add validation of bmp magic bytes

src/bmp_valid.zig

@@ -0,0 +1,26 @@
+const std = @import("std");
+
+pub const BMPValidError = error{InvalidMagic};
+
+const VALID_MAGICS = [_][]const u8{
+    "BM",
+    "BA",
+
+    "CI",
+    "CP",
+    "IC",
+    "PT",
+};
+
+pub fn magicValid(magic: []const u8) !void {
+    var valid = false;
+
+    for (VALID_MAGICS) |valid_magic| {
+        if (std.mem.eql(u8, magic, valid_magic)) valid = true;
+    }
+
+    if (!valid) {
+        std.debug.warn("\tINVALID HEADER: '{}'\n", magic);
+        return BMPValidError.InvalidMagic;
+    }
+}

src/image.zig

@@ -2,6 +2,7 @@ const std = @import("std");
 const lv2 = @import("lv2_helpers.zig");
 const c = lv2.c;
 const custom = @import("custom.zig");
+const bmp = @import("bmp_valid.zig");
 
 const plugins = @import("plugin.zig");
 
@@ -235,6 +236,22 @@ pub const Image = struct {
         std.debug.warn("\timage: reopened on '{}'\n", self.curpath);
     }
 
+    pub fn checkValid(self: *Image) !void {
+        var file = try std.fs.File.openRead(self.path);
+        defer file.close();
+
+        // main bmp header:
+        //  2 bytes for magic header
+        //  4 bytes for size in bytes
+        //  2 bytes ?
+        //  2 bytes ?
+        //  4 bytes for pixel array offset
+        var magic = [2]u8{ 0, 0 };
+        _ = try file.read(&magic);
+
+        try bmp.magicValid(&magic);
+    }
+
     /// Run a plugin over the image.
     /// This setups a new lilv world/plugin among other things.
     /// The internal SNDFILE pointer is modified to point to the output of the
@@ -354,6 +371,7 @@ pub const Image = struct {
         _ = c.sf_close(self.sndfile);
 
         try self.reopen(tmpnam);
+        try self.checkValid();
 
         var time_taken = timer.read();
         std.debug.warn("\ttook {d:.2}ms running plugin\n", time_taken / std.time.millisecond);
@@ -441,5 +459,6 @@ pub const Image = struct {
 
         // reopen the file as SFM_READ so we can run plugin chains etc
         try self.reopen(tmpnam);
+        try self.checkValid();
     }
 };