Support option to only download on upgrade

Closes #14

README.md

@@ -132,6 +132,8 @@ Application Options:
       --all            extract all candidate files
   -q, --quiet          only print essential output
       --download-only  stop after downloading the asset (no extraction)
+      --upgrade-only   only download if release is more recent than current
+                       version
   -a, --asset=         download a specific asset containing the given string; can be specified multiple times for additional
                        filtering
       --sha256         show the SHA-256 hash of the downloaded asset

eget.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"bytes"
+	"errors"
 	"fmt"
 	"io"
 	"io/fs"
@@ -104,10 +105,18 @@ func getFinder(project string, opts *Flags) (finder Finder, tool string) {
 			tag = fmt.Sprintf("tags/%s", opts.Tag)
 		}
 
+		var mint time.Time
+		if opts.UpgradeOnly {
+			parts := strings.Split(project, "/")
+			last := parts[len(parts)-1]
+			mint = bintime(last)
+		}
+
 		finder = &GithubAssetFinder{
 			Repo:       repo,
 			Tag:        tag,
 			Prerelease: opts.Prerelease,
+			MinTime:    mint,
 		}
 	}
 	return finder, tool
@@ -227,6 +236,18 @@ func userSelect(choices []interface{}) int {
 	return choice
 }
 
+func bintime(bin string) (t time.Time) {
+	dir := "."
+	if ebin := os.Getenv("EGET_BIN"); ebin != "" {
+		dir = ebin
+	}
+	fi, err := os.Stat(filepath.Join(dir, bin))
+	if err != nil {
+		return
+	}
+	return fi.ModTime()
+}
+
 func main() {
 	var opts Flags
 	flagparser := flags.NewParser(&opts, flags.PassDoubleDash|flags.PrintErrors)
@@ -270,6 +291,10 @@ func main() {
 	finder, tool := getFinder(args[0], &opts)
 	assets, err := finder.Find()
 	if err != nil {
+		if errors.Is(err, ErrNoUpgrade) {
+			fmt.Fprintf(output, "%v\n", err)
+			os.Exit(0)
+		}
 		fatal(err)
 	}
 

find.go

@@ -2,9 +2,11 @@ package main
 
 import (
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"net/http"
+	"time"
 )
 
 // A Finder returns a list of URLs making up a project's assets.
@@ -18,8 +20,9 @@ type GithubRelease struct {
 		DownloadURL string `json:"browser_download_url"`
 	} `json:"assets"`
 
-	Prerelease bool   `json:"prerelease"`
-	Tag        string `json:"tag_name"`
+	Prerelease bool      `json:"prerelease"`
+	Tag        string    `json:"tag_name"`
+	CreatedAt  time.Time `json:"created_at"`
 }
 
 type GithubError struct {
@@ -49,8 +52,11 @@ type GithubAssetFinder struct {
 	Repo       string
 	Tag        string
 	Prerelease bool
+	MinTime    time.Time // release must be after MinTime to be found
 }
 
+var ErrNoUpgrade = errors.New("requested release is not more recent than current version")
+
 func (f *GithubAssetFinder) Find() ([]string, error) {
 	if f.Prerelease && f.Tag == "latest" {
 		tag, err := f.getLatestTag()
@@ -94,6 +100,10 @@ func (f *GithubAssetFinder) Find() ([]string, error) {
 		return nil, err
 	}
 
+	if release.CreatedAt.Before(f.MinTime) {
+		return nil, ErrNoUpgrade
+	}
+
 	// accumulate all assets from the json into a slice
 	assets := make([]string, 0, len(release.Assets))
 	for _, a := range release.Assets {

flags.go

@@ -9,6 +9,7 @@ type Flags struct {
 	All         bool     `long:"all" description:"extract all candidate files"`
 	Quiet       bool     `short:"q" long:"quiet" description:"only print essential output"`
 	DLOnly      bool     `long:"download-only" description:"stop after downloading the asset (no extraction)"`
+	UpgradeOnly bool     `long:"upgrade-only" description:"only download if release is more recent than current version"`
 	Asset       []string `short:"a" long:"asset" description:"download a specific asset containing the given string; can be specified multiple times for additional filtering"`
 	Hash        bool     `long:"sha256" description:"show the SHA-256 hash of the downloaded asset"`
 	Verify      string   `long:"verify-sha256" description:"verify the downloaded asset checksum against the one provided"`

man/eget.md

@@ -83,6 +83,10 @@ header: Eget Manual
 
 :    Stop after downloading the asset. This prevents Eget from performing extraction, allowing you to perform manual installation after the asset is downloaded.
 
+   --upgrade-only
+
+:    Only download the asset if the release is more recent than an existing asset with the same name in `$EGET_BIN`, or the current directory if `$EGET_BIN` is not defined.
+
   `-a, --asset=`
 
 :    Download a specific asset containing the given string. If there is an exact match with an asset, that asset is used regardless. This option can be specified multiple times for additional filtering. Example: **`eget --asset nvim.appimage neovim/neovim`**. Example **`eget --download-only --asset amd64.deb --asset musl sharkdp/bat`**.