From 43cd111198d7839684f81a47cb12874a59b1c65b Mon Sep 17 00:00:00 2001
From: Jef Driesen <jefdriesen@users.sourceforge.net>
Date: Sun, 27 May 2012 23:46:30 +0200
Subject: [PATCH] Add support for an application defined logging function.

An application can now register an application defined callback
function, which will perform the actual logging. This provides
additional flexibility compared to logging to stderr with a hardcoded
format. Applications can now easily display the messages in their user
interface, customize the format, etc.

Although the internal logging function is a printf like function, the
arguments are converted into a plain string before being passed to the
callback function. This greatly improves interoperability with
programming languages which don't support C style variadic functions
(e.g. Python, C#, etc).
---
 include/libdivecomputer/context.h |  5 +++++
 src/context.c                     | 34 ++++++++++++++++++++++++++++++-
 src/libdivecomputer.symbols       |  1 +
 3 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/include/libdivecomputer/context.h b/include/libdivecomputer/context.h
index 10f21b4..861dbeb 100644
--- a/include/libdivecomputer/context.h
+++ b/include/libdivecomputer/context.h
@@ -39,6 +39,8 @@ typedef enum dc_loglevel_t {
 	DC_LOGLEVEL_ALL
 } dc_loglevel_t;
 
+typedef void (*dc_logfunc_t) (dc_context_t *context, dc_loglevel_t loglevel, const char *file, unsigned int line, const char *function, const char *message, void *userdata);
+
 dc_status_t
 dc_context_new (dc_context_t **context);
 
@@ -48,6 +50,9 @@ dc_context_free (dc_context_t *context);
 dc_status_t
 dc_context_set_loglevel (dc_context_t *context, dc_loglevel_t loglevel);
 
+dc_status_t
+dc_context_set_logfunc (dc_context_t *context, dc_logfunc_t logfunc, void *userdata);
+
 #ifdef __cplusplus
 }
 #endif /* __cplusplus */
diff --git a/src/context.c b/src/context.c
index f9d720a..2e0c62b 100644
--- a/src/context.c
+++ b/src/context.c
@@ -28,8 +28,19 @@
 
 struct dc_context_t {
 	dc_loglevel_t loglevel;
+	dc_logfunc_t logfunc;
+	void *userdata;
+	char msg[4096];
 };
 
+static void
+logfunc (dc_context_t *context, dc_loglevel_t loglevel, const char *file, unsigned int line, const char *function, const char *msg, void *userdata)
+{
+	const char *loglevels[] = {"NONE", "ERROR", "WARNING", "INFO", "DEBUG", "ALL"};
+
+	fprintf (stderr, "%s: %s [in %s:%d (%s)]\n", loglevels[loglevel], msg, file, line, function);
+}
+
 dc_status_t
 dc_context_new (dc_context_t **out)
 {
@@ -43,6 +54,10 @@ dc_context_new (dc_context_t **out)
 		return DC_STATUS_NOMEMORY;
 
 	context->loglevel = DC_LOGLEVEL_WARNING;
+	context->logfunc = logfunc;
+	context->userdata = NULL;
+
+	memset (context->msg, 0, sizeof (context->msg));
 
 	*out = context;
 
@@ -68,6 +83,18 @@ dc_context_set_loglevel (dc_context_t *context, dc_loglevel_t loglevel)
 	return DC_STATUS_SUCCESS;
 }
 
+dc_status_t
+dc_context_set_logfunc (dc_context_t *context, dc_logfunc_t logfunc, void *userdata)
+{
+	if (context == NULL)
+		return DC_STATUS_INVALIDARGS;
+
+	context->logfunc = logfunc;
+	context->userdata = userdata;
+
+	return DC_STATUS_SUCCESS;
+}
+
 dc_status_t
 dc_context_log (dc_context_t *context, dc_loglevel_t loglevel, const char *file, unsigned int line, const char *function, const char *format, ...)
 {
@@ -79,9 +106,14 @@ dc_context_log (dc_context_t *context, dc_loglevel_t loglevel, const char *file,
 	if (loglevel > context->loglevel)
 		return DC_STATUS_SUCCESS;
 
+	if (context->logfunc == NULL)
+		return DC_STATUS_SUCCESS;
+
 	va_start (ap, format);
-	vfprintf (stderr, format, ap);
+	vsnprintf (context->msg, sizeof (context->msg), format, ap);
 	va_end (ap);
 
+	context->logfunc (context, loglevel, file, line, function, context->msg, context->userdata);
+
 	return DC_STATUS_SUCCESS;
 }
diff --git a/src/libdivecomputer.symbols b/src/libdivecomputer.symbols
index fbc599d..652c011 100644
--- a/src/libdivecomputer.symbols
+++ b/src/libdivecomputer.symbols
@@ -20,6 +20,7 @@ dc_datetime_mktime
 dc_context_new
 dc_context_free
 dc_context_set_loglevel
+dc_context_set_logfunc
 
 dc_iterator_next
 dc_iterator_free