add osmo_talloc_asprintf() and ctrl_cmd_reply_printf()

Add macro to append to a CTRL commands' reply string, ctrl_cmd_reply_printf().
The talloc_asprintf() part of it is generic enough to qualify for a separate
macro, osmo_talloc_asprintf().

The idea is to not have to decide for each bit added to a string whether the
string is already allocated or not, but simply be able to issue printf commands
and let the macro worry about initial allocation or reallocation.

This originally came from osmo-hlr change
I1bd62ae0d4eefde7e1517db15a2155640a1bab58, where it was requested to move this
bit to libosmocore.

Change-Id: Ic9dba0e4a1eb5a7dc3cee2f181b9024ed4fc7005

1 files changed, 18 insertions, 0 deletions

diff --git a/include/osmocom/core/utils.h b/include/osmocom/core/utils.h
index 5f412139..4b083f6c 100644
--- a/include/osmocom/core/utils.h
+++ b/include/osmocom/core/utils.h
@@ -85,6 +85,24 @@ static inline void osmo_talloc_replace_string(void *ctx, char **dst, const char
 	*dst = talloc_strdup(ctx, newstr);
 }
 
+/*! Append to a string and re-/allocate if necessary.
+ * \param[in] ctx  Talloc context to use for initial allocation.
+ * \param[in,out] dest  char* to re-/allocate and append to.
+ * \param[in] fmt  printf-like string format.
+ * \param[in] args  Arguments for fmt.
+ *
+ * \a dest may be passed in NULL, or a string previously allocated by talloc.
+ * If an existing string is passed in, it will remain associated with whichever
+ * ctx it was allocated before, regardless whether it matches \a ctx or not.
+ */
+#define osmo_talloc_asprintf(ctx, dest, fmt, args ...) \
+	do { \
+		if (!dest) \
+			dest = talloc_asprintf(ctx, fmt, ## args); \
+		else \
+			dest = talloc_asprintf_append((char*)dest, fmt, ## args); \
+	} while (0)
+
 int osmo_constant_time_cmp(const uint8_t *exp, const uint8_t *rel, const int count);
 uint64_t osmo_decode_big_endian(const uint8_t *data, size_t data_len);
 uint8_t *osmo_encode_big_endian(uint64_t value, size_t data_len);