ui/app: (iOS) redirect standard Go logger to NSLog

Signed-off-by: Elias Naur <mail@eliasnaur.com>

ui/app/log_ios.go

@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+// +build ios
+
+package app
+
+/*
+#include "log_ios.h"
+*/
+import "C"
+
+import (
+	"bufio"
+	"io"
+	"log"
+	"unsafe"
+)
+
+func init() {
+	// macOS Console already includes timstamps.
+	log.SetFlags(log.Flags() &^ log.LstdFlags)
+	log.SetOutput(newNSLogWriter())
+}
+
+func newNSLogWriter() io.Writer {
+	r, w := io.Pipe()
+	go func() {
+		// 1024 is an arbitrary truncation limit, taken from Android's
+		// log buffer size.
+		lineBuf := bufio.NewReaderSize(r, 1024)
+		// The buffer to pass to C, including the terminating '\0'.
+		buf := make([]byte, lineBuf.Size()+1)
+		cbuf := (*C.char)(unsafe.Pointer(&buf[0]))
+		for {
+			line, _, err := lineBuf.ReadLine()
+			if err != nil {
+				break
+			}
+			copy(buf, line)
+			buf[len(line)] = 0
+			C.nslog(cbuf)
+		}
+	}()
+	return w
+}

ui/app/log_ios.h

@@ -0,0 +1,3 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+__attribute__ ((visibility ("hidden"))) void nslog(char *str);

ui/app/log_ios.m

@@ -0,0 +1,11 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+// +build ios
+
+@import Foundation;
+
+#include "log_ios.h"
+
+void nslog(char *str) {
+	NSLog(@"%@", @(str));
+}