Behavior of fd_write changed, seems to not be printing entire supplied array

[DenialAdams]

I recently updated my local version of wasmtime and noticed that the behavior of fd_write seems to have changed. I am supplying two strings to print: a supplied string, and a newline character. This used to print the newline character, which is what I expect, but seems to no longer do so. I bisected the behavior change back to PR #2444, but I didn't see this behavior change explicitly called out.

Basically, I'm wondering:

1. Is this new behavior intended, or a bug?
2. If this new behavior is intended, what am I doing wrong in the example program?

Thanks for reading!

Test Case

(module
  (import "wasi_unstable" "fd_write" (func $fd_write (param i32 i32 i32 i32) (result i32)))
  (memory 1)
  (export "memory" (memory 0))
  (data 0 (i32.const 16) "\n")
  (data 0 (i32.const 18) "world on a new line!")
  (data 0 (i32.const 47) "Hello,")
  (func $print (param i32) (param i32)
    (i32.store (i32.const 0) (local.get 0))
    (i32.store (i32.const 4) (local.get 1))
    (i32.store (i32.const 8) (i32.const 16))
    (i32.store (i32.const 12) (i32.const 1))
    (call $fd_write (i32.const 1) (i32.const 0) (i32.const 2) (i32.const 0))
    drop
  )
  (func $main
    (export "_start")
    i32.const 47
    i32.const 6
    call $print
    i32.const 18
    i32.const 20
    call $print
  )
)

Steps to Reproduce

1. wasmtime repro.wast (contents above)
2. Observe that the newline is not printed

Expected Results

Hello,
world on a new line!

Actual Results

Hello,world on a new line!

Versions and Environment

I first observed this behavior on wasmtime 0.29.0. I bisected the issue back to PR #2444, which seems to be where the behavior changed.

Operating system: Windows 10

Architecture: x86

[bjorn3]

fd_write returns the amount of bytes written. You have to call it in a loop until all bytes are written. This matches the posix write syscall. From the man page of the write syscall:

The number of bytes written may be less than count if, for example, there is insufficient space on the underlying physical medium, or the RLIMIT_FSIZE resource limit is encountered (see setrlimit(2)), or the call was interrupted by a signal handler after having written less than count bytes. (See also pipe(7).)

Higher level api's generally do this loop for you.

[DenialAdams]

fd_write returns the amount of bytes written. You have to call it in a loop until all bytes are written. This matches the posix write syscall. From the man page of the write syscall:

The number of bytes written may be less than count if, for example, there is insufficient space on the underlying physical medium, or the RLIMIT_FSIZE resource limit is encountered (see setrlimit(2)), or the call was interrupted by a signal handler after having written less than count bytes. (See also pipe(7).)

Higher level api's generally do this loop for you.

Thank you, this makes a lot of sense! Sorry for the false report