rud.is

There are a plethora of amazingly useful Golang libraries, and it has been possible for quite some time to use Go libraries with Swift. The advent of the release of the new Apple Silicon/M1/arm64 architecture for macOS created the need for a new round of “fat”/”universal” binaries and libraries to bridge the gap between legacy Intel Macs and the new breed of Macs.

I didn’t see an “all-in-one-place” snippet for how to build cross-platform + fat/universal Golang static libraries and then use them in Swift to make a fat/universal macOS binary, and it is likely I’m not the only one who wished this existed, so here’s a snippet that takes the static HTML library example from Young Dynasty and shows how to prepare the static library for use in Swift, then how to build a Swift universal binary. This is a command line app and we’re building everything without the Xcode editor to keep it concise and straightforward.

The rest of the explanatory text is in the comments in the code block.

# make a space to play in
mkdir universal-static-test
cd universal-static-test

# libhtmlscraper via: https://youngdynasty.net/posts/writing-mac-apps-in-go/
# make the small HTML escaper library Golang source
cat > main.go << EOF
package main

import (
  "C"
  "html"
)

//export escape_html
func escape_html(input *C.char) *C.char {
  s := html.EscapeString(C.GoString(input))
  return C.CString(s)
}

//export unescape_html
func unescape_html(input *C.char) *C.char {
  s := html.UnescapeString(C.GoString(input))
  return C.CString(s)
}

// We need an entry point; it's ok for this to be empty
func main() {}
EOF

# build the Go library for ARM
CGO_ENABLED=1 GOOS=darwin GOARCH=arm64 go build --buildmode=c-archive -o libhtmlescaper-arm64.a

# build the Go library for AMD
CGO_ENABLED=1 GOOS=darwin GOARCH=amd64 go build --buildmode=c-archive -o libhtmlescaper-amd64.a

# Make a universal static archive
lipo -create libhtmlescaper-arm64.a libhtmlescaper-amd64.a -o libhtmlescaper.a

# we don't need this anymore
rm libhtmlescaper-amd64.h

# this is a better name
mv libhtmlescaper-arm64.h libhtmlescaper.h

# make the objective-c bridging header so we can use the library in Swift
cat > bridge.h <<EOF
#include "libhtmlescaler.h"
EOF

# creaate a lame/super basic test swift file that uses the Go library
cat > main.swift <<EOF
print(String(cString: escape_html(strdup("<b>bold</b>"))))
EOF

# make the swift executatble for amd64
swiftc -target x86_64-apple-macos11.0 -import-objc-header bridge.h main.swift libhtmlescaper.a -o main-amd64

# make the swift executatble for arm64
swiftc -target arm64-apple-macos11.0 -import-objc-header bridge.h main.swift libhtmlescaper.a -o main-arm64 

# Make a universal binary
lipo -create main-amd64 main-arm64 -o main

# Make sure it's universal
file main
## main: Mach-O universal binary with 2 architectures: [x86_64:Mach-O 64-bit executable x86_64] [arm64]
## main (for architecture x86_64): Mach-O 64-bit executable x86_64
## main (for architecture arm64):  Mach-O 64-bit executable arm64

# try it out
./main.swift
## "<b>bold</b>"