Automate handling of notice file

Here's a hacky tool to migrate our ongoing v0.0.1 measurement once it's
done.  I.e., just split-up the NOTICE prints we have in collect.stdout,
putting them in per-log notice files that happens automatically now.

```
// Package main provides a hacky tool that extracts NOTICE: <log desc> prints
// from a file collect.stdout, putting them in the logs data directories as
// notice.txt.  Only meant to migrate away from v0.0.1 that did not store
// per-log notice files automatically, which makes things less error-prone.
package main

import (
	"bytes"
	"encoding/json"
	"fmt"
	logger "log"
	"os"
	"strings"

	"gitlab.torproject.org/rgdd/ct/pkg/metadata"
)

func main() {
	directory := "../data"
	logDirectory := fmt.Sprintf("%s/logs", directory)
	noticeFile := "../collect.stdout"

	b, err := os.ReadFile(fmt.Sprintf("%s/metadata.json", directory))
	if err != nil {
		logger.Fatal(err)
	}
	var md metadata.Metadata
	if err := json.Unmarshal(b, &md); err != nil {
		logger.Fatal(err)
	}
	if b, err = os.ReadFile(noticeFile); err != nil {
		logger.Fatal(err)
	}

	lines := bytes.Split(b, []byte("\n"))
	for _, log := range logs(md) {
		id, _ := log.Key.ID()
		desc := *log.Description

		var notes []byte
		var numNotes int
		for _, line := range lines[:len(lines)-1] {
			if strings.Contains(string(line), fmt.Sprintf("NOTICE: %s", desc)) {
				notes = append(notes, line...)
				notes = append(notes, []byte("\n")...)
				numNotes += 1
			}
		}

		if len(notes) == 0 {
			logger.Printf("%s: no notices", desc)
			continue
		}

		logger.Printf("%s: %d notices", desc, numNotes)
		if err := os.WriteFile(fmt.Sprintf("%s/%x/notice.txt", logDirectory, id[:]), notes, 0644); err != nil {
			logger.Fatal(err)
		}
	}
}

func logs(md metadata.Metadata) (logs []metadata.Log) {
	for _, operators := range md.Operators {
		for _, log := range operators.Logs {
			if log.Description == nil {
				logger.Printf("WARNING: skipping log without description")
				continue
			}
			if log.State == nil {
				continue // skip logs with unknown states
			}
			if log.State.Name == metadata.LogStatePending {
				continue // pending logs do not count towards CT-compliance
			}
			if log.State.Name == metadata.LogStateRetired {
				continue // retired logs are not necessarily reachable
			}
			if log.State.Name == metadata.LogStateRejected {
				continue // rejected logs do not count towards CT-compliance
			}

			logs = append(logs, log)
		}
	}
	return
}
```

1 files changed, 23 insertions, 6 deletions

diff --git a/cmd_collect.go b/cmd_collect.go
index 4d93271..742884a 100644
--- a/cmd_collect.go
+++ b/cmd_collect.go
@@ -3,7 +3,6 @@ package main
 import (
 	"container/heap"
 	"context"
-	"crypto/sha256"
 	"encoding/json"
 	"fmt"
 	logger "log"
@@ -121,15 +120,18 @@ func collect(opts options) error {
 			// chunk that a single sequencer can verify and persist
 			//
 			callback := func(eb scanner.EntryBatch) {
-				leafHashes := [][sha256.Size]byte{}
+				c := &chunk.Chunk{Start: eb.Start}
 				for i := 0; i < len(eb.Entries); i++ {
-					leafHashes = append(leafHashes, merkle.HashLeafNode(eb.Entries[i].LeafInput))
+					c.LeafHashes = append(c.LeafHashes, merkle.HashLeafNode(eb.Entries[i].LeafInput))
 				}
-				sans, errs := x509.SANsFromLeafEntries(eb.Start, eb.Entries)
+
+				var errs []error
+				c.SANs, errs = x509.SANsFromLeafEntries(eb.Start, eb.Entries)
 				for _, err := range errs {
-					logger.Printf("NOTICE: %s: %v", *log.Description, err)
+					c.Notes = append(c.Notes, fmt.Sprintf("NOTICE: %s: %v", *log.Description, err))
 				}
-				chunksCh <- &chunk.Chunk{eb.Start, leafHashes, sans}
+
+				chunksCh <- c
 			}
 
 			if err := fetcher.Run(ctx, callback); err != nil {
@@ -275,6 +277,21 @@ func persist(c *chunk.Chunk,
 		return false, err
 	}
 
+	// Persist notes to disk
+	if len(c.Notes) > 0 {
+		fpn, err := os.OpenFile(fmt.Sprintf("%s/%x/%s", opts.logDirectory, logID, opts.noticeFile), os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0644)
+		if err != nil {
+			return false, err
+		}
+		defer fpn.Close()
+		if _, err := fpn.WriteString(strings.Join(c.Notes, "\n") + "\n"); err != nil {
+			return false, err
+		}
+		if err := fpn.Sync(); err != nil {
+			return false, err
+		}
+	}
+
 	// Persist new tree state to disk
 	b, err := json.Marshal(&newTH)
 	if err != nil {