In Standard ML, I have opened a file using TextIO.openIn "myfile.txt". This returns a value of type TextIO.instream. How do I get the POSIX file descriptor of type Posix.FileSys.file_desc from this instream?
Here's a function which does it, returning a Posix.FileSys.file_desc option.
fun instreamToPosixFD (ins: TextIO.instream) : Posix.FileSys.file_desc option =
let
val (TextPrimIO.RD reader, _) =
TextIO.StreamIO.getReader (TextIO.getInstream ins)
in
case #ioDesc reader of
NONE => NONE
| SOME id => Posix.FileSys.iodToFD id
end
The use of option for the output is consistent with the types in the Basis Library. As far as I can tell, if you open a file with TextIO.openIn and pass the result to this function, you will get a SOME result. My guess is that NONE is only possible for a TextIO.instream that is not backed by an open file.
Related
I'm a rust noob. Have been trying to upload a simple text file to S3 using rusoto but haven't been able to convert a file into Stream. How to convert a file into a Stream acceptable by rusoto S3 upload.
let s3_client = S3Client::new(Region::UsEast1);
let file = File::open("text.txt").await?;
let mut reader = BufReader::new(file);
let mut buffer: Stream = Vec::new();
file.read_to_end(&mut buffer).await?;
let result = s3_client.put_object(PutObjectRequest {
bucket: String::from("bucket-name"),
key: "text.txt".to_string(),
body: Some(StreamingBody::new(buffer)),
..Default::default()
});
The StreamingBody type used in the S3 client is an alias for ByteStream from rusoto_core, which can be made either from a type implementing futures_core::stream::Stream or from a Vec<u8>.
The most correct way to accomplish this would be to use a async read of the file via Tokyo, and then create a ByteStream from the resulting Stream of bytes. But reading a file as a Stream doesn't have a fully fleshed out solution in the async ecosystem at the moment. See this SO question, especially the links at the bottom of the accepted answer, for more details.
Another way is to read the file fully into memory, as you are doing in the provided code example, and then create a ByteStream from the resulting Vec<u8>. If you do that your code is pretty close.
use tokio::io::AsyncReadExt;
use rusoto_s3::*;
use rusoto_core::*;
async fn do_upload() -> Result<(), Box<dyn std::error::Error>> {
let s3_client = S3Client::new(Region::UsEast1);
let mut file = tokio::fs::File::open("text.txt").await?;
let mut buffer = Vec::new();
file.read_to_end(&mut buffer).await?;
let result = s3_client.put_object(PutObjectRequest {
bucket: String::from("bucket-name"),
key: "text.txt".to_string(),
body: Some(StreamingBody::from(buffer)),
..Default::default()
}).await?;
// do thing with result
Ok(())
}
The only real changes are:
removing the Stream annotation from buffer, which doesn't really make sense because Stream is a trait and not a concrete type. Also, we can't use it easily for the aforementioned reasons.
StreamingBody::from rather than ::new, because we are using a Vec and not a type implementing Stream.
I am a newbie in PowerBi and currently working on a POC where I need to load data from a folder or directory. Before this load, I need to check if
1) the respective folder exists
2) the file under the folder is with.csv extension.
Ex. Let suppose we have a file '/MyDoc2004/myAction.csv'.
Here first we need to check if MyDoc2004 exists and then if myAction file is with.csv extension.
Is there any way we can do this using Power Query?
1. Check if the folder exists
You can apply Folder.Contents function with the absolute path of the folder, and handle the error returned when the folder does not exist with try ... otherwise ... syntax.
let
absoluteFolderPath = "C:/folder/that/may/not/exist",
folderContentsOrError = Folder.Contents(absoluteFolderPath),
alternativeResult = """" & absoluteFolderPath & """ is not a valid folder path",
result = try folderContentsOrError otherwise alternativeResult
in
result
2. Check if the file is with .csv extension
I'm not sure what output you are expecting.
Here is a way to get the content of the file by full path including ".csv", or return an alternative result if not found.
let
absoluteFilePath = "C:/the/path/myAction.csv",
fileContentsOrError = File.Contents(absoluteFilePath),
alternativeResult = """" & absoluteFilePath & """ is not a valid file path",
result = try fileContentsOrError otherwise alternativeResult
in
result
If this is not what you are looking for, please update the question with the expected output.
Hope it helps.
I am working on an Ocsigen example (http://ocsigen.org/tuto/manual/macaque).
I get an error when trying to compile the program, as follows.
File "testDB.ml", line 15, characters 14-81 (end at line 18, character 4):
While finding quotation "table" in a position of "expr":
Available quotation expanders are:
svglist (in a position of expr)
svg (in a position of expr)
html5list (in a position of expr)
html5 (in a position of expr)
xhtmllist (in a position of expr)
xhtml (in a position of expr)
Camlp4: Uncaught exception: Not_found
My code is:
module Lwt_thread = struct
include Lwt
include Lwt_chan
end
module Lwt_PGOCaml = PGOCaml_generic.Make(Lwt_thread)
module Lwt_Query = Query.Make_with_Db(Lwt_thread)(Lwt_PGOCaml)
let get_db : unit -> unit Lwt_PGOCaml.t Lwt.t =
let db_handler = ref None in
fun () ->
match !db_handler with
| Some h -> Lwt.return h
| None -> Lwt_PGOCaml.connect ~database:"testbase" ()
let table = <:table< users (
login text NOT NULL,
password text NOT NULL
) >>
..........
I used eliom-destillery to generate the basic files.
I used "make" to compile the program.
I've tried many different things and done a google search but I can't figure out the problem. Any hints are greatly appreciated.
Generally speaking, the error message indicates that CamlP4 does not know the quotation you used, here table, which is used in your code as <:table< ... >>. The quotations can be added by CamlP4 extensions pa_xxx.cmo (or pa_xxx.cma) modules. Unless you made a typo of the quotation name, you failed to load an extension which provides it to CamlP4.
According to http://ocsigen.org/tuto/manual/macaque , Macaque (or its underlying libraries? I am not sure since I have never used it) provides the quotation table. So you have to instruct CamlP4 to load the corresponding extension. I believe the vanilla eliom-destillery is minimum for the basic eliom programming and does not cover for the extensions for Macaque.
Actually the document http://ocsigen.org/tuto/manual/macaque points out it:
We need to reference macaque in the Makefile :
SERVER_PACKAGE := macaque.syntax
This should be the CamlP4 syntax extension name required for table.
I am trying to find a process by which to edit and write to a resource .rc file; I attempted to use the sample code listed at
How to increment values in resourse file by using vbscript but the last line in both samples returned the same error ( fso.OpenTextFile(rcfile, 2).Write rctext ) :
Error: Invalid procedure call or argument
Code: 800A0005
Source: Microsoft VBScript runtime error
I modified the script to write out to a .txt file and that worked fine, but I'm baffled as to what may be causing the problem writing out to a .rc file.
From the linked sample (simplified)
rctext = fso.OpenTextFile(rcfile).ReadAll
rctext = ....
fso.OpenTextFile(rcfile, 2).Write rctext
The idea is read all the file, and as far as there is no variable holding a reference to the opened file, it is closed, then change what needs to be changed and open again the file, now for writing, and write the changed content to file
And, usually, it works. But sometimes the file opened for reading is not closed fast enough to later open it for writing.
To ensure the file is closed and then can be opened for writing, change the reading code to
set f = fso.OpenTextFile(rcfile)
rctext = f.ReadAll
f.Close
As your line
fso.OpenTextFile(rcfile, 2).Write rctext
does three things (access fso, open file, write to it), there are many things that could go wrong. Please see this answer for ideas wrt to problems concerning the first two actions. Another answer concerns the write.
In your case, the evidence - works with a.txt, but not with b.rc - makes it highly improbable that the file's opening is to blame (so .Close won't save you). I suspect that the .rc contains Unicode (UTF-8/UTF-16) data that the textstream can't encode.
So either use the unicode parameter to read/write open the file with UTF-16 encoding or an ADODB.Stream for UTF-8.
It seems that the answer to my question required both of your answers(#MC ND and #Ekkehard.Horner); also, once I changed the vbs script to open and write to the .rc file in Unicode, which I'm not sure why I have to, the script was able to execute without error.
Here is the vbs script in it's final form:
Const ForReading = 1, ForWriting = 2
Const TristateUseDefault = -2, TristateTrue = -1, TristateFalse = 0
Const DoNotCreate = false
rcFile = "C:\Path\To\RC\File.rc"
major = 4
minor = 3
maint = 2
build = 1
version = major & "," & minor & "," & maint & "," & build
Set fso = CreateObject("Scripting.FileSystemObject")
Set fileObj = fso.OpenTextFile(rcFile, ForReading, DoNotCreate, TristateTrue)
rcText = fileObj.ReadAll
fileObj.Close
Set regex = New RegExp
regex.Global = True
regex.Pattern = "(PRODUCTVERSION|FILEVERSION) \d+,\d+,\d+,\d+"
rcText = regex.Replace(rcText, "$1 " & version)
regex.Pattern = "(""(ProductVersion|FileVersion)"",) ""\d+, \d+, \d+, \d+"""
rcText = regex.Replace(rcText, "$1 """ & Replace(version, ",", ", ") & """")
Set fileObj = fso.GetFile(rcFile)
Set textStream = fileObj.OpenAsTextStream(ForWriting, TristateTrue)
textStream.Write rcText
textStream.Close
The only thing that does not seem to work is the regex for replacing the ProduceVersion|FileVersion values, but hopefully I can hammer that out within a reasonable time.
I am trying to write a query that simply drops a table.
let drop_table dbh table_name =
let query = String.concat " " ["drop table"; table_name] in
PGSQL(dbh) query
I am receiving the following error from the query
File "save.ml", line 37, characters 10-11:
Parse error: STRING _ expected after ")" (in [expr])
File "save.ml", line 1:
Error: Preprocessor error
Why am I getting this error? It appears that this function is valid Ocaml syntax.
Thanks guys!
You cannot construct query when using PG'OCaml's syntax extension. You must provide a literal string. This is the tradeoff for getting PG'Ocaml's compile time query validation. If query could be any OCaml expression, PG'OCaml wouldn't know how to validate it at compile time.
Personally, I've stopped using the syntax extension completely. My feeling is it doesn't scale to large projects. Instead I call prepare and execute directly. For example, this function will create a new database connection (assuming the connection parameters are previously defined), run the given query, and close the connection:
let exec query =
let db = PGOCaml.connect ~host ~user ~database ~port ~password ()
PGOCaml.prepare db ~query ();
let ans = PGOCaml.execute db ~params:[] () in
PGOCaml.close db;
ans
Of course, this isn't a robust implementation and shouldn't be used in production code. It doesn't handle errors and isn't asynchronous.