swap ssize_t for gint64 where possible

Some versions of the Windows headers define ssize_t as unsigned. This
patch removes (where possible) use of ssize_t inside libvips, esp. in
the new stream API.

See https://github.com/libvips/libvips/issues/1494#issuecomment-568254731

libvips/foreign/vipspng.c

@@ -180,7 +180,7 @@ typedef struct {
 	 */
 	unsigned char input_buffer[INPUT_BUFFER_SIZE];
 	unsigned char *next_byte;
-	ssize_t bytes_in_buffer;
+	gint64 bytes_in_buffer;
 
 } Read;
 
@@ -225,10 +225,10 @@ vips_png_read_stream( png_structp pPng, png_bytep data, png_size_t length )
 	 * syscall for each one. Read via our own buffer.
 	 */
 	while( length > 0 ) {
-		ssize_t bytes_available;
+		gint64 bytes_available;
 
 		if( read->bytes_in_buffer <= 0 ) {
-			ssize_t bytes_read;
+			gint64 bytes_read;
 
 			bytes_read = vips_streami_read( read->streami, 
 				read->input_buffer, INPUT_BUFFER_SIZE );

libvips/include/vips/stream.h

@@ -184,8 +184,11 @@ typedef struct _VipsStreamiClass {
 
 	/* Read from the stream into the supplied buffer, args exactly as
 	 * read(2). Set errno on error.
+	 *
+	 * We must return gint64, since ssize_t is often defined as unsigned
+	 * on Windows.
 	 */
-	ssize_t (*read)( VipsStreami *, void *, size_t );
+	gint64 (*read)( VipsStreami *, void *, size_t );
 
 	/* Seek to a certain position, args exactly as lseek(2). Set errno on
 	 * error.
@@ -211,7 +214,7 @@ VipsStreami *vips_streami_new_from_options( const char *options );
 void vips_streami_minimise( VipsStreami *streami );
 int vips_streami_unminimise( VipsStreami *streami );
 int vips_streami_decode( VipsStreami *streami );
-ssize_t vips_streami_read( VipsStreami *streami, void *data, size_t length );
+gint64 vips_streami_read( VipsStreami *streami, void *data, size_t length );
 gboolean vips_streami_is_mappable( VipsStreami *streami );
 const void *vips_streami_map( VipsStreami *streami, size_t *length );
 VipsBlob *vips_streami_map_blob( VipsStreami *streami );
@@ -314,8 +317,11 @@ typedef struct _VipsStreamoClass {
 	VipsStreamClass parent_class;
 
 	/* Write to output. Args exactly as write(2).
+	 *
+	 * We must return gint64, since ssize_t is often defined as unsigned
+	 * on Windows.
 	 */
-	ssize_t (*write)( VipsStreamo *, const void *, size_t );
+	gint64 (*write)( VipsStreamo *, const void *, size_t );
 
 	/* Output has been generated, so do any clearing up,
 	 * eg. copy the bytes we saved in memory to the stream blob.

libvips/iofuncs/bufis.c

@@ -132,10 +132,10 @@ vips_bufis_unbuffer( VipsBufis *bufis )
 
 /* Returns -1 on error, 0 on EOF, otherwise bytes read.
  */
-static ssize_t
+static gint64
 vips_bufis_refill( VipsBufis *bufis )
 {
-	ssize_t bytes_read;
+	gint64 bytes_read;
 
 	VIPS_DEBUG_MSG( "vips_bufis_refill:\n" );
 

libvips/iofuncs/streami.c

@@ -276,12 +276,12 @@ vips_streami_build( VipsObject *object )
 	return( 0 );
 }
 
-static ssize_t
+static gint64
 vips_streami_read_real( VipsStreami *streami, void *data, size_t length )
 {
 	VipsStream *stream = VIPS_STREAM( streami );
 
-	ssize_t bytes_read;
+	gint64 bytes_read;
 
 	VIPS_DEBUG_MSG( "vips_streami_read_real:\n" );
 
@@ -624,14 +624,14 @@ vips_streami_decode( VipsStreami *streami )
  *
  * Arguments exactly as read(2).
  *
- * Returns: the number of bytes raed, 0 on end of file, -1 on error.
+ * Returns: the number of bytes read, 0 on end of file, -1 on error.
  */
-ssize_t
+gint64
 vips_streami_read( VipsStreami *streami, void *buffer, size_t length )
 {
 	VipsStreamiClass *class = VIPS_STREAMI_GET_CLASS( streami );
 
-	ssize_t bytes_read;
+	gint64 total_read;
 
 	VIPS_DEBUG_MSG( "vips_streami_read:\n" );
 
@@ -641,19 +641,19 @@ vips_streami_read( VipsStreami *streami, void *buffer, size_t length )
 		vips_streami_test_features( streami ) )
 		return( -1 );
 
-	bytes_read = 0;
+	total_read = 0;
 
 	if( streami->data ) {
 		/* The whole thing is in memory somehow.
 		 */
-		ssize_t available = VIPS_MIN( length,
+		gint64 available = VIPS_MIN( length,
 			streami->length - streami->read_position );
 
 		VIPS_DEBUG_MSG( "    %zd bytes from memory\n", available );
 		memcpy( buffer, 
 			streami->data + streami->read_position, available );
 		streami->read_position += available;
-		bytes_read += available;
+		total_read += available;
 	}
 	else {
 		/* Some kind of filesystem or custom source. 
@@ -663,7 +663,7 @@ vips_streami_read( VipsStreami *streami, void *buffer, size_t length )
 		 */
 		if( streami->header_bytes &&
 			streami->read_position < streami->header_bytes->len ) {
-			ssize_t available = VIPS_MIN( length, 
+			gint64 available = VIPS_MIN( length, 
 				streami->header_bytes->len - 
 					streami->read_position );
 
@@ -676,18 +676,19 @@ vips_streami_read( VipsStreami *streami, void *buffer, size_t length )
 			streami->read_position += available;
 			buffer += available;
 			length -= available;
-			bytes_read += available;
+			total_read += available;
 		}
 
 		/* Any more bytes requested? Call the read() vfunc.
 		 */
 		if( length > 0 ) {
-			ssize_t n;
+			gint64 bytes_read;
 
 			VIPS_DEBUG_MSG( "    calling class->read()\n" );
-			n = class->read( streami, buffer, length );
-			VIPS_DEBUG_MSG( "    %zd bytes from read()\n", n );
-			if( n == -1 ) {
+			bytes_read = class->read( streami, buffer, length );
+			VIPS_DEBUG_MSG( "    %zd bytes from read()\n", 
+				bytes_read );
+			if( bytes_read == -1 ) {
 				vips_error_system( errno, 
 					vips_stream_nick( 
 						VIPS_STREAM( streami ) ), 
@@ -701,20 +702,20 @@ vips_streami_read( VipsStreami *streami, void *buffer, size_t length )
 			if( streami->header_bytes &&
 				streami->is_pipe &&
 				!streami->decode &&
-				n > 0 ) 
+				bytes_read > 0 ) 
 				g_byte_array_append( streami->header_bytes, 
-					buffer, n );
+					buffer, bytes_read );
 
-			streami->read_position += n;
-			bytes_read += n;
+			streami->read_position += bytes_read;
+			total_read += bytes_read;
 		}
 	}
 
-	VIPS_DEBUG_MSG( "    %zd bytes total\n", bytes_read );
+	VIPS_DEBUG_MSG( "    %zd bytes total\n", total_read );
 
 	SANITY( streami );
 
-	return( bytes_read );
+	return( total_read );
 }
 
 /* -1 on a pipe isn't actually unbounded. Have a limit to prevent
@@ -753,7 +754,7 @@ vips_streami_pipe_read_to_position( VipsStreami *streami, gint64 target )
 
 	while( target == -1 ||
 		streami->read_position < target ) {
-		ssize_t bytes_read;
+		gint64 bytes_read;
 
 		bytes_read = vips_streami_read( streami, buffer, 4096 );
 		if( bytes_read == -1 )
@@ -805,7 +806,7 @@ vips_streami_read_to_memory( VipsStreami *streami )
 	read_position = 0;
 	q = byte_array->data;
 	while( read_position < streami->length ) {
-		ssize_t bytes_read;
+		gint64 bytes_read;
 
 		bytes_read = vips_streami_read( streami, q, 
 			VIPS_MAX( 4096, streami->length - read_position ) );
@@ -1187,7 +1188,7 @@ vips_streami_sniff_at_most( VipsStreami *streami,
 	read_position = 0; 
 	q = streami->sniff->data;
 	while( read_position < length ) {
-		ssize_t bytes_read;
+		gint64 bytes_read;
 
 		bytes_read = vips_streami_read( streami, q, 
 			length - read_position );

libvips/iofuncs/streamiu.c

@@ -70,7 +70,7 @@ enum {
 
 static guint vips_streamiu_signals[SIG_LAST] = { 0 };
 
-static ssize_t
+static gint64
 vips_streamiu_read_real( VipsStreami *streami, 
 	void *buffer, size_t length )
 {

libvips/iofuncs/streamo.c

@@ -142,7 +142,7 @@ vips_streamo_build( VipsObject *object )
 	return( 0 );
 }
 
-static ssize_t 
+static gint64 
 vips_streamo_write_real( VipsStreamo *streamo, const void *data, size_t length )
 {
 	VipsStream *stream = VIPS_STREAM( streamo );
@@ -305,14 +305,14 @@ vips_streamo_write_unbuffered( VipsStreamo *streamo,
 		g_byte_array_append( streamo->memory_buffer, data, length );
 	else 
 		while( length > 0 ) { 
-			ssize_t n;
+			gint64 bytes_written;
 
-			n = class->write( streamo, data, length );
+			bytes_written = class->write( streamo, data, length );
 
 			/* n == 0 isn't strictly an error, but we treat it as 
 			 * one to make sure we don't get stuck in this loop.
 			 */
-			if( n <= 0 ) {
+			if( bytes_written <= 0 ) {
 				vips_error_system( errno, 
 					vips_stream_nick( 
 						VIPS_STREAM( streamo ) ),
@@ -320,8 +320,8 @@ vips_streamo_write_unbuffered( VipsStreamo *streamo,
 				return( -1 ); 
 			}
 
-			length -= n;
-			data += n;
+			length -= bytes_written;
+			data += bytes_written;
 		}
 
 	return( 0 );

libvips/iofuncs/streamou.c

@@ -70,7 +70,7 @@ enum {
 
 static guint vips_streamou_signals[SIG_LAST] = { 0 };
 
-static ssize_t
+static gint64
 vips_streamou_write_real( VipsStreamo *streamo, 
 	const void *data, size_t length )
 {

libvips/iofuncs/vips.c

@@ -549,8 +549,8 @@ parser_read_fd( XML_Parser parser, int fd )
 {
 	const int chunk_size = 1024; 
 
-	ssize_t bytes_read;
-	ssize_t len;
+	gint64 bytes_read;
+	gint64 len;
 
 	bytes_read = 0;
 
@@ -563,7 +563,7 @@ parser_read_fd( XML_Parser parser, int fd )
 			return( -1 );
 		}
 		len = read( fd, buf, chunk_size );
-		if( len == (ssize_t) -1 ) {
+		if( len == -1 ) {
 			vips_error( "VipsImage", 
 				"%s", _( "read error while fetching XML" ) );
 			return( -1 );