utils.h: add OSMO_NAME_C_IMPL() macro

Provide a common implementation for foo_name_c() functions that base on
foo_name_buf() functions.

  char *foo_name_c(void *ctx, example_t arg)
  {
          OSMO_NAME_C_IMPL(ctx, 64, "ERROR", foo_name_buf, arg)
  }

Rationale: the most efficient way of composing strings that have optional parts
or require loops for composition is by writing to a ready char[], and this in
turn is easiest done by using OSMO_STRBUF_* API. Using such a basic name string
implementation which typically returns a length, I often want a more convenient
version that returns a char*, which can just be inlined in a "%s" string format
-- crucially: skipping string composition when inlined in a LOGP(). This common
implementation allows saving code dup, only the function signature is needed.

Why not include the function signature in the macro? The two sets of varargs
(1: signature args, 2: function call args) are hard to do. Also, having an
explicit signature is good for readability and code grepping / ctags.

Upcoming uses: in libosmocore in the mslookup (D-GSM) implementation
(osmo_mslookup_result_name_c()), and in osmo_msc's codec negotiation
implementation (sdp_audio_codecs_name_c(), sdp_msg_name_c(), ...).
I54b6c0810f181259da307078977d9ef3d90458c9 (libosmocore)
If3ce23cd5bab15e2ab4c52ef3e4c75979dffe931 (osmo-msc)

Change-Id: Ida5ba8d9640ea641aafef0236800f6d489d3d322

1 files changed, 17 insertions, 0 deletions

diff --git a/tests/utils/utils_test.ok b/tests/utils/utils_test.ok
index c150a8d0..b6036476 100644
--- a/tests/utils/utils_test.ok
+++ b/tests/utils/utils_test.ok
@@ -360,3 +360,20 @@ osmo_str_startswith("abc", "ab") == true
 osmo_str_startswith("abc", "abc") == true
 osmo_str_startswith("abc", "abcd") == false
 osmo_str_startswith("abc", "xyz") == false
+
+name_c_impl_test
+ 0: "test"
+   OSMO_NAME_C_IMPL(10, "ERROR") -> "test"  allocated 1  10 bytes, name 'foo_name_c'
+      OSMO_NAME_C_IMPL(10, NULL) -> "test"  allocated 1  10 bytes, name 'foo_name_c_null'
+    OSMO_NAME_C_IMPL(0, "ERROR") -> "test"  allocated 1  5 bytes, name 'foo_name_c_zero'
+       OSMO_NAME_C_IMPL(0, NULL) -> "test"  allocated 1  5 bytes, name 'foo_name_c_zero_null'
+ 1: "longer than 10 chars"
+   OSMO_NAME_C_IMPL(10, "ERROR") -> "longer than 10 chars"  allocated 1  21 bytes, name 'foo_name_c'
+      OSMO_NAME_C_IMPL(10, NULL) -> "longer than 10 chars"  allocated 1  21 bytes, name 'foo_name_c_null'
+    OSMO_NAME_C_IMPL(0, "ERROR") -> "longer than 10 chars"  allocated 1  21 bytes, name 'foo_name_c_zero'
+       OSMO_NAME_C_IMPL(0, NULL) -> "longer than 10 chars"  allocated 1  21 bytes, name 'foo_name_c_zero_null'
+ 2: NULL
+   OSMO_NAME_C_IMPL(10, "ERROR") -> "ERROR"  allocated 1  6 bytes, name 'foo_name_c'
+      OSMO_NAME_C_IMPL(10, NULL) -> NULL  allocated 0
+    OSMO_NAME_C_IMPL(0, "ERROR") -> "ERROR"  allocated 1  6 bytes, name 'foo_name_c_zero'
+       OSMO_NAME_C_IMPL(0, NULL) -> NULL  allocated 0