Add a tool to extract information from WebP

1 files changed, 129 insertions, 0 deletions

diff --git a/tools/webpinfo.c b/tools/webpinfo.c
new file mode 100644
index 0000000..f13ef28
--- /dev/null
+++ b/tools/webpinfo.c
@@ -0,0 +1,129 @@
+//
+// webpinfo.c: acquire information about WebP 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 <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+// --- WebP --------------------------------------------------------------------
+// https://github.com/webmproject/libwebp/blob/master/doc/webp-container-spec.txt
+// https://github.com/webmproject/libwebp/blob/master/doc/webp-lossless-bitstream-spec.txt
+// https://datatracker.ietf.org/doc/html/rfc6386
+
+static jv
+parse_webp(jv o, const uint8_t *p, size_t len)
+{
+	// libwebp won't let us simply iterate over all chunks, so handroll it.
+	if (len < 12 || memcmp(p, "RIFF", 4) || memcmp(p + 8, "WEBP", 4))
+		return add_error(o, "not a WEBP file");
+
+	// TODO(p): This can still be parseable.
+	// TODO(p): Warn on trailing data.
+	uint32_t size = unle.u32(p + 4);
+	if (8 + size < len)
+		return add_error(o, "truncated file");
+
+	const uint8_t *end = p + 8 + size;
+	p += 12;
+
+	jv chunks = jv_array();
+	while (p < end) {
+		if (end - p < 8) {
+			o = add_warning(o, "framing mismatch");
+			printf("%ld", end - p);
+			break;
+		}
+
+		uint32_t chunk_size = unle.u32(p + 4);
+		uint32_t chunk_advance = (chunk_size + 1) & ~1;
+		if (p + 8 + chunk_advance > end) {
+			o = add_warning(o, "runaway chunk payload");
+			break;
+		}
+
+		char fourcc[5] = "";
+		memcpy(fourcc, p, 4);
+		chunks = jv_array_append(chunks, jv_string(fourcc));
+		p += 8;
+
+		// TODO(p): Decode VP8 and VP8L chunk metadata.
+		if (!strcmp(fourcc, "EXIF"))
+			o = parse_exif(o, p, chunk_size);
+		if (!strcmp(fourcc, "ICCP"))
+			o = parse_icc(o, p, chunk_size);
+		p += chunk_advance;
+	}
+	return jv_set(o, jv_string("chunks"), chunks);
+}
+
+// --- 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;
+	}
+
+	o = parse_webp(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[])
+{
+	(void) parse_psir;
+
+	// 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;
+}