Contracts and edge cases

Platform spec article

Contracts and edge cases

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Spec standingStandard

Owner

Piotr Mikstacki pmikstacki@cybernomad.it

Submitter

Piotr Mikstacki pmikstacki@cybernomad.it

Current document

ADRs (3)

1. 0010-split-stream-modules Split stream modules per fd Accepted

   stdin/stdout/stderr use separate System modules.

   Context

   A single Console IO type obscures direction and syscall descriptors.

   Decision

   Rule	Detail
   Modules	System.Input, System.Output, System.Error
   Forbidden	Monolithic console IO type for standard streams

   Consequences

   Each module binds one StandardStream descriptor; cross-stream APIs stay separate.

   Verification anchors

   packages/runtime/src/System/Input.bd, Output.bd, Error.bd.

   Open full ADR page

2. 0011-write-panic-read-result Write panics; read returns Result Accepted

   Syscall write failures panic; reads surface Result.

   Context

   v1 write helpers are infallible at the type level; read paths need explicit error handling.

   Decision

   Rule	Detail
   Write	Write / WriteLine must panic on WriteWith failure
   Read	Read / ReadLine return Result<string, SyscallError>

   Consequences

   Diagnostics for write failures use fixed panic strings; callers cannot catch write errors in Beskid v1.

   Verification anchors

   Corelib stream tests; syscall integration in beskid_runtime.

   Open full ADR page

3. 0012-writeline-unix-lf WriteLine emits Unix LF Accepted

   WriteLine appends a single LF byte sequence.

   Context

   Cross-platform hosts may translate line endings below the Beskid API.

   Decision

   Rule	Detail
   Ending	WriteLine must append \n only
   Windows	Host/platform layer may translate later without API change

   Consequences

   Authors see consistent Beskid source semantics; CRLF is not encoded in corelib strings.

   Verification anchors

   Output.bd / Error.bd tests; platform IO docs.

   Open full ADR page

Articles

• Contracts and edge cases MUST rules for standard stream reads, writes, and error handling. article Standard Reviewed Thu May 21
• Design model Stream module boundaries and syscall descriptor model for standard I/O. article Standard Reviewed Thu May 21
• Examples Standard stream read and write usage patterns. article Standard Reviewed Thu May 21
• Flow and algorithm Read and write algorithms for standard stream helpers. article Standard Reviewed Thu May 21
• Verification and traceability Runtime syscall and corelib anchors for standard stream I/O. article Standard Reviewed Thu May 21

History

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Completeness

OKfeature · 3 SpecSection(s) · 1 H2 heading(s)

Section id	Required	Found
what-this-feature-specifies	yes	yes
implementation-anchors	yes	yes

Full tree: run pnpm verify:platform-spec-layout (writes src/generated/platform-spec-layout-report.json).

Related spec docs

• Feature
  Console I/O streams

  Parent feature hub

Purpose

Document contracts and edge cases for the Console Io Streams feature: role-specific normative detail beyond the feature hub.

Canonical references

• Feature hub: Console Io Streams
• Sibling articles in this bundle (design model, contracts, flow, examples, verification)

Detailed behavior

Normative requirements

ID	Requirement
IO-001	System.Input.Read and ReadLine must target stdin only via Descriptor::Standard(Stdin).
IO-002	System.Output.Write / WriteLine must target stdout only; System.Error must target stderr only.
IO-003	WriteLine(text) must perform Write(text) then Write("\n") as two syscall writes (or equivalent atomic policy documented in runtime).
IO-004	Write helpers must panic with a stable message when WriteWith returns an error (System.Output.Write failed / stderr variant).
IO-005	Read helpers must not panic on EOF; they return Result with an empty or partial string per syscall contract.
IO-006	Modules must not interpret ANSI sequences; validation of escape syntax is the responsibility of ANSI escape model.

Function contracts

Function	Behavior
Input.Read()	Read up to default byte limit from stdin
Input.ReadLine()	Read until \n or EOF; line without trailing newline
Output.Write(text)	Write UTF-8 bytes to stdout, no newline
Output.WriteLine(text)	Write(text) + Write("\n")
Error.Write / WriteLine	Same as output, descriptor stderr

Edge cases

• Redirected stdout: Still writable; TTY detection happens only in Console capabilities, not in System.Output.
• Binary data: string is UTF-8 text; writing invalid UTF-8 is undefined at the language level—console APIs assume valid strings.
• Large writes: Syscall layer may chunk; stream helpers do not expose partial-write Result in v1.
• Concurrent fibers: Multiple fibers writing stdout may interleave bytes; line-safe logging is the caller’s responsibility (channels or mutex).

Verification

See the verification and traceability article in this bundle and compiler/corelib/beskid_corelib/tests/corelib_tests/src/console/.

Related topics

• Parent feature hub and Terminal and console area