improve alloc stats interface; fix admin command formatting

Signed-off-by: Jason Volk <jason@zemos.net>

src/core/alloc/default.rs

@@ -1,9 +1,9 @@
 //! Default allocator with no special features
 
-/// Always returns the empty string
+/// Always returns None
 #[must_use]
-pub fn memory_stats() -> String { String::default() }
+pub fn memory_stats() -> Option<String> { None }
 
-/// Always returns the empty string
+/// Always returns None
 #[must_use]
-pub fn memory_usage() -> String { String::default() }
+pub fn memory_usage() -> Option<String> { None }

src/core/alloc/hardened.rs

@@ -4,9 +4,10 @@
 static HMALLOC: hardened_malloc_rs::HardenedMalloc = hardened_malloc_rs::HardenedMalloc;
 
 #[must_use]
-pub fn memory_usage() -> String {
-	String::default() //TODO: get usage
-}
+//TODO: get usage
+pub fn memory_usage() -> Option<string> { None }
 
 #[must_use]
-pub fn memory_stats() -> String { "Extended statistics are not available from hardened_malloc.".to_owned() }
+pub fn memory_stats() -> Option<String> {
+	Some("Extended statistics are not available from hardened_malloc.".to_owned())
+}

src/core/alloc/je.rs

@@ -10,7 +10,7 @@ use tikv_jemallocator as jemalloc;
 static JEMALLOC: jemalloc::Jemalloc = jemalloc::Jemalloc;
 
 #[must_use]
-pub fn memory_usage() -> String {
+pub fn memory_usage() -> Option<String> {
 	use mallctl::stats;
 
 	let mibs = |input: Result<usize, mallctl::Error>| {
@@ -27,14 +27,14 @@ pub fn memory_usage() -> String {
 	let metadata = mibs(stats::metadata::read());
 	let resident = mibs(stats::resident::read());
 	let retained = mibs(stats::retained::read());
-	format!(
+	Some(format!(
 		"allocated: {allocated:.2} MiB\nactive: {active:.2} MiB\nmapped: {mapped:.2} MiB\nmetadata: {metadata:.2} \
 		 MiB\nresident: {resident:.2} MiB\nretained: {retained:.2} MiB\n"
-	)
+	))
 }
 
 #[must_use]
-pub fn memory_stats() -> String {
+pub fn memory_stats() -> Option<String> {
 	const MAX_LENGTH: usize = 65536 - 4096;
 
 	let opts_s = "d";
@@ -51,7 +51,7 @@ pub fn memory_stats() -> String {
 	unsafe { ffi::malloc_stats_print(Some(malloc_stats_cb), opaque, opts_p) };
 
 	str.truncate(MAX_LENGTH);
-	format!("<pre><code>{str}</code></pre>")
+	Some(format!("<pre><code>{str}</code></pre>"))
 }
 
 extern "C" fn malloc_stats_cb(opaque: *mut c_void, msg: *const c_char) {