arche

The opinionated backend foundation for Axum applications.

Cloud integrations, databases, auth, LLM inference, tool-calling agents, encryption, streaming JSON/CSV, WebSockets, and structured error handling — wired up and ready to go.

arche sits around Axum, not in place of it.

Getting Started · Modules · API Reference · Design Principles

Why arche?

Every backend service re-implements the same infrastructure plumbing — cloud SDK setup, database pools, auth primitives, error handling, config resolution. arche bundles these into a single, cohesive Rust crate built on well-established libraries so you can skip the boilerplate and focus on business logic.

Getting Started

Add arche to your Cargo.toml:

[dependencies]
arche = "4.7.0"

Modules

Module	What it does
`aws`	S3, SES, KMS, and CloudFront via official AWS SDKs
`gcp`	Generic GCP REST client + Vertex AI (Gemini + Claude); wrappers for Sheets, Drive, Cloud KMS, Cloud Storage, Cloud CDN, and Google OAuth login
`llm`	Canonical LLM types + `LlmProvider` trait — backend-agnostic
`agent`	Tool-calling agent engine, session state, SSE streaming
`database`	Postgres, Redis, and ClickHouse connection pooling with health checks
`jwt`	HS256 token generation, verification, and expiry helpers
`csv`	Async CSV read/write — batch, streaming, and from URL
`json`	Streaming JSON array parsing with metadata extraction
`crypto`	AES-128-CBC encryption with PBKDF2 key derivation
`sockets`	WebSocket connection registry with broadcast
`error`	Axum-compatible structured error responses (400–503)
`utils`	Alphanumeric nano IDs, timestamp validation, date/time conversions, pagination

Every service module exports a config builder so you can wire up credentials programmatically — or omit it entirely and let arche resolve everything from environment variables.

// Pass None to resolve entirely from env vars
let pool = arche::database::pg::get_pg_pool(None).await?;

// Or configure explicitly
let config = arche::database::pg::PgConfigBuilder::default()
    .host(Some("localhost".into()))
    .port(Some(5432))
    .build();
let pool = arche::database::pg::get_pg_pool(config).await?;

All components are modular and explicit — nothing is hidden or magical.

API Reference

AWS

AWS SDK integrations built on official SDKs. Default region: ap-south-1.

S3

use arche::aws::s3::{get_s3_client, S3ConfigBuilder};

// From env vars
let client = get_s3_client(None).await?;

// Or with explicit config
let config = S3ConfigBuilder::default()
    .credential_source(Some("env".into()))
    .access_key_id(Some("AKIA...".into()))
    .secret_access_key(Some("secret".into()))
    .build();
let client = get_s3_client(config).await?;

Env Var	Description
`S3_CRED_SOURCE`	`"IAM"` (default) or `"env"`
`S3_ACCESS_KEY_ID`	Required when source is `"env"`
`S3_SECRET_ACCESS_KEY`	Required when source is `"env"`
`S3_REGION`	AWS region (default: `ap-south-1`)

KMS

use arche::aws::kms::KMSClient;

// Default region
let kms = KMSClient::new_with_region("ap-south-1").await;

// Encrypt / decrypt
let ciphertext = kms.encrypt("alias/my-key", b"sensitive data").await?;
let plaintext = kms.decrypt(&ciphertext).await?;

// Decrypt base64-encoded ciphertext directly
let plaintext = kms.decrypt_base64("base64string...").await?;

Env Var	Description
`AWS_REGION`	AWS region (default: `ap-south-1`)

SES

use arche::aws::ses::SESClient;

let ses = SESClient::new_with_region("ap-south-1").await;

// Plain email (with optional HTML body)
let message_id = ses.send_email(
    "from@example.com",
    "to@example.com",
    "Subject line",
    "Plain text body",
    Some("<h1>HTML body</h1>"),
).await?;

// Templated email
let message_id = ses.send_templated_email(
    "from@example.com",
    "to@example.com",
    "TemplateName",
    r#"{"name": "Alice"}"#,
).await?;

Env Var	Description
`AWS_REGION`	AWS region (default: `ap-south-1`)

CloudFront

use arche::aws::cloudfront::{get_cloudfront_client, CloudFrontClient, CloudFrontConfigBuilder};

let aws = get_cloudfront_client(None).await;
let cf = CloudFrontClient::new(aws, None);

Invalidate paths — submits a CloudFront invalidation and returns immediately with the invalidation ID and status (typically "InProgress").

let result = cf.invalidate_paths(
    Some("E1ABCXYZ"),
    vec!["/index.html".into(), "/assets/*".into()],
    None, // caller_reference: None auto-generates a nanoid (not retry-safe); pass a stable value for idempotent retries
).await?;
println!("{} -> {}", result.id, result.status);

Per CloudFront limits: paths must start with /, max 3000 paths per call, caller reference ≤ 128 chars.

Get invalidation status — fetch the current status of a previously created invalidation. Returns the same InvalidationResult shape; status transitions from "InProgress" to "Completed" (typically 5–15 minutes).

let status = cf.get_invalidation(Some("E1ABCXYZ"), &result.id).await?;
println!("{}", status.status);

Default distribution ID — set once on the client (or via CLOUDFRONT_DISTRIBUTION_ID env) so per-call distribution_id can be None:

let config = CloudFrontConfigBuilder::default()
    .distribution_id("E1ABCXYZ")
    .build();
let cf = CloudFrontClient::new(aws, config);

cf.invalidate_paths(None, vec!["/index.html".into()], None).await?;
cf.get_invalidation(None, "I2J3K4L5...").await?;

Env Var	Description
`AWS_REGION`	AWS region (default: `ap-south-1`)
`CLOUDFRONT_DISTRIBUTION_ID`	Optional default distribution ID

GCP

Service-account-authenticated REST client for any Google Cloud API, plus ergonomic wrappers for Sheets, Drive, and Vertex AI. Built on reqwest — honors HTTPS_PROXY / NO_PROXY like everything else.

Service account credentials

ServiceAccountKey is the canonical credential type. Two ways to construct:

use arche::gcp::ServiceAccountKey;

// From individual fields (e.g. separate env vars or a secrets manager)
let key = ServiceAccountKey::new(client_email, private_key);

// Or from a GCP service-account JSON file on disk
let key = ServiceAccountKey::from_path("/etc/secrets/sa.json").await?;

\n literals from .env-style storage are normalized to real newlines automatically. The private_key is never readable back from the struct and is masked in Debug output.

Authentication modes

Every GcpClient constructor accepts credentials in three forms, tried in order:

Explicit ServiceAccountKey — GcpClient::new(Some(key), None, scopes).
Path to a service-account JSON file — GcpClient::new(None, Some(path), scopes).
Neither → GKE / GCE metadata server (Workload Identity). When both are None, arche falls back to ${GCP_METADATA_URL:-http://metadata.google.internal} and exchanges the pod's bound service account for an OAuth token. This is the standard no-secrets-on-disk flow for pods running on GKE, Cloud Run, or GCE.

// Workload Identity — no creds passed in, no env vars required on GKE.
let kms = arche::gcp::kms::get_kms_client(None, None, None).await?;

Tokens are cached with a 60 s safety margin, single-flighted per scope set, and retried once on transient failures — uniformly across all three modes.

Caveats for the metadata-server path:

Scopes are ignored. The metadata endpoint returns whatever scopes the pod's bound service account has, regardless of what you pass to the client. If you need narrower scopes, use an explicit ServiceAccountKey.
GCP_METADATA_URL is read at construction time. Changing the env var after the client is built has no effect — set it before the first GcpClient::new(None, None, …) call. Useful for pointing tests at a mock HTTP server.
Signed URLs are unsupported. V4 signed URLs (GcsClient::sign_*) require the SA's private key, which the metadata server never exposes. Those calls return a clear error on this path — use an explicit ServiceAccountKey for signed-URL workflows.

Sheets

let sheets = arche::gcp::sheets::client(Some(key), None).await?;

let resp = sheets
    .get(format!(
        "https://sheets.googleapis.com/v4/spreadsheets/{spreadsheet_id}/values/{range}",
    ))
    .await?
    .send()
    .await?;

Pass either Some(key) or Some(path) — never both. Scope is preset to https://www.googleapis.com/auth/spreadsheets.

Drive

let drive = arche::gcp::drive::client(None, Some("/etc/secrets/sa.json".into())).await?;

let bytes = drive
    .get(format!("https://www.googleapis.com/drive/v3/files/{file_id}?alt=media"))
    .await?
    .send().await?
    .bytes().await?;

Scope is preset to https://www.googleapis.com/auth/drive.

Cloud KMS

Encrypt and decrypt against Google Cloud KMS using the same service-account JWT auth as the rest of the GCP family — token caching, retries, and concurrent-fetch deduplication come for free via GcpClient.

use arche::gcp::kms::{get_kms_client, GcpKmsConfig, GcpKmsKey};

// Build the client. Any unset field falls back to its GCP_KMS_* env var.
let kms = get_kms_client(
    Some(key),
    None,
    GcpKmsConfig::builder().project_id("my-project").build(),
).await?;

// Or fully env-driven (project_id required; location defaults to "global"):
let kms = get_kms_client(Some(key), None, None).await?;

// Key identifier — passed per call so one client can target multiple keys
let kms_key = GcpKmsKey::new("my-keyring", "my-key");
// or: let kms_key = GcpKmsKey::from_env()?;  // GCP_KMS_KEY_RING + GCP_KMS_KEY_NAME

// Encrypt — returns ciphertext + the key version that wrapped it
let out = kms.encrypt(&kms_key, b"sensitive data").await?;
// out.ciphertext: Vec<u8>
// out.key_version: e.g. "projects/.../cryptoKeys/my-key/cryptoKeyVersions/3"
//   Persist this alongside the ciphertext for key-rotation auditing.

let plaintext = kms.decrypt(&kms_key, &out.ciphertext).await?;

// If the ciphertext is already base64 (e.g. read from a DB column):
let plaintext = kms.decrypt_base64(&kms_key, &b64_string).await?;

Env Var	Description
`GCP_KMS_PROJECT_ID`	GCP project hosting the KMS key (required)
`GCP_KMS_LOCATION`	KMS location (default: `global`)
`GCP_KMS_BASE_URL`	Override the Cloud KMS endpoint (testing / VPC-SC)
`GCP_KMS_KEY_RING`	Used by `GcpKmsKey::from_env()`
`GCP_KMS_KEY_NAME`	Used by `GcpKmsKey::from_env()`

Already have a GcpClient configured for other services? Reuse it via the exported scope — keeps a single token cache across Sheets / Drive / KMS:

let kms_gcp = my_gcp_client.with_scopes([arche::gcp::kms::KMS_SCOPE]);
let kms = arche::gcp::kms::GcpKmsClient::new(
    kms_gcp,
    "my-project".into(),
    "global".into(),
    None,
);

Cloud Storage (GCS)

Object upload / download / delete / list / head, plus V4-signed GET URLs. Bucket is per-call so one client can target many buckets. Uploads and downloads buffer the full object in memory — keep this in mind for large files.

use arche::gcp::gcs::{get_gcs_client, GcsConfig};
use std::collections::HashMap;
use std::time::Duration;

// All fields optional — gcs_base_url and signed-URL expiry default fine.
let gcs = get_gcs_client(Some(key), None, None).await?;

// Upload with optional user metadata (e.g. `modified_by`)
let mut meta = HashMap::new();
meta.insert("modified_by".into(), "alice".into());
let object = gcs.upload(
    "my-bucket",
    "reports/q4.pdf",
    pdf_bytes,
    "application/pdf",
    meta,
).await?;
// object.generation: Option<i64>  — round-trippable into download/head/delete

// Read it back
let bytes = gcs.download("my-bucket", "reports/q4.pdf", None).await?;

// Or a specific historical version (requires Object Versioning on the bucket)
let old = gcs.download("my-bucket", "reports/q4.pdf", Some(1_700_000_123_456_789)).await?;

// Metadata-only fetch
let meta = gcs.head("my-bucket", "reports/q4.pdf", None).await?;

// Merge-patch user metadata (existing keys overwritten, others untouched)
let mut update = HashMap::new();
update.insert("reviewed_by".into(), "bob".into());
gcs.patch_metadata("my-bucket", "reports/q4.pdf", update).await?;

// List a prefix; pass `versions: true` to include non-current generations
let page = gcs.list("my-bucket", Some("reports/"), None, false).await?;

// V4-signed GET URL (defaults to client's expiry, max 7 days). Always
// points at `storage.googleapis.com` regardless of GCS_BASE_URL.
let url = gcs.signed_get_url("my-bucket", "reports/q4.pdf", Some(Duration::from_secs(600)))?;

Env Var	Description
`GCS_BASE_URL`	Override the storage endpoint (testing / VPC-SC; ignored for signed URLs)
`GCS_SIGNED_URL_EXPIRY_SECS`	Default expiry for `signed_get_url` (default: 900, max: 604800)

upload switches automatically to multipart when called — user metadata travels with the bytes in one request, no separate PATCH needed. Object names containing / are URL-encoded for the JSON-API path but left literal in V4-signed paths, matching GCS spec.

Cloud CDN

Cache invalidation against a global URL map, plus operation polling.

use arche::gcp::cdn::{get_cdn_client, GcpCdnConfig};

let cdn = get_cdn_client(
    Some(key),
    None,
    GcpCdnConfig::builder()
        .project_id("my-project")
        .url_map("my-lb-url-map") // optional default; pass per-call to override
        .build(),
).await?;

// Invalidate. `path` must start with `/` and may use `*` as a suffix wildcard.
// `host` scopes the invalidation to a hostname routed by the URL map.
let op = cdn.invalidate(None, "/static/*", Some("cdn.example.com")).await?;
// op.name — the operation name; pass it to `invalidation_status` to poll
// op.status — "PENDING" / "RUNNING" / "DONE"
// op.progress — Option<i32>, 0..=100

// Poll until done
let status = cdn.invalidation_status(&op.name).await?;
assert_eq!(status.status, "DONE");

Env Var	Description
`GCP_CDN_PROJECT_ID`	GCP project hosting the URL map (required)
`GCP_CDN_URL_MAP`	Optional default URL map name
`GCP_CDN_BASE_URL`	Override the Compute API endpoint

Scope: global URL maps only — regional URL maps (/regions/{region}/urlMaps/...) are not supported and will return 404.

Google OAuth (Sign in with Google)

Server-side OAuth 2.0 + OpenID Connect: build the authorize URL, exchange the returned code for tokens, verify the issued ID token. JWKS are cached in-memory and key rotation is handled transparently — every algorithm other than RS256 is rejected.

use arche::gcp::oauth::{get_oauth_client, GcpOAuthConfig, Verifier, build_auth_url, exchange_code};

// All three fields fall back to GCP_OAUTH_CLIENT_ID / _CLIENT_SECRET / _REDIRECT_URI.
let oauth = get_oauth_client(
    GcpOAuthConfig::builder()
        .client_id("123.apps.googleusercontent.com")
        .client_secret("secret")
        .redirect_uri("https://app.example/auth/google/callback")
        .build(),
)?;

// 1. Redirect the user to Google's consent screen.
let url = build_auth_url(&oauth, &state, &pkce_challenge);

// 2. On callback, trade `code` for tokens.
let tokens = exchange_code(&oauth, &code, &pkce_verifier).await?;

// 3. Verify the ID token. `audiences` is the allow-list — your client_id(s).
let verifier = Verifier::new()?;
let claims = verifier
    .verify_id_token(&tokens.id_token, &["123.apps.googleusercontent.com"])
    .await?;
println!("verified sub={}", claims.sub);

Env Var	Description
`GCP_OAUTH_CLIENT_ID`	OAuth 2.0 client ID
`GCP_OAUTH_CLIENT_SECRET`	OAuth 2.0 client secret
`GCP_OAUTH_REDIRECT_URI`	Registered redirect URI

Verifier is cheap to construct and Clone — typically held once on AppState. Verification failures (bad signature, wrong audience, expired, unknown kid after a forced refresh) all surface as AppError::Unauthorized. JWKS / token-endpoint outages surface as AppError::DependencyFailed { upstream: "gcp-oauth", … }.

See docs/gcp/oauth.md for the end-to-end flow diagram and the Google Cloud Console setup steps.

Any other GCP REST API

GcpClient works for any Google API that accepts Authorization: Bearer …:

use arche::gcp::GcpClient;

let pubsub = GcpClient::new(
    Some(key),
    None,
    ["https://www.googleapis.com/auth/pubsub"],
).await?;

pubsub
    .post(format!("https://pubsub.googleapis.com/v1/projects/{p}/topics/{t}:publish"))
    .await?
    .json(&payload)
    .send().await?;

For full HTTP control (custom timeouts, TLS config, connection pool), bring your own reqwest::Client:

let http = reqwest::Client::builder()
    .connect_timeout(std::time::Duration::from_secs(5))
    .build()?;

let storage = GcpClient::with_http(
    http,
    Some(key),
    None,
    ["https://www.googleapis.com/auth/devstorage.read_only"],
).await?;

One service account, multiple APIs — share a single token cache:

let drive   = arche::gcp::drive::client(Some(key), None).await?;
let sheets  = drive.with_scopes(["https://www.googleapis.com/auth/spreadsheets"]);
let storage = drive.with_scopes(["https://www.googleapis.com/auth/devstorage.read_only"]);

Vertex AI

VertexClient implements arche::llm::LlmProvider for Gemini and Anthropic Claude models on Google Cloud. The provider (Gemini or Anthropic) is captured at construction; the model is specified per-request.

use arche::gcp::vertex::{get_vertex_client, VertexConfig, VertexProvider};
use arche::gcp::ServiceAccountKey;
use arche::llm::{GenerateRequest, LlmProvider, Message, StreamChunk};

// Gemini via API key (resolved from VERTEX_API_KEY / GEMINI_API_KEY env)
let client = get_vertex_client(VertexProvider::Gemini, None).await?;

// Service-account auth (required for Anthropic, optional for Gemini)
let key = ServiceAccountKey::new(client_email, private_key);
let client = get_vertex_client(
    VertexProvider::Anthropic,
    Some(VertexConfig::default()
        .with_service_account_key(key)
        .with_project_id("my-project")
        .with_region("us-east5")),
).await?;

let request = GenerateRequest::new(
    "gemini-2.0-flash",
    vec![Message::user("Explain quantum computing in one sentence.")],
)
.with_system("You are a helpful assistant.")
.with_max_tokens(256)
.with_temperature(0.7);

// Non-streaming
let response = client.generate(&request).await?;
println!("{}", response.text().unwrap_or_default());

// Streaming
use futures::StreamExt;
let mut stream = client.stream_generate(&request).await?;
while let Some(chunk) = stream.next().await {
    match chunk? {
        StreamChunk::Text(text) => print!("{text}"),
        StreamChunk::ToolCall { name, arguments, .. } => { /* dispatch tool */ }
        StreamChunk::Done { finish_reason, usage } => {
            println!("\n[{finish_reason}] usage={usage:?}");
        }
    }
}

Function calling (typed schemas via arche::llm::ParameterSchema):

use arche::llm::{ParameterSchema, ToolDefinition};

let tools = vec![
    ToolDefinition::new("get_weather", "Get current weather for a city")
        .with_parameters(
            ParameterSchema::object()
                .with_property("city", ParameterSchema::string("City name"))
                .with_required(["city"]),
        ),
];

let request = GenerateRequest::new(
    "gemini-2.0-flash",
    vec![Message::user("What's the weather in Tokyo?")],
)
.with_tools(tools);

Authentication:

Method	When	Source
API Key	Gemini only	`VertexConfig::with_api_key(...)` or `VERTEX_API_KEY` / `GEMINI_API_KEY` env
Service Account	Gemini + Anthropic	`VertexConfig::with_service_account_key(ServiceAccountKey)` or `with_service_account_key_path("/path/to/sa.json")`

If an API key is present, it takes priority. Service account auth is required for Anthropic models. VERTEX_PROJECT_ID / VERTEX_REGION env vars override config; default region is asia-south1. Service-account credentials must be passed via VertexConfig — arche does not auto-resolve GOOGLE_APPLICATION_CREDENTIALS.

Token cache — every GCP REST call goes through a process-local token cache: JWT-bearer flow against oauth2.googleapis.com/token, signed RS256 with the service-account key, retried once on transient failures, refreshed 60 s before expiry, single-flighted per (client_email, scopes) pair.

LLM

Canonical, provider-agnostic types and the LlmProvider trait that every backend implements. Use it directly when you just want to call an LLM; build on top of it when you want tool-calling orchestration (see agent).

use arche::llm::{GenerateRequest, LlmProvider, Message, ParameterSchema, ToolDefinition};

// `client` is anything implementing `LlmProvider` —
// VertexClient, or your own OpenAi/Bedrock/Ollama/local impl.
let request = GenerateRequest::new(
    "gemini-2.0-flash",
    vec![Message::user("Hello!")],
)
.with_system("Be concise.")
.with_temperature(0.3);

let response = client.generate(&request).await?;

Types you'll use:

Type	Purpose
`LlmProvider` (trait)	`generate()` + `stream_generate()` on a canonical `GenerateRequest`. Implement this to add a backend.
`GenerateRequest` / `GenerateResponse`	Canonical request/response, provider-neutral
`Message`, `Role`, `ContentPart`	Conversation turns — text, tool calls, tool results
`StreamChunk`	`Text(String)` \| `ToolCall { id, name, arguments }` \| `Done { finish_reason, usage }`
`ToolDefinition` + `ParameterSchema`	Strictly-typed tool descriptions; serializes to valid JSON Schema
`Usage`	Token accounting (input/output/total)

Writing a custom backend:

use arche::llm::{GenerateRequest, GenerateResponse, LlmProvider, LlmStream};
use arche::error::AppError;
use std::future::Future;
use std::pin::Pin;

pub struct OpenAiClient { /* http client, api key */ }

impl LlmProvider for OpenAiClient {
    fn generate<'a>(&'a self, request: &'a GenerateRequest)
        -> Pin<Box<dyn Future<Output = Result<GenerateResponse, AppError>> + Send + 'a>>
    { Box::pin(async move { /* POST, convert */ todo!() }) }

    fn stream_generate<'a>(&'a self, request: &'a GenerateRequest)
        -> Pin<Box<dyn Future<Output = Result<LlmStream, AppError>> + Send + 'a>>
    { Box::pin(async move { /* POST stream, convert SSE */ todo!() }) }
}

Drops into arche::agent::get_agent_engine(my_client, config) with no other changes.

Agent

Tool-calling agent engine: orchestrates LLM rounds, invokes your tools, streams SSE events to the client, manages session history (with optional compaction).

use arche::agent::{get_agent_engine, AgentConfig, AgentFlow, AgentSession, ToolOutput, to_sse_event};
use arche::gcp::vertex::{get_vertex_client, VertexProvider};
use arche::llm::{ParameterSchema, ToolDefinition};

struct ShoppingFlow;

impl AgentFlow for ShoppingFlow {
    fn system_prompt(&self) -> String {
        "You help shoppers find products.".into()
    }

    fn tool_definitions(&self) -> Vec<ToolDefinition> {
        vec![
            ToolDefinition::new("search_catalog", "Search products by query")
                .with_parameters(
                    ParameterSchema::object()
                        .with_property("query", ParameterSchema::string("Query"))
                        .with_required(["query"]),
                ),
        ]
    }

    fn execute_tool<'a>(
        &'a self,
        name: &'a str,
        args: &'a serde_json::Value,
        _session: &'a AgentSession,
    ) -> std::pin::Pin<Box<dyn std::future::Future<Output = Result<ToolOutput, arche::error::AppError>> + Send + 'a>> {
        Box::pin(async move {
            // Run your business logic, return text for the LLM + optional data for the client
            Ok(ToolOutput::text("Found 3 matches")
                .data("product_list", serde_json::json!([/* ... */])))
        })
    }
}

// Wire it up
let client = get_vertex_client(VertexProvider::Gemini, None).await?;
let config = AgentConfig::builder("gemini-2.0-flash").build()?;
let engine = get_agent_engine(client, config)
    .with_default_summarizer("gemini-2.0-flash-lite"); // optional, cheap summarization

// Per request
let mut session = AgentSession::new("sess-1", "shopping");
let stream = engine.run(&ShoppingFlow, &mut session, "find red shoes");
// Map each SseEvent via `to_sse_event(..)` to an axum SSE Event.

What arche provides vs. what you write:

Arche provides	You write
Orchestration loop, streaming, SSE event types, session mutation, tool-calling loop, history compaction	System prompt, tool schemas, tool executors (`impl AgentFlow`), HTTP handler, session persistence

Extension points:

Need	Plug point
Different LLM backend	`impl LlmProvider for YourClient`
Custom history compaction (vector recall, server-side memory)	`impl HistoryCompactor`
Custom UI events from tools	`ToolOutput::text(..).data(type, payload)` → reaches client via `SseEvent::Data`

Deeper reading:

docs/agent/architecture.md — module layering, component diagram with hover tooltips
docs/agent/sequence.md — request lifecycle, error paths, SSE wire format
docs/agent/extending.md — step-by-step guides for each plug point

Database

Postgres

Connection pooling with sqlx, configurable credentials, and health checks.

use arche::database::pg::{get_pg_pool, test_pg, PgConfigBuilder};

let pool = get_pg_pool(None).await?;
let is_healthy = test_pg(pool.clone()).await?;

Env Var	Description
`PG_HOST`	Database host
`PG_PORT`	Database port
`PG_DATABASE`	Database name
`PG_MAX_CONN`	Maximum pool connections
`PG_USERNAME`	Username
`PG_PASSWORD`	Password
`PG_CREDENTIALS`	JSON string `{"username":"...","password":"..."}` (alternative to separate vars)

Redis

Connection pooling with bb8, optional password auth, and health checks.

use arche::database::redis::{get_redis_pool, test_redis, RedisConfigBuilder};

let pool = get_redis_pool(None).await?;
let is_healthy = test_redis(pool.clone()).await?;

Env Var	Description
`REDIS_HOST`	Redis host
`REDIS_PORT`	Redis port
`REDIS_MAX_CONN`	Maximum pool connections
`REDIS_PASSWORD`	Optional password

ClickHouse

Read-only connection pooling with bb8 (round-robin across replicas) and a typed row API. SQL templates are &'static str — a compile-time check that prevents user input from being concatenated into a query.

use arche::database::clickhouse::{
    get_clickhouse_pool, ClickHousePoolExt, Row, Deserialize,
};

let pool = get_clickhouse_pool(None).await?;
let conn = pool.get_conn().await?;

#[derive(Row, Deserialize)]
struct EventCount { event: String, n: u64 }

let counts: Vec<EventCount> = conn
    .query("SELECT event, count() AS n FROM events WHERE day = ? GROUP BY event")
    .bind("2026-05-25")
    .fetch_all().await?;

Notes:

Bare SELECT * / SELECT t.* are blocked. Call .allow_select_star() on a query, set .allow_select_star(true) on the config, or set CLICKHOUSE_ALLOW_SELECT_STAR=true to bypass.
For runtime-constructed SQL use conn.query_dynamic(string) / conn.execute_dynamic(string) — these accept String and shift injection-safety responsibility to the caller.
Writes go through Kafka → Kafka Connect ClickHouse Sink, not this connector.

Env Var	Description	Default
`CLICKHOUSE_HOSTS`	Comma-separated replica hostnames	— (required)
`CLICKHOUSE_HOST`	Single-host fallback if `CLICKHOUSE_HOSTS` is unset	—
`CLICKHOUSE_PORT`	Server port	8443 (secure) / 8123 (plain)
`CLICKHOUSE_DATABASE`	Default database	`default`
`CLICKHOUSE_USERNAME`	Username	`default`
`CLICKHOUSE_PASSWORD`	Password	(empty)
`CLICKHOUSE_SECURE`	HTTPS toggle	`true`
`CLICKHOUSE_MAX_POOL_SIZE`	Max pool connections	`32`
`CLICKHOUSE_CONNECTION_TIMEOUT_MS`	Pool-acquire timeout	`5000`
`CLICKHOUSE_REQUEST_TIMEOUT_MS`	Per-request `max_execution_time`	`30000`
`CLICKHOUSE_COMPRESSION`	`lz4` or `none`	`none`
`CLICKHOUSE_ALLOW_SELECT_STAR`	Global `SELECT *` escape hatch	`false`

JWT

Token generation and verification using HS256.

use arche::jwt::{generate_tokens, verify_token, generate_expiry_time};
use serde::{Serialize, Deserialize};

#[derive(Serialize, Deserialize)]
struct Claims {
    sub: String,
    exp: usize,
}

// Generate an access + refresh token pair
let tokens = generate_tokens(
    Claims { sub: "user_123".into(), exp: generate_expiry_time(3600) },
    Claims { sub: "user_123".into(), exp: generate_expiry_time(86400) },
    &access_secret,
    &refresh_secret,
)?;

// Verify a token
let data = verify_token::<Claims>(&tokens.access_token, &access_secret, None)?;

CSV

Async CSV processing powered by csv-async. Supports reading from bytes, files, and URLs — with both batch and streaming modes.

use arche::csv::CsvClient;

// Default config (comma-delimited, with headers)
let csv = CsvClient::new();

// Or customize
let csv = CsvClient::new()
    .delimiter(b';')
    .has_headers(true)
    .flexible(true);

Reading

use serde::Deserialize;

#[derive(Deserialize)]
struct Record { name: String, age: u32, city: String }

// From bytes
let records: Vec<Record> = csv.read().from_bytes(data).deserialize().await?;

// From file
let records: Vec<Record> = csv.read().from_file("data.csv").deserialize().await?;

// From URL
let records: Vec<Record> = csv.read().from_url("https://example.com/data.csv")
    .deserialize().await?;

// Batch processing (memory-efficient for large files)
csv.read().from_file("large.csv")
    .deserialize_batched(1000, |batch: Vec<Record>| async move {
        // Process 1000 records at a time
        Ok(())
    }).await?;

Writing

use serde::Serialize;

#[derive(Serialize)]
struct Output { name: String, score: f64 }

let records = vec![
    Output { name: "Alice".into(), score: 95.5 },
    Output { name: "Bob".into(),   score: 87.0 },
];

// To bytes
let bytes: Vec<u8> = csv.write_all(&records).await?;

// To file
csv.write_file("output.csv", &records).await?;

Streaming

// Record-by-record reading
let mut stream = csv.read().from_file("large.csv").stream().await?;
while let Some(record) = stream.next_deserialized::<Record>().await {
    let record = record?;
}

// Record-by-record writing
let mut writer = csv.writer_to_file("output.csv").await?;
writer.serialize(&Output { name: "Alice".into(), score: 95.5 }).await?;
writer.finish().await?;

JSON

Streaming JSON array parsing optimized for large payloads. Extracts metadata fields before the target array and streams array elements one-by-one or in batches — without loading the full document into memory.

use arche::json::JsonClient;
use serde::Deserialize;

#[derive(Deserialize)]
struct Item { id: u64, name: String }

let json = JsonClient::new();

// Stream a root-level JSON array from bytes
let source = json.from_bytes(data);
let mut stream = source.stream_root_array();

while let Some(item) = stream.next::<Item>().await {
    let item = item?;
}

// Stream a nested array with metadata capture
// Given: {"total": 1000, "items": [{...}, {...}, ...]}
let json = JsonClient::new();
let source = json.from_bytes(data);
let mut stream = source.stream_array("items").await;

while let Some(item) = stream.next::<Item>().await {
    let item = item?;
}
let total: u64 = stream.field("total")?;

// Batch iteration
let batch = stream.next_batch::<Item>(100).await;

// Stream directly from S3
let source = JsonClient::new().from_s3(&s3_client, "my-bucket", "data.json").await?;
let mut stream = source.stream_array("results").await;

Crypto

AES-128-CBC encryption with PBKDF2-HMAC-SHA1 key derivation (65,536 iterations).

use arche::crypto::{encrypt_cbc, decrypt_cbc};

let secret = "my-secret-key";
let salt = "my-salt-value-16"; // minimum 16 bytes

// Encrypt — returns raw ciphertext bytes
let ciphertext = encrypt_cbc(secret, salt, "sensitive data")?;

// Decrypt — expects base64-encoded ciphertext input
let plaintext = decrypt_cbc(secret, salt, &base64_ciphertext)?;

Sockets

WebSocket connection registry with broadcast support. Manages a thread-safe map of active connections for fan-out messaging.

use arche::sockets::SocketConnectionManager;

let manager = SocketConnectionManager::new();

// Register a connection (typically in a WebSocket upgrade handler)
manager.add(&connection_id, sender)?;

// Broadcast to all connected clients
manager.broadcast("Hello, everyone!".into())?;

// List active connections
let ids = manager.get_connections()?;

// Remove a connection on disconnect
manager.remove(connection_id)?;

Error

Axum-compatible structured error handling. Every variant converts to a JSON response with the appropriate HTTP status code.

use arche::error::AppError;

async fn handler() -> Result<impl axum::response::IntoResponse, AppError> {
    Err(AppError::Unauthorized)
}

Variants:

Variant	Status	Constructor
`BadRequest`	400	`AppError::bad_request(errors, message, description)`
`Unauthorized`	401	Direct construction
`Forbidden`	403	Direct construction
`NotFound`	404	`AppError::not_found("resource")`
`Conflict`	409	`AppError::conflict("message")`
`UnprocessableEntity`	422	`AppError::unprocessable_entity(errors, message, description)`
`DependencyFailed`	424	`AppError::dependency_failed("upstream", "detail")`
`InternalError`	500	`AppError::internal_error(error, message)`
`Unavailable`	503	Direct construction

InternalError responses are sanitized by default — no leaked SQL or infra details. Enable verbose-errors to expose raw error details (dev/staging only):

arche = { version = "4.7.0", features = ["verbose-errors"] }

Utils

ID generation, date/time conversion traits, and pagination helpers.

Nano IDs

URL-safe, strictly alphanumeric unique IDs (0-9 a-z A-Z — no - or _), so they're safe in subdomains, file names, and anywhere symbol characters cause friction:

use arche::utils::{nano_id, nano_id_of};

// 21 characters — same collision resistance class as a standard nanoid
let id = nano_id();          // e.g. "V1StGXR8Z5jdHi6BmyT9k"

// Custom length
let short = nano_id_of(8);   // e.g. "fX3kQ9aZ"

Date/time & pagination

use arche::utils::{validate_timestamp, FromOffsetDateTime, PaginationParams};
use time::OffsetDateTime;

// Check if a timestamp is in the future
let is_valid = validate_timestamp(timestamp, false)?;

// Convert OffsetDateTime to ISO string
let iso = offset_dt.to_iso_string()?;

// Pagination query params (for Axum extractors)
let params = PaginationParams { page_number: Some(1), page_size: Some(20) };

Re-exported Dependencies

arche re-exports these crates so you don't need to add them separately:

axum · tokio · serde · serde_json · sqlx · time · tracing · tracing-subscriber · reqwest · jsonwebtoken · nanoid · thiserror · base64 · bb8 · bb8-redis · clickhouse (as ch_client) · csv-async · futures · tokio-stream · dotenv · aws-config · aws-sdk-s3 · aws-sdk-sesv2 · aws-sdk-kms · aws-sdk-cloudfront

Design Principles

Explicit over implicit — no hidden global state or magic
Composition over inheritance — thin wrappers you combine as needed
Production-first defaults — sane defaults, sanitized errors, pooled connections
Async-native — built on Tokio from the ground up

What arche is not

A framework that replaces Axum
A code generator or project template
A monolithic abstraction over third-party libraries

License

MIT

arche 4.8.0