fiv/tools/jpeginfo.c

//
// jpeginfo.c: acquire information about JPEG files in JSON format
//
// 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 "info.h"

#include <jv.h>

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

// --- 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));
}

// --- Multi-Picture Format ----------------------------------------------------

enum {
	MPF_MPFVersion = 45056,
	MPF_NumberOfImages = 45057,
	MPF_MPEntry = 45058,
	MPF_ImageUIDList = 45059,
	MPF_TotalFrames = 45060,

	MPF_MPIndividualNum = 45313,
	MPF_PanOrientation = 45569,
	MPF_PanOverlap_H = 45570,
	MPF_PanOverlap_V = 45571,
	MPF_BaseViewpointNum = 45572,
	MPF_ConvergenceAngle = 45573,
	MPF_BaselineLength = 45574,
	MPF_VerticalDivergence = 45575,
	MPF_AxisDistance_X = 45576,
	MPF_AxisDistance_Y = 45577,
	MPF_AxisDistance_Z = 45578,
	MPF_YawAngle = 45579,
	MPF_PitchAngle = 45580,
	MPF_RollAngle = 45581
};

static struct tiff_entry mpf_entries[] = {
	{"MP Format Version Number", MPF_MPFVersion, NULL},
	{"Number of Images", MPF_NumberOfImages, NULL},
	{"MP Entry", MPF_MPEntry, NULL},
	{"Individual Image Unique ID List", MPF_ImageUIDList, NULL},
	{"Total Number of Captured Frames", MPF_TotalFrames, NULL},

	{"MP Individual Image Number", MPF_MPIndividualNum, NULL},
	{"Panorama Scanning Orientation", MPF_PanOrientation, NULL},
	{"Panorama Horizontal Overlap", MPF_PanOverlap_H, NULL},
	{"Panorama Vertical Overlap", MPF_PanOverlap_V, NULL},
	{"Base Viewpoint Number", MPF_BaseViewpointNum, NULL},
	{"Convergence Angle", MPF_ConvergenceAngle, NULL},
	{"Baseline Length", MPF_BaselineLength, NULL},
	{"Divergence Angle", MPF_VerticalDivergence, NULL},
	{"Horizontal Axis Distance", MPF_AxisDistance_X, NULL},
	{"Vertical Axis Distance", MPF_AxisDistance_Y, NULL},
	{"Collimation Axis Distance", MPF_AxisDistance_Z, NULL},
	{"Yaw Angle", MPF_YawAngle, NULL},
	{"Pitch Angle", MPF_PitchAngle, NULL},
	{"Roll Angle", MPF_RollAngle, NULL},
	{}
};

static uint32_t
parse_mpf_mpentry(jv *a, const uint8_t *p, struct tiffer *T)
{
	uint32_t attrs = T->un->u32(p);
	uint32_t offset = T->un->u32(p + 8);

	uint32_t type_number = attrs & 0xFFFFFF;
	jv type = jv_number(type_number);
	switch (type_number) {
	break; case 0x030000: type = jv_string("Baseline MP Primary Image");
	break; case 0x010001: type = jv_string("Large Thumbnail - VGA");
	break; case 0x010002: type = jv_string("Large Thumbnail - Full HD");
	break; case 0x020001: type = jv_string("Multi-Frame Image Panorama");
	break; case 0x020002: type = jv_string("Multi-Frame Image Disparity");
	break; case 0x020003: type = jv_string("Multi-Frame Image Multi-Angle");
	break; case 0x000000: type = jv_string("Undefined");
	}

	uint32_t format_number = (attrs >> 24) & 0x7;
	jv format = jv_number(format_number);
	if (format_number == 0)
		format = jv_string("JPEG");

	*a = jv_array_append(*a, JV_OBJECT(
		jv_string("Individual Image Attribute"), JV_OBJECT(
			jv_string("Dependent Parent Image"), jv_bool((attrs >> 31) & 1),
			jv_string("Dependent Child Image"), jv_bool((attrs >> 30) & 1),
			jv_string("Representative Image"), jv_bool((attrs >> 29) & 1),
			jv_string("Reserved"), jv_number((attrs >> 27) & 0x3),
			jv_string("Image Data Format"), format,
			jv_string("MP Type Code"), type
		),
		jv_string("Individual Image Size"),
		jv_number(T->un->u32(p + 4)),
		jv_string("Individual Image Data Offset"),
		jv_number(offset),
		jv_string("Dependent Image 1 Entry Number"),
		jv_number(T->un->u16(p + 12)),
		jv_string("Dependent Image 2 Entry Number"),
		jv_number(T->un->u16(p + 14))
	));

	// Don't report non-JPEGs, even though they're unlikely.
	return format_number == 0 ? offset : 0;
}

static jv
parse_mpf_index_entry(jv o, const uint8_t ***offsets, struct tiffer *T,
	struct tiffer_entry *entry)
{
	// 5.2.3.3. MP Entry
	if (entry->tag != MPF_MPEntry || entry->type != UNDEFINED ||
		entry->remaining_count % 16) {
		return parse_exif_entry(o, T, entry, mpf_entries);
	}

	uint32_t count = entry->remaining_count / 16;
	jv a = jv_array_sized(count);
	const uint8_t **out = *offsets = calloc(sizeof *out, count + 1);
	for (uint32_t i = 0; i < count; i++) {
		uint32_t offset = parse_mpf_mpentry(&a, entry->p + i * 16, T);
		if (offset)
			*out++ = T->begin + offset;
	}
	return jv_set(o, jv_string("MP Entry"), a);
}

static jv
parse_mpf_index_ifd(const uint8_t ***offsets, struct tiffer *T)
{
	jv ifd = jv_object();
	struct tiffer_entry entry = {};
	while (tiffer_next_entry(T, &entry))
		ifd = parse_mpf_index_entry(ifd, offsets, T, &entry);
	return ifd;
}

static jv
parse_mpf(jv o, const uint8_t ***offsets, const uint8_t *p, size_t len)
{
	struct tiffer T;
	if (!tiffer_init(&T, p, len) || !tiffer_next_ifd(&T))
		return add_warning(o, "invalid MPF segment");

	// First image: IFD0 is Index IFD, any IFD1 is Attribute IFD.
	// Other images: IFD0 is Attribute IFD, there is no Index IFD.
	if (!*offsets) {
		o = add_to_subarray(o, "MPF", parse_mpf_index_ifd(offsets, &T));
		if (!tiffer_next_ifd(&T))
			return o;
	}

	// This isn't optimal, but it will do.
	return add_to_subarray(o, "MPF", parse_exif_ifd(&T, mpf_entries));
}

// --- JPEG --------------------------------------------------------------------
// Because the JPEG file format is simple, just do it manually.
// See: https://www.w3.org/Graphics/JPEG/itu-t81.pdf

enum {
	TEM = 0x01,
	SOF0 = 0xC0, SOF1, SOF2, SOF3,
	DHT = 0xC4,
	SOF5, SOF6, SOF7,
	JPG = 0xC8,
	SOF9, SOF10, SOF11,
	DAC = 0xCC,
	SOF13, SOF14, SOF15,

	RST0 = 0xD0, RST1, RST2, RST3, RST4, RST5, RST6, RST7,

	SOI = 0xD8,
	EOI = 0xD9,
	SOS = 0xDA,
	DQT = 0xDB,
	DNL = 0xDC,
	DRI = 0xDD,
	DHP = 0xDE,
	EXP = 0xDF,

	APP0 = 0xE0, APP1, APP2, APP3, APP4, APP5, APP6, APP7,
	APP8, APP9, APP10, APP11, APP12, APP13, APP14, APP15,

	JPG0 = 0xF0, JPG1, JPG2, JPG3, JPG4, JPG5, JPG6, JPG7,
	JPG8, JPG9, JPG10, JPG11, JPG12, JPG13,

	COM = 0xFE
};

// The rest is "RES (Reserved)", except for 0xFF (filler) and 0x00 (invalid).
static const char *marker_ids[0xFF] = {
	[TEM]   = "TEM",
	[SOF0]  = "SOF0",  [SOF1]  = "SOF1",  [SOF2]  = "SOF2",  [SOF3]  = "SOF3",
	[DHT]   = "DHT",   [SOF5]  = "SOF5",  [SOF6]  = "SOF6",  [SOF7]  = "SOF7",
	[JPG]   = "JPG",   [SOF9]  = "SOF9",  [SOF10] = "SOF10", [SOF11] = "SOF11",
	[DAC]   = "DAC",   [SOF13] = "SOF13", [SOF14] = "SOF14", [SOF15] = "SOF15",
	[RST0]  = "RST0",  [RST1]  = "RST1",  [RST2]  = "RST2",  [RST3]  = "RST3",
	[RST4]  = "RST4",  [RST5]  = "RST5",  [RST6]  = "RST6",  [RST7]  = "RST7",
	[SOI]   = "SOI",   [EOI]   = "EOI",   [SOS]   = "SOS",   [DQT]   = "DQT",
	[DNL]   = "DNL",   [DRI]   = "DRI",   [DHP]   = "DHP",   [EXP]   = "EXP",
	[APP0]  = "APP0",  [APP1]  = "APP1",  [APP2]  = "APP2",  [APP3]  = "APP3",
	[APP4]  = "APP4",  [APP5]  = "APP5",  [APP6]  = "APP6",  [APP7]  = "APP7",
	[APP8]  = "APP8",  [APP9]  = "APP9",  [APP10] = "APP10", [APP11] = "APP11",
	[APP12] = "APP12", [APP13] = "APP13", [APP14] = "APP14", [APP15] = "APP15",
	[JPG0]  = "JPG0",  [JPG1]  = "JPG1",  [JPG2]  = "JPG2",  [JPG3]  = "JPG3",
	[JPG4]  = "JPG4",  [JPG5]  = "JPG5",  [JPG6]  = "JPG6",  [JPG7]  = "JPG7",
	[JPG8]  = "JPG8",  [JPG9]  = "JPG9",  [JPG10] = "JPG10", [JPG11] = "JPG11",
	[JPG12] = "JPG12", [JPG13] = "JPG13", [COM]   = "COM"
};

// The rest is "RES (Reserved)", except for 0xFF (filler) and 0x00 (invalid).
static const char *marker_descriptions[0xFF] = {
	[TEM]   = "For temporary private use in arithmetic coding",
	[SOF0]  = "Baseline DCT",
	[SOF1]  = "Extended sequential DCT",
	[SOF2]  = "Progressive DCT",
	[SOF3]  = "Lossless (sequential)",
	[DHT]   = "Define Huffman table(s)",
	[SOF5]  = "Differential sequential DCT",
	[SOF6]  = "Differential progressive DCT",
	[SOF7]  = "Differential lossless (sequential)",
	[JPG]   = "Reserved for JPEG extensions",
	[SOF9]  = "Extended sequential DCT",
	[SOF10] = "Progressive DCT",
	[SOF11] = "Lossless (sequential)",
	[DAC]   = "Define arithmetic coding conditioning(s)",
	[SOF13] = "Differential sequential DCT",
	[SOF14] = "Differential progressive DCT",
	[SOF15] = "Differential lossless (sequential)",
	[RST0]  = "Restart with module 8 count 0",
	[RST1]  = "Restart with module 8 count 1",
	[RST2]  = "Restart with module 8 count 2",
	[RST3]  = "Restart with module 8 count 3",
	[RST4]  = "Restart with module 8 count 4",
	[RST5]  = "Restart with module 8 count 5",
	[RST6]  = "Restart with module 8 count 6",
	[RST7]  = "Restart with module 8 count 7",
	[SOI]   = "Start of image",
	[EOI]   = "End of image",
	[SOS]   = "Start of scan",
	[DQT]   = "Define quantization table(s)",
	[DNL]   = "Define number of lines",
	[DRI]   = "Define restart interval",
	[DHP]   = "Define hierarchical progression",
	[EXP]   = "Expand reference component(s)",
	[APP0]  = "Reserved for application segments, 0",
	[APP1]  = "Reserved for application segments, 1",
	[APP2]  = "Reserved for application segments, 2",
	[APP3]  = "Reserved for application segments, 3",
	[APP4]  = "Reserved for application segments, 4",
	[APP5]  = "Reserved for application segments, 5",
	[APP6]  = "Reserved for application segments, 6",
	[APP7]  = "Reserved for application segments, 7",
	[APP8]  = "Reserved for application segments, 8",
	[APP9]  = "Reserved for application segments, 9",
	[APP10] = "Reserved for application segments, 10",
	[APP11] = "Reserved for application segments, 11",
	[APP12] = "Reserved for application segments, 12",
	[APP13] = "Reserved for application segments, 13",
	[APP14] = "Reserved for application segments, 14",
	[APP15] = "Reserved for application segments, 15",
	[JPG0]  = "Reserved for JPEG extensions, 0",
	[JPG1]  = "Reserved for JPEG extensions, 1",
	[JPG2]  = "Reserved for JPEG extensions, 2",
	[JPG3]  = "Reserved for JPEG extensions, 3",
	[JPG4]  = "Reserved for JPEG extensions, 4",
	[JPG5]  = "Reserved for JPEG extensions, 5",
	[JPG6]  = "Reserved for JPEG extensions, 6",
	[JPG7]  = "Reserved for JPEG extensions, 7",
	[JPG8]  = "Reserved for JPEG extensions, 8",
	[JPG9]  = "Reserved for JPEG extensions, 9",
	[JPG10] = "Reserved for JPEG extensions, 10",
	[JPG11] = "Reserved for JPEG extensions, 11",
	[JPG12] = "Reserved for JPEG extensions, 12",
	[JPG13] = "Reserved for JPEG extensions, 13",
	[COM]   = "Comment",
};

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

struct data {
	bool ended;
	uint8_t *exif, *icc, *psir;
	size_t exif_len, icc_len, psir_len;
	int icc_sequence, icc_done;
	const uint8_t **mpf_offsets, **mpf_next;
};

static void
parse_append(uint8_t **buffer, size_t *buffer_len, const uint8_t *p, size_t len)
{
	size_t buffer_longer = *buffer_len + len;
	*buffer = realloc(*buffer, buffer_longer);
	memcpy(*buffer + *buffer_len, p, len);
	*buffer_len = buffer_longer;
}

static const uint8_t *
parse_marker(uint8_t marker, const uint8_t *p, const uint8_t *end,
	struct data *data, jv *o)
{
	// Suspected: MJPEG? Undetected format recursion, e.g., thumbnails?
	// Found: Random metadata! Multi-Picture Format!
	if ((data->ended = marker == EOI)) {
		// TODO(p): Handle Exifs independently--flush the last one.
		if ((data->mpf_next || (data->mpf_next = data->mpf_offsets)) &&
			*data->mpf_next)
			return *data->mpf_next++;
		if (p != end)
			*o = add_warning(*o, "trailing data");
	}

	// These markers stand alone, not starting a marker segment.
	switch (marker) {
	case RST0:
	case RST1:
	case RST2:
	case RST3:
	case RST4:
	case RST5:
	case RST6:
	case RST7:
		*o = add_warning(*o, "unexpected restart marker");
		// Fall-through
	case SOI:
	case EOI:
	case TEM:
		return p;
	}

	uint16_t length = p[0] << 8 | p[1];
	const uint8_t *payload = p + 2;
	if ((p += length) > end) {
		*o = add_error(*o, "runaway marker segment");
		return NULL;
	}

	switch (marker) {
	case SOF0:
	case SOF1:
	case SOF2:
	case SOF3:
	case SOF5:
	case SOF6:
	case SOF7:
	case SOF9:
	case SOF10:
	case SOF11:
	case SOF13:
	case SOF14:
	case SOF15:
	case DHP:  // B.2.2 and B.3.2.
		// As per B.2.5, Y can be zero, then there needs to be a DNL segment.
		*o = add_to_subarray(*o, "info", JV_OBJECT(
			jv_string("type"), jv_string(marker_descriptions[marker]),
			jv_string("bits"), jv_number(payload[0]),
			jv_string("height"), jv_number(payload[1] << 8 | payload[2]),
			jv_string("width"), jv_number(payload[3] << 8 | payload[4]),
			jv_string("components"), jv_number(payload[5])
		));
		return p;
	}

	// See B.1.1.5, we can brute-force our way through the entropy-coded data.
	if (marker == SOS) {
		while (p + 2 <= end && (p[0] != 0xFF || p[1] < 0xC0 || p[1] > 0xFE ||
				(p[1] >= RST0 && p[1] <= RST7)))
			p++;
		return p;
	}

	// "The interpretation is left to the application."
	if (marker == COM) {
		int superascii = 0;
		char *buf = calloc(3, p - payload), *bufp = buf;
		for (const uint8_t *q = payload; q < p; q++) {
			if (*q < 128) {
				*bufp++ = *q;
			} else {
				superascii++;
				*bufp++ = 0xC0 | (*q >> 6);
				*bufp++ = 0x80 | (*q & 0x3F);
			}
		}
		*bufp++ = 0;
		*o = add_to_subarray(*o, "comments", jv_string(buf));
		free(buf);

		if (superascii)
			*o = add_warning(*o, "super-ASCII comments");
	}

	// These mostly contain an ASCII string header, following JPEG FIF:
	//
	// "Application-specific APP0 marker segments are identified
	//  by a zero terminated string which identifies the application
	//  (not 'JFIF' or 'JFXX')."
	if (marker >= APP0 && marker <= APP15) {
		const uint8_t *nul = memchr(payload, 0, p - payload);
		int unprintable = !nul;
		if (nul) {
			for (const uint8_t *q = payload; q < nul; q++)
				unprintable += *q < 32 || *q >= 127;
		}
		*o = add_to_subarray(*o, "apps",
			unprintable ? jv_null() : jv_string((const char *) payload));
	}

	// CIPA DC-007 (Multi-Picture Format) 5.2
	// http://fileformats.archiveteam.org/wiki/Multi-Picture_Format
	if (marker == APP2 && p - payload >= 8 && !memcmp(payload, "MPF\0", 4)) {
		payload += 4;
		*o = parse_mpf(*o, &data->mpf_offsets, payload, p - payload);
	}

	// CIPA DC-006 (Stereo Still Image Format for Digital Cameras)
	// TODO(p): Handle by properly skipping trailing data (use Stim offsets).

	// https://www.w3.org/Graphics/JPEG/jfif3.pdf
	if (marker == APP0 && p - payload >= 14 && !memcmp(payload, "JFIF\0", 5)) {
		payload += 5;

		jv units = jv_number(payload[2]);
		switch (payload[2]) {
		break; case 0: units = jv_null();
		break; case 1: units = jv_string("DPI");
		break; case 2: units = jv_string("dots per cm");
		}

		// The rest is picture data.
		*o = add_to_subarray(*o, "JFIF", JV_OBJECT(
			jv_string("version"), jv_number(payload[0] * 100 + payload[1]),
			jv_string("units"), units,
			jv_string("density-x"), jv_number(payload[3] << 8 | payload[4]),
			jv_string("density-y"), jv_number(payload[5] << 8 | payload[6]),
			jv_string("thumbnail-w"), jv_number(payload[7]),
			jv_string("thumbnail-h"), jv_number(payload[8])
		));
	}
	if (marker == APP0 && p - payload >= 6 && !memcmp(payload, "JFXX\0", 5)) {
		payload += 5;

		jv extension = jv_number(payload[0]);
		switch (payload[0]) {
		break; case 0x10: extension = jv_string("JPEG thumbnail");
		break; case 0x11: extension = jv_string("Paletted thumbnail");
		break; case 0x13: extension = jv_string("RGB thumbnail");
		}

		// The rest is picture data.
		*o = add_to_subarray(*o, "JFXX",
			JV_OBJECT(jv_string("extension"), extension));
	}

	// https://www.cipa.jp/std/documents/e/DC-008-2012_E.pdf 4.7.2
	// Adobe XMP Specification Part 3: Storage in Files, 2020/1, 1.1.3
	if (marker == APP1 && p - payload >= 6 && !memcmp(payload, "Exif\0", 5)) {
		payload += 6;
		if (payload[-1] != 0)
			*o = add_warning(*o, "weirdly padded Exif header");
		if (data->exif)
			*o = add_warning(*o, "multiple Exif segments");
		parse_append(&data->exif, &data->exif_len, payload, p - payload);
	}

	// https://www.color.org/specification/ICC1v43_2010-12.pdf B.4
	if (marker == APP2 && p - payload >= 14 &&
		!memcmp(payload, "ICC_PROFILE\0", 12) && !data->icc_done &&
		payload[12] == ++data->icc_sequence && payload[13] >= payload[12]) {
		payload += 14;
		parse_append(&data->icc, &data->icc_len, payload, p - payload);
		data->icc_done = payload[-1] == data->icc_sequence;
	}

	// Adobe XMP Specification Part 3: Storage in Files, 2020/1, 1.1.3 + 3.1.3
	// https://www.adobe.com/devnet-apps/photoshop/fileformatashtml/
	if (marker == APP13 && p - payload >= 14 &&
		!memcmp(payload, "Photoshop 3.0\0", 14)) {
		payload += 14;
		parse_append(&data->psir, &data->psir_len, payload, p - payload);
	}
	return p;
}

static jv
parse_jpeg(jv o, const uint8_t *p, size_t len)
{
	struct data data = {};
	const uint8_t *end = p + len;
	jv markers = jv_array();
	while (p) {
		// This is an expectable condition, use a simple warning.
		if (p + 2 > end) {
			if (!data.ended)
				o = add_warning(o, "unexpected EOF");
			break;
		}
		if (*p++ != 0xFF || *p == 0) {
			if (!data.ended)
				o = add_error(o, "no marker found where one was expected");
			break;
		}

		// Markers may be preceded by fill bytes.
		if (*p == 0xFF) {
			o = jv_object_set(o, jv_string("fillers"), jv_bool(true));
			continue;
		}

		uint8_t marker = *p++;
		markers = jv_array_append(markers,
			jv_string(marker_ids[marker] ? marker_ids[marker] : "RES"));
		p = parse_marker(marker, p, end, &data, &o);
	}

	if (data.exif) {
		o = parse_exif(o, data.exif, data.exif_len);
		free(data.exif);
	}
	if (data.icc) {
		if (data.icc_done)
			o = parse_icc(o, data.icc, data.icc_len);
		else
			o = add_warning(o, "bad ICC profile sequence");
		free(data.icc);
	}
	if (data.psir) {
		o = parse_psir(o, data.psir, data.psir_len);
		free(data.psir);
	}

	free(data.mpf_offsets);
	return jv_set(o, jv_string("markers"), markers);
}

// --- I/O ---------------------------------------------------------------------

static jv
do_file(const char *filename, jv o)
{
	const char *err = NULL;
	FILE *fp = fopen(filename, "rb");
	if (!fp) {
		err = strerror(errno);
		goto error;
	}

	uint8_t *data = NULL, buf[256 << 10];
	size_t n, len = 0;
	while ((n = fread(buf, sizeof *buf, sizeof buf / sizeof *buf, fp))) {
		data = realloc(data, len + n);
		memcpy(data + len, buf, n);
		len += n;
	}
	if (ferror(fp)) {
		err = strerror(errno);
		goto error_read;
	}

#if 0
	// Not sure if I want to ensure their existence...
	o = jv_object_set(o, jv_string("info"), jv_array());
	o = jv_object_set(o, jv_string("warnings"), jv_array());
#endif

	o = parse_jpeg(o, data, len);
error_read:
	fclose(fp);
	free(data);
error:
	if (err)
		o = add_error(o, err);
	return o;
}

int
main(int argc, char *argv[])
{
	// XXX: Can't use `xargs -P0`, there's a risk of non-atomic writes.
	// Usage: find . -iname *.png -print0 | xargs -0 ./pnginfo
	for (int i = 1; i < argc; i++) {
		const char *filename = argv[i];

		jv o = jv_object();
		o = jv_object_set(o, jv_string("filename"), jv_string(filename));
		o = do_file(filename, o);
		jv_dumpf(o, stdout, 0 /* Might consider JV_PRINT_SORTED. */);
		fputc('\n', stdout);
	}
	return 0;
}