CodeSampleX

Sample

go.step.sm/crypto v0.89.0: tlsutil

Verified sample for golang go.step.sm/crypto v0.89.0: tlsutil. The contract ran on go 1.26 · linux debian/x64 · docker and passed.

sha256:ffe14b0a04e1fd807d2503cc36ce9255e6b870eff9bd105fd01623d7bbf8dcb8

This network offers one thing: a sample that builds. It ran the sample in a sandbox and kept the signed receipt. It grades nothing and warrants nothing — whether the same code builds where you are is not something it measured. How many distinct signing keys filed a passing contract receipt. One is the author alone; more than one means somebody else built it too. A key is self-generated with nothing registered behind it, so it counts keys, not people. MIT-0

Execution evidence

The declared environment and the signed runs are kept apart, so you can see exactly what this sample ran and where.

Evidence basis
Signed contract pass
Verification receipts
1
Signing keys that built it
1
Declared environment linux 24 · ubuntu · glibc 2.39 x64 go

Verification-run environments

Environment Contract Stages Run
go 1.26 · linux debian/x64 · docker ed25519:c1973797be207ac4 PASS compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS
CONTAINER_RUN · golang@1golang:1.26@sha256:e30143be198a…		 2026-09-02

Case

HOW
Goal
verify go.step.sm/crypto/tlsutil in pkg:golang/go.step.sm/crypto@v0.89.0
Packages
Symbols
  • go.step.sm/crypto/tlsutil
Created
2026-09-02T22:42:49Z

Contract

  1. tlsutil.SanitizeName converts domain names to ASCII punycode and rejects invalid or empty domains
  2. tlsutil.SanitizeHost sanitizes host strings with optional port suffix and delegates hostname sanitization
  3. tlsutil.NewRenewer manages TLS certificates and config lifecycle
  4. tlsutil.NewServerCredentials dynamically provisions certificates per SNI

Files

  • PROMPT.md
  • csx.json
  • go.mod
  • go.sum
  • spec.json
  • test/contract.go
  • tlsutil.go

Download the source artifact (tar.gz)

Source

PROMPT.md
Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: verify go.step.sm/crypto/tlsutil in pkg:golang/go.step.sm/crypto@v0.89.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/go.step.sm/crypto@v0.89.0
Demonstrate these symbols/APIs:
  - go.step.sm/crypto/tlsutil

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.
csx.json
{"case":{"caseId":"case:sha256:bd72427fdf168fe653685b3e017ef3bdb609fa6b6f659f9a14f8ffe176b84a0f","contract":["tlsutil.SanitizeName converts domain names to ASCII punycode and rejects invalid or empty domains","tlsutil.SanitizeHost sanitizes host strings with optional port suffix and delegates hostname sanitization","tlsutil.NewRenewer manages TLS certificates and config lifecycle","tlsutil.NewServerCredentials dynamically provisions certificates per SNI"],"goal":"verify go.step.sm/crypto/tlsutil in pkg:golang/go.step.sm/crypto@v0.89.0","kind":"HOW","packages":["pkg:golang/go.step.sm/crypto@v0.89.0"],"schemaVersion":1,"symbols":["go.step.sm/crypto/tlsutil"]},"contractCommand":["go","run","./test"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"go","schemaVersion":1},"license":"MIT-0","packages":["pkg:golang/go.step.sm/crypto@v0.89.0"],"schemaVersion":1,"subject":"pkg:golang/go.step.sm/crypto@v0.89.0","symbols":["go.step.sm/crypto/tlsutil"],"verifierAdapter":"golang@1"}
go.mod
module example.com/tlsutil-sample

go 1.26.6

require go.step.sm/crypto v0.89.0

require (
	dario.cat/mergo v1.0.1 // indirect
	filippo.io/edwards25519 v1.2.0 // indirect
	github.com/Masterminds/goutils v1.1.1 // indirect
	github.com/Masterminds/semver/v3 v3.3.0 // indirect
	github.com/Masterminds/sprig/v3 v3.3.0 // indirect
	github.com/go-jose/go-jose/v3 v3.0.5 // indirect
	github.com/google/uuid v1.6.0 // indirect
	github.com/huandu/xstrings v1.5.0 // indirect
	github.com/mitchellh/copystructure v1.2.0 // indirect
	github.com/mitchellh/reflectwalk v1.0.2 // indirect
	github.com/pkg/errors v0.9.1 // indirect
	github.com/shopspring/decimal v1.4.0 // indirect
	github.com/spf13/cast v1.7.0 // indirect
	golang.org/x/crypto v0.54.0 // indirect
	golang.org/x/net v0.57.0 // indirect
	golang.org/x/sys v0.47.0 // indirect
	golang.org/x/text v0.40.0 // indirect
)
go.sum
dario.cat/mergo v1.0.1 h1:Ra4+bf83h2ztPIQYNP99R6m+Y7KfnARDfID+a+vLl4s=
dario.cat/mergo v1.0.1/go.mod h1:uNxQE+84aUszobStD9th8a29P2fMDhsBdgRYvZOxGmk=
filippo.io/edwards25519 v1.2.0 h1:crnVqOiS4jqYleHd9vaKZ+HKtHfllngJIiOpNpoJsjo=
filippo.io/edwards25519 v1.2.0/go.mod h1:xzAOLCNug/yB62zG1bQ8uziwrIqIuxhctzJT18Q77mc=
github.com/Masterminds/goutils v1.1.1 h1:5nUrii3FMTL5diU80unEVvNevw1nH4+ZV4DSLVJLSYI=
github.com/Masterminds/goutils v1.1.1/go.mod h1:8cTjp+g8YejhMuvIA5y2vz3BpJxksy863GQaJW2MFNU=
github.com/Masterminds/semver/v3 v3.3.0 h1:B8LGeaivUe71a5qox1ICM/JLl0NqZSW5CHyL+hmvYS0=
github.com/Masterminds/semver/v3 v3.3.0/go.mod h1:4V+yj/TJE1HU9XfppCwVMZq3I84lprf4nC11bSS5beM=
github.com/Masterminds/sprig/v3 v3.3.0 h1:mQh0Yrg1XPo6vjYXgtf5OtijNAKJRNcTdOOGZe3tPhs=
github.com/Masterminds/sprig/v3 v3.3.0/go.mod h1:Zy1iXRYNqNLUolqCpL4uhk6SHUMAOSCzdgBfDb35Lz0=
github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc h1:U9qPSI2PIWSS1VwoXQT9A3Wy9MM3WgvqSxFWenqJduM=
github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
github.com/frankban/quicktest v1.14.6 h1:7Xjx+VpznH+oBnejlPUj8oUpdxnVs4f8XU8WnHkI4W8=
github.com/frankban/quicktest v1.14.6/go.mod h1:4ptaffx2x8+WTWXmUCuVU6aPUX1/Mz7zb5vbUoiM6w0=
github.com/go-jose/go-jose/v3 v3.0.5 h1:BLLJWbC4nMZOfuPVxoZIxeYsn6Nl2r1fITaJ78UQlVQ=
github.com/go-jose/go-jose/v3 v3.0.5/go.mod h1:5b+7YgP7ZICgJDBdfjZaIt+H/9L9T/YQrVfLAMboGkQ=
github.com/google/go-cmp v0.5.9/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
github.com/google/uuid v1.6.0 h1:NIvaJDMOsjHA8n1jAhLSgzrAzy1Hgr+hNrb57e+94F0=
github.com/google/uuid v1.6.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
github.com/huandu/xstrings v1.5.0 h1:2ag3IFq9ZDANvthTwTiqSSZLjDc+BedvHPAp5tJy2TI=
github.com/huandu/xstrings v1.5.0/go.mod h1:y5/lhBue+AyNmUVz9RLU9xbLR0o4KIIExikq4ovT0aE=
github.com/kr/pretty v0.3.1 h1:flRD4NNwYAUpkphVc1HcthR4KEIFJ65n8Mw5qdRn3LE=
github.com/kr/pretty v0.3.1/go.mod h1:hoEshYVHaxMs3cyo3Yncou5ZscifuDolrwPKZanG3xk=
github.com/kr/text v0.2.0 h1:5Nx0Ya0ZqY2ygV366QzturHI13Jq95ApcVaJBhpS+AY=
github.com/kr/text v0.2.0/go.mod h1:eLer722TekiGuMkidMxC/pM04lWEeraHUUmBw8l2grE=
github.com/mitchellh/copystructure v1.2.0 h1:vpKXTN4ewci03Vljg/q9QvCGUDttBOGBIa15WveJJGw=
github.com/mitchellh/copystructure v1.2.0/go.mod h1:qLl+cE2AmVv+CoeAwDPye/v+N2HKCj9FbZEVFJRxO9s=
github.com/mitchellh/reflectwalk v1.0.2 h1:G2LzWKi524PWgd3mLHV8Y5k7s6XUvT0Gef6zxSIeXaQ=
github.com/mitchellh/reflectwalk v1.0.2/go.mod h1:mSTlrgnPZtwu0c4WaC2kGObEpuNDbx0jmZXqmk4esnw=
github.com/pkg/errors v0.9.1 h1:FEBLx1zS214owpjy7qsBeixbURkuhQAwrK5UwLGTwt4=
github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2 h1:Jamvg5psRIccs7FGNTlIRMkT8wgtp5eCXdBlqhYGL6U=
github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
github.com/rogpeppe/go-internal v1.9.0 h1:73kH8U+JUqXU8lRuOHeVHaa/SZPifC7BkcraZVejAe8=
github.com/rogpeppe/go-internal v1.9.0/go.mod h1:WtVeX8xhTBvf0smdhujwtBcq4Qrzq/fJaraNFVN+nFs=
github.com/shopspring/decimal v1.4.0 h1:bxl37RwXBklmTi0C79JfXCEBD1cqqHt0bbgBAGFp81k=
github.com/shopspring/decimal v1.4.0/go.mod h1:gawqmDU56v4yIKSwfBSFip1HdCCXN8/+DMd9qYNcwME=
github.com/spf13/cast v1.7.0 h1:ntdiHjuueXFgm5nzDRdOS4yfT43P5Fnud6DH50rz/7w=
github.com/spf13/cast v1.7.0/go.mod h1:ancEpBxwJDODSW/UG4rDrAqiKolqNNh2DX3mk86cAdo=
github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu7U=
github.com/stretchr/testify v1.11.1/go.mod h1:wZwfW3scLgRK+23gO65QZefKpKQRnfz6sD981Nm4B6U=
github.com/yuin/goldmark v1.4.13/go.mod h1:6yULJ656Px+3vBD8DxQVa3kxgyrAnzto9xy5taEt/CY=
go.step.sm/crypto v0.89.0 h1:NPxryE+cZ4XDwXOQY2U6Gu+mOzOihuRLPIsX7WtPzZM=
go.step.sm/crypto v0.89.0/go.mod h1:IEgE6DndnYojbDyHU7eYXpwWzpu4ftkouw7nyI6jsxg=
golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
golang.org/x/crypto v0.0.0-20210921155107-089bfa567519/go.mod h1:GvvjBRRGRdwPK5ydBHafDWAxML/pGHZbMvKqRZ5+Abc=
golang.org/x/crypto v0.19.0/go.mod h1:Iy9bg/ha4yyC70EfRS8jz+B6ybOBKMaSxLj6P6oBDfU=
golang.org/x/crypto v0.54.0 h1:YLIA59K4fiNzHzjnZt2tUJQjQtUWfWbeHBqKtk3eScw=
golang.org/x/crypto v0.54.0/go.mod h1:KWL8ny2AZdGR2cWmzeHrp2azQPGogOv+HeQaVEXC2dk=
golang.org/x/mod v0.6.0-dev.0.20220419223038-86c51ed26bb4/go.mod h1:jJ57K6gSWd91VN4djpZkiMVwK6gcyfeH4XE8wZrZaV4=
golang.org/x/mod v0.8.0/go.mod h1:iBbtSCu2XBx23ZKBPSOrRkjjQPZFPuis4dIYUhu/chs=
golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
golang.org/x/net v0.0.0-20210226172049-e18ecbb05110/go.mod h1:m0MpNAwzfU5UDzcl9v0D8zg8gWTRqZa9RBIspLL5mdg=
golang.org/x/net v0.0.0-20220722155237-a158d28d115b/go.mod h1:XRhObCWvk6IyKnWLug+ECip1KBveYUHfp+8e9klMJ9c=
golang.org/x/net v0.6.0/go.mod h1:2Tu9+aMcznHK/AK1HMvgo6xiTLG5rD5rZLDS+rp2Bjs=
golang.org/x/net v0.10.0/go.mod h1:0qNGK6F8kojg2nk9dLZ2mShWaEBan6FAoqfSigmmuDg=
golang.org/x/net v0.57.0 h1:K5+3DljvIuDG9/Jv9rvyMywYNFCQ9RSUY6OOTTkT+tE=
golang.org/x/net v0.57.0/go.mod h1:KpXc8iv+r3XplLAG/f7Jsf9RPszJzdR0f58q9vGOuEU=
golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
golang.org/x/sync v0.0.0-20220722155255-886fb9371eb4/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
golang.org/x/sync v0.1.0/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
golang.org/x/sys v0.0.0-20210615035016-665e8c7367d1/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
golang.org/x/sys v0.0.0-20220520151302-bc2c85ada10a/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
golang.org/x/sys v0.0.0-20220722155257-8c9f86f7a55f/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
golang.org/x/sys v0.5.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
golang.org/x/sys v0.8.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
golang.org/x/sys v0.17.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
golang.org/x/sys v0.47.0 h1:o7XGOvZQCADBQQ4Y7VNq2dRWQR7JmOUW8Kxx4ZsNgWs=
golang.org/x/sys v0.47.0/go.mod h1:4GL1E5IUh+htKOUEOaiffhrAeqysfVGipDYzABqnCmw=
golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
golang.org/x/term v0.0.0-20210927222741-03fcf44c2211/go.mod h1:jbD1KX2456YbFQfuXm/mYQcufACuNUgVhRMnK/tPxf8=
golang.org/x/term v0.5.0/go.mod h1:jMB1sMXY+tzblOD4FWmEbocvup2/aLOaQEp7JmGp78k=
golang.org/x/term v0.8.0/go.mod h1:xPskH00ivmX89bAKVGSKKtLOWNx2+17Eiy94tnKShWo=
golang.org/x/term v0.17.0/go.mod h1:lLRBjIVuehSbZlaOtGMbcMncT+aqLLLmKrsjNrUguwk=
golang.org/x/term v0.45.0 h1:NwWyBmoJCbfTHpxrWoZ9C6/VxOf7ic219I8xZZFdrf0=
golang.org/x/term v0.45.0/go.mod h1:9aqxs0blBcrm/n0L9QW0aRVD+ktan8ssZromtqJC43w=
golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
golang.org/x/text v0.3.3/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
golang.org/x/text v0.3.7/go.mod h1:u+2+/6zg+i71rQMx5EYifcz6MCKuco9NR6JIITiCfzQ=
golang.org/x/text v0.7.0/go.mod h1:mrYo+phRRbMaCq/xk9113O4dZlRixOauAjOtrjsXDZ8=
golang.org/x/text v0.9.0/go.mod h1:e1OnstbJyHTd6l/uOt8jFFHp6TRDWZR/bV3emEE/zU8=
golang.org/x/text v0.14.0/go.mod h1:18ZOQIKpY8NJVqYksKHtTdi31H5itFRjB5/qKTNYzSU=
golang.org/x/text v0.40.0 h1:Ub2Z6/xjgF1WrYQz2nuITOEegKFtiIy+rieRJ5lHZKs=
golang.org/x/text v0.40.0/go.mod h1:hpnzDAfGV753zIKo+wk3u1bVKCGPbrnF7+7LBF/UHVY=
golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
golang.org/x/tools v0.0.0-20191119224855-298f0cb1881e/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
golang.org/x/tools v0.1.12/go.mod h1:hNGJHUnrk76NpqgfD5Aqm5Crs+Hm0VOH/i9J2+nxYbc=
golang.org/x/tools v0.6.0/go.mod h1:Xwgl3UAJ/d3gWutnCtw505GrjyAbvKui8lOU390QaIU=
golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
spec.json
{
  "schemaVersion": 1,
  "goal": "verify go.step.sm/crypto/tlsutil in pkg:golang/go.step.sm/crypto@v0.89.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/go.step.sm/crypto@v0.89.0"
  ],
  "symbols": [
    "go.step.sm/crypto/tlsutil"
  ]
}
test/contract.go
package main

import (
	"crypto/tls"
	"fmt"
	"os"

	sample "example.com/tlsutil-sample"
	"go.step.sm/crypto/tlsutil"
)

func main() {
	// Assertion 1: SanitizeName converts domains to ASCII punycode and rejects invalid or empty domains
	got, err := tlsutil.SanitizeName("example.com")
	if err != nil || got != "example.com" {
		fmt.Fprintf(os.Stderr, "FAIL: SanitizeName(example.com) = %q, err = %v\n", got, err)
		os.Exit(1)
	}

	got, err = tlsutil.SanitizeName("bücher.example.com")
	if err != nil || got != "xn--bcher-kva.example.com" {
		fmt.Fprintf(os.Stderr, "FAIL: SanitizeName(bücher.example.com) = %q, err = %v\n", got, err)
		os.Exit(1)
	}

	if _, err := tlsutil.SanitizeName(""); err == nil {
		fmt.Fprintf(os.Stderr, "FAIL: SanitizeName(\"\") expected error but got nil\n")
		os.Exit(1)
	}

	if _, err := tlsutil.SanitizeName("xn--bücher.example.com"); err == nil {
		fmt.Fprintf(os.Stderr, "FAIL: SanitizeName with invalid punycode expected error\n")
		os.Exit(1)
	}

	// Assertion 2: SanitizeHost handles host:port combinations and delegates hostname sanitization
	got, err = tlsutil.SanitizeHost("example.com:443")
	if err != nil || got != "example.com" {
		fmt.Fprintf(os.Stderr, "FAIL: SanitizeHost(example.com:443) = %q, err = %v\n", got, err)
		os.Exit(1)
	}

	got, err = tlsutil.SanitizeHost("bücher.example.com:8443")
	if err != nil || got != "xn--bcher-kva.example.com" {
		fmt.Fprintf(os.Stderr, "FAIL: SanitizeHost(bücher.example.com:8443) = %q, err = %v\n", got, err)
		os.Exit(1)
	}

	if _, err := tlsutil.SanitizeHost(":443"); err == nil {
		fmt.Fprintf(os.Stderr, "FAIL: SanitizeHost(\":443\") expected error but got nil\n")
		os.Exit(1)
	}

	// Assertion 3: NewRenewer manages TLS certificates and config lifecycle
	testCert, err := sample.GenerateTestCertificate("localhost")
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: GenerateTestCertificate: %v\n", err)
		os.Exit(1)
	}

	baseCfg := &tls.Config{
		MinVersion: tls.VersionTLS12,
	}

	renewCount := 0
	renewFunc := func() (*tls.Certificate, *tls.Config, error) {
		renewCount++
		return testCert, baseCfg, nil
	}

	renewer, err := tlsutil.NewRenewer(testCert, baseCfg, renewFunc)
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: NewRenewer failed: %v\n", err)
		os.Exit(1)
	}
	defer renewer.Stop()

	retrievedCert, err := renewer.GetCertificate(&tls.ClientHelloInfo{ServerName: "localhost"})
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: renewer.GetCertificate failed: %v\n", err)
		os.Exit(1)
	}
	if retrievedCert != testCert {
		fmt.Fprintf(os.Stderr, "FAIL: retrieved certificate does not match input certificate\n")
		os.Exit(1)
	}

	cfg := renewer.GetConfig()
	if cfg.MinVersion != tls.VersionTLS12 {
		fmt.Fprintf(os.Stderr, "FAIL: expected MinVersion TLS 1.2, got %d\n", cfg.MinVersion)
		os.Exit(1)
	}
	if cfg.GetCertificate == nil {
		fmt.Fprintf(os.Stderr, "FAIL: expected config GetCertificate to be set\n")
		os.Exit(1)
	}

	// Assertion 4: NewServerCredentials dynamically provisions certificates per SNI
	sc, err := tlsutil.NewServerCredentials(func(hello *tls.ClientHelloInfo) (*tls.Certificate, *tls.Config, error) {
		c, err := sample.GenerateTestCertificate(hello.ServerName)
		if err != nil {
			return nil, nil, err
		}
		return c, &tls.Config{MinVersion: tls.VersionTLS12}, nil
	})
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: NewServerCredentials failed: %v\n", err)
		os.Exit(1)
	}

	sniCert, err := sc.GetCertificate(&tls.ClientHelloInfo{ServerName: "example.com"})
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: sc.GetCertificate(example.com) failed: %v\n", err)
		os.Exit(1)
	}
	if sniCert == nil || sniCert.Leaf == nil || sniCert.Leaf.Subject.CommonName != "example.com" {
		fmt.Fprintf(os.Stderr, "FAIL: sc.GetCertificate(example.com) returned unexpected cert\n")
		os.Exit(1)
	}

	// Empty SNI should return an error
	if _, err := sc.GetCertificate(&tls.ClientHelloInfo{ServerName: ""}); err == nil {
		fmt.Fprintf(os.Stderr, "FAIL: sc.GetCertificate(\"\") expected error but succeeded\n")
		os.Exit(1)
	}

	fmt.Println("PASS: all tlsutil contract assertions verified")
}
tlsutil.go
package tlsutilsample

import (
	"crypto/ecdsa"
	"crypto/elliptic"
	"crypto/rand"
	"crypto/tls"
	"crypto/x509"
	"crypto/x509/pkix"
	"fmt"
	"math/big"
	"time"

	"go.step.sm/crypto/tlsutil"
)

// GenerateTestCertificate creates an in-memory self-signed TLS certificate valid for 1 hour.
func GenerateTestCertificate(commonName string) (*tls.Certificate, error) {
	priv, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
	if err != nil {
		return nil, fmt.Errorf("failed to generate private key: %w", err)
	}

	notBefore := time.Now().Add(-1 * time.Minute)
	notAfter := notBefore.Add(1 * time.Hour)

	serialNumber, err := rand.Int(rand.Reader, new(big.Int).Lsh(big.NewInt(1), 128))
	if err != nil {
		return nil, fmt.Errorf("failed to generate serial number: %w", err)
	}

	template := &x509.Certificate{
		SerialNumber: serialNumber,
		Subject: pkix.Name{
			CommonName: commonName,
		},
		NotBefore:             notBefore,
		NotAfter:              notAfter,
		KeyUsage:              x509.KeyUsageDigitalSignature | x509.KeyUsageKeyEncipherment,
		ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
		BasicConstraintsValid: true,
		DNSNames:              []string{commonName},
	}

	derBytes, err := x509.CreateCertificate(rand.Reader, template, template, &priv.PublicKey, priv)
	if err != nil {
		return nil, fmt.Errorf("failed to create certificate: %w", err)
	}

	leaf, err := x509.ParseCertificate(derBytes)
	if err != nil {
		return nil, fmt.Errorf("failed to parse certificate: %w", err)
	}

	cert := &tls.Certificate{
		Certificate: [][]byte{derBytes},
		PrivateKey:  priv,
		Leaf:        leaf,
	}
	return cert, nil
}

// CreateRenewer creates a TLS renewer for the given certificate and base tls.Config.
func CreateRenewer(cert *tls.Certificate, cfg *tls.Config, fn tlsutil.RenewFunc) (*tlsutil.Renewer, error) {
	return tlsutil.NewRenewer(cert, cfg, fn)
}

// CreateServerCredentials creates dynamic server credentials backed by the given ServerRenewFunc.
func CreateServerCredentials(fn tlsutil.ServerRenewFunc) (*tlsutil.ServerCredentials, error) {
	return tlsutil.NewServerCredentials(fn)
}

// SanitizeDomain wraps tlsutil.SanitizeName.
func SanitizeDomain(domain string) (string, error) {
	return tlsutil.SanitizeName(domain)
}

// SanitizeAddress wraps tlsutil.SanitizeHost.
func SanitizeAddress(host string) (string, error) {
	return tlsutil.SanitizeHost(host)
}

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