Refactor some utils.go; add another tool 'tiledump'

internal/utils/utils.go

@@ -0,0 +1,114 @@
+// Package utils provides shared functionality for dumping CT log tile entries.
+// (C) Copyright 2026 Pim van Pelt <pim@ipng.ch>
+package utils
+
+import (
+	"bytes"
+	"compress/gzip"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+
+	"filippo.io/sunlight"
+)
+
+const maxCompressRatio = 100
+
+// FetchURL fetches data from a URL.
+func FetchURL(url string) ([]byte, error) {
+	resp, err := http.Get(url)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("HTTP %d", resp.StatusCode)
+	}
+
+	return io.ReadAll(resp.Body)
+}
+
+// Decompress decompresses gzip-compressed data, or returns the data as-is if not compressed.
+func Decompress(data []byte) ([]byte, error) {
+	r, err := gzip.NewReader(bytes.NewReader(data))
+	if err != nil {
+		// Not gzipped, return as-is
+		return data, nil
+	}
+	maxSize := int64(len(data)) * maxCompressRatio
+	return io.ReadAll(io.LimitReader(r, maxSize))
+}
+
+// DumpAllEntries reads and dumps all entries from tile data.
+func DumpAllEntries(tileData []byte) error {
+	entryNum := 0
+	for len(tileData) > 0 {
+		e, remaining, err := sunlight.ReadTileLeaf(tileData)
+		if err != nil {
+			return fmt.Errorf("failed to read entry %d: %w", entryNum, err)
+		}
+		tileData = remaining
+
+		dumpEntry(e, entryNum)
+		fmt.Println()
+		entryNum++
+	}
+
+	fmt.Printf("Total entries: %d\n", entryNum)
+	return nil
+}
+
+// DumpEntryAtPosition reads and dumps a specific entry at the given position.
+func DumpEntryAtPosition(tileData []byte, position int, expectedIndex int64) error {
+	entryNum := 0
+	for len(tileData) > 0 {
+		e, remaining, err := sunlight.ReadTileLeaf(tileData)
+		if err != nil {
+			return fmt.Errorf("failed to read entry %d: %w", entryNum, err)
+		}
+		tileData = remaining
+
+		if entryNum == position {
+			if e.LeafIndex != expectedIndex {
+				fmt.Fprintf(os.Stderr, "WARNING: Expected leaf index %d but found %d at position %d\n",
+					expectedIndex, e.LeafIndex, position)
+			}
+			dumpEntry(e, entryNum)
+			return nil
+		}
+		entryNum++
+	}
+
+	return fmt.Errorf("position %d not found in tile (only %d entries)", position, entryNum)
+}
+
+func dumpEntry(e *sunlight.LogEntry, entryNum int) {
+	fmt.Printf("=== Entry %d ===\n", entryNum)
+	fmt.Printf("Leaf Index: %d\n", e.LeafIndex)
+	fmt.Printf("Timestamp: %d\n", e.Timestamp)
+	fmt.Printf("Is Precert: %v\n", e.IsPrecert)
+
+	if e.IsPrecert {
+		fmt.Printf("Issuer Key Hash: %x\n", e.IssuerKeyHash)
+	}
+
+	fmt.Printf("Certificate: %d bytes\n", len(e.Certificate))
+	if e.PreCertificate != nil {
+		fmt.Printf("PreCertificate: %d bytes\n", len(e.PreCertificate))
+	}
+
+	fmt.Printf("Chain Fingerprints: %d entries\n", len(e.ChainFingerprints))
+	for i, fp := range e.ChainFingerprints {
+		fmt.Printf("  [%d]: %x\n", i, fp)
+	}
+
+	// Try to extract parsed certificate info
+	if trimmed, err := e.TrimmedEntry(); err == nil {
+		if data, err := json.MarshalIndent(trimmed, "  ", "  "); err == nil {
+			fmt.Printf("Parsed Certificate Info:\n  %s\n", data)
+		}
+	}
+}