improve IndexedDB use

1 files changed, 157 insertions, 71 deletions

diff --git a/common/indexeddb.js b/common/indexeddb.js
index d0bacc4..c6302fa 100644
--- a/common/indexeddb.js
+++ b/common/indexeddb.js
@@ -55,8 +55,8 @@ const nr_reductor = ([i, s], num) => [i - 1, s + num * 1024 ** i];
 const version_nr = ver => Array.reduce(ver.slice(0, 3), nr_reductor, [2, 0])[1];
 
 const stores = 	[
-    ["files",     {keyPath: "sha256"}],
-    ["file_uses", {keyPath: "sha256"}],
+    ["files",     {keyPath: "hash_key"}],
+    ["file_uses", {keyPath: "hash_key"}],
     ["resources", {keyPath: "identifier"}],
     ["mappings",  {keyPath: "identifier"}]
 ];
@@ -92,7 +92,7 @@ async function idb_del(transaction, store_name, key)
 }
 
 /* Open haketilo database, asynchronously return an IDBDatabase object. */
-async function get_db(initialization_data=initial_data)
+async function get_db(data=initial_data)
 {
     if (db)
 	return db;
@@ -120,9 +120,9 @@ async function get_db(initialization_data=initial_data)
 	for (const [store_name, key_mode] of stores)
 	    store = opened_db.createObjectStore(store_name, key_mode);
 
-	await new Promise(resolve => store.transaction.oncomplete = resolve);
+	const context = make_context(store.transaction, data.files);
 
-	save_items(db, initialization_data);
+	await _save_items(data.resources, data.mappings, context);
     }
 
     db = opened_db;
@@ -130,6 +130,105 @@ async function get_db(initialization_data=initial_data)
     return db;
 }
 
+/* Helper function used by start_items_transaction() and get_db(). */
+function make_context(transaction, files)
+{
+    files = files || {};
+    const context = {transaction, files, file_uses: {}};
+
+    let resolve, reject;
+    context.result = new Promise((...cbs) => [resolve, reject] = cbs);
+
+    context.transaction.oncomplete = resolve;
+    context.transaction.onerror = reject;
+
+    return context;
+}
+
+/*
+ * item_store_names should be an array with either string "mappings", string
+ * "resources" or both. files should be a dict with values being contents of
+ * files that are to be possibly saved in this transaction and keys of the form
+ * `sha256-<file's-sha256-sum>`.
+ *
+ * Returned is a context object wrapping the transaction and handling the
+ * counting of file references in IndexedDB.
+ */
+async function start_items_transaction(item_store_names, files)
+{
+    const db = await haketilodb.get();
+    const scope = [...item_store_names, "files", "file_uses"];
+    return make_context(db.transaction(scope, "readwrite"), files);
+}
+
+async function incr_file_uses(context, file_ref, by=1)
+{
+    const hash_key = file_ref.hash_key;
+    let uses = context.file_uses[hash_key];
+    if (uses === undefined) {
+	uses = await idb_get(context.transaction, "file_uses", hash_key);
+	if (uses)
+	    [uses.new, uses.initial] = [false, uses.uses];
+	else
+	    uses = {hash_key, uses: 0, new: true, initial: 0};
+
+	context.file_uses[hash_key] = uses;
+    }
+
+    uses.uses = uses.uses + by;
+}
+
+const decr_file_uses = (ctx, file_ref) => incr_file_uses(ctx, file_ref, -1);
+
+async function finalize_items_transaction(context)
+{
+    for (const uses of Object.values(context.file_uses)) {
+	if (uses.uses < 0)
+	    console.error("internal error: uses < 0 for file " + uses.hash_key);
+
+	const is_new       = uses.new;
+	const initial_uses = uses.initial;
+	const hash_key     = uses.hash_key;
+
+	delete uses.new;
+	delete uses.initial;
+
+	if (uses.uses < 1) {
+	    if (!is_new) {
+		idb_del(context.transaction, "file_uses", hash_key);
+		idb_del(context.transaction, "files",     hash_key);
+	    }
+
+	    continue;
+	}
+
+	if (uses.uses === initial_uses)
+	    continue;
+
+	idb_put(context.transaction, "file_uses", uses);
+
+	if (initial_uses > 0)
+	    continue;
+
+	const file = context.files[hash_key];
+	if (file === undefined) {
+	    context.transaction.abort();
+	    throw "file not present: " + hash_key;
+	}
+
+	idb_put(context.transaction, "files", {hash_key, contents: file});
+    }
+
+    return context.result;
+}
+
+async function with_items_transaction(cb, item_store_names, files={})
+{
+    const context = await start_items_transaction(item_store_names, files);
+    await cb(context);
+    await finalize_items_transaction(context);
+}
+
 /*
  * How a sample data argument to the function below might look like:
  *
@@ -167,97 +266,84 @@ async function get_db(initialization_data=initial_data)
  *     }
  * }
  */
-async function save_items(db, data)
+async function save_items(transaction, data)
 {
-    const files = data.files;
-    const resources =
-	  Object.values(data.resources || []).map(entities.get_newest);
-    const mappings =
-	  Object.values(data.mappings || []).map(entities.get_newest);
+    const items_store_names = ["resources", "mappings"];
+    const context = start_items_transaction(items_store_names, data.files);
 
-    resources.concat(mappings).forEach(i => save_item(i, data.files, db));
+    return _save_items(data.resources, data.mappings, context);
 }
 
-/* helper function of save_item() */
-async function get_file_uses(transaction, file_uses_sha256, file_ref)
+async function _save_items(resources, mappings, context)
 {
-    let uses = file_uses_sha256[file_ref.sha256];
-    if (uses === undefined) {
-	uses = await idb_get(transaction, "file_uses", file_ref.sha256);
-	if (uses)
-	    [uses.new, uses.initial] = [false, uses.uses];
-	else
-	    uses = {sha256: file_ref.sha256, uses: 0, new: true, initial: 0};
+    resources = Object.values(resources || {}).map(entities.get_newest);
+    mappings  = Object.values(mappings  || {}).map(entities.get_newest);
 
-	file_uses_sha256[file_ref.sha256] = uses;
-    }
+    for (const item of resources.concat(mappings))
+	await save_item(item, context);
 
-    return uses;
+    await finalize_items_transaction(context);
 }
 
 /*
  * Save given definition of a resource/mapping to IndexedDB. If the definition
  * (passed as `item`) references files that are not already present in
  * IndexedDB, those files should be present as values of the `files_sha256`
- * object with keys being their sha256 sums.
+ * object with keys being of the form `sha256-<file's-sha256-sum>`.
+ *
+ * context should be one returned from start_items_transaction() and should be
+ * later passed to finalize_items_transaction() so that files depended on are
+ * added to IndexedDB and files that are no longer depended on after this
+ * operation are removed from IndexedDB.
  */
-async function save_item(item, files_sha256, db)
+async function save_item(item, context)
 {
     const store_name = {resource: "resources", mapping: "mappings"}[item.type];
-    const transaction =
-	  db.transaction([store_name, "files", "file_uses"], "readwrite");
-
-    let resolve, reject;
-    const result = new Promise((...cbs) => [resolve, reject] = cbs);
-    transaction.oncomplete = resolve;
-    transaction.onerror = reject;
 
-    const uses_sha256 = {};
     for (const file_ref of entities.get_files(item))
-	(await get_file_uses(transaction, uses_sha256, file_ref)).uses++;
+	await incr_file_uses(context, file_ref);
 
-    const old_item = await idb_get(transaction, store_name, item.identifier);
-    if (old_item !== undefined) {
-	for (const file_ref of entities.get_files(old_item))
-	    (await get_file_uses(transaction, uses_sha256, file_ref)).uses--;
-    }
-
-    for (const uses of Object.values(uses_sha256)) {
-	if (uses.uses < 0)
-	    console.error("internal error: uses < 0 for file " + uses.sha256);
-
-	const [is_new, initial_uses] = [uses.new, uses.initial];
-	delete uses.new;
-	delete uses.initial;
-
-	if (uses.uses < 1) {
-	    if (!is_new) {
-		idb_del(transaction, "file_uses", uses.sha256);
-		idb_del(transaction, "files",     uses.sha256);
-	    }
-
-	    continue;
-	}
-
-	if (uses.uses === initial_uses)
-	    continue;
-
-	const file = files_sha256[uses.sha256];
-	if (file === undefined)
-	    throw "file not present: " + uses.sha256;
+    await _remove_item(store_name, item.identifier, context, false);
+    await idb_put(context.transaction, store_name, item);
+}
 
-	idb_put(transaction, "files", {sha256: uses.sha256, contents: file});
-	idb_put(transaction, "file_uses", uses);
+/* Helper function used by remove_item() and save_item(). */
+async function _remove_item(store_name, identifier, context)
+{
+    const item = await idb_get(context.transaction, store_name, identifier);
+    if (item !== undefined) {
+	for (const file_ref of entities.get_files(item))
+	    await decr_file_uses(context, file_ref);
     }
+}
 
-    idb_put(transaction, store_name, item);
-
-    return result;
+/*
+ * Remove definition of a resource/mapping from IndexedDB.
+ *
+ * context should be one returned from start_items_transaction() and should be
+ * later passed to finalize_items_transaction() so that files depended on are
+ * added to IndexedDB and files that are no longer depended on after this
+ * operation are removed from IndexedDB.
+ */
+async function remove_item(store_name, identifier, context)
+{
+    await _remove_item(store_name, identifier, context);
+    await idb_del(context.transaction, store_name, identifier);
 }
 
+const remove_resource =
+      (identifier, ctx) => remove_item("resources", identifier, ctx);
+const remove_mapping =
+      (identifier, ctx) => remove_item("mappings",  identifier, ctx);
+
 const haketilodb = {
-    get:       get_db,
-    save_item: save_item
+    get: get_db,
+    save_items,
+    save_item,
+    remove_resource,
+    remove_mapping,
+    start_items_transaction,
+    finalize_items_transaction
 };
 
 /*