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-rw-r--r--libpanto/src/image.zig358
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diff --git a/libpanto/src/image.zig b/libpanto/src/image.zig
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-//! Native image processing for tool-returned attachments.
-//!
-//! Two responsibilities:
-//!
-//! 1. `detectCodec` — identify an attachment's codec from its leading
-//! bytes (magic numbers), not its file extension.
-//! 2. `maybeResize` — bound raster images to `max_dim` on each side so a
-//! single screenshot can't blow out the model's context. PDFs and
-//! already-small images pass through untouched.
-//!
-//! Raster codecs go through the vendored stb single-header trio
-//! (decode -> Mitchell resize -> re-encode in the *same* codec). WEBP is
-//! decode-only (jebp), so a resized WEBP is re-encoded as JPEG.
-
-const std = @import("std");
-const Allocator = std.mem.Allocator;
-
-const c = @cImport({
- @cInclude("stb_image.h");
- @cInclude("stb_image_resize2.h");
- @cInclude("stb_image_write.h");
- @cInclude("jebp.h");
-});
-
-/// Longest side (px) allowed before we resize. pi uses 2000x2000.
-pub const max_dim: u32 = 2000;
-/// JPEG quality used when re-encoding (WEBP path, and JPEG inputs).
-const jpeg_quality: c_int = 80;
-
-pub const Codec = enum { png, jpeg, gif, bmp, webp, pdf };
-
-/// The MIME type string for a codec (static; do not free).
-pub fn mediaTypeForCodec(codec: Codec) []const u8 {
- return switch (codec) {
- .png => "image/png",
- .jpeg => "image/jpeg",
- .gif => "image/gif",
- .bmp => "image/bmp",
- .webp => "image/webp",
- .pdf => "application/pdf",
- };
-}
-
-/// Detect a supported codec from leading bytes (magic numbers).
-pub fn detectCodec(bytes: []const u8) ?Codec {
- if (bytes.len >= 8 and std.mem.eql(u8, bytes[0..8], &.{ 0x89, 'P', 'N', 'G', 0x0D, 0x0A, 0x1A, 0x0A }))
- return .png;
- if (bytes.len >= 3 and bytes[0] == 0xFF and bytes[1] == 0xD8 and bytes[2] == 0xFF)
- return .jpeg;
- if (bytes.len >= 6 and (std.mem.eql(u8, bytes[0..6], "GIF87a") or std.mem.eql(u8, bytes[0..6], "GIF89a")))
- return .gif;
- if (bytes.len >= 2 and bytes[0] == 'B' and bytes[1] == 'M')
- return .bmp;
- // WEBP: "RIFF"????"WEBP"
- if (bytes.len >= 12 and std.mem.eql(u8, bytes[0..4], "RIFF") and std.mem.eql(u8, bytes[8..12], "WEBP"))
- return .webp;
- if (bytes.len >= 5 and std.mem.eql(u8, bytes[0..5], "%PDF-"))
- return .pdf;
- return null;
-}
-
-/// Map a media-type string back to a codec (for callers that already have
-/// the MIME string). Returns null for unsupported types.
-pub fn codecForMediaType(media_type: []const u8) ?Codec {
- if (std.mem.eql(u8, media_type, "image/png")) return .png;
- if (std.mem.eql(u8, media_type, "image/jpeg")) return .jpeg;
- if (std.mem.eql(u8, media_type, "image/gif")) return .gif;
- if (std.mem.eql(u8, media_type, "image/bmp")) return .bmp;
- if (std.mem.eql(u8, media_type, "image/webp")) return .webp;
- if (std.mem.eql(u8, media_type, "application/pdf")) return .pdf;
- return null;
-}
-
-/// The result of `maybeResize`. `media_type` is the MIME type of `data`
-/// (may differ from the input when a WEBP was re-encoded as JPEG).
-/// `data` is always an owned slice the caller must free.
-pub const Processed = struct {
- media_type: []const u8, // static string, do not free
- data: []u8, // owned by `allocator`
-};
-
-/// Full attachment pipeline for a tool-returned media part: resolve the
-/// media type (detecting from magic bytes when `hint` is null), then
-/// resize. Returns owned raw bytes + the resolved media type.
-///
-/// Errors `error.UnknownMediaType` when neither the hint nor magic-byte
-/// detection recognizes the bytes — the caller decides how to surface
-/// that (e.g. drop the attachment, or fall back to text).
-pub fn process(allocator: Allocator, bytes: []const u8, hint: ?[]const u8) !Processed {
- const codec = blk: {
- if (hint) |h| {
- if (codecForMediaType(h)) |hinted| break :blk hinted;
- }
- break :blk detectCodec(bytes) orelse return error.UnknownMediaType;
- };
- return maybeResize(allocator, bytes, codec);
-}
-
-/// Resize `bytes` so neither dimension exceeds `max_dim`, preserving the
-/// input codec where possible. Returns an owned copy of the (possibly
-/// unchanged) bytes plus the resulting media type.
-///
-/// - PDF: returned verbatim (a copy), media type unchanged.
-/// - raster <= max_dim on both sides: returned verbatim (a copy) — we
-/// skip the decode/encode round-trip to avoid quality loss + CPU.
-/// - stb-supported raster larger than max_dim: decode -> resize -> same
-/// codec.
-/// - WEBP larger than max_dim: jebp decode -> resize -> JPEG.
-pub fn maybeResize(allocator: Allocator, bytes: []const u8, codec: Codec) !Processed {
- const media_type = mediaTypeForCodec(codec);
-
- if (codec == .pdf)
- return .{ .media_type = media_type, .data = try allocator.dupe(u8, bytes) };
-
- if (codec == .webp) return resizeWebp(allocator, bytes, media_type);
- return resizeStb(allocator, bytes, media_type, codec);
-}
-
-/// Probe a raster image's dimensions without fully decoding. Returns null
-/// on failure.
-fn probeDims(bytes: []const u8) ?struct { w: u32, h: u32 } {
- var w: c_int = 0;
- var h: c_int = 0;
- var comp: c_int = 0;
- const ok = c.stbi_info_from_memory(bytes.ptr, @intCast(bytes.len), &w, &h, &comp);
- if (ok == 0 or w <= 0 or h <= 0) return null;
- return .{ .w = @intCast(w), .h = @intCast(h) };
-}
-
-/// Compute target dimensions that fit within `max_dim` x `max_dim` while
-/// preserving aspect ratio. Returns null when no resize is needed.
-fn targetDims(w: u32, h: u32) ?struct { w: u32, h: u32 } {
- if (w <= max_dim and h <= max_dim) return null;
- const wf: f64 = @floatFromInt(w);
- const hf: f64 = @floatFromInt(h);
- const scale = @min(@as(f64, @floatFromInt(max_dim)) / wf, @as(f64, @floatFromInt(max_dim)) / hf);
- const nw: u32 = @max(1, @as(u32, @intFromFloat(@round(wf * scale))));
- const nh: u32 = @max(1, @as(u32, @intFromFloat(@round(hf * scale))));
- return .{ .w = nw, .h = nh };
-}
-
-const StbWriteCtx = struct {
- list: *std.ArrayList(u8),
- allocator: Allocator,
- failed: bool = false,
-};
-
-fn stbWriteCb(ctx_opaque: ?*anyopaque, data: ?*anyopaque, size: c_int) callconv(.c) void {
- const ctx: *StbWriteCtx = @ptrCast(@alignCast(ctx_opaque.?));
- if (ctx.failed or size <= 0) return;
- const bytes: [*]const u8 = @ptrCast(data.?);
- ctx.list.appendSlice(ctx.allocator, bytes[0..@intCast(size)]) catch {
- ctx.failed = true;
- };
-}
-
-fn resizeStb(allocator: Allocator, bytes: []const u8, media_type: []const u8, codec: Codec) !Processed {
- const dims = probeDims(bytes) orelse
- // Can't parse it; pass through rather than fail the read.
- return .{ .media_type = media_type, .data = try allocator.dupe(u8, bytes) };
-
- const target = targetDims(dims.w, dims.h) orelse
- return .{ .media_type = media_type, .data = try allocator.dupe(u8, bytes) };
-
- // Decode to RGBA (4 channels) for a uniform resize path.
- var w: c_int = 0;
- var h: c_int = 0;
- var comp: c_int = 0;
- const pixels = c.stbi_load_from_memory(bytes.ptr, @intCast(bytes.len), &w, &h, &comp, 4);
- if (pixels == null)
- return .{ .media_type = media_type, .data = try allocator.dupe(u8, bytes) };
- defer c.stbi_image_free(pixels);
-
- const out_pixels = try allocator.alloc(u8, @as(usize, target.w) * @as(usize, target.h) * 4);
- defer allocator.free(out_pixels);
-
- const res = c.stbir_resize_uint8_srgb(
- pixels,
- w,
- h,
- 0,
- out_pixels.ptr,
- @intCast(target.w),
- @intCast(target.h),
- 0,
- c.STBIR_RGBA,
- );
- if (res == null)
- return error.ResizeFailed;
-
- var out: std.ArrayList(u8) = .empty;
- errdefer out.deinit(allocator);
- var ctx = StbWriteCtx{ .list = &out, .allocator = allocator };
-
- const tw: c_int = @intCast(target.w);
- const th: c_int = @intCast(target.h);
- const ok = switch (codec) {
- .png => c.stbi_write_png_to_func(stbWriteCb, &ctx, tw, th, 4, out_pixels.ptr, tw * 4),
- .bmp => c.stbi_write_bmp_to_func(stbWriteCb, &ctx, tw, th, 4, out_pixels.ptr),
- // stb has no GIF encoder; re-encode resized GIFs as PNG (lossless).
- .gif => c.stbi_write_png_to_func(stbWriteCb, &ctx, tw, th, 4, out_pixels.ptr, tw * 4),
- .jpeg => c.stbi_write_jpg_to_func(stbWriteCb, &ctx, tw, th, 4, out_pixels.ptr, jpeg_quality),
- else => unreachable,
- };
- if (ok == 0 or ctx.failed) return error.EncodeFailed;
-
- const result_media: []const u8 = switch (codec) {
- .gif => "image/png", // re-encoded
- else => media_type,
- };
- return .{ .media_type = result_media, .data = try out.toOwnedSlice(allocator) };
-}
-
-fn resizeWebp(allocator: Allocator, bytes: []const u8, media_type: []const u8) !Processed {
- var img: c.jebp_image_t = std.mem.zeroes(c.jebp_image_t);
- // Peek at the header first to learn dimensions cheaply.
- if (c.jebp_decode_size(&img, bytes.len, bytes.ptr) != c.JEBP_OK)
- return .{ .media_type = media_type, .data = try allocator.dupe(u8, bytes) };
-
- const w: u32 = @intCast(img.width);
- const h: u32 = @intCast(img.height);
- const target = targetDims(w, h) orelse
- return .{ .media_type = media_type, .data = try allocator.dupe(u8, bytes) };
-
- // Full decode to RGBA (jebp_color_t is 4 contiguous bytes per pixel).
- if (c.jebp_decode(&img, bytes.len, bytes.ptr) != c.JEBP_OK)
- return .{ .media_type = media_type, .data = try allocator.dupe(u8, bytes) };
- defer c.jebp_free_image(&img);
-
- const src: [*]const u8 = @ptrCast(img.pixels);
- const out_pixels = try allocator.alloc(u8, @as(usize, target.w) * @as(usize, target.h) * 4);
- defer allocator.free(out_pixels);
-
- const res = c.stbir_resize_uint8_srgb(
- src,
- @intCast(w),
- @intCast(h),
- 0,
- out_pixels.ptr,
- @intCast(target.w),
- @intCast(target.h),
- 0,
- c.STBIR_RGBA,
- );
- if (res == null) return error.ResizeFailed;
-
- // TODO: when the source WEBP has an alpha layer, re-encoding to JPEG
- // flattens transparency, which can look wrong for screenshots and
- // diagrams. Consider re-encoding to PNG when alpha is present. For now
- // we always emit JPEG: there is no small single-header WEBP encoder,
- // and token size matters more than fidelity for LLM input.
- var out: std.ArrayList(u8) = .empty;
- errdefer out.deinit(allocator);
- var ctx = StbWriteCtx{ .list = &out, .allocator = allocator };
- const tw: c_int = @intCast(target.w);
- const th: c_int = @intCast(target.h);
- const ok = c.stbi_write_jpg_to_func(stbWriteCb, &ctx, tw, th, 4, out_pixels.ptr, jpeg_quality);
- if (ok == 0 or ctx.failed) return error.EncodeFailed;
-
- return .{ .media_type = "image/jpeg", .data = try out.toOwnedSlice(allocator) };
-}
-
-// -----------------------------------------------------------------------------
-// Tests
-// -----------------------------------------------------------------------------
-
-const testing = std.testing;
-
-test "detectCodec + mediaTypeForCodec - magic bytes" {
- try testing.expectEqualStrings("image/png", mediaTypeForCodec(detectCodec(&.{ 0x89, 'P', 'N', 'G', 0x0D, 0x0A, 0x1A, 0x0A }).?));
- try testing.expectEqualStrings("image/jpeg", mediaTypeForCodec(detectCodec(&.{ 0xFF, 0xD8, 0xFF, 0xE0 }).?));
- try testing.expectEqualStrings("image/gif", mediaTypeForCodec(detectCodec("GIF89a....").?));
- try testing.expectEqualStrings("image/bmp", mediaTypeForCodec(detectCodec("BM....").?));
- try testing.expectEqualStrings("application/pdf", mediaTypeForCodec(detectCodec("%PDF-1.7").?));
- const webp = "RIFF" ++ &[_]u8{ 0, 0, 0, 0 } ++ "WEBP";
- try testing.expectEqualStrings("image/webp", mediaTypeForCodec(detectCodec(webp).?));
- try testing.expect(detectCodec("not an image") == null);
- try testing.expect(detectCodec(&.{0x89}) == null);
-}
-
-test "targetDims - skip when small, scale when large preserving aspect" {
- try testing.expect(targetDims(100, 100) == null);
- try testing.expect(targetDims(max_dim, max_dim) == null);
- const t = targetDims(4000, 2000).?;
- try testing.expectEqual(@as(u32, 2000), t.w);
- try testing.expectEqual(@as(u32, 1000), t.h);
- const t2 = targetDims(1000, 8000).?;
- try testing.expectEqual(@as(u32, 250), t2.w);
- try testing.expectEqual(@as(u32, 2000), t2.h);
-}
-
-test "process - detects type from raw bytes when hint absent" {
- const a = testing.allocator;
- // A tiny PNG (header + IHDR enough for stbi_info) — but simplest is to
- // round-trip an stb-encoded small PNG and feed it with no hint.
- const w: c_int = 4;
- const h: c_int = 4;
- var px: [4 * 4 * 4]u8 = undefined;
- @memset(&px, 0x40);
- var png: std.ArrayList(u8) = .empty;
- defer png.deinit(a);
- var ctx = StbWriteCtx{ .list = &png, .allocator = a };
- try testing.expect(c.stbi_write_png_to_func(stbWriteCb, &ctx, w, h, 4, &px, w * 4) != 0);
-
- const out = try process(a, png.items, null);
- defer a.free(out.data);
- try testing.expectEqualStrings("image/png", out.media_type);
-
- // Unknown bytes -> error so the caller can fall back / drop.
- try testing.expectError(error.UnknownMediaType, process(a, "totally not an image", null));
-}
-
-test "maybeResize - PDF passes through unchanged" {
- const a = testing.allocator;
- const pdf = "%PDF-1.7\nfake pdf body";
- const out = try maybeResize(a, pdf, .pdf);
- defer a.free(out.data);
- try testing.expectEqualStrings("application/pdf", out.media_type);
- try testing.expectEqualStrings(pdf, out.data);
-}
-
-test "maybeResize - small PNG round-trips, large PNG shrinks and stays PNG" {
- const a = testing.allocator;
-
- // Build a small (8x8) RGBA PNG via stb and confirm pass-through.
- const small_w: c_int = 8;
- const small_h: c_int = 8;
- var small_px: [8 * 8 * 4]u8 = undefined;
- for (&small_px, 0..) |*b, i| b.* = @truncate(i);
- var small_png: std.ArrayList(u8) = .empty;
- defer small_png.deinit(a);
- var sctx = StbWriteCtx{ .list = &small_png, .allocator = a };
- try testing.expect(c.stbi_write_png_to_func(stbWriteCb, &sctx, small_w, small_h, 4, &small_px, small_w * 4) != 0);
-
- const small_out = try maybeResize(a, small_png.items, .png);
- defer a.free(small_out.data);
- try testing.expectEqualStrings("image/png", small_out.media_type);
- // Small image is returned verbatim (byte-identical copy).
- try testing.expectEqualSlices(u8, small_png.items, small_out.data);
-
- // Build a large (2400x100) PNG and confirm it shrinks to <= max_dim.
- const big_w: c_int = 2400;
- const big_h: c_int = 100;
- const big_px = try a.alloc(u8, @as(usize, @intCast(big_w * big_h * 4)));
- defer a.free(big_px);
- @memset(big_px, 0x7F);
- var big_png: std.ArrayList(u8) = .empty;
- defer big_png.deinit(a);
- var bctx = StbWriteCtx{ .list = &big_png, .allocator = a };
- try testing.expect(c.stbi_write_png_to_func(stbWriteCb, &bctx, big_w, big_h, 4, big_px.ptr, big_w * 4) != 0);
-
- const big_out = try maybeResize(a, big_png.items, .png);
- defer a.free(big_out.data);
- try testing.expectEqualStrings("image/png", big_out.media_type);
- const dims = probeDims(big_out.data).?;
- try testing.expectEqual(@as(u32, 2000), dims.w);
- try testing.expect(dims.w <= max_dim and dims.h <= max_dim);
-}
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