magervalp / mvpcstruct

Class for packing and unpacking C structs in Swift

C struct handling for Swift

Class for packing and unpacking C structs in Swift, modeled after the struct module in Python.

Sample Code

import MVPCStruct

// Receiver expects a message with a header like this:
//  typedef struct {
//      uint16_t version;  // Message format version, currently 0x0100.
//      uint16_t reserved; // Reserved for future use.
//      uint32_t length;   // Length of data in bytes.
//      uint8_t data[];    // Binary encoded plist.
//  } __attribute__((packed)) mma_msg_t;
func sendMessageHeader(msgData: NSData) -> Bool {
    var error: NSError?
    
    let version = 0x0100
    let reserved = 0
    
    let packer = CStruct(format: "=HHI")
    if let packedHeader = packer.pack([version, reserved, msgData.length], error: &error) {
        return 8 == send(socket_fd, packedHeader.bytes, packedHeader.length)
    } else {
        return false
    }
}

Tasks

Creating CStruct Objects

- initWithFormat:

init(format: String)

Unpacking data

- unpack:format:error:

func unpack(data: NSData, format: String, error: NSErrorPointer) -> AnyObject[]?

- unpack:error:

func unpack(data: NSData, error: NSErrorPointer) -> AnyObject[]?

Packing values

- pack:format:error:

func pack(values: AnyObject[], format: String, error: NSErrorPointer) -> NSData?

- pack:error:

func pack(values: AnyObject[], error: NSErrorPointer) -> NSData? {

Format strings

Control characters

	BYTE ORDER	SIZE	ALIGNMENT
@	native	native	native
=	native	standard	none
<	little-endian	standard	none
>	big-endian	standard	none
!	network (BE)	standard	none

Format characters

FORMAT	C TYPE	SWIFT TYPE	SIZE
x	pad byte	no value
c	char	String of length 1	1
b	signed char	Int	1
B	unsigned char	UInt	1
?	_Bool	Bool	1
h	short	Int	2
H	unsigned short	UInt	2
i	int	Int	4
I	unsigned int	UInt	4
l	long	Int	4
L	unsigned long	UInt	4
q	long long	Int	8
Q	unsigned long long	UInt	8
f	float	Float	4
d	double	Double	8
s	char[]	String
p	char[]	String
P	void *	UInt	4/8

mvpcstruct's Issues

Suggested improvements

I would like to see 2 features in this project:

1. Packing and unpacking of bit fields.
   The bit fields would allow a value to occupy 1 or more bits. See https://en.wikipedia.org/wiki/C_syntax#Bit_fields
2. Packing and unpacking of packed BCD encoded values for integer types.
   A value of 1234 would be stored as 0x1234

I will be happy to try to add these features to this project.

Fails in Swift 2

Just tried the swift code and it looks like it is failing in XCode 7

License?

Is this project under any kind of open source license? If it is, it would be appropriate to specify it in a LICENSE file or in the README, otherwise it's technically illegal for anyone to copy, fork or use this code without explicit permission for each case.

Thanks,

/ Markus

upgrade to latest Swift

Will you upgrade this awesome repo to latest Swift? Try it myself and drown by the pointer :<

Update to Xcode 6 - Beta 6

There's been some syntax changes (among other things) to Swift since this was first written. In particular regarding array declarations and for loop ranges. I made the updates but I'm having issues building the project (may or may not be related to beta 4), otherwise I'd send a PR.

• https://developer.apple.com/swift/blog/?id=3