✨Add list_files function #615 #615

Gracelu128 · 2023-10-27T20:16:00Z

Summary:

Adds functionality to list the files on a sd card.

Motivation:

Made wrapper function for the CPP api that returns a vector of strings of file names. Renamed original function as list_files_raw in both CPP api and C api.

Test Plan:

Get vector of file names in the default directory
Get vector of file names in a sub directory
Test invalid directory

…tring of file names Will return a vector of std::strings of file names, will return a vector containing one std::string PROS_ERR if error occurs.

…c API as well to raw

Function to return vector containing specific error state errno is set to, if none of the error states will set to FILE I/O error

djava · 2023-10-27T21:14:13Z

include/pros/misc.hpp

+ * // Given vector of std::string file names, print each file name
+ * // Note that if there is an error, the vector will contain one element, PROS_ERR
+ * // Print each file name
+ * for (std::string file : files) {


for (std::string& file : files) {

That & is very important for performance reasons.

Implemented this suggestion in commit on Oct 30, 3d41ca6

djava · 2023-10-27T21:15:37Z

include/pros/misc.hpp

+ * // Print each file name
+ * for (std::string file : files) {
+ * std::cout << file << std::endl;
+ * }
 * }
 * \endcode
 */


Surely the docs should explain the params as well?

Added param in header for funcs in commit 3d41ca6 and 4247fb1

djava · 2023-10-27T21:18:05Z

src/devices/vdml_usd.cpp

+ return usd_list_files_raw(path, buffer, len);
+}
+
+std::vector<std::string> list_files(const char* path, char* buffer, int32_t len) {


This function should definitely not require users to pass in their own buffer and len. You should just allocate a buffer yourself at the top of this function body then free it after it's done being used.

Implemented this change in commit 4247fb1

Looks good, can I ask if the number 10000 came from somewhere or was it chosen arbitrarily?

Came from an estimate of the worst case that is realistic to happen. We needed to chose a number, and decided that 100 files in a single directory with an approximate average length of 100 (really 99 if you include the separators) will be enough for every feasible use case we could come up with.

Ok, fair enough. If you're choosing a number, a power of 2 (or sum of powers of 2) might be nice for memory allocator friendliness :)

(I have no idea what allocation strategy VexOS uses, this may be completely irrelevant)

djava · 2023-10-27T21:19:23Z

src/devices/vdml_usd.cpp

+ // Store char * buffer as std::string in str
+ // Store delimiter in std::string, '\n'
+ std::string str(buffer);
+ std::string delimiter = "\n";


char delimeter = '\n';

You definitely don't need a whole std::string for just \n, which is only a single char.

Implemented this change in commit 3d41ca6

djava · 2023-10-27T21:20:16Z

src/devices/vdml_usd.cpp

+ // Parse buffer given call successful, split by '/n'
+ // Store char * buffer as std::string in str
+ // Store delimiter in std::string, '\n'
+ std::string str(buffer);


There's no reason to allocate a whole additional std::string for this, use std::string_view over the already-existing buffer instead. You can still use .find() the same way.

Implemented this change in commit 3d41ca6.

djava · 2023-10-27T21:22:23Z

src/devices/vdml_usd.cpp

+ // file_name is the string from the beginning of str to the first '\n', excluding '\n'
+ file_name = str.substr(0, position);
+ // Add token to files vector
+ files.push_back(file_name);


You should move file_name into the vector instead of copying it. This will reuse the already allocated heap buffer instead of copying over a new one, resulting in each file name being copied once instead of twice or more.

files.emplace_back(std::move(file_name));

Alternatively, file_name could be a std::string_view that you emplace_back. Since files::value_type is std::string, that will result in the file name being copied (for the first time). Actually I think I like this solution better than the move anyway.

Implemented this change in commit 3d41ca6. Made file_name a std::string_view.

djava · 2023-10-27T21:27:02Z

src/devices/vdml_usd.cpp

+ // Add token to files vector
+ files.push_back(file_name);
+ // Erase file_name from str, would be pos + 1 if we wanted to include '\n'
+ str.erase(0, position + 1);


This won't work if you use a std::string_view for str (and it's very unnecessarily slow even as a std::string). You should either keep track of the index to start at for the next iteration, or maybe str = str.substr(...)?

Implemented this change in commit 3d41ca6. Altered code to instead have index to keep track of start for next iteration.

Very nice! Thanks

djava · 2023-10-27T21:29:41Z

src/devices/vdml_usd.cpp

+ // Check if call successful, if error return vector containing error state
+ if (success == PROS_ERR) {
+ // Check errno to see which error state occurred
+ // push back error state to files vector as std::string


mmm I'm definitely not convinced that this error handling strategy is a good approach. Maybe an out-param for the vector is better so you have some other way to return errors? That's more inline with how pros usually does things anyway. (returning errors via return type)

Either file i/o error or path not found

djava · 2023-11-03T02:16:08Z

@Gracelu128 it would be helpful if, when you make changes to address review comments I've made, you could respond to the review comment to let me know (maybe with the commit hash that you addressed it in as well). Would you be able to go through and do that here so it's easier to dig through this pile of commits?

Thanks!

djava · 2023-11-03T06:21:36Z

src/devices/vdml_usd.cpp

+ char *buffer = (char *) malloc(10000);
 // Call the C function
- int32_t success = usd_list_files_raw(path, buffer, len);
+ int32_t success = usd_list_files_raw(path, buffer, 10000);


Could you have a constexpr size_t buffer_size = 10000; to reuse between these two instances?

djava · 2023-11-03T06:23:31Z

src/devices/vdml_usd.cpp

- // Erase file_name from str, would be pos + 1 if we wanted to include '\n'
- str.erase(0, position + 1);
- }
+ files.emplace_back(file_name);


Since it happens via an implicit conversion, it would be nice to have a comment here noting that this is the point where the string containing the file name is copied into its own std::string, since everything before this was just std::string_views over the pre-existing buffer.

djava · 2023-11-03T06:26:15Z

src/devices/vdml_usd.cpp

 // file_name used to store each file name
- size_t position = 0;
- std::string file_name;
+ size_t delimiter_pos, index = 0;


C++ footgun alert!! index is initialized to 0 here, but delimiter_pos is left uninitialized (and therefore in an unspecified state). Admittedly, it doesn't matter here since the first use is an assignment, but I generally advise to avoid multiple declaration and always initialize primitive types to avoid even the potential of such mistakes causes issues, since those can be very hard to track down later.

djava · 2023-11-03T06:27:02Z

src/devices/vdml_usd.cpp

+ // Add token to files vector
+ files.push_back(file_name);
+ // Erase file_name from str, would be pos + 1 if we wanted to include '\n'
+ str.erase(0, position + 1);


Very nice! Thanks

djava · 2023-11-03T06:31:16Z

src/devices/vdml_usd.cpp

@@ -29,6 +29,15 @@ std::vector<std::string> list_files(const char* path) {
 std::vector<std::string> files = {};
 // malloc buffer to store file names
 char *buffer = (char *) malloc(10000);
+ if (buffer == NULL) {
+ // try again smaller buffer to see if that works
+ buffer = (char *) malloc(500);


Keeping a buffer_size variable is even more pertinent with this addition, wouldn't want to put 10000 entries into a buffer of size 500! It can't be constexpr anymore now though, so ignore that part of the above comment.

djava · 2023-11-03T06:35:34Z

Looks a lot better, thanks for the changes! Most of what's left is small or stylistic.

djava · 2023-11-03T06:47:57Z

Just a thought - right now there's no standard prefix to the error messages, so there's not really a clean way to programmatically check if the function errored. Perhaps they can all start with "ERROR - " or similar, so that one can at least write something like this to check for errors?

auto file_list = pros::usd::list_files("/");
if (file_list.front().starts_with("ERROR")) {
    // do error stuff
} else {
    // We know file_list is valid now
}

I'm not sure how you'd do this as is. errno isn't reliable, since it could have been set by a previous function call, and theres no return code from this function that tells us succinctly that we have to check errno, right?

Gosh, thank god for C++20 adding std::string::starts_with. Not sure what the clean way to do this otherwise would be.

Gracelu128 · 2023-11-04T20:45:41Z

Looks a lot better, thanks for the changes! Most of what's left is small or stylistic.

I just implemented your suggested stylistic changes in the new commit 490a3ca.

djava · 2023-11-05T04:16:33Z

src/devices/vdml_usd.cpp

+ std::vector<std::string> files = {};
+ // malloc buffer to store file names
+ size_t buffer_size = 10000;
+ char *buffer = (char *) malloc(buffer_size);


You should use the C++ new char[buffer_size];instead of C's malloc (and later deleteinstead of `free).

It's a bit less scary type-wise and very widely considered better stylistically for C++.

Actually even better would be std::unique_ptr<char[]> buffer = std::make_shared<char[]>(buffer_size)and then passing buffer.get() to the C function. Then the deletehappens automatically when you exit the function scope.

Altered to return the file path instead of file names. Ex. "/usd/path/file_name".

WillXuCodes

this review might be slightly outdated... please ignore any outdated comments I just forgot to hit submit 💀

WillXuCodes · 2023-10-30T03:00:40Z

src/devices/vdml_usd.c

+ EEXIST, EINVAL, EROFS, ENXIO, ENOBUFS, ENXIO, EIO, EACCES, // FR_LOCKED
+ ENOBUFS, ENFILE, EINVAL};
+
+int32_t usd_list_files_raw(const char* path, char* buffer, int32_t len) {


this might be handled by vexFileDirectoryGet already, but can we add nullchecks for these parameters?

WillXuCodes · 2023-10-30T03:00:59Z

src/devices/vdml_usd.cpp

+ return usd_list_files_raw(path, buffer, len);
+}
+
+std::vector<std::string> list_files(const char* path, char* buffer, int32_t len) {


use a std::string instead of a c_string pls.

std::string_view actually

WillXuCodes · 2023-10-30T03:01:31Z

src/devices/vdml_usd.cpp

@@ -21,5 +21,80 @@ std::int32_t is_installed(void) {
 return usd_is_installed();
 }

+std::int32_t list_files_raw(const char* path, char* buffer, int32_t len) {


for our C++ API please use std::string and .c_str to call the internal C funcs.

make sure all of the std::strings are also references pls*

std::string_view

std::string_view

I understand that's more C++onic but for the sake of our users I think a std::string would be a little more approachable... saves everyone a google search.

😖 wasted allocation for every call with a string literal for path, which I assume is the typical case.

make sure all of the std::strings are also references pls*

If you choose to use std::string instead of string_view do make sure its const refs, as mutable refs will cause other issues (won't accept temporaries i.e. string literals that convert to std::string)

WillXuCodes · 2023-11-10T07:36:56Z

src/devices/vdml_usd.cpp

+ std::string_view file_name;
+
+ // Loop until delimiter '\n' can not be found anymore
+ while ((delimiter_pos = str.find('\n', index)) != std::string::npos) {


If we really wanted to optimize this even more you could write a sentinel function (or whatever people call it I'm tired atm) that grabs all the delimter indexes, and then another loop that stores all the delimter positions in a data structure such as a vector, and then another loop that iterates through the data structure. This changes the O(N * M) behavior of this to O(N + M) where N is the size of the string and M is the number of delimeters.

I'm not sure where you got O(N*M). If I'm reading correctly, you're seeing it as a full loop through all N characters each time we loop? That's not true, though, as index changes where the iteration starts each time (starting further along the string on each iteration), and each iteration stops as soon as it locates '\n'. Therefore, this is only O(N).

I'm not sure where you got O(N*M). If I'm reading correctly, you're seeing it as a full loop through all N characters each time we loop? That's not true, though, as index changes where the iteration starts each time (starting further along the string on each iteration), and each iteration stops as soon as it locates '\n'. Therefore, this is only O(N).

ah you're right, I didn't notice the index parameter last night.

djava · 2023-11-10T08:02:18Z

src/devices/vdml_usd.cpp

+ std::string_view path_sv(path);
+ size_t found = path_sv.find("usd");
+ if (found == 0 || found == 1) {
+ // Deal with when user prepends path with usd
+ // as either "usd/..." or "/usd/..."
+ path_sv.remove_prefix(3);
+ }


How does hardcoding the 3 here deal with both cases? Wouldn't it be 3 + found?

Also to avoid the magic-number-ness of this 3, I'd probably write this as:

constexpr std::string_view usd_prefix {"usd"}; std::string_view path_sv {path}; const size_t usd_prefix_idx = path_sv.find(usd_prefix); if (usd_prefix_idx == 0 || usd_prefix_idx == 1) { path_sv.remove_prefix(usd_prefix.length() + usd_prefix_idx); }

Also what happens here if they don't include the usd prefix? We just make it work the same as if they did? May be weird, since we also always return paths prefixed with /usd/.

My preference here would be to return a "path not found" error, as just assuming they wanted an implicit /usd/ makes doing anything with a VFS outside of /usd/ in the future into a backwards compatibility break. It also improves consistency, since nothing else in PROS would accept that path.

djava · 2023-11-10T08:03:53Z

src/devices/vdml_usd.cpp

+ }
+
+ // set path to path_sv.data()
+ path = path_sv.data();


path_sv is already pointing to *path. It's a read-only "view" over a string that exists elsewhere in memory, hence the name.

djava · 2023-11-10T08:40:02Z

src/devices/vdml_usd.cpp

@@ -76,7 +89,7 @@ std::vector<std::string> list_files(const char* path) {
 file_name = std::string_view(str.data() + index, delimiter_pos - index);
 // This is point where content of the std::string_view file name is copied to its
 // own std::string and added to the files vector
- files.emplace_back(file_name);
+ files.emplace_back("/usd" + std::string(path) + "/" + std::string(file_name));


You can't do it like this, this creates 7 different std::strings (each of which "may" allocate and pretty likely at least 2 will, wasting a lot of performance).
I don't believe the version of libstdc++ (the standard library) PROS uses supports std::format but if so you could write the very nice:

files.emplace_back(std::format("/{}/{}", path, file_name));

if not i would recommend something more like

const size_t path_size = 1 + usd_prefix.length() + path.length() + 1 + file_name.length(); // +1's for the slashes std::string buf; buf.reserve(path_size); // Reserve enough space in the internal array that we can snprintf right into it // The %.*s format specifier allows passing the size of a format arg before the value of the arg, so it lets // us use the string_view into `str` with the C-style snprintf function even though it does not have the // null terminator that would usually be required to know when a string ends. // We also add 1 to path_size for the `n` argument for the null terminator, the space for which is // implicitly included by the std::string::reserve call std::snprintf(buf.data(), path_size + 1, "/%s/%.*s", path, static_cast<int>(file_name.length()), file_name.data()); files.push_back(std::move(buf));

This retains the property of the old version that it only had to allocate the string once.

(EDIT: removed the + 1 in path_size calculation for null terminator, as I realized that std::string::reserve implicitly adds 1 for that by itself, and add it back in snprintf)

I don't believe the version of libstdc++ (the standard library) PROS uses supports std::format

Sadly it does not :(

@Gracelu128 Ty but

I would recommend keeping the comments (or rewriting them in your own words if you want). Always better to explain what you're doing, especially if it may be non-obvious why (and I think readers of this code may not immediately understand what the %.*s does, and why its needed. I know I wouldn't know what that format specifier means at first glance)

Sorry, I actually made an edit to the code block after you looked at it I think:

(EDIT: removed the + 1 in path_size calculation for null terminator, as I realized that std::string::reserve implicitly adds 1 for that by itself, and add it back in snprintf)

You could also just subtract 1 from the param to the reserve call if you think thats preferable.

…d" in file path

noam987 and others added 6 commits October 23, 2023 19:24

Add list_files

7fa0947

renamed c function

40aa222

Clarify the docs

90e0bba

Changed list_files function in vdml_usd.cpp to return vector of std:s…

a8ed32b

…tring of file names Will return a vector of std::strings of file names, will return a vector containing one std::string PROS_ERR if error occurs.

Added #include <vector>

4983f3b

Readded original func as list_files_raw, made sure to update func in …

c80a4aa

…c API as well to raw

Gracelu128 changed the title ~~✨Add list_files function #612~~ ✨Add list_files function #615 Oct 27, 2023

noam987 self-requested a review October 27, 2023 20:17

Gracelu128 added 2 commits October 27, 2023 16:38

Altered how list_files func deals with error

ba4a55b

Function to return vector containing specific error state errno is set to, if none of the error states will set to FILE I/O error

Updated header regarding example for list_files func

da47f28

djava suggested changes Oct 27, 2023

View reviewed changes

Gracelu128 added 6 commits October 30, 2023 17:13

Edits to list_files func, function header

3d41ca6

Edits to list_files function

4247fb1

Update header for list_files and list_files_raw function

8df65db

List_files dealt with possible memory allocation error

f4aa620

edit dealing with memory allocation error in list_files

db8c2ee

Update on dealing with errors

a4bc889

Either file i/o error or path not found

djava reviewed Nov 3, 2023

View reviewed changes

djava suggested changes Nov 3, 2023

View reviewed changes

Made stylistic edits to list_files function

490a3ca

djava suggested changes Nov 5, 2023

View reviewed changes

list_files function

b7b773e

Altered to return the file path instead of file names. Ex. "/usd/path/file_name".

WillXuCodes requested changes Nov 10, 2023

View reviewed changes

WillXuCodes reviewed Nov 10, 2023

View reviewed changes

djava suggested changes Nov 10, 2023

View reviewed changes

Edits to list_files function on handling file paths, inclusion of "us…

1c42992

…d" in file path

✨Add list_files function #615 #615

Are you sure you want to change the base?

✨Add list_files function #615 #615

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Gracelu128 commented Oct 27, 2023 • edited by phinc23 Loading

Summary:

Motivation:

Test Plan:

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Gracelu128 commented Oct 27, 2023 •

edited by phinc23

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