Unmarshal(data, &s); err != nil {
+		return
+	}
+	pp.Regexp, err = regexp.Compile(strings.ReplaceAll(s, `\\`, `\`))
+	return
+}
+
+type TemplateData struct{ Package, Repository, VCS string }
+
+type Transformer struct {
+	Pattern     *Pattern `json:"pattern"`
+	Replacement string   `json:"replacement"`
+	VCS         string   `json:"vcs"`
+}
diff --git a/pkg/redirector/redirector_test.go b/pkg/redirector/redirector_test.go
new file mode 100644
index 0000000..8761185
--- /dev/null
+++ b/pkg/redirector/redirector_test.go
@@ -0,0 +1,130 @@
+package redirector_test
+
+import (
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"regexp"
+	"testing"
+
+	"go.awhk.org/core"
+	"go.awhk.org/go-import-redirect/pkg/redirector"
+)
+
+func TestRedirector_ServeHTTP(s *testing.T) {
+	t := core.T{T: s}
+
+	meta := regexp.MustCompile(`<meta name="go-import" content="(.+?)">`)
+	redir := &redirector.Redirector{
+		Template: redirector.DefaultTemplate,
+		Transformers: []redirector.Transformer{
+			{
+				Pattern:     &redirector.Pattern{regexp.MustCompile("go.example.com/x/baz(?:/.+)?")},
+				Replacement: "https://git.example.net/elsewhere/baz",
+				VCS:         "git",
+			},
+			{
+				Pattern:     &redirector.Pattern{regexp.MustCompile("go.example.com/x/([^/]+)(?:/.+)?")},
+				Replacement: "https://git.example.net/y/$1",
+				VCS:         "git",
+			},
+			{
+				Pattern:     &redirector.Pattern{regexp.MustCompile("go.example.com/x/qux(?:/.+)?")},
+				Replacement: "https://git.example.net/elsewhere/qux",
+				VCS:         "git",
+			},
+		},
+	}
+
+	for _, tc := range []struct {
+		name   string
+		method string
+		url    string
+
+		expGetStatusCode   int
+		expGetGoImport     string
+		expVisitStatusCode int
+		expVisitLocation   string
+	}{
+		{
+			name:   "Match",
+			method: http.MethodGet,
+			url:    "https://go.example.com/x/foo",
+
+			expGetStatusCode:   http.StatusOK,
+			expGetGoImport:     "go.example.com/x/foo git https://git.example.net/y/foo",
+			expVisitStatusCode: http.StatusFound,
+			expVisitLocation:   "https://pkg.go.dev/go.example.com/x/foo",
+		},
+		{
+			name:   "MatchDirectory",
+			method: http.MethodGet,
+			url:    "https://go.example.com/x/foo/bar",
+
+			expGetStatusCode:   http.StatusOK,
+			expGetGoImport:     "go.example.com/x/foo/bar git https://git.example.net/y/foo",
+			expVisitStatusCode: http.StatusFound,
+			expVisitLocation:   "https://pkg.go.dev/go.example.com/x/foo/bar",
+		},
+		{
+			name:   "MatchIgnored",
+			method: http.MethodGet,
+			url:    "https://go.example.com/x/qux",
+
+			expGetStatusCode:   http.StatusOK,
+			expGetGoImport:     "go.example.com/x/qux git https://git.example.net/y/qux",
+			expVisitStatusCode: http.StatusFound,
+			expVisitLocation:   "https://pkg.go.dev/go.example.com/x/qux",
+		},
+		{
+			name:   "MatchSpecific",
+			method: http.MethodGet,
+			url:    "https://go.example.com/x/baz",
+
+			expGetStatusCode:   http.StatusOK,
+			expGetGoImport:     "go.example.com/x/baz git https://git.example.net/elsewhere/baz",
+			expVisitStatusCode: http.StatusFound,
+			expVisitLocation:   "https://pkg.go.dev/go.example.com/x/baz",
+		},
+		{
+			name:   "BadMethod",
+			method: http.MethodPost,
+			url:    "https://go.example.com/x/baz",
+
+			expGetStatusCode:   http.StatusMethodNotAllowed,
+			expVisitStatusCode: http.StatusMethodNotAllowed,
+		},
+	} {
+		t.Run("Get"+tc.name, func(t *core.T) {
+			var (
+				req = httptest.NewRequest(tc.method, tc.url+"?go-get=1", nil)
+				w   = httptest.NewRecorder()
+			)
+			redir.ServeHTTP(w, req)
+
+			resp := w.Result()
+			t.AssertEqual(tc.expGetStatusCode, resp.StatusCode)
+			t.AssertEqual("", resp.Header.Get("Location"))
+
+			match := meta.FindSubmatch(core.Must(io.ReadAll(resp.Body)))
+			if tc.expGetGoImport == "" {
+				t.AssertEqual(0, len(match))
+				return
+			}
+			if t.AssertEqual(2, len(match)) {
+				t.AssertEqual(tc.expGetGoImport, string(match[1]))
+			}
+		})
+		t.Run("Visit"+tc.name, func(t *core.T) {
+			var (
+				req = httptest.NewRequest(tc.method, tc.url, nil)
+				w   = httptest.NewRecorder()
+			)
+			redir.ServeHTTP(w, req)
+
+			resp := w.Result()
+			t.AssertEqual(tc.expVisitStatusCode, resp.StatusCode)
+			t.AssertEqual(tc.expVisitLocation, resp.Header.Get("Location"))
+		})
+	}
+}
diff --git a/pkg/redirector/template.tpl b/pkg/redirector/template.tpl
new file mode 100644
index 0000000..422024a
--- /dev/null
+++ b/pkg/redirector/template.tpl
@@ -0,0 +1,3 @@
+<!doctype html>
+<meta name="go-import" content="{{.Package}} {{.VCS}} {{.Repository}}">
+<title>go-import-redirect</title>