feat(storage): add signed post policy v4 by dmitri-lerko · Pull Request #5576 · googleapis/google-cloud-rust

dmitri-lerko · 2026-05-03T18:07:07Z

Summary

add canonical Rust Signed V4 POST Policy support for Cloud Storage using the existing signer abstraction
expose PostPolicyV4Builder, PostPolicyV4, PolicyV4Fields, and policy condition helpers from google-cloud-storage
validate local protocol invariants required to construct a valid policy, including bucket name shape, expiration bounds, conflicting exact-match fields, and unsafe metadata fields
keep this PR scoped to POST Policy only per maintainer feedback; no src/gax, src/gax-internal, Requester Pays, emulator, or report/plan Markdown changes are included

Testing

cargo test -p google-cloud-storage post_policy
cargo clippy -p google-cloud-storage --all-targets -- --deny warnings
git diff --check

Latest local focused result: 19 passed, 623 filtered out for cargo test -p google-cloud-storage post_policy.

google-cla · 2026-05-03T18:07:12Z

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View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

gemini-code-assist · 2026-05-03T18:07:17Z

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces support for Signed V4 POST policies in the Rust Cloud Storage SDK, aligning it with the capabilities of the Go Storage package. It also establishes a formal roadmap and testing framework to ensure future parity efforts are consistent, well-documented, and rigorously validated against Go reference behaviors.

Highlights

Signed V4 POST Policy Support: Added Rust implementation for Signed V4 POST policies, enabling unauthenticated uploads via multipart HTML forms with robust condition validation.
Go/Rust Parity Plan: Introduced a comprehensive parity plan, including a capability matrix and a durable report to track and guide future efforts toward feature parity with the Go Storage SDK.
Conformance and Boundary Testing: Implemented extensive test coverage, including Go-equivalent conformance fixtures, boundary tests for metadata and expiration, and property-based checks for JSON escaping.

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Code Review

This pull request establishes a comprehensive plan and initial implementation for bringing the Rust Storage SDK toward parity with the Go Storage library. It introduces a detailed parity report and matrix to track progress across various feature groups, such as ACLs, HMAC keys, and notifications. The initial implementation slice adds support for Signed V4 POST policies, including a new builder, condition types, and extensive conformance testing against existing cross-language fixtures. The feedback provided suggests a minor documentation refinement to point directly to the implementation file in the parity matrix for better clarity.

gemini-code-assist · 2026-05-03T18:14:25Z

+| HMAC keys | `storage.HMACKeyHandle` and client methods | Missing | No Rust HMAC helper module | No Rust parity tests yet |
+| Pub/Sub notifications | `storage.Notification` helpers | Missing | No Rust notification helper module | No Rust parity tests yet |
+| Signed V4 URLs | `storage.SignedURL` and bucket signed URLs | Implemented | `src/storage/src/storage/signed_url.rs` | Cross-language conformance coverage exists |
+| Signed V4 POST policies | `storage.GenerateSignedPostPolicyV4` | Implemented | `src/storage/src/storage/post_policy_v4.rs`, `src/storage/src/post_policy_v4.rs` | Go-equivalent conformance, boundary, endpoint style, and Send tests exist |


For clarity, you could remove the redundant path to the re-export module from the Evidence column, so it points directly to the implementation file.

Suggested change

| Signed V4 POST policies | `storage.GenerateSignedPostPolicyV4` | Implemented | `src/storage/src/storage/post_policy_v4.rs`, `src/storage/src/post_policy_v4.rs` | Go-equivalent conformance, boundary, endpoint style, and Send tests exist |

| Signed V4 POST policies | `storage.GenerateSignedPostPolicyV4` | Implemented | `src/storage/src/storage/post_policy_v4.rs` | Go-equivalent conformance, boundary, endpoint style, and Send tests exist |

coryan · 2026-05-03T19:07:56Z

Thanks for the PR. You will need to sign the CLA or we cannot accept the PR at all.

Please split the changes to src/gax and src/gax-internal to a separate PR.

I think the work for user project duplicates the work in #5490

We would also prefer if you split the work for STORAGE_EMULATOR_HOST to a separate PR from the work for the POST Policy changes.

@joshuatants I believe most of the review here will fall on your shoulders.

dmitri-lerko · 2026-05-03T20:20:16Z

Thanks for the PR. You will need to sign the CLA or we cannot accept the PR at all.

Please split the changes to src/gax and src/gax-internal to a separate PR.

I think the work for user project duplicates the work in #5490

We would also prefer if you split the work for STORAGE_EMULATOR_HOST to a separate PR from the work for the POST Policy changes.

@joshuatants I believe most of the review here will fall on your shoulders.

Hi @coryan ,

Thank you for your prompt reply. I am happy to take it a step at a time. I'd love to see Go <> Rust SDK parity when it comes to Cloud Storage and Cloud Monitoring. For the latter I am running my own fork in production, but would love to move it over here piecemeal.

Please let me know what I can do to make your jobs as easy as possible here.

joshuatants · 2026-05-04T01:18:53Z

Hi @dmitri-lerko thank you very much for this.

We actually have someone working on the signed post policy v4 and are tracking the issue here (#4746). I should've been more prompt with updating the issue to reflect this.

@xlai20 - can you have a look at Dmitri's work? How far along are you with your implementation? How much of Dmitri's work can be used?

xlai20

Thanks for the PR. It looks moving to the right direction. I've left some comments to request minor changes.

xlai20 · 2026-05-08T07:10:43Z

+
+/// A constraint that the uploaded multipart form must satisfy.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum PostPolicyV4Condition {


According to https://docs.cloud.google.com/storage/docs/authentication/signatures#policy-document, there are 3 types of policy conditions: Exact Match, Starts With, and Content Length Range. As here it misses out the Exact Match type, user cannot have the freedom to define exact match condition on fields, whilst such capability is supported in other sdk.

xlai20 · 2026-05-08T07:39:21Z

+        Self::ContentLengthRange { start, end }
+    }
+
+    fn is_empty(&self) -> bool {


I think this is_empty() function and its use in filtering out "invalid" policy document conditions is better to be removed in an SDK implementation.

As per the documentation https://docs.cloud.google.com/storage/docs/authentication/signatures#policy-document,

"If a field's value has no restrictions, use the starts-with condition with ["starts-with", "$field", ""],

this suggest that the GCS backend is expecting a starts-with empty string condition. Doing a filtering might end up passing incorrect inputs to the backend.

xlai20 · 2026-05-08T07:39:57Z

+impl PostPolicyV4Condition {
+    /// Creates a `starts-with` condition.
+    ///
+    /// Empty values are ignored, matching the Go Storage SDK behavior.


Ditto my another comment, don't ignore empty values.

xlai20 · 2026-05-08T08:08:41Z

+    JsonCondition::Object(BTreeMap::from([(name.to_string(), value.into())]))
+}
+
+fn escape_like_go_json(json: &str) -> String {


Rename this function to "escape_json_str" or "escape_invalid_char".

xlai20 · 2026-05-08T08:12:41Z

+    escaped
+}
+
+fn push_json_unicode_escape(output: &mut String, ch: char) {


This function is a bit too low-level styled, unlike the usual high-level coding style in Rust, is there a way to improve it?

xlai20 · 2026-05-08T08:14:55Z

+fn push_json_unicode_escape(output: &mut String, ch: char) {
+    let code = ch as u32;
+    if code <= 0xffff {
+        output.push_str(&format!("\\u{code:04x}"));


As this function is called within the loop of escape function, the use of format! can be a performance hit. Calling the format! macro always allocates a new String on the heap. Try to explore if can change to write! macro to avoid allocations.

dmitri-lerko · 2026-05-08T15:55:20Z

Thanks for the PR. It looks moving to the right direction. I've left some comments to request minor changes.

Thank you for your guidance and thorough review, I'll aim to iterate on the feedback within a week,

product-auto-label Bot added the api: storage Issues related to the Cloud Storage API. label May 3, 2026

gemini-code-assist Bot reviewed May 3, 2026

View reviewed changes

dmitri-lerko changed the title ~~feat(storage): add signed post policy v4~~ feat(storage): add signed post policy and requester pays parity May 3, 2026

dmitri-lerko changed the title ~~feat(storage): add signed post policy and requester pays parity~~ feat(storage): add storage go parity features May 3, 2026

dmitri-lerko force-pushed the feat/storage-go-parity branch from 405dbd0 to 89e396f Compare May 3, 2026 20:04

dmitri-lerko added 2 commits May 3, 2026 21:06

feat(storage): add signed post policy v4

5f9cb17

test(storage): harden signed post policy

dc5b7bb

dmitri-lerko force-pushed the feat/storage-go-parity branch from 89e396f to dc5b7bb Compare May 3, 2026 20:08

dmitri-lerko changed the title ~~feat(storage): add storage go parity features~~ feat(storage): add signed post policy v4 May 3, 2026

dmitri-lerko marked this pull request as ready for review May 3, 2026 20:18

dmitri-lerko requested review from a team as code owners May 3, 2026 20:18

joshuatants requested a review from xlai20 May 4, 2026 01:19

xlai20 requested changes May 8, 2026

View reviewed changes

	\| Signed V4 POST policies \| `storage.GenerateSignedPostPolicyV4` \| Implemented \| `src/storage/src/storage/post_policy_v4.rs`, `src/storage/src/post_policy_v4.rs` \| Go-equivalent conformance, boundary, endpoint style, and Send tests exist \|
	\| Signed V4 POST policies \| `storage.GenerateSignedPostPolicyV4` \| Implemented \| `src/storage/src/storage/post_policy_v4.rs` \| Go-equivalent conformance, boundary, endpoint style, and Send tests exist \|

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