feat(*)!: Adds cas operation and fixes keys cursor

This PR incorporates some feedback received on the current draft interface.
First off, this changes the cursor for listing keys to be a string instead
of a number in order to support more systems.

The second changes adds back in a CAS operation as multiple people had
been asking for it. See the discussion in WebAssembly#44 for more context.

Because these are breaking changes and there are multiple draft
implementations out there, I bumped this to draft2. Ideally we should be
able to move to an RC soon with these changes added in

Closes WebAssembly#44
Closes WebAssembly#45

Signed-off-by: Taylor Thomas <taylor@cosmonic.com>

imports.md

@@ -9,13 +9,13 @@ Components targeting this world will be able to do:</p>
 <ul>
 <li>Imports:
 <ul>
-<li>interface <a href="#wasi:keyvalue_store_0.2.0_draft"><code>wasi:keyvalue/store@0.2.0-draft</code></a></li>
-<li>interface <a href="#wasi:keyvalue_atomics_0.2.0_draft"><code>wasi:keyvalue/atomics@0.2.0-draft</code></a></li>
-<li>interface <a href="#wasi:keyvalue_batch_0.2.0_draft"><code>wasi:keyvalue/batch@0.2.0-draft</code></a></li>
+<li>interface <a href="#wasi:keyvalue_store_0.2.0_draft2"><code>wasi:keyvalue/store@0.2.0-draft2</code></a></li>
+<li>interface <a href="#wasi:keyvalue_atomics_0.2.0_draft2"><code>wasi:keyvalue/atomics@0.2.0-draft2</code></a></li>
+<li>interface <a href="#wasi:keyvalue_batch_0.2.0_draft2"><code>wasi:keyvalue/batch@0.2.0-draft2</code></a></li>
 </ul>
 </li>
 </ul>
-<h2><a name="wasi:keyvalue_store_0.2.0_draft"></a>Import interface wasi:keyvalue/store@0.2.0-draft</h2>
+<h2><a name="wasi:keyvalue_store_0.2.0_draft2"></a>Import interface wasi:keyvalue/store@0.2.0-draft2</h2>
 <p>A keyvalue interface that provides eventually consistent key-value operations.</p>
 <p>Each of these operations acts on a single key-value pair.</p>
 <p>The value in the key-value pair is defined as a <code>u8</code> byte array and the intention is that it is
@@ -66,7 +66,7 @@ still see A or B</p>
 <p>The list of keys returned by the query.
 </li>
 <li>
-<p><a name="key_response.cursor"></a><code>cursor</code>: option&lt;<code>u64</code>&gt;</p>
+<p><a name="key_response.cursor"></a><code>cursor</code>: option&lt;<code>string</code>&gt;</p>
 <p>The continuation token to use to fetch the next page of keys. If this is `null`, then
 there are no more keys to fetch.
 </li>
@@ -172,13 +172,13 @@ for more information.</p>
 <h5>Params</h5>
 <ul>
 <li><a name="method_bucket.list_keys.self"></a><code>self</code>: borrow&lt;<a href="#bucket"><a href="#bucket"><code>bucket</code></a></a>&gt;</li>
-<li><a name="method_bucket.list_keys.cursor"></a><code>cursor</code>: option&lt;<code>u64</code>&gt;</li>
+<li><a name="method_bucket.list_keys.cursor"></a><code>cursor</code>: option&lt;<code>string</code>&gt;</li>
 </ul>
 <h5>Return values</h5>
 <ul>
 <li><a name="method_bucket.list_keys.0"></a> result&lt;<a href="#key_response"><a href="#key_response"><code>key-response</code></a></a>, <a href="#error"><a href="#error"><code>error</code></a></a>&gt;</li>
 </ul>
-<h2><a name="wasi:keyvalue_atomics_0.2.0_draft"></a>Import interface wasi:keyvalue/atomics@0.2.0-draft</h2>
+<h2><a name="wasi:keyvalue_atomics_0.2.0_draft2"></a>Import interface wasi:keyvalue/atomics@0.2.0-draft2</h2>
 <p>A keyvalue interface that provides atomic operations.</p>
 <p>Atomic operations are single, indivisible operations. When a fault causes an atomic operation to
 fail, it will appear to the invoker of the atomic operation that the action either completed
@@ -213,7 +213,23 @@ to the given delta.</p>
 <ul>
 <li><a name="increment.0"></a> result&lt;<code>u64</code>, <a href="#error"><a href="#error"><code>error</code></a></a>&gt;</li>
 </ul>
-<h2><a name="wasi:keyvalue_batch_0.2.0_draft"></a>Import interface wasi:keyvalue/batch@0.2.0-draft</h2>
+<h4><a name="compare_and_swap"></a><code>compare-and-swap: func</code></h4>
+<p>Atomically set the value associated with the key in the store to the given value. It returns
+<code>true</code> if the value was set properly, or <code>false</code> if the swap failed.</p>
+<p>If setting a new value, a <code>none</code> value should be passed for the <code>old</code> parameter. If the key
+already exists in the store, it will be swapped with the new value only if the current value
+is equal to the old value. To delete a key-value pair, pass <code>none</code> for the <code>new</code> parameter.</p>
+<h5>Params</h5>
+<ul>
+<li><a name="compare_and_swap.key"></a><code>key</code>: <code>string</code></li>
+<li><a name="compare_and_swap.old"></a><code>old</code>: option&lt;list&lt;<code>u8</code>&gt;&gt;</li>
+<li><a name="compare_and_swap.new"></a><code>new</code>: option&lt;list&lt;<code>u8</code>&gt;&gt;</li>
+</ul>
+<h5>Return values</h5>
+<ul>
+<li><a name="compare_and_swap.0"></a> result&lt;<code>bool</code>, <a href="#error"><a href="#error"><code>error</code></a></a>&gt;</li>
+</ul>
+<h2><a name="wasi:keyvalue_batch_0.2.0_draft2"></a>Import interface wasi:keyvalue/batch@0.2.0-draft2</h2>
 <p>A keyvalue interface that provides batch operations.</p>
 <p>A batch operation is an operation that operates on multiple keys at once.</p>
 <p>Batch operations are useful for reducing network round-trip time. For example, if you want to

watch-service.md

@@ -2,18 +2,18 @@
 <ul>
 <li>Imports:
 <ul>
-<li>interface <a href="#wasi:keyvalue_store_0.2.0_draft"><code>wasi:keyvalue/store@0.2.0-draft</code></a></li>
-<li>interface <a href="#wasi:keyvalue_atomics_0.2.0_draft"><code>wasi:keyvalue/atomics@0.2.0-draft</code></a></li>
-<li>interface <a href="#wasi:keyvalue_batch_0.2.0_draft"><code>wasi:keyvalue/batch@0.2.0-draft</code></a></li>
+<li>interface <a href="#wasi:keyvalue_store_0.2.0_draft2"><code>wasi:keyvalue/store@0.2.0-draft2</code></a></li>
+<li>interface <a href="#wasi:keyvalue_atomics_0.2.0_draft2"><code>wasi:keyvalue/atomics@0.2.0-draft2</code></a></li>
+<li>interface <a href="#wasi:keyvalue_batch_0.2.0_draft2"><code>wasi:keyvalue/batch@0.2.0-draft2</code></a></li>
 </ul>
 </li>
 <li>Exports:
 <ul>
-<li>interface <a href="#wasi:keyvalue_watcher_0.2.0_draft"><code>wasi:keyvalue/watcher@0.2.0-draft</code></a></li>
+<li>interface <a href="#wasi:keyvalue_watcher_0.2.0_draft2"><code>wasi:keyvalue/watcher@0.2.0-draft2</code></a></li>
 </ul>
 </li>
 </ul>
-<h2><a name="wasi:keyvalue_store_0.2.0_draft"></a>Import interface wasi:keyvalue/store@0.2.0-draft</h2>
+<h2><a name="wasi:keyvalue_store_0.2.0_draft2"></a>Import interface wasi:keyvalue/store@0.2.0-draft2</h2>
 <p>A keyvalue interface that provides eventually consistent key-value operations.</p>
 <p>Each of these operations acts on a single key-value pair.</p>
 <p>The value in the key-value pair is defined as a <code>u8</code> byte array and the intention is that it is
@@ -64,7 +64,7 @@ still see A or B</p>
 <p>The list of keys returned by the query.
 </li>
 <li>
-<p><a name="key_response.cursor"></a><code>cursor</code>: option&lt;<code>u64</code>&gt;</p>
+<p><a name="key_response.cursor"></a><code>cursor</code>: option&lt;<code>string</code>&gt;</p>
 <p>The continuation token to use to fetch the next page of keys. If this is `null`, then
 there are no more keys to fetch.
 </li>
@@ -170,13 +170,13 @@ for more information.</p>
 <h5>Params</h5>
 <ul>
 <li><a name="method_bucket.list_keys.self"></a><code>self</code>: borrow&lt;<a href="#bucket"><a href="#bucket"><code>bucket</code></a></a>&gt;</li>
-<li><a name="method_bucket.list_keys.cursor"></a><code>cursor</code>: option&lt;<code>u64</code>&gt;</li>
+<li><a name="method_bucket.list_keys.cursor"></a><code>cursor</code>: option&lt;<code>string</code>&gt;</li>
 </ul>
 <h5>Return values</h5>
 <ul>
 <li><a name="method_bucket.list_keys.0"></a> result&lt;<a href="#key_response"><a href="#key_response"><code>key-response</code></a></a>, <a href="#error"><a href="#error"><code>error</code></a></a>&gt;</li>
 </ul>
-<h2><a name="wasi:keyvalue_atomics_0.2.0_draft"></a>Import interface wasi:keyvalue/atomics@0.2.0-draft</h2>
+<h2><a name="wasi:keyvalue_atomics_0.2.0_draft2"></a>Import interface wasi:keyvalue/atomics@0.2.0-draft2</h2>
 <p>A keyvalue interface that provides atomic operations.</p>
 <p>Atomic operations are single, indivisible operations. When a fault causes an atomic operation to
 fail, it will appear to the invoker of the atomic operation that the action either completed
@@ -211,7 +211,23 @@ to the given delta.</p>
 <ul>
 <li><a name="increment.0"></a> result&lt;<code>u64</code>, <a href="#error"><a href="#error"><code>error</code></a></a>&gt;</li>
 </ul>
-<h2><a name="wasi:keyvalue_batch_0.2.0_draft"></a>Import interface wasi:keyvalue/batch@0.2.0-draft</h2>
+<h4><a name="compare_and_swap"></a><code>compare-and-swap: func</code></h4>
+<p>Atomically set the value associated with the key in the store to the given value. It returns
+<code>true</code> if the value was set properly, or <code>false</code> if the swap failed.</p>
+<p>If setting a new value, a <code>none</code> value should be passed for the <code>old</code> parameter. If the key
+already exists in the store, it will be swapped with the new value only if the current value
+is equal to the old value. To delete a key-value pair, pass <code>none</code> for the <code>new</code> parameter.</p>
+<h5>Params</h5>
+<ul>
+<li><a name="compare_and_swap.key"></a><code>key</code>: <code>string</code></li>
+<li><a name="compare_and_swap.old"></a><code>old</code>: option&lt;list&lt;<code>u8</code>&gt;&gt;</li>
+<li><a name="compare_and_swap.new"></a><code>new</code>: option&lt;list&lt;<code>u8</code>&gt;&gt;</li>
+</ul>
+<h5>Return values</h5>
+<ul>
+<li><a name="compare_and_swap.0"></a> result&lt;<code>bool</code>, <a href="#error"><a href="#error"><code>error</code></a></a>&gt;</li>
+</ul>
+<h2><a name="wasi:keyvalue_batch_0.2.0_draft2"></a>Import interface wasi:keyvalue/batch@0.2.0-draft2</h2>
 <p>A keyvalue interface that provides batch operations.</p>
 <p>A batch operation is an operation that operates on multiple keys at once.</p>
 <p>Batch operations are useful for reducing network round-trip time. For example, if you want to
@@ -290,7 +306,7 @@ fail.</p>
 <ul>
 <li><a name="delete_many.0"></a> result&lt;_, <a href="#error"><a href="#error"><code>error</code></a></a>&gt;</li>
 </ul>
-<h2><a name="wasi:keyvalue_watcher_0.2.0_draft"></a>Export interface wasi:keyvalue/watcher@0.2.0-draft</h2>
+<h2><a name="wasi:keyvalue_watcher_0.2.0_draft2"></a>Export interface wasi:keyvalue/watcher@0.2.0-draft2</h2>
 <hr />
 <h3>Types</h3>
 <h4><a name="bucket"></a><code>type bucket</code></h4>

wit/atomic.wit

@@ -19,4 +19,12 @@ interface atomics {
 	///
 	/// If any other error occurs, it returns an `Err(error)`.
 	increment: func(bucket: borrow<bucket>, key: string, delta: u64) -> result<u64, error>;
+
+	/// Atomically set the value associated with the key in the store to the given value. It returns
+	/// `true` if the value was set properly, or `false` if the swap failed.
+	/// 
+	/// If setting a new value, a `none` value should be passed for the `old` parameter. If the key
+	/// already exists in the store, it will be swapped with the new value only if the current value
+	/// is equal to the old value. To delete a key-value pair, pass `none` for the `new` parameter.
+	compare-and-swap: func(key: string, old: option<list<u8>>, new: option<list<u8>>) -> result<bool, error>;
 }

wit/store.wit

@@ -43,7 +43,7 @@ interface store {
         keys: list<string>,
         /// The continuation token to use to fetch the next page of keys. If this is `null`, then
         /// there are no more keys to fetch.
-        cursor: option<u64>
+        cursor: option<string>
     }
 
     /// Get the bucket with the specified identifier.
@@ -117,6 +117,6 @@ interface store {
         /// MAY show an out-of-date list of keys if there are concurrent writes to the store.
         /// 
         /// If any error occurs, it returns an `Err(error)`.
-        list-keys: func(cursor: option<u64>) -> result<key-response, error>;
+        list-keys: func(cursor: option<string>) -> result<key-response, error>;
     }
 }

wit/world.wit

@@ -1,4 +1,4 @@
-package wasi:keyvalue@0.2.0-draft;
+package wasi:keyvalue@0.2.0-draft2;
 
 /// The `wasi:keyvalue/imports` world provides common APIs for interacting with key-value stores.
 /// Components targeting this world will be able to do: