rem/aufile: test and fix aufile_set_position nread (#1010)

Also fix a bug: wav files can contain data after the data chunk. If we don't update nread in aufile_set_position, we can read invalid data.

rem/aufile/aufile.c

@@ -294,8 +294,12 @@ int aufile_set_position(struct aufile *af, const struct aufile_prm *prm,
 	off_t pos = (off_t)(prm->srate * aufmt_sample_size(prm->fmt)
 		* prm->channels * pos_ms / 1000);
 
+	pos = min((off_t)datasize, pos);
+
 	if (fseek(af->f, pos, SEEK_CUR) < 0)
 		return errno;
 
+	af->nread = pos;
+
 	return 0;
 }

test/CMakeLists.txt

@@ -72,6 +72,7 @@ set(SRCS
   aubuf.c
   aulength.c
   aulevel.c
+  aupos.c
   auresamp.c
   av1.c
   base64.c

test/aupos.c

@@ -0,0 +1,61 @@
+/**
+ * @file src/aupos.c audio file setposition test
+ *
+ * Copyright (C) 2023 Lars Immisch
+ */
+
+#include <re.h>
+#include <rem.h>
+#include "test.h"
+
+
+#define DEBUG_MODULE "auposition"
+#define DEBUG_LEVEL 5
+#include <re_dbg.h>
+
+
+int test_auposition(void)
+{
+	struct aufile *af = NULL;
+	struct aufile_prm prm;
+	char path[256];
+	uint8_t buffer[512];
+
+	re_snprintf(path, sizeof(path), "%s/beep.wav", test_datapath());
+
+	int err = aufile_open(&af, &prm, path, AUFILE_READ);
+	TEST_ERR(err);
+
+	err = aufile_set_position(af, &prm, 67);
+	TEST_ERR(err);
+
+	/* That file is exactly 67 ms long, so we shouldn't read anything */
+	size_t size = sizeof(buffer);
+	err = aufile_read(af, buffer, &size);
+	TEST_ERR(err);
+
+	/* It's possible we read data up to a ms */
+	TEST_ASSERT(size < 16);
+
+	af = mem_deref(af);
+
+	err = aufile_open(&af, &prm, path, AUFILE_READ);
+	TEST_ERR(err);
+
+	err = aufile_set_position(af, &prm, 37);
+	TEST_ERR(err);
+
+	size = sizeof(buffer);
+	err = aufile_read(af, buffer, &size);
+	TEST_ERR(err);
+
+	/* 30 ms should be left, at 8000Hz/s, one channels and 16 bit samples
+	   that's 480 bytes */
+	TEST_ASSERT(size - 480 < 16);
+
+
+out:
+	mem_deref(af);
+
+	return err;
+}

test/test.c

@@ -55,6 +55,7 @@ static const struct test tests[] = {
 	TEST(test_aubuf),
 	TEST(test_aulength),
 	TEST(test_aulevel),
+	TEST(test_auposition),
 	TEST(test_auresamp),
 	TEST(test_async),
 	TEST(test_av1),

test/test.h

@@ -160,6 +160,7 @@ int test_aes_gcm(void);
 int test_aubuf(void);
 int test_aulevel(void);
 int test_aulength(void);
+int test_auposition(void);
 int test_auresamp(void);
 int test_async(void);
 int test_av1(void);