how can I wrap zlib in golang?

Question

I tried to fix the golang's slowest zip implementation by calling the c zlib from golang using cgo

but I get an error

error: 'deflateInit' undeclared (first use in this function)

deflateInit is defined in zlib.h

Am I missing something? thanks for any hints.

package main

/*
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <assert.h>
#include "zlib.h"
*/
import "C"

import (
    "fmt"
)

func main() {
    fmt.Println("hmmm....")
    fmt.Println(int(C.random()))
    var strm C.struct_z_stream
    fmt.Println(strm)
    ret := C.deflateInit(&strm, 5) // trouble here
}

Answer 1

Here is a fixed version of your code. Note the #cgo LDFLAGS: -lz to link with the zlib library and the little C function myDeflateInit which deals with the fact that deflateInit is a macro rather than a function. Note also the change in definition of strm.

C macros are rather irritating to deal with from Go unfortunately - I couldn't think of a better way than a small C shim function.

package main

/*
#cgo LDFLAGS: -lz
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <assert.h>
#include "zlib.h"

int myDeflateInit(z_streamp s, int n) {
     return deflateInit(s, n);
}
*/
import "C"

import (
    "fmt"
)

func main() {
    fmt.Println("hmmm....")
    fmt.Println(int(C.random()))
    var strm C.z_stream
    fmt.Println(strm)
    ret := C.myDeflateInit(&strm, 5)
    fmt.Println(ret)
}