Merge pull request #5354 from Kelimion/init_net

Allow `core:net` to be imported with `-default-to-panic-allocator`.

core/net/common.odin

@@ -261,6 +261,9 @@ DNS_Configuration :: struct {
 	resolv_conf: string,
 	hosts_file:  string,
 
+	resolv_conf_buf: [128]u8,
+	hosts_file_buf:  [128]u8,
+
 	// TODO: Allow loading these up with `reload_configuration()` call or the like,
 	// so we don't have to do it each call.
 	name_servers:       []Endpoint,

core/net/dns.odin

@@ -22,21 +22,22 @@ package net
 		Haesbaert:       Security fixes
 */
 
+@(require) import "base:runtime"
 import "core:mem"
 import "core:strings"
 import "core:time"
 import "core:os"
 import "core:math/rand"
-/*
+@(require) import "core:sync"
-	Default configuration for DNS resolution.
+
-*/
+dns_config_initialized: sync.Once
 when ODIN_OS == .Windows {
-	DEFAULT_DNS_CONFIGURATION :: DNS_Configuration{
+	dns_configuration := DNS_Configuration{
 		resolv_conf = "",
 		hosts_file  = "%WINDIR%\\system32\\drivers\\etc\\hosts",
 	}
 } else when ODIN_OS == .Linux || ODIN_OS == .Darwin || ODIN_OS == .FreeBSD || ODIN_OS == .OpenBSD || ODIN_OS == .NetBSD {
-	DEFAULT_DNS_CONFIGURATION :: DNS_Configuration{
+	dns_configuration := DNS_Configuration{
 		resolv_conf = "/etc/resolv.conf",
 		hosts_file  = "/etc/hosts",
 	}
@@ -44,25 +45,20 @@ when ODIN_OS == .Windows {
 	#panic("Please add a configuration for this OS.")
 }
 
-@(init)
-init_dns_configuration :: proc() {
 /*
-		Resolve %ENVIRONMENT% placeholders in their paths.
+	Replaces environment placeholders in `dns_configuration`. Only necessary on Windows.
+	Is automatically called, once, by `get_dns_records_*`.
 */
-	dns_configuration.resolv_conf = os.replace_environment_placeholders(dns_configuration.resolv_conf)
+@(private)
-	dns_configuration.hosts_file  = os.replace_environment_placeholders(dns_configuration.hosts_file)
+init_dns_configuration :: proc() {
+	when ODIN_OS == .Windows {
+		runtime.DEFAULT_TEMP_ALLOCATOR_TEMP_GUARD()
+		val := os.replace_environment_placeholders(dns_configuration.hosts_file, context.temp_allocator)
+		copy(dns_configuration.hosts_file_buf[:], val)
+		dns_configuration.hosts_file = string(dns_configuration.hosts_file_buf[:len(val)])
 	}
-
-@(fini, private)
-destroy_dns_configuration :: proc() {
-	delete(dns_configuration.resolv_conf)
-	dns_configuration.resolv_conf = ""
-	delete(dns_configuration.hosts_file)
-	dns_configuration.hosts_file = ""
 }
 
-dns_configuration := DEFAULT_DNS_CONFIGURATION
-
 /*
 	Resolves a hostname to exactly one IP4 and IP6 endpoint.
 	It's then up to you which one you use.
@@ -182,6 +178,9 @@ resolve_ip6 :: proc(hostname_and_maybe_port: string) -> (ep6: Endpoint, err: Net
 	See `destroy_records`.
 */
 get_dns_records_from_os :: proc(hostname: string, type: DNS_Record_Type, allocator := context.allocator) -> (records: []DNS_Record, err: DNS_Error) {
+	when ODIN_OS == .Windows {
+		sync.once_do(&dns_config_initialized, init_dns_configuration)
+	}
 	return _get_dns_records_os(hostname, type, allocator)
 }
 
@@ -197,6 +196,9 @@ get_dns_records_from_os :: proc(hostname: string, type: DNS_Record_Type, allocat
 	See `destroy_records`.
 */
 get_dns_records_from_nameservers :: proc(hostname: string, type: DNS_Record_Type, name_servers: []Endpoint, host_overrides: []DNS_Record, allocator := context.allocator) -> (records: []DNS_Record, err: DNS_Error) {
+	when ODIN_OS == .Windows {
+		sync.once_do(&dns_config_initialized, init_dns_configuration)
+	}
 	context.allocator = allocator
 
 	if type != .SRV {
@@ -418,6 +420,8 @@ load_hosts :: proc(hosts_file_path: string, allocator := context.allocator) -> (
 		splits := strings.fields(line)
 		defer delete(splits)
 
+		(len(splits) >= 2) or_continue
+
 		ip_str := splits[0]
 		addr := parse_address(ip_str)
 		if addr == nil {