media: Format description struct, stubs for more formats

packages/media/src/jpeg.zig

@@ -0,0 +1,139 @@
+const std = @import("std");
+
+const Format = @import("Format.zig");
+
+const format: Format = .{
+    .magic_length = magic.len,
+    // NOTE The information (like width and height) is not in a fixed position
+    .info_length = magic.len,
+    .extension = "jpeg",
+    .media_type = "image/jpeg",
+    .isFormat = isJpeg,
+};
+
+const magic = "\xFF\xD8\xFF";
+
+const Info = union(enum) {
+    partial: void,
+    full: Header,
+
+    pub fn makeFull(full: Header) Info {
+        return .{ .full = full };
+    }
+};
+
+const Header = struct {
+    width: u32,
+    height: u32,
+};
+
+const Marker = enum(u8) {
+    /// Start of frame, Huffman coding, Baseline DCT
+    SOF_0 = 0xC0,
+    /// Start of frame, Huffman coding, Extended sequential DCT
+    SOF_1 = 0xC1,
+    /// Start of frame, Huffman coding, Progressive DCT
+    SOF_2 = 0xC2,
+    /// Start of frame, Huffman coding, Lossless (sequential)
+    SOF_3 = 0xC3,
+    /// Start of frame, Huffman coding, Differential sequential DCT
+    SOF_5 = 0xC5,
+    /// Start of frame, Huffman coding, Differential progressive DCT
+    SOF_6 = 0xC6,
+    /// Start of frame, Huffman coding, Differential lossless (sequential)
+    SOF_7 = 0xC7,
+    /// Start of frame, arithmetic coding, Extended sequential DCT
+    SOF_9 = 0xC9,
+    /// Start of frame, arithmetic coding, Progressive DCT
+    SOF_10 = 0xCA,
+    /// Start of frame, arithmetic coding, Lossless (sequential)
+    SOF_11 = 0xCB,
+    /// Start of frame, arithmetic coding, Differential sequential DCT
+    SOF_13 = 0xCD,
+    /// Start of frame, arithmetic coding, Differential progressive DCT
+    SOF_14 = 0xCE,
+    /// Start of frame, arithmetic coding, Differential lossless (sequential)
+    SOF_15 = 0xCF,
+    /// Define Huffman table(s)
+    DHT = 0xC4,
+    /// Define arithmetic coding conditioning(s)
+    DAC = 0xCC,
+    /// Start of image
+    SOI = 0xD8,
+    /// End of image
+    EOI = 0xD9,
+    /// Start of scan
+    SOS = 0xDA,
+    /// Define quantization table(s)
+    DQT = 0xDB,
+    /// Define number of lines
+    DNL = 0xDC,
+    /// Define restart interval
+    DRI = 0xDD,
+    /// Define hierarchical progression
+    DHP = 0xDE,
+    /// Expand reference component(s)
+    EXP = 0xDF,
+    /// Comment
+    COM = 0xFE,
+    /// For temporary private use in arithmetic coding
+    TEM = 0x01,
+
+    _,
+
+    /// Restart with modulo 8 count `m`
+    pub fn RST(m: u3) Marker {
+        return @enumFromInt(0xD0 | m);
+    }
+
+    pub fn isRST(self: Marker) ?u3 {
+        return if (@intFromEnum(self) & 0b1111_1000 == 0xD0) @intCast(@intFromEnum(self) & 0b0000_0111) else null;
+    }
+
+    /// Reserved for application segments
+    pub fn APP(n: u4) Marker {
+        return @enumFromInt(0xE0 | n);
+    }
+
+    pub fn isAPP(self: Marker) ?u3 {
+        return if (@intFromEnum(self) & 0b1111_0000 == 0xE0) @intCast(@intFromEnum(self) & 0b0000_1111) else null;
+    }
+
+    /// A standalone marker has no content and are not followed by segment
+    /// length parameter.
+    pub fn isStandalone(self: Marker) bool {
+        return self.isRST() != null or
+            self == .SOI or
+            self == .EOI or
+            self == .TEM;
+    }
+};
+
+/// The caller asserts that the buffer is at least `format.magic_length` bytes
+/// long.
+pub fn isJpeg(buffer: []const u8) bool {
+    return std.mem.eql(u8, buffer[0..format.magic_length], magic);
+}
+
+/// The caller asserts that the buffer is at least `format.info_length` bytes
+/// long. The information is not in a fixed position, so you need to provide a
+/// substantial amount of data, in the order of kilobytes. Depending on the
+/// amount of metadata, the information might be in the first kilobyte or dozens
+/// of kilobytes in.
+///
+/// This function returns:
+///
+/// - `null` when the buffer is not a JPEG or it's a malformed JPEG
+/// - `.partial` when the buffer appears to be a part of a JPEG, but the
+///   information could not be found within the buffer provided
+/// - `.full` when the buffer appears to be a part of a JPEG and the information
+///   was fully contained within the buffer provided
+pub fn info(buffer: []const u8) ?Info {
+    std.debug.assert(buffer.len >= format.info_length);
+
+    if (!isJpeg(buffer)) {
+        return null;
+    }
+
+    @panic("TODO");
+}