Application running using os.exec doesn't load java libraries properly

Question

I would really appreciate if you helped me. I'm rewriting a simple Minecraft launcher from Java to Go. Everything is good, in exception of one thing. I have a start function which executes using os.Exec this command:

java -Xincgc -Xmx1024M -Djava.library.path="/minecraft/bin/natives/" -cp "/minecraft/bin/*" -Dfml.ignoreInvalidMinecraftCertificates=true -Dfml.ignorePatchDiscrepancies=true net.minecraft.launchwrapper.Launch --username user --session session --version 1.6.4 --gameDir "/minecraft" --assetsDir "/minecraft" --tweakClass cpw.mods.fml.common.launcher.FMLTweaker

Everything is fine running this through bash or cmd, but when executed with Go function it returns the following:

Could not find or load main class net.minecraft.launchwrapper.Launch

I think os.exec(Command) cannot properly interpet this part of command:

-cp "/minecraft/bin/*"

Maybe that's because I quoted string "/minecraft/bin/*" with strconv.Quote() function or because of asterisk. I really don't know what's heppening. Ah, btw, the command os.exec has run is correct, though (I read it in stdout with fmt for debugging purposes).

program:

func start(login string, session string, ram string) {
//start game

app := "java"
arg0 := "-Xincgc"
arg1 := "-Xmx" + ram + "M"
arg2 := "-Djava.library.path=" + strconv.Quote(filepath.FromSlash(client+"bin/natives/"))
arg3 := "-cp"
arg4 := strconv.Quote(filepath.FromSlash(client + "bin/*"))
arg5 := "-Dfml.ignoreInvalidMinecraftCertificates=true"
arg6 := "-Dfml.ignorePatchDiscrepancies=true"
arg7 := "net.minecraft.launchwrapper.Launch"
arg8 := "--username"
//arg9 is login
arg10 := "--session"
//arg11 is session
arg12 := "--version 1.6.4"
arg13 := "--gameDir"
arg14 := strconv.Quote(filepath.FromSlash(client))
arg15 := "--assetsDir"
arg16 := strconv.Quote(filepath.FromSlash(client + "assets"))
arg17 := "--tweakClass cpw.mods.fml.common.launcher.FMLTweaker"

cmd := exec.Command(app, arg0, arg1, arg2, arg3, arg4, arg5, arg6, arg7, arg8, login, arg10, session, arg12, arg13, arg14, arg15, arg16, arg17)
cmd.Stdout = os.Stdout
cmd.Stderr = os.Stderr
cmd.Run()
fmt.Println(app, arg0, arg1, arg2, arg3, arg4, arg5, arg6, arg7, arg8, login, arg10, session, arg12, arg13, arg14, arg15, arg16, arg17)
}

Your `minecraft` directory is really under the root directory (`/`)? It isn't under your home directory? — RealSkeptic, Dec 17 '14 at 15:04
You should keep the arguments separated: `arg12 := "--version 1.6.4"` becomes `arg12 := "--version"` and `arg13 := "1.6.4"` — topskip, Dec 17 '14 at 15:08
Yes, it works! @topskip, big thanks for your help! I'm always doing stupid mistakes... — , Dec 17 '14 at 15:16
@topskip sorry, I wrote my answer before seing the edits and your comments. If you write an answer accepted by the OP, I'll delete mine. — VonC, Dec 17 '14 at 15:24
@VonC Your answer looks fine (except that I am confused with the double quotes), so there is no need for another answer. — topskip, Dec 17 '14 at 15:32

score 1 · Answer 1 · edited May 23 '17 at 11:46

The question "Properly pass arguments to Go Exec" mentions:

exec.Command(...) adds double quotes to the parameters if there is spaces in them, so you only need to escape \" where you need them.

In your case, -cp "/minecraft/bin/*" would be passed to exec.Command as two separate parameters.

If you need quotes within one parameter, you could use a string literal to keep them (as commented in "How do you add spaces to exec.command in golang").

But if, in your case, you need the cp (classpath) to be expended by the shell (as mentioned in "double quotes escaping in golang exec"), then remove the quotes:

exec.Command(..., "-cp", `/minecraft/bin/*`, ...)

Application running using os.exec doesn't load java libraries properly

1 Answers1

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