utils: Add HDLC decode utility

This utility can be used to decode any raw ISDN HDLC bitstream from
a file, such as a raw B-channel capture created by osmo-isdntap.

Change-Id: Ie3a2f9300b2d7ebff66064d5d7f81a1a2f684a6c

2 files changed, 96 insertions, 0 deletions

diff --git a/utils/Makefile.am b/utils/Makefile.am
index 9d56f63a..96d37e46 100644
--- a/utils/Makefile.am
+++ b/utils/Makefile.am
@@ -48,3 +48,7 @@ endif
 v110_decode_SOURCES = v110_decode.c
 v110_decode_LDADD = $(LDADD) $(top_builddir)/src/isdn/libosmoisdn.la -losmotrau # HACK!
 noinst_PROGRAMS += v110_decode
+
+hdlc_decode_SOURCES = hdlc_decode.c
+hdlc_decode_LDADD = $(LDADD) #$(top_builddir)/src/isdn/libosmoisdn.la -losmotrau # HACK!
+noinst_PROGRAMS += hdlc_decode
diff --git a/utils/hdlc_decode.c b/utils/hdlc_decode.c
new file mode 100644
index 00000000..125b0bc6
--- /dev/null
+++ b/utils/hdlc_decode.c
@@ -0,0 +1,92 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <string.h>
+#include <unistd.h>
+
+#include <osmocom/core/isdnhdlc.h>
+#include <osmocom/core/utils.h>
+
+static struct osmo_isdnhdlc_vars g_hdlc;
+
+/* process input buffer of given length; find + process any HDLC frames contained inside,
+ * and return the number of bytes consumed from start of inbuf */
+static int process_buf(const uint8_t *inbuf, size_t inlen)
+{
+	uint8_t outbuf[4096];
+	int rc, count;
+	size_t in_offset = 0;
+
+#if 0
+	while ((rc = osmo_isdnhdlc_decode(&g_hdlc, inbuf + in_offset, inlen - in_offset, &count,
+					  outbuf, sizeof(outbuf))) != 2) {
+#else
+	while (true) {
+		rc = osmo_isdnhdlc_decode(&g_hdlc, inbuf + in_offset, inlen - in_offset, &count,
+					  outbuf, sizeof(outbuf));
+#endif
+		//printf("rc=%d, inlen=%zu, in_offset=%zu, count=%d\n", rc, inlen, in_offset, count);
+		if (rc > 0) {
+			int frlen = rc;
+			printf("%s\n", osmo_hexdump(outbuf, frlen));
+		} else {
+			switch (rc) {
+			case -OSMO_HDLC_FRAMING_ERROR:
+				fprintf(stderr, "FRAMING_ERR\n");
+				break;
+			case -OSMO_HDLC_CRC_ERROR:
+				fprintf(stderr, "CRC_ERR\n");
+				break;
+			case -OSMO_HDLC_LENGTH_ERROR:
+				fprintf(stderr, "LEN_ERR\n");
+				break;
+			}
+		}
+		in_offset += count;
+		if (in_offset >= inlen)
+			break;
+	}
+
+	return in_offset;
+}
+
+static int open_and_process(const char *fname)
+{
+	int fd = open(fname, O_RDONLY);
+	if (fd < 0)
+		return fd;
+
+	int read_offset = 0;
+
+	while (true) {
+		uint8_t inbuf[4096];
+		int rc, inlen, count;
+
+		/* read a chunk of data */
+		rc = read(fd, inbuf + read_offset, sizeof(inbuf) - read_offset);
+		if (rc <= 0)
+			return rc;
+		/* available length */
+		inlen = read_offset + rc;
+		//printf("read %d bytes to read_offset=%u => %d available bytes\n", rc, read_offset, inlen);
+
+		count = process_buf(inbuf, inlen);
+		//printf("processed %d bytes from inbuf\n", count);
+		if (count == inlen) {
+			read_offset = 0;
+		} else  if (count < inlen) {
+			//printf("moving %d remaining bytes to start of inbuf\n", inlen-count);
+			memmove(inbuf, inbuf + count, inlen - count);
+			read_offset = inlen - count;
+		}
+	}
+}
+
+int main(int argc, char **argv)
+{
+	osmo_isdnhdlc_rcv_init(&g_hdlc, OSMO_HDLC_F_BITREVERSE);
+
+	return open_and_process(argv[1]);
+}