feat(esp_libc): picolibc: add fopencookie implementation

components/esp_libc/CMakeLists.txt

@@ -80,6 +80,7 @@ else()
          "src/picolibc/errno.c")
     if(CONFIG_LIBC_PICOLIBC_NEWLIB_COMPATIBILITY)
         list(APPEND srcs "src/picolibc/getreent.c")
+        list(APPEND srcs "src/picolibc/fopencookie.c")
     endif()
 endif()
 

components/esp_libc/platform_include/stdio.h

@@ -1,5 +1,5 @@
 /*
- * SPDX-FileCopyrightText: 2024-2025 Espressif Systems (Shanghai) CO LTD
+ * SPDX-FileCopyrightText: 2024-2026 Espressif Systems (Shanghai) CO LTD
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -40,6 +40,20 @@ FILE    *funopen(const void *cookie,
 void flockfile(FILE *);
 void funlockfile(FILE *);
 FILE *open_memstream(char **, size_t *);
+
+typedef ssize_t cookie_read_function_t(void *cookie, char *buf, size_t n);
+typedef ssize_t cookie_write_function_t(void *cookie, const char *buf, size_t n);
+typedef int cookie_seek_function_t(void *cookie, __off_t *off, int whence);
+typedef int cookie_close_function_t(void *cookie);
+typedef struct {
+    /* These four struct member names are dictated by Linux; hopefully,
+       they don't conflict with any macros.  */
+    cookie_read_function_t  *read;
+    cookie_write_function_t *write;
+    cookie_seek_function_t  *seek;
+    cookie_close_function_t *close;
+} cookie_io_functions_t;
+FILE *fopencookie(void *cookie, const char *mode, cookie_io_functions_t functions);
 #endif
 
 #ifdef __cplusplus

components/esp_libc/src/picolibc/fopencookie.c

@@ -0,0 +1,64 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include "esp_compiler.h"
+
+struct cookie_wrap {
+    void *cookie;
+    cookie_io_functions_t fn;
+};
+
+static int fun_read(void *c, char *buf, int size)
+{
+    struct cookie_wrap *w = c;
+    return (int)w->fn.read(w->cookie, buf, (size_t)size);
+}
+
+static int fun_write(void *c, const char *buf, int size)
+{
+    struct cookie_wrap *w = c;
+    return (int)w->fn.write(w->cookie, buf, (size_t)size);
+}
+
+static off_t fun_seek(void *c, off_t off, int whence)
+{
+    struct cookie_wrap *w = c;
+    return w->fn.seek(w->cookie, &off, whence);
+}
+
+static int fun_close(void *c)
+{
+    struct cookie_wrap *w = c;
+    int r = w->fn.close ? w->fn.close(w->cookie) : 0;
+    free(w);
+    return r;
+}
+
+FILE *fopencookie(void *cookie, __attribute__((unused)) const char *mode,
+                  cookie_io_functions_t fn)
+{
+    ESP_COMPILER_DIAGNOSTIC_PUSH_IGNORE("-Wanalyzer-malloc-leak")
+    struct cookie_wrap *w = malloc(sizeof * w);
+    if (!w) {
+        return NULL;
+    }
+
+    w->cookie = cookie;
+    w->fn = fn;
+
+    FILE *fp = funopen(w,
+                       fn.read  ? fun_read  : NULL,
+                       fn.write ? fun_write : NULL,
+                       fn.seek  ? fun_seek  : NULL,
+                       fun_close);
+
+    if (!fp) {
+        free(w);
+    }
+    return fp;
+    ESP_COMPILER_DIAGNOSTIC_POP("-Wanalyzer-malloc-leak")
+}