1 files changed, 69 insertions, 0 deletions
diff --git a/src/jpg/segment.zig b/src/jpg/segment.zig
new file mode 100644
index 0000000..ec1346a
--- /dev/null
+++ b/src/jpg/segment.zig
@@ -0,0 +1,69 @@
+const std = @import("std");
+const jpg = @import("root.zig");
+
+pub const Segment = union(jpg.Marker.Kind) {
+    temporary: void,
+    reset: void,
+    start_of_image: void,
+    end_of_image: void,
+    start_of_frame: void,
+    define_quantization_table: void,
+    define_huffman_table: void,
+    define_restart_interval: void,
+    define_number_of_lines: void,
+    define_hierarchy_progression: void,
+    extend_huffman_table: void,
+    application_segment: void,
+    comment: void,
+    start_of_scan: void,
+
+    const Self = @This();
+
+    pub fn read(gpa: std.mem.Allocator, reader: *std.Io.Reader) !Self {
+        if (try reader.peekByte() != 0xff) {
+            return error.InvalidMarkerHeader;
+        }
+        reader.toss(1);
+
+        const marker  = jpg.Marker.from_u8(try reader.peekByte())
+            catch return error.InvalidMarkerByte;
+        reader.toss(1);
+
+        return switch (marker) {
+            .temporary => .{ .temporary = void{} },
+            .reset => .{ .reset = void{} },
+            .start_of_image => .{ .start_of_image = void{} },
+            .end_of_image => .{ .end_of_image = void{} },
+            .start_of_frame => data: {
+                const buffer = try read_data_with_length(gpa, reader);
+                defer gpa.free(buffer);
+                break :data .{ .start_of_frame = void{} };
+            },
+            .application_segment => data: {
+                const buffer = try read_data_with_length(gpa, reader);
+                defer gpa.free(buffer);
+                break :data .{ .application_segment = void{} };
+            },
+            else => {
+                std.debug.panic("unimplemented tag '{s}'\n", .{@tagName(marker)});
+            },
+        };
+    }
+
+    fn read_data_with_length(gpa: std.mem.Allocator, reader: *std.Io.Reader) ![]u8 {
+        const length = try reader.takeInt(u16, .big);
+        return try reader.readAlloc(gpa, @intCast(length));
+    }
+};
+
+
+test "file" {
+    const buffer = @embedFile("../testing/rgb.jpg");
+    var reader: std.Io.Reader = .fixed(buffer);
+
+    var segment: Segment = try .read(std.testing.allocator, &reader);
+    try std.testing.expectEqual(.start_of_image, std.meta.activeTag(segment));
+
+    segment = try .read(std.testing.allocator, &reader);
+    try std.testing.expectEqual(.application_segment, std.meta.activeTag(segment));
+}