thodg/libgit2

diff --git a/src/refs.c b/src/refs.c
index e71d8c6..693870a 100644
--- a/src/refs.c
+++ b/src/refs.c
@@ -1952,11 +1952,18 @@ cleanup:
 	return error;
 }
 
+int git_reference__is_valid_name(
+	const char *refname,
+	unsigned int flags)
+{
+	giterr_clear();
+	return git_reference__normalize_name(NULL, refname, flags) == 0;
+}
+
 int git_reference_is_valid_name(
 	const char *refname)
 {
-	return git_reference__normalize_name(
-		NULL,
+	return git_reference__is_valid_name(
 		refname,
-		GIT_REF_FORMAT_ALLOW_ONELEVEL) == 0;
+		GIT_REF_FORMAT_ALLOW_ONELEVEL);
 }
diff --git a/src/refs.h b/src/refs.h
index 0105034..54359f0 100644
--- a/src/refs.h
+++ b/src/refs.h
@@ -55,6 +55,7 @@ void git_repository__refcache_free(git_refcache *refs);
 
 int git_reference__normalize_name_lax(char *buffer_out, size_t out_size, const char *name);
 int git_reference__normalize_name(git_buf *buf, const char *name, unsigned int flags);
+int git_reference__is_valid_name(const char *refname, unsigned int flags);
 int git_reference__update(git_repository *repo, const git_oid *oid, const char *ref_name);
 
 /**
diff --git a/src/refspec.c b/src/refspec.c
index b6b1158..1265c56 100644
--- a/src/refspec.c
+++ b/src/refspec.c
@@ -11,6 +11,119 @@
 #include "refspec.h"
 #include "util.h"
 #include "posix.h"
+#include "refs.h"
+
+int git_refspec__parse(git_refspec *refspec, const char *input, bool is_fetch)
+{
+	// Ported from https://github.com/git/git/blob/f06d47e7e0d9db709ee204ed13a8a7486149f494/remote.c#L518-636
+
+	size_t llen;
+	int is_glob = 0;
+	const char *lhs, *rhs;
+	int flags;
+
+	assert(refspec && input);
+
+	memset(refspec, 0x0, sizeof(git_refspec));
+
+	lhs = input;
+	if (*lhs == '+') {
+		refspec->force = 1;
+		lhs++;
+	}
+
+	rhs = strrchr(lhs, ':');
+
+	/*
+	 * Before going on, special case ":" (or "+:") as a refspec
+	 * for matching refs.
+	 */
+	if (!is_fetch && rhs == lhs && rhs[1] == '\0') {
+		refspec->matching = 1;
+		return 0;
+	}
+
+	if (rhs) {
+		size_t rlen = strlen(++rhs);
+		is_glob = (1 <= rlen && strchr(rhs, '*'));
+		refspec->dst = git__strndup(rhs, rlen);
+	}
+
+	llen = (rhs ? (size_t)(rhs - lhs - 1) : strlen(lhs));
+	if (1 <= llen && memchr(lhs, '*', llen)) {
+		if ((rhs && !is_glob) || (!rhs && is_fetch))
+			goto invalid;
+		is_glob = 1;
+	} else if (rhs && is_glob)
+		goto invalid;
+
+	refspec->pattern = is_glob;
+	refspec->src = git__strndup(lhs, llen);
+	flags = GIT_REF_FORMAT_ALLOW_ONELEVEL
+		| (is_glob ? GIT_REF_FORMAT_REFSPEC_PATTERN : 0);
+
+	if (is_fetch) {
+		/*
+			* LHS
+			* - empty is allowed; it means HEAD.
+			* - otherwise it must be a valid looking ref.
+			*/
+		if (!*refspec->src)
+			; /* empty is ok */
+		else if (!git_reference__is_valid_name(refspec->src, flags))
+			goto invalid;
+		/*
+			* RHS
+			* - missing is ok, and is same as empty.
+			* - empty is ok; it means not to store.
+			* - otherwise it must be a valid looking ref.
+			*/
+		if (!refspec->dst)
+			; /* ok */
+		else if (!*refspec->dst)
+			; /* ok */
+		else if (!git_reference__is_valid_name(refspec->dst, flags))
+			goto invalid;
+	} else {
+		/*
+			* LHS
+			* - empty is allowed; it means delete.
+			* - when wildcarded, it must be a valid looking ref.
+			* - otherwise, it must be an extended SHA-1, but
+			*   there is no existing way to validate this.
+			*/
+		if (!*refspec->src)
+			; /* empty is ok */
+		else if (is_glob) {
+			if (!git_reference__is_valid_name(refspec->src, flags))
+				goto invalid;
+		}
+		else {
+			; /* anything goes, for now */
+		}
+		/*
+			* RHS
+			* - missing is allowed, but LHS then must be a
+			*   valid looking ref.
+			* - empty is not allowed.
+			* - otherwise it must be a valid looking ref.
+			*/
+		if (!refspec->dst) {
+			if (!git_reference__is_valid_name(refspec->src, flags))
+				goto invalid;
+		} else if (!*refspec->dst) {
+			goto invalid;
+		} else {
+			if (!git_reference__is_valid_name(refspec->dst, flags))
+				goto invalid;
+		}
+	}
+
+	return 0;
+
+ invalid:
+	return -1;
+}
 
 int git_refspec_parse(git_refspec *refspec, const char *str)
 {
diff --git a/src/refspec.h b/src/refspec.h
index 2db5049..2f46b3e 100644
--- a/src/refspec.h
+++ b/src/refspec.h
@@ -20,6 +20,10 @@ struct git_refspec {
 };
 
 int git_refspec_parse(struct git_refspec *refspec, const char *str);
+int git_refspec__parse(
+	struct git_refspec *refspec,
+	const char *str,
+	bool is_fetch);
 
 /**
  * Transform a reference to its target following the refspec's rules,
diff --git a/tests-clar/network/refspecs.c b/tests-clar/network/refspecs.c
new file mode 100644
index 0000000..bfe0af4
--- /dev/null
+++ b/tests-clar/network/refspecs.c
@@ -0,0 +1,83 @@
+#include "clar_libgit2.h"
+#include "refspec.h"
+#include "remote.h"
+
+static void assert_refspec(unsigned int direction, const char *input, bool is_expected_to_be_valid)
+{
+	git_refspec refspec;
+	int error;
+
+	error = git_refspec__parse(&refspec, input, direction == GIT_DIR_FETCH);
+
+	if (is_expected_to_be_valid)
+		cl_assert_equal_i(0, error);
+	else
+		cl_assert_equal_i(GIT_ERROR, error);
+}
+
+void test_network_refspecs__parsing(void)
+{
+	// Ported from https://github.com/git/git/blob/abd2bde78bd994166900290434a2048e660dabed/t/t5511-refspec.sh
+
+	assert_refspec(GIT_DIR_PUSH, "", false);
+	assert_refspec(GIT_DIR_PUSH, ":", true);
+	assert_refspec(GIT_DIR_PUSH, "::", false);
+	assert_refspec(GIT_DIR_PUSH, "+:", true);
+
+	assert_refspec(GIT_DIR_FETCH, "", true);
+	assert_refspec(GIT_DIR_PUSH, ":", true);
+	assert_refspec(GIT_DIR_FETCH, "::", false);
+
+	assert_refspec(GIT_DIR_PUSH, "refs/heads/*:refs/remotes/frotz/*", true);
+	assert_refspec(GIT_DIR_PUSH, "refs/heads/*:refs/remotes/frotz", false);
+	assert_refspec(GIT_DIR_PUSH, "refs/heads:refs/remotes/frotz/*", false);
+	assert_refspec(GIT_DIR_PUSH, "refs/heads/master:refs/remotes/frotz/xyzzy", true);
+
+	/*
+	 * These have invalid LHS, but we do not have a formal "valid sha-1
+	 * expression syntax checker" so they are not checked with the current
+	 * code.  They will be caught downstream anyway, but we may want to
+	 * have tighter check later...
+	 */
+	//assert_refspec(GIT_DIR_PUSH, "refs/heads/master::refs/remotes/frotz/xyzzy", false);
+	//assert_refspec(GIT_DIR_PUSH, "refs/heads/maste :refs/remotes/frotz/xyzzy", false);
+
+	assert_refspec(GIT_DIR_FETCH, "refs/heads/*:refs/remotes/frotz/*", true);
+	assert_refspec(GIT_DIR_FETCH, "refs/heads/*:refs/remotes/frotz", false);
+	assert_refspec(GIT_DIR_FETCH, "refs/heads:refs/remotes/frotz/*", false);
+	assert_refspec(GIT_DIR_FETCH, "refs/heads/master:refs/remotes/frotz/xyzzy", true);
+	assert_refspec(GIT_DIR_FETCH, "refs/heads/master::refs/remotes/frotz/xyzzy", false);
+	assert_refspec(GIT_DIR_FETCH, "refs/heads/maste :refs/remotes/frotz/xyzzy", false);
+
+	assert_refspec(GIT_DIR_PUSH, "master~1:refs/remotes/frotz/backup", true);
+	assert_refspec(GIT_DIR_FETCH, "master~1:refs/remotes/frotz/backup", false);
+	assert_refspec(GIT_DIR_PUSH, "HEAD~4:refs/remotes/frotz/new", true);
+	assert_refspec(GIT_DIR_FETCH, "HEAD~4:refs/remotes/frotz/new", false);
+
+	assert_refspec(GIT_DIR_PUSH, "HEAD", true);
+	assert_refspec(GIT_DIR_FETCH, "HEAD", true);
+	assert_refspec(GIT_DIR_PUSH, "refs/heads/ nitfol", false);
+	assert_refspec(GIT_DIR_FETCH, "refs/heads/ nitfol", false);
+
+	assert_refspec(GIT_DIR_PUSH, "HEAD:", false);
+	assert_refspec(GIT_DIR_FETCH, "HEAD:", true);
+	assert_refspec(GIT_DIR_PUSH, "refs/heads/ nitfol:", false);
+	assert_refspec(GIT_DIR_FETCH, "refs/heads/ nitfol:", false);
+
+	assert_refspec(GIT_DIR_PUSH, ":refs/remotes/frotz/deleteme", true);
+	assert_refspec(GIT_DIR_FETCH, ":refs/remotes/frotz/HEAD-to-me", true);
+	assert_refspec(GIT_DIR_PUSH, ":refs/remotes/frotz/delete me", false);
+	assert_refspec(GIT_DIR_FETCH, ":refs/remotes/frotz/HEAD to me", false);
+
+	assert_refspec(GIT_DIR_FETCH, "refs/heads/*/for-linus:refs/remotes/mine/*-blah", false);
+	assert_refspec(GIT_DIR_PUSH, "refs/heads/*/for-linus:refs/remotes/mine/*-blah", false);
+
+	assert_refspec(GIT_DIR_FETCH, "refs/heads*/for-linus:refs/remotes/mine/*", false);
+	assert_refspec(GIT_DIR_PUSH, "refs/heads*/for-linus:refs/remotes/mine/*", false);
+
+	assert_refspec(GIT_DIR_FETCH, "refs/heads/*/*/for-linus:refs/remotes/mine/*", false);
+	assert_refspec(GIT_DIR_PUSH, "refs/heads/*/*/for-linus:refs/remotes/mine/*", false);
+
+	assert_refspec(GIT_DIR_FETCH, "refs/heads/*/for-linus:refs/remotes/mine/*", true);
+	assert_refspec(GIT_DIR_PUSH, "refs/heads/*/for-linus:refs/remotes/mine/*", true);
+}