Kasper

HTTP toolkit for Go. Drop-in gorilla/mux replacement with WebSocket, OpenAPI, and middleware support. Inspired by FastAPI.

go get github.com/vitalvas/kasper

Requires Go 1.25+.

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mux github.com/vitalvas/kasper/mux

HTTP request multiplexer. API-compatible with gorilla/mux.

Feature	Details
Path variables	Regex constraints and macros: uuid, int, float, slug, alpha, alphanum, date, hex, domain
Matchers	Host, method, header, query, scheme, custom MatcherFunc
Routing	Subrouters, middleware, named routes, URL building
Request/Response	BindJSON, BindXML, ResponseJSON, ResponseXML
Standards	Strict slash (RFC 7538), path cleaning (RFC 3986), route walking

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websocket github.com/vitalvas/kasper/websocket

RFC 6455 / RFC 8441 WebSocket implementation.

Feature	Details
Connections	Client (Dialer) and server (Upgrader)
Messaging	Text/binary, streaming (NextReader/NextWriter), JSON helpers
Control	Ping, pong, close frames, subprotocol negotiation
Compression	permessage-deflate (RFC 7692), stateless
Performance	PreparedMessage for broadcasting, BufferPool for buffer reuse
Network	Proxy support (HTTP CONNECT)

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openapi github.com/vitalvas/kasper/openapi

Automatic OpenAPI v3.1.0 spec generation from mux routes via reflection and struct tags.

Feature	Details
Schema	JSON Schema Draft 2020-12, struct tags (openapi:"format=email,minLength=1"), Namer/Exampler interfaces
Routes	Named routes (Op), direct attachment (Route), groups for shared metadata
Security	Basic, bearer, OAuth2, API key schemes
Content	Webhooks, callbacks, multiple content types, generic type support
Docs UI	Swagger UI, RapiDoc, Redoc
Export	doc.JSON(), doc.YAML(), JSON/YAML schema endpoints
Parsing	DocumentFromJSON, DocumentFromYAML
Merge	MergeDocuments combines multiple specs with conflict detection
Standalone	SchemaGenerator.Document produces a spec without a mux router

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httpsig github.com/vitalvas/kasper/httpsig

HTTP Message Signatures (RFC 9421) with optional Content-Digest (RFC 9530).

Feature	Standard	Details
Signing	RFC 9421	SignRequest adds Signature and Signature-Input headers
Verification	RFC 9421	VerifyRequest with key resolver, max age, required components
Client Transport	RFC 9421	http.RoundTripper for automatic request signing
Server Middleware	RFC 9421	mux.MiddlewareFunc for automatic request verification
Content-Digest	RFC 9530	SHA-256/SHA-512 body digest generation and verification
Algorithms	RFC 9421	Ed25519, ECDSA P-256/P-384, RSA-PSS, RSA v1.5, HMAC-SHA256

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muxhandlers github.com/vitalvas/kasper/muxhandlers

HTTP middleware for the mux router.

Middleware	Standard	Details
CORSMiddleware	Fetch Standard	Origin validation, preflight, wildcard/subdomain patterns
BasicAuthMiddleware	RFC 7617	Static or dynamic credentials, constant-time comparison
ProxyHeadersMiddleware	RFC 7239	X-Forwarded-For/Proto/Host, Forwarded header, trusted proxy validation
RecoveryMiddleware	--	Panic recovery, 500 response, optional log callback
RequestIDMiddleware	RFC 9562	UUID v4/v7 generation/propagation via X-Request-ID header
RequestSizeLimitMiddleware	--	Body size enforcement via http.MaxBytesReader, 413 on excess
TimeoutMiddleware	--	Handler execution time limit via http.TimeoutHandler, 503 on timeout
CompressionMiddleware	--	Gzip/deflate response compression with sync.Pool, quality-based encoding selection, min-length threshold
SecurityHeadersMiddleware	--	X-Content-Type-Options, X-Frame-Options, Referrer-Policy, HSTS, CSP, Permissions-Policy
MethodOverrideMiddleware	--	HTTP method override via configurable header, POST-only, allowed method validation
ContentTypeCheckMiddleware	--	Content-Type validation with case-insensitive matching, parameter-ignoring, 415 on mismatch
ServerMiddleware	--	Sets X-Server-Hostname response header, resolved once via os.Hostname or static value
CacheControlMiddleware	--	Sets Cache-Control and Expires response headers based on Content-Type prefix rules, case-insensitive matching
StaticFilesHandler	--	Serves static files from any fs.FS via http.FileServerFS, directory listing disabled by default, SPA fallback support