objdump: recognize some file types

lib/compiler/objdump.zig

@@ -1,29 +1,89 @@
 const std = @import("std");
 const Io = std.Io;
 const fatal = std.process.fatal;
+const mem = std.mem;
+const assert = std.debug.assert;
+
+var stdout_buffer: [4000]u8 = undefined;
 
 pub fn main(init: std.process.Init) !void {
     const io = init.io;
     const args = try init.minimal.args.toSlice(init.arena.allocator());
 
-    var input_path: ?[]const u8 = null;
-    var i: usize = 0;
+    var opt_input_path: ?[]const u8 = null;
+    var i: usize = 1;
     while (i < args.len) : (i += 1) {
         const arg = args[i];
-        if (std.mem.startsWith(u8, arg, "-")) {
-            if (std.mem.eql(u8, arg, "-h") or std.mem.eql(u8, arg, "--help")) {
+        if (mem.startsWith(u8, arg, "-")) {
+            if (mem.eql(u8, arg, "-h") or mem.eql(u8, arg, "--help")) {
                 return Io.File.stdout().writeStreamingAll(io, usage);
             } else {
                 fatal("unrecognized argument: {s}", .{arg});
             }
-        } else if (input_path == null) {
-            input_path = arg;
+        } else if (opt_input_path == null) {
+            opt_input_path = arg;
         } else {
             fatal("unexpected positional: {s}", .{arg});
         }
     }
+
+    const input_path = opt_input_path orelse fatal("missing input file path positional argument", .{});
+
+    var file = std.Io.Dir.cwd().openFile(io, input_path, .{}) catch |err|
+        fatal("failed to open {s}: {t}", .{ input_path, err });
+    defer file.close(io);
+
+    var buffer: [4000]u8 = undefined;
+    var file_reader = file.reader(io, &buffer);
+    var stdout_writer = std.Io.File.stdout().writerStreaming(io, &stdout_buffer);
+    dump(&file_reader.interface, &stdout_writer.interface) catch |err| switch (err) {
+        error.ReadFailed => return file_reader.err.?,
+        error.WriteFailed => return stdout_writer.err.?,
+        error.UnknownFile => fatal("unrecognized file: {s}", .{input_path}),
+        else => |e| return e,
+    };
+    try stdout_writer.flush();
 }
 
+fn dump(r: *Io.Reader, w: *Io.Writer) !void {
+    try r.fill(4);
+    elf: {
+        if (!mem.eql(u8, r.buffered()[0..4], std.elf.MAGIC)) break :elf;
+        return elf.dump(r, w);
+    }
+    macho: {
+        if (mem.readInt(u32, r.buffered()[0..4], .little) != std.macho.MH_MAGIC_64) break :macho;
+        return macho.dump(r, w);
+    }
+    wasm: {
+        comptime assert(std.wasm.magic.len == 4);
+        if (!mem.eql(u8, r.buffered()[0..4], &std.wasm.magic)) break :wasm;
+        return wasm.dump(r, w);
+    }
+    return error.UnknownFile;
+}
+
+const elf = struct {
+    fn dump(r: *Io.Reader, w: *Io.Writer) !void {
+        _ = r;
+        try w.writeAll("TODO dump elf file\n");
+    }
+};
+
+const macho = struct {
+    fn dump(r: *Io.Reader, w: *Io.Writer) !void {
+        _ = r;
+        try w.writeAll("TODO dump macho file\n");
+    }
+};
+
+const wasm = struct {
+    fn dump(r: *Io.Reader, w: *Io.Writer) !void {
+        _ = r;
+        try w.writeAll("TODO dump wasm file\n");
+    }
+};
+
 const usage =
     \\Usage: zig objdump [options] file
     \\