passsage 0.5.1

S3-backed caching proxy for mitmproxy (Pas³age = Passage + S3)

Passsage proxy

Passsage (or Pas³age to emphasize the backend choice) is named for the three S's in S3: it uses Amazon S3 or an S3-compatible object store to persist its cached objects.

A caching HTTP(S) proxy built on mitmproxy that stores responses in S3 storage. Useful for caching package repositories, API responses, and other HTTP traffic for improved performance and offline access.

Mitmproxy is used so Passsage can terminate TLS, inspect HTTP responses, and cache HTTPS content instead of blindly tunneling encrypted bytes. In explicit proxy mode, clients connect to the proxy and issue CONNECT requests for HTTPS; mitmproxy completes the upstream TLS handshake, generates a matching interception certificate signed by its local CA, and then speaks TLS with the client so it can read and cache the HTTP payloads. See https://docs.mitmproxy.org/stable/concepts/how-mitmproxy-works/ for the details.

Features

• S3-backed caching: Store cached responses in AWS S3 or S3-compatible storage (MinIO, LocalStack, etc.)
• Flexible caching policies: Configure how different URLs are cached
  • NoRefresh: Serve from cache without revalidation; fetch on miss
  • Standard: RFC 9111 compliant caching and revalidation
  • StaleIfError: Serve stale cache on upstream failure (4xx/5xx/timeout)
  • AlwaysUpstream: Always fetch from upstream, cache as fallback
  • NoCache: Pass through without caching
  • Default policy when no rule matches: Standard (override via a policy file)
• Automatic failover: Serve cached content when upstream is unavailable
• Presigned URL normalization: Strip ephemeral signing parameters from cache keys so differently-signed requests share a single cache entry

Cache hits and misses

Passsage resolves each request to a cache policy, then uses Elasticsearch metadata and xs3lerator to decide whether to serve from cache or go upstream. In brief:

• GET requests are routed through xs3lerator, which handles parallel downloads from both S3 (cache hits) and upstream HTTP servers (cache misses), and simultaneously uploads data to S3 on miss. Passsage manages metadata only (Elasticsearch indexes, vary indexes).
• HEAD requests are served synthetically from Elasticsearch metadata when fresh, or forwarded to xs3lerator otherwise.
• Object metadata is stored in Elasticsearch (passsage_meta index) for fast real-time lookups by document _id. The data objects themselves are immutable content-addressed chunks in S3.
• Elasticsearch document _id format is <scheme>/<host>/<sha224> (or <scheme>/<host>/<sha224>+<vary_sha224> for vary-aware keys). Vary index documents use <scheme>/<host>/_vary/<sha224>.
• S3 data keys use hash-prefixed format data/<h>/<a>/<s>/<h>/<sha256> for content-addressed chunks.
• NoRefresh serves from cache immediately on a hit (no revalidation).
• Standard revalidates via conditional GET through xs3lerator when stale; if the upstream returns 304, the cached object is served. If the content changed, xs3lerator fetches and caches the new version.
• StaleIfError serves stale cache on upstream failure, and Standard honors stale-if-error / stale-while-revalidate directives when present.
• AlwaysUpstream always fetches from upstream, even if cached.
• NoCache bypasses cache lookup for non-GET/HEAD or policy override.

Standard follows RFC 9111 HTTP caching semantics; stale-if-error and stale-while-revalidate are supported when present.

On cache misses, the response is fetched from upstream and streamed to the client. Data fetching and S3 upload is handled by xs3lerator; Passsage only saves metadata (.meta and vary index). Responses are saved to S3 unless caching is disabled by policy or response headers (Cache-Control: no-store or private, or Vary: *). When Vary is present, cache keys include the Vary request headers so separate variants are stored and served.

Architecture

A typical deployment uses Passsage as the TLS-terminating policy engine with xs3lerator handling all data transfer. On a cache hit, Passsage rewrites the GET request to xs3lerator, which serves the data from S3 using parallel range-GETs. On a cache miss, xs3lerator fetches from the real upstream with adaptive parallel downloads and simultaneously uploads to S3. Clients point HTTP_PROXY/HTTPS_PROXY at Passsage.

┌──────────────┐     ┌──────────────┐     ┌────────────┐
│   Client     │────▶│   Passsage   │────▶│  Upstream   │
│ (pip, curl,  │◀────│ (policy +    │◀────│  Servers    │
│  docker...)  │     │  metadata)   │     │ (PyPI etc)  │
└──────────────┘     └──────┬───────┘     └────────────┘
                            │
                  GET       │   metadata
                  requests  │   read/write
                            ▼
                     ┌──────────────┐        ┌───────────────┐
                     │  xs3lerator  │◀──────▶│    AWS S3     │
                     │ (data plane) │        │   (cache)     │
                     └──────────────┘        └───────────────┘
                                                    ▲
                     ┌──────────────┐               │
                     │Elasticsearch │◀──────────────┘
                     │(passsage_meta│  metadata index
                     │  index)      │
                     └──────────────┘

Both --elasticsearch-url and --xs3lerator-url are required.

Installation

pip install passsage

For development:

pip install -e ".[dev]"

Usage

Basic Usage

# Run with required services (Elasticsearch + xs3lerator must be running)
passsage --elasticsearch-url http://localhost:9200 \
    --xs3lerator-url http://localhost:8888

# Run on a specific port
passsage -p 9090 --elasticsearch-url http://localhost:9200 \
    --xs3lerator-url http://localhost:8888

# Run with web interface
passsage --web --elasticsearch-url http://localhost:9200 \
    --xs3lerator-url http://localhost:8888

The easiest way to get started is with Docker Compose, which starts all required services (see Docker Development).

Client Setup (Certificate + Proxy Env Vars)

Passsage runs on mitmproxy, so clients must trust the mitmproxy CA certificate to avoid TLS errors. Mitmproxy exposes a magic domain, mitm.it, which serves the local certificate authority for download; see https://docs.mitmproxy.org/stable/concepts/certificates/. The examples below assume a localhost proxy; if you deploy Passsage on an intranet host, replace localhost:8080 with the proxy hostname/IP.

1. Start Passsage (example on localhost):

docker compose up --build

2. Run the proxy env script (it embeds the cert, installs it, and exports proxy env vars):

curl -x http://localhost:${PASSSAGE_PORT} http://mitm.it/proxy-env.sh -o /tmp/passsage-proxy-env.sh
. /tmp/passsage-proxy-env.sh

You can also source it in one line:

. <(curl -fsSL -x http://localhost:${PASSSAGE_PORT} http://mitm.it/proxy-env.sh)

It also tries to write ~/.passsage/proxy-env.sh for reuse in other shells.

If the proxy is behind a load balancer or deployed in Kubernetes, the internal listen address (e.g. 0.0.0.0:8080) is not reachable by clients. Set --public-proxy-url to the externally reachable address so the onboarding script exports the correct HTTP_PROXY/HTTPS_PROXY values:

passsage --public-proxy-url http://proxy.example.com:3128

You can also set it via the environment variable:

export PASSSAGE_PUBLIC_PROXY_URL=http://proxy.example.com:3128
passsage

Environment Variables

Variable	Description	Default
PASSSAGE_PORT	Proxy listen port	8080
PASSSAGE_HOST	Proxy bind host	0.0.0.0
S3_BUCKET	S3 bucket name for cache storage	proxy-cache
S3_ENDPOINT_URL	Custom S3 endpoint URL	None (uses AWS)
PASSSAGE_MODE	Proxy mode: regular, transparent, wireguard, or upstream	regular
PASSSAGE_PUBLIC_PROXY_URL	Externally reachable proxy URL for the onboarding script (e.g. http://proxy.example.com:3128). Required behind a load balancer or in Kubernetes.	None
PASSSAGE_NO_PROXY_EXTRA	Extra comma-separated hosts to add to NO_PROXY in the onboarding script	None
PASSSAGE_ELASTICSEARCH_URL	Elasticsearch URL for metadata storage (required)	(required)
PASSSAGE_ELASTICSEARCH_META_INDEX	Elasticsearch index for metadata	passsage_meta
PASSSAGE_ELASTICSEARCH_REPLICAS	Number of ES index replicas	1
PASSSAGE_ELASTICSEARCH_SHARDS	Number of ES index shards	9
PASSSAGE_ELASTICSEARCH_FLUSH_INTERVAL	Interval for batched last_access updates (seconds)	30
PASSSAGE_XS3LERATOR_URL	xs3lerator base URL (required). All GET requests are routed through xs3lerator for parallel downloads and S3 caching.	(required)
PASSSAGE_ACCESS_LOGS	Enable Parquet access logs	1 (enabled)
PASSSAGE_ACCESS_LOG_PREFIX	S3 prefix for access logs	__passsage_logs__
PASSSAGE_ACCESS_LOG_DIR	Local spool dir for access logs	/tmp/passsage-logs
PASSSAGE_ACCESS_LOG_FLUSH_SECONDS	Flush interval in seconds	30
PASSSAGE_ACCESS_LOG_FLUSH_BYTES	Flush size threshold	1G
PASSSAGE_ACCESS_LOG_HEADERS	Headers to include in access logs	accept,accept-encoding,cache-control,content-type,content-encoding,etag,last-modified,range,user-agent,via,x-cache,x-cache-lookup,x-amz-request-id
PASSSAGE_ERROR_LOGS	Enable Parquet error logs	1 (enabled)
PASSSAGE_ERROR_LOG_PREFIX	S3 prefix for error logs	__passsage_error_logs__
PASSSAGE_ERROR_LOG_DIR	Local spool dir for error logs	/tmp/passsage-errors
PASSSAGE_ERROR_LOG_FLUSH_SECONDS	Flush interval in seconds	30
PASSSAGE_ERROR_LOG_FLUSH_BYTES	Flush size threshold	256M
PASSSAGE_CONNECTION_STRATEGY	Mitmproxy connection strategy: lazy (default) or eager	lazy
PASSSAGE_MITM_CA_CERT	mitmproxy CA certificate (PEM file path or inline PEM). Written to ~/.mitmproxy/mitmproxy-ca-cert.pem before startup.	None
PASSSAGE_MITM_CA	mitmproxy CA key+cert bundle (PEM file path or inline PEM). Written to ~/.mitmproxy/mitmproxy-ca.pem before startup.	None
PASSSAGE_VERBOSE	Enable verbose logging	0
PASSSAGE_DEBUG	Enable debug logging for proxy internals	0
PASSSAGE_DEBUG_PROXY	Enable debug logging for passsage proxy only	0
PASSSAGE_WEB	Enable mitmproxy web interface	0
PASSSAGE_POLICY_FILE	Path to Python file defining policy overrides	None
PASSSAGE_ALLOW_POLICY_HEADER	Allow client policy override via X-Passsage-Policy header	0
PASSSAGE_S3_HASH_PREFIX_DEPTH	Number of hash characters to use as S3 path prefix segments (e.g. 4 produces f/f/3/0/hash...). Distributes objects across prefixes to avoid S3 throttling.	4

CLI Options

Usage: passsage [OPTIONS] COMMAND [ARGS]...

  Passsage (Pas³age) - S3-backed caching proxy.

Options:
  -p, --port INTEGER              Port to listen on (env: PASSSAGE_PORT, default: 8080)
  -b, --bind TEXT                 Address to bind to (env: PASSSAGE_HOST, default: 0.0.0.0)
  --s3-bucket TEXT                S3 bucket for cache storage (env: S3_BUCKET)
  --s3-endpoint TEXT              S3 endpoint URL for S3-compatible services (env: S3_ENDPOINT_URL)
  -m, --mode [regular|transparent|wireguard|upstream]
                                  Proxy mode (env: PASSSAGE_MODE, default: regular)
  -v, --verbose                   Enable verbose logging (env: PASSSAGE_VERBOSE)
  --debug                         Enable debug logging for proxy internals (env: PASSSAGE_DEBUG)
  --debug-proxy                   Enable debug logging for passsage proxy only
                                  (env: PASSSAGE_DEBUG_PROXY)
  --web                           Enable mitmproxy web interface (env: PASSSAGE_WEB)
  --policy-file TEXT              Path to Python file defining policy overrides
                                  (env: PASSSAGE_POLICY_FILE)
  --allow-policy-header           Allow client policy override via X-Passsage-Policy
                                  (env: PASSSAGE_ALLOW_POLICY_HEADER)
  --public-proxy-url TEXT         Public proxy URL embedded in mitm.it/proxy-env responses
                                  (env: PASSSAGE_PUBLIC_PROXY_URL)
  --no-proxy-extra TEXT           Extra comma-separated hosts to add to NO_PROXY in
                                  mitm.it/proxy-env responses (env: PASSSAGE_NO_PROXY_EXTRA)
  --access-logs / --no-access-logs
                                  Enable S3 access logs in Parquet format (default: enabled)
                                  (env: PASSSAGE_ACCESS_LOGS)
  --access-log-prefix TEXT        S3 prefix for access logs (env: PASSSAGE_ACCESS_LOG_PREFIX)
  --access-log-dir TEXT           Local spool directory for access logs
  --access-log-flush-seconds TEXT Flush interval in seconds for access logs
  --access-log-flush-bytes TEXT   Flush size threshold for access logs
  --access-log-headers TEXT       Headers to include in access logs
  --error-logs / --no-error-logs  Enable S3 error logs in Parquet format (default: enabled)
                                  (env: PASSSAGE_ERROR_LOGS)
  --error-log-prefix TEXT         S3 prefix for error logs (env: PASSSAGE_ERROR_LOG_PREFIX)
  --error-log-dir TEXT            Local spool directory for error logs
  --error-log-flush-seconds TEXT  Flush interval in seconds for error logs
  --error-log-flush-bytes TEXT    Flush size threshold for error logs
  --health-port INTEGER           Health endpoint port (env: PASSSAGE_HEALTH_PORT, 0 disables)
  --health-host TEXT              Health endpoint bind host (env: PASSSAGE_HEALTH_HOST)
  --connection-strategy [lazy|eager]
                                  Upstream TLS connection strategy (default: lazy)
  --mitm-ca-cert TEXT             mitmproxy CA certificate (PEM path or inline)
                                  (env: PASSSAGE_MITM_CA_CERT)
  --mitm-ca TEXT                  mitmproxy CA key+cert bundle (PEM path or inline)
                                  (env: PASSSAGE_MITM_CA)
  --elasticsearch-url TEXT        Elasticsearch URL for metadata (required)
                                  (env: PASSSAGE_ELASTICSEARCH_URL)
  --elasticsearch-meta-index TEXT ES index name (default: passsage_meta)
                                  (env: PASSSAGE_ELASTICSEARCH_META_INDEX)
  --elasticsearch-replicas INT    Number of ES replicas (default: 1)
                                  (env: PASSSAGE_ELASTICSEARCH_REPLICAS)
  --elasticsearch-shards INT      Number of ES shards (default: 9)
                                  (env: PASSSAGE_ELASTICSEARCH_SHARDS)
  --elasticsearch-flush-interval FLOAT
                                  Batch flush interval seconds (default: 30)
                                  (env: PASSSAGE_ELASTICSEARCH_FLUSH_INTERVAL)
  --xs3lerator-url TEXT           xs3lerator base URL (required). All GET requests are routed
                                  through xs3lerator for parallel downloads and S3 caching.
                                  (env: PASSSAGE_XS3LERATOR_URL)
  --s3-hash-prefix-depth INT      Hash prefix depth for S3 key partitioning (default: 4)
                                  (env: PASSSAGE_S3_HASH_PREFIX_DEPTH)
  --version                       Show the version and exit.
  --help                          Show this message and exit.

Commands:
  cache-keys  Detect query parameters that fragment the cache.
  errors      Browse or export error logs.
  logs        Browse or export access logs.

Access Logs

Passsage can emit structured access logs to S3 as Parquet for diagnostics and performance analysis.

S3 layout:

s3://<bucket>/__passsage_logs__/date=YYYY-MM-DD/hour=HH/<file>.parquet

Enable logging:

# Access and error logs are enabled by default. To disable:
passsage --no-access-logs

Log UI:

pip install "passsage[ui]"
passsage logs --start-date 2026-02-01 --end-date 2026-02-02

Error Logs

S3 layout:

s3://<bucket>/__passsage_error_logs__/date=YYYY-MM-DD/hour=HH/<file>.parquet

Enable error logging:

# Error logs are enabled by default. To disable:
passsage --no-error-logs

Error UI:

pip install "passsage[ui]"
passsage errors --start-date 2026-02-01 --end-date 2026-02-02

Cache Key Analysis

The cache-keys subcommand scans access logs for query parameters that fragment the cache and cause unnecessary misses. It identifies parameters with many distinct values appearing across multiple URL paths — strong candidates for cache key stripping (e.g. tracking IDs, session tokens, cache-busters).

pip install "passsage[ui]"

# Analyze today's logs
passsage cache-keys --s3-bucket my-proxy-cache

# Analyze a date range with stricter thresholds
passsage cache-keys --start-date 2026-02-01 --end-date 2026-02-10 \
    --min-distinct 50 --min-misses 500

Health and Debug Endpoints

Passsage starts a lightweight HTTP server for health checks and diagnostics on a separate port (default 8082).

Endpoint	Description
/health	S3 bucket connectivity check. Returns 200 if healthy, 503 otherwise.
/debug/threads	Dumps all Python thread tracebacks.
/debug/connections	Dumps TCP connections from /proc/net/tcp.
/debug/memory	GC object type profiling and RSS info. Append ?tracemalloc for a tracemalloc snapshot.

curl -f http://localhost:8082/health
curl http://localhost:8082/debug/threads
curl http://localhost:8082/debug/memory

Configure via environment variables:

export PASSSAGE_HEALTH_PORT=8082   # set to 0 to disable
export PASSSAGE_HEALTH_HOST=0.0.0.0

As a mitmproxy Script

You can also use Passsage directly as a mitmproxy script:

mitmproxy -s $(python -c "import passsage; print(passsage.get_proxy_path())")

Docker Development

The easiest way to develop and test Passsage is with Docker Compose, which sets up all required services automatically.

Quick Start

# Production-like setup
docker compose up --build

# Development setup (with live code editing; mitmproxy reloads proxy on change)
docker compose -f docker-compose.yml -f docker-compose.dev.yml up --build

This starts:

• LocalStack S3 on port 4566 with pre-configured proxy-cache bucket
• Elasticsearch on port 9200 (single-node, metadata storage)
• xs3lerator on port 8888 (data plane: parallel downloads + S3 caching)
• Passsage proxy on port 8080, health endpoint on port 8082

Development Workflow

1. Start dev environment: docker compose -f docker-compose.yml -f docker-compose.dev.yml up --build
2. Edit code in src/passsage/; mitmproxy reloads the proxy on change

See DEVELOPMENT.md for the full guide.

Building and Publishing

Build the Package

pip install build
python -m build

This creates dist/passsage-*.whl and dist/passsage-*.tar.gz.

Publish to PyPI

pip install twine

# Upload to Test PyPI first
twine upload --repository testpypi dist/*

# Upload to PyPI
twine upload dist/*

Publish to Private PyPI (CodeArtifact, etc.)

# Configure your repository in ~/.pypirc or use environment variables
twine upload --repository your-repo dist/*

Development

# Install with dev dependencies
pip install -e ".[dev]"

# Run tests
pytest

# Run linter
ruff check src/

# Format code
ruff format src/

Integration tests with Docker Compose

The integration suite expects a running proxy that allows X-Passsage-Policy overrides. Start Passsage with --allow-policy-header or set PASSSAGE_ALLOW_POLICY_HEADER=1.

# Default port 8080 and health port 8082
PASSSAGE_ALLOW_POLICY_HEADER=1 docker compose up --build

# Override the host port mappings
PROXY_PORT=9090 HEALTH_PORT=9092 PASSSAGE_ALLOW_POLICY_HEADER=1 docker compose up --build

When the proxy runs in a container, the test server must be reachable by Passsage. On Linux, set the bind host and public host so the proxy can reach the test server:

export PASSSAGE_TEST_SERVER_BIND_HOST=0.0.0.0
export PASSSAGE_TEST_SERVER_HOST=host.docker.internal
export PROXY_URL=http://localhost:9090
pytest -m "not slow"

Content Delivery Services

Passsage ships with built-in handling for common content delivery and object storage services. Two mechanisms work together to make caching effective: URL normalization removes ephemeral query parameters so that different signed URLs for the same object produce a single cache entry, and default caching policies assign a sensible policy to well-known hosts.

Presigned URL normalization

Object storage services authenticate access through presigned URLs — URLs that embed short-lived credentials, timestamps, and signatures as query parameters. Each request for the same object carries a different set of parameters, which would produce a unique cache key and defeat caching entirely.

Passsage normalizes presigned URLs by stripping the signature-related query parameters before computing the cache key. The original URL (with all parameters intact) is still used when talking to the upstream server, so authentication continues to work. Only the cache key sees the stripped version.

Signing parameters are stripped from all URLs regardless of host, since the parameter names are unambiguous credentials/signatures:

Signing scheme	Stripped parameters
AWS Signature V4 (S3, R2, HuggingFace xethub, etc.)	All X-Amz-* params (Algorithm, Credential, Date, Expires, Signature, Security-Token, SignedHeaders, ...)
AWS CloudFront signed URLs	Expires, Policy, Signature, Key-Pair-Id
Azure SAS tokens (GitHub Container Registry, Azure Blob, etc.)	se, sig, sp, spr, sr, sv, ske, skoid, sks, skt, sktid, skv, hmac

After stripping, any remaining query parameters are sorted by key to avoid cache misses from different parameter orderings.

Why this matters for CI/CD pipelines: build jobs typically depend on artifacts hosted on these services — container base images, Python packages, Debian packages, pre-built binaries. During high-load periods (e.g. security patch rollouts, popular release days), upstream registries can become slow or return transient errors. Because Passsage collapses all presigned variants of the same object into one cache entry, a single successful fetch serves every subsequent build. Combined with the StaleIfError policy, pipelines keep running from cache even while the upstream is struggling.

Default caching policies

Passsage assigns caching policies to known hosts and URL patterns out of the box. These defaults can be overridden with a policy file (see Policy Overrides below).

Pattern	Policy	Rationale
*.files.pythonhosted.org	StaleIfError	PyPI package files are immutable once published
pypi.org/simple/*	StaleIfError + forced SWR (24h)	Simple index pages; stale index is better than a build failure. Background revalidation keeps the index fresh without blocking requests.
*.deb, /Packages, /Packages.gz, /Packages.xz, /InRelease, APT by-hash paths	StaleIfError	Debian/Ubuntu repository metadata and packages
mran.microsoft.com/snapshot/*	StaleIfError	MRAN R package snapshots
*.amazonaws.com (except CodeArtifact)	NoCache	S3 API calls, STS tokens — must not be cached
Cloud metadata endpoints (169.254.169.*, 169.254.170.*, 100.100.100.*, Azure/GCP metadata)	NoCache	Instance metadata must always be live
/mitm.it/*	NoCache	mitmproxy's own certificate distribution page

Extending normalization rules

Add custom cache key rules via a policy file (the same file used for policy overrides):

# /path/to/policies.py
from passsage.cache_key import CallableRule

def strip_my_cdn_token(ctx):
    if ctx.host and "cdn.example.com" in ctx.host:
        return ctx.url.split("?", 1)[0]
    return None

def get_cache_key_rules():
    return [CallableRule(strip_my_cdn_token)]

Export one of get_cache_key_rules(), CACHE_KEY_RULES, get_cache_key_resolver(), or CACHE_KEY_RESOLVER from the file. See default_cache_keys.py for the full built-in implementation.

Important: Do Not Use S3 Object Expiration

Never enable S3 lifecycle expiration rules on the whole cache bucket (you can expire the logs though). Passsage stores each cached response as an S3 object with associated metadata: a vary index object (_vary/ prefix). S3 lifecycle rules delete objects independently — an expiration rule could remove the vary index but leave the content object (or vice versa). This leads to cache corruption: stale metadata pointing to missing content, or orphaned content with no metadata.

If you need to control cache size, use a cleanup script that deletes all related objects atomically (content + vary index), or use S3 Intelligent-Tiering to move cold objects to cheaper storage without deleting them.

Policy Overrides

You can override caching policies by pointing Passsage at a Python file. The file can define a RULES list, a get_rules() function, or a get_resolver() function. These are evaluated in this order:

1. get_resolver() -> return a PolicyResolver
2. get_rules() -> return a list of rules
3. RULES -> a list of rules

The file is loaded at runtime and does not need to be installed as a package.

Header-based policy override (client-side)

You can force a policy per request by sending the X-Passsage-Policy header. This override is disabled by default and must be enabled on the proxy.

passsage --allow-policy-header

curl -x http://localhost:8080 \
  -H "X-Passsage-Policy: NoRefresh" \
  http://example.com/data.csv

Supported values: NoRefresh, Standard, StaleIfError, AlwaysUpstream, NoCache.

Security note: this allows clients to bypass normal policy rules. A malicious or misconfigured client could force caching of sensitive responses or disable caching to increase upstream load. Only expose the proxy to trusted clients if you rely on header overrides.

Use a custom policy file

passsage --policy-file /path/to/policies.py

You can also set the environment variable:

export PASSSAGE_POLICY_FILE=/path/to/policies.py
passsage

Example: simple rules list

# /path/to/policies.py
from passsage.policy import NoCache, NoRefresh, PathContainsRule, RegexRule

RULES = [
    PathContainsRule("/assets/", NoRefresh),
    RegexRule(r".*\\.csv$", NoRefresh),
    PathContainsRule("/api/private", NoCache),
]

Example: programmatic rules with defaults

# /path/to/policies.py
from passsage.default_policies import default_rules
from passsage.policy import AlwaysUpstream, PathContainsRule

def get_rules():
    rules = default_rules()
    rules.insert(0, PathContainsRule("/debug/", AlwaysUpstream))
    return rules

Example: full resolver with custom default policy

# /path/to/policies.py
from passsage.default_policies import default_rules
from passsage.policy import PolicyResolver, Standard

def get_resolver():
    return PolicyResolver(rules=default_rules(), default_policy=Standard)

Example: dynamic rule based on headers

# /path/to/policies.py
from passsage.policy import CallableRule, Context, NoCache, NoRefresh

def choose_policy(ctx: Context):
    for key, value in (ctx.headers or []):
        if key.lower() == "x-no-cache" and value == "1":
            return NoCache
    return NoRefresh

RULES = [
    CallableRule(choose_policy),
]

Upstream Timeout Overrides

When Passsage is deployed with xs3lerator, you can configure per-rule upstream timeouts. These override xs3lerator's server-wide defaults (--upstream-connect-timeout and --upstream-read-timeout) on a per-request basis.

xs3lerator defaults to a 30 s connect timeout and a 300 s (5 min) read timeout, matching common HTTP clients like pip and curl. Rules can tighten or relax these as needed.

Timeouts are specified with TimeoutConfig and attached to any rule type via the timeouts keyword argument:

# /path/to/policies.py
from passsage.default_policies import default_rules
from passsage.policy import (
    HostContainsRule,
    PolicyResolver,
    StaleIfError,
    Standard,
    SuffixRule,
    TimeoutConfig,
)

def get_rules():
    rules = default_rules()

    # Large ML model files: allow up to 15 min read timeout
    rules.insert(0, SuffixRule(
        ".safetensors",
        StaleIfError,
        timeouts=TimeoutConfig(read_timeout=900),
    ))

    # Slow internal registry: longer connect + read timeouts
    rules.insert(0, HostContainsRule(
        "registry.internal.example.com",
        StaleIfError,
        timeouts=TimeoutConfig(connect_timeout=60, read_timeout=600),
    ))

    # Fast API that should fail quickly
    rules.insert(0, HostContainsRule(
        "api.example.com",
        Standard,
        timeouts=TimeoutConfig(connect_timeout=5, read_timeout=30),
    ))

    return rules

TimeoutConfig fields:

Field	Type	Meaning
connect_timeout	float | None	TCP/TLS handshake timeout in seconds. None = use xs3lerator default (30 s).
read_timeout	float | None	Idle time between data chunks in seconds. None = use xs3lerator default (300 s). 0 = no timeout.

Under the hood, Passsage sends X-Xs3lerator-Connect-Timeout and X-Xs3lerator-Read-Timeout headers on the rewritten request. xs3lerator creates (or reuses) an HTTP client configured with those timeouts. The headers are stripped from client responses.

License

See LICENSE and NOTICE for copyright and attribution details.

MIT License - see LICENSE for details.