Add helper functions to convert UUID to/from strings

Add some helper functions to convert the binary UUID data structure to
and from their human readable string representation.

contrib/android/Android.mk

@@ -9,6 +9,7 @@ LOCAL_SRC_FILES := \
 	src/array.c \
 	src/atomics_cobalt.c \
 	src/atomics_cobalt_parser.c \
+	src/ble.c \
 	src/bluetooth.c \
 	src/buffer.c \
 	src/checksum.c \

contrib/msvc/libdivecomputer.vcxproj

@@ -177,6 +177,7 @@
     <ClCompile Include="..\..\src\array.c" />
     <ClCompile Include="..\..\src\atomics_cobalt.c" />
     <ClCompile Include="..\..\src\atomics_cobalt_parser.c" />
+    <ClCompile Include="..\..\src\ble.c" />
     <ClCompile Include="..\..\src\bluetooth.c" />
     <ClCompile Include="..\..\src\buffer.c" />
     <ClCompile Include="..\..\src\checksum.c" />

include/libdivecomputer/ble.h

@@ -60,11 +60,47 @@ extern "C" {
 #define DC_IOCTL_BLE_CHARACTERISTIC_READ  DC_IOCTL_IOR('b', 3, DC_IOCTL_SIZE_VARIABLE)
 #define DC_IOCTL_BLE_CHARACTERISTIC_WRITE DC_IOCTL_IOW('b', 3, DC_IOCTL_SIZE_VARIABLE)
 
+/**
+ * The minimum number of bytes (including the terminating null byte) for
+ * formatting a bluetooth UUID as a string.
+ */
+#define DC_BLE_UUID_SIZE 37
+
 /**
  * Bluetooth UUID (128 bits).
  */
 typedef unsigned char dc_ble_uuid_t[16];
 
+/**
+ * Convert a bluetooth UUID to a string.
+ *
+ * The bluetooth UUID is formatted as
+ * XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX, where each XX pair is a
+ * hexadecimal number specifying an octet of the UUID.
+ * The minimum size for the buffer is #DC_BLE_UUID_SIZE bytes.
+ *
+ * @param[in]  uuid     A bluetooth UUID.
+ * @param[in]  str      The memory buffer to store the result.
+ * @param[in]  size     The size of the memory buffer.
+ * @returns The null-terminated string on success, or NULL on failure.
+ */
+char *
+dc_ble_uuid2str (const dc_ble_uuid_t uuid, char *str, size_t size);
+
+/**
+ * Convert a string to a bluetooth UUID.
+ *
+ * The string is expected to be in the format
+ * XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX, where each XX pair is a
+ * hexadecimal number specifying an octet of the UUID.
+ *
+ * @param[in]  str      A null-terminated string.
+ * @param[in]  uuid     The memory buffer to store the result.
+ * @returns Non-zero on success, or zero on failure.
+ */
+int
+dc_ble_str2uuid (const char *str, dc_ble_uuid_t uuid);
+
 #ifdef __cplusplus
 }
 #endif /* __cplusplus */

src/Makefile.am

@@ -88,6 +88,7 @@ libdivecomputer_la_SOURCES = \
 	irda.c \
 	usb.c \
 	usbhid.c \
+	ble.c \
 	bluetooth.c \
 	custom.c
 

src/ble.c

@@ -0,0 +1,97 @@
+/*
+ * libdivecomputer
+ *
+ * Copyright (C) 2024 Jef Driesen
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
+ * MA 02110-1301 USA
+ */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <string.h>
+
+#include <libdivecomputer/ble.h>
+
+#include "platform.h"
+
+char *
+dc_ble_uuid2str (const dc_ble_uuid_t uuid, char *str, size_t size)
+{
+	if (str == NULL || size < DC_BLE_UUID_SIZE)
+		return NULL;
+
+	int n = dc_platform_snprintf(str, size,
+		"%02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-%02x%02x%02x%02x%02x%02x",
+		uuid[0], uuid[1], uuid[2], uuid[3],
+		uuid[4], uuid[5],
+		uuid[6], uuid[7],
+		uuid[8], uuid[9],
+		uuid[10], uuid[11], uuid[12],
+		uuid[13], uuid[14], uuid[15]);
+	if (n < 0 || (size_t) n >= size)
+		return NULL;
+
+	return str;
+}
+
+int
+dc_ble_str2uuid (const char *str, dc_ble_uuid_t uuid)
+{
+	dc_ble_uuid_t tmp = {0};
+
+	if (str == NULL || uuid == NULL)
+		return 0;
+
+	unsigned int i = 0;
+	unsigned char c = 0;
+	while ((c = *str++) != '\0') {
+		if (c == '-') {
+			if (i != 8 && i != 12 && i != 16 && i != 20) {
+				return 0; /* Invalid character! */
+			}
+			continue;
+		} else if (c >= '0' && c <= '9') {
+			c -= '0';
+		} else if (c >= 'A' && c <= 'F') {
+			c -= 'A' - 10;
+		} else if (c >= 'a' && c <= 'f') {
+			c -= 'a' - 10;
+		} else {
+			return 0; /* Invalid character! */
+		}
+
+		if ((i & 1) == 0) {
+			c <<= 4;
+		}
+
+		if (i >= 2 * sizeof(tmp)) {
+			return 0; /* Too many characters! */
+		}
+
+		tmp[i / 2] |= c;
+		i++;
+	}
+
+	if (i != 2 * sizeof(tmp)) {
+		return 0; /* Not enough characters! */
+	}
+
+	memcpy (uuid, tmp, sizeof(tmp));
+
+	return 1;
+}

src/libdivecomputer.symbols

@@ -66,6 +66,9 @@ dc_bluetooth_device_free
 dc_bluetooth_iterator_new
 dc_bluetooth_open
 
+dc_ble_uuid2str
+dc_ble_str2uuid
+
 dc_irda_device_get_address
 dc_irda_device_get_name
 dc_irda_device_free