From da7a09c358a041d8a922d41c2c926569edc18879 Mon Sep 17 00:00:00 2001
From: James Brown <jbrown@svix.com>
Date: Wed, 29 Apr 2026 12:33:16 -0700
Subject: [PATCH] feat: expose mi_stats_get_json and a safe wrapper around it

---
 libmimalloc-sys/src/extended.rs |  8 +++++++-
 src/extended.rs                 | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/libmimalloc-sys/src/extended.rs b/libmimalloc-sys/src/extended.rs
index d37adba..2d60c48 100644
--- a/libmimalloc-sys/src/extended.rs
+++ b/libmimalloc-sys/src/extended.rs
@@ -447,6 +447,12 @@ extern "C" {
     ///
     /// Note: This function is thread safe.
     pub fn mi_register_error(out: mi_error_fun, arg: *mut c_void);
+
+    /// Get the statistics for the current subprocess aggregated over all its heaps as JSON.
+    ///
+    /// Returns pointer to the buffer or NULL on failure. Use mi_free() to free the buffer if the buf parameter was NULL.
+    #[cfg(not(feature = "v2"))]
+    pub fn mi_stats_get_json(buf_size: usize, buf: *mut c_char) -> *mut c_char;
 }
 
 /// An output callback. Must be thread-safe.
@@ -1092,7 +1098,7 @@ mod tests {
 
     #[test]
     fn it_calculates_usable_size() {
-        let ptr = unsafe { mi_malloc(32) } as *mut u8;
+        let ptr = unsafe { crate::mi_malloc(32) } as *mut u8;
         let usable_size = unsafe { mi_usable_size(ptr as *mut c_void) };
         assert!(
             usable_size >= 32,
diff --git a/src/extended.rs b/src/extended.rs
index be9614c..6861dde 100644
--- a/src/extended.rs
+++ b/src/extended.rs
@@ -1,5 +1,7 @@
 use crate::MiMalloc;
 use core::ffi::c_void;
+#[cfg(not(feature = "v2"))]
+use core::ffi::{c_char, CStr};
 
 impl MiMalloc {
     /// Get the mimalloc version.
@@ -17,6 +19,29 @@ impl MiMalloc {
     pub unsafe fn usable_size(&self, ptr: *const u8) -> usize {
         ffi::mi_usable_size(ptr as *const c_void)
     }
+
+    /// Call the given function with a string version of the JSON stats for the whole process
+    ///
+    /// Allocates (using mimalloc itself) to store the JSON structure.
+    #[cfg(not(feature = "v2"))]
+    pub fn with_stats_json<F, O>(f: F) -> Result<O, &'static str>
+    where
+        F: FnOnce(&str) -> O,
+    {
+        unsafe {
+            let buf = ffi::mi_stats_get_json(0, core::ptr::null::<c_char>() as *mut _);
+            if buf.is_null() {
+                return Err("failed to call mi_stats_get_json");
+            }
+            let cstr = CStr::from_ptr(buf);
+            let slice = cstr
+                .to_str()
+                .map_err(|_| "mi_stats_get_json contained invalid UTF-8")?;
+            let o = f(slice);
+            ffi::mi_free(buf as _);
+            Ok(o)
+        }
+    }
 }
 
 #[cfg(test)]
@@ -43,4 +68,12 @@ mod test {
             assert!(usable_size >= 8);
         }
     }
+
+    #[test]
+    #[cfg(not(feature = "v2"))]
+    fn test_with_stats_json() {
+        let (first_char, len) = MiMalloc::with_stats_json(|f| (f.chars().next(), f.len())).unwrap();
+        assert_eq!(first_char, Some('{'));
+        assert!(len > 1);
+    }
 }