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Implement resume feature for downloads #6

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59f865c
Implement resume feature for downloads
DrJapan Feb 9, 2026
dd0bc43
Refactor channel handling in State methods
DrJapan Feb 12, 2026
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228 changes: 203 additions & 25 deletions tor-dl.go
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,9 @@ package main

/*
tor-dl - fast large file downloader over locally installed Tor
Copyright © 2025 Bryan Cuneo <https://github.com/BryanCuneo/tor-dl/>
Copyright © 2026 Bryan Cuneo <https://github.com/BryanCuneo/tor-dl/>

-resume added by DrJapan

Based on torget by Michał Trojnara <https://github.com/mtrojnar/torget>

Expand All @@ -22,6 +24,7 @@ package main
import (
"bufio"
"context"
"encoding/json"
"errors"
"flag"
"fmt"
Expand All @@ -46,6 +49,20 @@ type chunk struct {
cancel context.CancelFunc
}

type resumeChunk struct {
Start int64 `json:"start"`
Length int64 `json:"length"`
}

type resumeState struct {
Version int `json:"version"`
Src string `json:"src"`
Output string `json:"output"`
BytesTotal int64 `json:"bytes_total"`
Circuits int `json:"circuits"`
Chunks []resumeChunk `json:"chunks"`
}

type State struct {
ctx context.Context
src string
Expand All @@ -63,6 +80,7 @@ type State struct {
}

const torBlock = 8000 // The longest plain text block in Tor
const resumeSuffix = ".tordl.resume"

// Basic function to determine human-readable file sizes
func humanReadableSize(sizeInBytes float32) string {
Expand Down Expand Up @@ -93,6 +111,78 @@ func httpClient(user string) *http.Client {
}
}

func resumeFilepath(output string) string {
return output + resumeSuffix
}

func loadResume(path string) (resumeState, error) {
data, err := os.ReadFile(path)
if err != nil {
return resumeState{}, err
}

var state resumeState
if err := json.Unmarshal(data, &state); err != nil {
return resumeState{}, err
}

return state, nil
}

func (s *State) snapshotResume() resumeState {
state := resumeState{
Version: 1,
Src: s.src,
Output: s.output,
BytesTotal: s.bytesTotal,
Circuits: s.circuits,
Chunks: make([]resumeChunk, s.circuits),
}

s.rwmutex.RLock()
for i := range s.chunks {
state.Chunks[i] = resumeChunk{Start: s.chunks[i].start, Length: s.chunks[i].length}
}
s.rwmutex.RUnlock()

return state
}

func (s *State) saveResume(path string) error {
state := s.snapshotResume()
data, err := json.MarshalIndent(state, "", " ")
if err != nil {
return err
}

tmp := path + ".tmp"
if err := os.WriteFile(tmp, data, 0644); err != nil {
return err
}

return os.Rename(tmp, path)
}

func (s *State) startResumeWriter(path string) chan struct{} {
:= make(chan struct{})
go func() {
ticker := time.NewTicker(2 * time.Second)
defer ticker.()
for {
select {
case <-:
return
case <-ticker.C:
if err := s.saveResume(path); err != nil {
s.log <- fmt.Sprintf("resume save: %s", err.Error())
}
}
}
}()

return
}

func NewState(ctx context.Context) *State {
var s State
s.circuits = circuits
Expand Down Expand Up @@ -233,7 +323,7 @@ func (s *State) printLogs() {
for i := 0; i < n; i++ {
logs[i] = <-s.log
}
logs[n] = "stop" // Not an expected log line
logs[n] = "" // Not an expected log line
sort.Strings(logs)
prevLog := "start" // Not an expected log line
cnt := 0
Expand Down Expand Up @@ -300,8 +390,8 @@ func (s *State) darwin() {
var slowest float64
now := time.Now()

s.rwmutex.RLock()
for id := range s.circuits {
s.rwmutex.Lock()
for id := range s.chunks {
if s.chunks[id].cancel == nil {
continue
}
Expand All @@ -320,7 +410,7 @@ func (s *State) darwin() {
s.chunks[victim].cancel()
s.chunks[victim].cancel = nil
}
s.rwmutex.RUnlock()
s.rwmutex.Unlock()
}

func (s *State) getOutputFilepath() {
Expand Down Expand Up @@ -366,16 +456,32 @@ func (s *State) getOutputFilepath() {
}

func (s *State) Fetch(src string) int {
var stop_status chan bool
var Status chan bool
var resume chan struct{}
var resumeData *resumeState

s.src = src
startTime := time.Now()

s.getOutputFilepath()
// If the file already exists and the -force argument was not used, exit
if _, err := os.Stat(s.output); err == nil && !force {
fmt.Fprintf(errorWriter, "ERROR: \"%s\" already exists. Skipping.\n", s.output)
return 1
resumePath := resumeFilepath(s.output)

// If the file already exists, the resume data exists and is available, and the -force argument was not used, exit
if resume {
if data, err := loadResume(resumePath); err == nil {
resumeData = &data
} else if !errors.Is(err, fs.ErrNotExist) {
fmt.Fprintf(messageWriter, "WARNING: Unable to read resume data: %v\n", err)
}
}

if resume && resumeData == nil {
if _, err := os.Stat(s.output); err == nil && !force {
fmt.Fprintf(errorWriter, "ERROR: \"%s\" already exists and no resume data found. Use -force to overwrite or delete the file.\n", s.output)
return 1
}
}

fmt.Fprintf(messageWriter, "Output file:\t\t%s\n", s.output)

// Get the target length
Expand All @@ -392,6 +498,46 @@ func (s *State) Fetch(src string) int {
s.bytesTotal = resp.ContentLength
fmt.Fprintf(messageWriter, "Download filesize:\t%s\n", humanReadableSize(float32(s.bytesTotal)))

//Resume data errors (URLs don't match, resume size doesn't match, resume data is invalid)
seq := 0
if resumeData != nil {
if _, err := os.Stat(s.output); err != nil {
fmt.Fprintf(errorWriter, "ERROR: Output file missing for resume: %s\n", s.output)
return 1
}

if resumeData.Circuits != s.circuits {
fmt.Fprintf(messageWriter, "WARNING: Resume data uses %d circuits; overriding -circuits.\n", resumeData.Circuits)
}
s.circuits = resumeData.Circuits
s.chunks = make([]chunk, s.circuits)
for i := range s.chunks {
s.chunks[i].start = resumeData.Chunks[i].Start
s.chunks[i].length = resumeData.Chunks[i].Length
s.chunks[i].circuit = i
}

remaining := int64(0)
for i := range s.chunks {
remaining += s.chunks[i].length
}
s.bytesPrev = s.bytesTotal - remaining

if remaining == 0 {
s.printPermanent("Download already complete.")
if err := os.Remove(resumePath); err != nil && !errors.Is(err, fs.ErrNotExist) {
fmt.Fprintf(messageWriter, "WARNING: Unable to remove resume file: %v\n", err)
}
return 0
}
seq = s.circuits
} else {
// If the file already exists and the -force argument was not used, exit
if _, err := os.Stat(s.output); err == nil && !force {
fmt.Fprintf(errorWriter, "ERROR: \"%s\" already exists. Skipping.\n", s.output)
return 1
}

// Create the output file. This will overwrite an existing file
file, err := os.Create(s.output)
if file != nil {
Expand All @@ -401,28 +547,40 @@ func (s *State) Fetch(src string) int {
fmt.Fprintln(messageWriter, err.Error())
return 1
}

if err := os.Remove(resumePath); err != nil && !errors.Is(err, fs.ErrNotExist) {
fmt.Fprintf(messageWriter, "WARNING: Unable to remove resume file: %v\n", err)
}

// Initialize chunks
chunkLen := s.bytesTotal / int64(s.circuits)
seq := 0
for id := range s.circuits {
s.chunks[id].start = int64(id) * chunkLen
s.chunks[id].length = chunkLen
s.chunks[id].circuit = seq
seq++
for id := range s.chunks {
s.chunks[id].start = int64(id) * chunkLen
s.chunks[id].length = chunkLen
s.chunks[id].circuit = seq
seq++
}
s.chunks[s.circuits-1].length += s.bytesTotal % int64(s.circuits)
}

// Start resume writer if enabled
if resume {
if err := s.saveResume(resumePath); err != nil {
fmt.Fprintf(messageWriter, "WARNING: Unable to write resume data: %v\n", err)
} else {
resume = s.startResumeWriter(resumePath)
}
}
s.chunks[s.circuits-1].length += s.bytesTotal % int64(s.circuits)

// If not -quiet or -silent, update status message every 1 second
if !quiet && !silent {
stop_status = make(chan bool)
stopStatus = make(chan bool)
go func() {
for {
time.Sleep(time.Second)

select {
case <-stop_status:
close(stop_status)
case <-stopStatus:
close(stopStatus)
return
default:
s.progress()
Expand All @@ -433,13 +591,16 @@ func (s *State) Fetch(src string) int {

// Spawn initial fetchers
go func() {
for id := range s.circuits {
for id := range s.chunks {
if s.chunks[id].length == 0 {
continue
}
client, req := s.chunkInit(id)
go s.chunkFetch(id, client, req)
time.Sleep(499 * time.Millisecond) // Be gentle to the local tor daemon
}
}()

// Spawn additional fetchers as needed
for {
select {
Expand Down Expand Up @@ -471,7 +632,18 @@ func (s *State) Fetch(src string) int {
howLong.Round(time.Second),
averageSpeed))

stop_status <- true
if resumeStop != nil {
close(resumeStop)
resumeStop = nil
}
if resume {
if err := os.Remove(resumePath); err != nil && !errors.Is(err, fs.ErrNotExist) {
fmt.Fprintf(messageWriter, "WARNING: Unable to remove resume file: %v\n", err)
}
}
if stopStatus != nil {
stopStatus <- true
}
return 0
}
if s.chunks[longest].length <= 5*torBlock {
Expand Down Expand Up @@ -502,6 +674,7 @@ var force bool
var minLifetime int
var name string
var quiet bool
var resume bool
var silent bool
var torPort int
var verbose bool
Expand Down Expand Up @@ -530,6 +703,9 @@ func init() {
flag.BoolVar(&quiet, "quiet", false, "Suppress most text output (still show errors).")
flag.BoolVar(&quiet, "q", false, "Suppress most text output (still show errors).")

flag.BoolVar(&resume, "resume", false, "Resume download if a matching .tordl.resume file exists.")
flag.BoolVar(&resume, "r", false, "Resume download if a matching .tordl.resume file exists.")

flag.BoolVar(&silent, "silent", false, "Suppress all text output (including errors).")
flag.BoolVar(&silent, "s", false, "Suppress all text output (including errors).")

Expand All @@ -543,7 +719,7 @@ func init() {
flag.Usage = func() {
w := flag.CommandLine.Output()
msg := `tor-dl - fast large file downloader over locally installed Tor
Copyright © 2025 Bryan Cuneo <https://github.com/BryanCuneo/tor-dl/>
Copyright © 2026 Bryan Cuneo <https://github.com/BryanCuneo/tor-dl/>
Licensed under GNU GPL version 3 <https://www.gnu.org/licenses/>
Based on torget by Michał Trojnara <https://github.com/mtrojnar/torget>

Expand All @@ -562,6 +738,8 @@ Usage: tor-dl [FLAGS] {file.txt | URL [URL2...]}
Output filename. (default filename from URL)
-quiet, -q bool
Suppress most text output (still show errors).
-resume, -r bool
Resume download if a matching .tordl.resume file exists.
-silent, -s bool
Suppress all text output (including errors).
-tor-port, -p int
Expand Down