Add a tool to extract information from JPEG images

3 files changed, 465 insertions, 1 deletions

diff --git a/tools/.gitignore b/tools/.gitignore
index 8463b6e..5888ef6 100644
--- a/tools/.gitignore
+++ b/tools/.gitignore
@@ -1 +1,2 @@
 /pnginfo
+/jpeginfo
diff --git a/tools/Makefile b/tools/Makefile
index c7fa1a5..a60c17d 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -4,7 +4,7 @@ CFLAGS = -g -O2 -Wall -Wextra `pkg-config --cflags $(deps)`
 LDLIBS = -ljq `pkg-config --libs $(deps)`
 
 deps = libpng
-targets = pnginfo
+targets = pnginfo jpeginfo
 
 all: $(targets)
 clean:
diff --git a/tools/jpeginfo.c b/tools/jpeginfo.c
new file mode 100644
index 0000000..fcfda0e
--- /dev/null
+++ b/tools/jpeginfo.c
@@ -0,0 +1,463 @@
+//
+// 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 <jv.h>
+
+#include <errno.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdbool.h>
+#include <stdarg.h>
+
+// --- JPEG --------------------------------------------------------------------
+// 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",
+};
+*/
+
+// --- Analysis ----------------------------------------------------------------
+// Because the JPEG file format is simple, just do it manually.
+
+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().
+	jv a = jv_object_get(jv_copy(o), jv_string(key));
+	return jv_set(o, jv_string(key),
+		jv_is_valid(jv_copy(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));
+}
+
+struct data {
+	bool ended;
+	char *exif, *icc;
+	size_t exif_len, icc_len;
+	int icc_sequence, icc_done;
+};
+
+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) && 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("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)
+	// http://fileformats.archiveteam.org/wiki/Multi-Picture_Format
+	// TODO(p): Handle by properly skipping trailing data (use MPF offsets).
+
+	// CIPA DC-006 (Stereo Still Image Format for Digital Cameras)
+	// http://fileformats.archiveteam.org/wiki/Multi-Picture_Format
+	// 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])
+		));
+	}
+
+	// https://www.w3.org/Graphics/JPEG/jfif3.pdf
+	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
+	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 Exifs");
+		} else {
+			data->exif = realloc(data->exif, (data->exif_len = p - payload));
+			memcpy(data->exif, payload, data->exif_len);
+		}
+	}
+
+	// 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;
+
+		size_t icc_longer = data->icc_len + (p - payload);
+		data->icc = realloc(data->icc, icc_longer);
+		memcpy(data->icc + data->icc_len, payload, p - payload);
+		data->icc_len = icc_longer;
+
+		data->icc_done = payload[-1] == data->icc_sequence;
+	}
+	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) {
+			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) {
+		// TODO(p): Decode.
+		free(data.exif);
+	}
+
+	if (data.icc) {
+		if (data.icc_done) {
+			// TODO(p): Decode.
+		} else {
+			o = add_warning(o, "bad ICC profile sequence");
+		}
+		free(data.icc);
+	}
+
+	return jv_set(o, jv_string("markers"), markers);
+}
+
+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;
+}