wg: retry resolution except when fatal

The reference to this is <https://sourceware.org/glibc/wiki/NameResolver>,
which mentions:

"From the perspective of the application that calls getaddrinfo() it
perhaps doesn't matter that much since EAI_FAIL, EAI_NONAME and
EAI_NODATA are all permanent failure codes and the causes are all
permanent failures in the sense that there is no point in retrying
later."

This should cover more early-boot situations.

While we're at it, we clean up the logic a bit so that we don't have a
retry message on the final non-retrying attempt. We also peer into errno
when receiving EAI_SYSTEM, to report to the user what actually happened.

Also, fix the quoting back tick front tick mess.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

src/config.c

@@ -51,7 +51,7 @@ static inline bool parse_port(uint16_t *port, uint32_t *flags, const char *value
 
 	ret = getaddrinfo(NULL, value, &hints, &resolved);
 	if (ret) {
-		fprintf(stderr, "%s: `%s`\n", gai_strerror(ret), value);
+		fprintf(stderr, "%s: `%s'\n", ret == EAI_SYSTEM ? strerror(errno) : gai_strerror(ret), value);
 		return false;
 	}
 
@@ -63,7 +63,7 @@ static inline bool parse_port(uint16_t *port, uint32_t *flags, const char *value
 		*port = ntohs(((struct sockaddr_in6 *)resolved->ai_addr)->sin6_port);
 		ret = 0;
 	} else
-		fprintf(stderr, "Neither IPv4 nor IPv6 address found: `%s`\n", value);
+		fprintf(stderr, "Neither IPv4 nor IPv6 address found: `%s'\n", value);
 
 	freeaddrinfo(resolved);
 	if (!ret)
@@ -98,7 +98,7 @@ static inline bool parse_fwmark(uint32_t *fwmark, uint32_t *flags, const char *v
 static inline bool parse_key(uint8_t key[static WG_KEY_LEN], const char *value)
 {
 	if (!key_from_base64(key, value)) {
-		fprintf(stderr, "Key is not the correct length or format: `%s`\n", value);
+		fprintf(stderr, "Key is not the correct length or format: `%s'\n", value);
 		return false;
 	}
 	return true;
@@ -115,7 +115,7 @@ static inline bool parse_ip(struct wgallowedip *allowedip, const char *value)
 			allowedip->family = AF_INET;
 	}
 	if (allowedip->family == AF_UNSPEC) {
-		fprintf(stderr, "Unable to parse IP address: `%s`\n", value);
+		fprintf(stderr, "Unable to parse IP address: `%s'\n", value);
 		return false;
 	}
 	return true;
@@ -146,13 +146,13 @@ static inline bool parse_endpoint(struct sockaddr *endpoint, const char *value)
 		end = strchr(mutable, ']');
 		if (!end) {
 			free(mutable);
-			fprintf(stderr, "Unable to find matching brace of endpoint: `%s`\n", value);
+			fprintf(stderr, "Unable to find matching brace of endpoint: `%s'\n", value);
 			return false;
 		}
 		*end++ = '\0';
 		if (*end++ != ':' || !*end) {
 			free(mutable);
-			fprintf(stderr, "Unable to find port of endpoint: `%s`\n", value);
+			fprintf(stderr, "Unable to find port of endpoint: `%s'\n", value);
 			return false;
 		}
 	} else {
@@ -160,32 +160,34 @@ static inline bool parse_endpoint(struct sockaddr *endpoint, const char *value)
 		end = strrchr(mutable, ':');
 		if (!end || !*(end + 1)) {
 			free(mutable);
-			fprintf(stderr, "Unable to find port of endpoint: `%s`\n", value);
+			fprintf(stderr, "Unable to find port of endpoint: `%s'\n", value);
 			return false;
 		}
 		*end++ = '\0';
 	}
 
-	for (unsigned int timeout = 1000000; timeout < 90000000; timeout = timeout * 3 / 2) {
+	for (unsigned int timeout = 1000000;;) {
 		ret = getaddrinfo(begin, end, &hints, &resolved);
-		if (ret != EAI_AGAIN)
+		if (!ret)
 			break;
-		fprintf(stderr, "%s: `%s`. Trying again in %.2f seconds...\n", gai_strerror(ret), value, timeout / 1000000.0);
+		timeout = timeout * 3 / 2;
+		/* The set of return codes that are "permanent failures". All other possibilities are potentially transient. */
+		if (ret == EAI_NONAME || ret == EAI_FAIL || ret == EAI_NODATA || timeout >= 90000000) {
+			free(mutable);
+			fprintf(stderr, "%s: `%s'\n", ret == EAI_SYSTEM ? strerror(errno) : gai_strerror(ret), value);
+			return false;
+		}
+		fprintf(stderr, "%s: `%s'. Trying again in %.2f seconds...\n", ret == EAI_SYSTEM ? strerror(errno) : gai_strerror(ret), value, timeout / 1000000.0);
 		usleep(timeout);
 	}
 
-	if (ret != 0) {
-		free(mutable);
-		fprintf(stderr, "%s: `%s`\n", gai_strerror(ret), value);
-		return false;
-	}
 	if ((resolved->ai_family == AF_INET && resolved->ai_addrlen == sizeof(struct sockaddr_in)) ||
 	    (resolved->ai_family == AF_INET6 && resolved->ai_addrlen == sizeof(struct sockaddr_in6)))
 		memcpy(endpoint, resolved->ai_addr, resolved->ai_addrlen);
 	else {
 		freeaddrinfo(resolved);
 		free(mutable);
-		fprintf(stderr, "Neither IPv4 nor IPv6 address found: `%s`\n", value);
+		fprintf(stderr, "Neither IPv4 nor IPv6 address found: `%s'\n", value);
 		return false;
 	}
 	freeaddrinfo(resolved);
@@ -206,7 +208,7 @@ static inline bool parse_persistent_keepalive(uint16_t *interval, uint32_t *flag
 
 	ret = strtoul(value, &end, 10);
 	if (!*value || *value == '-' || *end || ret > 65535) {
-		fprintf(stderr, "The persistent keepalive interval must be 0/off or 1-65535. Found: `%s`\n", value);
+		fprintf(stderr, "The persistent keepalive interval must be 0/off or 1-65535. Found: `%s'\n", value);
 		return false;
 	}
 
@@ -431,7 +433,7 @@ static bool read_keyfile(char dst[WG_KEY_LEN_BASE64], const char *path)
 
 	while ((c = getc(f)) != EOF) {
 		if (!isspace(c)) {
-			fprintf(stderr, "Found trailing character in key file: `%c`\n", c);
+			fprintf(stderr, "Found trailing character in key file: `%c'\n", c);
 			goto out;
 		}
 	}

src/show.c

@@ -352,7 +352,7 @@ static bool ugly_print(struct wgdevice *device, const char *param, bool with_int
 	} else if (!strcmp(param, "dump"))
 		dump_print(device, with_interface);
 	else {
-		fprintf(stderr, "Invalid parameter: `%s`\n", param);
+		fprintf(stderr, "Invalid parameter: `%s'\n", param);
 		show_usage();
 		return false;
 	}

src/wg.c

@@ -14,7 +14,7 @@ static const struct {
 	const char *description;
 } subcommands[] = {
 	{ "show", show_main, "Shows the current configuration and device information" },
-	{ "showconf", showconf_main, "Shows the current configuration of a given WireGuard interface, for use with `setconf`" },
+	{ "showconf", showconf_main, "Shows the current configuration of a given WireGuard interface, for use with `setconf'" },
 	{ "set", set_main, "Change the current configuration, add peers, remove peers, or change peers" },
 	{ "setconf", setconf_main, "Applies a configuration file to a WireGuard interface" },
 	{ "addconf", setconf_main, "Appends a configuration file to a WireGuard interface" },
@@ -61,7 +61,7 @@ findsubcommand:
 		goto findsubcommand;
 	}
 
-	fprintf(stderr, "Invalid subcommand: `%s`\n", argv[1]);
+	fprintf(stderr, "Invalid subcommand: `%s'\n", argv[1]);
 	show_usage(stderr);
 	return 1;
 }