commit e0e19240b5be5204709f1ea5705c23ec6291b006
Author: Romain de Laage <romain.delaage@rdelaage.ovh>
Date:   Tue May 4 14:17:12 2021 +0200

    Initial commit

diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..b48dafc
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,3 @@
+module main
+
+go 1.16
diff --git a/main.go b/main.go
new file mode 100644
index 0000000..e20dd12
--- /dev/null
+++ b/main.go
@@ -0,0 +1,227 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"archive/zip"
+	"bufio"
+	"strings"
+	"time"
+	"strconv"
+)
+
+type BookInfo struct {
+	Title        string
+	GpubVersion  string
+	Index        string
+	Author       string
+	Language     string
+	Charset      string
+	Description  string
+	Published    string
+	PublishDate  string
+	RevisionDate string
+	Copyright    string
+	License      string
+	Version      string
+	Cover        string
+}
+
+var fileSystem map[string]*zip.File
+var bookInfo BookInfo
+
+func main() {
+	if len(os.Args) < 2 {
+		fmt.Println("USAGE:", os.Args[0], "filename")
+		os.Exit(1)
+	}
+
+	fmt.Println("Opening", os.Args[1])
+	file, err := zip.OpenReader(os.Args[1])
+	if err != nil {
+		fmt.Println("Failed to open", os.Args[1], err)
+	}
+	defer file.Close()
+
+	fileSystem = make(map[string]*zip.File)
+	if !validate(&file.Reader) {
+		fmt.Println(os.Args[1], "could not be validated...")
+		os.Exit(1)
+	} else {
+		fmt.Println(os.Args[1], "has been validated")
+		printBookInfo()
+	}
+}
+
+func printBookInfo() {
+	if bookInfo.Title != "" {
+		fmt.Println("Title:", bookInfo.Title)
+	}
+	if bookInfo.GpubVersion != "" {
+		fmt.Println("GpubVersion:", bookInfo.GpubVersion)
+	}
+}
+
+func validate(archive *zip.Reader) bool {
+	isThereMetadata := false
+
+	for _, f := range archive.File { // looking for metadata first, and put all files in map
+		if f.Name == "metadata.txt" {
+			if !isValidMetadata(f) {
+				fmt.Println("FATAL:", f.Name,"present but not valid")
+				return false
+			}
+
+			isThereMetadata = true
+		}
+
+		fileSystem[f.Name] = f
+	}
+
+	if isThereMetadata {
+		if bookInfo.Index == "" {
+			fmt.Println("WARNING: No index provided, checking default index.gmi")
+			return isValidContent("index.gmi")
+		} else {
+			return isValidContent(bookInfo.Index)
+		}
+	} else {
+		fmt.Println("WARNING: This is not a book but a capsule archive")
+
+		f, ok := fileSystem["index.gmi"]
+		if !ok {
+			fmt.Println("FATAL: This is a capsule archive but index.gmi is not present at root")
+			return false
+		}
+
+		if f.FileHeader.FileInfo().IsDir() {
+			fmt.Println("FATAL:", f.Name, "is a directory")
+			return false
+		}
+
+		return true
+	}
+}
+
+func isValidMetadata(file *zip.File) bool {
+	isThereTitle := false
+	isThereGpubVersion := false
+
+	if file.FileHeader.FileInfo().IsDir() {
+		fmt.Println("FATAL:", file.Name, "is a directory !")
+		return false
+	}
+
+	reader, err := file.Open()
+	if err != nil {
+		fmt.Println("FATAL:", file.Name, "can't be opened")
+		return false
+	}
+	defer reader.Close()
+
+	scanner := bufio.NewScanner(reader)
+	for scanner.Scan() {
+		line := scanner.Text()
+		if strings.Trim(line, " ") != "" {
+			columnPosition := strings.Index(line, ":")
+			if columnPosition == -1 {
+				fmt.Println("FATAL: invalid line in", file.Name, line)
+				return false
+			}
+
+			key := strings.Trim(line[:columnPosition], " ")
+			value := strings.Trim(line[columnPosition+1:], " ")
+
+			switch key {
+			case "title":
+				bookInfo.Title = value
+				isThereTitle = true
+			case "gpubVersion":
+				bookInfo.GpubVersion = value
+				isThereGpubVersion = true
+			case "index":
+				bookInfo.Index = value
+			case "author":
+				bookInfo.Author = value
+			case "language":
+				//todo is language tag valid ? BCP 47
+				bookInfo.Language = value
+			case "charset":
+				bookInfo.Charset = value
+			case "description":
+				bookInfo.Description = value
+			case "published":
+				_, err := strconv.ParseUint(value, 10, 32)
+				if err != nil {
+					fmt.Println("FATAL: Bad format in", key, err)
+				}
+				bookInfo.Published = value
+			case "publishDate":
+				_, err := time.Parse(time.RFC3339, value)
+				if err != nil {
+					fmt.Println("FATAL: Bad date format in", key, err)
+					return false
+				}
+				bookInfo.PublishDate = value
+			case "revisionDate":
+				_, err := time.Parse(time.RFC3339, value)
+				if err != nil {
+					fmt.Println("FATAL: Bad date format in", key, err)
+					return false
+				}
+				bookInfo.RevisionDate = value
+			case "copyright":
+				bookInfo.Copyright = value
+			case "license":
+				bookInfo.License = value
+			case "version":
+				bookInfo.Version = value
+			case "cover":
+				bookInfo.Cover = value
+			default:
+				fmt.Println("FATAL: Unknown key in", file.Name, key)
+				return false
+			}
+		}
+	}
+	if err := scanner.Err(); err != nil {
+		fmt.Println("FATAL: error while scanning", file.Name, err)
+		return false
+	}
+
+	if !isThereTitle { // only two fields are mandatory
+		fmt.Println("FATAL: No title provided !")
+		return false
+	} else if !isThereGpubVersion {
+		fmt.Println("FATAL: No GpubVersion provided !")
+		return false
+	} else { // the last thing we need to test is version validity
+		return isVersionValid()
+	}
+}
+
+func isValidContent(filePath string) bool {
+	if filePath == "" || filePath == "/" { //we want index
+		filePath = "index.gmi"
+	} else if strings.HasPrefix(filePath, "/") { //we must ingore the leading slash
+		filePath = filePath[1:]
+	}
+
+	file, ok := fileSystem[filePath]
+	if !ok {
+		fmt.Println("FATAL:", filePath, "doesn't exist !")
+		return false
+	}
+
+	if file.FileHeader.FileInfo().IsDir() { //this is a dir, we look at index.gmi
+		return isValidContent(filePath + "index.gmi")
+	}
+
+	//todo
+
+	return true
+}
+
+func isVersionValid() bool {
+	return bookInfo.GpubVersion == "1.0.0"
+}