Error when reading asynchronous text file line by line

[mrhdias]

When I tried to read a text file asynchronous line by line it gives an error and only reads the first line.

Example

import asyncdispatch, asyncfile, os

proc main() {.async.} =
  var filename = "test.txt"
  var file = openAsync(filename, fmRead)
  while true:
    let line = await file.readLine()
    if line.len == 0: break
    echo line
  
  file.close()

waitFor main()

Current Output

Exception message: index out of bounds
Exception type: [IndexError]
Error: execution of an external program failed: '/home/hdias/Downloads/tmp/test '

Additional Information

$ nim -v
Nim Compiler Version 0.19.4 [Linux: amd64]
Compiled at 2019-02-01
Copyright (c) 2006-2018 by Andreas Rumpf

git hash: b6d96cafc8bcad1f3d32f2910b25cd11a93f7751
active boot switches: -d:release

[mrhdias]

With fix #10640 I get another error:

proc main() {.async.} =
    var fh = openAsync("test.txt", fmRead)
    while (let line = await fh.readLine(); line.len) > 0:
        echo line
    fh.close()

waitFor main()

$ nim c -r test.nim
...
Exception message: EOF reached
Exception type: [EOFError]
Error: execution of an external program failed: '/home/hdias/tmp/test '

[LemonBoy]

I get another error

It's not an error, if you read past the EOF you get an EOFError the same way you'd get one by using the synchronous variant.

[mrhdias]

Ok, how to find the end of a file in this case?
The readLine() return a string. If not return nothing for me is the EOF.

proc main() {.async.} =
    var fh = openAsync("test.txt", fmRead)
    while (let line = await fh.readLine(); line.len) > 0:
        echo line
    fh.close()

waitFor main()

Example in C:

while((ch = fgetc(fp)) != EOF) {
    str[len++] = ch;
    if (ch=='\n')
        break;
}
str[len]= '\0';
return(str);

[LemonBoy]

Ok, how to find the end of a file in this case?

proc main() {.async.} =
    var fh = openAsync("test.txt", fmRead)
    try:
        let line = await fh.readLine()
        echo line
    except EOFError:
        discard
    finally:
        fh.close()

waitFor main()

[mrhdias]

Ok, how to find the end of a file in this case?

proc main() {.async.} =
    var fh = openAsync("test.txt", fmRead)
    try:
        let line = await fh.readLine()
        echo line
    except EOFError:
        discard
    finally:
        fh.close()

waitFor main()

But with your code I read only one line!!!

[mrhdias]

Ok, how to find the end of a file in this case?

proc main() {.async.} =
    var fh = openAsync("test.txt", fmRead)
    try:
        let line = await fh.readLine()
        echo line
    except EOFError:
        discard
    finally:
        fh.close()

waitFor main()

But with your code I read only one line!!!

I find a way to make this work:

proc main() {.async.} =
    var fh = openAsync("test.txt", fmRead)
    while true:
        try:
            let line = await fh.readLine()
            echo line
        except EOFError:
            break
    fh.close()

waitFor main()