Nasal library/io

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This page contains documentation for the io namespace in Nasal. This namespace provides APIs for input/output (IO) operations on files. The io namespace is sourced from fgdata/Nasal/io.nas and simgear/simgear/nasal/iolib.c.

Functions

open(filename, mode="r")

Opens the file with the specified mode (as per ANSI fopen()) and returns a ghost object representing the filehandle. Failures are thrown as runtime errors as per die().

close(filehandle)

Closes the specified file as per ANSI fclose().

read(filehandle, buf, len)

Attempts to read length bytes from the filehandle into the beginning of the mutable string buf. Failures (including overruns when length > size(buf)) are thrown as runtime errors as per die(). Returns the number of bytes successfully read.

write(filehandle, str)

Attempts to write the entirety of the specified string to the filehandle. Failures are thrown as runtime errors as per die(). Returns the number of bytes successfully written.

=== seek(filehandle, position, whence) As ANSI fseek(). Attempts to seek to the specified position based on the whence value (which must be one of io.SEEK_SET, io.SEEK_END, or io.SEEK_CUR).

tell(filehandle)

Returns the current seek position of the filehandle.

readln(filehandle)

Reads and returns a single text line from the filehandle. Interprets both "\n" and "\r\n" as end of line markers, and does not include the "\r" or "\n" bytes in the returned string. End of file or error is signaled by returning nil.

stat(filename)

Calls unix or win32 stat() on the specified file name and returns a seven element array whose contents are, in order: dev, ino, mode, nlink, uid, gid, rdef, size, atime, mtime, ctime. Errors are signaled as exceptions as per die().

basename()

Works like standard Unix command basename. Returns the file name from a given path.

io.basename(<path>);

dirname()

Works like standard Unix command dirname. Returns the directory part from a given path.

io.basename(<path>);

readfile()

Reads and returns a complete file as a string. Failures are thrown as runtime errors as per die().

io.readfile(file);

read_properties()

Load XML file in FlightGear's native <PropertyList> format. If the second, optional target parameter is set, then the properties are loaded to this node in the global property tree. Otherwise they are returned as a separate props.Node tree. Returns the data as a props.Node on success or nil on error.

Usage:   io.read_properties(<filename> [, <props.Node or property-path>]);

Examples:

var target = props.globals.getNode("/sim/model");           
io.read_properties("/tmp/foo.xml", target);                 
                                                            
var data = io.read_properties("/tmp/foo.xml", "/sim/model");
var data = io.read_properties("/tmp/foo.xml");

read_airport_properties()

Load XML file in FlightGear's native <PropertyList> format. File will be located in the airport-scenery directories according to ICAO and filename, i,e in Airports/I/C/A/ICAO.filename.xml

If the second, optional target parameter is set, then the properties are loaded to this node in the global property tree. Otherwise they are returned as a separate props.Node tree. Returns the data as a props.Node on success or nil on error.

Usage:   io.read_properties(<filename> [, <props.Node or property-path>]);

Example:

var data = io.read_airport_properties("KSFO", "rwyuse");

write_properties()

Write XML file in FlightGear's native <PropertyList> format. Returns the filename on success or nil on error. If the source is a props.Node that refers to a node in the main tree, then the data are directly written from the tree, yielding a more accurate result. Otherwise the data need to be copied first, which may slightly change node types (FLOAT becomes DOUBLE etc.)

Usage:   io.write_properties(<filename>, <props.Node or property-path>);

Examples:

var data = props.Node.new({ a:1, b:2, c:{ d:3, e:4 } }); 
io.write_properties("/tmp/foo.xml", data);               
io.write_properties("/tmp/foo.xml", "/sim/model");

Note  The following two functions are for reading generic XML files into the property tree and for writing them from there to the disk. The built-in fgcommands (load, save, loadxml, savexml) are for FlightGear's own <PropertyList> XML files only, as they only handle a limited number of very specific attributes. The io.readxml() loader turns attributes into regular children with a configurable prefix prepended to their name, while io.writexml() turns such nodes back into attributes. The two functions have their own limitations, but can easily get extended to whichever needs. The underlying parsexml() command will handle any XML file.

readxml()

Reads an XML file from an absolute path and returns it as property tree. All nodes will be of type STRING. Data are only written to leafs. Attributes are written as regular nodes with the optional prefix prepended to the name. If the prefix is nil, then attributes are ignored. Returns nil on error.

Usage:  io.readxml(path[,prefix = "___"]);

io.readxml(path,prefix);

writexml()

Writes a property tree as returned by readxml() to a file. Children with name starting with <prefix> are again turned into attributes of their parent. <node> must contain exactly one child, which will become the XML file's outermost element.

Usage:  io.writexml(path, node[,indent = "\t"][, prefix = "___"]);

io.writexml(path, node, indent,prefix);