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Remove the default output buffer limit #45

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Remove the default output buffer limit #45

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27648e7
Remove the default output buffer limit
iCharlesHu May 15, 2025
212047f
Modify header doc to indicate that .string and .bytes outputs have un…
iCharlesHu May 15, 2025
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18 changes: 11 additions & 7 deletions Sources/Subprocess/IO/Output.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -46,7 +46,7 @@ public protocol OutputProtocol: Sendable, ~Copyable {
#endif
extension OutputProtocol {
/// The max amount of data to collect for this output.
public var maxSize: Int { 128 * 1024 }
public var maxSize: Int { .max }
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@iCharlesHu Why are we fixing a hang with increasing the buffer size to infinity? That's not quite the right fix I think.

if you're not streaming and you blow through the max size you should get an error, not a hang. That's also what AsyncProcess does.

in fact, you will now see a hang (followed by an OOM kill) if you run for example cat /dev/zero.

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I understand your point, but struggling a bit to find the right answer here. If we put a limit in, and during testing someone only uses file sizes < 128k (for example), then a customer of the app is the one who hits the error. If we are unlimited, then it'll just use infinite memory, which is also a problem.

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Safe and unexpected is better than unsafe an unexpected IMHO. So a limit is IMHO a must.

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If you get an error telling you "too much data to collect", it's immediately actionable. If your process just grinds to a halt or gets OOM killed, you need to do much more work to even figure out what the problem is.

}

/// A concrete `Output` type for subprocesses that indicates that
Expand Down Expand Up @@ -240,10 +240,12 @@ extension OutputProtocol where Self == FileDescriptorOutput {
@available(SubprocessSpan, *)
#endif
extension OutputProtocol where Self == StringOutput<UTF8> {
/// Create a `Subprocess` output that collects output as
/// UTF8 String with 128kb limit.
/// Create a `Subprocess` output that collects output as UTF8 String
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I think the documentation comment here should say that the buffer is unlimited, so the amount of memory required is proportional to the size of the output.

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Sounds good

/// with an unlimited buffer size. The memory requirement for collecting
/// output is directly proportional to the size of the output
/// emitted by the child process.
public static var string: Self {
.init(limit: 128 * 1024, encoding: UTF8.self)
.init(limit: .max, encoding: UTF8.self)
}
}

Expand All @@ -265,9 +267,11 @@ extension OutputProtocol {
@available(SubprocessSpan, *)
#endif
extension OutputProtocol where Self == BytesOutput {
/// Create a `Subprocess` output that collects output as
/// `Buffer` with 128kb limit.
public static var bytes: Self { .init(limit: 128 * 1024) }
/// Create a `Subprocess` output that collects output as a `Buffer`
/// with an unlimited buffer size. The memory requirement for collecting
/// output is directly proportional to the size of the output
/// emitted by the child process.
public static var bytes: Self { .init(limit: .max) }

/// Create a `Subprocess` output that collects output as
/// `Buffer` up to limit it bytes.
Expand Down
19 changes: 19 additions & 0 deletions Tests/SubprocessTests/SubprocessTests+Unix.swift
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Expand Up @@ -955,6 +955,25 @@ extension SubprocessUnixTests {
}
#expect(result == .unhandledException(SIGKILL))
}

@Test func testUnlimitedBufferByDefault() async throws {
guard #available(SubprocessSpan , *) else {
return
}

// Make sure we can read long text from standard input
let expected: Data = try Data(
contentsOf: URL(filePath: theMysteriousIsland.string)
)
// Launch cat with default output `.string`
let cat = try await Subprocess.run(
.path("/bin/cat"),
arguments: ["\(theMysteriousIsland.string)"]
)
#expect(cat.terminationStatus.isSuccess)
// Make sure we read all bytes
#expect(cat.standardOutput!.data(using: .utf8) == expected)
}
}

// MARK: - Utils
Expand Down