feat: add resume support to Gemini protocol

internal/protocol/gemini/gemini.go

@@ -15,11 +15,13 @@ import (
 	"net"
 	"net/url"
 	"os"
+	"path/filepath"
 	"strconv"
 	"strings"
 	"time"
 
 	"codeberg.org/petrbalvin/goget/internal/core"
+	"codeberg.org/petrbalvin/goget/internal/output"
 	"codeberg.org/petrbalvin/goget/internal/protocol"
 )
 
@@ -39,7 +41,7 @@ func NewProtocol() *Protocol {
 			Name:        "GEMINI",
 			Scheme:      "gemini",
 			DefaultPort: 1965,
-			Features:    []string{},
+			Features:    []string{"resume"},
 		}),
 	}
 }
@@ -96,6 +98,14 @@ func (p *Protocol) downloadWithRedirects(ctx context.Context, req *core.Download
 
 	conn.SetDeadline(time.Now().Add(30 * time.Second))
 
+	// Close the connection when the context is cancelled so any
+	// blocking Read returns immediately instead of waiting for the
+	// 30-second deadline.
+	go func() {
+		<-ctx.Done()
+		conn.Close()
+	}()
+
 	// Send request: URL + CRLF
 	requestURL := req.URL.String()
 	if _, err := fmt.Fprintf(conn, "%s\r\n", requestURL); err != nil {
@@ -178,43 +188,129 @@ func (p *Protocol) downloadWithRedirects(ctx context.Context, req *core.Download
 	}
 
 	// Category 2x: success — continue to read body
-	var totalRead int64
+	var totalRead int64 // total bytes received from server (including skipped)
 	var writer io.Writer
+	var file *os.File
+	resumed := false
+	var startOffset int64 // bytes to skip on resume
 
-	if req.Writer != nil {
-		writer = req.Writer
-	} else {
-		writer = io.Discard
+	// Set up output destination. When req.Output is set and no external
+	// Writer was provided, we open the file directly. This covers both
+	// fresh downloads (create) and resume (append). When req.Writer is
+	// set (caller manages the file), we use it as-is.
+	if req.Output != "" && req.Output != "-" {
+		if req.Resume {
+			canResume, resumeMeta, rerr := output.CanResume(req.Output, req.URL.String())
+			if rerr != nil {
+				if req.Verbose {
+					fmt.Fprintf(os.Stderr, "[gemini] Resume check failed: %v\n", rerr)
+				}
+				output.CleanupResumeFiles(req.Output)
+			} else if canResume && resumeMeta != nil {
+				file, rerr = os.OpenFile(req.Output, os.O_APPEND|os.O_WRONLY, 0644)
+				if rerr != nil {
+					return nil, core.NewFileError("failed to open file for resume", rerr)
+				}
+				defer file.Close()
+				writer = file
+				startOffset = resumeMeta.Downloaded
+				resumed = true
+				if req.Verbose {
+					fmt.Fprintf(os.Stderr, "[gemini] Resuming from byte %d\n", startOffset)
+				}
+			}
+		}
+		if writer == nil && req.Writer == nil {
+			// Fresh download — create the output file.
+			dir := filepath.Dir(req.Output)
+			if dir != "" && dir != "." {
+				if err := os.MkdirAll(dir, 0755); err != nil {
+					return nil, core.NewFileError("failed to create output directory", err)
+				}
+			}
+			file, err = os.Create(req.Output)
+			if err != nil {
+				return nil, core.NewFileError("failed to create output file", err)
+			}
+			defer file.Close()
+			writer = file
+		}
 	}
+	if writer == nil {
+		if req.Writer != nil {
+			writer = req.Writer
+		} else {
+			writer = io.Discard
+		}
+	}
+
+	// Gemini does not support range requests, so resume re-downloads
+	// the full content and skips the bytes already saved to disk.
+	var skipped int64
 
 	buf := make([]byte, 32*1024)
 	for {
 		select {
 		case <-ctx.Done():
+			saveGeminiResume(req, totalRead)
 			return nil, ctx.Err()
 		default:
 		}
 		n, err := reader.Read(buf)
 		if n > 0 {
-			if _, werr := writer.Write(buf[:n]); werr != nil {
-				return nil, core.NewFileError("failed to write gemini data", werr)
-			}
 			totalRead += int64(n)
+			chunk := buf[:n]
+			// On resume, discard bytes we already have on disk.
+			if skipped < startOffset {
+				remain := startOffset - skipped
+				if int64(n) <= remain {
+					skipped += int64(n)
+					chunk = nil
+				} else {
+					skipped += remain
+					chunk = chunk[int(remain):]
+				}
+			}
+			if len(chunk) > 0 {
+				if _, werr := writer.Write(chunk); werr != nil {
+					saveGeminiResume(req, totalRead)
+					return nil, core.NewFileError("failed to write gemini data", werr)
+				}
+			}
 			if req.ProgressCallback != nil {
 				speed := float64(totalRead) / time.Since(startTime).Seconds()
 				req.ProgressCallback(totalRead, -1, speed)
 			}
 		}
 		if err == io.EOF {
+			// The connection may have been closed by our context
+			// cancellation goroutine. If so, the EOF is not a genuine
+			// end-of-data but a side-effect of the cancel.
+			if ctx.Err() != nil {
+				saveGeminiResume(req, totalRead)
+				return nil, ctx.Err()
+			}
 			break
 		}
 		if err != nil {
+			saveGeminiResume(req, totalRead)
+			if ctx.Err() != nil {
+				return nil, ctx.Err()
+			}
 			return nil, core.NewNetworkError("failed to read gemini response body", err, core.SafeURL(req.URL))
 		}
 	}
 
+	// Download complete — remove resume metadata sidecar.
+	if req.Output != "" && req.Output != "-" {
+		output.DeleteResumeMetadata(req.Output)
+	}
+
 	duration := time.Since(startTime)
-	speed := float64(totalRead) / duration.Seconds()
+	speed := float64(0)
+	if duration.Seconds() > 0 {
+		speed = float64(totalRead) / duration.Seconds()
+	}
 
 	return &core.DownloadResult{
 		BytesDownloaded: totalRead,
@@ -224,5 +320,20 @@ func (p *Protocol) downloadWithRedirects(ctx context.Context, req *core.Download
 		IPVersion:       4,
 		Speed:           speed,
 		OutputPath:      req.Output,
+		Resumed:         resumed,
 	}, nil
 }
+
+// saveGeminiResume persists partial Gemini download progress to the
+// standard `.goget.meta` sidecar. No-op for stdout writes or zero-byte
+// transfers. Gemini does not expose Content-Length in the response
+// header, so Total is recorded as 0 (size unknown).
+func saveGeminiResume(req *core.DownloadRequest, downloaded int64) {
+	if req == nil || req.Output == "" || req.Output == "-" || downloaded <= 0 {
+		return
+	}
+	meta := output.NewResumeMetadata(req.URL.String(), "", "", downloaded, 0)
+	if err := meta.Save(req.Output); err != nil && req.Verbose {
+		fmt.Fprintf(os.Stderr, "[gemini] Warning: failed to save resume metadata: %v\n", err)
+	}
+}