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Add entity-tags and conditional requests (RFC 9110 §8.8.3, §13) #34

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Merged
hellerve merged 3 commits into from
Aug 21, 2026
Merged

Add entity-tags and conditional requests (RFC 9110 §8.8.3, §13) #34

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efcb8aa
Add entity-tags and conditional requests (RFC 9110 §8.8.3, §13)
Aug 19, 2026
d04a867
Regenerate ETag docs after the doc example fix
Aug 19, 2026
185af3a
Pin the method Request.preconditions reads, and two ETag.parse guards
Aug 19, 2026
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33 changes: 33 additions & 0 deletions README.md
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Expand Up @@ -168,6 +168,36 @@ is the `416` case.
(Result.Error e) (IO.errorln &e))
```

### Conditional requests

`Precondition` evaluates the RFC 9110 §13 conditional request headers —
`If-Match`, `If-Unmodified-Since`, `If-None-Match` and `If-Modified-Since` —
against the validators of the representation the server selected, in the
precedence §13.2.2 lays down, and answers with the status they demand.

```clojure
(match (Request.preconditions &req &etag &modified)
(Maybe.Just code) (Response.respond code {} @"") ; 304 or 412
(Maybe.Nothing) (Response.ok {} @"the body"))
```

A failed `If-None-Match` is a `304` for a `GET` or a `HEAD` and a `412` for
anything else; every other failure is a `412`. `If-Match` compares entity-tags
strongly and `If-None-Match` weakly, per §13.1.1 and §13.1.2.

`ETag` reads and writes one entity-tag, `ETagList` the `*`-or-list field value
of an `If-Match` or `If-None-Match` header.

```clojure
(ETag.str &(ETag.init @"xyzzy" true)) ; => W/"xyzzy"

(match (ETag.parse "W/\"xyzzy\"")
(Result.Success e) (println* (ETag.weak &e)) ; => true
(Result.Error e) (IO.errorln &e))
```

`If-Range` is not evaluated yet.

### Status codes

```clojure
Expand Down Expand Up @@ -202,6 +232,9 @@ Status.not-found ; => 404
| `CacheControl` | `Cache-Control` directive parser (RFC 7234 §5.2) |
| `TransferEncoding` | Chunked transfer-encoding decoder |
| `HttpDate` | HTTP-date parser and formatter (RFC 9110 §5.6.7) |
| `ETag` | one entity-tag, strong or weak (RFC 9110 §8.8.3) |
| `ETagList` | the `*`-or-list value of an `If-Match` or `If-None-Match` header |
| `Precondition` | conditional request evaluator (RFC 9110 §13) |

## Testing

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ContentRange
</a>
</li>
<li>
<a href="ETag.html">
ETag
</a>
</li>
<li>
<a href="ETagList.html">
ETagList
</a>
</li>
<li>
<a href="Precondition.html">
Precondition
</a>
</li>
<li>
<a href="CacheControl.html">
CacheControl
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ContentRange
</a>
</li>
<li>
<a href="ETag.html">
ETag
</a>
</li>
<li>
<a href="ETagList.html">
ETagList
</a>
</li>
<li>
<a href="Precondition.html">
Precondition
</a>
</li>
<li>
<a href="CacheControl.html">
CacheControl
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ContentRange
</a>
</li>
<li>
<a href="ETag.html">
ETag
</a>
</li>
<li>
<a href="ETagList.html">
ETagList
</a>
</li>
<li>
<a href="Precondition.html">
Precondition
</a>
</li>
<li>
<a href="CacheControl.html">
CacheControl
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ContentRange
</a>
</li>
<li>
<a href="ETag.html">
ETag
</a>
</li>
<li>
<a href="ETagList.html">
ETagList
</a>
</li>
<li>
<a href="Precondition.html">
Precondition
</a>
</li>
<li>
<a href="CacheControl.html">
CacheControl
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ContentRange
</a>
</li>
<li>
<a href="ETag.html">
ETag
</a>
</li>
<li>
<a href="ETagList.html">
ETagList
</a>
</li>
<li>
<a href="Precondition.html">
Precondition
</a>
</li>
<li>
<a href="CacheControl.html">
CacheControl
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ContentRange
</a>
</li>
<li>
<a href="ETag.html">
ETag
</a>
</li>
<li>
<a href="ETagList.html">
ETagList
</a>
</li>
<li>
<a href="Precondition.html">
Precondition
</a>
</li>
<li>
<a href="CacheControl.html">
CacheControl
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ContentRange
</a>
</li>
<li>
<a href="ETag.html">
ETag
</a>
</li>
<li>
<a href="ETagList.html">
ETagList
</a>
</li>
<li>
<a href="Precondition.html">
Precondition
</a>
</li>
<li>
<a href="CacheControl.html">
CacheControl
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ContentRange
</a>
</li>
<li>
<a href="ETag.html">
ETag
</a>
</li>
<li>
<a href="ETagList.html">
ETagList
</a>
</li>
<li>
<a href="Precondition.html">
Precondition
</a>
</li>
<li>
<a href="CacheControl.html">
CacheControl
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ContentRange
</a>
</li>
<li>
<a href="ETag.html">
ETag
</a>
</li>
<li>
<a href="ETagList.html">
ETagList
</a>
</li>
<li>
<a href="Precondition.html">
Precondition
</a>
</li>
<li>
<a href="CacheControl.html">
CacheControl
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ContentRange
</a>
</li>
<li>
<a href="ETag.html">
ETag
</a>
</li>
<li>
<a href="ETagList.html">
ETagList
</a>
</li>
<li>
<a href="Precondition.html">
Precondition
</a>
</li>
<li>
<a href="CacheControl.html">
CacheControl
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