Hi, That’s curious. Isn’t the point of non-blocking connections that you keep them open across multiple read calls? So why would it be useful to default-open unz() as non-blocking only to close it again?
The most similar connection type to unz() seems to me to be gzfile() which is opened as blocking by default [1] and is also special-cased to avoid the readLines() push-back [2]. I wonder why it’s useful for unz() not to behave the same? Especially considering that at least readLines() from an open non-blocking unz() is just an error currently. Best, Mikko [1]: https://github.com/wch/r-source/blob/69af5a3859b0a45432a01f118dbecf5d8831085b/src/main/connections.c#L2451 [2]: https://github.com/wch/r-source/blob/69af5a3859b0a45432a01f118dbecf5d8831085b/src/main/connections.c#L4163 From: Iris Simmons <ikwsi...@gmail.com> Sent: Friday, 25 October 2024 14:38 To: Marttila Mikko <mikko.martt...@orionpharma.com> Cc: R help Mailing list <r-help@r-project.org> Subject: Re: [R] readLines() and unz() and non-empty final line Hi again, The unz connection is non-blocking by default. I checked do_unz which calls R_newunz which calls init_con and the only place in any of those functions that sets 'blocking' is init_con which sets it to FALSE: https://github.com/wch/r-source/blob/0c26529e807a9b1dd65f7324958c17bf72e1de1a/src/main/connections.c#L713 I'll open an issue on R-bugzilla and see if they're willing to do something similar to 'file()'; that is, add a 'blocking' argument to unz. It's hard to say whether they would choose 'blocking = FALSE' for back compatibility or 'blocking = TRUE' for consistency with 'file()'. Regards, Iris On Fri, Oct 25, 2024, 04:47 Marttila Mikko <mikko.martt...@orionpharma.com<mailto:mikko.martt...@orionpharma.com>> wrote: Thanks Iris, Bert, and Tim. Whether unz() is blocking or not by default doesn’t seem to be documented. Indeed, thank you Iris for finding out that explicitly opening it as blocking would work. That made me wonder if it’s non-blocking by default then, which would have been surprising. However, explicitly opening it as non-blocking seems to lead to problems as well: > local({ + con <- unz("hello.zip", "hello.txt") + open(con, blocking = FALSE) + on.exit(close(con)) + res <- readLines(con) + res + }) Error in readLines(con) : seek not enabled for this connection Calls: local ... eval.parent -> eval -> eval -> eval -> eval -> readLines Execution halted So, the behaviour of unz() seems to be different depending on whether it was explicitly opened before passed to readLines(). Should this be fixed or documented? Best, Mikko From: Bert Gunter <bgunter.4...@gmail.com<mailto:bgunter.4...@gmail.com>> Sent: Thursday, 24 October 2024 18:13 To: Iris Simmons <ikwsi...@gmail.com<mailto:ikwsi...@gmail.com>> Cc: Marttila Mikko <mikko.martt...@orionpharma.com<mailto:mikko.martt...@orionpharma.com>>; r-help@r-project.org<mailto:r-help@r-project.org> Subject: Re: [R] readLines() and unz() and non-empty final line You don't often get email from bgunter.4...@gmail.com<mailto:bgunter.4...@gmail.com>. Learn why this is important<https://aka.ms/LearnAboutSenderIdentification> But note: > zip("hello.zip", "hello.txt") updating: hello.txt (stored 0%) > readChar(unz("hello.zip","hello.txt"),100) [1] "hello" I leave it to you and other wiser heads to figure out. Cheers, Bert On Thu, Oct 24, 2024 at 8:57 AM Iris Simmons <ikwsi...@gmail.com<mailto:ikwsi...@gmail.com>> wrote: Hi Mikko, I tried running a few different things, and it seems as though explicitly using `open()` and opening a blocking connection works. ```R cat("hello", file = "hello.txt") zip("hello.zip", "hello.txt") local({ conn <- unz("hello.zip", "hello.txt") on.exit(close(conn)) ## you can use "r" instead of "rt" ## ## 'blocking = TRUE' is the default, so remove if desired open(conn, "rb", blocking = TRUE) readLines(conn) }) ``` A blocking connection might be undesirable for you, in which case someone else might have a better solution. On Thu, Oct 24, 2024 at 10:58 AM Marttila Mikko via R-help <r-help@r-project.org<mailto:r-help@r-project.org>> wrote: > > Dear list, > > I'm seeing a strange interaction with readLines() and unz() when reading > a file without an empty final line. The final line gets dropped silently: > > > cat("hello", file = "hello.txt") > > zip("hello.zip", "hello.txt") > adding: hello.txt (stored 0%) > > readLines(unz("hello.zip", "hello.txt")) > character(0) > > The documentation for readLines() says if the final line is incomplete for > "non-blocking text-mode connections" the line is "pushed back, silently" > but otherwise "accepted with a warning". > > My understanding is that the unz() here is blocking so the line should be > accepted. Is that incorrect? If so, how would I go about reading such > lines from a zip file? > > Best, > > Mikko > > > This e-mail transmission may contain confidential or legally privileged > information that is intended only for the individual or entity named in the > e-mail address. If you are not the intended recipient, you are hereby > notified that any disclosure, copying, distribution, or reliance upon the > contents of this e-mail is strictly prohibited. If you have received this > e-mail transmission in error, please reply to the sender, so that they can > arrange for proper delivery, and then please delete the message from your > computer systems. Thank you. > > ______________________________________________ > R-help@r-project.org<mailto:R-help@r-project.org> mailing list -- To > UNSUBSCRIBE and more, see > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide https://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. ______________________________________________ R-help@r-project.org<mailto:R-help@r-project.org> mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide https://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. 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