Enable using development display libraries

Also add useful routines.

1 files changed, 72 insertions, 7 deletions

diff --git a/src/disp.c b/src/disp.c
index c4c1cd6..6fb25eb 100644
--- a/src/disp.c
+++ b/src/disp.c
@@ -1,12 +1,76 @@
+#include <assert.h>
 #include <dlfcn.h>
 #include <limits.h>
-#include <string.h>
+#include <stdarg.h>
 #include <stdio.h>
 #include <stdlib.h>
-#include <assert.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <errno.h>
 
 #include "disp.h"
 
+void
+/* Internals of strbuild. */
+__strbuild(char *buf, int size,
+	   const char *file, int line,
+	   const char *fmt, ...)
+{
+	va_list ap;
+	int len;
+
+	va_start(ap, fmt);
+	len = vsnprintf(NULL, 0, fmt, ap);
+	va_end(ap);
+
+	if (len < 0)
+	{
+		fprintf(stderr, "%s:%d: ", file, line);
+		perror("");
+		exit(EXIT_FAILURE);
+	}
+	if (len >= size)
+	{
+		fprintf(stderr, "%s:%d: error: not enough space, "
+			"have %d, need at least %d\n",
+			file, line,
+			size, len + 1);
+		exit(EXIT_FAILURE);
+	}
+
+	va_start(ap, fmt);
+	len = vsnprintf(buf, size, fmt, ap);
+	va_end(ap);
+
+	assert(len >= 0);
+}
+
+/* Safely create a formatted string and write it to BUF. BUF shall be a buffer
+ * of size at least SIZE. BUF can be stack-allocated. If the formatting cannot
+ * be performed, exit(3) is called. This function is not meant to be called
+ * directly: the macro strbuild should be used. The code is adapted from the
+ * make_message function of the vsnprintf(3) manual page, section "examples". */
+#define strbuild(buf, fmt, ...) \
+	__strbuild(buf, sizeof(buf), __FILE__, __LINE__, fmt, __VA_ARGS__)
+
+#define strbuild_with_size(buf, size, fmt, ...)				\
+	__strbuild(buf, size, __FILE__, __LINE__, fmt, __VA_ARGS__)
+
+int
+file_exists(const char *path)
+{
+	struct stat statbuf __attribute__((unused));
+	int rc = stat(path, &statbuf);
+	if (rc == 0)
+		return 1;
+	else if ((rc == -1) && (errno == ENOENT))
+		return 0;
+	fprintf(stderr, "stat: \"%s\": ", path);
+	perror("");
+	exit(EXIT_FAILURE);
+}
+
+
 static void *
 load_generic_symbol(struct disp *disp, char *base_name)
 {
@@ -57,12 +121,13 @@ load_symbols(struct disp *disp)
 struct disp *
 get_disp(char *disp_name)
 {
-	/* displays are shared libraries */
 	char so_path[128];
-	strcpy(so_path, CALCULER_PREFIX);
-	strcat(so_path, "/lib/calculer/lib");
-	strcat(so_path, disp_name);
-	strcat(so_path, ".so");
+	/* local lookup, useful while developing */
+	strbuild(so_path, "./lib%s.so", disp_name);
+
+	if (!file_exists(so_path))
+		strbuild(so_path, "%s/lib/calculer/lib%s.so", CALCULER_PREFIX, disp_name);
+
 	struct disp *disp = malloc(sizeof(*disp));
 	disp->so_path = strdup(so_path);
 	disp->name = disp_name;