1 file changed, 54 insertions, 0 deletions
diff --git a/source/filter.h b/source/filter.h
new file mode 100644
index 0000000..861578c
--- /dev/null
+++ b/source/filter.h
@@ -0,0 +1,54 @@
+/*
+ * Output filters, the hook that lets a site pass page fragments through an
+ * external program or an embedded Lua script on their way to the browser. A
+ * filter takes over stdout between an open and a close call, so at most one
+ * can be active at a time. The exec and Lua backends both hide behind the
+ * struct cgit_filter call table, so callers never learn which is in use.
+ */
+
+#ifndef CGIT_FILTER_H
+#define CGIT_FILTER_H
+
+#include <stdarg.h>
+#include <stdio.h>
+
+typedef enum {
+	ABOUT, COMMIT, SOURCE, EMAIL, AUTH
+} filter_type;
+
+struct cgit_filter {
+	int (*open)(struct cgit_filter *, va_list ap);
+	int (*close)(struct cgit_filter *);
+	void (*fprintfp)(struct cgit_filter *, FILE *, const char *prefix);
+	void (*cleanup)(struct cgit_filter *);
+	int argument_count;
+};
+
+struct cgit_exec_filter {
+	struct cgit_filter base;
+	char *cmd;
+	char **argv;
+	int old_stdout;
+	int pid;
+};
+
+extern struct cgit_filter *cgit_new_filter(const char *cmd,
+					   filter_type filtertype);
+extern void cgit_exec_filter_init(struct cgit_exec_filter *filter, char *cmd,
+				  char **argv);
+
+/*
+ * Redirect stdout into the filter and pass it the variadic arguments its type
+ * expects, then hand stdout back and return the filter's exit status.
+ */
+extern int cgit_open_filter(struct cgit_filter *filter, ...);
+extern int cgit_close_filter(struct cgit_filter *filter);
+
+// Describe the filter the way cgitrc would have configured it.
+extern void cgit_fprintf_filter(struct cgit_filter *filter, FILE *f,
+				const char *prefix);
+
+extern void cgit_init_filters(void);
+extern void cgit_cleanup_filters(void);
+
+#endif // CGIT_FILTER_H