Create public filter object and use it

This creates include/sys/filter.h with a basic definition of a
git_filter and then converts the internal code to use it.  There
are related internal objects (git_filter_list) that we will want
to publish at some point, but this is a first step.

2 files changed, 119 insertions, 1 deletions

diff --git a/include/git2/filter.h b/include/git2/filter.h
index 3bc4a9037..478f3a6ad 100644
--- a/include/git2/filter.h
+++ b/include/git2/filter.h
@@ -39,7 +39,10 @@ typedef enum {
  * A filter that can transform file data
  *
  * This represents a filter that can be used to transform or even replace
- * file data.  Libgit2 currently includes one built in filter:
+ * file data.  Libgit2 includes one built in filter and it is possible to
+ * write your own (see git2/sys/filter.h for information on that).
+ *
+ * The built in filter is:
  *
  * * "crlf" which uses the complex rules with the "text", "eol", and
  *   "crlf" file attributes to decide how to convert between LF and CRLF
@@ -47,6 +50,17 @@ typedef enum {
  */
 typedef struct git_filter git_filter;
 
+GIT_EXTERN(git_filter *) git_filter_lookup(const char *name);
+
+#define GIT_FILTER_CRLF "crlf"
+
+GIT_EXTERN(int) git_filter_apply_to_buffer(
+	git_buffer *out,
+	git_filter *filter,
+	const git_buffer *input,
+	const char *as_path,
+	git_filter_mode_t mode);
+
 GIT_END_DECL
 
 /** @} */
diff --git a/include/git2/sys/filter.h b/include/git2/sys/filter.h
new file mode 100644
index 000000000..2264be080
--- /dev/null
+++ b/include/git2/sys/filter.h
@@ -0,0 +1,104 @@
+/*
+ * Copyright (C) the libgit2 contributors. All rights reserved.
+ *
+ * This file is part of libgit2, distributed under the GNU GPL v2 with
+ * a Linking Exception. For full terms see the included COPYING file.
+ */
+#ifndef INCLUDE_sys_git_config_backend_h__
+#define INCLUDE_sys_git_config_backend_h__
+
+#include "git2/filter.h"
+
+/**
+ * @file git2/sys/filter.h
+ * @brief Git filter backend and plugin routines
+ * @defgroup git_backend Git custom backend APIs
+ * @ingroup Git
+ * @{
+ */
+GIT_BEGIN_DECL
+
+/**
+ * A filter source represents a file/blob to be processed
+ */
+typedef struct git_filter_source git_filter_source;
+struct git_filter_source {
+	git_repository *repo;
+	const char     *path;
+	git_oid         oid;  /* zero if unknown (which is likely) */
+	uint16_t        filemode; /* zero if unknown */
+};
+
+/**
+ * Callback to actually perform the data filtering
+ */
+typedef int (*git_filter_apply_fn)(
+	git_filter        *self,
+	void              **payload, /* may be read and/or set */
+	git_filter_mode_t mode,
+	git_buffer        *to,
+	const git_buffer  *from,
+	const git_filter_source *src);
+
+/**
+ * Callback to decide if a given source needs this filter
+ */
+typedef int (*git_filter_check_fn)(
+	git_filter        *self,
+	void              **payload, /* points to NULL ptr on entry, may be set */
+	git_filter_mode_t mode,
+	const git_filter_source *src);
+
+/**
+ * Callback to clean up after filtering has been applied
+ */
+typedef void (*git_filter_cleanup_fn)(
+	git_filter *self,
+	void       *payload);
+
+/**
+ * Filter structure used to register a new filter.
+ *
+ * To associate extra data with a filter, simply allocate extra data
+ * and put the `git_filter` struct at the start of your data buffer,
+ * then cast the `self` pointer to your larger structure when your
+ * callback is invoked.
+ *
+ * `version` should be set to GIT_FILTER_VERSION
+ *
+ * `apply` is the callback that actually filters data.
+ *
+ * `check` is an optional callback that checks if filtering is needed for
+ * a given source.
+ *
+ * `cleanup` is an optional callback that is made after the filter has
+ * been applied.  Both the `check` and `apply` callbacks are able to
+ * allocate a `payload` to keep per-source filter state, and this callback
+ * is given that value and can clean up as needed.
+ */
+struct git_filter {
+	unsigned int          version;
+	git_filter_apply_fn   apply;
+	git_filter_check_fn   check;
+	git_filter_cleanup_fn cleanup;
+};
+
+#define GIT_FILTER_VERSION 1
+
+/**
+ * Register a filter under a given name
+ *
+ * Two filters will be preregistered with libgit2: GIT_FILTER_CRLF and
+ * GIT_FILTER_IDENT.
+ */
+GIT_EXTERN(int) git_filter_register(
+	const char *name, const git_filter *filter);
+
+/**
+ * Remove the filter with the given name
+ */
+GIT_EXTERN(int) git_filter_unregister(const char *name);
+
+/** @} */
+GIT_END_DECL
+#endif