replace io/ioutil with os

I've seen a container (private one) whose filenames start with ./, but
the layer name does not have the prefix, causing undocker to fail.

Let's always normalize the names to not have the prefix.

.build.yml

@@ -9,12 +9,11 @@ sources:
 tasks:
   - setup: |
       go install honnef.co/go/tools/cmd/staticcheck@latest
-  - test: |
-      make -C undocker coverage.html
-  - lint: |
-      make -C undocker -O -j$(nproc) lint
-  - binaries: |
-      make -C undocker -O -j$(nproc) all
-      cat undocker/sha256sum-*.txt
+  - built-test-lint: |
+      make -C undocker -O -j$(nproc) undocker coverage.html lint
+  - usage: |
+      # like 'grep -q', but prints output too.
+      # | tee /dev/stderr doesn't work on sourcehut workers; permission denied.
+      ./undocker/undocker |& awk 'BEGIN{c=1};/Built with /{c=0};{print};END{exit c}'
 artifacts:
   - undocker/coverage.html

Makefile

@@ -1,32 +1,15 @@
 SCRIPTS = $(shell awk '/#!\/bin\/(ba)?sh/&&FNR==1{print FILENAME}' $(shell git ls-files))
 GODEPS = $(shell git ls-files '*.go' go.mod go.sum)
-GOOSARCHS = $(sort darwin/amd64 linux/amd64)
 
 VSN ?= $(shell git describe --dirty)
 VSNHASH = $(shell git rev-parse --verify HEAD)
 LDFLAGS = -ldflags "-X main.Version=$(VSN) -X main.VersionHash=$(VSNHASH)"
 
 undocker: ## builds binary for the current architecture
-	CGO_ENABLED=0 go build $(LDFLAGS) -o $@
+	go build $(LDFLAGS) -o $@
 
 .PHONY: test
-test:
-	go test -race -cover ./...
-
-define undockertarget
-UNDOCKERS += undocker-$(1)-$(2)-$(VSN)
-undocker-$(1)-$(2)-$(VSN): $(GODEPS)
-	CGO_ENABLED=0 GOOS=$(1) GOARCH=$(2) go build $(LDFLAGS) -o $$@
-endef
-
-$(foreach goosarch,$(GOOSARCHS),\
-	$(eval $(call undockertarget,$(word 1,$(subst /, ,$(goosarch))),$(word 2,$(subst /, ,$(goosarch))))))
-
-.PHONY: all
-all: $(UNDOCKERS) sha256sum-$(VSN).txt
-
-.PHONY: sha256sum-asc
-sha256sum-asc: sha256sum-$(VSN).txt.asc
+test: coverage.out
 
 .PHONY: lint
 lint:
@@ -36,17 +19,11 @@ lint:
 
 .INTERMEDIATE: coverage.out
 coverage.out: $(GODEPS)
-	go test -coverprofile $@ ./...
+	go test -race -cover -coverprofile $@ ./...
 
 coverage.html: coverage.out
 	go tool cover -html=$< -o $@
 
-sha256sum-$(VSN).txt: $(UNDOCKERS)
-	sha256sum $(UNDOCKERS) > $@
-
-sha256sum-$(VSN).txt.asc: sha256sum-$(VSN).txt
-	gpg --clearsign $<
-
 .PHONY: clean
 clean:
-	rm -f undocker-*-v* coverage.html sha256sum*.txt sha256sum*.txt.asc
+	rm -f undocker coverage.html

README.md

@@ -18,17 +18,20 @@ and application isolation ("container") runtimes: once the docker image is
 extracted, it can be run with old-fashioned tools: lxc, systemd-nspawn,
 systemd, FreeBSD Jails, and many others.
 
-Undocker has no dependencies outside Golang stdlib.
 
 Installation
 ------------
 
-You may use [officially released binaries][3], or build it:
+Build it like this for the "current" platform:
 
 ```
 $ make undocker
 ```
 
+`make -B` will print the extra flags (`-X <...>`) for cross-compiling with
+other archs. It's all `go build <...>` in the back, and depends only on Go's
+compiler and stdlib.
+
 Usage: convert docker image to rootfs
 -------------------------------------
 

main_test.go

@@ -4,7 +4,6 @@ import (
 	"bytes"
 	"errors"
 	"io"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"regexp"
@@ -28,7 +27,7 @@ func TestExecute(t *testing.T) {
 			infile: "t10-in.txt",
 			fixture: func(t *testing.T, dir string) {
 				fname := filepath.Join(dir, "t10-in.txt")
-				if err := ioutil.WriteFile(fname, _foo, 0644); err != nil {
+				if err := os.WriteFile(fname, _foo, 0644); err != nil {
 					t.Fatalf("unexpected error: %v", err)
 				}
 			},
@@ -39,7 +38,7 @@ func TestExecute(t *testing.T) {
 			infile: "t20-in.txt",
 			fixture: func(t *testing.T, dir string) {
 				fname := filepath.Join(dir, "t20-in.txt")
-				if err := ioutil.WriteFile(fname, _foo, 0644); err != nil {
+				if err := os.WriteFile(fname, _foo, 0644); err != nil {
 					t.Fatalf("unexpected error: %v", err)
 				}
 			},
@@ -50,7 +49,7 @@ func TestExecute(t *testing.T) {
 			infile: "t30-in.txt",
 			fixture: func(t *testing.T, dir string) {
 				fname := filepath.Join(dir, "t30-in.txt")
-				if err := ioutil.WriteFile(fname, _foo, 0644); err != nil {
+				if err := os.WriteFile(fname, _foo, 0644); err != nil {
 					t.Fatalf("unexpected error: %v", err)
 				}
 			},
@@ -122,7 +121,7 @@ func TestExecute(t *testing.T) {
 			if tt.outfile == "-" {
 				out = stdout.Bytes()
 			} else {
-				out, err = ioutil.ReadFile(tt.outfile)
+				out, err = os.ReadFile(tt.outfile)
 				if err != nil {
 					t.Fatalf("unexpected error: %v", err)
 				}

release

@@ -1,39 +1,25 @@
 #!/bin/bash
 set -euo pipefail
 
-err() {
-    >&2 echo "ERROR: $*"
-    exit 1
-}
+_err(){ >&2 echo "ERROR: $*"; exit 1; }
 
 git status --porcelain | grep -q "" &&
-    err "working tree is dirty, commit your changes first."
+    _err "working tree is dirty, commit your changes first."
 
-# https://raimue.blog/2010/09/09/bash-for-loop-with-glob-patterns/
-shopt -s nullglob
-for file in sha256sum-*; do
-    err "found $file from previous release, delete it first"
-done
-shopt -u nullglob
-
-[[ "$1" =~ ^v([0-9]+)\.([0-9]+)(\.([0-9]+))?$ ]] || \
-    err "arg1 accepts the following formats: v1.0 v1.0.0"
+[[ "$1" =~ ^v([0-9]+)\.([0-9]+)(\.([0-9]+))?(-rc([0-9]+))?$ ]] || \
+    _err "arg1 accepts the following formats: v1.0 v1.0.0 v1.0-rc1 v1.0.1-rc1"
 
 git tag | grep -q "^$1$" &&
-    err "tag $1 already exists"
+    _err "tag $1 already exists"
+
+# sanity test: do the tests pass?
+make -B -j"$(nproc)" test lint
 
 last_tag=$(git tag | tail -1)
 
-make -B -j"$(nproc)" VSN="$1" sha256sum-asc
-
 {
     echo undocker "$1"
     echo
     echo Changelog since "$last_tag":
-    git log --pretty=format:"- [%cn] %s" "$last_tag"..HEAD
-    echo
-    echo
-    echo sha256sums of released binaries:
-    cat sha256sum-*.txt
-    echo
+    git log --pretty=format:"- [%an] %s" "$last_tag"..HEAD
 } | git tag -u motiejus@jakstys.lt -F - "$1"

rootfs/rootfs.go

@@ -69,7 +69,7 @@ func Flatten(rd io.ReadSeeker, w io.Writer) (_err error) {
 			if err != nil {
 				return err
 			}
-			layerOffsets[hdr.Name] = here
+			layerOffsets[strings.TrimPrefix(hdr.Name, "./")] = here
 		}
 	}
 
@@ -82,7 +82,7 @@ func Flatten(rd io.ReadSeeker, w io.Writer) (_err error) {
 	for i, name := range manifest[0].Layers {
 		layers[i] = nameOffset{
 			name:   name,
-			offset: layerOffsets[name],
+			offset: layerOffsets[strings.TrimPrefix(name, "./")],
 		}
 	}