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83 lines
3.2 KiB
Text
83 lines
3.2 KiB
Text
interface File
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exposes [ FileReadErr, FileOpenErr, FileWriteErr, DirReadErr, readUtf8 ]
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imports [ Task.{ Task }, fx.Effect.{ after }, Path ]
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Path : Path.Path
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# These various file errors come from the POSIX errno values - see
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# http://www.virtsync.com/c-error-codes-include-errno for the actual codes, and
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# https://www.gnu.org/software/libc/manual/html_node/Error-Codes.html for documentation
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#
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# The goal of this design is:
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# * Whenever a function returns a `Task`, that task's error type represents all the errors that could happen.
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# * The errors are union-friendly; if I run a task that reads, and then another that writes, I should get all the read *and* write errors.
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# * To make the errors friendlier to chaining, they should always include the `Path` of the attempted operation. This way it's possible to tell which one failed after the fact.
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## These errors can happen when opening a file, before attempting to read from
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## it or write to it. The #FileReadErr and #FileWriteErr tag unions begin with
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## these tags and then add more specific ones.
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FileOpenErr a :
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[
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FileNotFound Path,
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PermissionDenied Path,
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SymLinkLoop Path,
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TooManyOpenFiles Path,
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IoError Path,
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UnknownError I64 Path,
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]a
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## Errors when attempting to read a non-directory file.
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FileReadErr a :
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FileOpenErr
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[
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FileWasDir Path,
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InvalidSeek Path,
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IllegalByteSequence Path,
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FileBusy Path,
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]a
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## Errors when attempting to read a directory.
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DirReadErr a :
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FileOpenErr
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[
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FileWasNotDir Path,
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]a
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## Errors when attempting to write a non-directory file.
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FileWriteErr a :
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FileOpenErr
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[
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FileWasDir Path,
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ReadOnlyFileSystem Path,
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]a
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## Read a file's raw bytes
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#readBytes : Path -> Task (List U8) (FileReadErr *)
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#readBytes = \path ->
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# Effect.readBytes (Path.toStr path)
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## Read a file's bytes and interpret them as UTF-8 encoded text.
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readUtf8 : Path -> Task.Task Str (FileReadErr [ BadUtf8 ]*)
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readUtf8 = \path ->
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Effect.map (Effect.readAllUtf8 (Path.toStr path)) \answer ->
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# errno values - see
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# https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/errno.h.html
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when answer.errno is
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0 -> Ok answer.bytes # TODO use Str.fromUtf8 to validate a byte list as UTF-8 and return (Err BadUtf8) if validation fails
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1 -> Err (PermissionDenied path)
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2 -> Err (FileNotFound path)
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19 -> Err (FileWasDir path)
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# TODO handle other errno scenarios that could come up
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_ -> Err (UnknownError answer.errno path)
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## Read a file's bytes, one chunk at a time, and use it to build up a state.
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##
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## After each chunk is read, it gets passed to a callback which builds up a
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## state - optionally while running other tasks.
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#readChunks : Path, U64, state, (state, List U8 -> Task state []err) -> Task state (FileReadErr err)
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## Like #readChunks except after each chunk you can either `Continue`,
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## specifying how many bytes you'd like to read next, or `Stop` early.
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#readChunksOrStop : Path, U64, state, (state, List U8 -> [ Continue U64 (Task state []err), Stop (Task state []err) ]) -> Task state (FileReadErr err)
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