konbata/main.go

package main

import (
	"context"
	"encoding/xml"
	"errors"
	"fmt"
	"io"
	"log"
	"net/url"
	"os"
	"sort"
	"strings"
	"time"

	"git.sr.ht/~adnano/go-gemini"
)

const TIMEOUT_NS time.Duration = time.Duration(60_000_000_000)
const MAX_FILE_SIZE int64 = 512 * 1024

func init() {
	err := populateHosts()
	if err != nil {
		log.Fatal(err)
	}

	err = populatePRedirs()
	if err != nil {
		log.Fatal(err)
	}

	err = populatePErrors()
	if err != nil {
		log.Fatal(err)
	}
}

func do(client gemini.Client, ctx context.Context, req *gemini.Request, via []*gemini.Request) (*gemini.Response, *gemini.Request, error) {
	if target, exists := predirs[req.URL.String()]; exists {
		via = append(via, req)
		if len(via) > 5 {
			return nil, req, errors.New("too many redirects")
		}

		redirect := *req
		redirect.URL = target
		return do(client, ctx, &redirect, via)
	}
	if perror, exists := perrors[req.URL.String()]; exists {
		return nil, req, errors.New(fmt.Sprintf("%d %s", perror.Code, perror.Message))
	}
	resp, err := client.Do(ctx, req)
	if err != nil {
		return resp, req, err
	}

	if resp.Status == gemini.StatusPermanentRedirect {
		target, err := url.Parse(resp.Meta)
		if err != nil {
			return resp, req, err
		}
		if target.Scheme != "gemini" && target.Scheme != "" {
			return resp, req, errors.New(fmt.Sprintf("tried to redirect to scheme %s", target.Scheme))
		}
		target = req.URL.ResolveReference(target)
		predirs[req.URL.String()] = target
		err = savePRedirs()
		if err != nil {
			return resp, req, err
		}
	}
	if resp.Status.Class() == gemini.StatusPermanentFailure {
		perrors[req.URL.String()] = PError{
			Code:    resp.Status,
			Message: resp.Meta,
		}
		err = savePErrors()
		if err != nil {
			return resp, req, err
		}
	}
	if resp.Status.Class() == gemini.StatusRedirect {
		via = append(via, req)
		if len(via) > 5 {
			return resp, req, errors.New("too many redirects")
		}

		target, err := url.Parse(resp.Meta)
		if err != nil {
			return resp, req, err
		}
		if target.Scheme != "gemini" && target.Scheme != "" {
			return resp, req, errors.New(fmt.Sprintf("tried to redirect to scheme %s", target.Scheme))
		}
		target = req.URL.ResolveReference(target)
		redirect := *req
		redirect.URL = target
		return do(client, ctx, &redirect, via)
	}
	if resp.Status.Class() != gemini.StatusSuccess {
		return resp, req, errors.New(fmt.Sprintf("%d %s", resp.Status, resp.Meta))
	}

	return resp, req, err
}

func main() {
	if len(os.Args) == 0 {
		fmt.Fprintf(os.Stderr, "Usage: konbata <url>\n")
		os.Exit(1)
	}
	if len(os.Args) != 2 {
		fmt.Fprintf(os.Stderr, "Usage: %s <url>\n", os.Args[0])
		os.Exit(1)
	}

	req, err := gemini.NewRequest(os.Args[1])
	if err != nil {
		log.Fatal(err)
	}

	client := gemini.Client{
		TrustCertificate: TrustCertificate,
	}
	ctx, cancel := context.WithTimeout(context.Background(), TIMEOUT_NS)
	defer cancel()
	resp, req, err := do(client, ctx, req, nil)
	if err != nil {
		log.Fatal(err)
	}
	limitedBody := io.LimitedReader{
		R: resp.Body,
		N: MAX_FILE_SIZE,
	}
	defer resp.Body.Close()

	mime, _, _ := strings.Cut(resp.Meta, ";")
	if mime == "application/rss+xml" || mime == "application/rss" ||
		mime == "application/atom+xml" || mime == "application/atom" ||
		mime == "application/xml" || mime == "text/xml" {
		out, err := io.ReadAll(&limitedBody)
		if err != nil {
			log.Fatal(err)
		}
		if limitedBody.N <= 0 {
			log.Fatalf("up to %d bytes read from the body", MAX_FILE_SIZE)
		}
		fmt.Print(string(out))
	} else if mime == "text/gemini" {
		aw := AtomWriter{
			Title: "",
			Items: nil,
		}
		gemini.ParseLines(&limitedBody, aw.Handle)
		if limitedBody.N <= 0 {
			log.Fatalf("up to %d bytes read from the body", MAX_FILE_SIZE)
		}
		sort.Sort(ByTime(aw.Items))
		feed := Feed{
			XMLNS: "http://www.w3.org/2005/Atom",
			Link: FeedLink{
				Href: req.URL.String(),
			},
			Id:      req.URL.String(),
			Entries: nil,
		}
		if aw.Title == "" {
			feed.Title = req.URL.String()
		} else {
			feed.Title = aw.Title
		}
		if len(aw.Items) == 0 {
			feed.Updated = time.Now().Format(time.RFC3339)
		} else {
			feed.Updated = aw.Items[len(aw.Items)-1].Date.Format(time.RFC3339)
		}
		for i := len(aw.Items); i != 0; i-- {
			item := aw.Items[i-1]
			link, err := req.URL.Parse(item.Link)
			if err != nil {
				log.Fatal(err)
			}
			feed.Entries = append(feed.Entries, FeedEntry{
				Title: item.Title,
				Link: EntryLink{
					Href: link.String(),
					Rel:  "alternate",
				},
				Id:      link.String(),
				Updated: item.Date.Format(time.RFC3339),
			})
		}
		out, err := xml.MarshalIndent(feed, "", "    ")
		if err != nil {
			log.Fatal(err)
		}
		fmt.Println(string(out))
	} else {
		log.Fatal("unsupported mime type: ", mime)
	}
}