reftable: check for trailing newline in 'tables.list'

In the reftable format, the 'tables.list' file contains a
newline separated list of tables. While we parse this file, we do not
check or care about the last newline. Tighten the parser in
`parse_names()` to return an appropriate error if the last newline is
missing.

This requires modification to `parse_names()` to now return the error
while accepting the output as a third argument.

Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: KarthikNayak

reftable/basics.c

@@ -195,44 +195,55 @@ size_t names_length(const char **names)
 	return p - names;
 }
 
-char **parse_names(char *buf, int size)
+int parse_names(char *buf, int size, char ***out)
 {
 	char **names = NULL;
 	size_t names_cap = 0;
 	size_t names_len = 0;
 	char *p = buf;
 	char *end = buf + size;
+	int err = 0;
 
 	while (p < end) {
 		char *next = strchr(p, '\n');
-		if (next && next < end) {
-			*next = 0;
+		if (!next) {
+			err = REFTABLE_FORMAT_ERROR;
+			goto done;
+		} else if (next < end) {
+			*next = '\0';
 		} else {
 			next = end;
 		}
+
 		if (p < next) {
 			if (REFTABLE_ALLOC_GROW(names, names_len + 1,
-						names_cap))
-				goto err;
+						names_cap)) {
+				err = REFTABLE_OUT_OF_MEMORY_ERROR;
+				goto done;
+			}
 
 			names[names_len] = reftable_strdup(p);
-			if (!names[names_len++])
-				goto err;
+			if (!names[names_len++]) {
+				err = REFTABLE_OUT_OF_MEMORY_ERROR;
+				goto done;
+			}
 		}
 		p = next + 1;
 	}
 
-	if (REFTABLE_ALLOC_GROW(names, names_len + 1, names_cap))
-		goto err;
+	if (REFTABLE_ALLOC_GROW(names, names_len + 1, names_cap)) {
+		err = REFTABLE_OUT_OF_MEMORY_ERROR;
+		goto done;
+	}
 	names[names_len] = NULL;
 
-	return names;
-
-err:
+	*out = names;
+	return 0;
+done:
 	for (size_t i = 0; i < names_len; i++)
 		reftable_free(names[i]);
 	reftable_free(names);
-	return NULL;
+	return err;
 }
 
 int names_equal(const char **a, const char **b)

reftable/basics.h

@@ -167,10 +167,11 @@ void free_names(char **a);
 
 /*
  * Parse a newline separated list of names. `size` is the length of the buffer,
- * without terminating '\0'. Empty names are discarded. Returns a `NULL`
- * pointer when allocations fail.
+ * without terminating '\0'. Empty names are discarded.
+ *
+ * Returns 0 on success, a reftable error code on error.
  */
-char **parse_names(char *buf, int size);
+int parse_names(char *buf, int size, char ***out);
 
 /* compares two NULL-terminated arrays of strings. */
 int names_equal(const char **a, const char **b);

reftable/stack.c

@@ -169,12 +169,7 @@ static int fd_read_lines(int fd, char ***namesp)
 	}
 	buf[size] = 0;
 
-	*namesp = parse_names(buf, size);
-	if (!*namesp) {
-		err = REFTABLE_OUT_OF_MEMORY_ERROR;
-		goto done;
-	}
-
+	err = parse_names(buf, size, namesp);
 done:
 	reftable_free(buf);
 	return err;

t/unit-tests/u-reftable-basics.c

@@ -9,6 +9,7 @@ license that can be found in the LICENSE file or at
 #include "unit-test.h"
 #include "lib-reftable.h"
 #include "reftable/basics.h"
+#include "reftable/reftable-error.h"
 
 struct integer_needle_lesseq_args {
 	int needle;
@@ -79,14 +80,18 @@ void test_reftable_basics__names_equal(void)
 void test_reftable_basics__parse_names(void)
 {
 	char in1[] = "line\n";
-	char in2[] = "a\nb\nc";
-	char **out = parse_names(in1, strlen(in1));
+	char in2[] = "a\nb\nc\n";
+	char **out = NULL;
+	int err = parse_names(in1, strlen(in1), &out);
+	cl_assert(err == 0);
 	cl_assert(out != NULL);
 	cl_assert_equal_s(out[0], "line");
 	cl_assert(!out[1]);
 	free_names(out);
 
-	out = parse_names(in2, strlen(in2));
+	out = NULL;
+	err = parse_names(in2, strlen(in2), &out);
+	cl_assert(err == 0);
 	cl_assert(out != NULL);
 	cl_assert_equal_s(out[0], "a");
 	cl_assert_equal_s(out[1], "b");
@@ -95,10 +100,21 @@ void test_reftable_basics__parse_names(void)
 	free_names(out);
 }
 
+void test_reftable_basics__parse_names_missing_newline(void)
+{
+	char in1[] = "line\nline2";
+	char **out = NULL;
+	int err = parse_names(in1, strlen(in1), &out);
+	cl_assert(err == REFTABLE_FORMAT_ERROR);
+	cl_assert(out == NULL);
+}
+
 void test_reftable_basics__parse_names_drop_empty_string(void)
 {
 	char in[] = "a\n\nb\n";
-	char **out = parse_names(in, strlen(in));
+	char **out = NULL;
+	int err = parse_names(in, strlen(in), &out);
+	cl_assert(err == 0);
 	cl_assert(out != NULL);
 	cl_assert_equal_s(out[0], "a");
 	/* simply '\n' should be dropped as empty string */