tlv: allocate tlv structs from within

let's let the fromwire__tlv methods allocate the tlv-objects and
return them. we also want to initialize all of their underlying
messages to NULL, and fail if we discover a duplicate mesage type.

if parsing fails, instead of returning a struct we return NULL.

Suggested-By: @rustyrussell

tools/generate-wire.py

@@ -504,8 +504,9 @@ class Message(object):
             elif f.is_tlv:
                 if not f.is_variable_size():
                     raise TypeError('TLV {} not variable size'.format(f.name))
-                subcalls.append('if (!fromwire__{tlv_name}(ctx, &cursor, &plen, &{tlv_len}, {tlv_name}))'
+                subcalls.append('{tlv_name} = fromwire__{tlv_name}(ctx, &cursor, &plen, &{tlv_len});'
                                 .format(tlv_name=f.name, tlv_len=f.lenvar))
+                subcalls.append('if (!{tlv_name})'.format(tlv_name=f.name))
                 subcalls.append('return false;')
             elif f.is_variable_size():
                 subcalls.append("//2nd case {name}".format(name=f.name))
@@ -846,10 +847,12 @@ tlv__type_impl_towire_template = """static void towire__{tlv_name}(const tal_t *
 {fields}}}
 """
 
-tlv__type_impl_fromwire_template = """static bool fromwire__{tlv_name}(const tal_t *ctx, const u8 **p, size_t *plen, const u16 *len, struct {tlv_name} *{tlv_name}) {{
+tlv__type_impl_fromwire_template = """static struct {tlv_name} *fromwire__{tlv_name}(const tal_t *ctx, const u8 **p, size_t *plen, const u16 *len) {{
 \tu8 msg_type, msg_len;
 \tif (*plen < *len)
-\t\treturn false;
+\t\treturn NULL;
+
+\tstruct {tlv_name} *{tlv_name} = talz(ctx, struct {tlv_name});
 
 \twhile (*plen) {{
 \t\tmsg_type = fromwire_u8(p, plen);
@@ -865,14 +868,25 @@ tlv__type_impl_fromwire_template = """static bool fromwire__{tlv_name}(const tal
 \t\t\tplen -= msg_len;
 \t\t}}
 \t}}
-\treturn *p != NULL;
+\tif (!*p) {{
+\t\ttal_free({tlv_name});
+\t\treturn NULL;
+\t}}
+\treturn {tlv_name};
 }}
 """
 
 case_tmpl = """\t\tcase {tlv_msg_enum}:
-\t\t\t{tlv_name}->{tlv_msg_name} = tal(ctx, struct tlv_msg_{tlv_msg_name});
-\t\t\tif (!fromwire_{tlv_name}_{tlv_msg_name}({ctx_arg}*p, plen, msg_len, {tlv_name}->{tlv_msg_name}))
-\t\t\t\treturn false;
+\t\t\tif ({tlv_name}->{tlv_msg_name} != NULL) {{
+\t\t\t\tfromwire_fail(p, plen);
+\t\t\t\ttal_free({tlv_name});
+\t\t\t\treturn NULL;
+\t\t\t}}
+\t\t\t{tlv_name}->{tlv_msg_name} = tal({tlv_name}, struct tlv_msg_{tlv_msg_name});
+\t\t\tif (!fromwire_{tlv_name}_{tlv_msg_name}({ctx_arg}*p, plen, msg_len, {tlv_name}->{tlv_msg_name})) {{
+\t\t\t\ttal_free({tlv_name});
+\t\t\t\treturn NULL;
+\t\t\t}}
 \t\t\tbreak;
 """
 
@@ -906,7 +920,7 @@ def print_tlv_towire(tlv_field_name, messages):
 def print_tlv_fromwire(tlv_field_name, messages):
     cases = ""
     for m in messages:
-        ctx_arg = 'ctx, ' if m.has_variable_fields else ''
+        ctx_arg = tlv_field_name + ', ' if m.has_variable_fields else ''
         cases += case_tmpl.format(ctx_arg=ctx_arg,
                                   tlv_msg_enum=m.enum.name,
                                   tlv_name=tlv_field_name,