passsage 0.2.3

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 with --default-policy)
• Automatic failover: Serve cached content when upstream is unavailable
• Ban management: Temporarily ban unresponsive upstreams to avoid timeouts

Cache hits and misses

Passsage resolves each request to a cache policy, then uses S3 object metadata to decide whether to serve from cache or go upstream. In brief:

• Cache hits are served by rewriting the request to the S3 object (Cache-Status is set to hit and Age is derived from the stored timestamp).
• Optionally, cache hits can be redirected to S3 (to avoid proxying bytes), using --cache-redirect or PASSSAGE_CACHE_REDIRECT=1. Signed URLs are the default for cache redirects and do not require a public bucket policy. Use --cache-redirect-public (or PASSSAGE_CACHE_REDIRECT_SIGNED_URL=0) to redirect to public S3 objects instead.
• When --s3-proxy-url is set (requires --cache-redirect), cache hit redirects point to the given S3 proxy instead of S3 directly. This is useful with a parallelizing proxy such as xs3lerator that fetches objects via multiple concurrent byte-range requests. As of early 2026, a single HTTP stream to S3 within the same region/AZ reaches only ~60 MiB/s (Standard class) or ~150 MiB/s (Express One Zone / directory buckets). A parallelizing proxy can sustain several GiB/s from the same bucket, which matters for large cached objects such as ML model checkpoints, datasets, or container images.
• S3 cache keys use the format <scheme>/<host>/<sha224>[.<ext>] (e.g. https/ftp.bme.hu/a1b2c3d4...56.iso). The original URL is stored in S3 object metadata (x-amz-meta-url). Vary-aware keys append +<sha224-of-vary-values>. Vary index objects live under <scheme>/<host>/_vary/. Keys are POSIX filesystem-safe and bounded at ~340 bytes, so they work both on S3 and on a local mountpoint-s3 mount.
• When --cache-redirect is enabled, clients must be able to fetch cached objects from S3 without AWS credentials. Configure a bucket policy to allow unauthenticated s3:GetObject/s3:ListBucket from your network:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Sid": "vpc_access",
      "Effect": "Allow",
      "Principal": {
        "AWS": "*"
      },
      "Action": [
        "s3:GetObject",
        "s3:ListBucket"
      ],
      "Resource": [
        "arn:aws:s3:::your-bucket/*",
        "arn:aws:s3:::your-bucket"
      ],
      "Condition": {
        "StringEquals": {
          "aws:SourceVpc": [
            "vpc-xxxxxxxx",
            "vpc-yyyyyyyy"
          ]
        }
      }
    },
    {
      "Sid": "ip_access",
      "Effect": "Allow",
      "Principal": {
        "AWS": "*"
      },
      "Action": [
        "s3:GetObject",
        "s3:ListBucket"
      ],
      "Resource": [
        "arn:aws:s3:::your-bucket/*",
        "arn:aws:s3:::your-bucket"
      ],
      "Condition": {
        "IpAddress": {
          "aws:SourceIp": [
            "203.0.113.10/32",
            "198.51.100.42/32"
          ]
        }
      }
    }
  ]
}

• NoRefresh serves from cache immediately on a hit (no revalidation).
• Standard revalidates with an upstream HEAD when stale; if the cached ETag/Last-Modified matches, the cached object is served.
• 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, Passsage fetches from upstream and streams the response to the client. 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.

Example production setup

A typical deployment uses Passsage as the TLS-terminating cache and an S3 parallel proxy (xs3lerator) for fast cache-hit delivery. Example internal DNS: Passsage at proxy-cache.example.internal:3128, xs3lerator at s3-proxy.example.internal:443. Clients point HTTP_PROXY/HTTPS_PROXY at Passsage; Passsage is configured with --cache-redirect and --s3-proxy-url https://s3-proxy.example.internal.

┌──────────────┐     ┌──────────────────────┐     ┌────────────┐
│   Client     │────▶│   Passsage           │────▶│  Upstream  │
│ (pip, curl,  │◀────│   (caching proxy)    │◀────│  Servers   │
│  docker...)  │     │   :3128              │     │ (PyPI etc) │
└──────────────┘     └──────┬──────┬────────┘     └────────────┘
                            │      │
                            │      │  uploads cached objects
                            │      │
                            │      ▼
                            │  ┌──────────┐
                            │  │  AWS S3  │
                            │  │ (cache)  │
                            │  └────┬─────┘
                            │       │
       302 redirect on      │       │  parallel chunked
       cache hit            │       │  downloads
                            │       │
                            ▼       ▼
                     ┌──────────────────────┐
                     │   xs3lerator         │
                     │   (S3 parallel proxy)│
                     │   :443               │
                     └──────────────────────┘
                                ▲
                                │ reads / writes
                                ▼
                     ┌──────────────────────┐
                     │   POSIX filesystem   │
                     │ (local SSD/EBS cache)│
                     └──────────────────────┘

Installation

pip install passsage

For development:

pip install -e ".[dev]"

Usage

Basic Usage

# Run with default settings (uses AWS S3)
passsage

# Run on a specific port (CLI or env var)
PASSSAGE_PORT=9090 passsage
passsage -p 9090

# Bind to a specific interface (CLI or env var)
PASSSAGE_HOST=127.0.0.1 passsage
passsage --bind 127.0.0.1

# Run with web interface
passsage --web

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):

PASSSAGE_PORT=8080 passsage

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

With LocalStack (Local Development)

Start LocalStack:

docker run --rm -p 4566:4566 localstack/localstack

Create and configure the bucket:

# Using awslocal (pip install awscli-local)
awslocal s3 mb s3://proxy-cache
awslocal s3api put-bucket-policy --bucket proxy-cache --policy '{
  "Version": "2012-10-17",
  "Statement": [{
    "Sid": "PublicRead",
    "Effect": "Allow",
    "Principal": "*",
    "Action": ["s3:GetObject", "s3:HeadObject"],
    "Resource": "arn:aws:s3:::proxy-cache/*"
  }]
}'

Run Passsage:

passsage --s3-endpoint http://localhost:4566 --s3-bucket proxy-cache

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	364189071156-ds-proxy-us-west-2 (AWS) or proxy-cache (custom endpoint)
S3_ENDPOINT_URL	Custom S3 endpoint URL	None (uses AWS)
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_S3_PROXY_URL	Redirect cache hits to this S3 proxy URL instead of S3 directly. Requires PASSSAGE_CACHE_REDIRECT=1. The proxy host is automatically added to the no_proxy list.	None
PASSSAGE_NO_REDIRECT_USER_AGENTS	Comma-separated User-Agent prefixes that should not receive cache-hit redirects. Matching clients are served through the proxy instead. Useful for clients like pip that ignore NO_PROXY.	None
PASSSAGE_ACCESS_LOGS	Enable Parquet access logs	0
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	0
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_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

CLI Options

Usage: passsage [OPTIONS]

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
  --s3-endpoint TEXT              S3 endpoint URL for S3-compatible services
  --test                          Run in test mode
  -m, --mode [regular|transparent|wireguard|upstream]
                                  Proxy mode (default: regular)
  -v, --verbose                   Enable verbose logging
  --public-proxy-url TEXT         Externally reachable proxy URL for client onboarding
                                  (env: PASSSAGE_PUBLIC_PROXY_URL)
  --cache-redirect                Redirect cache hits to S3 instead of streaming through the proxy
  --s3-proxy-url TEXT             Redirect cache hits to this S3 proxy URL instead of directly
                                  to S3 (requires --cache-redirect) (env: PASSSAGE_S3_PROXY_URL)
  --access-logs                   Enable S3 access logs in Parquet format
  --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                    Enable S3 error logs in Parquet format
  --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)
  --web                           Enable mitmproxy web interface
  --version                       Show the version and exit.
  --help                          Show this message and exit.

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:

passsage --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:

passsage --error-logs

Error UI:

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

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 LocalStack S3 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
• Passsage proxy on port 8080
• Health endpoint on port 8082 (/health)

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"

Health endpoint

Passsage starts a lightweight HTTP server for health checks on a separate port.

curl -f http://localhost:8082/health

Configure it via environment variables:

export PASSSAGE_HEALTH_PORT=8082
export PASSSAGE_HEALTH_HOST=0.0.0.0

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.

Normalization rules are applied based on the request hostname using a suffix trie for fast matching. The built-in rules cover:

Service / host suffix	Stripped parameters
*.amazonaws.com (S3, CloudFront signed URLs)	All X-Amz-* params (Algorithm, Credential, Date, Expires, Signature, Security-Token, SignedHeaders, …)
*.r2.cloudflarestorage.com (Cloudflare R2)	All X-Amz-* params (R2 uses S3-compatible signing)
*.production.cloudflare.docker.com (Cloudflare Docker registry)	expires, signature, version
*.pkg-containers.githubusercontent.com (GitHub Container Registry blobs)	Azure SAS token params: 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	Simple index pages; stale index is better than a build failure
*.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.*, 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.

No-Redirect User Agents

Some HTTP clients (notably pip) do not honor the NO_PROXY / no_proxy environment variable. When --cache-redirect is enabled, these clients attempt to follow the redirect through the proxy itself, so it's better to serve them through the proxy instead.

The --no-redirect-user-agents option (or PASSSAGE_NO_REDIRECT_USER_AGENTS env var) accepts a comma-separated list of User-Agent prefixes. When a request's User-Agent header starts with any of these prefixes, Passsage serves the cached content through the proxy instead of issuing a redirect.

passsage --cache-redirect --no-redirect-user-agents "pip/"

Or via environment variable:

export PASSSAGE_NO_REDIRECT_USER_AGENTS="pip/,legacy-client/"
passsage --cache-redirect

Note: uv (the fast Python package manager) correctly honors NO_PROXY and does not need this workaround. If possible, prefer uv over pip.

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),
]

License

See LICENSE and NOTICE for copyright and attribution details.

MIT License - see LICENSE for details.