Re: [Libguestfs] [PATCH] generator: Fix API of functions that return RBufferOut

Subject: [PATCH] generator: Fix API of functions that return RBufferOut (NB: The API / ABI doesn't actually change here - it's just made much simpler to use). The API for RBufferOut functions was unexpectedly hard to use in the case where a zero-length buffer might be returned. For discussion on this see:

diff --git a/src/generator.ml b/src/generator.ml index c5f21df..2317541 100644 --- a/src/generator.ml +++ b/src/generator.ml @@ -5107,7 +5109,7 @@ and generate_client_actions () = #define error guestfs_error //#define perrorf guestfs_perrorf -//#define safe_malloc guestfs_safe_malloc +#define safe_malloc guestfs_safe_malloc #define safe_realloc guestfs_safe_realloc //#define safe_strdup guestfs_safe_strdup #define safe_memdup guestfs_safe_memdup @@ -5396,8 +5398,20 @@ check_state (guestfs_h *g, const char *caller) pr " /* caller will free this */\n"; pr " return safe_memdup (g, &ret.%s, sizeof (ret.%s));\n" n n | RBufferOut n -> - pr " *size_r = ret.%s.%s_len;\n" n n; - pr " return ret.%s.%s_val; /* caller will free */\n" n n + pr " /* RBufferOut is tricky: If the buffer is zero-length, then\n"; + pr " * _val might be NULL here. To make the API saner for\n"; + pr " * callers, we turn this case into a unique pointer (using\n"; + pr " * malloc(1)).\n"; + pr " */\n"; + pr " if (ret.%s.%s_len > 0) {\n" n n; + pr " *size_r = ret.%s.%s_len;\n" n n; + pr " return ret.%s.%s_val; /* caller will free */\n" n n; + pr " } else {\n"; + pr " free (ret.%s.%s_val);\n" n n; + pr " char *p = safe_malloc (g, 1);\n"; + pr " *size_r = ret.%s.%s_len;\n" n n; + pr " return p;\n"; + pr " }\n";