Add attributes to filters and fix registry

The filter registry as implemented was too primitive to actually
work once multiple filters were coming into play.  This expands
the implementation of the registry to handle multiple prioritized
filters correctly.

Additionally, this adds an "attributes" field to a filter that
makes it really really easy to implement filters that are based
on one or more attribute values.  The lookup and even simple value
checking can all happen automatically without custom filter code.

Lastly, with the registry improvements, this fills out the filter
lifecycle callbacks, with initialize and shutdown callbacks that
will be called before the filter is first used and after it is
last invoked.  This allows for system-wide initialization and
cleanup by the filter.

include/git2/errors.h

@@ -68,6 +68,7 @@ typedef enum {
 	GITERR_FETCHHEAD,
 	GITERR_MERGE,
 	GITERR_SSH,
+	GITERR_FILTER,
 } git_error_t;
 
 /**

include/git2/sys/filter.h

@@ -46,16 +46,26 @@ GIT_EXTERN(uint16_t) git_filter_source_filemode(const git_filter_source *src);
  */
 GIT_EXTERN(const git_oid *) git_filter_source_id(const git_filter_source *src);
 
+/*
+ * struct git_filter
+ *
+ * The filter lifecycle:
+ * - initialize - first use of filter
+ * - shutdown   - filter removed/unregistered from system
+ * - check      - considering for file
+ * - apply      - applied to file
+ * - cleanup    - done with file
+ */
+
 /**
- * Callback to actually perform the data filtering
+ * Initialize callback on filter
  */
-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);
+typedef int (*git_filter_init_fn)(git_filter *self);
+
+/**
+ * Shutdown callback on filter
+ */
+typedef void (*git_filter_shutdown_fn)(git_filter *self);
 
 /**
  * Callback to decide if a given source needs this filter
@@ -64,6 +74,18 @@ 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,
+	const char        **attr_values);
+
+/**
+ * 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);
 
 /**
@@ -83,10 +105,32 @@ typedef void (*git_filter_cleanup_fn)(
  *
  * `version` should be set to GIT_FILTER_VERSION
  *
- * `apply` is the callback that actually filters data.
+ * `attributes` is a list of attributes to check on a file to see if the
+ * filter applies.  The format is a whitespace-delimited list of names
+ * (like "eol crlf text").  Each name may have an optional value that will
+ * be tested even without a `check` callback.  If the value does not
+ * match, the filter will be skipped.  The values are specified as in a
+ * .gitattributes file (e.g. "myattr=foobar" or "myattr" or "-myattr").
+ * If a check function is supplied, then the values of the attributes will
+ * be passed to that function.
+ *
+ * `initialize` is an optional callback invoked before a filter is first
+ * used.  It will be called once at most.
+ *
+ * `shutdown` is an optional callback invoked when the filter is
+ * unregistered or when libgit2 is shutting down.  It will be called once
+ * at most and should free any memory as needed.
  *
  * `check` is an optional callback that checks if filtering is needed for
- * a given source.
+ * a given source.  It should return 0 if the filter should be applied
+ * (i.e. success), GIT_ENOTFOUND if the filter should not be applied, or
+ * an other error code to fail out of the filter processing pipeline and
+ * return to the caller.
+ *
+ * `apply` is the callback that actually filters data.  If it successfully
+ * writes the output, it should return 0.  Like `check`, it can return
+ * GIT_ENOTFOUND to indicate that the filter doesn't actually want to run.
+ * Other error codes will stop filter processing and return to the caller.
  *
  * `cleanup` is an optional callback that is made after the filter has
  * been applied.  Both the `check` and `apply` callbacks are able to
@@ -94,25 +138,46 @@ typedef void (*git_filter_cleanup_fn)(
  * 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;
+	unsigned int           version;
+	const char            *attributes;
+	git_filter_init_fn     initialize;
+	git_filter_shutdown_fn shutdown;
+	git_filter_check_fn    check;
+	git_filter_apply_fn    apply;
+	git_filter_cleanup_fn  cleanup;
 };
 
 #define GIT_FILTER_VERSION 1
 
 /**
- * Register a filter under a given name
+ * Register a filter under a given name with a given priority.
+ *
+ * If non-NULL, the filter's initialize callback will be invoked before
+ * the first use of the filter, so you can defer expensive operations (in
+ * case libgit2 is being used in a way that doesn't need the filter).
  *
- * Two filters will be preregistered with libgit2: GIT_FILTER_CRLF and
- * GIT_FILTER_IDENT.
+ * A filter's attribute checks and `check` and `apply` callbacks will be
+ * issued in order of `priority` on smudge (to workdir), and in reverse
+ * order of `priority` on clean (to odb).
+ *
+ * One filter will be preregistered with libgit2:
+ * - GIT_FILTER_CRLF with priority of 0.
+ *
+ * Currently the filter registry is not thread safe, so any registering or
+ * deregistering of filters must be done outside of any possible usage of
+ * the filters (i.e. during application setup or shutdown).
  */
 GIT_EXTERN(int) git_filter_register(
-	const char *name, const git_filter *filter);
+	const char *name, git_filter *filter, int priority);
 
 /**
  * Remove the filter with the given name
+ *
+ * It is not allowed to remove the builtin libgit2 filters.
+ *
+ * Currently the filter registry is not thread safe, so any registering or
+ * deregistering of filters must be done outside of any possible usage of
+ * the filters (i.e. during application setup or shutdown).
  */
 GIT_EXTERN(int) git_filter_unregister(const char *name);
 

src/attr.c

@@ -26,7 +26,6 @@ git_attr_t git_attr_value(const char *attr)
 	return GIT_ATTR_VALUE_T;
 }
 
-
 static int collect_attr_files(
 	git_repository *repo,
 	uint32_t flags,
@@ -103,8 +102,6 @@ int git_attr_get_many(
 	attr_get_many_info *info = NULL;
 	size_t num_found = 0;
 
-	memset((void *)values, 0, sizeof(const char *) * num_attr);
-
 	if (git_attr_path__init(&path, pathname, git_repository_workdir(repo)) < 0)
 		return -1;
 
@@ -141,6 +138,11 @@ int git_attr_get_many(
 		}
 	}
 
+	for (k = 0; k < num_attr; k++) {
+		if (!info[k].found)
+			values[k] = NULL;
+	}
+
 cleanup:
 	git_vector_free(&files);
 	git_attr_path__free(&path);

src/crlf.c

@@ -74,39 +74,6 @@ static int crlf_input_action(struct crlf_attrs *ca)
 	return ca->crlf_action;
 }
 
-static int crlf_load_attributes(
-	struct crlf_attrs *ca, git_repository *repo, const char *path)
-{
-#define NUM_CONV_ATTRS 3
-
-	static const char *attr_names[NUM_CONV_ATTRS] = {
-		"crlf", "eol", "text",
-	};
-
-	const char *attr_vals[NUM_CONV_ATTRS];
-	int error;
-
-	error = git_attr_get_many(attr_vals,
-		repo, 0, path, NUM_CONV_ATTRS, attr_names);
-
-	if (error == GIT_ENOTFOUND) {
-		ca->crlf_action = GIT_CRLF_GUESS;
-		ca->eol = GIT_EOL_UNSET;
-		return 0;
-	}
-
-	if (error == 0) {
-		ca->crlf_action = check_crlf(attr_vals[2]); /* text */
-		if (ca->crlf_action == GIT_CRLF_GUESS)
-			ca->crlf_action = check_crlf(attr_vals[0]); /* clrf */
-
-		ca->eol = check_eol(attr_vals[1]); /* eol */
-		return 0;
-	}
-
-	return -1;
-}
-
 static int has_cr_in_index(const git_filter_source *src)
 {
 	git_repository *repo = git_filter_source_repo(src);
@@ -283,7 +250,8 @@ static int crlf_check(
 	git_filter        *self,
 	void              **payload, /* points to NULL ptr on entry, may be set */
 	git_filter_mode_t mode,
-	const git_filter_source *src)
+	const git_filter_source *src,
+	const char **attr_values)
 {
 	int error;
 	struct crlf_attrs ca;
@@ -291,11 +259,16 @@ static int crlf_check(
 	GIT_UNUSED(self);
 	GIT_UNUSED(mode);
 
-	/* Load gitattributes for the path */
-	error = crlf_load_attributes(
-		&ca, git_filter_source_repo(src), git_filter_source_path(src));
-	if (error < 0)
-		return error;
+	if (!attr_values) {
+		ca.crlf_action = GIT_CRLF_GUESS;
+		ca.eol = GIT_EOL_UNSET;
+	} else {
+		ca.crlf_action = check_crlf(attr_values[2]); /* text */
+		if (ca.crlf_action == GIT_CRLF_GUESS)
+			ca.crlf_action = check_crlf(attr_values[0]); /* clrf */
+		ca.eol = check_eol(attr_values[1]); /* eol */
+	}
+	ca.auto_crlf = GIT_AUTO_CRLF_DEFAULT;
 
 	/*
 	 * Use the core Git logic to see if we should perform CRLF for this file
@@ -350,7 +323,11 @@ static void crlf_cleanup(
 git_filter *git_crlf_filter_new(void)
 {
 	struct crlf_filter *f = git__calloc(1, sizeof(struct crlf_filter));
+
 	f->f.version = GIT_FILTER_VERSION;
+	f->f.attributes = "crlf eol text";
+	f->f.initialize = NULL;
+	f->f.shutdown   = NULL;
 	f->f.check   = crlf_check;
 	f->f.apply   = crlf_apply;
 	f->f.cleanup = crlf_cleanup;

src/filter.c

@@ -12,6 +12,7 @@
 #include "repository.h"
 #include "git2/config.h"
 #include "blob.h"
+#include "attr_file.h"
 
 struct git_filter_source {
 	git_repository *repo;
@@ -35,9 +36,187 @@ struct git_filter_list {
 typedef struct {
 	const char *filter_name;
 	git_filter *filter;
+	int priority;
+	size_t nattrs, nmatches;
+	char *attrdata;
+	const char *attrs[GIT_FLEX_ARRAY];
 } git_filter_def;
 
-static git_array_t(git_filter_def) filter_registry = GIT_ARRAY_INIT;
+static int filter_def_priority_cmp(const void *a, const void *b)
+{
+	int pa = ((const git_filter_def *)a)->priority;
+	int pb = ((const git_filter_def *)b)->priority;
+	return (pa < pb) ? -1 : (pa > pb) ? 1 : 0;
+}
+
+static git_vector git__filter_registry = {
+	0, filter_def_priority_cmp, NULL, 0, 0
+};
+
+static int filter_def_scan_attrs(
+	git_buf *attrs, size_t *nattr, size_t *nmatch, const char *attr_str)
+{
+	const char *start, *scan = attr_str;
+	int has_eq;
+
+	*nattr = *nmatch = 0;
+
+	if (!scan)
+		return 0;
+
+	while (*scan) {
+		while (git__isspace(*scan)) scan++;
+
+		for (start = scan, has_eq = 0; *scan && !git__isspace(*scan); ++scan) {
+			if (*scan == '=')
+				has_eq = 1;
+		}
+
+		if (scan > start) {
+			(*nattr)++;
+			if (has_eq || *scan == '-' || *scan == '+' || *scan == '!')
+				(*nmatch)++;
+
+			if (has_eq)
+				git_buf_putc(attrs, '=');
+			git_buf_put(attrs, start, scan - start);
+			git_buf_putc(attrs, '\0');
+		}
+	}
+
+	return 0;
+}
+
+static void filter_def_set_attrs(git_filter_def *fdef)
+{
+	char *scan = fdef->attrdata;
+	size_t i;
+
+	for (i = 0; i < fdef->nattrs; ++i) {
+		const char *name, *value;
+
+		switch (*scan) {
+		case '=':
+			name = scan + 1;
+			for (scan++; *scan != '='; scan++) /* find '=' */;
+			*scan++ = '\0';
+			value = scan;
+			break;
+		case '-':
+			name = scan + 1; value = git_attr__false; break;
+		case '+':
+			name = scan + 1; value = git_attr__true;  break;
+		case '!':
+			name = scan + 1; value = git_attr__unset; break;
+		default:
+			name = scan;     value = NULL; break;
+		}
+
+		fdef->attrs[i] = name;
+		fdef->attrs[i + fdef->nattrs] = value;
+
+		scan += strlen(scan) + 1;
+	}
+}
+
+int git_filter_register(
+	const char *name, git_filter *filter, int priority)
+{
+	git_filter_def *fdef;
+	size_t nattr = 0, nmatch = 0;
+	git_buf attrs = GIT_BUF_INIT;
+
+	if (git_filter_lookup(name) != NULL) {
+		giterr_set(
+			GITERR_FILTER, "Attempt to reregister existing filter '%s'", name);
+		return -1;
+	}
+
+	if (filter_def_scan_attrs(&attrs, &nattr, &nmatch, filter->attributes) < 0)
+		return -1;
+
+	fdef = git__calloc(
+		sizeof(git_filter_def) + 2 * nattr * sizeof(char *), 1);
+	GITERR_CHECK_ALLOC(fdef);
+
+	fdef->filter_name = name;
+	fdef->filter      = filter;
+	fdef->priority    = priority;
+	fdef->nattrs      = nattr;
+	fdef->nmatches    = nmatch;
+	fdef->attrdata    = git_buf_detach(&attrs);
+
+	filter_def_set_attrs(fdef);
+
+	if (git_vector_insert(&git__filter_registry, fdef) < 0) {
+		git__free(fdef->attrdata);
+		git__free(fdef);
+		return -1;
+	}
+
+	git_vector_sort(&git__filter_registry);
+	return 0;
+}
+
+static int filter_def_name_key_check(const void *key, const void *fdef)
+{
+	const char *name =
+		fdef ? ((const git_filter_def *)fdef)->filter_name : NULL;
+	return name ? -1 : git__strcmp(key, name);
+}
+
+static git_filter_def *filter_find_by_name(size_t *pos, const char *name)
+{
+	git_filter_def *fdef = NULL;
+
+	if (!git_vector_search2(
+			pos, &git__filter_registry, filter_def_name_key_check, name))
+		fdef = git_vector_get(&git__filter_registry, *pos);
+
+	return fdef;
+}
+
+int git_filter_unregister(const char *name)
+{
+	size_t pos;
+	git_filter_def *fdef;
+
+	/* cannot unregister default filters */
+	if (!strcmp(GIT_FILTER_CRLF, name)) {
+		giterr_set(GITERR_FILTER, "Cannot unregister filter '%s'", name);
+		return -1;
+	}
+
+	if ((fdef = filter_find_by_name(&pos, name)) == NULL) {
+		giterr_set(GITERR_FILTER, "Cannot find filter '%s' to unregister", name);
+		return GIT_ENOTFOUND;
+	}
+
+	(void)git_vector_remove(&git__filter_registry, pos);
+
+	if (fdef->filter->shutdown)
+		fdef->filter->shutdown(fdef->filter);
+
+	git__free(fdef->attrdata);
+	git__free(fdef);
+
+	return 0;
+}
+
+git_filter *git_filter_lookup(const char *name)
+{
+	size_t pos;
+	git_filter_def *fdef = filter_find_by_name(&pos, name);
+	return fdef ? fdef->filter : NULL;
+}
+
+static int filter_load_defaults(void)
+{
+	if (!git_vector_length(&git__filter_registry))
+		return git_filter_register(GIT_FILTER_CRLF, git_crlf_filter_new(), 0);
+
+	return 0;
+}
 
 git_repository *git_filter_source_repo(const git_filter_source *src)
 {
@@ -59,20 +238,6 @@ const git_oid *git_filter_source_id(const git_filter_source *src)
 	return git_oid_iszero(&src->oid) ? NULL : &src->oid;
 }
 
-static int filter_load_defaults(void)
-{
-	if (!git_array_size(filter_registry)) {
-		git_filter_def *fdef = git_array_alloc(filter_registry);
-		GITERR_CHECK_ALLOC(fdef);
-
-		fdef->filter_name = GIT_FILTER_CRLF;
-		fdef->filter = git_crlf_filter_new();
-		GITERR_CHECK_ALLOC(fdef->filter);
-	}
-
-	return 0;
-}
-
 static int git_filter_list_new(
 	git_filter_list **out, git_filter_mode_t mode, const git_filter_source *src)
 {
@@ -92,6 +257,47 @@ static int git_filter_list_new(
 	return 0;
 }
 
+static int filter_list_check_attributes(
+	const char ***out, git_filter_def *fdef, const git_filter_source *src)
+{
+	int error;
+	size_t i;
+	const char **strs = git__calloc(fdef->nattrs, sizeof(const char *));
+	GITERR_CHECK_ALLOC(strs);
+
+	error = git_attr_get_many(
+		strs, src->repo, 0, src->path, fdef->nattrs, fdef->attrs);
+
+	/* if no values were found but no matches are needed, it's okay! */
+	if (error == GIT_ENOTFOUND && !fdef->nmatches) {
+		giterr_clear();
+		git__free(strs);
+		return 0;
+	}
+
+	for (i = 0; !error && i < fdef->nattrs; ++i) {
+		const char *want = fdef->attrs[fdef->nattrs + i];
+		git_attr_t want_type, found_type;
+
+		if (!want)
+			continue;
+
+		want_type  = git_attr_value(want);
+		found_type = git_attr_value(strs[i]);
+
+		if (want_type != found_type ||
+			(want_type == GIT_ATTR_VALUE_T && strcmp(want, strs[i])))
+			error = GIT_ENOTFOUND;
+	}
+
+	if (error)
+		git__free(strs);
+	else
+		*out = strs;
+
+	return error;
+}
+
 int git_filter_list_load(
 	git_filter_list **filters,
 	git_repository *repo,
@@ -102,7 +308,8 @@ int git_filter_list_load(
 	git_filter_list *fl = NULL;
 	git_filter_source src = { 0 };
 	git_filter_entry *fe;
-	uint32_t f;
+	size_t idx;
+	git_filter_def *fdef;
 
 	if (filter_load_defaults() < 0)
 		return -1;
@@ -110,15 +317,27 @@ int git_filter_list_load(
 	src.repo = repo;
 	src.path = path;
 
-	for (f = 0; f < git_array_size(filter_registry); ++f) {
+	git_vector_foreach(&git__filter_registry, idx, fdef) {
+		const char **values = NULL;
 		void *payload = NULL;
-		git_filter_def *fdef = git_array_get(filter_registry, f);
 
 		if (!fdef || !fdef->filter)
 			continue;
 
+		if (fdef->nattrs > 0) {
+			error = filter_list_check_attributes(&values, fdef, &src);
+			if (error == GIT_ENOTFOUND) {
+				error = 0;
+				continue;
+			} else if (error < 0)
+				break;
+		}
+
 		if (fdef->filter->check)
-			error = fdef->filter->check(fdef->filter, &payload, mode, &src);
+			error = fdef->filter->check(
+				fdef->filter, &payload, mode, &src, values);
+
+		git__free(values);
 
 		if (error == GIT_ENOTFOUND)
 			error = 0;
@@ -171,6 +390,7 @@ int git_filter_list_apply(
 	uint32_t i;
 	unsigned int src;
 	git_buf *dbuffer[2];
+	git_filter_entry *fe;
 
 	if (!fl) {
 		git_buf_swap(dest, source);
@@ -188,11 +408,14 @@ int git_filter_list_apply(
 		return -1;
 
 	for (i = 0; i < git_array_size(fl->filters); ++i) {
-		git_filter_entry *fe = git_array_get(fl->filters, i);
 		unsigned int dst = 1 - src;
 
 		git_buf_clear(dbuffer[dst]);
 
+		fe = git_array_get(
+			fl->filters, (fl->mode == GIT_FILTER_TO_ODB) ?
+			i : git_array_size(fl->filters) - 1 - i);
+
 		/* Apply the filter from dbuffer[src] to the other buffer;
 		 * if the filtering is canceled by the user mid-filter,
 		 * we skip to the next filter without changing the source

tests-clar/attr/repo.c

@@ -100,6 +100,22 @@ void test_attr_repo__get_many(void)
 	cl_assert_equal_s("yes", values[3]);
 }
 
+void test_attr_repo__get_many_in_place(void)
+{
+	const char *vals[4] = { "repoattr", "rootattr", "missingattr", "subattr" };
+
+	/* it should be legal to look up values into the same array that has
+	 * the attribute names, overwriting each name as the value is found.
+	 */
+
+	cl_git_pass(git_attr_get_many(vals, g_repo, 0, "sub/subdir_test1", 4, vals));
+
+	cl_assert(GIT_ATTR_TRUE(vals[0]));
+	cl_assert(GIT_ATTR_TRUE(vals[1]));
+	cl_assert(GIT_ATTR_UNSPECIFIED(vals[2]));
+	cl_assert_equal_s("yes", vals[3]);
+}
+
 static int count_attrs(
 	const char *name,
 	const char *value,