[PATCH] Customizable error handlers

[Petr Baudis <pasky@xxxxxxx>]

This patch makes the usage(), die() and error() handlers customizable.
Nothing in the git code itself uses that but many other libgit users
(like Git.pm) will.

This is implemented using the mutator functions primarily because you
cannot directly modifying global variables of libgit from a program that
dlopen()ed it, apparently. But having functions for that is a better API
anyway.

Signed-off-by: Petr Baudis <pasky@xxxxxxx>
---

 git-compat-util.h |   10 +++++++---
 usage.c           |   50 +++++++++++++++++++++++++++++++++++++++++++++-----
 2 files changed, 52 insertions(+), 8 deletions(-)

diff --git a/git-compat-util.h b/git-compat-util.h
index 5d543d2..e954002 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -36,9 +36,13 @@ #endif
 #endif
 
 /* General helper functions */
-extern void usage(const char *err) NORETURN;
-extern void die(const char *err, ...) NORETURN __attribute__((format (printf, 1, 2)));
-extern int error(const char *err, ...) __attribute__((format (printf, 1, 2)));
+void usage(const char *err) NORETURN;
+void die(const char *err, ...) NORETURN __attribute__((format (printf, 1, 2)));
+int error(const char *err, ...) __attribute__((format (printf, 1, 2)));
+
+void set_usage_routine(void (*routine)(const char *err) NORETURN);
+void set_die_routine(void (*routine)(const char *err, va_list params) NORETURN);
+void set_error_routine(int (*routine)(const char *err, va_list params));
 
 #ifdef NO_MMAP
 
diff --git a/usage.c b/usage.c
index 1fa924c..445456d 100644
--- a/usage.c
+++ b/usage.c
@@ -12,28 +12,68 @@ static void report(const char *prefix, c
 	fputs("\n", stderr);
 }
 
-void usage(const char *err)
+void usage_builtin(const char *err)
 {
 	fprintf(stderr, "usage: %s\n", err);
 	exit(129);
 }
 
+void die_builtin(const char *err, va_list params)
+{
+	report("fatal: ", err, params);
+	exit(128);
+}
+
+int error_builtin(const char *err, va_list params)
+{
+	report("error: ", err, params);
+	return -1;
+}
+
+
+/* If we are in a dlopen()ed .so write to a global variable would segfault
+ * (ugh), so keep things static. */
+static void (*usage_routine)(const char *err) NORETURN = usage_builtin;
+static void (*die_routine)(const char *err, va_list params) NORETURN = die_builtin;
+static int (*error_routine)(const char *err, va_list params) = error_builtin;
+
+void set_usage_routine(void (*routine)(const char *err) NORETURN)
+{
+	usage_routine = routine;
+}
+
+void set_die_routine(void (*routine)(const char *err, va_list params) NORETURN)
+{
+	die_routine = routine;
+}
+
+void set_error_routine(int (*routine)(const char *err, va_list params))
+{
+	error_routine = routine;
+}
+
+
+void usage(const char *err)
+{
+	usage_routine(err);
+}
+
 void die(const char *err, ...)
 {
 	va_list params;
 
 	va_start(params, err);
-	report("fatal: ", err, params);
+	die_routine(err, params);
 	va_end(params);
-	exit(128);
 }
 
 int error(const char *err, ...)
 {
 	va_list params;
+	int ret;
 
 	va_start(params, err);
-	report("error: ", err, params);
+	ret = error_routine(err, params);
 	va_end(params);
-	return -1;
+	return ret;
 }
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