README.md

@@ -2031,6 +2031,29 @@ Because each `database` target has its own archive file, a target's
 webhook with different expiries keep two archives, each pruned on its
 own schedule.
 
+Each `database` target on the webhook page has a **Download** button,
+which returns its archive as one gzipped JSON file,
+`archive-{webhook_name}-{target_name}-{YYYYMMDDTHHMMSSZ}.json.gz`, the
+names made safe as above and the time in UTC. The file holds one
+object: `webhook` and `target`, each an `id` and a `name`;
+`exported_at`; and `archived_events`, one object per archived row with
+every column, keyed by column name. A body that is not valid UTF-8 is
+written in base64, with `"body_encoding": "base64"` beside it. An
+archive that does not exist yet, or was moved away, downloads with an
+empty `archived_events`; the download never creates the file.
+
+The download streams: each row is read and written out compressed
+before the next is read, so neither the archive nor the JSON is held in
+memory. It reads on a connection of its own, inside one read-only
+transaction, so the file holds the archive as it stood when the
+download started, and archive writes go on meanwhile, since under WAL a
+reader never blocks a writer. While it runs, the `-wal` cannot be
+checkpointed past what it reads, so a long download lets the `-wal`
+grow. It finds the file by the stored names under the lock that webhook
+edits, target edits and target creation hold, and lets go once the file
+is open: a rename during the download moves the file without affecting
+it.
+
 Deleting a webhook releases its archives: the delivery engine's cached
 archive writers are dropped and their file handles closed, so nothing
 lingers after the webhook is gone. The archive **files themselves are
@@ -2898,6 +2921,7 @@ returns to the page that was asked for.
 | `POST` | `/hook/{id}/targets`     | Add target to webhook |
 | `GET`  | `/hook/{id}/targets/{targetID}/edit` | Edit target form. The one page that renders a target's destination URL and header values in full, rather than masked |
 | `POST` | `/hook/{id}/targets/{targetID}/edit` | Edit target submission |
+| `GET`  | `/hook/{id}/targets/{targetID}/download` | Download a `database` target's archive as one gzipped JSON file. See [Database Architecture](#database-architecture) |
 | `POST` | `/hook/{id}/targets/{targetID}/delete` | Delete a target |
 | `POST` | `/hook/{id}/targets/{targetID}/toggle` | Enable or disable a target |
 
@@ -2979,6 +3003,7 @@ webhooker/
 │   │   ├── target_slack.go    # Slack/Mattermost incoming-webhook target
 │   │   ├── target_database.go # Database archive target
 │   │   ├── target_database_archive.go  # Archive file lifecycle and pruning
+│   │   ├── target_database_export.go   # Archive download as gzipped JSON
 │   │   ├── target_log.go      # Log target (stdout)
 │   │   ├── target_config_view.go  # Masked target config for templates
 │   │   ├── archive_sweeper.go # Periodic pruning of idle archives

internal/delivery/target_database.go

@@ -3,7 +3,6 @@ package delivery
 import (
 	"context"
 	"fmt"
-	"path/filepath"
 	"strings"
 	"sync"
 	"time"
@@ -277,10 +276,9 @@ func (t *databaseTarget) releaseSweepWriter(
 }
 
 // newWriter builds the writer for a database target's archive. The
-// file lives beside the webhook's event database in the data
-// directory and is named for the webhook and the target as the main
-// database has them now; from then on only rename changes the name
-// the writer uses. It does not touch the archive file.
+// file is the one ArchivePath gives for the webhook and the target as
+// the main database names them now; from then on only rename changes
+// the name the writer uses. It does not touch the archive file.
 func (t *databaseTarget) newWriter(
 	targetID string,
 ) (*archiveWriter, error) {
@@ -299,12 +297,10 @@ func (t *databaseTarget) newWriter(
 		)
 	}
 
-	dir := filepath.Dir(t.eng.dbManager.DBPath(target.WebhookID))
-	name := ArchiveFileName(
-		target.Webhook.Name, target.Name, target.ID,
+	w := newArchiveWriter(
+		ArchivePath(t.eng.dbManager, &target.Webhook, &target),
+		t.eng.log,
 	)
-
-	w := newArchiveWriter(filepath.Join(dir, name), t.eng.log)
 	w.webhookID = target.WebhookID
 
 	return w, nil

internal/delivery/target_database_export.go

@@ -0,0 +1,275 @@
+package delivery
+
+import (
+	"compress/gzip"
+	"context"
+	"database/sql"
+	"encoding/base64"
+	"encoding/json"
+	"fmt"
+	"io"
+	"log/slog"
+	"path/filepath"
+	"time"
+	"unicode/utf8"
+
+	"gorm.io/driver/sqlite"
+	"gorm.io/gorm"
+	"sneak.berlin/go/webhooker/internal/database"
+	"sneak.berlin/go/webhooker/internal/gormlog"
+)
+
+// archiveTableQuery counts the archive's table: 0 when the archive
+// writer has created the file but not yet the table in it.
+const archiveTableQuery = "SELECT count(*) FROM sqlite_master " +
+	"WHERE type = 'table' AND name = 'archived_events'"
+
+// ArchivePath returns where a database target's archive file is: in
+// the data directory, beside the webhook's event database, under the
+// name ArchiveFileName gives it.
+func ArchivePath(
+	dbMgr *database.WebhookDBManager,
+	webhook *database.Webhook,
+	target *database.Target,
+) string {
+	return filepath.Join(
+		filepath.Dir(dbMgr.DBPath(webhook.ID)),
+		ArchiveFileName(webhook.Name, target.Name, target.ID),
+	)
+}
+
+// ArchiveExportFileName returns the name a database target's archive
+// downloads under:
+// archive-WEBHOOKNAME-TARGETNAME-YYYYMMDDTHHMMSSZ.json.gz, the names
+// made safe as in ArchiveFileName and the time in UTC.
+func ArchiveExportFileName(
+	webhookName, targetName string, at time.Time,
+) string {
+	return "archive-" + archiveNamePart(webhookName) + "-" +
+		archiveNamePart(targetName) + "-" +
+		at.UTC().Format("20060102T150405Z") + ".json.gz"
+}
+
+// ArchiveExport is a database target's archive opened for download.
+// It reads the file on its own connection, inside one read-only
+// transaction, so it writes out the archive as it stood when
+// OpenArchiveExport returned.
+//
+// Archives are in WAL mode, where a reader works from a snapshot and
+// never blocks a writer: archive writes go on while an export is open,
+// and the export does not see them. SQLite cannot checkpoint the -wal
+// past an open snapshot, so the -wal grows until the export is closed.
+type ArchiveExport struct {
+	db *sql.DB
+	tx *gorm.DB
+
+	// empty is true when there is nothing to read: no file, or a file
+	// without the archive's table yet.
+	empty bool
+}
+
+// exportedName is how an export names its webhook and its target.
+type exportedName struct {
+	ID   string `json:"id"`
+	Name string `json:"name"`
+}
+
+// OpenArchiveExport opens the archive file at path for export and
+// takes the snapshot the export reads. It never creates the file: with
+// no file at path, the export has no rows.
+//
+// Once it has returned, the file is open, so a rename or a move of it
+// does not affect the export, which reads the same file under its new
+// name.
+//
+// The transaction lasts as long as ctx does, so ctx must last for the
+// whole export.
+func OpenArchiveExport(
+	ctx context.Context, path string, log *slog.Logger,
+) (*ArchiveExport, error) {
+	if !fileExists(path) {
+		return &ArchiveExport{empty: true}, nil
+	}
+
+	db, err := database.OpenSQLite(path, archiveModeExisting)
+	if err != nil {
+		return nil, fmt.Errorf("opening archive %s: %w", path, err)
+	}
+
+	gdb, err := gorm.Open(
+		sqlite.Dialector{Conn: db}, &gorm.Config{
+			// Never leave this at GORM's default. See
+			// internal/gormlog.
+			Logger: gormlog.New(log),
+		},
+	)
+	if err != nil {
+		_ = db.Close()
+
+		return nil, fmt.Errorf("opening archive %s: %w", path, err)
+	}
+
+	// ReadOnly makes the driver begin a deferred transaction in place
+	// of the BEGIN IMMEDIATE the connection string asks for, so the
+	// export never takes the archive's write lock.
+	tx := gdb.WithContext(ctx).Begin(&sql.TxOptions{ReadOnly: true})
+	if tx.Error != nil {
+		_ = db.Close()
+
+		return nil, fmt.Errorf("reading archive %s: %w", path, tx.Error)
+	}
+
+	// The transaction's first read is what takes the snapshot.
+	var tables int
+
+	err = tx.Raw(archiveTableQuery).Row().Scan(&tables)
+	if err != nil {
+		_ = tx.Rollback()
+		_ = db.Close()
+
+		return nil, fmt.Errorf("reading archive %s: %w", path, err)
+	}
+
+	return &ArchiveExport{db: db, tx: tx, empty: tables == 0}, nil
+}
+
+// WriteGzipJSON writes the export to w as one gzipped JSON object:
+// webhook and target, each an id and a name; exported_at; and
+// archived_events, one object per archived row, keyed by column name.
+// A body that is not valid UTF-8 cannot be a JSON string, so it is
+// written in base64, with "body_encoding": "base64" beside it.
+//
+// Each row is written out before the next is read, so neither the
+// archive nor its JSON is ever held in memory whole. After an error
+// the gzip stream is left unfinished, so what was written does not
+// decompress as a whole file.
+func (x *ArchiveExport) WriteGzipJSON(
+	ctx context.Context,
+	w io.Writer,
+	webhook *database.Webhook,
+	target *database.Target,
+	exportedAt time.Time,
+) error {
+	head, err := json.Marshal(map[string]any{
+		"webhook":     exportedName{ID: webhook.ID, Name: webhook.Name},
+		"target":      exportedName{ID: target.ID, Name: target.Name},
+		"exported_at": exportedAt.UTC(),
+	})
+	if err != nil {
+		return fmt.Errorf("encoding archive export: %w", err)
+	}
+
+	zw := gzip.NewWriter(w)
+
+	err = x.writeJSON(ctx, zw, head)
+	if err != nil {
+		return fmt.Errorf("writing archive export: %w", err)
+	}
+
+	return zw.Close()
+}
+
+// Close ends the export's transaction and closes its connection.
+func (x *ArchiveExport) Close() error {
+	if x.db == nil {
+		return nil
+	}
+
+	_ = x.tx.Rollback()
+
+	return x.db.Close()
+}
+
+// writeJSON writes head with archived_events added as its last key,
+// the rows going into it one at a time.
+func (x *ArchiveExport) writeJSON(
+	ctx context.Context, w io.Writer, head []byte,
+) error {
+	// head goes out without its closing brace, so that
+	// archived_events can follow it.
+	_, err := w.Write(head[:len(head)-1])
+	if err != nil {
+		return err
+	}
+
+	_, err = io.WriteString(w, `,"archived_events":[`)
+	if err != nil {
+		return err
+	}
+
+	err = x.writeRows(ctx, w)
+	if err != nil {
+		return err
+	}
+
+	_, err = io.WriteString(w, "\n]}\n")
+
+	return err
+}
+
+// writeRows writes each archived row to w, oldest first, one per line,
+// separated by commas.
+func (x *ArchiveExport) writeRows(ctx context.Context, w io.Writer) error {
+	if x.empty {
+		return nil
+	}
+
+	rows, err := x.tx.WithContext(ctx).
+		Model(&archivedEvent{}).Order("id").Rows()
+	if err != nil {
+		return err
+	}
+
+	defer func() { _ = rows.Close() }()
+
+	for sep := "\n"; rows.Next(); sep = ",\n" {
+		var ev archivedEvent
+
+		err = x.tx.ScanRows(rows, &ev)
+		if err != nil {
+			return err
+		}
+
+		_, err = io.WriteString(w, sep)
+		if err != nil {
+			return err
+		}
+
+		err = writeRow(w, &ev)
+		if err != nil {
+			return err
+		}
+	}
+
+	return rows.Err()
+}
+
+// writeRow writes an archived row to w as a JSON object keyed by
+// column name, its body in base64 when it is not valid UTF-8.
+func writeRow(w io.Writer, ev *archivedEvent) error {
+	row := map[string]any{
+		"id":            ev.ID,
+		"event_id":      ev.EventID,
+		"webhook_id":    ev.WebhookID,
+		"entrypoint_id": ev.EntrypointID,
+		"method":        ev.Method,
+		"headers":       ev.Headers,
+		"body":          ev.Body,
+		"content_type":  ev.ContentType,
+		"archived_at":   ev.ArchivedAt.UTC(),
+	}
+
+	if !utf8.ValidString(ev.Body) {
+		row["body"] = base64.StdEncoding.EncodeToString([]byte(ev.Body))
+		row["body_encoding"] = "base64"
+	}
+
+	line, err := json.Marshal(row)
+	if err != nil {
+		return err
+	}
+
+	_, err = w.Write(line)
+
+	return err
+}

internal/delivery/target_database_export_test.go

@@ -0,0 +1,412 @@
+package delivery_test
+
+import (
+	"bufio"
+	"bytes"
+	"compress/gzip"
+	"crypto/rand"
+	"encoding/base64"
+	"encoding/json"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"runtime"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"sneak.berlin/go/webhooker/internal/database"
+	"sneak.berlin/go/webhooker/internal/delivery"
+)
+
+// The webhook and the target the export tests' archives belong to.
+const (
+	exportWebhookID   = "wh-export"
+	exportWebhookName = "Orders (EU)"
+	exportTargetID    = "tgt-export"
+	exportTargetName  = "Long-term archive"
+)
+
+const (
+	// binaryBody is a body that is not valid UTF-8.
+	binaryBody = "\xff\xfe\x00\x01binary\x80"
+
+	// openedEventID is the event the snapshot tests archive before
+	// they open the export.
+	openedEventID = "opened"
+)
+
+// writeExportTo writes export to w as the archive of the export tests'
+// webhook and target, exported at 2026-10-02T12:03:04Z.
+func writeExportTo(
+	t *testing.T, export *delivery.ArchiveExport, w io.Writer,
+) error {
+	t.Helper()
+
+	return export.WriteGzipJSON(
+		t.Context(), w,
+		&database.Webhook{
+			BaseModel: database.BaseModel{ID: exportWebhookID},
+			Name:      exportWebhookName,
+		},
+		&database.Target{
+			BaseModel: database.BaseModel{ID: exportTargetID},
+			Name:      exportTargetName,
+		},
+		time.Date(2026, 10, 2, 12, 3, 4, 0, time.UTC),
+	)
+}
+
+// exportArchive runs a whole export of the archive at path and returns
+// its JSON, decompressed and parsed.
+func exportArchive(t *testing.T, path string) map[string]any {
+	t.Helper()
+
+	export, err := delivery.OpenArchiveExport(
+		t.Context(), path, archiveTestLogger(),
+	)
+	require.NoError(t, err)
+
+	defer func() { require.NoError(t, export.Close()) }()
+
+	return writeExport(t, export)
+}
+
+// writeExport writes an opened export and returns its JSON,
+// decompressed and parsed. Reading to the end makes the gzip reader
+// check that the stream was finished.
+func writeExport(
+	t *testing.T, export *delivery.ArchiveExport,
+) map[string]any {
+	t.Helper()
+
+	var buf bytes.Buffer
+
+	require.NoError(t, writeExportTo(t, export, &buf))
+
+	zr, err := gzip.NewReader(&buf)
+	require.NoError(t, err)
+
+	raw, err := io.ReadAll(zr)
+	require.NoError(t, err)
+
+	var got map[string]any
+
+	require.NoError(t, json.Unmarshal(raw, &got))
+
+	return got
+}
+
+// exportedEvents returns an export's archived_events.
+func exportedEvents(t *testing.T, got map[string]any) []map[string]any {
+	t.Helper()
+
+	list, ok := got["archived_events"].([]any)
+	require.True(t, ok, "archived_events must be an array: %v", got)
+
+	events := make([]map[string]any, len(list))
+
+	for i, v := range list {
+		events[i], ok = v.(map[string]any)
+		require.True(t, ok, "an archived event must be an object: %v", v)
+	}
+
+	return events
+}
+
+// exportedEventIDs returns the event_id of each of an export's
+// archived_events.
+func exportedEventIDs(t *testing.T, got map[string]any) []string {
+	t.Helper()
+
+	events := exportedEvents(t, got)
+	ids := make([]string, 0, len(events))
+
+	for _, ev := range events {
+		ids = append(ids, fmt.Sprint(ev["event_id"]))
+	}
+
+	return ids
+}
+
+// TestArchiveExport_MatchesStoredRows proves an export holds the
+// webhook, the target, the time, and every column of every stored
+// row: a body that is valid UTF-8 as a string, and one that is not in
+// base64, marked as such.
+func TestArchiveExport_MatchesStoredRows(t *testing.T) {
+	t.Parallel()
+
+	path := filepath.Join(t.TempDir(), "archive.db")
+	w := delivery.NewExportArchiveWriter(path, archiveTestLogger(), 0)
+	bodies := []string{`{"order":1}`, "plain text", "", binaryBody}
+
+	for i, body := range bodies {
+		require.NoError(t, w.Write(delivery.ExportArchivedEvent{
+			EventID:      fmt.Sprintf("ev-%d", i),
+			WebhookID:    exportWebhookID,
+			EntrypointID: "ep-1",
+			Method:       "POST",
+			Headers:      `{"X-Test":["yes"]}`,
+			Body:         body,
+			ContentType:  testContentType,
+		}, 0))
+	}
+
+	var stored []delivery.ExportArchivedEvent
+
+	require.NoError(t, openArchiveDBForRead(t, path).
+		Order("id").Find(&stored).Error)
+
+	got := exportArchive(t, path)
+
+	assert.Equal(t,
+		map[string]any{"id": exportWebhookID, "name": exportWebhookName},
+		got["webhook"],
+	)
+	assert.Equal(t,
+		map[string]any{"id": exportTargetID, "name": exportTargetName},
+		got["target"],
+	)
+	assert.Equal(t, "2026-10-02T12:03:04Z", got["exported_at"])
+
+	events := exportedEvents(t, got)
+	require.Len(t, events, len(bodies))
+
+	for i, row := range stored {
+		assertExportedRow(t, row, events[i])
+	}
+}
+
+// assertExportedRow checks that ev, from an export, holds every column
+// of the stored row.
+func assertExportedRow(
+	t *testing.T, row delivery.ExportArchivedEvent, ev map[string]any,
+) {
+	t.Helper()
+
+	archivedAt, err := time.Parse(
+		time.RFC3339Nano, fmt.Sprint(ev["archived_at"]),
+	)
+	require.NoError(t, err)
+	assert.True(t, archivedAt.Equal(row.ArchivedAt))
+
+	assert.EqualValues(t, row.ID, ev["id"])
+	assert.Equal(t, row.EventID, ev["event_id"])
+	assert.Equal(t, row.WebhookID, ev["webhook_id"])
+	assert.Equal(t, row.EntrypointID, ev["entrypoint_id"])
+	assert.Equal(t, row.Method, ev["method"])
+	assert.Equal(t, row.Headers, ev["headers"])
+	assert.Equal(t, row.ContentType, ev["content_type"])
+
+	if row.Body != binaryBody {
+		assert.Equal(t, row.Body, ev["body"])
+		assert.Len(t, ev, 9, "the nine columns and nothing else: %v", ev)
+
+		return
+	}
+
+	body, err := base64.StdEncoding.DecodeString(fmt.Sprint(ev["body"]))
+	require.NoError(t, err)
+	assert.Equal(t, binaryBody, string(body))
+	assert.Equal(t, "base64", ev["body_encoding"])
+	assert.Len(t, ev, 10, "the nine columns and body_encoding: %v", ev)
+}
+
+// TestArchiveExport_Empty proves an archive with nothing in it exports
+// as an empty archived_events: no file, which the export must not
+// create; a file the archive writer has not yet put its table in; and
+// a table with no rows.
+func TestArchiveExport_Empty(t *testing.T) {
+	t.Parallel()
+
+	dir := t.TempDir()
+	missing := filepath.Join(dir, "missing.db")
+	noTable := filepath.Join(dir, "no-table.db")
+	noRows := filepath.Join(dir, "no-rows.db")
+
+	require.NoError(t, os.WriteFile(noTable, nil, 0o600))
+	require.NoError(t,
+		delivery.NewExportArchiveWriter(noRows, archiveTestLogger(), 0).
+			Open(0),
+	)
+
+	for _, path := range []string{missing, noTable, noRows} {
+		assert.Empty(t, exportedEvents(t, exportArchive(t, path)), path)
+	}
+
+	for _, suffix := range archiveFileSuffixes() {
+		assert.NoFileExists(t, missing+suffix)
+	}
+}
+
+// TestArchiveExport_ReadsOneSnapshot proves an export writes the
+// archive as it was when it was opened, and holds up no archive
+// write: a row written while the export is open is stored, and is not
+// in the export. A write held up for the whole busy timeout would
+// fail.
+func TestArchiveExport_ReadsOneSnapshot(t *testing.T) {
+	t.Parallel()
+
+	path := filepath.Join(t.TempDir(), "archive.db")
+	w := delivery.NewExportArchiveWriter(path, archiveTestLogger(), 0)
+
+	require.NoError(t, w.Write(delivery.ExportArchivedEvent{EventID: openedEventID}, 0))
+
+	export, err := delivery.OpenArchiveExport(
+		t.Context(), path, archiveTestLogger(),
+	)
+	require.NoError(t, err)
+
+	defer func() { require.NoError(t, export.Close()) }()
+
+	require.NoError(t, w.Write(delivery.ExportArchivedEvent{EventID: "during"}, 0))
+
+	assert.Equal(t,
+		[]string{openedEventID}, exportedEventIDs(t, writeExport(t, export)),
+	)
+
+	var stored int64
+
+	require.NoError(t, openArchiveDBForRead(t, path).
+		Model(&delivery.ExportArchivedEvent{}).Count(&stored).Error)
+	assert.Equal(t, int64(2), stored)
+}
+
+// TestArchiveExport_SurvivesRename proves that renaming the archive
+// while an export of it is open, as renaming its webhook or target
+// does, leaves the export reading the same file.
+func TestArchiveExport_SurvivesRename(t *testing.T) {
+	t.Parallel()
+
+	path := filepath.Join(t.TempDir(), "archive-old.db")
+	w := delivery.NewExportArchiveWriter(path, archiveTestLogger(), 0)
+
+	require.NoError(t, w.Write(delivery.ExportArchivedEvent{EventID: openedEventID}, 0))
+
+	export, err := delivery.OpenArchiveExport(
+		t.Context(), path, archiveTestLogger(),
+	)
+	require.NoError(t, err)
+
+	defer func() { require.NoError(t, export.Close()) }()
+
+	require.NoError(t, w.Rename("archive-new.db"))
+	require.NoError(t, w.Write(delivery.ExportArchivedEvent{EventID: "after"}, 0))
+	require.NoFileExists(t, path)
+
+	assert.Equal(t,
+		[]string{openedEventID}, exportedEventIDs(t, writeExport(t, export)),
+	)
+}
+
+// heapPeak is an io.Writer that discards what it is given and records
+// the largest heap it saw at a write. It collects garbage before each
+// reading, so the heap it reads is what is still held.
+type heapPeak struct {
+	max uint64
+}
+
+func (p *heapPeak) Write(b []byte) (int, error) {
+	var m runtime.MemStats
+
+	runtime.GC()
+	runtime.ReadMemStats(&m)
+	p.max = max(p.max, m.HeapAlloc)
+
+	return len(b), nil
+}
+
+// exportHeapGrowth exports an archive of rows random bodies, each
+// bodySize bytes of base64, and returns how far the heap rose above
+// where it stood when the export began, at its highest.
+func exportHeapGrowth(t *testing.T, rows, bodySize int) uint64 {
+	t.Helper()
+
+	path := filepath.Join(t.TempDir(), "archive.db")
+	w := delivery.NewExportArchiveWriter(path, archiveTestLogger(), 0)
+
+	// Base64 makes four characters of every three bytes.
+	random := make([]byte, bodySize/4*3)
+
+	for range rows {
+		_, _ = rand.Read(random)
+
+		require.NoError(t, w.Write(delivery.ExportArchivedEvent{
+			Body: base64.StdEncoding.EncodeToString(random),
+		}, 0))
+	}
+
+	export, err := delivery.OpenArchiveExport(
+		t.Context(), path, archiveTestLogger(),
+	)
+	require.NoError(t, err)
+
+	defer func() { require.NoError(t, export.Close()) }()
+
+	runtime.GC()
+
+	var start runtime.MemStats
+
+	runtime.ReadMemStats(&start)
+
+	// Through a buffer, the heap is read once per 8 KiB of output
+	// rather than at each of gzip's small writes, which takes far
+	// longer.
+	peak := &heapPeak{max: start.HeapAlloc}
+	buffered := bufio.NewWriterSize(peak, 8<<10)
+
+	require.NoError(t, writeExportTo(t, export, buffered))
+	require.NoError(t, buffered.Flush())
+
+	return peak.max - start.HeapAlloc
+}
+
+// TestArchiveExport_Streams proves an export holds neither the archive
+// nor its output in memory whole: exporting 384 KiB more of archive
+// raises the heap's peak by less than half of that. The export's own
+// memory, mostly gzip's compressor, is the same for both archives, so
+// it cancels out. The bodies are random bytes in base64, which gzip
+// shrinks by only a quarter, so an export that read every row before
+// writing, or built the JSON or the gzipped file before writing it,
+// would raise the peak by at least three quarters of the difference.
+//
+// The smaller archive has two rows so that its export, too, writes
+// out more than the 8 KiB buffer in exportHeapGrowth before it ends:
+// the heap must be read while the export's own memory is held.
+//
+//nolint:paralleltest // It measures the heap, which tests share.
+func TestArchiveExport_Streams(t *testing.T) {
+	const (
+		bodySize  = 16 << 10
+		smallRows = 2
+		largeRows = smallRows + 24
+		limit     = (largeRows - smallRows) * bodySize / 2
+	)
+
+	small := exportHeapGrowth(t, smallRows, bodySize)
+	large := exportHeapGrowth(t, largeRows, bodySize)
+
+	assert.Less(t, large, small+limit,
+		"the heap rose by %d for %d rows and by %d for %d rows",
+		small, smallRows, large, largeRows,
+	)
+}
+
+// TestArchiveExportFileName proves the download is named for the
+// webhook and the target, with the names made safe as for the archive
+// file, and the export time in UTC.
+func TestArchiveExportFileName(t *testing.T) {
+	t.Parallel()
+
+	cest := time.FixedZone("CEST", int((2 * time.Hour).Seconds()))
+
+	assert.Equal(t,
+		"archive-orders-eu-long-term-archive-20261002T120304Z.json.gz",
+		delivery.ArchiveExportFileName(
+			exportWebhookName, exportTargetName,
+			time.Date(2026, 10, 2, 14, 3, 4, 0, cest),
+		),
+	)
+}

internal/handlers/handlers.go

@@ -97,7 +97,8 @@ type Handlers struct {
 	// names through the archive rename, the save and any move back.
 	// Interleaved, one could rename an archive between another's
 	// rename and save, leaving the file named for one edit and the
-	// stored names from the other.
+	// stored names from the other. An archive download holds it while
+	// it reads the stored names and opens the file they give.
 	renameMu sync.Mutex
 
 	// dummyVerifications counts the equivalent-cost verifications

internal/handlers/source_management_test.go

@@ -191,6 +191,7 @@ func storedRetentionDays(
 type sourceTestEnv struct {
 	handlers *handlers.Handlers
 	db       *database.Database
+	dbMgr    *database.WebhookDBManager
 	archives *recordingArchives
 	cookies  []*http.Cookie
 }
@@ -204,9 +205,11 @@ func setupSourceTest(t *testing.T) *sourceTestEnv {
 
 	var db *database.Database
 
+	var dbMgr *database.WebhookDBManager
+
 	var archives *recordingArchives
 
-	app := newTestApp(t, &h, &sess, &db, &archives)
+	app := newTestApp(t, &h, &sess, &db, &dbMgr, &archives)
 	app.RequireStart()
 
 	t.Cleanup(app.RequireStop)
@@ -214,6 +217,7 @@ func setupSourceTest(t *testing.T) *sourceTestEnv {
 	return &sourceTestEnv{
 		handlers: h,
 		db:       db,
+		dbMgr:    dbMgr,
 		archives: archives,
 		cookies: authenticatedCookies(
 			t, sess, sourceTestUserID, "sourceuser",

internal/handlers/target_download.go

@@ -0,0 +1,121 @@
+package handlers
+
+import (
+	"context"
+	"errors"
+	"net/http"
+	"time"
+
+	"sneak.berlin/go/webhooker/internal/database"
+	"sneak.berlin/go/webhooker/internal/delivery"
+)
+
+// downloadWriteTimeout is how long one write of a download may wait
+// for a client that has stopped reading.
+const downloadWriteTimeout = 60 * time.Second
+
+// HandleTargetDownload serves a database target's archive as one
+// gzipped JSON file, named for the webhook, the target and the time;
+// see delivery.ArchiveExport.WriteGzipJSON for what it holds. Other
+// target types have no archive and are a 404.
+//
+// A download runs for as long as the client keeps reading: it reads
+// under a context the request limit does not cancel, and gives each
+// write its own deadline in place of the server's write timeout. It
+// stops when a write fails.
+func (h *Handlers) HandleTargetDownload() http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		ctx := context.WithoutCancel(r.Context())
+
+		webhook, target, export, ok := h.openTargetArchive(ctx, w, r)
+		if !ok {
+			return
+		}
+
+		defer func() { _ = export.Close() }()
+
+		now := time.Now()
+
+		w.Header().Set("Content-Type", "application/gzip")
+		w.Header().Set(
+			"Content-Disposition",
+			`attachment; filename="`+delivery.ArchiveExportFileName(
+				webhook.Name, target.Name, now,
+			)+`"`,
+		)
+
+		err := export.WriteGzipJSON(
+			ctx,
+			downloadWriter{w: w, rc: http.NewResponseController(w)},
+			&webhook, target, now,
+		)
+		if err != nil {
+			h.log.Error(
+				"failed to export archive",
+				"target_id", target.ID,
+				"error", err,
+			)
+
+			// The 200 has gone out. Aborting the connection is what
+			// tells the client the file is incomplete.
+			panic(http.ErrAbortHandler)
+		}
+	}
+}
+
+// downloadWriter writes a download to the client, giving each write
+// downloadWriteTimeout to finish.
+type downloadWriter struct {
+	w  http.ResponseWriter
+	rc *http.ResponseController
+}
+
+func (d downloadWriter) Write(b []byte) (int, error) {
+	// A writer that has no write deadline, such as a test's recorder,
+	// answers http.ErrNotSupported and needs none extended.
+	err := d.rc.SetWriteDeadline(time.Now().Add(downloadWriteTimeout))
+	if err != nil && !errors.Is(err, http.ErrNotSupported) {
+		return 0, err
+	}
+
+	return d.w.Write(b)
+}
+
+// openTargetArchive opens the archive of the request's database target
+// for export, with its reads under ctx. It reports false once it has
+// written the response.
+//
+// It holds renameMu, which every archive rename runs under, while it
+// reads the stored names and opens the file, so the file it opens is
+// the one those names give. It lets go before the export is streamed:
+// once the file is open, a rename does not affect the export.
+func (h *Handlers) openTargetArchive(
+	ctx context.Context,
+	w http.ResponseWriter,
+	r *http.Request,
+) (database.Webhook, *database.Target, *delivery.ArchiveExport, bool) {
+	h.renameMu.Lock()
+	defer h.renameMu.Unlock()
+
+	webhook, target, ok := h.ownedTarget(w, r)
+	if !ok {
+		return database.Webhook{}, nil, nil, false
+	}
+
+	if target.Type != database.TargetTypeDatabase {
+		h.renderError(w, r, http.StatusNotFound)
+
+		return database.Webhook{}, nil, nil, false
+	}
+
+	export, err := delivery.OpenArchiveExport(
+		ctx, delivery.ArchivePath(h.dbMgr, &webhook, target), h.log,
+	)
+	if err != nil {
+		h.serverError(w, r, "failed to open archive for export", err)
+
+		return database.Webhook{}, nil, nil, false
+	}
+
+	return webhook, target, export, true
+}

internal/handlers/target_download_test.go

@@ -0,0 +1,379 @@
+package handlers_test
+
+import (
+	"bytes"
+	"compress/gzip"
+	"context"
+	"crypto/rand"
+	"encoding/json"
+	"errors"
+	"io"
+	"log/slog"
+	"net"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"sneak.berlin/go/webhooker/internal/config"
+	"sneak.berlin/go/webhooker/internal/database"
+	"sneak.berlin/go/webhooker/internal/delivery"
+	"sneak.berlin/go/webhooker/internal/middleware"
+)
+
+// errClientGone is the write failure of a client that has gone away.
+var errClientGone = errors.New("client gone")
+
+// downloadPath is the archive download route of a target.
+func downloadPath(webhookID, targetID string) string {
+	return "/hook/" + webhookID + "/targets/" + targetID + "/download"
+}
+
+// renameTarget submits the edit form renaming a target to Renamed.
+func renameTarget(
+	env *sourceTestEnv, webhookID, targetID string,
+) *httptest.ResponseRecorder {
+	form := url.Values{}
+	form.Set("name", "Renamed")
+
+	return submitTargetEdit(env, webhookID, targetID, form)
+}
+
+// TestHandleTargetDownload proves a database target's archive
+// downloads as a gzipped JSON attachment named for the webhook, the
+// target and the time, here with no archive file yet, so with no
+// rows; and that a target of another type has no download.
+func TestHandleTargetDownload(t *testing.T) {
+	t.Parallel()
+
+	env := setupSourceTest(t)
+	wh := seedWebhookWithRetention(t, env.db, 7)
+	archive := seedTarget(t, env.db, wh.ID, database.TargetTypeDatabase)
+	logTarget := seedTarget(t, env.db, wh.ID, database.TargetTypeLog)
+
+	w := serveTarget(
+		env, http.MethodGet, downloadPath(wh.ID, archive.ID), nil,
+	)
+	require.Equal(t, http.StatusOK, w.Code, w.Body.String())
+	assert.Equal(t, "application/gzip", w.Header().Get("Content-Type"))
+	assert.Regexp(t,
+		`^attachment; filename="archive-seeded-t-database-`+
+			`\d{8}T\d{6}Z\.json\.gz"$`,
+		w.Header().Get("Content-Disposition"),
+	)
+
+	zr, err := gzip.NewReader(w.Body)
+	require.NoError(t, err)
+
+	var got map[string]json.RawMessage
+
+	require.NoError(t, json.NewDecoder(zr).Decode(&got))
+	assert.JSONEq(t,
+		`{"id":"`+archive.ID+`","name":"t-database"}`,
+		string(got["target"]),
+	)
+	assert.JSONEq(t, `[]`, string(got["archived_events"]))
+
+	w = serveTarget(
+		env, http.MethodGet, downloadPath(wh.ID, logTarget.ID), nil,
+	)
+	assert.Equal(t, http.StatusNotFound, w.Code)
+}
+
+// TestHandleTargetDownload_WaitsForRename proves a download reads the
+// target's names and opens its archive under the lock a rename holds:
+// started while an edit is renaming the archive, it waits, and is
+// named for the target's new name.
+func TestHandleTargetDownload_WaitsForRename(t *testing.T) {
+	t.Parallel()
+
+	env := setupSourceTest(t)
+	wh := seedWebhookWithRetention(t, env.db, 7)
+	archive := seedTarget(t, env.db, wh.ID, database.TargetTypeDatabase)
+
+	renaming, release := env.archives.BlockNextRename()
+	edited := make(chan *httptest.ResponseRecorder, 1)
+
+	go func() {
+		edited <- renameTarget(env, wh.ID, archive.ID)
+	}()
+
+	<-renaming
+
+	downloaded := make(chan *httptest.ResponseRecorder, 1)
+
+	go func() {
+		downloaded <- serveTarget(
+			env, http.MethodGet, downloadPath(wh.ID, archive.ID), nil,
+		)
+	}()
+
+	select {
+	case <-downloaded:
+		release()
+		t.Fatal("the download did not wait for the rename")
+	case <-time.After(100 * time.Millisecond):
+	}
+
+	release()
+	require.Equal(t, http.StatusSeeOther, (<-edited).Code)
+
+	w := <-downloaded
+	require.Equal(t, http.StatusOK, w.Code)
+	assert.Contains(t,
+		w.Header().Get("Content-Disposition"), "archive-seeded-renamed-",
+	)
+}
+
+// stalledWriter is a response writer whose first write waits until
+// resume is closed, closing writing when it starts to wait.
+type stalledWriter struct {
+	*httptest.ResponseRecorder
+
+	once    sync.Once
+	writing chan struct{}
+	resume  chan struct{}
+}
+
+func (s *stalledWriter) Write(b []byte) (int, error) {
+	s.once.Do(func() {
+		close(s.writing)
+		<-s.resume
+	})
+
+	return s.ResponseRecorder.Write(b)
+}
+
+// TestHandleTargetDownload_StreamsWithoutTheLock proves a download
+// lets go of the rename lock once its archive is open: while the
+// download is stalled writing, an edit can still rename the target.
+func TestHandleTargetDownload_StreamsWithoutTheLock(t *testing.T) {
+	t.Parallel()
+
+	env := setupSourceTest(t)
+	wh := seedWebhookWithRetention(t, env.db, 7)
+	archive := seedTarget(t, env.db, wh.ID, database.TargetTypeDatabase)
+
+	req := httptest.NewRequestWithContext(
+		t.Context(), http.MethodGet, downloadPath(wh.ID, archive.ID), nil,
+	)
+	for _, c := range env.cookies {
+		req.AddCookie(c)
+	}
+
+	sw := &stalledWriter{
+		ResponseRecorder: httptest.NewRecorder(),
+		writing:          make(chan struct{}),
+		resume:           make(chan struct{}),
+	}
+	downloaded := make(chan struct{})
+
+	go func() {
+		targetRouter(env).ServeHTTP(sw, req)
+		close(downloaded)
+	}()
+
+	<-sw.writing
+
+	edited := make(chan *httptest.ResponseRecorder, 1)
+
+	go func() {
+		edited <- renameTarget(env, wh.ID, archive.ID)
+	}()
+
+	select {
+	case w := <-edited:
+		assert.Equal(t, http.StatusSeeOther, w.Code)
+	case <-time.After(10 * time.Second):
+		t.Error("the rename waited for the download")
+	}
+
+	close(sw.resume)
+	<-downloaded
+	assert.Equal(t, http.StatusOK, sw.Code)
+}
+
+// seedArchive writes rows to the archive file at path, each with a
+// body of bodySize random bytes, which do not compress. Its table has
+// only the columns the test fills; an export writes the others empty.
+func seedArchive(t *testing.T, path string, rows, bodySize int) {
+	t.Helper()
+
+	db, err := database.OpenSQLite(path, database.SQLiteModeCreate)
+	require.NoError(t, err)
+
+	defer func() { require.NoError(t, db.Close()) }()
+
+	_, err = db.ExecContext(t.Context(),
+		"CREATE TABLE archived_events (id INTEGER PRIMARY KEY, body TEXT)",
+	)
+	require.NoError(t, err)
+
+	body := make([]byte, bodySize)
+
+	for range rows {
+		_, _ = rand.Read(body)
+
+		_, err = db.ExecContext(t.Context(),
+			"INSERT INTO archived_events (body) VALUES (?)", string(body),
+		)
+		require.NoError(t, err)
+	}
+}
+
+// limitedServer serves the target routes as the server does, behind the
+// access log, whose lines it returns, and the request limit, here
+// limit, which is also its write timeout. Each connection's send buffer
+// is a few KiB, so a larger response is still being written while its
+// client is not reading.
+func limitedServer(
+	t *testing.T, env *sourceTestEnv, limit time.Duration,
+) (*httptest.Server, *bytes.Buffer) {
+	t.Helper()
+
+	const sendBuffer = 4 << 10
+
+	logBuf := new(bytes.Buffer)
+	mw := middleware.NewForTest(
+		slog.New(slog.NewJSONHandler(logBuf, nil)),
+		&config.Config{Environment: config.EnvironmentDev},
+		nil,
+	)
+
+	srv := httptest.NewUnstartedServer(
+		mw.Logging()(mw.Timeout(limit)(targetRouter(env))),
+	)
+	srv.Config.WriteTimeout = limit
+	srv.Config.ConnContext = func(
+		ctx context.Context, c net.Conn,
+	) context.Context {
+		tcp, ok := c.(*net.TCPConn)
+		if assert.True(t, ok) {
+			assert.NoError(t, tcp.SetWriteBuffer(sendBuffer))
+		}
+
+		return ctx
+	}
+	srv.Start()
+	t.Cleanup(srv.Close)
+
+	return srv, logBuf
+}
+
+// TestHandleTargetDownload_OutlastsTheRequestLimit proves a download
+// runs for as long as the client keeps reading, and is logged as the
+// 200 it was. Behind a request limit and a server write timeout of a
+// tenth of a second, the client stops reading once the response has
+// started, waits three times as long, and still gets the whole file.
+// The archive is larger than the connection holds, so the download is
+// still being written while the client waits.
+func TestHandleTargetDownload_OutlastsTheRequestLimit(t *testing.T) {
+	t.Parallel()
+
+	const (
+		limit    = 100 * time.Millisecond
+		rows     = 8
+		bodySize = 64 << 10
+	)
+
+	env := setupSourceTest(t)
+	wh := seedWebhookWithRetention(t, env.db, 7)
+	archive := seedTarget(t, env.db, wh.ID, database.TargetTypeDatabase)
+	seedArchive(
+		t, delivery.ArchivePath(env.dbMgr, &wh, archive), rows, bodySize,
+	)
+
+	srv, accessLog := limitedServer(t, env, limit)
+
+	req, err := http.NewRequestWithContext(
+		t.Context(), http.MethodGet,
+		srv.URL+downloadPath(wh.ID, archive.ID), nil,
+	)
+	require.NoError(t, err)
+
+	for _, c := range env.cookies {
+		req.AddCookie(c)
+	}
+
+	resp, err := srv.Client().Do(req)
+	require.NoError(t, err)
+
+	defer func() { _ = resp.Body.Close() }()
+
+	require.Equal(t, http.StatusOK, resp.StatusCode)
+
+	time.Sleep(3 * limit)
+
+	zr, err := gzip.NewReader(resp.Body)
+	require.NoError(t, err)
+
+	var (
+		got    map[string]json.RawMessage
+		events []json.RawMessage
+	)
+
+	require.NoError(t, json.NewDecoder(zr).Decode(&got))
+	require.NoError(t, json.Unmarshal(got["archived_events"], &events))
+	assert.Len(t, events, rows)
+
+	// Reading to the end makes the gzip reader check that the file was
+	// finished.
+	_, err = io.ReadAll(zr)
+	require.NoError(t, err)
+
+	// Close waits for the handler, so the access log line is written.
+	srv.Close()
+
+	var access map[string]any
+
+	require.NoError(t, json.Unmarshal(accessLog.Bytes(), &access))
+	assert.EqualValues(t, http.StatusOK, access["status"])
+	assert.GreaterOrEqual(t,
+		access["latency_ms"], float64(limit.Milliseconds()),
+		"the download must outlast the request limit",
+	)
+}
+
+// brokenWriter is a response writer whose writes fail once the
+// response has started, as they do when the client goes away.
+type brokenWriter struct {
+	*httptest.ResponseRecorder
+}
+
+func (b brokenWriter) Write(p []byte) (int, error) {
+	if b.Body.Len() > 0 {
+		return 0, errClientGone
+	}
+
+	return b.ResponseRecorder.Write(p)
+}
+
+// TestHandleTargetDownload_AbortsWhenItFails proves a download that
+// fails after its response has started aborts the connection, so the
+// client sees a failed download rather than a file that looks
+// complete and does not decompress.
+func TestHandleTargetDownload_AbortsWhenItFails(t *testing.T) {
+	t.Parallel()
+
+	env := setupSourceTest(t)
+	wh := seedWebhookWithRetention(t, env.db, 7)
+	archive := seedTarget(t, env.db, wh.ID, database.TargetTypeDatabase)
+
+	req := httptest.NewRequestWithContext(
+		t.Context(), http.MethodGet, downloadPath(wh.ID, archive.ID), nil,
+	)
+	for _, c := range env.cookies {
+		req.AddCookie(c)
+	}
+
+	w := brokenWriter{ResponseRecorder: httptest.NewRecorder()}
+
+	assert.PanicsWithValue(t, http.ErrAbortHandler, func() {
+		targetRouter(env).ServeHTTP(w, req)
+	})
+	assert.Equal(t, http.StatusOK, w.Code)
+}

internal/handlers/target_edit_test.go

@@ -37,14 +37,18 @@ const (
 	editAuthHeader   = "Authorization: Bearer " + editBearerSecret
 )
 
-// targetRouter mounts the target create and edit routes on a chi
-// router so the handlers see the URL parameters they read.
+// targetRouter mounts the target create, edit and download routes on
+// a chi router so the handlers see the URL parameters they read.
 func targetRouter(env *sourceTestEnv) *chi.Mux {
 	router := chi.NewRouter()
 	router.Post(
 		"/hook/{sourceID}/targets",
 		env.handlers.HandleTargetCreate(),
 	)
+	router.Get(
+		"/hook/{sourceID}/targets/{targetID}/download",
+		env.handlers.HandleTargetDownload(),
+	)
 	router.Get(
 		"/hook/{sourceID}/targets/{targetID}/edit",
 		env.handlers.HandleTargetEdit(),

internal/middleware/timeout.go

@@ -0,0 +1,71 @@
+package middleware
+
+import (
+	"context"
+	"errors"
+	"net/http"
+	"time"
+)
+
+// Timeout returns middleware that gives each request limit to finish:
+// it cancels the request's context once limit has passed, and answers
+// 504 when the handler then returns without having started its
+// response.
+//
+// It replaces chi's middleware.Timeout, which writes that 504 even
+// after the handler has sent its own status. A download that outlasts
+// the limit has already sent its 200 and the whole file, so the late
+// 504 changes nothing for the client: the access log and the metrics
+// would record it in place of the 200, and net/http would complain of
+// a superfluous WriteHeader.
+func (s *Middleware) Timeout(
+	limit time.Duration,
+) func(http.Handler) http.Handler {
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(
+			w http.ResponseWriter,
+			r *http.Request,
+		) {
+			ctx, cancel := context.WithTimeout(r.Context(), limit)
+			defer cancel()
+
+			tw := &timeoutResponseWriter{ResponseWriter: w}
+
+			next.ServeHTTP(tw, r.WithContext(ctx))
+
+			if !tw.started &&
+				errors.Is(ctx.Err(), context.DeadlineExceeded) {
+				w.WriteHeader(http.StatusGatewayTimeout)
+			}
+		})
+	}
+}
+
+// timeoutResponseWriter records whether the handler has started its
+// response.
+type timeoutResponseWriter struct {
+	http.ResponseWriter
+
+	started bool
+}
+
+func (w *timeoutResponseWriter) WriteHeader(code int) {
+	w.started = true
+
+	w.ResponseWriter.WriteHeader(code)
+}
+
+func (w *timeoutResponseWriter) Write(b []byte) (int, error) {
+	// A Write without a WriteHeader starts the response too: net/http
+	// sends 200 in front of it.
+	w.started = true
+
+	//nolint:wrapcheck // Pass the writer's own error through unchanged.
+	return w.ResponseWriter.Write(b)
+}
+
+// Unwrap lets http.ResponseController reach the writer underneath, so
+// a handler can still set a write deadline through this wrapper.
+func (w *timeoutResponseWriter) Unwrap() http.ResponseWriter {
+	return w.ResponseWriter
+}

internal/middleware/timeout_test.go

@@ -0,0 +1,56 @@
+package middleware_test
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// TestTimeout proves the request limit answers 504 to a handler that
+// outlasts it without starting its response, and leaves a response the
+// handler has started with the status it sent. Both are what the
+// access log records.
+func TestTimeout(t *testing.T) {
+	t.Parallel()
+
+	const limit = 10 * time.Millisecond
+
+	for _, tc := range []struct {
+		name string
+		sent int // the status the handler sends, or 0 for none
+		want int
+	}{
+		{name: "not started", sent: 0, want: http.StatusGatewayTimeout},
+		{name: "started", sent: http.StatusOK, want: http.StatusOK},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			m, buf := capturingMiddleware(t)
+			handler := m.Logging()(m.Timeout(limit)(http.HandlerFunc(
+				func(w http.ResponseWriter, r *http.Request) {
+					if tc.sent != 0 {
+						w.WriteHeader(tc.sent)
+					}
+
+					<-r.Context().Done()
+				},
+			)))
+
+			w := httptest.NewRecorder()
+			handler.ServeHTTP(w, httptest.NewRequestWithContext(
+				t.Context(), http.MethodGet, "/", nil,
+			))
+
+			assert.Equal(t, tc.want, w.Code)
+
+			entries := accessLogEntries(t, buf)
+			require.Len(t, entries, 1)
+			assert.EqualValues(t, tc.want, entries[0]["status"])
+		})
+	}
+}

internal/server/archive_download_test.go

@@ -0,0 +1,69 @@
+package server_test
+
+import (
+	"compress/gzip"
+	"encoding/json"
+	"net/http"
+	"regexp"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"gorm.io/gorm/clause"
+	"sneak.berlin/go/webhooker/internal/database"
+)
+
+// TestHook_DownloadArchive follows the Download link the webhook page
+// shows for a database target, and only for it, and gets the archive
+// as a gzipped JSON file. Signed out, the link leads to the login page.
+func TestHook_DownloadArchive(t *testing.T) {
+	t.Parallel()
+
+	env := newTestEnv(t)
+
+	userID, _ := env.seedUser(t, "archivist", "somepassword")
+	cookies := env.authCookies(t, userID, "archivist")
+	wh := env.seedWebhook(t, userID)
+	env.seedTarget(t, wh.ID)
+
+	archive := &database.Target{
+		WebhookID: wh.ID,
+		Name:      "kept",
+		Type:      database.TargetTypeDatabase,
+		Active:    true,
+	}
+	require.NoError(t,
+		env.db.DB().Omit(clause.Associations).Create(archive).Error,
+	)
+
+	page := env.get("/hook/"+wh.ID, cookies)
+	require.Equal(t, http.StatusOK, page.Code)
+
+	links := regexp.MustCompile(
+		`href="(/hook/[^/"]+/targets/[^/"]+/download)"`,
+	).FindAllStringSubmatch(page.Body.String(), -1)
+	require.Len(t, links, 1, "only the database target has a Download")
+
+	link := links[0][1]
+	assert.Equal(t,
+		"/hook/"+wh.ID+"/targets/"+archive.ID+"/download", link,
+	)
+
+	w := env.get(link, cookies)
+	require.Equal(t, http.StatusOK, w.Code)
+	assert.Equal(t, "application/gzip", w.Header().Get("Content-Type"))
+
+	zr, err := gzip.NewReader(w.Body)
+	require.NoError(t, err)
+
+	var got map[string]json.RawMessage
+
+	require.NoError(t, json.NewDecoder(zr).Decode(&got))
+	assert.JSONEq(t,
+		`{"id":"`+wh.ID+`","name":"routed"}`, string(got["webhook"]),
+	)
+
+	w = env.get(link, nil)
+	assert.Equal(t, http.StatusSeeOther, w.Code)
+	assert.Contains(t, w.Header().Get("Location"), "/pages/login")
+}

internal/server/routes.go

@@ -73,7 +73,7 @@ func (s *Server) setupGlobalMiddleware() {
 	}
 
 	s.router.Use(s.mw.CORS())
-	s.router.Use(middleware.Timeout(requestTimeout))
+	s.router.Use(s.mw.Timeout(requestTimeout))
 
 	// Panic recovery, deliberately here rather than first. It has to
 	// run inside every middleware that observes the response, so the
@@ -312,6 +312,10 @@ func (s *Server) setupSourceRoutes() {
 			"/targets/{targetID}/edit",
 			s.h.HandleTargetEditSubmit(),
 		)
+		r.Get(
+			"/targets/{targetID}/download",
+			s.h.HandleTargetDownload(),
+		)
 		r.Post(
 			"/targets/{targetID}/delete",
 			s.h.HandleTargetDelete(),

templates/source_detail.html

@@ -157,6 +157,9 @@
                             {{else}}
                             <span class="badge-error">Inactive</span>
                             {{end}}
+                            {{if eq .Type "database"}}
+                            <a href="/hook/{{$.Webhook.ID}}/targets/{{.ID}}/download" class="btn-small" title="Download the archive as gzipped JSON">Download</a>
+                            {{end}}
                             <a href="/hook/{{$.Webhook.ID}}/targets/{{.ID}}/edit" class="btn-small" title="Edit">Edit</a>
                             <form method="POST" action="/hook/{{$.Webhook.ID}}/targets/{{.ID}}/toggle" class="inline">
                                 <input type="hidden" name="csrf_token" value="{{$.CSRFToken}}">