From 185a9fa221753d9e7add96c8f7d5acb1d7cf5dfc Mon Sep 17 00:00:00 2001
From: Jonas 'Sortie' Termansen <sortie@maxsi.org>
Date: Sun, 26 Jul 2020 00:06:09 +0200
Subject: [PATCH] Support IPv6 shorthand and IPv4-mapped addresses in
 inet_{pton,ntop}(3).

---
 libc/arpa/inet/inet_ntop.c | 59 ++++++++++++++++++++++++++++--------
 libc/arpa/inet/inet_pton.c | 61 ++++++++++++++++++++++++++++++++++----
 2 files changed, 103 insertions(+), 17 deletions(-)

diff --git a/libc/arpa/inet/inet_ntop.c b/libc/arpa/inet/inet_ntop.c
index 0197eb1d..7d1dacd5 100644
--- a/libc/arpa/inet/inet_ntop.c
+++ b/libc/arpa/inet/inet_ntop.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016 Jonas 'Sortie' Termansen.
+ * Copyright (c) 2016, 2020 Jonas 'Sortie' Termansen.
  *
  * Permission to use, copy, modify, and distribute this software for any
  * purpose with or without fee is hereby granted, provided that the above
@@ -21,8 +21,8 @@
 
 #include <errno.h>
 #include <arpa/inet.h>
-#include <netinet/in.h>
 #include <stdio.h>
+#include <string.h>
 
 const char* inet_ntop(int af,
                       const void* restrict src,
@@ -42,18 +42,53 @@ const char* inet_ntop(int af,
 	}
 	else if ( af == AF_INET6 )
 	{
-		// TODO: Support for :: syntax.
-		// TODO: Support for x:x:x:x:x:x:d.d.d.d syntax.
+		// TODO: When should x:x:x:x:x:x:d.d.d.d notation be used?
 		const unsigned char* ip = (const unsigned char*) src;
-		int len = snprintf(dst, size, "%x:%x:%x:%x:%x:%x:%x:%x",
-		                   ip[0] << 8 | ip[1], ip[2] << 8 | ip[3],
-		                   ip[4] << 8 | ip[5], ip[6] << 8 | ip[7],
-		                   ip[8] << 8 | ip[9], ip[10] << 8 | ip[11],
-		                   ip[12] << 8 | ip[13], ip[14] << 8 | ip[15]);
-		if ( len < 0 )
-			return NULL;
-		if ( size <= (size_t) len )
+		size_t longest_zeroes_offset = 0;
+		size_t longest_zeroes_length = 0;
+		size_t current_zeroes_offset = 0;
+		size_t current_zeroes_length = 0;
+		for ( size_t i = 0; i < 8; i++ )
+		{
+			const unsigned char* data = ip + i * 2;
+			if ( !data[0] && !data[1] )
+			{
+				current_zeroes_length++;
+				if ( longest_zeroes_length < current_zeroes_length )
+				{
+					longest_zeroes_offset = current_zeroes_offset;
+					longest_zeroes_length = current_zeroes_length;
+				}
+			}
+			else
+			{
+				current_zeroes_offset = i + 1;
+				current_zeroes_length = 0;
+			}
+		}
+		char buffer[INET6_ADDRSTRLEN];
+		size_t offset = 0;
+		for ( size_t i = 0; i < 8; i++ )
+		{
+			const unsigned char* data = ip + i * 2;
+			if ( i == longest_zeroes_offset && 2 <= longest_zeroes_length )
+			{
+				buffer[offset++] = ':';
+				buffer[offset++] = ':';
+				i += longest_zeroes_length - 1;
+			}
+			else
+			{
+				if ( offset && buffer[offset - 1] != ':' )
+					buffer[offset++] = ':';
+				offset += snprintf(buffer + offset, sizeof(buffer) - offset,
+				                   "%x", data[0] << 8 | data[1]);
+			}
+		}
+		buffer[offset] = '\0';
+		if ( size <= (size_t) offset )
 			return errno = ENOSPC, (const char*) NULL;
+		memcpy(dst, buffer, offset + 1);
 		return dst;
 	}
 	else
diff --git a/libc/arpa/inet/inet_pton.c b/libc/arpa/inet/inet_pton.c
index 1751af0f..73fb2d21 100644
--- a/libc/arpa/inet/inet_pton.c
+++ b/libc/arpa/inet/inet_pton.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016 Jonas 'Sortie' Termansen.
+ * Copyright (c) 2016, 2020 Jonas 'Sortie' Termansen.
  *
  * Permission to use, copy, modify, and distribute this software for any
  * purpose with or without fee is hereby granted, provided that the above
@@ -61,15 +61,55 @@ int inet_pton(int af, const char* restrict src, void* restrict dst)
 	{
 		unsigned char ip[16];
 		size_t index = 0;
-		// TODO: Support for :: syntax.
-		// TODO: Support for x:x:x:x:x:x:d.d.d.d syntax.
-		for ( int i = 0; i < 8; i++ )
+		int compressed_at = -1;
+		int i;
+		for ( i = 0; i < 8; i++ )
 		{
-			if ( i && src[index++] != ':' )
+			if ( compressed_at == -1 &&
+			     src[index + 0] == ':' &&
+			     src[index + 1] == ':' )
+			{
+				index += 2;
+				compressed_at = i;
+			}
+			else if ( !src[index] )
+				break;
+			else if ( i && src[index++] != ':' )
 				return 0;
 			int num = 0;
 			for ( int j = 0; j < 4; j++ )
 			{
+				if ( src[index] == '.' &&
+				     ((compressed_at == -1 && i == 6) ||
+				      (0 < compressed_at && i <= 6)) )
+				{
+					index -= j;
+					for ( int n = 0; n < 4; n++ )
+					{
+						if ( n && src[index++] != '.' )
+							return 0;
+						num = 0;
+						for ( int m = 0; m < 3; m++ )
+						{
+							if ( !m && src[index] == '0' )
+							{
+								index++;
+								break;
+							}
+							if ( '0' <= src[index] && src[index] <= '9' )
+								num = num * 10 + src[index++] - '0';
+							else if ( !m )
+								return 0;
+							else
+								break;
+						}
+						if ( 255 < num )
+							return 0;
+						ip[2 * i + n] = num;
+					}
+					i += 2;
+					goto done;
+				}
 				int dgt;
 				if ( '0' <= src[index] && src[index] <= '9' )
 					dgt = src[index] - '0';
@@ -89,8 +129,19 @@ int inet_pton(int af, const char* restrict src, void* restrict dst)
 			ip[2 * i + 0] = num >> 8 & 0xFF;
 			ip[2 * i + 1] = num >> 0 & 0xFF;
 		}
+done:
 		if ( src[index] )
 			return 0;
+		if ( 0 <= compressed_at )
+		{
+			if ( i == 8 )
+				return 0;
+			memmove(ip + 16 - 2 * (i - compressed_at), ip + 2 * compressed_at,
+			        (i - compressed_at) * 2);
+			memset(ip + 2 * compressed_at, 0, (8 - i) * 2);
+		}
+		else if ( i < 8 )
+			return 0;
 		memcpy(dst, ip, sizeof(ip));
 		return 1;
 	}