Add support for HTTP rewrites (#1062)

This adds a new configuration option for the HTTP client to replace URI prefixes when making outbound calls.

Follows the design of https://github.com/apple/pkl-evolution/pull/17

pkl-server/src/main/kotlin/org/pkl/server/ServerMessagePackDecoder.kt

@@ -95,7 +95,13 @@ class ServerMessagePackDecoder(unpacker: MessageUnpacker) : BaseMessagePackDecod
     val httpMap = getNullable(this, "http")?.asMapValue()?.map() ?: return null
     val proxy = httpMap.unpackProxy()
     val caCertificates = getNullable(httpMap, "caCertificates")?.asBinaryValue()?.asByteArray()
-    return Http(caCertificates, proxy)
+    val rewrites =
+      getNullable(httpMap, "rewrites")
+        ?.asMapValue()
+        ?.map()
+        ?.mapKeys { it.key.asStringValue().asString() }
+        ?.mapValues { it.value.asStringValue().asString() }
+    return Http(caCertificates, proxy, rewrites)
   }
 
   private fun Map<Value, Value>.unpackProxy(): Proxy? {

pkl-server/src/main/kotlin/org/pkl/server/ServerMessagePackEncoder.kt

@@ -36,7 +36,7 @@ class ServerMessagePackEncoder(packer: MessagePacker) : BaseMessagePackEncoder(p
   }
 
   private fun MessagePacker.packHttp(http: Http) {
-    packMapHeader(0, http.caCertificates, http.proxy)
+    packMapHeader(0, http.caCertificates, http.proxy, http.rewrites)
     http.caCertificates?.let { packKeyValue("caCertificates", it) }
     http.proxy?.let { proxy ->
       packString("proxy")
@@ -44,6 +44,14 @@ class ServerMessagePackEncoder(packer: MessagePacker) : BaseMessagePackEncoder(p
       packKeyValue("address", proxy.address?.toString())
       packKeyValue("noProxy", proxy.noProxy)
     }
+    http.rewrites?.let { rewrites ->
+      packString("rewrites")
+      packMapHeader(rewrites.size)
+      for ((key, value) in rewrites) {
+        packString(key)
+        packString(value)
+      }
+    }
   }
 
   private fun MessagePacker.packDependencies(dependencies: Map<String, Dependency>) {

pkl-server/src/main/kotlin/org/pkl/server/ServerMessages.kt

@@ -56,6 +56,8 @@ data class Http(
   val caCertificates: ByteArray?,
   /** Proxy settings */
   val proxy: Proxy?,
+  /** HTTP rewrites */
+  val rewrites: Map<String, String>?,
 ) {
   override fun equals(other: Any?): Boolean {
     if (this === other) return true
@@ -65,12 +67,13 @@ data class Http(
       if (other.caCertificates == null) return false
       if (!caCertificates.contentEquals(other.caCertificates)) return false
     } else if (other.caCertificates != null) return false
-    return Objects.equals(proxy, other.proxy)
+    return Objects.equals(rewrites, other.rewrites) && Objects.equals(proxy, other.proxy)
   }
 
   override fun hashCode(): Int {
     var result = caCertificates?.contentHashCode() ?: 0
     result = 31 * result + (proxy?.hashCode() ?: 0)
+    result = 31 * result + (rewrites?.hashCode() ?: 0)
     return result
   }
 }

pkl-server/src/test/kotlin/org/pkl/server/ServerMessagePackCodecTest.kt

@@ -96,6 +96,7 @@ class ServerMessagePackCodecTest {
           Http(
             proxy = Proxy(URI("http://foo.com:1234"), listOf("bar", "baz")),
             caCertificates = byteArrayOf(1, 2, 3, 4),
+            rewrites = mapOf("https://foo.com" to "https://bar.com"),
           ),
         externalModuleReaders = mapOf("external" to externalReader, "external2" to externalReader),
         externalResourceReaders = mapOf("external" to externalReader),