[musl] EAI_NODATA in musl

[Rich Felker <dalias@libc.org>]

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I just posted on libc-coord about an idea that sounded good, and it
turns out glibc and nearly everyone else have had it for a long time:

https://www.openwall.com/lists/libc-coord/2022/09/19/2

I'd like to bring the same to musl, even though it's not standardized
yet, since it's a clear candidate for standardization and solves a
major problem with the libc DNS API, namely inability to distinguish
NxDomain from NODATA.

Aside from that, it should help justify musl's distinguishing of these
two (very different) results in how search domain fallbacks work and
how results for one of the A or AAAA erroring out get handled. Our
misleadingly reporting "name exists but has no address" as "name
doesn't exist" has made it hard for folks to understand why we don't
keep going on the search when "name does not exist".

Draft patch attached, untested.


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diff --git a/include/netdb.h b/include/netdb.h
index d096c781..3af065e2 100644
--- a/include/netdb.h
+++ b/include/netdb.h
@@ -44,6 +44,7 @@ struct addrinfo {
 #define EAI_NONAME     -2
 #define EAI_AGAIN      -3
 #define EAI_FAIL       -4
+#define EAI_NODATA     -5
 #define EAI_FAMILY     -6
 #define EAI_SOCKTYPE   -7
 #define EAI_SERVICE    -8
diff --git a/src/network/gai_strerror.c b/src/network/gai_strerror.c
index 9596580e..56b71503 100644
--- a/src/network/gai_strerror.c
+++ b/src/network/gai_strerror.c
@@ -6,7 +6,7 @@ static const char msgs[] =
 	"Name does not resolve\0"
 	"Try again\0"
 	"Non-recoverable error\0"
-	"Unknown error\0"
+	"Name has no usable address\0"
 	"Unrecognized address family or invalid length\0"
 	"Unrecognized socket type\0"
 	"Unrecognized service\0"
diff --git a/src/network/lookup_name.c b/src/network/lookup_name.c
index bec6ba22..37d481f9 100644
--- a/src/network/lookup_name.c
+++ b/src/network/lookup_name.c
@@ -79,7 +79,7 @@ static int name_from_hosts(struct address buf[static MAXADDRS], char canon[stati
 		case 0:
 			continue;
 		default:
-			badfam = EAI_NONAME;
+			badfam = EAI_NODATA;
 			break;
 		}
 
@@ -175,7 +175,7 @@ static int name_from_dns(struct address buf[static MAXADDRS], char canon[static
 		__dns_parse(abuf[i], alens[i], dns_parse_callback, &ctx);
 
 	if (ctx.cnt) return ctx.cnt;
-	return EAI_NONAME;
+	return EAI_NODATA;
 }
 
 static int name_from_dns_search(struct address buf[static MAXADDRS], char canon[static 256], const char *name, int family)