1 files changed, 165 insertions, 0 deletions
diff --git a/src/lib/data-stack.h b/src/lib/data-stack.h
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+++ b/src/lib/data-stack.h
@@ -0,0 +1,165 @@
+#ifndef DATA_STACK_H
+#define DATA_STACK_H
+
+/* Data stack makes it very easy to implement functions returning dynamic data
+   without having to worry much about memory management like freeing the
+   result or having large enough buffers for the result.
+
+   t_ prefix was chosen to describe functions allocating memory from data
+   stack. "t" meaning temporary.
+
+   Advantages over control stack and alloca():
+    - Functions can return a value allocated from data stack
+    - We can portably specify how much data we want to allocate at runtime
+
+   Advantages over malloc():
+    - FAST, most of the time allocating memory means only updating a couple of
+      pointers and integers. Freeing the memory all at once also is a fast
+      operation.
+    - No need to free() each allocation resulting in prettier code
+    - No memory leaks
+    - No memory fragmentation
+
+   Disadvantages:
+    - Allocating memory inside loops can accidentally allocate a lot of memory
+      if the loops are long and you forgot to place t_push() and t_pop() there.
+    - t_malloc()ed data could be accidentally stored into permanent location
+      and accessed after it's already been freed. const'ing the return values
+      helps for most uses though (see the t_malloc() description).
+    - Debugging invalid memory usage may be difficult using existing tools,
+      although compiling with DEBUG enabled helps finding simple buffer
+      overflows.
+*/
+
+#ifndef STATIC_CHECKER
+typedef unsigned int data_stack_frame_t;
+#else
+typedef struct data_stack_frame *data_stack_frame_t;
+#endif
+
+extern unsigned int data_stack_frame_id;
+
+/* All t_..() allocations between t_push*() and t_pop() are freed after t_pop()
+   is called. Returns the current stack frame number, which can be used
+   to detect missing t_pop() calls:
+
+   x = t_push(marker); .. if (!t_pop(x)) abort();
+
+   In DEBUG mode, t_push_named() makes a temporary allocation for the name,
+   but is safe to call in a loop as it performs the allocation within its own
+   frame. However, you should always prefer to use T_BEGIN { ... } T_END below.
+*/
+data_stack_frame_t t_push(const char *marker) ATTR_HOT;
+data_stack_frame_t t_push_named(const char *format, ...) ATTR_HOT ATTR_FORMAT(1, 2);
+/* Returns TRUE on success, FALSE if t_pop() call was leaked. The caller
+   should panic. */
+bool t_pop(data_stack_frame_t *id) ATTR_HOT;
+/* Same as t_pop(), but move str out of the stack frame if it is inside.
+   This can be used to easily move e.g. error strings outside stack frames. */
+bool t_pop_pass_str(data_stack_frame_t *id, const char **str);
+
+/* Pop the last data stack frame. This shouldn't be called outside test code. */
+void t_pop_last_unsafe(void);
+
+/* Usage: T_BEGIN { code } T_END */
+#define T_STRING(x)	#x
+#define T_XSTRING(x)	T_STRING(x)	/* expand and then stringify */
+#define T_BEGIN \
+	STMT_START { \
+		data_stack_frame_t _data_stack_cur_id = t_push(__FILE__ ":" T_XSTRING(__LINE__));
+#define T_END \
+	STMT_START { \
+		if (unlikely(!t_pop(&_data_stack_cur_id))) \
+			i_panic("Leaked t_pop() call"); \
+	} STMT_END; \
+	} STMT_END
+
+/* Usage:
+   const char *error;
+   T_BEGIN {
+     ...
+     if (ret < 0)
+       error = t_strdup_printf("foo() failed: %m");
+   } T_END_PASS_STR_IF(ret < 0, &error);
+   // error is still valid
+*/
+#define T_END_PASS_STR_IF(pass_condition, str) \
+	STMT_START { \
+		if (unlikely(!t_pop_pass_str(&_data_stack_cur_id, (pass_condition) ? (str) : NULL))) \
+			i_panic("Leaked t_pop() call"); \
+	} STMT_END; \
+	} STMT_END
+/*
+   Usage:
+   const char *result;
+   T_BEGIN {
+     ...
+     result = t_strdup_printf(...);
+   } T_END_PASS_STR(&result);
+   // result is still valid
+*/
+#define T_END_PASS_STR(str) \
+	T_END_PASS_STR_IF(TRUE, str)
+
+/* WARNING: Be careful when using these functions, it's too easy to
+   accidentally save the returned value somewhere permanently.
+
+   You probably should never use these functions directly, rather
+   create functions that return 'const xxx*' types and use t_malloc()
+   internally in them. This is a lot safer, since usually compiler
+   warns if you try to place them in xxx*. See strfuncs.c for examples.
+
+   t_malloc() calls never fail. If there's not enough memory left,
+   i_panic() will be called. */
+void *t_malloc_no0(size_t size) ATTR_MALLOC ATTR_RETURNS_NONNULL;
+void *t_malloc0(size_t size) ATTR_MALLOC ATTR_RETURNS_NONNULL;
+
+/* Try growing allocated memory. Returns TRUE if successful. Works only
+   for last allocated memory in current stack frame. */
+bool t_try_realloc(void *mem, size_t size);
+
+/* Returns the number of bytes available in data stack without allocating
+   more memory. */
+size_t t_get_bytes_available(void) ATTR_PURE;
+
+#define t_new(type, count) \
+	((type *) t_malloc0(MALLOC_MULTIPLY((unsigned int)sizeof(type), (count))) + \
+	 COMPILE_ERROR_IF_TRUE(sizeof(type) > UINT_MAX))
+
+/* Returns pointer to a temporary buffer you can use. The buffer will be
+   invalid as soon as next t_malloc() is called!
+
+   If you wish to grow the buffer, you must give the full wanted size
+   in the size parameter. If return value doesn't point to the same value
+   as last time, you need to memcpy() data from the old buffer to the
+   new one (or do some other trickery). See t_buffer_reget(). */
+void *t_buffer_get(size_t size) ATTR_RETURNS_NONNULL;
+
+/* Grow the buffer, memcpy()ing the memory to new location if needed. */
+void *t_buffer_reget(void *buffer, size_t size) ATTR_RETURNS_NONNULL;
+
+/* Make the last t_buffer_get()ed buffer permanent. Note that size MUST be
+   less or equal than the size you gave with last t_buffer_get() or the
+   result will be undefined. */
+void t_buffer_alloc(size_t size);
+/* Allocate the last t_buffer_get()ed data entirely. */
+void t_buffer_alloc_last_full(void);
+
+/* Returns TRUE if ptr is allocated within the given data stack frame.
+   Currently this assert-crashes if the data stack frame isn't the latest. */
+bool data_stack_frame_contains(data_stack_frame_t *id, const void *ptr);
+
+/* Returns the number of bytes malloc()ated for data stack. */
+size_t data_stack_get_alloc_size(void);
+/* Returns the number of bytes currently used in data stack. */
+size_t data_stack_get_used_size(void);
+
+/* Free all the memory that is currently unused (i.e. reserved for growing
+   data stack quickly). */
+void data_stack_free_unused(void);
+
+void data_stack_init(void);
+void data_stack_deinit_event(void);
+void data_stack_deinit(void);
+
+#endif