1 files changed, 251 insertions, 0 deletions
diff --git a/tools/pnginfo.c b/tools/pnginfo.c
new file mode 100644
index 0000000..afb3d50
--- /dev/null
+++ b/tools/pnginfo.c
@@ -0,0 +1,251 @@
+//
+// pnginfo.c: acquire information about PNG 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 <png.h>
+#include <jv.h>
+
+#include <errno.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdbool.h>
+#include <stdarg.h>
+#include <setjmp.h>
+
+// --- Utilities ---------------------------------------------------------------
+
+#if defined __GNUC__
+#define ATTRIBUTE_PRINTF(x, y) __attribute__((format (printf, x, y)))
+#else // ! __GNUC__
+#define ATTRIBUTE_PRINTF(x, y)
+#endif // ! __GNUC__
+
+static char *strfmt(const char *format, ...) ATTRIBUTE_PRINTF(1, 2);
+
+static char *
+strvfmt(const char *format, va_list ap)
+{
+	va_list aq;
+	va_copy(aq, ap);
+	int size = vsnprintf(NULL, 0, format, aq);
+	va_end(aq);
+	if (size < 0)
+		return NULL;
+
+	char buf[size + 1];
+	size = vsnprintf(buf, sizeof buf, format, ap);
+	if (size < 0)
+		return NULL;
+
+	return strdup(buf);
+}
+
+static char *
+strfmt(const char *format, ...)
+{
+	va_list ap;
+	va_start(ap, format);
+	char *result = strvfmt(format, ap);
+	va_end(ap);
+	return result;
+}
+
+// --- Analysis ----------------------------------------------------------------
+
+static void
+redirect_libpng_error(png_structp pngp, const char* message)
+{
+	char **storage = png_get_error_ptr(pngp);
+	*storage = strfmt("%s", message);
+}
+
+static jv
+retrieve_texts(png_structp pngp, png_infop infop)
+{
+	int texts_len = 0;
+	png_textp texts = NULL;
+	png_get_text(pngp, infop, &texts, &texts_len);
+
+	jv o = jv_object();
+	for (int i = 0; i < texts_len; i++) {
+		png_textp text = texts + i;
+		o = jv_object_set(o, jv_string(text->key), jv_string(text->text));
+	}
+	return o;
+}
+
+static jv
+extract_chunks(png_structp pngp, png_infop infop)
+{
+	jv o = jv_object();
+
+	// With a fully separated infop from the end of the file,
+	// png_get_IHDR() causes a warning and an error. Avoid that.
+	uint32_t width = 0, height = 0;
+	int bit_depth = 0, color_type = 0, interlace_method = 0;
+	if (png_get_image_width(pngp, infop)
+	 && png_get_IHDR(pngp, infop, &width, &height, &bit_depth, &color_type,
+			&interlace_method, NULL, NULL)) {
+		const char *color = "?";
+		switch (color_type) {
+		case 0:
+		case 4: color = "gray";       break;
+		case 2:
+		case 6: color = "rgb";        break;
+		case 3: color = "palette";    break;
+		}
+
+		o = jv_object_set(o, jv_string("depth"), jv_number(bit_depth));
+		o = jv_object_set(o, jv_string("width"), jv_number(width));
+		o = jv_object_set(o, jv_string("height"), jv_number(height));
+		o = jv_object_set(o, jv_string("interlace"), jv_bool(interlace_method));
+		o = jv_object_set(o, jv_string("color"), jv_string(color));
+		o = jv_object_set(o, jv_string("alpha"),
+			jv_bool((color_type & PNG_COLOR_MASK_ALPHA) ||
+				png_get_valid(pngp, infop, PNG_INFO_tRNS)));
+	}
+
+	double gamma = 0;
+	if (png_get_gAMA(pngp, infop, &gamma))
+		// XXX: Might want to round it or store as integer.
+		o = jv_object_set(o, jv_string("gamma"), jv_number(1 / gamma));
+
+	// Note that sRGB overrides both gAMA and cHRM.
+	int intent = -1;
+	if (png_get_sRGB(pngp, infop, &intent)) {
+		const char *name = "?";
+		switch (intent) {
+		case PNG_sRGB_INTENT_PERCEPTUAL: name = "perceptual"; break;
+		case PNG_sRGB_INTENT_RELATIVE:   name = "relative";   break;
+		case PNG_sRGB_INTENT_SATURATION: name = "saturation"; break;
+		case PNG_sRGB_INTENT_ABSOLUTE:   name = "absolute";   break;
+		}
+		o = jv_object_set(o, jv_string("sRGB"), jv_string(name));
+	}
+
+	// Note that iCCP overrides both gAMA and cHRM.
+	char *name = NULL;
+	png_bytep profile = NULL;
+	uint32_t profile_len = 0;
+	if (png_get_iCCP(pngp, infop, &name, NULL, &profile, &profile_len))
+		o = jv_object_set(o, jv_string("ICC"), jv_string(name));
+
+	jv set = jv_object();
+	png_unknown_chunkp unknowns = NULL;
+	int unknowns_len = png_get_unknown_chunks(pngp, infop, &unknowns);
+	for (int i = 0; i < unknowns_len; i++)
+		set = jv_object_set(set,
+			jv_string((const char *) unknowns[i].name), jv_true());
+
+	jv a = jv_array();
+	jv_object_keys_foreach(set, key)
+		a = jv_array_append(a, jv_copy(key));
+	o = jv_object_set(o, jv_string("chunks"), a);
+	jv_free(set);
+
+	o = jv_object_set(o, jv_string("texts"), retrieve_texts(pngp, infop));
+	return o;
+}
+
+static jv
+do_file(const char *filename, volatile jv o)
+{
+	png_bytep volatile buffer = NULL;
+	png_bytepp volatile rows = NULL;
+
+	char *volatile err = NULL;
+	FILE *fp = fopen(filename, "rb");
+	if (!fp) {
+		err = strfmt("%s", strerror(errno));
+		goto error;
+	}
+
+	png_structp pngp = png_create_read_struct(PNG_LIBPNG_VER_STRING,
+		(png_voidp) &err, redirect_libpng_error, NULL);
+	if (!pngp) {
+		err = strfmt("%s", strerror(errno));
+		goto error_png;
+	}
+
+	// We want to read these separately, which libpng allows and spng doesn't.
+	png_infop infop = png_create_info_struct(pngp);
+	png_infop endp = png_create_info_struct(pngp);
+	if (!infop || !endp) {
+		err = strfmt("%s", strerror(errno));
+		goto error_decode;
+	}
+
+	png_init_io(pngp, fp);
+	if (setjmp(png_jmpbuf(pngp)))
+		goto error_decode;
+
+	// Following the list of PNG_INFO_*, we just scan for their existence.
+	png_byte basic[] =
+		"cHRM\0bKGD\0hIST\0pHYs\0oFFs\0tIME\0pCAL\0sPLT\0sCAL\0eXIf";
+	png_set_keep_unknown_chunks(pngp, PNG_HANDLE_CHUNK_ALWAYS, basic,
+		sizeof basic / 5);
+	png_set_keep_unknown_chunks(pngp, PNG_HANDLE_CHUNK_ALWAYS, NULL, 0);
+
+	png_read_info(pngp, infop);
+	o = jv_object_set(o, jv_string("info"), extract_chunks(pngp, infop));
+
+	// Run over the data in the simplest possible manner.
+	size_t height = png_get_image_height(pngp, infop);
+	size_t row_bytes = png_get_rowbytes(pngp, infop);
+
+	if (!(buffer = calloc(height, row_bytes))
+	 || !(rows = calloc(height, sizeof(png_bytep))))
+		png_error(pngp, strerror(errno));
+	for (size_t i = 0; i < height; i++)
+		rows[i] = buffer + i * row_bytes;
+
+	if (!getenv("PNGINFO_SKIP_TRAILING")) {
+		png_read_image(pngp, rows);
+
+		png_read_end(pngp, endp);
+		o = jv_object_set(o, jv_string("end"), extract_chunks(pngp, endp));
+	}
+
+error_decode:
+	free(buffer);
+	free(rows);
+	png_destroy_read_struct(&pngp, &infop, &endp);
+error_png:
+	fclose(fp);
+error:
+	if (err) {
+		o = jv_object_set(o, jv_string("error"), jv_string(err));
+		free(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;
+}