datastore: Add datastoreusage command

datastoreusage returns the total_bytes that are stored under a given
{Key} or from root. {Key} is the entry point from which we begin to
traverse the datastore.

Changelog-Added: JSON-RPC: `datastoreusage`: returns the total bytes that are stored under a given key.

Signed-off-by: Peter Neuroth <pet.v.ne@gmail.com>

doc/Makefile

@@ -32,6 +32,7 @@ MANPAGES := doc/lightning-cli.1 \
 	doc/lightning-createinvoice.7 \
 	doc/lightning-createrune.7 \
 	doc/lightning-datastore.7 \
+	doc/lightning-datastoreusage.7 \
 	doc/lightning-decodepay.7 \
 	doc/lightning-decode.7 \
 	doc/lightning-deldatastore.7 \

doc/index.rst

@@ -38,6 +38,7 @@ Core Lightning Documentation
    lightning-createonion <lightning-createonion.7.md>
    lightning-createrune <lightning-createrune.7.md>
    lightning-datastore <lightning-datastore.7.md>
+   lightning-datastoreusage <lightning-datastoreusage.7.md>
    lightning-decode <lightning-decode.7.md>
    lightning-decodepay <lightning-decodepay.7.md>
    lightning-deldatastore <lightning-deldatastore.7.md>

doc/lightning-datastore.7.md

@@ -60,7 +60,7 @@ Rusty Russell <<rusty@rustcorp.com.au>> is mainly responsible.
 SEE ALSO
 --------
 
-lightning-listdatastore(7), lightning-deldatastore(7)
+lightning-listdatastore(7), lightning-deldatastore(7), lightning-datastoreusage(7)
 
 RESOURCES
 ---------

doc/lightning-datastoreusage.7.md

@@ -0,0 +1,43 @@
+lightning-datastoreusage -- Command for listing datastore usage info
+============================================================
+
+SYNOPSIS
+--------
+
+**datastoreusage**
+
+DESCRIPTION
+-----------
+
+The **datastoreusage** RPC command allows the caller to fetch the 
+total bytes that are stored under a certain *key* (or from the root),
+including the size of the *key*.
+
+All descendants of the *key* (or root) are taken into account.
+RETURN VALUE
+------------
+
+[comment]: # (GENERATE-FROM-SCHEMA-START)
+On success, an object containing **datastoreusage** is returned.  It is an object containing:
+
+- **key** (string): The key from which the database was traversed.
+- **total\_bytes** (u64): The total bytes that are stored under the *key*, including the all descendants data and the size of the keys themselves.
+
+[comment]: # (GENERATE-FROM-SCHEMA-END)
+
+AUTHOR
+------
+
+Peter Neuroth <<pet.v.ne@gmail.com>> is mainly responsible.
+
+SEE ALSO
+--------
+
+lightning-datastore(7), lightning-deldatastore(7), lightning-listdatastore(7)
+
+RESOURCES
+---------
+
+Main web site: <https://github.com/ElementsProject/lightning>
+
+[comment]: # ( SHA256STAMP:743b3308974872f191362fcd0b1af647ea1efd28ae30ea04f6deb22418871a17)

doc/lightning-deldatastore.7.md

@@ -43,7 +43,7 @@ Rusty Russell <<rusty@rustcorp.com.au>> is mainly responsible.
 SEE ALSO
 --------
 
-lightning-listdatastore(7), lightning-datastore(7)
+lightning-listdatastore(7), lightning-datastore(7), lightning-datastoreusage(7)
 
 RESOURCES
 ---------

doc/lightning-listdatastore.7.md

@@ -41,7 +41,7 @@ Rusty Russell <<rusty@rustcorp.com.au>> is mainly responsible.
 SEE ALSO
 --------
 
-lightning-datastore(7), lightning-deldatastore(7)
+lightning-datastore(7), lightning-deldatastore(7), lightning-datastoreusage(7)
 
 RESOURCES
 ---------

doc/schemas/datastoreusage.request.json

@@ -0,0 +1,23 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "type": "object",
+  "additionalProperties": false,
+  "required": [],
+  "added": "v23.11",
+  "properties": {
+    "key": {
+      "oneOf": [
+        {
+          "type": "array",
+          "description": "key is an array of values (though a single value is treated as a one-element array). Used as the starting point to traverse the datastore.",
+          "items": {
+            "type": "string"
+          }
+        },
+        {
+          "type": "string"
+        }
+      ]
+    }
+  }
+}

doc/schemas/datastoreusage.schema.json

@@ -0,0 +1,28 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "type": "object",
+  "additionalProperties": false,
+  "required": [
+    "datastoreusage"
+  ],
+  "properties": {
+    "datastoreusage": {
+      "type": "object",
+      "additionalProperties": false,
+      "required": [
+        "key",
+        "total_bytes"
+      ],
+      "properties": {
+        "key": {
+          "type": "string",
+          "description": "The key from which the database was traversed."
+        },
+        "total_bytes": {
+          "type": "u64",
+          "description": "The total bytes that are stored under the *key*, including the all descendants data and the size of the keys themselves."
+        }
+      }
+    }
+  }
+}

lightningd/datastore.c

@@ -289,6 +289,54 @@ static struct command_result *json_deldatastore(struct command *cmd,
 	return command_success(cmd, response);
 }
 
+static struct command_result *json_datastoreusage(struct command *cmd,
+						 const char *buffer,
+						 const jsmntok_t *obj UNNEEDED,
+						 const jsmntok_t *params)
+{
+	struct json_stream *response;
+	const char **k, **key;
+	struct db_stmt *stmt;
+	const u8 *data;
+	u64 gen, total_bytes = 0;
+
+	if (!param(cmd, buffer, params,
+		   p_opt("key", param_list_or_string, &key),
+		   NULL))
+		return command_param_failed();
+
+	// We ignore an empty key string or key array.
+	if (key && *key[0] == '\0')
+		key = NULL;
+
+	response = json_stream_success(cmd);
+	json_object_start(response, "datastoreusage");
+	json_add_string(response, "key", datastore_key_fmt(tmpctx, key));
+
+	for (stmt = wallet_datastore_first(cmd, cmd->ld->wallet, key,
+					   &k, &data, &gen);
+	     stmt;
+	     stmt = wallet_datastore_next(cmd, key, stmt,
+	     				  &k, &data, &gen)) {
+
+		u64 self_bytes = tal_bytelen(data);
+		/* The key is stored as a binary blob where each string is separated by
+		 * a '\0'. Therefore we add an additional `len(k) - 1`. k is the primary
+		 * key of the table and can not be NULL */
+		self_bytes += tal_count(k) - 1;
+		for (size_t i = 0; i < tal_count(k); i++) {
+			self_bytes += strlen(k[i]);
+		};
+		total_bytes += self_bytes;
+	};
+	tal_free(stmt);
+
+	json_add_u64(response, "total_bytes", total_bytes);
+	json_object_end(response);
+
+	return command_success(cmd, response);
+}
+
 static const struct json_command datastore_command = {
 	"datastore",
 	"utility",
@@ -312,3 +360,11 @@ static const struct json_command listdatastore_command = {
 	"List the datastore, optionally only {key}",
 };
 AUTODATA(json_command, &listdatastore_command);
+
+static const struct json_command datastoreusage_command = {
+	"datastoreusage",
+	"utility",
+	json_datastoreusage,
+	"List the datastore usage, starting from an optional {key}",
+};
+AUTODATA(json_command, &datastoreusage_command);