[FL-2713] Buffered file streams fix (#1515)

* Fix incorrect buffered stream behaviour
* Add specific tests
* Make the test fail on wrong behaviour
* Better names

Co-authored-by: あく <alleteam@gmail.com>

2 files changed, 52 insertions, 3 deletions

diff --git a/applications/unit_tests/stream/stream_test.c b/applications/unit_tests/stream/stream_test.c
index 36155e33..b5a2d398 100644
--- a/applications/unit_tests/stream/stream_test.c
+++ b/applications/unit_tests/stream/stream_test.c
@@ -387,6 +387,34 @@ MU_TEST(stream_split_test) {
     furi_record_close(RECORD_STORAGE);
 }
 
+MU_TEST(stream_buffered_write_after_read_test) {
+    const char* prefix = "I write ";
+    const char* substr = "Hello there";
+
+    const size_t substr_len = strlen(substr);
+    const size_t prefix_len = strlen(prefix);
+    const size_t buf_size = substr_len + 1;
+
+    char buf[buf_size];
+    memset(buf, 0, buf_size);
+
+    Storage* storage = furi_record_open(RECORD_STORAGE);
+    Stream* stream = buffered_file_stream_alloc(storage);
+    mu_check(buffered_file_stream_open(
+        stream, EXT_PATH("filestream.str"), FSAM_READ_WRITE, FSOM_CREATE_ALWAYS));
+    mu_assert_int_eq(strlen(stream_test_data), stream_write_cstring(stream, stream_test_data));
+    mu_check(stream_rewind(stream));
+    mu_assert_int_eq(prefix_len, stream_read(stream, (uint8_t*)buf, prefix_len));
+    mu_assert_string_eq(prefix, buf);
+    mu_assert_int_eq(substr_len, stream_write(stream, (uint8_t*)substr, substr_len));
+    mu_check(stream_seek(stream, prefix_len, StreamOffsetFromStart));
+    mu_assert_int_eq(substr_len, stream_read(stream, (uint8_t*)buf, substr_len));
+    mu_assert_string_eq(substr, buf);
+
+    stream_free(stream);
+    furi_record_close(RECORD_STORAGE);
+}
+
 MU_TEST(stream_buffered_large_file_test) {
     string_t input_data;
     string_t output_data;
@@ -470,6 +498,7 @@ MU_TEST_SUITE(stream_suite) {
     MU_RUN_TEST(stream_write_read_save_load_test);
     MU_RUN_TEST(stream_composite_test);
     MU_RUN_TEST(stream_split_test);
+    MU_RUN_TEST(stream_buffered_write_after_read_test);
     MU_RUN_TEST(stream_buffered_large_file_test);
 }
 
diff --git a/lib/toolbox/stream/buffered_file_stream.c b/lib/toolbox/stream/buffered_file_stream.c
index 5db276d3..2f2359a0 100644
--- a/lib/toolbox/stream/buffered_file_stream.c
+++ b/lib/toolbox/stream/buffered_file_stream.c
@@ -1,5 +1,6 @@
 #include "buffered_file_stream.h"
 
+#include "core/check.h"
 #include "stream_i.h"
 #include "file_stream.h"
 #include "stream_cache.h"
@@ -38,6 +39,8 @@ const StreamVTable buffered_file_stream_vtable = {
     .delete_and_insert = (StreamDeleteAndInsertFn)buffered_file_stream_delete_and_insert,
 };
 
+static bool buffered_file_stream_unread(BufferedFileStream* stream);
+
 Stream* buffered_file_stream_alloc(Storage* storage) {
     BufferedFileStream* stream = malloc(sizeof(BufferedFileStream));
 
@@ -125,8 +128,12 @@ static size_t buffered_file_stream_size(BufferedFileStream* stream) {
 
 static size_t
     buffered_file_stream_write(BufferedFileStream* stream, const uint8_t* data, size_t size) {
-    stream_cache_drop(stream->cache);
-    return stream_write(stream->file_stream, data, size);
+    size_t need_to_write = size;
+    do {
+        if(!buffered_file_stream_unread(stream)) break;
+        need_to_write -= stream_write(stream->file_stream, data, size);
+    } while(false);
+    return size - need_to_write;
 }
 
 static size_t buffered_file_stream_read(BufferedFileStream* stream, uint8_t* data, size_t size) {
@@ -150,6 +157,19 @@ static bool buffered_file_stream_delete_and_insert(
     size_t delete_size,
     StreamWriteCB write_callback,
     const void* ctx) {
+    return buffered_file_stream_unread(stream) &&
+           stream_delete_and_insert(stream->file_stream, delete_size, write_callback, ctx);
+}
+
+// Drop read cache and adjust the underlying stream seek position
+static bool buffered_file_stream_unread(BufferedFileStream* stream) {
+    bool success = true;
+    const size_t cache_size = stream_cache_size(stream->cache);
+    const size_t cache_pos = stream_cache_pos(stream->cache);
+    if(cache_pos < cache_size) {
+        const int32_t offset = cache_size - cache_pos;
+        success = stream_seek(stream->file_stream, -offset, StreamOffsetFromCurrent);
+    }
     stream_cache_drop(stream->cache);
-    return stream_delete_and_insert(stream->file_stream, delete_size, write_callback, ctx);
+    return success;
 }