Support conditional R2Bucket#put()

Author: mrbbot

packages/tre/src/plugins/r2/gateway.ts

@@ -102,7 +102,17 @@ export class R2Gateway {
     value: Uint8Array,
     options: R2PutOptions
   ): Promise<R2Object> {
-    const checksums = validate.key(key).size(value).hash(value, options);
+    let meta: R2Object | undefined;
+    try {
+      meta = await this.head(key);
+    } catch (e) {
+      if (!(e instanceof NoSuchKey)) throw e;
+    }
+    const checksums = validate
+      .key(key)
+      .size(value)
+      .condition(meta, options.onlyIf)
+      .hash(value, options);
 
     // build metadata
     const md5Hash = crypto.createHash("md5").update(value).digest("hex");

packages/tre/src/plugins/r2/validator.ts

@@ -94,10 +94,11 @@ export class Validator {
     return checksums;
   }
 
-  condition(meta: R2Object, onlyIf?: R2Conditional): Validator {
-    // test conditional should it exist
-    if (!testR2Conditional(onlyIf, meta) || meta?.size === 0) {
-      throw new PreconditionFailed().attach(meta);
+  condition(meta?: R2Object, onlyIf?: R2Conditional): Validator {
+    if (onlyIf !== undefined && !testR2Conditional(onlyIf, meta)) {
+      let error = new PreconditionFailed();
+      if (meta !== undefined) error = error.attach(meta);
+      throw error;
     }
     return this;
   }