backend/app/controllers/posts_controller.rb

@@ -1,6 +1,5 @@
 class PostsController < ApplicationController
   Event = Struct.new(:post, :tag, :user, :change_type, :timestamp, keyword_init: true)
-  MAX_BULK_THUMBNAIL_BYTES = 20 * 1024 * 1024
   MAX_BULK_REQUEST_BYTES = 40 * 1024 * 1024
 
   class VideoMsParseError < ArgumentError
@@ -178,7 +177,7 @@ class PostsController < ApplicationController
     preflight = PostCreatePreflight.new(
         attributes: post_create_attributes,
         thumbnail: params[:thumbnail]).run
-    return render json: preflight if bool?(:dry)
+    return render json: dry_run_json(preflight) if bool?(:dry)
 
     post = PostCreator.new(actor: current_user,
                            attributes: post_create_attributes.merge(
@@ -191,7 +190,10 @@ class PostsController < ApplicationController
                                    :original_created_from,
                                    :original_created_before,
                                    :duration,
-                                   :video_ms).symbolize_keys).merge(
+                                   :video_ms,
+                                   :normalised_tags,
+                                   :tag_sections,
+                                   :normalised_parent_post_ids).symbolize_keys).merge(
                                thumbnail: params[:thumbnail])).create!
 
     post.reload
@@ -566,7 +568,6 @@ class PostsController < ApplicationController
       unless value.is_a?(ActionDispatch::Http::UploadedFile)
         raise ArgumentError, 'thumbnail upload が不正です．'
       end
-      raise ArgumentError, 'thumbnail file size が大きすぎます．' if value.size > MAX_BULK_THUMBNAIL_BYTES
 
       thumbnails[index] = value
     end
@@ -581,6 +582,22 @@ class PostsController < ApplicationController
     PostCompactRepr.base(post)
   end
 
+  def dry_run_json preflight
+    preflight.slice(
+        :url,
+        :title,
+        :thumbnail_base,
+        :tags,
+        :parent_post_ids,
+        :original_created_from,
+        :original_created_before,
+        :duration,
+        :video_ms,
+        :field_warnings,
+        :base_warnings,
+        :existing_post)
+  end
+
   def sync_parent_posts! post, parent_post_ids
     if parent_post_ids.include?(post.id)
       post.errors.add :parent_post_ids, '自分自身を親投稿にはできません．'

backend/app/services/post_bulk_creator.rb

@@ -1,21 +1,54 @@
 class PostBulkCreator
   def initialize actor:, posts:, thumbnails:
-    @actor = actor
+    @actor_id = actor.id
     @posts = posts
     @thumbnails = thumbnails
   end
 
   def run
-    results = @posts.each_with_index.map { |attributes, index|
-      create_row(attributes, index)
-    }
+    results = Array.new(@posts.length)
+    mutex = Mutex.new
+    next_index = 0
+
+    workers = Array.new(2) do
+      Thread.new do
+        ActiveRecord::Base.connection_pool.with_connection do
+          actor = User.find(@actor_id)
+          loop do
+            index = nil
+            begin
+              index = mutex.synchronize do
+                current = next_index
+                next_index += 1
+                current
+              end
+              break if index >= @posts.length
+
+              attributes = @posts[index]
+              results[index] = create_row(actor, attributes, index)
+            rescue StandardError => e
+              Rails.logger.error(
+                  "post_bulk_creator_worker_failure #{ { error: e.class.name,
+                                                        message: e.message,
+                                                        index: }.to_json }")
+              results[index] = {
+                  status: 'failed',
+                  recoverable: false,
+                  errors: { base: ['登録中にエラーが発生しました．'] },
+                  base_errors: [] }
+            end
+          end
+        end
+      end
+    end
+    workers.each(&:join)
 
     { results: }
   end
 
   private
 
-  def create_row attributes, index
+  def create_row actor, attributes, index
     preflight =
         PostCreatePreflight.new(
             attributes: attributes,
@@ -27,7 +60,7 @@ class PostBulkCreator
     end
 
     post = PostCreator.new(
-        actor: @actor,
+        actor: actor,
         attributes: normalised_attributes(attributes, preflight, index)).create!
     result = {
         status: 'created',
@@ -122,7 +155,10 @@ class PostBulkCreator
         original_created_from: preflight[:original_created_from],
         original_created_before: preflight[:original_created_before],
         duration: preflight[:duration],
-        video_ms: preflight[:video_ms] }
+        video_ms: preflight[:video_ms],
+        normalised_tags: preflight[:normalised_tags],
+        tag_sections: preflight[:tag_sections],
+        normalised_parent_post_ids: preflight[:normalised_parent_post_ids] }
   end
 
   def thumbnail_for index, attributes

backend/app/services/post_create_plan.rb

@@ -0,0 +1,95 @@
+class PostCreatePlan
+  def initialize attributes:
+    @attributes = attributes.symbolize_keys
+  end
+
+  def build!
+    Tag.normalise_tags!(tag_names, with_tagme: false, deny_deprecated: true,
+                                   with_sections: true) =>
+        { tags:, sections: }
+
+    tags = Tag.expand_parent_tags(tags).reject(&:deprecated?)
+    video_ms = normalise_video_ms(tags)
+    validate_video_sections!(video_ms, sections)
+    parent_post_ids = normalise_parent_post_ids
+    validate_parent_post_ids!(parent_post_ids)
+
+    {
+        url: @attributes[:url],
+        title: @attributes[:title].to_s,
+        thumbnail_base: @attributes[:thumbnail_base].presence,
+        original_created_from: @attributes[:original_created_from].presence,
+        original_created_before: @attributes[:original_created_before].presence,
+        tags: serialised_tags(tags, sections),
+        duration: @attributes[:duration].to_s,
+        video_ms: video_ms,
+        parent_post_ids: parent_post_ids.join(' '),
+        normalised_tags: tags,
+        tag_sections: sections,
+        normalised_parent_post_ids: parent_post_ids }
+  end
+
+  private
+
+  def tag_names = @attributes[:tags].to_s.split
+
+  def normalise_parent_post_ids
+    Array(@attributes[:parent_post_ids]).flat_map { _1.to_s.split }.map { |token|
+      id = Integer(token, exception: false)
+      raise ArgumentError, "親投稿 Id. が不正です: #{ token }" if id.nil? || id <= 0
+
+      id
+    }.uniq.sort
+  end
+
+  def validate_parent_post_ids! ids
+    missing = ids - Post.where(id: ids).pluck(:id)
+    raise ArgumentError, "存在しない親投稿 Id. があります: #{ missing.join(' ') }" if missing.present?
+  end
+
+  def serialised_tags tags, sections
+    tags.uniq(&:id).map { |tag|
+      "#{ tag.name }#{ sections[tag.id].to_a.map { Post.section_literal(_1) }.join }"
+    }.sort.join(' ')
+  end
+
+  def normalise_video_ms tags
+    return nil unless tags.any? { _1.id == Tag.video.id }
+
+    video_ms = @attributes[:video_ms]
+    if video_ms.present?
+      value = Integer(video_ms, exception: false)
+      raise PostCreator::VideoMsParseError unless value&.positive?
+
+      return value
+    end
+
+    duration = @attributes[:duration]
+    return nil if duration.blank?
+
+    value = Tag.time_to_ms!(duration.to_s, tag_name: '動画時間')
+    raise PostCreator::VideoMsParseError unless value.positive?
+
+    value
+  rescue Tag::SectionLiteralParseError
+    raise PostCreator::VideoMsParseError
+  end
+
+  def validate_video_sections! video_ms, sections
+    return unless video_ms
+
+    sections.each_value do |ranges|
+      ranges.each do |begin_ms, end_ms|
+        post = Post.new
+        if begin_ms >= video_ms
+          post.errors.add :video_ms, 'タグ区間の開始が動画時間以上です．'
+          raise ActiveRecord::RecordInvalid, post
+        end
+        if end_ms && end_ms > video_ms
+          post.errors.add :video_ms, 'タグ区間の終端が動画時間を超えてゐます．'
+          raise ActiveRecord::RecordInvalid, post
+        end
+      end
+    end
+  end
+end

backend/app/services/post_create_preflight.rb

@@ -18,24 +18,54 @@ class PostCreatePreflight
     preview = PostImportPreviewer.new.preview_rows(
         rows: [preview_row],
         fetch_metadata: false).first
-
-    validate_thumbnail_upload!
+    if preview[:existing_post_id].present?
+      return {
+          url: preview[:url],
+          title: preview[:attributes]['title'],
+          thumbnail_base: preview[:attributes]['thumbnail_base'],
+          tags: preview[:attributes]['tags'],
+          parent_post_ids: preview[:attributes]['parent_post_ids'],
+          original_created_from: preview[:attributes]['original_created_from'],
+          original_created_before: preview[:attributes]['original_created_before'],
+          duration: preview[:attributes]['duration'],
+          video_ms: preview[:attributes]['video_ms'],
+          field_warnings: final_field_warnings(preview[:field_warnings] || { }),
+          base_warnings: preview[:base_warnings],
+          existing_post: existing_post_compact(preview[:existing_post_id]) }
+    end
 
     if preview[:validation_errors].present?
       raise ValidationFailed.new(fields: preview[:validation_errors])
     end
 
+    validate_thumbnail_upload!
+
+    plan = PostCreatePlan.new(
+        attributes: {
+            url: preview[:url],
+            title: preview[:attributes]['title'],
+            thumbnail_base: preview[:attributes]['thumbnail_base'],
+            tags: preview[:attributes]['tags'],
+            parent_post_ids: preview[:attributes]['parent_post_ids'],
+            original_created_from: preview[:attributes]['original_created_from'],
+            original_created_before: preview[:attributes]['original_created_before'],
+            duration: preview[:attributes]['duration'],
+            video_ms: preview[:attributes]['video_ms'] }).build!
+
     {
-        url: preview[:url],
-        title: preview[:attributes]['title'],
-        thumbnail_base: preview[:attributes]['thumbnail_base'],
-        tags: preview[:attributes]['tags'],
-        parent_post_ids: preview[:attributes]['parent_post_ids'],
-        original_created_from: preview[:attributes]['original_created_from'],
-        original_created_before: preview[:attributes]['original_created_before'],
-        duration: preview[:attributes]['duration'],
-        video_ms: preview[:attributes]['video_ms'],
-        field_warnings: preview[:field_warnings],
+        url: plan[:url],
+        title: plan[:title],
+        thumbnail_base: plan[:thumbnail_base],
+        tags: plan[:tags],
+        parent_post_ids: plan[:parent_post_ids],
+        original_created_from: plan[:original_created_from],
+        original_created_before: plan[:original_created_before],
+        duration: plan[:duration],
+        video_ms: plan[:video_ms],
+        normalised_tags: plan[:normalised_tags],
+        tag_sections: plan[:tag_sections],
+        normalised_parent_post_ids: plan[:normalised_parent_post_ids],
+        field_warnings: final_field_warnings(preview[:field_warnings] || { }),
         base_warnings: preview[:base_warnings],
         existing_post: existing_post_compact(preview[:existing_post_id]) }
   end
@@ -78,10 +108,9 @@ class PostCreatePreflight
     return if @attributes[:thumbnail_base].present?
     return if @thumbnail.blank?
 
-    attachment = Post.resized_thumbnail_attachment(@thumbnail)
-    attachment[:io].close if attachment[:io].respond_to?(:close)
-  rescue MiniMagick::Error
-    raise ValidationFailed.new(fields: { thumbnail: ['サムネイル画像の変換に失敗しました．'] })
+    PostThumbnailUploadValidator.validate!(@thumbnail)
+  rescue PostThumbnailUploadValidator::InvalidUpload => e
+    raise ValidationFailed.new(fields: { thumbnail: [e.message] })
   end
 
   def existing_post_compact post_id
@@ -90,4 +119,15 @@ class PostCreatePreflight
     post = Post.with_attached_thumbnail.find_by(id: post_id)
     PostCompactRepr.base(post)
   end
+
+  def final_field_warnings field_warnings
+    thumbnail_warnings = (field_warnings['thumbnail_base'] || []).reject { _1 == 'サムネールなし' }
+    if @attributes[:thumbnail_base].blank? && @thumbnail.blank?
+      thumbnail_warnings = (thumbnail_warnings + ['サムネールなし']).uniq
+    end
+
+    {
+        **field_warnings,
+        'thumbnail_base' => thumbnail_warnings }
+  end
 end

backend/app/services/post_creator.rb

@@ -21,15 +21,13 @@ class PostCreator
     ApplicationRecord.transaction do
       post.save!
       post.thumbnail.attach(thumbnail_attachment) if thumbnail_attachment.present?
-      Tag.normalise_tags!(tag_names, deny_deprecated: true, with_sections: true) =>
-          { tags:, sections: }
+      tags = planned_tags
+      sections = planned_sections
       TagVersioning.record_tag_snapshots!(tags, created_by_user: @actor)
-      tags = Tag.expand_parent_tags(tags).reject(&:deprecated?)
-      post.video_ms = normalise_video_ms(tags)
-      validate_video_sections!(post.video_ms, sections)
+      post.video_ms = planned_video_ms
       post.save!
       sync_post_tags!(post, tags, sections)
-      sync_parent_posts!(post, parent_post_ids)
+      sync_parent_posts!(post, planned_parent_post_ids)
       PostVersionRecorder.record!(post:, event_type: :create, created_by_user: @actor)
     end
     post
@@ -46,52 +44,26 @@ class PostCreator
         thumbnail_base: @attributes[:thumbnail_base].presence)
   end
 
-  def tag_names = @attributes[:tags].to_s.split
+  def planned_tags = planned_create_attributes[:normalised_tags]
 
-  def parent_post_ids
-    Array(@attributes[:parent_post_ids]).flat_map { _1.to_s.split }.map { |token|
-      id = Integer(token, exception: false)
-      raise ArgumentError, "親投稿 Id. が不正です: #{ token }" if id.nil? || id <= 0
+  def planned_sections = planned_create_attributes[:tag_sections]
 
-      id
-    }.uniq
+  def planned_parent_post_ids = planned_create_attributes[:normalised_parent_post_ids]
+
+  def planned_video_ms
+    planned_create_attributes[:video_ms]
   end
 
-  def normalise_video_ms tags
-    return nil unless tags.any? { _1.id == Tag.video.id }
-
-    video_ms = @attributes[:video_ms]
-    if video_ms.present?
-      value = Integer(video_ms, exception: false)
-      raise VideoMsParseError unless value&.positive?
-
-      return value
-    end
-    duration = @attributes[:duration]
-    return nil if duration.blank?
-
-    value = Tag.time_to_ms!(duration.to_s, tag_name: '動画時間')
-    raise VideoMsParseError unless value.positive?
-
-    value
-  rescue Tag::SectionLiteralParseError
-    raise VideoMsParseError
-  end
-
-  def validate_video_sections! video_ms, sections
-    return unless video_ms
-
-    sections.each_value do |ranges|
-      ranges.each do |begin_ms, end_ms|
-        post = Post.new
-        if begin_ms >= video_ms
-          post.errors.add :video_ms, 'タグ区間の開始が動画時間以上です．'
-          raise ActiveRecord::RecordInvalid, post
-        end
-        if end_ms && end_ms > video_ms
-          post.errors.add :video_ms, 'タグ区間の終端が動画時間を超えてゐます．'
-          raise ActiveRecord::RecordInvalid, post
-        end
+  def planned_create_attributes
+    @planned_create_attributes ||= begin
+      if @attributes.key?(:normalised_tags)
+        {
+            normalised_tags: @attributes[:normalised_tags],
+            tag_sections: @attributes[:tag_sections] || { },
+            normalised_parent_post_ids: @attributes[:normalised_parent_post_ids] || [],
+            video_ms: @attributes[:video_ms] }
+      else
+        PostCreatePlan.new(attributes: @attributes).build!
       end
     end
   end

backend/app/services/post_import_previewer.rb

@@ -487,6 +487,8 @@ class PostImportPreviewer
   end
 
   def parse_video_ms attributes, errors
+    return nil unless attributes['tags'].to_s.split.include?('動画')
+
     video_ms = attributes['video_ms']
     if video_ms.present?
       value = Integer(video_ms, exception: false)

backend/app/services/post_import_url_list_parser.rb

@@ -1,25 +0,0 @@
-class PostImportUrlListParser
-  MAX_ROWS = 100
-  MAX_BYTES = 1.megabyte
-  MAX_URL_BYTES = 20.kilobytes
-
-  def self.parse source
-    raw = source.to_s
-    raise ArgumentError, '入力が大きすぎます．' if raw.bytesize > MAX_BYTES
-
-    rows = raw.split(/\r\n|\n|\r/).each_with_index.filter_map { |line, index|
-      url = line.strip
-      next if url.blank?
-
-      if url.bytesize > MAX_URL_BYTES
-        raise ArgumentError, "#{ index + 1 } 行目: URL が長すぎます．"
-      end
-
-      { source_row: index + 1, url: }
-    }
-    raise ArgumentError, 'URL を入力してください．' if rows.empty?
-    raise ArgumentError, "取込件数は #{ MAX_ROWS } 件までです．" if rows.length > MAX_ROWS
-
-    rows
-  end
-end

backend/app/services/post_thumbnail_upload_validator.rb

@@ -0,0 +1,18 @@
+class PostThumbnailUploadValidator
+  MAX_THUMBNAIL_BYTES = 20 * 1024 * 1024
+
+  class InvalidUpload < StandardError; end
+
+  def self.validate! thumbnail
+    return if thumbnail.blank?
+    raise InvalidUpload, 'thumbnail upload が不正です．' unless thumbnail.is_a?(ActionDispatch::Http::UploadedFile)
+    raise InvalidUpload, 'thumbnail file size が大きすぎます．' if thumbnail.size > MAX_THUMBNAIL_BYTES
+
+    attachment = Post.resized_thumbnail_attachment(thumbnail)
+    attachment[:io].close if attachment[:io].respond_to?(:close)
+  rescue MiniMagick::Error
+    raise InvalidUpload, 'サムネイル画像の変換に失敗しました．'
+  ensure
+    thumbnail&.rewind if thumbnail.respond_to?(:rewind)
+  end
+end

frontend/src/lib/postImportStorage.ts

@@ -11,6 +11,9 @@ const SESSION_VERSION = 3
 const SESSION_PREFIX = 'post-import-session:'
 const SOURCE_DRAFT_KEY = 'post-import-source-draft'
 const SESSION_MAX_AGE_MS = 24 * 60 * 60 * 1000
+const MAX_SESSION_JSON_BYTES = 262_144
+const MAX_SESSION_ROWS = 100
+const MAX_SOURCE_BYTES = 262_144
 const SESSION_ID_PATTERN =
     /^[0-9a-f]{8}-[0-9a-f]{4}-[1-5][0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/i
 const ATTRIBUTE_KEYS = [
@@ -50,11 +53,15 @@ const SESSION_KEYS = [
     'source',
     'rows',
     'repairMode'] as const
+const textEncoder = new TextEncoder ()
 
 
 const isPlainObject = (value: unknown): value is Record<string, unknown> =>
     typeof value === 'object' && value != null && !(Array.isArray (value))
 
+const byteLength = (value: string): number =>
+    textEncoder.encode (value).byteLength
+
 
 export const validatePostImportSessionId = (value: unknown): string | null => {
     if (typeof value !== 'string')
@@ -184,6 +191,14 @@ const hasOnlyKeys = (
 const sanitiseResetSnapshot = (value: unknown): PostImportResetSnapshot | null => {
     if (!(isPlainObject (value)))
       return null
+    if (!(hasOnlyKeys (value, ['url',
+			       'attributes',
+			       'provenance',
+			       'tagSources',
+			       'fieldWarnings',
+			       'baseWarnings',
+			       'metadataUrl'])))
+      return null
     if (typeof value.url !== 'string')
       return null
     if (!(isPlainObject (value.attributes)))
@@ -353,6 +368,8 @@ const sanitiseRow = (value: unknown): PostImportRow | null => {
       return null
     if (typeof value.url !== 'string')
       return null
+    if (byteLength (value.url) > 20_480)
+      return null
     if (!(isPlainObject (value.attributes)))
       return null
     if (!(isPlainObject (value.provenance)))
@@ -450,17 +467,23 @@ const sanitiseSession = (value: unknown): PostImportSession | null => {
       return null
     if (value.version !== SESSION_VERSION || !(Array.isArray (value.rows)))
       return null
+    if (value.rows.length === 0 || value.rows.length > MAX_SESSION_ROWS)
+      return null
     if (typeof value.expiresAt !== 'string' || isExpiredSession (value.expiresAt))
       return null
+    if (typeof value.source !== 'string' || byteLength (value.source) > MAX_SOURCE_BYTES)
+      return null
 
     const rows = value.rows.map (sanitiseRow)
     if (rows.some (row => row == null))
       return null
+    if ((new Set (rows.map (row => row?.sourceRow))).size !== rows.length)
+      return null
 
     return {
         version: SESSION_VERSION,
         expiresAt: value.expiresAt,
-        source: typeof value.source === 'string' ? value.source : '',
+        source: value.source,
         rows: (rows as PostImportRow[]).map (row => recalculateThumbnailWarning (row)),
         repairMode: value.repairMode === 'failed' ? 'failed' : 'all' }
 }
@@ -497,6 +520,12 @@ export const cleanupExpiredPostImportSessions = (
           const raw = sessionStorage.getItem (key)
           if (raw == null)
             continue
+          if (byteLength (raw) > MAX_SESSION_JSON_BYTES)
+            {
+              sessionStorage.removeItem (key)
+              --i
+              continue
+            }
 
           try
           {
@@ -585,6 +614,11 @@ export const loadPostImportSession = (
     const raw = readStorage (sessionKey (validatedId), onError)
     if (raw == null)
       return null
+    if (byteLength (raw) > MAX_SESSION_JSON_BYTES)
+      {
+        removeStorage (sessionKey (validatedId), onError)
+        return null
+      }
 
     try
     {
@@ -598,6 +632,7 @@ export const loadPostImportSession = (
     }
     catch
     {
+      removeStorage (sessionKey (validatedId), onError)
       return null
     }
 }

frontend/src/lib/postNewQueryState.ts

@@ -84,13 +84,55 @@ const STATE_KEYS = [
     'created_post_id',
     'recoverable'] as const
 const SINGLE_ROW_KEYS = [...BASIC_KEYS, ...STATE_KEYS, 'session_id'] as const
+const ENCODED_ROW_KEYS = [
+    'n',
+    'u',
+    't',
+    'h',
+    'f',
+    'b',
+    'x',
+    'd',
+    'g',
+    'p',
+    'm',
+    's',
+    'e',
+    'i',
+    'c',
+    'r'] as const
+const ALLOWED_MANUAL_FIELDS = [
+    'title',
+    'thumbnailBase',
+    'originalCreatedFrom',
+    'originalCreatedBefore',
+    'duration',
+    'tags',
+    'parentPostIds'] as const
 const MAX_REGULAR_URL_LENGTH = 768
 const MAX_COMPRESSED_STATE_LENGTH = 767
 const COMPRESSED_STATE_PREFIX = 'z1.'
+const MAX_COMPRESSED_STATE_PARAM_LENGTH = 8_192
+const MAX_COMPRESSED_STATE_BYTES = 16_384
+const MAX_DECOMPRESSED_STATE_BYTES = 262_144
+const MAX_STATE_ROWS = 100
+const MAX_QUERY_STRING_BYTES = 20_480
 
 const textEncoder = new TextEncoder ()
 const textDecoder = new TextDecoder ()
 
+const isPlainObject = (value: unknown): value is Record<string, unknown> =>
+    typeof value === 'object' && value != null && !(Array.isArray (value))
+
+const hasOnlyKeys = (
+    value:        Record<string, unknown>,
+    allowedKeys:  readonly string[],
+): boolean =>
+    Object.keys (value).every (key => allowedKeys.includes (key))
+
+const byteLength = (value: string): number =>
+    textEncoder.encode (value).byteLength
+
 const isValidSkipReason = (value: unknown): value is PostImportSkipReason =>
     value === 'existing' || value === 'manual'
 
@@ -202,18 +244,25 @@ const compressBytes = async (value: Uint8Array): Promise<Uint8Array> => {
 const decompressBytes = async (value: Uint8Array): Promise<Uint8Array> => {
   const stream =
       new Blob ([value]).stream ().pipeThrough (new DecompressionStream ('gzip'))
-  return new Uint8Array (await new Response (stream).arrayBuffer ())
+  const bytes = new Uint8Array (await new Response (stream).arrayBuffer ())
+  if (bytes.byteLength > MAX_DECOMPRESSED_STATE_BYTES)
+    throw new Error ('decompressed state too large')
+  return bytes
 }
 
 
 const decodeCompressedState = async (value: string): Promise<string | null> => {
   if (!(value.startsWith (COMPRESSED_STATE_PREFIX)))
     return null
+  if (value.length > MAX_COMPRESSED_STATE_PARAM_LENGTH)
+    return null
 
   const encoded = value.slice (COMPRESSED_STATE_PREFIX.length)
   const compressed = decodeBase64UrlBytes (encoded)
   if (compressed == null)
     return null
+  if (compressed.byteLength > MAX_COMPRESSED_STATE_BYTES)
+    return null
 
   try
   {
@@ -318,6 +367,10 @@ const parseManual = (value: string | null): string[] =>
     .filter (entry => entry !== '')
 
 
+const hasOnlyAllowedManualFields = (value: string[]): boolean =>
+    value.every (field => ALLOWED_MANUAL_FIELDS.includes (field as never))
+
+
 const isStringArray = (value: unknown): value is string[] =>
     Array.isArray (value) && value.every (entry => typeof entry === 'string')
 
@@ -326,10 +379,12 @@ const parseEncodedRow = (
     value:      unknown,
     requireUrl: boolean,
 ): FullRowState | null => {
-  if (typeof value !== 'object' || value == null || Array.isArray (value))
+  if (!(isPlainObject (value)))
     return null
 
   const row = value as Record<string, unknown>
+  if (!(hasOnlyKeys (row, ENCODED_ROW_KEYS)))
+    return null
   const url = row['u']
   const manual = row['m']
   const skip = decodeSkip (row['s'])
@@ -341,8 +396,12 @@ const parseEncodedRow = (
 
   if (requireUrl && typeof url !== 'string')
     return null
+  if (typeof url === 'string' && byteLength (url) > MAX_QUERY_STRING_BYTES)
+    return null
   if (manual != null && !(isStringArray (manual)))
     return null
+  if ((manual ?? []).some (field => !(ALLOWED_MANUAL_FIELDS.includes (field as never))))
+    return null
   if (row['s'] != null && skip == null)
     return null
   if (row['i'] != null && importStatus == null)
@@ -382,6 +441,8 @@ const parseEncodedRow = (
 	  const fieldValue = row[key]
 	  if (fieldValue != null && typeof fieldValue !== 'string')
 	    throw new Error ('invalid row')
+	  if (typeof fieldValue === 'string' && byteLength (fieldValue) > MAX_QUERY_STRING_BYTES)
+	    throw new Error ('invalid row')
 	  return [target, fieldValue ?? '']
 	}),
     ) as Record<(typeof stringFields)[number][1], string>
@@ -418,6 +479,8 @@ const parseSingleRow = (params: URLSearchParams): ParsedPostNewState | null => {
   const url = params.get ('url')
   if (url == null || url === '')
     return null
+  if (byteLength (url) > MAX_QUERY_STRING_BYTES)
+    return null
 
   const hasOnlyUrl = Array.from (params.keys ()).every (
       key => key === 'url' || key === 'session_id')
@@ -460,6 +523,8 @@ const parseSingleRow = (params: URLSearchParams): ParsedPostNewState | null => {
     return null
   if (importStatus != null && !(isValidImportStatus (importStatus)))
     return null
+  if (!(hasOnlyAllowedManualFields (parseManual (params.get ('manual')))))
+    return null
 
   const row = buildRow ({
       source_row: 1,
@@ -509,7 +574,12 @@ const parseMetaRows = (
     return null
 
   const urls = urlsValue.split (' ').filter (url => url !== '')
-  if (urls.length < 2 || urls.length !== parsed.rows.length)
+  if (urls.length < 2
+      || urls.length > MAX_STATE_ROWS
+      || urls.length !== parsed.rows.length
+      || parsed.rows.length > MAX_STATE_ROWS)
+    return null
+  if (urls.some (url => byteLength (url) > MAX_QUERY_STRING_BYTES))
     return null
 
   const fullRows = parsed.rows.map ((row, index) => {
@@ -520,6 +590,8 @@ const parseMetaRows = (
   })
   if (fullRows.some (row => row == null))
     return null
+  if ((new Set (fullRows.map (row => (row as FullRowState).source_row))).size !== fullRows.length)
+    return null
 
   const rows = fullRows.map (row => buildRow (row as FullRowState))
   return {
@@ -545,12 +617,17 @@ const parseFullState = async (stateValue: string): Promise<ParsedPostNewState |
     return null
   }
 
-  if (parsed.v !== 1 || !(Array.isArray (parsed.rows)) || parsed.rows.length === 0)
+  if (parsed.v !== 1
+      || !(Array.isArray (parsed.rows))
+      || parsed.rows.length === 0
+      || parsed.rows.length > MAX_STATE_ROWS)
     return null
 
   const fullRows = parsed.rows.map (row => parseEncodedRow (row, true))
   if (fullRows.some (row => row == null))
     return null
+  if ((new Set (fullRows.map (row => (row as FullRowState).source_row))).size !== fullRows.length)
+    return null
 
   const rows = fullRows.map (row => buildRow (row as FullRowState))
   return {

frontend/src/pages/posts/PostImportReviewPage.tsx

@@ -68,6 +68,7 @@ type PreviewResponse = {
   thumbnailBase?:        string
   originalCreatedFrom?:  string
   originalCreatedBefore?: string
+  parentPostIds?:        string
   duration?:             string
   videoMs?:              number
   tags?:                 string
@@ -137,8 +138,7 @@ const mergeDryRunRow = (
     currentRow: PostImportRow,
     result:     PreviewResponse,
 ): PostImportRow =>
-    applyThumbnailWarning (
-	initialisePreviewRows ([{
+    applyThumbnailWarning ({
         ...currentRow,
         url: result.url,
         attributes: {
@@ -150,7 +150,7 @@ const mergeDryRunRow = (
             duration: result.duration ?? '',
             videoMs: result.videoMs ?? '',
             tags: result.tags ?? '',
-            parentPostIds: String (currentRow.attributes.parentPostIds ?? '') },
+            parentPostIds: String (result.parentPostIds ?? currentRow.attributes.parentPostIds ?? '') },
         fieldWarnings: result.fieldWarnings ?? { },
         baseWarnings: result.baseWarnings ?? [],
         validationErrors: { },
@@ -167,7 +167,38 @@ const mergeDryRunRow = (
             currentRow.importStatus === 'created'
             ? 'created'
             : 'pending',
-        recoverable: undefined }])[0])
+        recoverable: undefined })
+
+
+const buildPreviewResetSnapshot = (
+    preview: PreviewResponse,
+): PostImportRow['resetSnapshot'] => ({
+    url: preview.url,
+    attributes: {
+	title: preview.title ?? '',
+	thumbnailBase: preview.thumbnailBase ?? '',
+	originalCreatedFrom: preview.originalCreatedFrom ?? '',
+	originalCreatedBefore: preview.originalCreatedBefore ?? '',
+	duration: preview.duration ?? '',
+	videoMs: preview.videoMs ?? '',
+	tags: preview.tags ?? '',
+	parentPostIds: String (preview.parentPostIds ?? '') },
+    provenance: {
+	url: 'manual',
+	title: 'automatic',
+	thumbnailBase: 'automatic',
+	originalCreatedFrom: 'automatic',
+	originalCreatedBefore: 'automatic',
+	duration: 'automatic',
+	videoMs: 'automatic',
+	tags: 'automatic',
+	parentPostIds: 'automatic' },
+    tagSources: {
+	automatic: preview.tags ?? '',
+	manual: '' },
+    fieldWarnings: preview.fieldWarnings ?? { },
+    baseWarnings: preview.baseWarnings ?? [],
+    metadataUrl: preview.url })
 
 
 const indexedBulkResults = (
@@ -216,6 +247,9 @@ const mergePreviewRow = (
     currentRow: PostImportRow,
     preview:    PreviewResponse,
 ): PostImportRow => {
+  const fieldWarnings = preview.fieldWarnings ?? { }
+  const baseWarnings = preview.baseWarnings ?? []
+  const metadataChanged = currentRow.metadataUrl !== preview.url
   const nextRow: PostImportRow = {
       ...currentRow,
       attributes: { ...currentRow.attributes },
@@ -224,8 +258,8 @@ const mergePreviewRow = (
 	  automatic: currentRow.tagSources?.automatic ?? '',
 	  manual: currentRow.tagSources?.manual ?? '' },
       url: preview.url,
-      fieldWarnings: preview.fieldWarnings ?? { },
-      baseWarnings: preview.baseWarnings ?? [],
+      fieldWarnings,
+      baseWarnings,
       existingPostId: preview.existingPost?.id,
       existingPost: preview.existingPost ?? undefined,
       skipReason:
@@ -234,9 +268,14 @@ const mergePreviewRow = (
           : currentRow.skipReason === 'manual'
             ? 'manual'
             : undefined,
+      metadataUrl: preview.url,
+      resetSnapshot:
+          metadataChanged
+          ? buildPreviewResetSnapshot (preview)
+          : currentRow.resetSnapshot,
       status:
-          Object.keys (preview.fieldWarnings ?? { }).length > 0
-          || (preview.baseWarnings?.length ?? 0) > 0
+          Object.keys (fieldWarnings).length > 0
+          || baseWarnings.length > 0
           ? 'warning'
           : 'ready' }
 
@@ -251,8 +290,10 @@ const mergePreviewRow = (
   if (currentRow.provenance.tags !== 'manual')
     {
       nextRow.attributes.tags = preview.tags ?? ''
-      nextRow.tagSources.automatic = preview.tags ?? ''
     }
+  nextRow.tagSources.automatic = preview.tags ?? ''
+  if (currentRow.provenance.parentPostIds !== 'manual')
+    nextRow.attributes.parentPostIds = String (preview.parentPostIds ?? '')
   if (currentRow.provenance.videoMs !== 'manual')
     nextRow.attributes.videoMs = preview.videoMs ?? ''
   if (currentRow.provenance.duration !== 'manual')
@@ -398,6 +439,7 @@ const PostImportReviewPage: FC<Props> = ({ user }) => {
 
     const refreshRows = async (baseSession: PostImportSession) => {
       let nextIndex = 0
+      const previews = new Map<number, PreviewResponse> ()
       const worker = async () => {
         while (active)
         {
@@ -421,15 +463,7 @@ const PostImportReviewPage: FC<Props> = ({ user }) => {
                 signal: controller.signal })
             if (!(active) || previewSequenceRef.current !== previewSequence)
               return
-
-            const latestSession = sessionRef.current ?? baseSession
-            const currentRow = latestSession.rows.find (
-                row => row.sourceRow === baseRow.sourceRow)
-            if (currentRow == null)
-              continue
-            const mergedRow = mergePreviewRow (currentRow, preview)
-            await persistSession (buildSession (
-                replaceImportRow (latestSession.rows, mergedRow)))
+            previews.set (baseRow.sourceRow, preview)
           }
           catch (requestError)
           {
@@ -437,11 +471,6 @@ const PostImportReviewPage: FC<Props> = ({ user }) => {
               return
             if (!(active) || previewSequenceRef.current !== previewSequence)
               return
-            const latestSession = sessionRef.current ?? baseSession
-            const currentRow = latestSession.rows.find (
-                row => row.sourceRow === baseRow.sourceRow)
-            if (currentRow == null)
-              continue
             if (!(isApiError (requestError)))
               continue
           }
@@ -454,6 +483,21 @@ const PostImportReviewPage: FC<Props> = ({ user }) => {
 
       await Promise.all (
           Array.from ({ length: Math.min (4, baseSession.rows.length) }, () => worker ()))
+      if (!(active) || previewSequenceRef.current !== previewSequence)
+        return
+
+      const latestSession = sessionRef.current ?? baseSession
+      const nextRows = latestSession.rows.map (row => {
+        const preview = previews.get (row.sourceRow)
+        if (preview == null
+            || row.skipReason === 'manual'
+            || row.importStatus === 'created'
+            || row.importStatus === 'skipped'
+            || isNonRecoverableFailedRow (row))
+          return row
+        return mergePreviewRow (row, preview)
+      })
+      await persistSession (buildSession (nextRows))
     }
 
     const hydrate = async () => {
@@ -494,7 +538,7 @@ const PostImportReviewPage: FC<Props> = ({ user }) => {
 		    duration: preview.duration ?? '',
 		    videoMs: preview.videoMs ?? '',
 		    tags: preview.tags ?? '',
-		    parentPostIds: '' },
+		    parentPostIds: String (preview.parentPostIds ?? '') },
 		fieldWarnings: preview.fieldWarnings ?? { },
 		baseWarnings: preview.baseWarnings ?? [],
 		validationErrors: { },
@@ -529,7 +573,7 @@ const PostImportReviewPage: FC<Props> = ({ user }) => {
 			duration: preview.duration ?? '',
 			videoMs: preview.videoMs ?? '',
 			tags: preview.tags ?? '',
-			parentPostIds: '' },
+			parentPostIds: String (preview.parentPostIds ?? '') },
 		    provenance: {
 			url: 'manual',
 			title: 'automatic',
@@ -544,7 +588,8 @@ const PostImportReviewPage: FC<Props> = ({ user }) => {
 			automatic: preview.tags ?? '',
 			manual: '' },
 		    fieldWarnings: preview.fieldWarnings ?? { },
-		    baseWarnings: preview.baseWarnings ?? [] } }])[0])]
+		    baseWarnings: preview.baseWarnings ?? [],
+		    metadataUrl: preview.url } }])[0])]
 	    const persisted = await persistSession (buildSession (rows))
 	    if (persisted == null)
 	      return
@@ -557,10 +602,6 @@ const PostImportReviewPage: FC<Props> = ({ user }) => {
 	  return
 	}
 
-      if (loadedSession == null)
-	{
-	  await persistSession (loaded)
-	}
       void refreshRows (loaded)
     }
 
@@ -612,8 +653,7 @@ const PostImportReviewPage: FC<Props> = ({ user }) => {
       if (row.sourceRow !== sourceRow)
 	return row
       if (isExistingSkipRow (row)
-          || row.importStatus === 'created'
-          || isNonRecoverableFailedRow (row))
+          || row.importStatus === 'created')
 	return row
       return {
 	  ...row,
@@ -779,23 +819,8 @@ const PostImportReviewPage: FC<Props> = ({ user }) => {
 
       const indexedResults = indexedBulkResults ([target], result.results)
       const latestAfterImport = sessionRef.current ?? pendingSession
-      const mergedRows = mergeImportResults (latestAfterImport.rows, indexedResults)
-      const recoverableRows = indexedResults.filter (row =>
-	  row.status === 'failed'
-	  && row.recoverable
-	  && Object.keys (row.errors ?? { }).length > 0)
-      const nextRows = mergedRows.map ((row): PostImportRow => {
-	const recoverable = recoverableRows.find (
-	    failedRow => failedRow.sourceRow === row.sourceRow)
-	if (recoverable == null)
-	  return applyThumbnailWarning (row)
-	return applyThumbnailWarning ({
-	    ...row,
-	    importStatus: 'pending',
-	    recoverable: true,
-	    validationErrors: recoverable.errors ?? { },
-	    importErrors: undefined })
-      })
+      const nextRows = mergeImportResults (latestAfterImport.rows, indexedResults)
+          .map (row => applyThumbnailWarning (row))
       const persisted = await persistSession (buildSession (nextRows))
       if (persisted != null
 	  && persisted.rows.every (row => isCompletedReviewRow (row)))
@@ -842,23 +867,8 @@ const PostImportReviewPage: FC<Props> = ({ user }) => {
 
       const indexedResults = indexedBulkResults (processingRows, result.results)
       const latestAfterImport = sessionRef.current ?? buildSession (currentSession.rows)
-      const mergedResults = mergeImportResults (latestAfterImport.rows, indexedResults)
-      const recoverableRows = indexedResults.filter (row =>
-	  row.status === 'failed'
-	  && row.recoverable
-	  && Object.keys (row.errors ?? { }).length > 0)
-      const nextRows = mergedResults.map ((row): PostImportRow => {
-	const recoverable = recoverableRows.find (
-	    failedRow => failedRow.sourceRow === row.sourceRow)
-	if (recoverable == null)
-	  return applyThumbnailWarning (row)
-	return applyThumbnailWarning ({
-	    ...row,
-	    importStatus: 'pending',
-	    recoverable: true,
-	    validationErrors: recoverable.errors ?? { },
-	    importErrors: undefined })
-      })
+      const nextRows = mergeImportResults (latestAfterImport.rows, indexedResults)
+          .map (row => applyThumbnailWarning (row))
       const persisted = await persistSession (buildSession (nextRows))
       if (persisted != null
 	  && persisted.rows.every (row => isCompletedReviewRow (row)))
@@ -940,8 +950,7 @@ const PostImportReviewPage: FC<Props> = ({ user }) => {
 			skipDisabled={
 			    busy
 			    || isExistingSkipRow (row)
-			    || row.importStatus === 'created'
-			    || isNonRecoverableFailedRow (row)}
+			    || row.importStatus === 'created'}
 			onEdit={() => editRow (row)}
 			onToggleSkip={checked => toggleManualSkip (row.sourceRow, checked)}
 			onRetry={canRetryResultRow (row) ? () => retry (row.sourceRow) : undefined}