Move unix-specific random_bytes() implementation to unix.c.

1 files changed, 67 insertions, 0 deletions

diff --git a/unix.c b/unix.c
index d25aeb2e..39ca5732 100644
--- a/unix.c
+++ b/unix.c
@@ -218,3 +218,70 @@ double gettime()
 	gettimeofday( time, 0 );
 	return( (double) time->tv_sec + (double) time->tv_usec / 1000000 );
 }
+
+/* A pretty reliable random number generator. Tries to use the /dev/random
+   devices first, and falls back to the random number generator from libc
+   when it fails. Opens randomizer devices with O_NONBLOCK to make sure a
+   lack of entropy won't halt BitlBee. */
+void random_bytes( unsigned char *buf, int count )
+{
+	static int use_dev = -1;
+	
+	/* Actually this probing code isn't really necessary, is it? */
+	if( use_dev == -1 )
+	{
+		if( access( "/dev/random", R_OK ) == 0 || access( "/dev/urandom", R_OK ) == 0 )
+			use_dev = 1;
+		else
+		{
+			use_dev = 0;
+			srand( ( getpid() << 16 ) ^ time( NULL ) );
+		}
+	}
+	
+	if( use_dev )
+	{
+		int fd;
+		
+		/* At least on Linux, /dev/random can block if there's not
+		   enough entropy. We really don't want that, so if it can't
+		   give anything, use /dev/urandom instead. */
+		if( ( fd = open( "/dev/random", O_RDONLY | O_NONBLOCK ) ) >= 0 )
+			if( read( fd, buf, count ) == count )
+			{
+				close( fd );
+				return;
+			}
+		close( fd );
+		
+		/* urandom isn't supposed to block at all, but just to be
+		   sure. If it blocks, we'll disable use_dev and use the libc
+		   randomizer instead. */
+		if( ( fd = open( "/dev/urandom", O_RDONLY | O_NONBLOCK ) ) >= 0 )
+			if( read( fd, buf, count ) == count )
+			{
+				close( fd );
+				return;
+			}
+		close( fd );
+		
+		/* If /dev/random blocks once, we'll still try to use it
+		   again next time. If /dev/urandom also fails for some
+		   reason, stick with libc during this session. */
+		
+		use_dev = 0;
+		srand( ( getpid() << 16 ) ^ time( NULL ) );
+	}
+	
+	if( !use_dev )
+	{
+		int i;
+		
+		/* Possibly the LSB of rand() isn't very random on some
+		   platforms. Seems okay on at least Linux and OSX though. */
+		for( i = 0; i < count; i ++ )
+			buf[i] = rand() & 0xff;
+	}
+}
+
+