foundation-smtp-transport

Shared host/port/TLS-mode/credentials -> lettre AsyncSmtpTransport<Tokio1Executor> builder, used by infrastructure-smtp and infrastructure-communication

What it is for

# foundation-smtp-transport

One function: host/port/TLS-mode/credentials -> a lettre AsyncSmtpTransport<Tokio1Executor>. Extracted (Gate 4 review finding, Sprint 3.45 follow-up) because infrastructure-smtp::SmtpSender::new (crates/infrastructure/smtp/src/sender.rs) and infrastructure-communication::smtp::SmtpOutboundSender::new (crates/infrastructure/communication/src/smtp.rs) had independently reimplemented the identical lettre 0.11 transport-builder logic (tokio1-native-tls, same version in both crates already) — two copies meant a TLS/timeout fix to one would not propagate to the other.

Why this crate, not a direct dependency between the two

Both infrastructure-smtp and infrastructure-communication are infrastructure-layer (docs/architecture/layers.toml). This workspace's layer rule (tools-xtask/src/main.rs::allowed_deps) is stricter than "depend only on a lower layer" — a non-tools library crate may depend on foundation ONLY, full stop, even same-layer imports are a violation with no exception list entry available for a new edge. So neither infrastructure crate may depend on the other; the only legal shared home for logic both need is a foundation-layer crate. Hence this crate, not (for example) infrastructure-communication depending on infrastructure-smtp directly.

No I/O happens in build_smtp_transport itself — lettre's SMTP transport connects lazily per send. The one exception is that AsyncSmtpTransportBuilder::build() spawns the connection pool's background task (the pool feature lettre defaults to), which needs a live Tokio reactor even though no network I/O happens yet — same reason both call sites' own construction tests are #tokio::test, not plain #test.

Capabilities

TlsMode

# foundation-smtp-transport

How to use it

No examples/ target and no doctest in this crate's rustdoc. The tests listed under Verification are the closest executable usage.

Module structure

No public modules: the crate root is its whole surface.

Public surface

`crate root`

No pub use re-exports: every item above is declared in this crate.

Boundary

Depends on no other workspace tier.

Shares tier foundation with 27 other crates: foundation-audit-log, foundation-basemodels, foundation-bounded-io, foundation-conversation-closure, foundation-crypto-sign, foundation-decisioning, foundation-encounter-vocabulary, foundation-fs-metadata, … (27 total).

_What this crate deliberately does NOT own is a judgment. No committed registry records one for it, so none is stated here._

Where it sits

Dependencies

Runtime, from outside the workspace.

Development, from outside the workspace.

Build. None.

Depended on by. 2 workspace crates.

Signal flow — what reaches this crate, and what it reaches.

flowchart LR
  n_infrastructure_communication["infrastructure-communication"] -->|uses| SELF
  n_infrastructure_smtp["infrastructure-smtp"] -->|uses| SELF
  SELF["foundation-smtp-transport"]
  classDef self fill:#1f883d,stroke:#1f883d,color:#fff;
  class SELF self;

Feature flags

No Cargo features are defined: every capability is unconditional, so no consumer can receive a half-wired crate.

Targets

Error model

No public error type was detected: no public item declares a type named *Error, and no public signature returns one.

Operational characteristics

No unsafe block, unsafe fn, unsafe impl or unsafe trait was found by the parser anywhere in this crate's source.

Configuration

No environment variable is read with a literal name anywhere in this crate. A variable whose key is computed at run time cannot be listed here, and is not claimed to be absent.

Related capabilities

2 workspace crates depend on this one: infrastructure-communication, infrastructure-smtp.

Verification

Evidence by module. How often each public module is named by something executable.

What the tests establish, by name:

• builds_for_tls_mode_implicit_with_credentials_ses_shaped — src/lib.rs
• builds_for_tls_mode_none_no_credentials_local_relay — src/lib.rs
• builds_for_tls_mode_start_tls_with_credentials — src/lib.rs
• tls_mode_defaults_to_start_tls — src/lib.rs
• tls_mode_none_still_accepts_credentials — src/lib.rs
• tls_mode_serializes_snake_case_and_round_trips — src/lib.rs

Documentation coverage

pie showData
    title Public items with rustdoc
    "Documented" : 2
    "No rustdoc detected" : 0

Metrics

pie showData
    title Public API by kind
    "enum" : 1
    "function" : 1

pie showData
    title Rust source composition
    "Code" : 86
    "Blank or comment" : 80

Generation

Rendered by tools-corpus corpus readme from repository evidence alone, renderer schema 2, lexicon current. No model, network service or database was consulted. Regenerate with tools-corpus corpus readme --write; verify with --check.