1 files changed, 154 insertions, 0 deletions
diff --git a/misc/url.go b/misc/url.go
new file mode 100644
index 0000000..b77d8ce
--- /dev/null
+++ b/misc/url.go
@@ -0,0 +1,154 @@
+// SPDX-License-Identifier: AGPL-3.0-only
+// SPDX-FileCopyrightText: Copyright (c) 2025 Runxi Yu <https://runxiyu.org>
+
+package misc
+
+import (
+	"errors"
+	"net/http"
+	"net/url"
+	"strings"
+)
+
+var (
+	ErrDupRefSpec = errors.New("duplicate ref spec")
+	ErrNoRefSpec  = errors.New("no ref spec")
+)
+
+// getParamRefTypeName looks at the query parameters in an HTTP request and
+// returns its ref name and type, if any.
+func GetParamRefTypeName(request *http.Request) (retRefType, retRefName string, err error) {
+	rawQuery := request.URL.RawQuery
+	queryValues, err := url.ParseQuery(rawQuery)
+	if err != nil {
+		return
+	}
+	done := false
+	for _, refType := range []string{"commit", "branch", "tag"} {
+		refName, ok := queryValues[refType]
+		if ok {
+			if done {
+				err = ErrDupRefSpec
+				return
+			}
+			done = true
+			if len(refName) != 1 {
+				err = ErrDupRefSpec
+				return
+			}
+			retRefName = refName[0]
+			retRefType = refType
+		}
+	}
+	if !done {
+		err = ErrNoRefSpec
+	}
+	return
+}
+
+// ParseReqURI parses an HTTP request URL, and returns a slice of path segments
+// and the query parameters. It handles %2F correctly.
+func ParseReqURI(requestURI string) (segments []string, params url.Values, err error) {
+	path, paramsStr, _ := strings.Cut(requestURI, "?")
+
+	segments, err = PathToSegments(path)
+	if err != nil {
+		return
+	}
+
+	params, err = url.ParseQuery(paramsStr)
+	return
+}
+
+func PathToSegments(path string) (segments []string, err error) {
+	segments = strings.Split(strings.TrimPrefix(path, "/"), "/")
+
+	for i, segment := range segments {
+		segments[i], err = url.PathUnescape(segment)
+		if err != nil {
+			return
+		}
+	}
+
+	return
+}
+
+// RedirectDir returns true and redirects the user to a version of the URL with
+// a trailing slash, if and only if the request URL does not already have a
+// trailing slash.
+func RedirectDir(writer http.ResponseWriter, request *http.Request) bool {
+	requestURI := request.RequestURI
+
+	pathEnd := strings.IndexAny(requestURI, "?#")
+	var path, rest string
+	if pathEnd == -1 {
+		path = requestURI
+	} else {
+		path = requestURI[:pathEnd]
+		rest = requestURI[pathEnd:]
+	}
+
+	if !strings.HasSuffix(path, "/") {
+		http.Redirect(writer, request, path+"/"+rest, http.StatusSeeOther)
+		return true
+	}
+	return false
+}
+
+// RedirectNoDir returns true and redirects the user to a version of the URL
+// without a trailing slash, if and only if the request URL has a trailing
+// slash.
+func RedirectNoDir(writer http.ResponseWriter, request *http.Request) bool {
+	requestURI := request.RequestURI
+
+	pathEnd := strings.IndexAny(requestURI, "?#")
+	var path, rest string
+	if pathEnd == -1 {
+		path = requestURI
+	} else {
+		path = requestURI[:pathEnd]
+		rest = requestURI[pathEnd:]
+	}
+
+	if strings.HasSuffix(path, "/") {
+		http.Redirect(writer, request, strings.TrimSuffix(path, "/")+rest, http.StatusSeeOther)
+		return true
+	}
+	return false
+}
+
+// RedirectUnconditionally unconditionally redirects the user back to the
+// current page while preserving query parameters.
+func RedirectUnconditionally(writer http.ResponseWriter, request *http.Request) {
+	requestURI := request.RequestURI
+
+	pathEnd := strings.IndexAny(requestURI, "?#")
+	var path, rest string
+	if pathEnd == -1 {
+		path = requestURI
+	} else {
+		path = requestURI[:pathEnd]
+		rest = requestURI[pathEnd:]
+	}
+
+	http.Redirect(writer, request, path+rest, http.StatusSeeOther)
+}
+
+// SegmentsToURL joins URL segments to the path component of a URL.
+// Each segment is escaped properly first.
+func SegmentsToURL(segments []string) string {
+	for i, segment := range segments {
+		segments[i] = url.PathEscape(segment)
+	}
+	return strings.Join(segments, "/")
+}
+
+// AnyContain returns true if and only if ss contains a string that contains c.
+func AnyContain(ss []string, c string) bool {
+	for _, s := range ss {
+		if strings.Contains(s, c) {
+			return true
+		}
+	}
+	return false
+}