umber: Set linebuf mode if UMBER_LINEBUF set

README.md

@@ -111,4 +111,14 @@ UMBER_LVL=*=never,fully.qualified.class.name=verbose
 
 These assignments are evaluated left-to-right, so latter ones will take precedence.
 
+## Enabling line buffering
+
+If you need to enable line buffering (e.g. you are reading the output of a program using Umber through a pipe let's say and you need `getline()` to return immediately when a new line is produced), you can use the `UMBER_LINEBUF` environment variable:
+
+```console
+UMBER_LINEBUF=true # This can be set to whatever except "", "0", or "false".
+```
+
+This will enable line buffering on both `stdout` and `stderr`.
+
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src/umber.c

@@ -38,6 +38,21 @@ struct umber_class_t {
 	umber_lvl_t lvl;
 };
 
+__attribute__((constructor)) void set_linebuf(void) {
+	char const* const val = getenv("UMBER_LINEBUF");
+
+	if (val == NULL) {
+		return;
+	}
+
+	if (*val == '\0' || *val == '0' || strcasecmp(val, "false") == 0) {
+		return;
+	}
+
+	setlinebuf(stdout);
+	setlinebuf(stderr);
+}
+
 umber_class_t const* umber_class_new(
 	char const* name,
 	umber_lvl_t const default_lvl,