fiv/tools/info.h

//
// info.h: metadata extraction utilities
//
// Copyright (c) 2021, Přemysl Eric Janouch <p@janouch.name>
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted.
//
// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
// SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
// OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
// CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
//

#include <jv.h>

#include <stdlib.h>
#include <string.h>
#include <stdbool.h>

// --- Utilities ---------------------------------------------------------------

static char *
binhex(const uint8_t *data, size_t len)
{
	static const char *alphabet = "0123456789abcdef";
	char *buf = calloc(1, len * 2 + 1), *p = buf;
	for (size_t i = 0; i < len; i++) {
		*p++ = alphabet[data[i] >> 4];
		*p++ = alphabet[data[i] & 0xF];
	}
	return buf;
}

static uint64_t
u64be(const uint8_t *p)
{
	return (uint64_t) p[0] << 56 | (uint64_t) p[1] << 48 |
		(uint64_t) p[2] << 40 | (uint64_t) p[3] << 32 |
		(uint64_t) p[4] << 24 | p[5] << 16 | p[6] << 8 | p[7];
}

static uint32_t
u32be(const uint8_t *p)
{
	return (uint32_t) p[0] << 24 | p[1] << 16 | p[2] << 8 | p[3];
}

static uint16_t
u16be(const uint8_t *p)
{
	return (uint16_t) p[0] << 8 | p[1];
}

static uint64_t
u64le(const uint8_t *p)
{
	return (uint64_t) p[7] << 56 | (uint64_t) p[6] << 48 |
		(uint64_t) p[5] << 40 | (uint64_t) p[4] << 32 |
		(uint64_t) p[3] << 24 | p[2] << 16 | p[1] << 8 | p[0];
}

static uint32_t
u32le(const uint8_t *p)
{
	return (uint32_t) p[3] << 24 | p[2] << 16 | p[1] << 8 | p[0];
}

static uint16_t
u16le(const uint8_t *p)
{
	return (uint16_t) p[1] << 8 | p[0];
}

// --- TIFF --------------------------------------------------------------------
// libtiff is a mess, and the format is not particularly complicated.
// Exiv2 is senselessly copylefted, and cannot do much.
// libexif is only marginally better.
// ExifTool is too user-oriented.

static struct un {
	uint64_t (*u64) (const uint8_t *);
	uint32_t (*u32) (const uint8_t *);
	uint16_t (*u16) (const uint8_t *);
} unbe = {u64be, u32be, u16be}, unle = {u64le, u32le, u16le};

struct tiffer {
	struct un *un;
	const uint8_t *begin, *p, *end;
	uint16_t remaining_fields;
};

static bool
tiffer_u32(struct tiffer *self, uint32_t *u)
{
	if (self->p < self->begin || self->p + 4 > self->end)
		return false;

	*u = self->un->u32(self->p);
	self->p += 4;
	return true;
}

static bool
tiffer_u16(struct tiffer *self, uint16_t *u)
{
	if (self->p < self->begin || self->p + 2 > self->end)
		return false;

	*u = self->un->u16(self->p);
	self->p += 2;
	return true;
}

// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

static bool
tiffer_init(struct tiffer *self, const uint8_t *tiff, size_t len)
{
	self->un = NULL;
	self->begin = self->p = tiff;
	self->end = tiff + len;
	self->remaining_fields = 0;

	const uint8_t
		le[4] = {'I', 'I', 42, 0},
		be[4] = {'M', 'M', 0, 42};

	if (tiff + 8 > self->end)
		return false;
	else if (!memcmp(tiff, le, sizeof le))
		self->un = &unle;
	else if (!memcmp(tiff, be, sizeof be))
		self->un = &unbe;
	else
		return false;

	self->p = tiff + 4;
	// The first IFD needs to be read by caller explicitly,
	// even though it's required to be present by TIFF 6.0.
	return true;
}

/// Read the next IFD in a sequence.
static bool
tiffer_next_ifd(struct tiffer *self)
{
	// All fields from any previous IFD need to be read first.
	if (self->remaining_fields)
		return false;

	uint32_t ifd_offset = 0;
	if (!tiffer_u32(self, &ifd_offset))
		return false;

	// There is nothing more to read, this chain has terminated.
	if (!ifd_offset)
		return false;

	// Note that TIFF 6.0 requires there to be at least one entry,
	// but there is no need for us to check it.
	self->p = self->begin + ifd_offset;
	return tiffer_u16(self, &self->remaining_fields);
}

/// Initialize a derived TIFF reader for a subIFD at the given location.
static bool
tiffer_subifd(struct tiffer *self, uint32_t offset, struct tiffer *subreader)
{
	*subreader = *self;
	subreader->p = subreader->begin + offset;
	return tiffer_u16(subreader, &subreader->remaining_fields);
}

enum tiffer_type {
	BYTE = 1, ASCII, SHORT, LONG, RATIONAL,
	SBYTE, UNDEFINED, SSHORT, SLONG, SRATIONAL, FLOAT, DOUBLE,
	IFD  // This last type from TIFF Technical Note 1 isn't really used much.
};

static size_t
tiffer_value_size(enum tiffer_type type)
{
	switch (type) {
	case BYTE:
	case SBYTE:
	case ASCII:
	case UNDEFINED:
		return 1;
	case SHORT:
	case SSHORT:
		return 2;
	case LONG:
	case SLONG:
	case FLOAT:
	case IFD:
		return 4;
	case RATIONAL:
	case SRATIONAL:
	case DOUBLE:
		return 8;
	default:
		return 0;
	}
}

/// A lean iterator for values within entries.
struct tiffer_entry {
	uint16_t tag;
	enum tiffer_type type;
	// For {S,}BYTE, ASCII, UNDEFINED, use these fields directly.
	const uint8_t *p;
	uint32_t remaining_count;
};

static bool
tiffer_next_value(struct tiffer_entry *entry)
{
	if (!entry->remaining_count)
		return false;

	entry->p += tiffer_value_size(entry->type);
	entry->remaining_count--;
	return true;
}

static bool
tiffer_integer(
	const struct tiffer *self, const struct tiffer_entry *entry, int64_t *out)
{
	if (!entry->remaining_count)
		return false;

	// Somewhat excessively lenient, intended for display.
	// TIFF 6.0 only directly suggests that a reader is should accept
	// any of BYTE/SHORT/LONG for unsigned integers.
	switch (entry->type) {
	case BYTE:
	case ASCII:
	case UNDEFINED:
		*out = *entry->p;
		return true;
	case SBYTE:
		*out = (int8_t) *entry->p;
		return true;
	case SHORT:
		*out = self->un->u16(entry->p);
		return true;
	case SSHORT:
		*out = (int16_t) self->un->u16(entry->p);
		return true;
	case LONG:
	case IFD:
		*out = self->un->u32(entry->p);
		return true;
	case SLONG:
		*out = (int32_t) self->un->u32(entry->p);
		return true;
	default:
		return false;
	}
}

static bool
tiffer_rational(const struct tiffer *self, const struct tiffer_entry *entry,
	int64_t *numerator, int64_t *denominator)
{
	if (!entry->remaining_count)
		return false;

	// Somewhat excessively lenient, intended for display.
	switch (entry->type) {
	case RATIONAL:
		*numerator = self->un->u32(entry->p);
		*denominator = self->un->u32(entry->p + 4);
		return true;
	case SRATIONAL:
		*numerator = (int32_t) self->un->u32(entry->p);
		*denominator = (int32_t) self->un->u32(entry->p + 4);
		return true;
	default:
		if (tiffer_integer(self, entry, numerator)) {
			*denominator = 1;
			return true;
		}
		return false;
	}
}

static bool
tiffer_real(
	const struct tiffer *self, const struct tiffer_entry *entry, double *out)
{
	if (!entry->remaining_count)
		return false;

	// Somewhat excessively lenient, intended for display.
	// Assuming the host architecture uses IEEE 754.
	switch (entry->type) {
		int64_t numerator, denominator;
	case FLOAT:
		*out = *(float *) entry->p;
		return true;
	case DOUBLE:
		*out = *(double *) entry->p;
		return true;
	default:
		if (tiffer_rational(self, entry, &numerator, &denominator)) {
			*out = (double) numerator / denominator;
			return true;
		}
		return false;
	}
}

static bool
tiffer_next_entry(struct tiffer *self, struct tiffer_entry *entry)
{
	if (!self->remaining_fields)
		return false;

	uint16_t type = entry->type = 0xFFFF;
	if (!tiffer_u16(self, &entry->tag) || !tiffer_u16(self, &type) ||
		!tiffer_u32(self, &entry->remaining_count))
		return false;

	// Short values may and will be inlined, rather than pointed to.
	size_t values_size = tiffer_value_size(type) * entry->remaining_count;
	uint32_t offset = 0;
	if (values_size <= sizeof offset) {
		entry->p = self->p;
		self->p += sizeof offset;
	} else if (tiffer_u32(self, &offset)) {
		entry->p = self->begin + offset;
	} else {
		return false;
	}

	// All entries are pre-checked not to overflow.
	if (entry->p + values_size > self->end)
		return false;

	// Setting it at the end may provide an indication while debugging.
	entry->type = type;
	self->remaining_fields--;
	return true;
}

// --- TIFF/Exif tags ----------------------------------------------------------

struct tiff_value {
	const char *name;
	uint16_t value;
};

struct tiff_entry {
	const char *name;
	uint16_t tag;
	struct tiff_value *values;
};

#include "tiff-tables.h"

// TODO(p): Consider if these can't be inlined into `tiff_entries`.
static struct {
	uint16_t tag;
	struct tiff_entry *entries;
} tiff_subifds[] = {
	{330, tiff_entries},   // SubIFDs
	{34665, exif_entries},  // Exif IFD Pointer
	{34853, exif_gps_entries},  // GPS Info IFD Pointer
	{40965, exif_interoperability_entries},  // Interoperability IFD Pointer
	{}
};

// --- Analysis ----------------------------------------------------------------

static jv
add_to_subarray(jv o, const char *key, jv value)
{
	// Invalid values are not allocated, and we use up any valid one.
	// Beware that jv_get() returns jv_null() rather than jv_invalid().
	// Also, the header comment is lying, jv_is_valid() doesn't unreference.
	jv a = jv_object_get(jv_copy(o), jv_string(key));
	return jv_set(o, jv_string(key),
		jv_is_valid(a) ? jv_array_append(a, value) : JV_ARRAY(value));
}

static jv
add_warning(jv o, const char *message)
{
	return add_to_subarray(o, "warnings", jv_string(message));
}

static jv
add_error(jv o, const char *message)
{
	return jv_object_set(o, jv_string("error"), jv_string(message));
}

// --- Exif --------------------------------------------------------------------

static jv parse_exif_ifd(struct tiffer *T, const struct tiff_entry *info);

static bool
parse_exif_subifds_entry(struct tiffer *T, const struct tiffer_entry *entry,
	struct tiffer *subT)
{
	int64_t offset = 0;
	return tiffer_integer(T, entry, &offset) &&
		offset >= 0 && offset <= UINT32_MAX && tiffer_subifd(T, offset, subT);
}

static jv
parse_exif_subifds(struct tiffer *T, struct tiffer_entry *entry,
	struct tiff_entry *info)
{
	struct tiffer subT = {};
	if (!parse_exif_subifds_entry(T, entry, &subT))
		return jv_null();

	jv a = jv_array();
	do a = jv_array_append(a, parse_exif_ifd(&subT, info));
	while (tiffer_next_ifd(&subT));

	// The chain should correspond to the values in the entry (see TIFF
	// Technical Note 1: "the NextIFD value of Child #1 must point to Child #2,
	// and so on"), but at least some Nikon NEFs do not follow this rule.
	if (jv_array_length(jv_copy(a)) == 1) {
		while (tiffer_next_value(entry) &&
			parse_exif_subifds_entry(T, entry, &subT))
			a = jv_array_append(a, parse_exif_ifd(&subT, info));
	}
	return a;
}

static jv
parse_exif_ascii(struct tiffer_entry *entry)
{
	// Adobe XMP Specification Part 3: Storage in Files, 2020/1, 2.4.2
	// The text may in practice contain any 8-bit encoding, but likely UTF-8.
	// TODO(p): Validate UTF-8, and assume Latin 1 if unsuccessful.
	jv a = jv_array();
	uint8_t *nul = 0;
	while ((nul = memchr(entry->p, 0, entry->remaining_count))) {
		size_t len = nul - entry->p;
		a = jv_array_append(a, jv_string_sized((const char *) entry->p, len));
		entry->remaining_count -= len + 1;
		entry->p += len + 1;
	}

	// Trailing NULs are required, but let's extract everything.
	if (entry->remaining_count) {
		a = jv_array_append(a,
			jv_string_sized((const char *) entry->p, entry->remaining_count));
	}
	return a;
}

static jv
parse_exif_undefined(struct tiffer_entry *entry)
{
	// Sometimes, it can be ASCII, but the safe bet is to hex-encode it.
	char *buf = binhex(entry->p, entry->remaining_count);
	jv s = jv_string(buf);
	free(buf);
	return s;
}

static jv
parse_exif_value(const struct tiff_value *values, double real)
{
	if (values) {
		for (; values->name; values++)
			if (values->value == real)
				return jv_string(values->name);
	}
	return jv_number(real);
}
static jv
parse_exif_extract_sole_array_element(jv a)
{
	return jv_array_length(jv_copy(a)) == 1 ? jv_array_get(a, 0) : a;
}

static jv
parse_exif_entry(jv o, struct tiffer *T, struct tiffer_entry *entry,
	const struct tiff_entry *info)
{
	static struct tiff_entry empty[] = {{}};
	if (!info)
		info = empty;

	for (; info->name; info++)
		if (info->tag == entry->tag)
			break;

	struct tiff_entry *subentries = NULL;
	for (size_t i = 0; tiff_subifds[i].tag; i++)
		if (tiff_subifds[i].tag == entry->tag)
			subentries = tiff_subifds[i].entries;

	jv v = jv_true();
	double real = 0;
	if (!entry->remaining_count) {
		v = jv_null();
	} else if (entry->type == IFD || subentries) {
		v = parse_exif_subifds(T, entry, subentries);
	} else if (entry->type == ASCII) {
		v = parse_exif_extract_sole_array_element(parse_exif_ascii(entry));
	} else if (entry->type == UNDEFINED && !info->values) {
		// Several Exif entries of UNDEFINED type contain single-byte numbers.
		v = parse_exif_undefined(entry);
	} else if (tiffer_real(T, entry, &real)) {
		v = jv_array();
		do v = jv_array_append(v, parse_exif_value(info->values, real));
		while (tiffer_next_value(entry) && tiffer_real(T, entry, &real));
		v = parse_exif_extract_sole_array_element(v);
	}

	if (info->name)
		return jv_set(o, jv_string(info->name), v);
	return jv_set(o, jv_string_fmt("%u", entry->tag), v);
}

static jv
parse_exif_ifd(struct tiffer *T, const struct tiff_entry *info)
{
	jv ifd = jv_object();
	struct tiffer_entry entry = {};
	while (tiffer_next_entry(T, &entry))
		ifd = parse_exif_entry(ifd, T, &entry, info);
	return ifd;
}

static jv
parse_exif(jv o, const uint8_t *p, size_t len)
{
	struct tiffer T = {};
	if (!tiffer_init(&T, p, len))
		return add_warning(o, "invalid Exif");
	while (tiffer_next_ifd(&T))
		o = add_to_subarray(o, "Exif", parse_exif_ifd(&T, tiff_entries));
	return o;
}

// --- Photoshop Image Resources -----------------------------------------------
// Adobe XMP Specification Part 3: Storage in Files, 2020/1, 1.1.3 + 3.1.3
// https://www.adobe.com/devnet-apps/photoshop/fileformatashtml/
// Unless otherwise noted, the descriptions are derived from the above document.

static struct {
	uint16_t id;
	const char *description;
} psir_descriptions[] = {
	{1000, "Number of channels, rows, columns, depth, mode"},
	{1001, "Macintosh print manager print info record"},
	{1002, "Macintosh page format information"},
	{1003, "Indexed color table"},
	{1005, "Resolution information"},
	{1006, "Names of alpha channels (Pascal strings)"},
	{1007, "Display information"},
	{1008, "Caption (Pascal string)"},  // XMP Part 3 3.3.3
	{1009, "Border information"},
	{1010, "Background color"},
	{1011, "Print flags"},
	{1012, "Grayscale and multichannel halftoning information"},
	{1013, "Color halftoning information"},
	{1014, "Duotone halftoning information"},
	{1015, "Grayscale and multichannel transfer function"},
	{1016, "Color transfer functions"},
	{1017, "Duotone transfer functions"},
	{1018, "Duotone image information"},
	{1019, "Effective B/W values for the dot range"},
	{1020, "Caption"},  // XMP Part 3 3.3.3
	{1021, "EPS options"},
	{1022, "Quick Mask information"},
	{1023, "(Obsolete)"},
	{1024, "Layer state information"},
	{1025, "Working path (not saved)"},
	{1026, "Layers group information"},
	{1027, "(Obsolete)"},
	{1028, "IPTC DataSets"},  // XMP Part 3 3.3.3
	{1029, "Image mode for raw format files"},
	{1030, "JPEG quality"},
	{1032, "Grid and guides information"},
	{1033, "Thumbnail resource"},
	{1034, "Copyright flag"},
	{1035, "Copyright information URL"},  // XMP Part 3 3.3.3
	{1036, "Thumbnail resource"},
	{1037, "Global lighting angle for effects layer"},
	{1038, "Color samplers information"},
	{1039, "ICC profile"},
	{1040, "Watermark"},
	{1041, "ICC untagged profile flag"},
	{1042, "Effects visible flag"},
	{1043, "Spot halftone"},
	{1044, "Document-specific IDs seed number"},
	{1045, "Unicode alpha names"},
	{1046, "Indexed color table count"},
	{1047, "Transparent color index"},
	{1049, "Global altitude"},
	{1050, "Slices"},
	{1051, "Workflow URL"},
	{1052, "Jump To XPEP"},
	{1053, "Alpha identifiers"},
	{1054, "URL list"},
	{1057, "Version info"},
	{1058, "Exif metadata 1"},
	{1059, "Exif metadata 3"},
	{1060, "XMP metadata"},
	{1061, "MD5 digest of IPTC data"},  // XMP Part 3 3.3.3
	{1062, "Print scale"},
	{1064, "Pixel aspect ratio"},
	{1065, "Layer comps"},
	{1066, "Alternate duotone colors"},
	{1067, "Alternate spot colors"},
	{1069, "Layer selection IDs"},
	{1070, "HDR toning information"},
	{1071, "Print info"},
	{1072, "Layer group(s) enabled ID"},
	{1073, "Color samplers"},
	{1074, "Measurement scale"},
	{1075, "Timeline information"},
	{1076, "Sheet disclosure"},
	{1077, "Display information to support floating point colors"},
	{1078, "Onion skins"},
	{1080, "Count information"},
	{1082, "Print information"},
	{1083, "Print style"},
	{1084, "Macintosh NSPrintInfo"},
	{1085, "Windows DEVMODE"},
	{1086, "Autosave file path"},
	{1087, "Autosave format"},
	{1088, "Path selection state"},
	// {2000-2997, "Saved paths"},
	{2999, "Name of clipping path"},
	{3000, "Origin path information"},
	// {4000-4999, "Plug-in resource"},
	{7000, "Image Ready variables"},
	{7001, "Image Ready data sets"},
	{7002, "Image Ready default selected state"},
	{7003, "Image Ready 7 rollover expanded state"},
	{7004, "Image Ready rollover expanded state"},
	{7005, "Image Ready save layer settings"},
	{7006, "Image Ready version"},
	{8000, "Lightroom workflow"},
	{10000, "Print flags"},
	{}
};

static jv
process_psir_thumbnail(jv res, const uint8_t *data, size_t len)
{
	uint32_t format_number   = u32be(data + 0);
	uint32_t compressed_size = u32be(data + 20);

	// TODO(p): Recurse into the thumbnail if it's a JPEG.
	jv format = jv_number(format_number);
	switch (format_number) {
	break; case 0: format = jv_string("kJpegRGB");
	break; case 1: format = jv_string("kRawRGB");
	}

	res = jv_object_merge(res, JV_OBJECT(
		jv_string("Format"),         format,
		jv_string("Width"),          jv_number(u32be(data + 4)),
		jv_string("Height"),         jv_number(u32be(data + 8)),
		jv_string("Stride"),         jv_number(u32be(data + 12)),
		jv_string("TotalSize"),      jv_number(u32be(data + 16)),
		jv_string("CompressedSize"), jv_number(compressed_size),
		jv_string("BitsPerPixel"),   jv_number(u16be(data + 24)),
		jv_string("Planes"),         jv_number(u16be(data + 26))
	));
	if (28 + compressed_size <= len) {
		char *buf = binhex(data + 28, compressed_size);
		res = jv_set(res, jv_string("Data"), jv_string(buf));
		free(buf);
	}
	return res;
}

static const char *
process_iptc_dataset(jv *a, const uint8_t **p, size_t len)
{
	const uint8_t *header = *p;
	if (len < 5)
		return "unexpected end of IPTC data";
	if (*header != 0x1c)
		return "invalid tag marker";

	uint8_t record = header[1];
	uint8_t dataset = header[2];
	uint16_t byte_count = header[3] << 8 | header[4];

	// TODO(p): Although highly unlikely to appear, we could decode it.
	if (byte_count & 0x8000)
		return "unsupported extended DataSet";
	if (len - 5 < byte_count)
		return "data overrun";

	char *buf = binhex(header + 5, byte_count);
	*p += 5 + byte_count;
	*a = jv_array_append(*a, JV_OBJECT(
		jv_string("DataSet"), jv_string_fmt("%u:%u", record, dataset),
		jv_string("Data"), jv_string(buf)
	));
	free(buf);
	return NULL;
}

static jv
process_psir_iptc(jv res, const uint8_t *data, size_t len)
{
	// https://iptc.org/standards/iim/
	// https://iptc.org/std/IIM/4.2/specification/IIMV4.2.pdf
	jv a = jv_array();
	const uint8_t *end = data + len;
	while (data < end) {
		const char *err = process_iptc_dataset(&a, &data, end - data);
		if (err) {
			a = jv_array_append(a, jv_string(err));
			break;
		}
	}
	return jv_set(res, jv_string("DataSets"), a);
}

static jv
process_psir(jv o, uint16_t resource_id, const char *name,
	const uint8_t *data, size_t len)
{
	const char *description = NULL;
	if (resource_id >= 2000 && resource_id <= 2997)
		description = "Saved paths";
	if (resource_id >= 4000 && resource_id <= 4999)
		description = "Plug-in resource";
	for (size_t i = 0; psir_descriptions[i].id; i++)
		if (psir_descriptions[i].id == resource_id)
			description = psir_descriptions[i].description;

	jv res = JV_OBJECT(
		jv_string("name"), jv_string(name),
		jv_string("id"), jv_number(resource_id),
		jv_string("description"),
			description ? jv_string(description) : jv_null(),
		jv_string("size"), jv_number(len)
	);

	// Both are thumbnails, older is BGR, newer is RGB.
	if ((resource_id == 1033 || resource_id == 1036) && len >= 28)
		res = process_psir_thumbnail(res, data, len);
	if (resource_id == 1028)
		res = process_psir_iptc(res, data, len);

	return add_to_subarray(o, "PSIR", res);
}

static jv
parse_psir_block(jv o, const uint8_t *p, size_t len, size_t *advance)
{
	*advance = 0;
	if (len < 8 || memcmp(p, "8BIM", 4))
		return add_warning(o, "bad PSIR block header");

	uint16_t resource_id = u16be(p + 4);
	uint8_t name_len = p[6];
	const uint8_t *name = &p[7];

	// Add one byte for the Pascal-ish string length prefix,
	// then another one for padding to make the length even.
	size_t name_len_full = (name_len + 2) & ~1U;

	size_t resource_len_offset = 6 + name_len_full,
		header_len = resource_len_offset + 4;
	if (len < header_len)
		return add_warning(o, "bad PSIR block header");

	uint32_t resource_len = u32be(p + resource_len_offset);
	size_t resource_len_padded = (resource_len + 1) & ~1U;
	if (resource_len_padded < resource_len ||
		len < header_len + resource_len_padded)
		return add_warning(o, "runaway PSIR block");

	char *cname = calloc(1, name_len_full);
	strncpy(cname, (const char *) name, name_len);
	o = process_psir(o, resource_id, cname, p + header_len, resource_len);
	free(cname);

	*advance = header_len + resource_len_padded;
	return o;
}

static jv
parse_psir(jv o, const uint8_t *p, size_t len)
{
	if (len == 0)
		return add_warning(o, "empty PSIR data");

	size_t advance = 0;
	while (len && (o = parse_psir_block(o, p, len, &advance), advance)) {
		p += advance;
		len -= advance;
	}
	return o;
}

// --- ICC profiles ------------------------------------------------------------
// v2 https://www.color.org/ICC_Minor_Revision_for_Web.pdf
// v4 https://www.color.org/specification/ICC1v43_2010-12.pdf

static jv
parse_icc_mluc(jv o, const uint8_t *tag, uint32_t tag_length)
{
	// v4 10.13
	if (tag_length < 16)
		return add_warning(o, "invalid ICC 'mluc' structure length");

	uint32_t count = u32be(tag + 8);
	if (count == 0)
		return add_warning(o, "unnamed ICC profile");

	// There is no particularly good reason for us to iterate, take the first.
	const uint8_t *record = tag + 16 /* + i * u32be(tag + 12) */;
	uint32_t len = u32be(&record[4]);
	uint32_t off = u32be(&record[8]);

	if (off + len > tag_length)
		return add_warning(o, "invalid ICC 'mluc' structure record");

	// Blindly assume simple ASCII, ensure NUL-termination.
	char name[len], *p = name;
	for (uint32_t i = 0; i < len / 2; i++)
		*p++ = tag[off + i * 2 + 1];
	*p++ = 0;
	return jv_set(o, jv_string("ICC"),
		JV_OBJECT(jv_string("name"), jv_string(name),
			jv_string("version"), jv_number(4)));
}

static jv
parse_icc_desc(jv o, const uint8_t *profile, size_t profile_len,
	uint32_t tag_offset, uint32_t tag_length)
{
	const uint8_t *tag = profile + tag_offset;
	if (tag_offset + tag_length > profile_len)
		return add_warning(o, "unexpected end of ICC profile");
	if (tag_length < 4)
		return add_warning(o, "invalid ICC tag structure length");

	// v2 6.5.17
	uint32_t sig = u32be(tag);
	if (sig == 0x6D6C7563 /* mluc */)
		return parse_icc_mluc(o, profile + tag_offset, tag_length);
	if (sig != 0x64657363 /* desc */)
		return add_warning(o, "invalid ICC 'desc' structure signature");
	if (tag_length < 12)
		return add_warning(o, "invalid ICC 'desc' structure length");

	uint32_t count = u32be(tag + 8);
	if (tag_length < 12 + count)
		return add_warning(o, "invalid ICC 'desc' structure length");

	// Double-ensure a trailing NUL byte.
	char name[count + 1];
	memcpy(name, tag + 12, count);
	name[count] = 0;
	return jv_set(o, jv_string("ICC"),
		JV_OBJECT(jv_string("name"), jv_string(name),
			jv_string("version"), jv_number(2)));
}

static jv
parse_icc(jv o, const uint8_t *profile, size_t profile_len)
{
	// v2 6, v4 7
	if (profile_len < 132)
		return add_warning(o, "ICC profile too short");
	if (u32be(profile) != profile_len)
		return add_warning(o, "ICC profile size mismatch");

	// TODO(p): May decode more of the header fields, and validate them.
	// Need to check both v2 and v4, this is all fairly annoying.
	uint32_t count = u32be(profile + 128);
	if (132 + count * 12 > profile_len)
		return add_warning(o, "unexpected end of ICC profile");

	for (uint32_t i = 0; i < count; i++) {
		const uint8_t *entry = profile + 132 + i * 12;
		uint32_t sig = u32be(&entry[0]);
		uint32_t off = u32be(&entry[4]);
		uint32_t len = u32be(&entry[8]);

		// v2 6.4.32, v4 9.2.41
		if (sig == 0x64657363 /* desc */)
			return parse_icc_desc(o, profile, profile_len, off, len);
	}
	// The description is required, so this should be unreachable.
	return jv_set(o, jv_string("ICC"), jv_bool(true));
}