From 053e07c3190c823f1c24f2c659975cdc06559885 Mon Sep 17 00:00:00 2001
From: mappu <mappu04@gmail.com>
Date: Sun, 30 Jun 2024 13:47:29 +1200
Subject: [PATCH] debconf: implement dat file parser

---
 debconf/debconf.go      | 92 +++++++++++++++++++++++++++++++++++++++++
 debconf/debconf_test.go | 30 ++++++++++++++
 2 files changed, 122 insertions(+)
 create mode 100644 debconf/debconf.go
 create mode 100644 debconf/debconf_test.go

diff --git a/debconf/debconf.go b/debconf/debconf.go
new file mode 100644
index 0000000..cd619b0
--- /dev/null
+++ b/debconf/debconf.go
@@ -0,0 +1,92 @@
+package debconf
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"strings"
+)
+
+const (
+	DefaultConfigDat    = `/var/cache/debconf/config.dat`
+	DefaultPasswordsDat = `/var/cache/debconf/passwords.dat`
+	DefaultTemplatesDat = `/var/cache/debconf/templates.dat`
+)
+
+type Entry struct {
+	Name       string
+	Properties [][2]string
+}
+
+type Database struct {
+	Entries        []Entry
+	AllColumnNames []string
+}
+
+func Parse(r io.Reader) (*Database, error) {
+	sc := bufio.NewScanner(r)
+
+	var entries []Entry
+	var wip Entry
+	var linenum int = 0
+
+	knownColumnNames := map[string]struct{}{
+		"Name": struct{}{},
+	}
+	var discoveredColumns []string
+
+	for sc.Scan() {
+		linenum++
+		line := sc.Text()
+
+		if line == "" {
+			if wip.Name != "" {
+				entries = append(entries, wip)
+				wip = Entry{}
+			}
+			continue
+		}
+
+		if line[0] == ' ' {
+			// continuation of last text entry
+			if len(wip.Properties) == 0 {
+				return nil, fmt.Errorf("Continuation of nonexistent entry on line %d", linenum)
+			}
+
+			wip.Properties[len(wip.Properties)-1][1] += line[1:]
+
+		} else {
+			// New pair on current element
+			key, rest, ok := strings.Cut(line, `:`)
+			if !ok {
+				return nil, fmt.Errorf("Missing : on line %d", linenum)
+			}
+
+			if _, ok := knownColumnNames[key]; !ok {
+				knownColumnNames[key] = struct{}{}
+				discoveredColumns = append(discoveredColumns, key)
+			}
+
+			if key == `Name` {
+				wip.Name = rest
+			} else {
+				wip.Properties = append(wip.Properties, [2]string{key, rest})
+			}
+
+		}
+
+	}
+
+	if sc.Err() != nil {
+		return nil, sc.Err()
+	}
+
+	if wip.Name != "" {
+		entries = append(entries, wip)
+	}
+
+	return &Database{
+		Entries:        entries,
+		AllColumnNames: discoveredColumns,
+	}, nil
+}
diff --git a/debconf/debconf_test.go b/debconf/debconf_test.go
new file mode 100644
index 0000000..53670e8
--- /dev/null
+++ b/debconf/debconf_test.go
@@ -0,0 +1,30 @@
+package debconf
+
+import (
+	"os"
+	"testing"
+)
+
+func TestDebconfParse(t *testing.T) {
+	src, err := os.Open(DefaultConfigDat)
+	if err != nil {
+		if os.IsNotExist(err) {
+			t.Skip(err)
+		}
+		t.Fatal(err)
+	}
+	defer src.Close()
+
+	db, err := Parse(src)
+	if err != nil {
+		t.Fatalf("Parse: %v", err)
+	}
+
+	if len(db.Entries) == 0 {
+		t.Errorf("expected >0 entries, got %v", len(db.Entries))
+	}
+
+	if len(db.AllColumnNames) == 0 {
+		t.Errorf("expected >0 column names, got %v", len(db.AllColumnNames))
+	}
+}